kupdf.net_deven-aranha-marine-diesel-scanned-1

By

DEVENARANHA

B.E. ( Mech.)

Class I Engineer

SHROFF P UBLISH ER S & D IS TR IB U TO R S PV T. LTD.

Marine Diesel Engines

M arine D iesel E ngines

By Deven Aranha

© Shroff Publishers and Distributors Pvt. Ltd.

A ll rights reserved. N o part o f the m aterial, protected by

this copyright notice, m ay be reproduced or utilized in any

form or by any means, electronic or m echanical, including

p h o tocopying, recording, o r by any inform ation storage

and retrieval system, w ithout the w ritten perm ission o f the

copyright owners, nor exported, without the written permission

o f the publishers.

First Edition : July 2004

Seventh Reprint: January 2013

ISBN 13: 978-81-7366-927-9

P u b lis h e d b y S h ro ff P u b lis h e rs a n d D is tr ib u to r s P v t. L td .

C -103, M IDC, TTC In d u s tria l A rea, P a w a n e , N av i M um bai

400 705, Tel: (91 2 2) 4 158 4 158, Fax: (91 22) 4158 4141,

e-mail: spdorders@ shroffpublishers.com , Printed at D ecora Book

Prints Pvt. Ltd., Mumbai.

CONTENTS

Table O f Contents

Preface

Acknowledgements

CHAPTER 1 :

INTERNAL COMBUSTION DIESEL ENGINES

Concept of Internal Combustion Engines......................... 01

Stroke....................................................................................01

Mean Piston Speed ............................................................02

Advantages / Disadvantages of Diesel Engines 03

Classification of 1C. Engines............................................ 04

Otto, Diesel. Dual and Actual Cycles................................06

2-Stroke C ycle.....................................................................09

4-Stroke C ycle................................................................... 12

2-Stroke vs. 4-Stroke Engines .................................... 16

CHAPTER 2 :

ENGINE COMPONENTS

Engine Structure...............................................L . 19

Top Bracing..... ................................................ 20

Fatigue Failure.....................................................................21

Bedplate............................................................................... 22

Entabulature. A-Frame. Tie-Bolts and Pinching Screws 24

Holding Down Bolts and Chocks ...................................... 25

Resin, Resilient Chocks............. 27

Piston : Water cooled. Oil cooled, Oros, Composite.....29

2-Stroke versus 4-Stroke Pistons, Defects,

Rotating Pistons.

Piston Rings : Compression Rings. Oil Scraper Rings 36

Failures. Running-in. Shapes. Coatings.

CPR Rings. Antipolishing Ring, SIPWA.

Stuffing Box G land............................................................. 44

Lmer. Liner W ear.................................................................45

Lubricating Quills and Accumulator 48

H



CONTENTS

■ Cylinder Head Cover.......................................................... 50

Exhaust V alve..................................... .............................. 51

Valve Springs.......................................................................53

Valve Rotators......................................................................55

Variable Exhaust Closing (VEC) 56

Crankshaft .......................................................................... 58

Crankshaft Stresses 62

Crankshaft Deflections.......................................................63

Chain Drive, Tightening and Inspection 64

Chain Elongation.................................................................67

Camshaft Readjustment after Chain Tightening 68

Bearings Plain Bush Journal, Pivot Pad Journal 69

Mam Bearings................................................................. 71

Connecting Rod and its Bearings 72

Bottom End Failures and Bolt Design 74

Crosshcad Bearings............................................................ 75

Puncture Valve.....................................................................77

Engine Materials 78

CHAPTER 3 :

AIR SYSTEM

Scavenging,..:..;;;......................;............;....u..i..:;.............. 81

Uniflow, Reverse, Loop and Cross Scavenging.............81

Gas Exchange Process.....S................................ 84

Supercharging......................................................................S5

Constant Pressure and Pulse Turbocharging 86

Series. Parallel Supercharging 89

TVo-Stage Supercharging 91

Single and Multiple TVbochargcr Systems 91

Power Take-In and Power Take-Off 92

Axial Flow Turbocharger 94

Uncooled Turbochargers 97

Surging................................................................................. 99

Compressor M a p .................................................................99

CONTENTS

CHAPTER 4 :

AIR COMPRESSORS

Isothermal Compression................................... 103

Adiabatic Compression and the Compression Cycle.... 103

Multistage Compression .................................... 104

Reciprocating,and Rotary Compressors....... *................ 104

Volumetric Efficiency and Bumping Clearance ............... 105

Compressor Valves................. .............. fan..................... 105

Compressor Faults.................. laSLari............................ 106

CHAPTER 5 :

FUEL SYSTEM

F u eliy p es.............................................................................109

Fuel Properties................................................................... 110

Fuel Specifications...................................... U 6

Combustion Phases............................................................ 117

Knock........................................................................... n s

Factors Affecting Combusuon.......................................... 119

Combustion Chamber and Piston Crown Designs ........ 121

Compression R atio............................................................ 121

Residual Heavy Fuel O ils................................................. 122

Bunkering ........................................................................... 123

Fuel Injectors................. 125

Injector types........................................................ 126

Injection Methods ...................... 130

Fuel Pum ps............................ 131

Suction Valve Controlled P um p..................................... 131

Suction and Spill Controlled Pum p.............................. 133

Port Controlled Jerk P um p............................................... 134

Injection Systems................................................................ 135

Variable Injection Timings (V1T)..................................... 136

Fuel Quality Setting (FQ S)............................................... 140

Super-V IT and Conventional V1T.................................... 140

Fuel C am .......................................................................... 146

High Pressure pipe safety ............................. 147

[ii]

[iii]



CHAPTER 6 :

Start Air Interlocks.............................................................187

LUBRICATION SYSTEM

Slow Turning...................................................................... 188

Friction and Friction Types...............................................149

Scavenge Air Limiter ................................................. 188

Lubrication Types.............................................................. 151

Firing Order of Cylinder................................................... 188

Lube Oil Properties..................................... ...................... 152

Lube Oil Testing................................ ............................... 156

Microbial Degradation..................................................... 161

Cylinder Lubrication Types and Systems........................162

Lubrication Pump U nit................................................... 166

Load Dependent Cylinder Lubrication..................... 167

Specific Cylinder Lube Oil Consumpuon..................... 169

Reversing M ethods.......................................... 190

Loss Motion and Gain M otion........................................ 194

Running Direction Interlock ............................................ 195

Crash Manoeuvring ....................—................................... 195

Manoeuvring Flow C h a n ................................................. 197

Manoeuvring Diagram .......... 198

Bridge Control System .......................................................202

CONTENTS

Frequency Controlled Electric Motor Lubricator..........169

Multilevel Cylinder Lubrication ............ 170

Crosshead Lubrication.................................. ....................171

CH A PTER7 :

COOLING SYSTEMS

Function.............................................................................. 173

Bore Cooled Liners............................................................ 174

Load Dependent Liner Cooling....................................... 174

Piston Oil Cooling System.................................. 175

Cooling Water TYeatment................................................... 175

CHAPTER 8 :

CONTENTS

CHAPTER 9 :

ENGINE STRESSES,VIBRATION AND DYNAMICS

Forces Acting in a Single Cylinder E ngine......................205

Irregularity Factor............................................................. 207

Static and Dynamic Balancing........................................... 208

Primary and Secondary Imbalance —.................................209

Vibration Definitions...................... ................................ 209

Torsional Crankshaft Vibration......................................... 211

Critical Speed ...................................... v.......................... 211

Barred Zone Range............................................................. 212

Detuners and Dampers........................................................213

STARTING , REVERSING AND MANOEUVRING

CHAPTER 10 :

Start System ....... .............................................................. 177

ENGINE OVERHAULS AND MAINTENANCE

Start Air Period.................................................. ............... 179

O verlap................................... ...................... ....................179

Start Air Receiver ...........................:............;................ 180

Start Air Pilot Valve.............. 182

Automatic Master Air Start Valve................................. 183

Start Air Cylinder Valve..................................................... 185

Start Air Distributor.... .................................. 186

Start Air C a m ....................................................................... 187

Unit Decarbomsation................................ 215

Cylinder Head R em oval................................................. 216

Hydraulic Nut Removal ..................................................... 217

Exhaust Valve Removal......................................................218

Piston Removal. Inspection and Clearances 220

Piston Mounting................................-............................... 223

Liner Removal. Inspection and Calibration..................... 224

Main Bearing Removal ..................... 225

[iv]

M



Crosshead Bearing R em oval..............................................227

Liner.................................. d lia u .J...... .......................... 296

Connecting Rod Bearing Removal.................................... 228

Cylinder Lubrication............. 297

Crosshead Pin Removal......................................................229

Piston...................................................................................297

Connecting Rod Removal................................................... 230

Crosshead............................... _„...~.^...._J.i..L.................298

Thrust Bearing Pad Removal............................. 231

Engine Components......................................................... 298

Bearing Clearances ...... 232

Fuel Pump Setting and Adjustment...................................236

CHAPTER 13 :

Fuel Pump Cut-out Checks................................................. 238

ENGINE EMISSIONS

Fuel Pump Cut-out............................................ 239

Engine Emissions.............. ................ ................................301

Fuel Pump Lead..............................------------------------- 239

SOx Effects and Remedy.................................................302

4-Stroke Medium Speed Engine Fuel Pump Timings 241

NOx Effects and Remedy................................'.................302

CONTENTS

Turbocharger Overhaul....................................................... 242

Turbocharger Out of Operation--------...-------- ------- ..... 243

Fuel Injector Overhaul............................. ....................... 244

Tie-Rod Tensioning.............................................................246

Air Compressor Overhaul .................................................. 249

Testing of Materials ........ 250

Heat Treatm ent............................ 250

CHAPTER 11:

ENGINE DESCRIPTIONS AND SPECIFICATIONS

Comparison of RD. RND and RTA Engines . . ...............253

RTA Engines........................................................................ 254

CONTENTS

Carbon Monoxide, Hydrocarbons, Particle Emission.... 304

Soot..........................................................KiihillsU............305

Smoke and Opacity.................................:j.".......A............ 305

CHAPTER 14:

ENGINE PERFORMANCE AND INDICATOR CARDS

Engine Performance Definitions and Parameters...........307

Heat Balance Diagram 310

Power Ratings...................................................................... 310

Testing of Marine Engines ........................ ................. 311

Test Bed and Sea T rials......................................................312

Load Diagram and Propeller C urve..................................314

RT-Flex Engines................................................................... 258

Safety Margins .................................................................... 316

SMC Engines.......................................................................271

Indicator Diagrams and Analysis.................................... 318

ME Engines........................ .........- ................................. 278

Faults with Indicator Instruments...................................... 327

CHAPTER 12 :

ENGINE DEVELOPMENTS

Fuel Injection System ............................... - ......................291

Turbocharger System...........- ........................... ................292

Scavenge System ............................................. - .............. , 296

Exhaust System.................................... - ............................296

Combustion Chamber.......................................................... 296

CHAPTER 15 :

GOVERNORS AND CONTROL

Governor Definitions................................

Mechanical G overnor...............................

Hydraulic Governor with Compensation.

Electric Governor.....................................

Governor Adjustments .............- .............

329

331

331

333

334

[vi]

[vii]



Load Sharing and The Necessity of D roop.....................335

Electronic Governor for Bridge Control........................ 337

Engine Turns on Air, Not on Fuel......................................362

Engine Does Not Fue .......................................................... 362

Violent Starting.....................................................................363

CONTENTS

CHAPTER 16 :

W ATCHKEEPING AND SAFETY

Thlcing Over An Engine Room W atch............................345

Walk Through Checks of The Engine Room................. 345

Checks During The Engine Room Watch 350

Problems During The Engine Room W atch................... 351

Crankcase Explosion and Relief Valve............................351

Scavenge Fires....................................................................353

Oil Spill................................................................................354

Collision............................................................ ..................354

Flooding.............................................................. ,............. 355

G rounding.......................„.v............................................... 355

Sudden Overspeeding........................................................ 355

Loss of Engine Pow er.............. ......................................... 356

Slack Tie-Rods...................................................................356

Incorrect Fuel Timings........................................,............. 356

Engine Speed Fluctuation..................................................356

Funnel S parks..................................................................... 357

Cylinder Relief Valve L ifting........ ..................................357

Reduced Compression Pressure .................................... 357

ONTENTS

Engine Not Reversing....................................................... 364

Cracked Piston......................................................................364

Broken Piston Ring.............................................................. 365

Cracked Liner.......................................................................365

Piston Running H ot......................................- ................... 365

Cracked Cylinder H ea d ...................................................... 366

Crankcase Inspection...........................................................366

Individual Piston Knocking at T D C .................................. 367

Bearing Temperature Increase............................................ 367

Lube Oil Sump Level Rising.............................................. 368

Automatic Stopping of E ngine......................................... 368

Knocking in an Engine Cylinder...................................... 368

Safeties in the Main Engine................................................ 369

Safeties in the Start Air System ..........................................371

Leaky Start Air Valves.....----- ........----------— ....... ......372

Start Air Line Explosion......................................................373

Safeguard Against O vet speeding.................... 373

Bibliography

Smoky E xhaust.................................................................. 358

All Cylinders Exhaust Temperature Increase .............. 358

One Unit Exhaust Temperature R ise ................................359

Engine Speed D rops...........................................................359

One Unit Exhaust Temperature Drops.,...;)./...*...............359

Charge Air Pressure D rops................................................360

Engine Running Irregularly.............................. ............. 360

Jacket Water Pressure Fluctuation.................................... 360

Jacket Water Temperature Increase ................................ 360

Running Gear H ot.............................................................. 361

Engine Fails to Start on A ir............................................. 361

[viii]

[ix]

PREFACE

O v er th e p ast decade, th ere have b een sig n ific a n t

advances in the field o f m arine diesel engines.The new

m illennium saw the advent o f a revolution in m arine

engineering technology, w ith the introduction o f the latest

‘C am shaft-less E lectronically C ontrolled Intelligent

E ngine’ series.

This book has been w ritten with a view to fulfilling the

need o f m arine engineers to be in touch w ith up-to-date

inform ation on present day engines, w hich have replaced.

the older series. In this age o f technological advancement,

it is o f vital im portance that today’s m arine engineers

keep abreast o f these developm ents and equip themselves

with thorough know ledge o f the engines that they work

on a regular basis.

A distinctive feature o f this book is that the text m atter

is presented in ‘easy-to-understand’ point form, for the

benefit o f marine engineering students. B esides providing

an in-depth understanding o f th e basic principles o f

m arine diesel engines, this book also gives an insight

into the working o f m odern engines.

This b ook w ill be useful to candidates appearing for the

Certificate o f C om petency examinations.

Deven Aranha

CHAPTER 1

INTERNAL COMBUSTION

DIESEL ENGINES

Concept of Internal Combustion Engines

Marine diesel engines are basically reciprocating engines using heavy

fuel oil or diesel oil in a Compression Ignition (C.I.) system. Unlike a

Spark Ignition system where a spark is used to ignite the fuel, a

Compression Ignition system uses heat from compression to ignite

the fuel in the combustion chamber.

Fuel upon ignition in the combustion chamber gives a combustion force

which pushes down the piston, i.e. work is done in the cylinder by

combustive gases. This reciprocating motion of the piston due to the

combustive gas forces, is transformed into rotary motion of the

crankshaft. This is done by means of the connecting rod and crank

mechanism.

Stroke (S)

Stroke is the distance covered by the piston between the top dead

centre (TDC) and the bottom dead centre (BDC).

Stroke = 2 ( Crank Radius)

Marine Diesel Engir

M ean Piston Speed

Internal Combustion Diesel Engines

Significance o f M ean Piston Speed

The significance can be seen if we study the power equation.

Power = Pm x (2 Sn) x A x n x constant.

where, mean piston speed = 2Sn

Therefore, Power depends on Mean Piston Speed.

Vc = Volumeofcompressionchamber Va = Volume o f the cylinder

Swept volume

Since,

= Volume swept by the piston from TDC to BDC

= Vs = (Area) x length = (fi.D2 ) S

4

Va= Vc + Vs .

Hence, Compression Ratio = = Vc + Vs 1+Vis'

Vc Vc Vc

Mean Piston Speed

= (Piston distance in one revolution)

x (R ate of crankshaft rotation)

= 2§_n

60

= Sr

30

where, 2S = Distance covered by the piston during

one revolution.

N = Number o f revolutions per second.

Limitations o f M ean Piston Speed

The limitations of mean piston speed are:

♦ The wear and life span o f the rotating and reciprocating parts due

to friction; high temperatures and pressures; and lubrication

conditions.

♦ Large forces due to rotating and reciprocating masses, which in

turn give rise to stresses especially fluctuating stress; and moving

parts due to inertia forces and dynamic forces.

♦ Gas exchange-scavenge period and efficiency: Higher the mean

piston speed, greater will be the resistance to gas flow and

exchange, when hot exhaust gases have to be expelled and fresh

air has to be taken in.

Advantages o f Diesel Engines over Steam Engines

♦ High actual efficiency = Heat equivalent of actual work done

Total Heat generated in the engine

♦ Actual Efficiency,

for steam engines = 12 to 18%

for steam turbines = 2 2 to 32%

for gas turbines = 2 5 to 36%

for diesel Engines = 36 to 42%

♦ High efficiency and recovery of waste heat.

3

“

Marine Diesel Engines_____________________________________________

♦ Highest use o f heat generated during combustion.

♦ Increased time period before refueling i.e. bunkering.

♦ Increased maneuvering abilities.

♦ Increased cargo carrying capacity since less space is required for

the boiler, water storage, water consumption; and a smaller size of

engine in comparison to a steam plant and auxiliaries.

♦ Increased standby reliability.

Disadvantages o f Diesel Engines

♦ High inertia loads due to reciprocating and rotating masses.

♦ High capital cost, complicated design and construction.

♦ Pressures and temperatures are always varying in the system.

♦ High lube oil costs in medium and high speed engines.

♦ High idling speed of crankshaft and irregular rotation.

Classification of I. C. Engines

Classification can be done under various categories:

1) 2-stroke or 4-stroke: Usually, 2-stroke is preferred for marine

engine propulsion while 4-stroke is preferred for auxiliary diesel

generation.

2) Fuel used: Petroleum fuel ( gasoline, naphtha, kerosene, gas oil,

diesel oil), heavy fuel ( motor oil, burner fuel), residual fuels,

gaseous fuels (natural or producer gas) and mixed fuel (liquid fuel

for starting combustion and gaseous fuel for running).

3) Single or Double Acting: A single acting engine is one where the

upper part of the cylinder is used for combustion. A double acting

engine is one w hich uses both the upper and lower part o f the

cylinder alternatively, e.g. Opposed piston engines.


4) Naturally Aspirated or Supercharged: In naturally aspirated

engines, the piston itself sucks in air (e.g. 4-stroke engines) or is

fed by a scavenge pump (2-stroke engines). In supercharged

engines, air under pressure is supplied to the cylinder which is

pressurized externally by mechanical means o r an exhaust blower.

5) Compression Ignition (marine diesel engines) or Spark Ignition

(carburetor and gas engines): In compression ignition, the fuel

ignites with the air due to high temperature caused by compression

of air. In spark ignition, an external electric spark is used for ignition.

6) Trunk type engines (4-stroke engines) o r Crosshead engines

(2-stroke engines): In trunk type engines, the piston has an

extended skirt which acts as a guide. In crosshead engines, there

is a crosshead which has shoes sliding over the crosshead guides.

7) Single or M ulti cylinder: Modem m arine engines use 4 to 12

cylinders.

8) V ,W or X pattern o f arrangement o f the cylinders.

9) Main Propulsion use (Ship’s propeller drive) o r A uxiliary

engine use (power generation & auxiliaries).

10) Low, Medium, a nd H igh Speed

Low speed (100 to 350 rpm)

Medium speed (350 to 750 rpm)

High speed (750 to 2500 rpm).

11) Mean Piston Speed

Low speed (4.5 m /s to 7 m/s)

Medium speed (7 m/s to 10 m/s)

High speed (10 m/s to 15 m/s).

12) Uni directional (sam e direction) or Reversible Engines

using a reversing mechanism.

13) Ahead direction in clockwise or anti-clockwise direction.



Cycles

The important cycles are discussed below.

D ual Cycle

Otto Cycle ( Constant Volume )

v

Fig-2

0-1 Charging of Fresh Air (o Point 1 1-2 Air Compressed Isentropically

2-3 Heat Added at Constant Volume 3-4 Air Expanded Isentropically

4-1 Heat Rejected at Constant Volume.____________

D iesel Cycle (Constant Pressure)

0-1 Charging of Fresh Air to Point 1 1-2 Air Compressed Isentropically

2-3 Heat Added at Constant Pressure 3-4 Air Expanded Isentropically

4-1 Heat Rejected at Constant Volume._____

4-5 Air Expanded Isentropically

1-2 Air Compressed Isentropically

3-4 Remaining Heat added at

Constant Pressure

5-1 Heat Rejected at Constant Volume

A ctual Cycle

The A ctual C ycle is slightly different from the theoretical cycle

in the following:

♦ From 1 to 2, the curve is

i similar in the compression

| stroke.

♦ From 2 to 3, compression is

n ot done under constant

1 volume because the piston is

already moving during the

stroke. It is not completely

adiabatic because o f heat

transfer through the cylinder

liner. Fig - 5

♦ From 3 to 4, during expansion stroke, there is heat transfer.

Marine Diesel Engines ________________________ j

♦ From 4 to 1, heat is rejected with changes in mass flow, specific

heat, lower pressures and temperatures.

♦ In the actual cycle, there are unavoidable thermal, hydraulic and

mechanical losses.

♦ The air admitted into the cylinder thermally interacts with the hot

cylinder liner and gases, and there is heat transfer.

♦ A certain amount of work is required to be done to overcome the

resistance of the inlet system through which the air is admitted.

♦ The amount o f filling o f air into the cylinder depends on its

temperature, speed and load o f the engine, engine construction

and service conditions.

♦ Adiabatic compression is compression when there is no heat transfer

with the surroundings. Thisisnotpossibleintheactualcycle. Here,

there is heat transfer with the gases and the cylinder walls, which

results in a change in pressure and temperature o f the compressed

air.The area of heat transfer is decreased as the piston moves

upwards to TDC.

♦ The actual compression is a polytropic curve with a continuously

varying exponent.

♦ It is more similar to isothermal and adiabatic processes due to the

high rate of compression of the air charge.

♦ The heatinput process is not ideal, since combustion o f fuel involves

complicated physical and chemical changes with thermal losses in

the final stage.

♦ Actual combustion overlaps the expansion stroke to some extent,

due to the volume o f the cylinder space increasing. This leads to

heat losses to the surroundings, impairing the effectiveness of heat

utilization in the cycle.

♦ Actual expansion is a poly tropic curve with a variable exponent.


♦ The heat transfer at this stage is varying, since some of the fuel still

bums in the expansion stroke. Even greater heat losses are involved

owing to the unused energy lost by the compressed hot gases,

when the exhaust ports are uncovered or exhaust valve opens before

the piston arrives.

♦ Action arising out of reciprocating, rotating and robbing components

also contribute to losses.

♦ Some energy is used to drive auxiliaries (lube oil pumps, jacket

water, scavenge pumps, etc).

♦ Cooling o f the liner is imperative to the cylinder, but this is also a

source of thermal loss.

'

2-Stroke Cycle

2 Strokes = 2 strokes o f the piston

= Piston going u p + Piston going down

= Once compression and once expansion

= 1 complete revolution gives 1 power stroke.

As the name implies, the cycle is completed in two strokes o f the

engine piston:

(1) The Compression (Scavenging and Suction) stroke

(2) The Power (Expansion and Exhaust) stroke.

These actual timings differ from engine to engine with respect to design

and construction features such as stroke/bore ratio, engine rpm, engine

rating, ratio o f connecting rod length to crank length, etc.

8

Marine Diesel Engir,


An example of 2-stroke valve timings are:

Inlet (scavenge) opens

Inlet closes

Exhaust opens

Exhaust closes

Injection starts

Injection ends

42 deg . before BDC

42 deg . after BDC

75 deg before BDC

60 deg after BDC

16 deg before TDC

20 deg after TDC.

Upstroke o f the Piston (Compression Stroke)

Fig-6

0 Scavenge ports are open

0- 1 Air is sucked in, which pushes out the residual exhaust gases

1 Piston is at BDC

1- 2 Completion of scavenge process and filling with fresh air for

combustion

2 Scavenge ports are closed

2- 3 Post scavenging takes place

3 Exhaust valve closes

3- 4 Compression of air

4 Fuel injection commences

5 Fuel ignition commences, near TDC .

6 Fuel injection and combustion completion

6- 7 Expansion of the heat energy from combustion,

being converted into work energy to push the piston downwards

7 Exhaust valve opens

7- 0 Blowdown o f exhaust gases seen as a sudden rapid pressure drop

ontheP.V.diagram.

\

The scavenge and exhaust ports are uncovered and pressurized air is

fed into the cylinder. This fresh air does the scavenge process i.e. it

cleans the cylinder of the exhaust gases from the previous cycle. The

piston then travels upwards closing the exhaust and scavenge ports

and starts compressing the air. A t the end o f the upward stroke, the

air pressure in the cylinder builds up to 32 to 45 bar and

correspondingly, it’s temperature rises to 650 to 800 deg. C.

10



Downstroke o f the Piston (Power Stroke)

I Inlet valve opens 1-2 Suction stroke 2 Inlet valve closes

2-3 Compression stroke 3 Injection 4 Injection ends

begins

4-1 Expansion stroke 5 Exhaust valve opens 5-6 Exhaust stroke

When fuel is supplied by the injector to the hot compressed air, it

reaches its self ignition temperature and ignites. The combustion causes

the expansion o f gases, which push the piston downwards towards

BDC. The piston being pushed downwards by the combustion gases

is doing work and hence, the stroke is called the Power or Expansion

stroke. The exhaust ports are uncovered at approximately 40 to 75

degrees o f crank shaft rotation, just before BDC. This allows the

exhaust gases to escape to the atmosphere and the pressure in the

cylinder now falls to around 2 to 4 bar. The temperature is high due to

the exhaust gases i.e. 250 to 500 deg. C. The exhaust ports are kept

uncovered for approximately 118 to 130 deg. of crank rotation. The

scavenge ports are kept open for 100 to 140 deg. o f crank rotation.

4-Stroke Cycle

4 Strokes = 4 strokes o f the Piston

= 2 (Piston going up + Piston going down)

= 2 complete revolutions give 1 power stroke.

12

An example o f 4-stroke valve timing is :

Inlet valve opens

20 deg. before TDC

Inlet valve closes

60 deg. after BDC

Injection begins

10 deg. before TDC

Injection ends

12 deg. after TDC

Exhaust opens

42 deg. before BDC

Exhaust closes

60 deg. after TDC.

A 4-Stroke engine operating cycle is completed in 4-strokes o f the

piston. These a re :

(1) Suction (induction) stroke

(2) Compression stroke

(3) Power (expansion) stroke

(4) Exhaust stroke.

13


(1) Suction Stroke

Fig-10

1 Exhaust value 9 Connecting Rod

2 Rocker Arm 10 Piston

3 Camshaft timing gear 11 Cylinder Liner

4 Camshaft 12 Cylinder Head

5 Oil 13 Rocker Arm

6 Crankcase 14 Inlet valve

7

8

Crankshaft

Path of crankpin

15 Fuel Injector

The piston is moving downwards and a pressure difference between

the cylinder pressure and the atmospheric pressure is created above

it. Atmospheric air is sucked inside through the open inlet valve. The

air admission is stopped when the inlet valve closes. The cylinder

pressure is now approximately 0.85 to 0.95 bar and the temperature

37 to 48 deg. C.

(2) Compression Stroke

This stroke includes the compression of air, mixing o f the fuel and air

charge, and the start of combustion. The air in the cylinder is now

compressed since inlet and exhaust valves

are closed, and piston is moving upwards

from BDC to TDC.

The air is pressurized to 32 to 45 bar and

correspondingly, its temperature rises to 600

to 700 deg. C. The fuel is injected at the end

of the compression stroke at a fuel pressure

o f 200 to 1500 bar, depending on the type

of fuel. This fuel is injected in the form of an

atomized fine spray, which mixes with the

high temperature air and self ignites. The fuel

injection timing is around 10 to 35 degrees

of crank shaft rotation.


F ig -ll

Optimum condition for fuel injection is when the fuel injection coincides

with the peak air temperature in the cylinder for best combustion. At

the end of combustion, the pressure in the cylinder is 60 to 80 bar,

and 1600 to 2000 deg. C.

(3) Expansion Stroke (Power Stroke)

In this stroke, work is done by the expansion

of gases, to push die piston down to the crank

pin through the connecting rod, converting

reciprocating linear motion of the piston into

a rotary motion o f the crank shaft, thereby i

turning the engine shaft. After expansion, the !

pressure and temperature decrease to 3.5 to

5 bar, at 750 to 900 deg. C.

F ig -12

14



(4) Exhaust Stroke

When the piston nears BDC, the exhaust valve

opens and the exhaust gases escape, since their

pressure is more than the atmospheric pressure

in the exhaust manifold. The exhaust gases are

expelled and the piston now starts moving

upwards. The pressure o f the gases now

decreases further to 1.1 to 1.2 bar, at a

corresponding temperature o f 430 to 530

deg. C.

2-Stroke versus 4-Stroke Engines

♦ The whole cycle ( suction, compression, expansion, and exhaust)

is completed in two strokes of the piston in a 2-stroke engine, as

compared to four strokes of the piston in a 4-stroke engine.

♦ A comparison should only be made between operating cycles of a

2-stroke engine and 4-stroke engine, having cylinders o f same

geometrical dimensions and crankshaft speeds. Theoretically, the

horsepower output of a 2-stroke engine is twice that of a 4-stroke

engine. In actual practice, the output o f a 2-stroke engine is 1.5 to

1.8 times of a 4-stroke engine. This is due to the actual operating

cycle being only a fraction of the total piston stroke, lasting between

TDC and the instant of uncovering the exhaust ports.

♦ At the start of the compression stroke, there are higher pressures

and temperatures in a 2-stroke engine than in a 4-stroke engine

(higher by 25 to 30%). This increase results in a 30 to 40%

increase in the thermal load. Therefore, there are higher thermal

stresses on the combustion chamber walls.

♦ There is more turning o f the crankshaft, since two idle strokes of

the 4-stroke engine are not present in the 2-stroke engine.

♦ High speed 2-stroke engines are less efficient due to less volumetric

efficiency.

♦ Fuel consumption is more in 2-stroke engines, since the engine

works on the Otto Cycle principle.

♦ Unlike 4-stroke engines where there are two separate piston strokes

for each of these purposes, 2-stroke engines have much less time

available for exhausting and scavenging. Hence in 2-stroke engines,

some of the combustion gases are left behind in the cylinder, which

interfere with the normal cycle operations. Thus, 2-stroke engines

appear to be less economical than 4-stroke.

♦ In the 2-stroke engine, tw o power strokes take place every two

revolutions, while in the 4-stroke engine, only one power stroke

takes place every two revolutions.

♦ 4-stroke trunk-piston engines have the advantage of requiring less

headroom than 2-stroke crosshead engines.

♦ Torque produced by a 2-stroke engine is less irregular than a 4-

stroke engine, due to the number of operating cycles in a 2-stroke

engine being twice that in a 4-stroke engine.

♦ The force applied to a piston of a 2-stroke engine coincides with

the axis o f the connecting rod at all times and never changes its

I direction during the cycle.Therefore, dynamic loads coming on the

| piston crowns in a 2-stroke engine are avoided unlike in a 4-stroke

engine.

♦ In m arine applications, 2-stroke engines are used in low speed

■ high-powered diesel main propulsion, while 4-stroke engines are

used in medium speed power generation.

♦ In modem engines for main propulsion, fuel costs require cheaper

| quality fuel to be used. This is possible in 2-stroke low-speed large

16

17


crosshead diesel engines which have a very long stroke, aiding in

more time for the scavenging- and exhaust process. Also, in

2-stroke crosshead engines, the cylinder space can be isolated

from the crank case. This avoids the contamination o f the crank

case oil due to the acidic residues entering the crank case, as in

4-stroke trunk-type engines.

CHAPTER 2

The total cost of the expensive lube oil for slow 2-stroke engines is

less than 4-stroke engines of equivalent power.

ENGINE COMPONENTS

ICngine Structure

l( is the foundation o f the main engine.

Requirements

1. Strength to resist fatigue failure.

2. Rigidity

a) to allow for crankshaft stresses which can cause excess bending

loads on the main bearings. It allows uniform loading on the main

bearings.

b) to control the structure’s natural frequency and keep it away

from the engine’s natural frequency. The engine will therefore be

designed to run above or below the critical rpm.

c) to allow for true alignment of the piston and the running gear, so

that no uneven loads fall over the crosshead guides, stuffing box

and cylinder blocks.

Engine Structure’s Transverse Strength

' I'lie engine’s structural transverse strength is provided b y :

♦ The transverse girder being rigidly fixed to the longitudinal girders.

It gives resistance to twisting.

18

19


Engine Components

♦ The transverse girder’s strength which allows for inertia and

combustion forces through the main bearing.

♦ The ‘A’ frame which transmits the guide forces to the bed plate.

♦ The top bracing units which dampen the lateral structural vibrations.

♦ The cylinder block units which provide strength against transverse

flexing.

♦ The tie bolts which put the structure under compressive stress and

reduces the tendency to separate.

E ngine Structure’s Longitudinal Strength

The longitudinal strength is provided by:

♦ Each ‘A’ frame u n it: This also reduces the chances o f fretting at

bolted joints.

♦ Rigid attachment to the stiffened tank top. Closely spaced framing

of 750 m m is the requirement for the double bottom construction.

♦ Ranges attached to the top and bottom of the longitudinal girder.

♦ Each cylinder block unit.

Top Bracing

This is usually of mechanical or

hydraulic type, fitted to the top

part o f the engine to provide

stiffening and support against

tw istin g fo rces fro m the

crosshead guide. Normally,

these braces are fitted to only

one side of the engine e.g. the

exhaust side.

Fig-14

A mechanical top bracing consists of shims 1 between two plates

hydraulically fastened by a bolt 4. The bracing stiffening plates 2 are

thereby attached to a strong support 3.

Engine Structure D efect Areas

♦ Below the main bearing due to bending stresses.

♦ At any change o f sections, where stress levels are concentrated

e.g. crosshead guides and holding down sites.

♦ Bolt holes and welds due to shear stresses.

♦ Anchor points for top bracing units.

E ngine Structural Cracks

Cracks in the engine structure are usually caused by fatigue failure.

Fatigue failures are discussed below.

Fatigue Failure

It is the failure of the material which has undergone fluctuating stresses.

Each fluctuation causes minute amounts of plastic strain. Fatigue cracks

start at the point of maximum concentration of tensile or shear stress.

The material fails at a point much below it’s elastic limit and therefore,

there is no distortion of surrounding material.

Factors A ffecting Fatigue Life

♦ Temperature: Increase in temperature lowers the endurance limit

of the material (usually, the endurance limit =108 cycles, i.e. 48%

of UTS for steel).

♦ Mean stress levels.

♦ Combined tensile and shear stresses.

♦ Cyclic stress frequency.

20

21


Engine Components

♦ Concentrated stress areas depending on the groove geometry and

sensitivity.

♦ Sharp notches, surface finish, corrosion, direction of grain structure

and heat treatment of the surface.

Fatigue Failure Causes

♦ Incorrect tension and maintenance of holding down bolts, tie bolts

and top bracing.

♦ Wrong engine operation with respect to overload, imbalance of

engine firing loads and imbalance of rotating masses (e.g. piston

removal).

♦ Manufacturing defects and poor quality materials.

♦. Ineffective vibration dampening units.

♦ Cold cracks due to the presence o f dissolved hydrogen or high

residual stress in the joint or a small triggering defect

Fig-15

1 Longitudinal girders, two in number, which1form the side walls and a set

of transverse I-beams or box girders strengthened with stiffness.

2 Transverse strength girders housing the main bearings.

3 Lower part of the bedplate has flanges for seating onto the hull foundation.

Fatigue Crack Detection M ethods

♦ Visual inspection at the stress concentration points.

♦ Dye penetrant method.

♦ Non destructive testing.

♦ Magnetic particle inspection.

♦ Checking of the tension of the surrounding bolts.

Bedplate

It is the base of the engine which carries the other components of the

engine structure. Strength and stiffness are required for the bedplate

to withstand the inertia loads of moving parts, dead loads o f supported

elements and forces from the firing cylinder gases.

Fig -16

Material fo r Bedplates

♦ Cast Iron (C .I.) absorbs and dampens vibration.

♦ M ild Steel (M.S.) plates or castings welded together are cheaper

and lighter.

22

23


E ntabulature, A -Fram e, Tie Bolts an d Pinching Screws

The position of the entabulature, A-frame and T-Bolts are shown in

the figure.

Tie Rods

Engine Components

Tie rods are bolts which keep the whole engine structure under

compression. They provide for fatigue strength. They also provide for

proper running gear alignment which prevents fretting. They help to

reduce the bending stress being transmitted to the transverse girder.

Tie rods transmit the gas forces which act on the cylinder head. The

firing pressure force o f the piston is directly transmitted to the main

bearing and consequently to the engine frame through the tie rod

support.

A-Fram e

As the name implies, these frames are

‘A’ in shape to provide support to the

cylinder block.

‘A’- frames are usually produced as a

single unit, as this helps in stiffening of

th e en g in e. A w elded ‘A’-fram e

contributes to 40% o f the engine’s

structural stiffness. The m aterial is

fabricated steel plates.

Fig-18

H olding D ow n Bolts a nd Chocks

Holding down bolts along with chocks have the following functions:

♦ To provide a clamping force through friction between bedplate,

chock and the ship’s structure in order to resist the propeller thrust.

♦ To provide stiffness to the engine.

♦ To position the engine within the ship’s structure.

♦ To provide good alignment of the engine and transmission shafting

and, hence equal load on all bearings.

1 Protecting Cap

2 Spherical Nut

3 Spherical Washer

4 Distance Pipe

5 Round Nut

6 Holding down Bolt

Fig-19

Slack Holding D own Bolts

They cause fretting between the bedplate, chock and the tank top.

M isalignment o f the bedplate will occur if these slack bolts are

24

25


retightened. Stiffness of the holding down arrangements is decreased,

whilst vibration of the engine and ship’s structure increases. Load on

other chocks increase and this may also cause fretting in them. Holding

down bolts may eventually shear in serious cases, although end-chocks

are provided to prevent this shear failure. Recurrence o f slackness

may increase, as the tension of the bolt has now changed with respect

to the whole holding down arrangement Torsional stresses will increase

as an effect o f fretting and misalignment. There will be an imbalance of

bearing loads.

Chocks

Resin Chocks

Engine Components

These are commonly used with the advantage of less manpower skill

and time. They are very useful for re-chocking repairs on fretted and

uneven foundation plates.

Advantages

♦ Cheaper installation and less skill for installing.

♦ No dependence on correct hand-fitting.

♦ Non corrosive and chemical resistant.

♦ 100% contact on uneven surfaces.

Fig-21

Disadvantages

♦ Maximum limit of temperature is 80 deg. C.

♦ In case o f overstressing o f holding down bolts, the chocks may

shatter and collapse.

♦ If incorrectly fitted, the chock life is decreased drastically.

M ain chocks are usually fitted beneath the longitudinal frame. Side

chocks are fitted in line with the main bearings. End chocks two in

number, are fitted at the aft end of the main engine. These are provided

with ‘through-bolts’ so that they limit the forward motion o f the engine.

Application Procedure

♦ Calculation is to be made for the chock area and the bolt tension.

♦ Engineis to be aligned with shafting.

♦ Allowance for chock compression is 1/1000 o f chock thickness.

♦ Class.approval is to be sanctioned.

♦ Clean the work area of the engine frame and tank tops of dirt and oil.

♦ All hull renewals and engine alignments should be complete.

26

27


♦ Dams are prepared using a metal sheet and putty sealant to hold

the chocking resin liquid.

♦ No heavy work during the cure period. Cure period is around 18

to 36 hours, depending on ambient temperature.

♦ Ambient temperature should be from 20 to 25 deg. C.

♦ Limit for chock thickness is 25 mm, or else use more steps.

♦ Tighten the holding down bolts after the cure period is completed.

♦ The hardness o f the.chock is checked.

Resilient Chocks

♦ These are normally used in case of medium speed engines (e.g. 4-

stroke engines for power generation). Basically, they help to dampen

the vibrations transmitted from the medium speed engine to the

tank top.

♦ 2-stroke main propulsion engines are heavy in weight and, therefore,

have high rotational and static masses causing higher out-of-balance

forces which preclude the use o f resilient chocks, whose design

would also have to take into consideration the heavy weight of the

engine.

♦ 4-stroke engines for power generation plants are smaller and lighter

in comparison. Therefore, they have lower out-of-balance forces,

whose natural frequency will be from 6 to 25 Hz for400 to 1500

rpm speeds. The natural frequency of the engine can be changed,

but not the natural frequency of the hull (2 to 5 Hz) or the bulkheads/

decks (10 to 15 Hz) or the stem (4 to 7 Hz).

♦ Resilient chocks consist of a number o f flexible rubber vertical

mounts used on under-slung engines. They have main mounts as

well as side and end mounts. Since these are flexible mounts, the

engine crank shaft center will move +/-1 mm and the top o f the

engine approximately +/- 5 mm during start up, depending on the

28

Engine Components

engine specifications. The rubber element can take compression

and also shear loads. They have in-built buffers to stop excessive

movements in heavy sea conditions as well as stopping and starting.

All mounts are loaded to the same amount. The tolerance o f 2

mm is given for conical mounts. Using shims, one can further adjust

these heights.

Piston

Requirements

♦ To withstand the mechanical stresses o f combustion gas pressure

and inertia forces.

♦ To withstand the thermal stresses during combustion.

Pistons are designed to take into consideration the follow ing:

♦ The crown is directly exposed to heat and gas load and hence, has

a tendency to deform. Hence, the material should not only be

thick for mechanical strength, but also thin enough to minimize

thermal stress.

♦ The cyclic loading causes the top and the sides of the crown to flex

which can lead to fatigue failure.

♦ The shape of the combustion space also depends on the shape of

the crown. Concave or convex pistons are used.

♦ Wall thickness can be reduced with strength provided for by internal

ribs o f radial or concentric designs.

♦ The topmost ring undergoes the brunt o f the direct flame and it is

much higher in position than the others.

♦ The material of the crown should take into consideration the

working temperature, the hardness of the ring groove landing areas,

the corrosiveness of the gas mixtures and the cooling of the piston.

♦ A high top land helps in more effective lubrication and moving the

ring pack to a cooler zone.

29


Engine Components

Water Cooled Pistons

Water cooled pistons (older designs) have internal support webs cast

in the crown for mechanical strength, but are prone to thermal stress

failures. Cooling is done by the ‘Cocktail Shaker effect’.

Oil Cooled Pistons

1. SHAKER 2. JET

GEEl OH

F ig-22

Oil cooled pistons employ a spray nozzle plate. Cooling oil (common

to bearing lube oil) is fed through swinging arm links into the crosshead,

which provides a ‘je t shaker-effect’ as the piston moves up and down.

Increased cooling o f the crown is provided by a number o f spray

nozzles which direct the cooling oil into the blind bores of the crown at

all crank angles. W hen the piston is atTD C , the ‘shaker’ cooling

effect of the oil takes place. When the piston is going towards BDC,

jet type cooling takes place.

Advantages o f Bore Cooled Pistons over Conventional Pistons

♦ Lower thermal stresses and strain.

♦ Problems involved in casting o f internal ribs are eliminated.

♦ Lower piston maximum temperature at the crown.

♦ Lower gas load stresses and better cooling efficiency.

30

1 Curve of maximum temperature of piston crow in conventional type

piston

2 Curve of maximum temperature of piston crow in bore water cooled

piston

3 Conventional internal support webs or ribs

4 Conventional piston

5 Self supporting bores

6 Bore water cooled piston.

Flow o f Piston Cooling Oil

The flow is from the main bearing lube oil to the crosshead pin, then

through slots in the piston rod. It then flows through the inlet oil pipe

in the piston rod which leads to the cooling bores through spray nozzles

in the spray plate. The oil then returns through the outlet piping in the

piston rod into the crosshead pin, where it emerges sideways to the

engine sump through internal drains; and temperature and flow alarms.

Piston Materials

Crown - Aluminium or cast steel (4-stroke).

Crown - Cast chrome nickel molybdenum alloy steel (2-stroke).

Skirt - Si-Aluminium alloy (4-stroke) or cast iron.

Rod - Forged steel.

31


Engine Components

Conventional Type

Oros Type

Gas side Mean Temp. 500 deg. C 409 deg. C

Max. Temp. 510 deg. C 420 deg. C

Cooling oil side Mean Temp. 197 deg. C 185 deg. C

Max.Temp. 209 deg. C 216 deg. C.

Composite Pistons

Composite pistons (fig - 25) are those pistons that are made up of

‘composite’ m aterials i.e. two or more parts (crown, skirt, etc.) o f

different materials. Medium speed engines use these pistons. The crown

withstands the high cylinder pressure gas loads as well as it limits the

inertia forces. Applications for heavy fuel oil use are suitable. They are

o f self supporting type. Concave or convex crowns are used which

have internal support. Gudgeon pins are free floating type at the

operating temperature o f the piston. The trunk or skirt is separate

from the crown. Hence, the name trunk-type piston is given.

‘OROS’ Piston

Anew design employed by MAN B&W, which has the advantage of

reduction in temperature and heat load at the piston crown. The

following is a table o f temperatures o f the piston at 100% load.

The trunk o r skirt provides the following advantages:

♦ Better thermal conductivity.

♦ Reasonable strength.

♦ Alow relative mass in comparison with the crown to reduce piston

weight.

♦ Better radial and vertical contact due to the elliptical barrel shape

reducing the load during horizontal guide thrust.

♦ Better manufacturing reproducibility.

♦ Better resistance to scuffing.

♦ Better expansion cold clearances.

♦ Better thickness since density is relatively lower.

♦ Better skirt stiffness.

32

33

Engine Components


1 Crown (Cast steel)

2 Skirt or trunk ( Al-Sf-Alloy

or nodular C.I.)

3 Bearing (Lead bronze) •

4 Gudgeon pin (Carburised steel)

5 Keep plate

6 Connecting rod (Forged steel).

Fig-25

Differences Between 2-Stroke and 4-Stroke Pistons

2-Stroke Pistons

(1) It is of crosshead type i.e. piston

rod connected to the crosshead

bearing both reciprocate along the

axis of the piston.

(2) The crosshead slipper transmits the

connecting rod angularity thrust to

the crosshead guides.

(3) More height for same power and

speed.

(4) Higher engine manufacturing costs.

(5) It has compression type piston rings.

(6) More head room.

(7) Usually, used in low speed engines.

34

4-Stroke Pistons

It is of trunk type i.e. the skirt

(no piston rod) is connected to

the connecting rod by means of

a gudgeon pin and bearing.

Trunk or ‘extension’ piece or

extended ‘skirt’ takes the connecting

rod angularity thrust and transmits

it to the side of the cylinder liner.

Less height for same power and

speed.

Lower engine manufacturing costs.

It has compression as well as oil scraper

rings.

Headroom is limited.

Usually, used in medium speed engines.

Piston Defects

♦ Deformation or burning o f the crown top surface due to direct

impingement of firing gas, poor injection or bad fuel.

♦ Cracks on the internal or external surfaces due to built up thermal

or mechanical stresses. The reasons for these stresses are poor

injection, bad fuel quality, poor cooling due to insufficient coolant

or fouled cooling spaces, corroded material, poor lubrication, and

bad operations like an overloaded engine.

♦ Scuffing due to overheating or poor lubrication.

♦ Worn ring grooves due to poor lubrication, overloaded or incorrect

operation, poor combustion, worn liner or piston rings, etc.

♦ Cooling spaces deterioration due to corrosion; coking or scale

build up caused by poor cooling water treatment; or low oil coolant

flow or overheating.

♦ Fretting due to incorrecttensioning and assembly of studs; damaged

studs; or overheating.

Rotating Pistons

These pistons are employed for medium speed 4-stroke engines. An

example is the Sulzer Z40 series. Rotation of the piston is accomplished

by using a spring loaded pawl and ratchet. It has the disadvantage of

a high initial cost. It has the advantages of lower specific bearing loads;

lower risk o f edge loading; lower risk o f piston seizing; smaller

clearances between piston and liner; lower vibration of cylinder wall

due to lower piston slap; lower cavitation erosion; lower heat variation;

more uniformity and distribution of heat; improved spreading of lube

oil on the piston and the liner; and a symmetrical crown and skirt

which reduces thermal stresses.

■35


Engine Components

Piston Rings

There are usually three to six compression rings and one or two oil

scraper rings.

Compression Rings

Their purpose is to prevent blow-by. They should provide an effective

seal of the combustion chamber space. The initial ‘compression’ of

the ring i.e. ring tension, puts a radial pressure onto the liner wall.

Further sealing is provided by the gas pressure itself entering the ‘back

clearance space’ between the piston and ring. They transfer a large

portion of heat from the piston to the cylinder liner, which in turn, has

jacket cooling. High piston speeds require less compression rings,

since there is a less possibility o f blow-by.

Fig-26

The figure shows the gas pressure ‘p ’ entering the back clearance

spaces of each compression ring and causing the ring sealing pressures

p i, p2, p3, p4, p5 to provide a sealing effect by pushing the rings

tightly against the liner. It uses the labyrinth principle of decrease in

pressure. Therefore, the gas pressure that is leaked in behind each

compression ring is successively decreased in steps with each ring, to

equal the pressure which acts on the underside of the piston. Hence,

radial pressure changes with the position of each compression ring. It

is highest at the top.

Oil Scraper Rings

They are rings which eliminate the possible ingress of oil into the

combustion chamber. They are fitted lowermost of the rings on the

skirt in trunk type pistons. The oil is scraped by the rings whilst the

piston goes downwards, and is returned to the crank case via oil drains

in the piston on the upstroke. The ring’s beveled side surfaces slide

over the oil film without dragging them upwards.

The figure shows the pumping action of the compression rings when

the liner bore of trunk type pistons becomes over lubricated. When

the piston is going down, the piston compression rings are pressed

against the upper sides

of the ring grooves and

oil enters the spaces

below the rings. When

the piston is traveling

upw ards, th e ring

presses upon the lower

sid es o f th e rin g

g rooves and oil is

forced through the

back and upper side

clearances towards the

combustion chamber.

36

37


Engine Components

Piston Ring Failures

(1) Collapse

It is the ‘collapse’ i.e. inward push of the ring against the piston body

due to gas pressure build up against the ‘running face’ o f the ring. It is

caused by the pressure build up against ring running face and liner wall

due to reduced axial clearance; poor ring and groove sealing; rings

not free to move in the groove; or poor lubrication on sealing surfaces.

In Fig. A, pressure P I decreases at the same rate as the cylinder

pressure, while ring pressure P2 falls at a slower rate than the cylinder

pressure.

In Fig. B, when P2 suddenly

becom es m ore than P I ,

m ovem ent occurs since P2

changes and this causes a flutter.

In both figures, observe the first

piston ring fluttering and moving

up and down in its own place.

Fig-29

(3) Excess wear

This is due to poor clearances, corrosion, abrasion, scuffing or

improper lubrication.

(4) Jammed or sticking piston rings

This is due, to the build up o f carbon deposits or poor clearances.

In Fig. A, the reduced axial clearance reduces the gas pressure P I,

building up behind the ring to form a reduced P2 ring pressure.

In Fig. B, as P2 increases slowly, P I gets between the liner and the

ring.

In Fig. C, the ring collapses against the piston groove body.

(2) Flutter

Flutter is the oscillation movement o f the piston ring along its own

plane. It is caused by a radially worn ring leading to a reduction in

radial areas, or pounding of piston rings in the grooves when the piston

changes its direction.

(5) Scuffing

It is the overall damage on the sliding contact surfaces, caused by the

formation o f local welds. These welds occur due to high local

temperature (800 deg. C+), which hardens the base metal, forming

hardened particles at that point.

Scuffing depends o n :

♦ Oil film quantity, oil retention and countered rings to promote oil

film generation.

♦ Rotating pistons moving around any of the dry hot spots which are

prone to welds.

♦ High temperatures due to poor sealing or poor heat transfer by

bore cooling.

38

39


Engine Components

♦ Running-in of new piston rings or liner.

♦ Correct scuff resistant m aterials used i.e. soft copper or

molybdenum for running in, and hard chromium or nitriding alloys

for normal use.

Running-In

It consists o f :

♦ A purposeful wear on the piston ring profile to match the liner

surfaces for proper gas sealing and lubrication. When the liner is

rough, the ring is not properly sealed, and a matching profile is

required.

♦ A wear running-in coating layer is used which is meant to be worn

out, thereby creating a correct profile o f the piston ring to match

with the liner wall.

♦ The engine load is increased during the running-in period to promote

increased wear of the running-in layer.

♦ Lower TBN cylinder lube oil is used to provide corrosive wear of

the rings.

♦ Fuel of high sulphur content (more than 0.5% sulphur) is used to

increase acid corrosive wear during the running-in period.

♦ Cylinder lube oil feed rate should be increased.

Piston Ring M aterial

The piston ring is made o f Cast Iron.

♦ Grey Cast Iron gives better wear and scuffing resistance.

♦ Nodular chromium-plated malleable Cast Iron gives better fatigue

resistance.

♦ Carbidic malleable Cast Iron gives better fatigue and wear resistance.

♦ R.VK with AL-Bronze as a running-in coating.

Piston R ing M anufacture

Pot Casting is done in oval pots o r by drum casting in static sand

moulds; or by centrifugal casting. Machining is carried out in a camturning

lathe and later, a gap is cut out or the ring is split. Tensioning is

done by hammering the inner surface to induce residual stress or by

inserting a distance piece in a cut ring and heating in an oven to relieve

stress.

Piston R ing Shapes

Different types of piston rings have different cross sections, as shown

in the figure.

1. P lain type is sim ple and

inexpensive.

2. Barrel faced chrome-plated

cooling type. The b arrel

enables better and faster

bedding-in with liner profile.

C hrom e-plating is a hard

coating given for increased

life.

3. M aidtypewheretheinnerlaid

material (molybdenum or electroplated chrome) provides scuff

resistance, while the outer laid provides edge protection and oil

control.

4. Taper running face provides faster bedding-in.

5. Stepped scraper provides oil scraping and gas sealing.

6. Beveled undercut provides downward oil removal.

7. Slotted oil passages for oil scraping.

8. Conformable oil scraper for consistent oil control.

40

41


Piston R ing Coatings

Wear resistance coatings

♦ Plasma Coating (using a plasm a spraying method where a gas

mixture is directed through an electric arc generated between a

tungsten electrode and a water cooled copper tube to create a

‘plasma state’ at 10,000 to 15,000 deg. C). This plasma state

melts and fuses any m etal, with gas m olecules and atoms

disassociating.

♦ Chrome plating: It is a hard outer galvanic chrome layer. Double

chrome plating is done on both sides of the ring. This increases the

wear and corrosion resistance.

♦ Tungsten carbide coating which gives a better wear resistance.

Running-in Coatings

These are soft coatings such as copper, graphite or phosphate which

are meant to wear quickly and give the ring a similar profile as the liner.

Controlled Pressure Relief (CPR) Rings

In CPR type, the topmost ring has

one double-lap ‘S ’ seal and six

controlled pressure relief grooves

cut across the face. This ensures

even pressure distribution and

decrease o f thermal load to the

second piston ring as well as the

liner. Other piston rings have an

Al-bronze coating and oblique

cuts.

42

Fig-31

3l/.."j

Piston R ing Life

Ring wear rate (around 0.1 mm/1000 hrs) depends on:

♦ Fouling of the turbocharger.

Engine Components

♦ Reduced scavenge air pressure due to more dirt in the ring pack

area.

♦ Overloaded engines or excessive pressure rise.

♦ Poor clearances.

♦ Poor fuel injection or poor fuel quality.

♦ Poor lubrication.

♦ Poor water shedding in scavenge air which produces water drops

on the cylinder liner affecting lubrication and causing scuffing.

♦ Poor maintenance of grooves or incorrect fitting of rings.

Piston Cleaning R ing

It is the ring which is embedded in the top edge of the liner just below

the cylinder head level. Its purpose is to remove the excessive

carboneous deposits at the top-land portion of the combustion chamber

wall which would otherwise contaminate and affect lubrication.

A nti-Polishing Ring

It is the ring 1 which reduces the polished effect of

the liner wall, which is formed due to the hard

deposits from combustion in contact with the liner.

Polishing is unwanted, since it does not allow oil

film retention on the liner wall, and the oil passes

over the ring pack portion to the combustion area

when it is burnt and wasted. Polishing depends on

oil feed rate, excessive peak pressures, ring and

liner materials, and an increase in combustion hard Fig - 32

products at liner-ring interface.

43

Marine Diesel Engir.

Engine Components

SIPW A (Sulzer’s Integrated Piston Wear Analysis)

It is a m ethod using a continuous online

feedback measurement o f the piston ring wear

condition.The piston ring has incorporated a

wear-band (shaded section). As wear down of. s

the piston ring takes place, a corresponding wear

down o f the copper wear-band takes place. A

sensor in the cylinder liner senses the wear of

the copper wear-band and transmits this signal

to an online electronic unit, which records and

prints any wear down, which can be used as a

pre-warning.

Piston Rod Stuffing Gland

t

Casing in two parts

2 Spacer ring

3,5 Oil scraper rings

4 Sealing ring

6,8 Screws

9 Ring in two parts

10 Piston rod

i

It is a seal between the scavenge spaces and the crankcase in the area

of the piston rod penetration. It seals the crankcase oil entering into

the scavenge space, and scavenge deposits or cylinder oil entering the

crankcase. It is made o f two sections. Each section consists of

segmented metal rings held against the piston rod by garter springs.

Materials

Housing - Cast iron or cast steel.

Rings - Cast iron or brass or bronze or PTFE

Lamellas - Cast iron or carbon.

Stuffing B ox Problems

♦ Poor sealing caused by worn out rings, badly aligned ring joints,

sticky rings, closed butt joints, weak springs, excessive axial

clearance or scoring/wearing of the piston rod.

♦ Consequences of stuffing box not performing properly is a loss of

crankcase oil, higher costs, contamination of crankcase with

scavenge deposits and unbumt cylinder oil.

♦ Indications of poor stuffing box gland sealing:

Crankcase oil contamination test giving poor results.

A case of no oil replenishment.

Increasing TBN or viscosity.

Reduced piston cooling effect.

Poor lubrication.

11 O-ring

12 Locating pin

Fig-34

Liner

M anufacture

Liners are usually sand cast (above 300 mm diameter size). They may

be of split type to avoid distortion o f bore shape due to non-uniform

heat deformation. Split type is usually seen in 2-stroke engines, where

there is a difference in liner temperature near the scavenge ports and

exhaust valve region. Liners are press fitted into the respective bore

of the cylinder block.

44

45


Engine Components

M aterial

Cast Iron with alloys o f nickel, chromium, molybdenum, vanadium,

copper and titanium is used.

Cast Iron is chosen because its high strength; refined grain structure

with inclusions of alloys; smooth sliding surface due to graphite content

for improved lubrication; porous surface which retains oil as well as

exposes a fresh surface in case of

scuffing or scoring; and wear and

corrosion resistance.

1 Water guide jacket

2 Exhaust valve seat

3 Cylinder head

4 Annular space in cylinder head

5 Lubricating quill

6 Upper lubrication grooves in liner

7 Cooling bores

8 Sealing metal ring

9 Lower lubrication grooves in liner

10 Cooling water space

11 Cooling water

12 O-ring

13 Outer Jacket

14 Ring space devoid of water

15 Sealing ring

16 O-ring

17 Cylinder block

18 Cylinder liner

19 Scavenge ports

20 Piston underside scavenge space

Liner Wear

There are three types of liner wear.

Corrosive Wear

It is the wear on the liner surface due to low temperature corrosion of

sulphur. Sulphur oxides in the gaseous state combine with water, which

has formed due to the condensation or sweating, when the temperature

is low. Thus, acids are formed which lead to corrosion.

Remedy

♦ Increase liner wall temperature above the dew point of the water -

acid mixture.

♦ Use o f an alkaline cylinder lube oil to neutralize the acid content at

the liner wall.

♦ Use o f a low sulphur content fuel with a limit on the sulphur value.

Abrasive Wear

It is due to hard particles of ash deposits and catalytic fines, which

continuously cut, scratch and plough the liner surfaces.

Friction or Adhesive Wear

Mechanical friction wear is due to the piston ring friction on the liner

wall. This wear takes place usually where the oil film has depleted or

broken down.

Clover L e a f Wear

It is the uneven wear in the shape of a clover leaf on the liner surface in

the radial mode.

Reason

Uneven distribution of cylinder lube oil causes the depletion of its TBN,

before it has completely covered the liner surface. High corrosive

wear occurs on the liner surface between oil injection points.

46

47

Marine Diesel Engir

Engine Components

areas)

Horizontal Section of Cylinder Li

Effects

In extreme cases, combustion gas blow-by takes place past the piston

rings, or failure of the liner can occur.

Lubricating Quills

These are non-retum valves passing through the jacket water space,

which supply cylinder lube oil under pressure to the liner surface.

Lubricating Accumulator

It is fitted at the outer end of the quill. It delivers oil through a non-retum

ball valve, only when the cylinder pressure falls below the accumulator

pressure. The accumulator is sealed against the oil space by a flexible

diaphragm. This diaphragm is pressed downwards by the spring force.

This builds up an oil pressure, which is somewhat higher than the charge

air pressure of the engine in the combustion cylinder. When the charge

air pressure o f the engine o r the cylinder pressure falls below the

accumulator pressure, oil flows into the cylinder. When the accumulator

pressure is less than the cylinder pressure, the ball valve of the accumulator

closes. Iftheaccumulatorfails, oil delivery still continues, controlled by

the cylinder lubrication pump’s delivery stroke.

1 Working piston

2 Piston rings

3 Cylinder liner

4 Support ring

5 Spring

6 Accumulator piston

7 Diaphragm

8 Passage for lubricating quill

9 Bush

10 Filling pin

11 Screw ______

Liner Failure Areas

Area 1 Excessive, incorrect or uneven

tightening of cylinder head studs causes

cracks.

Area2 Poor liner support shows hoop stress

cracks.

Area3 Upper ring area is prone to wear ridge

circumferential cracks.

Area4 Flame impingement region in the

combustion space leads to star

shaped cracks.

Area5 Jacket water leaks at the lube oil quill

piping causes star shaped cracks.

Area6 Scavenge port areas due to scavenge

fires or overloaded engine operation.

Area7 Clover leafing wear near fuel injection

points.

12 Joint

13 Flange

14 Flange

15 Lubricating quill

16 Non-retum valve

17 O-ring

18 Set screw

19 Oil space

20 Lube oil inlet

21 Jacket water space

22 Lubricating oil grooves in the cylinder.

48

49


Cylinder Head Cover

The cylinder head is a cover for the cylinder liner and block, which

also seals the combustion chamber at the top. It sustains dynamic

thermal and mechanical loads caused by the combustion pressure and

temperature. It houses the exhaust value, fuel injectors, starting air

valve, safety valve, indicator cock and cooling water passages.

1 Cylinder head

2 Nut

2a Cylinder head stud

3 Cooling water outlet

4 Leak oil outlet

5 Exhaust valve cage

5a Stud of exhaust valve

6 Connection for the lubrication 6

7 Fuel injection valve 5

8 Starting valve

9 Connection for hydraulic oil

10 Indicator valve

11 Relief valve

12 Air inlet for valve spring

13 Water guide jacket

R Eye screw

Materials

Requirements

♦ Good casting characteristics (Cast Iron is good, while Cast Steel

is prone to defects).

♦ High strength, high thermal resistance and high corrosive resistance.

Cylinder heads are made o f:

♦ Composite structure i.e. Grey Cast Iron which has a good tensile

strength and casting characteristics.

Engine Components

♦ Molybdenum Steel for elasticity and strength (0.3 % C, Mo 1.5%).

♦ Steel casting or forging o f deep section, single piece, bore cooled

and machined at sealing faces.

Cylinder H ead Defects

♦ Cracks due to thermal changes in the cooling water temperature;

sudden overloading or heating of the engine; or uneven incorrect

tightening of studs.

♦ Distortion due to temperature variations.

♦ Cooling space fouling due to poor water treatment; and scaleorsludge

deposits.

♦ Corrosion on the lower side being exposed to the combustion

chamber.

♦ Gas erosion and acidic corrosion due to leaking exhaust valve cage

seats.

E xhaust Valve

1 Cam to operate hydraulic pump

2 Hydraulic pump piston

3 ' Oil from crosshead system

4 Cooling water outlet

5 Air spring piston

6 Hydraulic piston

7 Hydraulic actuator

8 Non return valve

9 Cam shaft L.O. system

10 Air spring action area

11 Valve guide

12 Exhaust gas deflector

13 Rotator vanes

14 Replaceable valve seat

15 Exhaust valve

16 Hydraulic oil

17 Control air at 7 Bar.

Fig-40

50

51


Engine Components

Hydraulic Exhaust Valve Working

Hydraulic pressure is provided by the cam operated hydraulic pump,

to the hydraulic piston o f the hydraulic actuator. Lube oil from the

camshaft system is used to actuate the hydraulic actuator to open the

exhaust valve by moving it downwards. Control air at 7 bar pressure

is supplied to the air piston to use it as an air spring, which closes the

exhaust valve when the pneumatic air force is greater than the hydraulic

oil force.

E xhaust Valve Types

They are usually poppet mushroom shaped valves. Opening and closing

are done by mechanisms such as valve springs and push rod-rocker

arm arrangements, o r hydraulic operation using camshaft lube oil

pressure to open and spring air to close the valve.

Large single valves have simpler valve construction, simpler cylinder

head construction and easier valve operation. Small size multiple valves

have lower inertia forces, lighter weight, better volumetric efficiency,

lower temperature of valve materials, less distortion of valve lid at

operating temperature and a smaller valve lift.

The exhaust valve consists of the valve, valve stem, valve face,'valve

seat, valve cage, valve rotator and valve gas deflector.

Valve Materials

Requirements are creep resistance at high temperatures; corrosion

and oxidation resistance; w ear resistance; erosion resistance;

machinability; high temperature strength; compatibility with valve guide

materials; impact resistance and surface hardness.

Valve

♦ Nickel based alloy (0.1 C, 0.1 Fe, 15 Cr, 1.0 Ti, 5 Al, 20 Co,

4 Mo, remainder Ni)

♦ Precipitation hardened steel (0.5 C, 25 Cr, 5 Ni, 3 Mo)

♦ Austenitic steel (Cr & N i 25 %)

♦ Si-Chrome steel (3 Si, 9 Cr).

Valve Face

A ‘Stellite’ layer is welded to provide superior hardness, corrosion

resistance, good surface finish and high temperature strength.This

portion is subjected to very high temperatures and thermal and

mechanical stresses.

‘Stellite’ : 2C, 50 Co, 20 Cr, 18 Mo, 10 Tungsten

Valve Seats

‘Stellite’ coating, since seats are also prone to corrosion and erosion.

Valve Cages

Cast Iron provides easy manufacture and compatibility with guide

material.

Valve Guide

‘Pearlite’ Cast Iron.

Valve Springs

They provide support to the valve in the cylinder head as well as

provide a spring force to close the valve. Single Spring type is simple,

has a lower natural frequency of vibration and a reduced risk of valve

bounce. There is a buckling risk for long single springs, while large

diameter springs have higher bending movements and stresses.

52

53


Engine Components

Series springs have less buckling and bending stresses, but their designs

are complex. A n example is shown in Fig - 41. Springs are shown in

series numbered 1 and 2.

Parallel springs are employed to alter the natural frequency. There is

no axial vibration, and less breakage due to resonance. The safety

factor is increased in case o f the failure o f one spring. A n example is

shown in Fig - 42. Springs are shown in parallel numbered 1 and 2.

E xhaust Seat Profile Change

D uring Load

Fig 1 shows the inner contact area

when exhaust valve is not loaded.

Fig 2 shows the effect o f thermal

load on the exhaust valve seat.

Fig 3 shows the increased even

loading seating area.

Fig-43

In closed position (Fig. A), the ‘Belleville’ washer disc is pushed against

the body with slight force and disc spring is not deflected. When the

valve opens (Fig. B), the ‘Belleville’ washer disc gets pushed against

the body with a higher force. This load is transferred to the balls,

which causes the balls to be pushed to the deeper recesses and induce

rotation. Relieving of pressure when valve closes, causes the balls and

the springs to return to the original position.

Valve Rotation Benefits

There are less deposits on seat passages and sealing faces. Corrosion

and erosion is reduced. Overheating o f a single spot is prevented as

the valve is rotating. Temperatures of the valve seat and sealing faces

are reduced. Rotation is needed when burning heavy fuel oils.

Rotating methods a r e :

♦ Rotating vanes e.g. used in hydraulically operated exhaust vfclves.

♦ Rotocaps e.g. mechanical rotators used in mechanical spring

operated exhaust valves as in 4-stroke engines.

54

55


Engine Components

Variable Exhaust Closing (VEC)

VEC = Variable Exhaust Closing

= Exhaust Valve closed earlier to increase the compression,

and consequently, Pcomp and Pmax.

When the exhaust valve is open, less amount o f compression is done

by the piston. When the exhaust valve is closed earlier, the piston can

start compression earlier, resulting in a longer period for compression.

VEC is carried out during 70 to 85% MCR load.

VEC Operation

In case o f a hydraulically operated exhaust valve, some of this hydraulic

oil pressure for opening the valve is leaked off, when the valve is still

in the open position. This results in the valve closing slightly when

open, and the valve fully closing earlier.

E xhaust Valve Failures

♦ High temperature corrosion by molten salts (sodium and calcium

sulphate); and compounds from the fuel due to sulphur, vanadium,

sodium, and catalyst fines (sulphur oxides, vanadium oxides, sodium

oxides, etc.).

♦ Erosion at the seat area and sealing faces.

♦ Dents and scratches caused by harder particles.

♦ Solid deposits o f molten salts causing leakage and cracks.

♦ Overheated spots due to after burning, poor cooling, improper

combustion or overload.

♦ Reseating failures due to incorrect tappet clearances, incorrect

expansion clearance, overheating, jamming in the guide, distortion

of valve or spindle, and creep failures.

♦ Mechanical impact loading due to banging, heavy seating, uneven

surfaces or hard deposits.

♦ Abrasive action by products fromfuel combustion orcylinderlubeoil.

♦ Fouling of valve or valve passages which limit the air or exhaust

gas flow rates.

♦ Valve mechanism failures of springs or rotating mechanisms.

♦ Valve lift reduction.

Leaky E xhaust Valve

It causes a high exhaust gas temperature and increased smoke. Pcomp

and Pmax reduce. The turbocharger may surge.

Curve A curve at 100 % load

Curve C curve without VEC at part load

Curve B curve with VEC at pan load Point p shows earlier closing of valve.

Fouled Inlet Valve

It causes a restriction in the air flow. Hence, scavengeefficiency reduces

and thermal stresses increase. The exhaust passages get fouled as a

result and there is more smoke from the exhaust.

56

57


Fouled E xhaust Valve

It causes a reduction in the exhaust gas flow; and fouling of the exhaust

passages, the turbocharger and the exhaust gas economizer. The

scavenge efficiency decreases, while exhaust temperatures increase.

Exhaust gas may leak back into the cylinder and get recycled.

Crankshaft

The crankshaft is a very important and heavily stressed component It

is subjected to fluctuating loads due to the inertia forces of rotating

masses, combustion gas pressure loads and high bending and torsion

loads. The crank angle for the angular arrangement o f each crank with

respect to the other depends on the number o f strokes and cylinders

of the engine. Balanced weights are fitted to the webs to balance inertia

forces of rotating and gyrating masses.

Types: (1) Fully Built (2) Semi-built (3) Solid single piece (4) Fully

welded type.

Fully B uilt Up Crankshafts

They have all parts separately manufactured by steel casting or forging,

and then fully built up i.e. assembled using a shrink fit (1/600 of pin

diameter). Shrink fit is the friction between the pin and web sufficient

enough to transmit the torque without stressing the pin and web. It is

done by cooling the pin in liquid nitrogen rather than heating the web.

Very few engines use fully built up crankshafts. It is only used on some

very large slow speed engines.

Advantages

Their construction and design is simple; easy replacement of damaged

parts; easy handling and machining of parts; any part of the crankshaft

can be repaired in sections if damages take place; and most o f the

machinery can be completed during the manufacturing stage itself before

assembly.

Engine Components

Plsad vantages

I The webs should have considerable strength to allow two shrunk fits.

J I I nee there is a lack of grain flow, there is no benefit of the same.

Sem i B uilt Up Cranshafts

[ They are shrunk fit assemblies of complete crank throws (one crank

[ pin and web together) and separate journal pins. They are widely

I used on slow speed 2-stroke engines and large 4-stroke medium speed

engines.

Fig-47

1 One crank throw 2 Journal pin

58

59


Engine Components

Advantages

Each crank throw is forged by continuous grain method which maintains

a path for the grain flow along the crank throw axis. Hence it can use

the benefit of grain flow. It has a better fatigue resistance, less shrink

fits, smaller webs and a lighter shaft weight. Larger pin diameters can

be used.

Solid Single Piece Crankshafts

They are those crankshafts where the whole crank shaft is forged or

cast as one single piece.

Advantages

It has a better fatigue resistance, lesser stresses, a smaller and lighter

shaft, continuous grain flow throughout shaft and no need for shrink fits.

Balanced counter weights can be fitted as shown in the figure.

Fully Welded Crankshafts

They are full, half forged, or cast crank throws joined to the journal

pins by continuous feed narrow gap, submerged arc welding.

Advantages

Here, there are no shrink fits or restrictions on the pin diameter. Smaller

and lighter shafts can be used.

| Half crank throw

2 Full crank throw

'

•I

Two half crank throws welded

leaving a small gap at the mating faces

Dummy piece backing.

Fig-49

Materials

♦ High carbon steel (0.35 to 0.45 C) for slow speeds.

♦ High carbon steel with alloys for medium high speeds.

♦ Chromium, tungsten, nickel and magnesium alloys are used in

percentage of 1.5 % each.

Crankshaft Failures

Fatigue and cyclic stress failures are mostly due to high frequency low

loads or low frequency high loads.

The areas of crankshaft failures are:

♦ Shrink fit stress raisers at dowel pins or keys.

♦ Any sharp changes in section where stresses get concentrated.

♦ Severe operating conditions and overload.

♦ Lube oil passages, holes and drilling sections. The radii of the lube

oil hole should be ample to reduce the stress concentration.

♦ Pin to web fillet section should have ample radii.

♦ Surface defects and sharp edges.

♦ Incorrect manufacture like slag inclusion and poor heat treatment.

♦ Torsional stresses giving a helical-shaped crack at 45 degrees to

the axis of the pin.

♦ Misalignment of main bearings.

60

61


Engine Components

♦ Slippage of shrink fits are seen when engine timings change over

some part of the engine only, with an increase in vibration at that

section and a shift in the ‘markings’ embossed at the pin/web

interface. This slippage can be due to piston seizure; hydraulic

lock in cylinder during starting; starting the engine with turning gears

engaged (in case o f no interlock on smaller engines); bottom end

bolt failure; etc. If minor slippage occurs, adjust timings and monitor.

If major slippage (greater than 4 degrees) occurs, then return to

original position using hydraulic jacks, strong backs and liquid

nitrogen. No heating is to be done to avoid stresses.

♦ Corrosion fatigue due to lube oil turning acidic caused by lube oil

contaminated by combustion products.

♦ Lubrication failures.

♦ Poor support from bedplate foundation and tie rods.

Crankshaft Stresses

1. Variable combustion gas load: The radial component causes the

pin and webs to bend and twist. The tangential component causes

. bending stress in webs and torsion stress in the journal.

2. Torsional vibration stress in web pins is due to the shaft being

wound up under torsional load and unwound due to its own stiffness.

3. Axial vibration stress due to the repeated in-plane flexing of webs

and the reaction the intermittent propeller thrust.

4. Misalignment of the main bearings leading to cyclic opening and

closing of the crank throw causing in-plane bending and tangential

bending stresses. Misalignment can be caused by:

(a) Wear or distortion of the bedplate or excessive bending of the

engine framework. e.g. grounding or incorrect cargo distribution.

(b) Worn main bearings due to incorrect adjustments, overloading,

vibration, or poor lubrication.

Crankshaft Deflections

The crankshaft will deflect i.e. webs open and close as the engine

turns, in the vertical as well as horizontal directions.

Fig-50

Fig-51

Closing o f crank throw is a negative reading as shown in Fig. 50-A.

Deflection Procedure

Place a dial gauge opposite the crank pin on the port side and set the

pointer to zero as shown in Fig. 51 -C. Looking in the forward

direction, read the dial gauge readings as shown Fig. 50-B.

62 63


Engine Components

Factors affecting Deflections

♦ A flexible shaft and not a stiff one is desirable. A stiff crank shaft is

one where the crank shaft is stiff enough to support itself across a

span including a low bearing i.e. the journal may not be sitting on

the bearing. Check by using a feeler gauge or jack the shaft onto

the bearing.

♦ Ambient temperature near the engine.

♦ Movements of the ship as in rough weather.

♦ Incorrect load condition i.e. hogging or sagging.

away from the guide bar. The limit o f slackness is half to one chain

pitchlink. Iftoo slack or too tight, adjust the chain tension. Adjustment

is done for slackness o f 1 pitch length.

Chain Drive

Chain drive is used to transmit the

power drive from the crankshaft to

the camshaft. An intermediate wheel

(for fuel pum p and exhaust cam

drives) serves as a guide, while an

adjuster wheel serves to adjust the

chain. The intermediate wheel may be

connected to a separate chain for

driving motion to the lubricators,

governor, air distributor, etc.

1 Fitting tool 2 Outer link plate ■ 3 Pin

4 Bush 5 Roller

Chain Tightening

Checking Tightness

Turn the engine so as to slacken the longest free lengths of the chain.

A t the middle o f the longest face length of the chain, pull the chain

Tightening Procedure

8

9

A, B, C, D

Lock washers

Thrust

Spring

Nuts

Fig-55

♦ The engine is turned so that slackness is on the same side as the

tightener unit.

♦ Loosen nuts A, B, C and D.

♦ Tighten the nut C till the free length is reduced by the dimension as

per the manufacturer’s guide book.

♦ Chain tightener bolt is moved and the chain is tightened.

64

65


Engine Components

♦ Lightly tighten nut B against pivot shaft face, while checking that

the spring is not further compressed, since compression reduces

chain tension.

♦ Tighten nut A and lock with lock nut and tab washer.

♦ Tighten nut C until the spring thrust disc bears against the distance

pipe of the bolt.

♦ The spring is further compressed, but this tension is not transmitted

to the chain on account of the already tightened nuts A and B.

♦ When the thrust disc presses tightly against the distance pipe, the

nut C is further tightened to manufacturer’s dimension setting

‘D-2’.

♦ Tighten lock nut D, locking both nuts with tab washer.

Chain Inspection

Check chain teeth w ear at point 1, as

shown in the figure. Place a short straight

edge plate, cover the points A and B, and

measure wear at point 1. Scratches on

teeth sides due to the side plates are

normal. Check for cracks on the possibly

defective rollers and side plates. Check

for seizure. Check the rollers run freely

and links m ove freely on pin and bush.

Check for one complete revolution. Check bolt, screw and nut

connections. Check lube oil pipe for damage and je t nozzle for

deformations. Check rubber track of guide-ways for cracks.

C hain Materials

(1) Link plates :Cr-M o steel

(2) Pin : Hardened steel (interference fit into outer link plate)

(3) Rollers : Alloy steel

Chain Drive Advantages

Easy timing adjustments are possible. Maximum flexibility exists for

positioning the gap between driven equipment. Its cost is economical

and very few spares are required. It has a very high drive efficiency

(98 %) andean cope with a certain extent of misalignment due to axial

movement of shafts.

Chain Elongation

Elongation or stretch of the chain is due to the wear between pins and

bushings, roller and sprocket wheel, and between bushing and rollers.

Elongation changes the camshaft position with respect to the crankshaft

Fuel and valve timings depend on the camshaft position and are altered

due to chain elongation. Maximum elongation allowed is 2%. At 1.5%

elongation renew the chain. Elongation is checked on a ‘taut’ chain by

measuring the length of a number of links from pin centre to pin centre.

It is the difference between measured length and new chain length.

Slack Chain

It results in excess strain during starting and reversing. There is a greater

shock loading during normal running and retarding o f timings in both

directions due to backlash, especially during maneuvering and load

changes. Vibration iri addition to cyclic stresses may cause possible

fatigue failure.

T ight Chain

It results in overloading o f the chain wheel bearings. This gives rise to

wear on rollers, links and bearings; and can cause cracking of links.

66

67


Engine Components

Camshaft Readjustment After Chain Tightening

Readjustment o f the camshaft’s angular position will be required to be

done, in case o f repeated chain tightening, as this causes the camshaft

position to be altered with respect to the crankshaft. The limit is a 2

degrees increase in lead angle over the initial angular position.

A bearing in a marine diesel engine is required to support the journal;

to float the journal so that there is no metal to metal contact; to transmit

the load via the lubricant; and to reduce rotational friction. Material

properties required are anti-friction resistant; running-in and grindingin

ability; noncorrosive by lubricants; should not scratch or score the

journal; build up adhesive oil films under boundary lubrication; allow

abrasive particles to be embedded in it without m ajor functional

disability; tensile and compressive strength; fatigue resistant; thermal

conductivity; high melting point especially when running hot; load

carrying capacity; and ductility.

Bearing M aterials

(1) While Metal Bearings :

Anti friction, tin-based, white metal alloys (called Babbitt) consist o f :

Tin (Sn) 88 % Soft matrix to allow for small changes in

alignment between bearing and journal.

Antimony (Sb) 8% H ad wear resistant cubes to absorb and

transmit load.

Copper (Cu) 4% To segregate and hold antimony cubes in a

tin matrix.

Turn crank throw o f No. 1 cylinder to TDC. Check camshaft angular

position using the pin gauge and marking. Remove plug screws for

hydraulic oil connection in the coupling flange. Mount snap-on hydraulic

connectors and piping to the hydraulic pump. Apply hydraulic oil

pressure to float the coupling ( coupling floats when oil seeps out

along shaft below coupling flange). 1\im and adjust coupling with a

special spanner and check position with pin gauge. Release oil pressure

after finishing. Wait for 15 minutes before plugging oil holes so as to

allow the coupling flange to set again.

(2) Thin Wall Shell Bearings:

These bearings are usually of tri-metal type, having 3 main layers and a steel

backing shell,

1“ layer (Flash)

2“ layer (Overlay)

3"1layer (Interlay)

4® layer (Lining)

Shell (Bottom)

1 micron thickness of lead / tin for corrosion

before installing bearing.

20 micron thick white metal.

5 micron thick nickel dam helps to reduce

corrosion of the white metal 2“ layer.

1 mm thick lead / bronze.

It is a steel backing shell for shape and support

68

69

Engine Components

K s h J o u r n a l Bearing

an 7 rotation o f the shaft,

due to'Ved§ePreSSUreis f0imed

d i v e r t bein^ draW nint° the

o f the' 1 secticm by the motion

j0lirnal. T h is oil pressure

separate^ the journ al and the

^ W . » p l a i n b ushtype, Fig-58

load but s effeCtlTe’ remaining two-thirds canies negligible

loss C{iti]i causes the oil film to shear. Ibis results in heat and friction

li'ews S * J m rn a ‘ Beari"g

journal ofjoP3^ the plain bush is repiaced by a series of

0Wn0“ ^ 1 t a 8 P,V0“ “ d t a t 0 “ t' S“ erato8itS

Advanta^

It is d e s i ^ ^ to geminate oil whirl.

. 6 cap^citv and efficiency is

S

V,^- The radial load ia

and n o tp ^ tbroughthaby oil films

, ■ , JUSt one oil film. It has a

thSi!»ort>'lo,ht* ad,5' The“ tof

y ,djusE

1 “ ? load, the feed and the

0Slty the oil- It allows for

to t e f a ? * 1' Of inisalignment due

adiustinst

adjusting tc>th

leivolingj°umalpads,

eoflheshaft

70

Bearing Faults and D efects

♦ Abrasive wear due to fine scoring by hard particles and impurities

in the lube oil.

♦ Corrosive wear due to acidic lube oil. The lube oil becomes acidic

due to oxidation, contamination from combustion products,'or

water ingress.

♦ Erosive wear due to cavitation.

♦ Adhesive wear due to galling, scoring or scuffing. In galling, the

softer metal tears due to the adhesive force which is a reaction of

the rubbing metal surfaces.

♦ Fatigue failure cracks at areas of stress concentration.

♦ Overheating due to poor lubrication supply or contaminated oil,

misalignment, incorrect clearances, uneven load distribution, poor

surface finish and overloading.

♦ Misalignment of the bearing due to distorted bedplate, adjacent

bearing failure, or imbalanced cylinder pressures.

♦ Incorrect clearances or incorrect tensioning o f bolts.

♦ Poor design, manufacture or low strength.

♦ Housing dimensions not perfectly suitable for bearing shells,

especially during replacement.

Bearings In the Engine

The following bearings in the engine are discussed below.

M ain Bearing

Main Bearings are the bearings which support the crankshaft of the

engine. The lower shell part o f the bearings are cut into the transverse

strength members of the bedplate. The upper shell cap is held in place

by special jack bolts or secured by wasted studs. Thin shell babbitt

71


Engine Components

(white metal) with a steel back is used for the main bearing. Babbitt has

a low fatigue strength and hence, pressures and temperatures are limited.

1 Hydraulic nut

2 Top cover cap

3 Wasted stud

4 Upper bearing shell

5 Crank shaft

6 Lower bearing shell

7 Bedplate transverse cylinder

Connecting Rod and Bearings

Connecting rod is the rod connecting the top-end bearing (crosshead

bearing in 2-stroke slow speed engines or the piston gudgeon bearing

in 4 stroke medium speed) and the bottom end bearing (crank pin

bearing). Its purpose is to convert reciprocating motion of the piston

into rotary motion of the crankshaft It is the most

highly stressed component of a diesel engine. It is

subjected to ahigh purely compressive force. It links

the piston rod and crosshead to the crankpin.

2-Stroke Connecting Rods ( Slow S p e e d )

They are of split type i.e. two halves for each small

and big end bearings. This helps in easy fitting and

repair. The round m id section changes to a

rectangular palm section at the bearing ends by

means of the elliptical fillet shape. A round section

is cheaper to manufacture. Examples are shown in

Fig - 61 and Fig - 62.

72

Fig-61

1 Top cover of top end

2,3 Bearing shells of top end

4,5 Hydraulic stud nut

7 Bottom end cover

6,8 Bearing shells of bottom end

0 Crosshead pin at top end

10 Crank pin at bottom end

Fig-62

4-Stroke Connecting Rods

(M edium Speed)

In these engines, only the big end

bearings are split, usually in an oblique

direction to reduce the big-end width,

lessen load on bolts and increase

crankpin diameter. The top-end may

be a bush type bearing. Rectangular

or I-sections, although more expensive

to manufacture, are necessary to resist

the high transverse inertia whip

loading, the gas loads, and to fulfil the

weight to strength requirements. It is

subjected to high compressive-low

tensile stresses o f bending as well as

axial type. It connects the crank pin

directly to the piston gudgeon pin.

1 Top end

3 Gudgeon pin

5 Obliquely split bottom-end

73

Bush bearing

Lubricating oil passages

Serrated edge


Engine Components

Connecting R od Failures

In slow speed 2-stroke engines, failures occur in veiy few cases, except

due to slight buckling, when starting the engine if oil or water has

leaked into the cylinder space. In medium and high speed 4-stroke

engines, fatigue cracks or fractures can occur in high stress

concentration areas. Thin walled steel back shell bearings have more

possibilities to fail rather than white metal bearings. Transverse buckling

is usually caused by crank pin bearing seizures.

Bottom E n d Failures

In 4-stroke engines, the bottom end of the connecting rod is more

susceptible to failure. The forces acting on bearings and bolts a re :

1. Constantly fluctuating inertia loads from reciprocating parts

swinging in a ‘whip’ motion.

2. Tensile load caused b y the centrifugal forces o f the mass of

connecting rod and crankpin.

3. Shear force tending to separate the two halves o f the bearing

housing.

Bottom E n d Bolt Design

♦ A pretension is given to the bolt while fitting. Incorrect pretension

is the m ost important cause o f fatigue failure o f the bolt which is

initiated at a mechanical defect.

♦ The resilient material used for the bolt should be less stiff than the

bearing housing.

♦ The diameter of the shank sections should be sm aller than the

threaded root portion so that this ensures greater stresses act at

the shanks rather than the threaded portion.

♦ The yield of threads is prevented by a portion of the shank having

a tight clearance in the hole bore. Here, the nut is tightened ‘square’

into the spot faced bearing housing.

♦ Large fillet radii are given, since fillets are stress concentration areas

as there is a change in the cross-section.

♦ Resilience o f bolts is increased by designing the housing part as

long as possible.

Large E n d Bolt D efects

If the large end bolts are defective, then they should be discarded in

case o f overspeed failure, piston seizure, exceeded tolerance,

completed designated life, acidic lube oil corrosion and mechanical

damage like cracks and fractures to the surfaces of land faces.

Crosshead Bearing

Unlike the main bearings,

b ig e n d b earin g s and

camshaft bearings, where

motion is only rotational,

crosshead bearings have to

take in to account

oscillatory motion at high

sliding speeds.

I 1 Rail 2 Shoe

| 3 Pin________________________ 4 Plate__________________________ |

In 2-stroke engines, a cyclic unidirectional combined gas and inertia

load acts continuously on the bearing in a downward direction. Hence,

the bottom half o f the crosshead bearings are more prone to wear. In

4-stroke engines, the bottom half has some load relief during the suction

and exhaust stroke where the inertia force is greater than the gas force.

Lubrication at this time is ideal.

74

75

Marine Diesel Engir

Engine Components

Crosshead Failures

Crosshead bearing failures are due to poor lubrication; misalignment

with running gear (piston and liner); white metal cracking; fatigue failure;

squeezing o f white metal causing partial blocking of oil holes;

overheating; corrosion; white metal quality; and reduced strength due

to improper thickness or type. Insufficient or contaminated oil results

in poor lubrication of the bearing. Another important aspect in

crosshead failures is the crosshead pin surface finish.

Crosshead Developments

♦ Oil grooves are cut into the bearing surfaces and the guides to act

as oil reservoirs.

♦ For crosshead design, the pin can be considered as a single beam

supported at the ends. Applying load only in the middle of the pin

creates a bending movement. This condition can be corrected by

increasing the pin stiffness by having a pin of a larger diameter for

the same length. There is better distribution of load since a larger

surface area is now available. Pin stiffness can be increased by

using a hollow pin for better section modulus.

♦ Use of flexible bearing mounts as in RND engines. Here, the pin

distortion is taken by the mounts and edge loading is reduced.

♦ A rigid support over the whole pin area is used rather than the

fork-end type in earlier engines.

♦ Mounting of the piston rod on top of the crosshead pin, so as to

use the full length of the bottom bearing. The bottom shell is of

‘continuous’ type.

♦ Superior surface finish o f the bearing and pin.This is done by

accurately grinding and then ‘super-finishing’ i.e. polishing the pin

w iththeaidofhonesonalathe. The load carrying-capacity of a

‘super-finished’ bearing surface is twice that of a very fine-ground

bearing surface. Surface finish is very important as not only is the

crosshead bearing under a very heavy instantaneous firing load, it

is also very difficult to supply and maintain the oil film. Surface

finish and roughness of ‘in-use’pins is the criteria for judging the

crosshead bearing’s further use.

♦ Alignment of crosshead is improved by changes in design and

manufacturing techniques. In fully welded design, only longitudinal

adjustment is provided.

♦ Improvedbearing materials are used like white metal, tin-aluminium,

tin-cadmium, etc.

♦ Bearing material thickness is reduced by bonding it to a lining and

steel backing. This improves overall strength. Example: Thin shell

tri-metal bearing.

Puncture Valve

♦ It is a device to positively stop the engine irrespective of the rack

position.

♦ It reduces the high pressure of the fuel oil by connecting the high

pressure side to the pump body, thereby stopping the injection of

fuel.

♦ Engine stops and shut downs are carried out using the puncture

valve.

♦ It allows fuel oil recirculation when the engine is stopped since oil

pressure is not totally bypassed.

♦ It is operated by pneumatic air pressure.

♦ It is used in MAN B&W engines.

76

77


Engine Components

E ngine M aterials

1 Exhaust Valve

Exhaust Valve Seat

Exhaust Valve Cage

2 Cylinder Head Cover.

3 Piston Crown

Skirt

Rod

Ring

5 Tie Rod

6 Entabulature

7 Stuffing Box Rings

8 Crosshead Bearing

9 Crosshead Guides

10 Connecting Rod

11 Crank Pin Bearing

12 Crankshaft Web

13 Main Bearing

14 Saddle

15 Bed Plate

16 A-Frame

Propeller

Hull

Coating ofStellite(iftemperature is less than 500deg. Q

or Nimonic (if temperature is greater than 500 deg. C)

Mo-Steel with Stellite coating

Pearlite Cast Iron

Lamellar Cast Iron

Cast Steel

Cast Iron

Forged Steel

Vermicular Cast Iron, RVK- C, R-C

Spheroidal Cast Bon, Ihrk Alloy, Tarkall-A, Tark-C

Mild Steel

Cast Iron

Bronze

Tin-Al-white metal thin shell bearing

Mild or Medium Steel (U.T.S. 500MN/sq.m.)

White metal bearing

0.2 to 0.4 % Carbon Mild Steel

Thin shell white metal bearing

Cast Steel

Forged Steel or Cast Iron

Forged Steel

Nicalium, Al-Bronze, Mg-Bronze

Mild Steel or High Tensile Steel (20 to 30 mm).

Fig-65

78

79

CHAPTER 3

AIR SYSTEM

Scavenging

It is the process in a diesel engine, in which low pressure air is

utilized to blow out the waste gases of combustion i.e. scavenging,

and refill the cylinder with fresh pressurized air for the next

compression stroke. The various types of scavenging are described

below.

Uniflow Scavenging

Uniflow, as the name suggests, is an

air flow in the same direction. Low

pressure air is allowed in at the bottom

of the cylinder with slight rotation and

the exhaust gas is pushed out from the

top o f th e cylinder. U niflow

scavenging is required in modern

engines to use the advantages o f slow

speed and a long stroke (which in tu rn ,_

requires better scavenge efficiency to

burn present day cheap heavy fuel

oils).

Fig-66


Air System

Advantages

The scavenge efficiency is the highest. There is n o exhaust and

scavenge intermixing. Working temperatures are reduced. Costly

cylinder lube o il consumption is reduced (0.3 gm/bhp/hr to 0.6

gm/bhp/hr for crosshead type engines). Less residual exhaust

gas remains in the cylinder after scavenging. T he air loss during

exhaust and scavenging is nil. It’s liner design is much simpler

than other types and a shorter piston skirt can be used. Thermal

stresses are also m uch less as compared to other scavenging

methods.

M ethods:

1. Using a single poppet type exhaust valve at

top of the engine cylinder. The large area at

the exhaust valve allows speedy exhaust gas

escape and improves scavenge efficiency.

M ost modem 2-stroke engines employ this

method.

Reverse Flow Scavenging

It consists o f Loop or Cross scavenging systems.

Advantages

The design is simpler. There is no valve gear maintenance nor

power consumption required for the same.

Disadvantages

Consumption o f expensive cylinder lube oil increases. Undesirable

mixing o f scavenge and exhaust gases is increased. Scavenge

efficiency is less. Exhaust back pressure may increase due to

narrow ing dow n o f exhaust passages w ith carbon deposits.

Chances o f cracks are possible due to thermal stresses at the

scavenge and exhaust ports area. The tem perature variation

between scavenge and exhaust ports is confined to a limited area

in the region o f the ports. Uneven w ear o f piston rings can cause

leaks. Liner costs are more as the liner design is more complicated.

It cannot use the advantage o f a modem engine’s increase in stroke

bore ratio, which is why it is rarely used nowadays.

2. Opposed piston method.

In opposed piston engines, one piston controls

the air inlet ports (bottom piston), while the

other controls the exhaust ports (top piston).

Only outdated older engines like Doxford

engines employed this method.

Fig-68

Loop Scavenging

In loop scavenging, the flow o f air and gas is

in a ‘loop’ path. The air inlet and exhaust ports

are arranged on the sam e side o f the cylinder.

Loop scavenging is best for stroke-bore ratios

o f less than 2:3, or else it is thermodynamically

disadvantageous. Hence, modem engines with

high stroke-bore ratios do not use the loop

type method.

Fig-69

82


Air System

Cross Scavenging

In cross scavenging, the air and gas flow is in

the ‘across’ path. i.e. air inlet and exhaust ports

are situated on opposite sides o f the cylinder.

Gas Exchange Process

Fig - 70

In a diesel engine, the gas exchange process consists o f :

1. Blow D own o f Exhaust Gases

It starts when exhaust valves open or exhaust ports are

uncovered. Exhaust gases are ‘blown down’ rapidly into the

manifold. They are helped by the sudden opening o f the exhaust

valves or ports. This advance in timing o f the opening of the

exhaust valve before the inlet valve is called Exhaust Lead.

The end o f this blow down period is when the inlet ports are

uncovered. The cylinder pressure falls below the scavenge

pressure after blow down.

2. Scavenging

Since the cylinder pressure is less than the scavenge box

pressure, the fresh scavenging air pushes the residual gases

out, the m oment the scavenge ports open.

3. Post-Scavenging

Post or After Scavenging period is the completion o f the

scavenge process and prevention o f any fresh air loss through

the exhaust valve or ports. This depends on the exhaust valve

closing precisely when fresh air has fully filled the cylinder

and residual gases have been fully pushed out. Inter mixing of

fresh air w ith exhaust gases is not desirable at this stage, as it

would contaminate the fresh air with exhaust and increase the

fresh air temperature. However, the sweeping action o f the

fresh air produces a cooling effect lowering the cylinder

temperature.

Super Charging or Pressure Charging

Combustion and power depend on the amount o f fuel and air

supplied, since proper combustion requires a stoichiometric air

fuel ratio of 14 : 1. The amount o f fuel to be burnt is limited by

the ratio o f air that can be supplied. If we increase the mass o f air

i.e. its density and pressure, w e can use more fuel for burning.

Hence supercharging o r pressure charging o f the combustion air

supplied allow s m ore pow er to b e developed w ith proper

combustion. Supercharging or Turbocharging is the pressure

charging o f air supplied to the cylinder at the beginning of

compression. In 2-stroke m arine engines, in order to achieve

correct combustion, good scavenging and effective cooling, thrice

the amount o f ideal combustion air quantity is supplied. This is

called Excess A ir for proper combustion.

Advantages o f super or pressure charging

Power is increased for the sam e engine dimensions and piston

speed. There is no appreciable increase in cylinder maximum

pressure. The initial costs are reduced, since a more powerful

engine can have smaller size, space and mass. It gives better

reliability and cylinder operating conditions. There is less

m aintenance. Fuel consum ption reduces w hile m echanical

efficiency increases. Codling is improved since a greater mass of

84

85


Air System

fresh cool air is supplied. There is better utilization o f waste

exhaust gas energy which can be used to drive the turbochargers.

S u p ercharg in g M ethods

1) Mechanical Supercharging using :

♦ A rotary air blower driven by the diesel engine crankshaft.

Here, some indicated engine power is wasted in the drive.

Hence there is less m echanical efficiency and more fuel

consumption. It is inefficient at higher pressures.

♦ Scavenge Pumps which are of engine driven reciprocating

type.

♦ Under Piston Space Scavenging using under piston spaces

to pump the air.

♦ Auxiliary Blowers which are of independently driven

type. These are used mostly in the first o r second stage

o f a combined supercharging system only as scavenge

assistance.

2) Turbine Supercharging

Turbochargers use waste heat o f the exhaust gas to drive

a turbine which in turn, drives a compressor (blower) on

the same shaft to supply pressurized air.

Turbocharging Types

Different types o f turbocharging methods are discussed below.

Constant Pressure Turbocharging

In this type, exhaust gas from each cylinder is lead to a common

exhaust m anifold w hich then supplies exhaust gas to the

turbocharger at a ‘constant pressure’. The exhaust manifold space

is large enough for the volume o f combined exhaust gases without

any pressure rise. Hence, a constant pressure is available to the

turbine. However, the exhaust manifold should not be too big, as

then there would be a longer time required for the desired exhaust

pressure rise in it. The exhaust gas flow into the manifold creates

eddies which, in turn, damp out any pressure waves or pulses.

Work is not done when exhaust gas is throttled through the exhaust

v alv e in to th e larg e

m anifold. W ork is done

when exhaust gases expand

through the turbine nozzle

and blades which is seen as

a thermodynamic drop i.e.

an utilization o f exhaust

gas heat.

1 Exhaust manifold

2 Turbine

3 Compressor

4 Aircooler

5 Air receiver

6 Engine piston

7 Engine cylinder

Advantages o f constant pressure type

It is m ore efficient. The turbine operation is better when a

constant pressure is available at th e turbine inlet. B etter

scavenging is possible at higher loads. Exhaust-grouping is not

required. It can use the advantage o f m odem ‘long stroke’

engines, since m ore tim e is available for expansion in the

combustion cylinder itself. Hence, greater use o f heat energy in

the cylinder and lower exhaust temperatures is possible. Since

exhaust pressure pulses are not used, more energy is available

fo r reco v ery at th e tu rb in e and com pressor. H ence, th e

86

87


Air System

com pressor output is increased. There is a greater utilization o f

waste exhaust energy used in m arine engines because the main

engine runs at a higher load m ost o f the tim e allowing a constant

load w ith less load changes.

Disadvantages

It cannot cope up at low or part loads. Here, the auxiliary electric

blowers supply air when the pressure falls below a preset value.

Due to the large exhaust manifold, there is a very slow response

to load changes.

Pulse Turbocharging

Pulse Turbocharging uses the pressure pulse w ave to expand the

gas further a t the turbine nozzles and blades. Exhaust gas from

each cylinder is directly lead to the turbine inlet. Here, pulses i.e.

pressure waves are created, when the exhaust valve suddenly opens

and exhaust is blown down into the exhaust piping of smaller

diameter, thereby pressurizing

it. For maximum usage o f the

pulse, the pulse should be as

close to the turbine inlet. Work

is done by th e exhaust gas

expanding fu rth e r at the

turbine nozzle and blades.

1 Turbine

2 Compressor

3 Air cooler

' 4 Air receiver

5 Rotor

6 Cylinder

7 Exhaust Piping

- VC

' 6

a r

The requirements o f efficient pulse turbocharging are :

♦ A rapid opening o f the exhaust valve.

♦ Exhaust piping o f a large diameter, but much smaller than the

exhaust valve opening to allow for creation o f pulses.

♦ Exhaust piping to be as near as possible to the turbine inlet to

use the pulse effectively as well as prevent any pulse reflection.

E xhaust Grouping

Exhaust grouping is necessary to prevent blow back of one cylinder

into another in pulse type turbocharging. Each exhaust pipe has a

separate inlet to the turbine. Example: Three cylinders are coupled

to one turbine, with a firing interval o f 120 deg. crank difference.

Advantages

It utilizes the high kinetic energy of the exhaust gas i.e. unutilized

energy from the combustion cylinder. It can wort: effectively even

at low loads. It has a good response to load changes. It is widely

used in auxiliary power generators, where load changes are

frequent and longer periods o f low load operation is common.

Series 2-Stage Supercharging

1 Turbine

2 Compressor

3 Air cooler

4 Air receiver

5 Scavenge pump

6 Scavenge ports

7 Exhaust valve

8 Exhaust manifold

9 Air cooler & receiver.

A Single air inlet for series

Fig-73

88

Marine Diesel Engin

■Air System

Here, there is only one air inlet. Supercharging is done in two

stages in series.

1“ staSe : Air is compressed (e.g. by the turbocharger) and then

cooled in an inter cooler and supplied to the inlet of the

2nd stage in series.

2nd stage: Air is further compressed (e.g. by a scavenge pump or

under piston spaces) and sent to an after cooler and then,

to the scavenge air ports.

Parallel Supercharging

A Separate air inlet

B

to turbocharger

Separate air inlet

to under piston spaces

1 Cylinder head

2 Tie bolts

3 Engine cylinder

4 Piston

5 Fuel injection pump

6 Camshaft

7 Engine frame

8 Control hand wheel

9 Bedplate

10 Connecting rod

11 Crosshead

12 Piston rod

13 Valve

14 Air cooler

15 Rotary exhaust valve

16 Turbine

17 Blower.

Here, there are two separate air inlets. Supercharging is done in

parallel. Sim ultaneous delivery o f air takes place from a

turbocharger and the under piston space pumping effect.

Two-Stage Supercharging

Supercharging in two stages gives the advantage o f more efficiency

and boost air pressure ratio, since work done in compressing the

air is reduced. Inter cooling between stages helps the compression

to approach isothermal conditions which reduce the work to be

done in compressing the air.

Single Turbocharger Systems

This type is usually used for constant pressure type turbo charging

systems.

Disadvantages

It relies only on one turbocharger and there is no standby in case

o f a failure, A larger capacity of the turbocharger is required

causing a slower response to load changes, since it will have a

higher inertia force. Spare parts replacem ent will be more

expensive.

Two Turbochargers System

This type is usually used for pulse type turbo charging systems,

since the pulse of one cylinder may interfere with another cylinder.

In case o f failure of one turbocharger, engine power output is still

sufficient although it is reduced. A t part loads, exhaust gas to one

turbocharger can be bypassed. In this case, although only one

turbocharger is in use, there will be an increase in air mass flow.

It provides better flexibility at part load.

91


Air Sysler.

Power Take-In ( P T I )

It is a system where power is ‘taken-in’ by the main engine. The

main engine has excess exhaust gas energy at full load i.e. in excess

of that required for scavenging and for the economizer. This excess

energy can be channeled back to the engine shaft to take-in and

utilize this waste exhaust gas energy. Part o f the exhaust gas can

be led to a turbine which can supply energy to the propeller shaft

through g earin g . It can be u sed only in h ig h ly e fficien t

turbochargers, where efficiency is greater than 64%.

Power Take-O ff (PTO)

It is a system w here power is ‘taken-off’ from the main engine.

Method (1): Here, exhaust gas is ‘taken-off’ from the exhaust

m anifold and is led to drive a turbine electrical

generator.

Method (2):

Here, power is ‘taken off’ from the main engine shaft

and supplied to an electric generator via a special

‘constant speed step-up gear’. This gear converts

variable engine speed into a constant speed supply

to the generator. PTO power can be tapped from 42%

power to overload. It reduces the costs of running,

maintaining, spares requirements, and lube oil

consumption o f additional diesel generators.

Method (3): Excess scavenge air from the main engine air receiver

can be led to supplem ent th e auxiliary diesel

generators, when the auxiliary diesel generators are

running on heavy fuel oil at low loads. The main

engine scavenge air is led either to the diesel

alternator’s scavenge receiver or to it’s turbocharger

compressor using nozzles.

T urbocharger Types

Basically, they are o f two types based on the flow :

♦ Axial Flow

Here, a single stage impulse reaction turbine drives a

centrifugal compressor. Exhaust gas flow in and out of

the turbine blades is along the axis o f the shaft. This type

is the m ost commonly used in marine applications.

♦ Radial Flow

Here, the exhaust flow into the turbine blade is along the

radial direction. The exhaust gas flows off the trailing

edge o f the blade and the outlet is along the axis of the

rotor. It is used in small high speed engines.

92

93


Air System

A xia l Flow Turbocharger

The figure shows an axial flow type o f turbocharger with details.

1 Volute casing 11 Lube oil sump

2 Stationary diffuser 12 Nozzle ring

3 Shaft protection sleeve 13 Exhaust gas inlet

4 Bearing (turbine side) 14 Exhaust gas outlet

5,6 Bearing lubrication from pump 15 Rotor shaft

7 Bearing (compressor side) 16 Inducer

8 Sealing air 17 Impeller

9 Air inlet 18 Labyrinth gland.

10 Lube oil pump

Construction

On the same shaft is mounted a single stage impulse reaction

turbine and a centrifugal compressor.

The Turbine consists o f a gas inlet casing with a nozzle ring; a

gas outlet casing; a turbine wheel forged integral w ith the shaft;

blades that are fitted through side entry slots; and a provision for

water cooling. In earlier designs, the casing was water-cooled,

but modem engines employ uncooled type turbochargers.

The Compressor consists o f a volute casing which houses the

impeller, inducer and diffuser. The inducer guides the air inlet

flow smoothly into the eye o f the impeller. The impeller throws

the air outwardly with a centrifugal force. The diffuser at the

discharge end converts the kinetic energy i.e. its velocity into

pressure energy, and leads the air to the volute casing. The volute

shaped casing decreases the velocity further and increases its

pressure.

Bearings are of ball and roller type combination or o f journal

sleeve type. Bearings are mounted in resilient type housings. These

housings have laminar springs which provide axial and radial

damping as well as they do not allow the bearing surfaces to chatter

or flutter when stopped.

Bearing Lubrication is integral or separate. It also allows transfer

of heat.

Roller Bearings have the advantages of less friction losses and

more accurate alignment. The disadvantages are that they are more

expensive; are prone to brinelling effect; and need higher grade

lubrication and frequent changing.

Sleeve Bearings : Although these bearings can run at higher

temperatures, running at low loads create high friction.

• 94

95


Air System

Seals : Labyrinth seals are used to prevent exhaust gas leaking

into the air side and into the bearing housing. Sealing air from the

air side is leaked off to cool and seal the shaft.

Binding w ire: A binding wire in small segments is loosely passed

through holes o f four to six blades. In order to fasten this binding

wire, it is welded to the first blade of that segment. It w orks on

the principle of centrifugal action, resulting in the loosely fitted

wire touching the outside o f the blade holes at high speeds. This

alters the frequency o f vibration and dampens it. In auxiliary

diesel generator engines, binding wires are not necessary because

they run at a constant rpm.

Fir-Tree Blade R o o t: It provides better and more even distribution

of stress at the root portion which is prone to failures. There is

less stress concentration at the joint o f the blade and the root.

Side entry fitting provides improved balance and easy replacement.

Damping wires are required which pass through the blades. These

dampen the low frequency blade vibrations. Locking o f the blade

is needed in the axial direction and a tab washer m ay be used to

secure the blade in place.

Compressor Impeller, Volute Casing, Diffuser & Inducer :

Aluminum alloy for light weight strength and smooth surface

finish.

Uncooled Dirbochargers

M odern marine engines use uncooled turbochargers, since the

exhaust gas temperatures are relatively lower than earlier types.

Instead of wasting the heat energy by cooling through water cooled

casings, this heat energy can be recovered in the exhaust gas

economizer. Thermal efficiency of the overall plant increases.

M ore heat is available at the exhaust gas econom izer inlet.

Corrosion defects are avoided which were due to the sulphur

products at low loads on the gas side o f water cooled casings.

Further details are listed in the chapter on Engine Developments.

M aterials

Turbine Wheel, Nozzle Ring, Rotor Shaft and Blades :

Nimonic 90 (Nickel-Chrome alloy) (Ni 75%, CO 18%, Ti 3%, A1

2%, C r 2%)

These have impact resistance, strength, thermal stability and creep

resistance at high temperatures of continuous operation upto 650

deg. C.

Turbine Casing :

Cast Iron with corrosion preventive plastic coatings in case of

water cooled turbochargers.

Pt. A is the temperature of exhaust gas leaving the turbocharger in a water cooled

Pi. B is the temperature of the exhaust gas leaving the turbocharger in an uncooled

Pt. B is much greater than Pt. A showing more heat available to the exhaust gas

96

97


Turbocharger Faults/Problems

♦ Fouling : The intake filter gets fouled due to oil carryover or

poor combustion at low loads which further leads to fouling

of turbine nozzle and blades. Fouled exhaust gas passages

cause a higher back pressure. M etal erosion is caused by

particles in the exhaust gas. Defective blower bearing oil seals

cause carryover o f oil to air side, thereby dirtying it. The air

cooler sea water and air side also get fouled and require constant

cleaning. Damping wires and blade roots get fouled during

running. The sealing air pipe to the compressor labyrinth may

be blocked. Hence, oil or vapour is sucked in through the

labyrinth.

♦ Bearing faults : These are due to overheating; vibration; poor

lubrication feed o r quality; misalignment; fouling imbalance;

and poor sealing and erosion o f bearing material, balls, or

rollers due to contaminated particles in the lube oil.

♦ Resilient mounting failures : These are due to poor support or

improperfitting.

♦ Vibration: It is caused due to loose foundation bolts; excitation

from external sources; water ingress due to casing leaks; and

poor combustion operations.

♦ Corrosion : The air side gets corroded due to corrosive

pollutants in the air intake area. The gas side gets corroded

due to sodium and vanadium sulphate from the exhaust gas

turning acidic at low tem peratures and also due to poor

combustion. The cooling water side gets corroded due to poor

jacket w ater treatment Or poor sealing or cracks, which lead

to exhaust gas leaking into w ater spaces.

Surging

Air System

It is the phenomenon o f irregular pulsations due to a change in

the m ass flow rate o f air w ith respect to its pressure ratio. First,

we have to understand ‘mass flow rate of air’ and ‘pressure ratio’.

The figure shows the mass flow rate of air and pressure ratio from

a compressor (blower) through a damper.

Incase ‘A ’, the damper is fully

open, m ass flow rate is

maximum, and pressure ratio

is minimum. The mass o f air

will flow easily without any

resistance from the damper.

CP — *

O3 —» z b

CP..— '...^ c

cow*

In case ‘B ’, the damper is

throttled slightly. Resistance

Fig-78

d ue to th e dam p er w ill

increase. Mass flow rate decreases, pressure ratio increases.

In case 'C', the damper is throttled significantly and suddenly.

Resistance due to the damper increases, mass flow rate is so low

and pressure ratio is so high that the m ass flow breaks down. At

this breakdown, the pressure pulsation is relieved backwards to

the compressor. This phenomenon is called ‘surging’ , where loud

‘gulps’, howling and banging sounds are heard.

Compressor M ap Characteristics

The C om pressor M ap show s the com pressor perform ance

characteristics. Here, the effect o f changes in speed (i.e. constant

speed lines at different percentages o f blower rpm N) are shown

with respect to the m ass flow rate and pressure ratio o f air.

Isentropic efficiency curves are shown for 80%, 75%, 70% and

98

99


Air System

In Case A - Normal flow through the impeller and diffuser is shown.

Fig-79

65% efficiency. Engine operation on the left side of the surge line

will bring about instability and surging. On the right side o f the surge

line, although there are changes in operation, the change in the amount

of air flow is matched o r balanced by a proportionate change in

pressure. A safety margin in the difference between the surge line and

the main engine operating line is shown.

Fig - 80

1 Impeller and Inducer of compressor wheel

2 Stationary diffuser.

In Case B - The effect of sudden speed changes cause incidence

losses at the diffuser entry. Eddies are formed in

the diffuser. This is the trigger for surging.

In Case C - The eddies produce a turbulent choking effect at the

diffuser w hich throttles the air flow like a damper.

Sudden pressure changes due to this choking o r throttling effect

cause a breakdown o f mass flow. A back flow of air now takes

place from the scavenge manifold at a higher pressure to the

turbocharger compressor side at a lower pressure. The reverse

flow pressure pulsations tend to drive the turbocharger in the

opposite direction, and partly stall it.

Summarizing, w e understand that if there is a pressure ratio

decrease in the compressor, air flows in the reverse direction in a

‘sufge’, due to higher pressure at the scavenge manifold than the

compressor. Immediately after this surge or reverse flow, the

compressor recovers its pressure ratio and functions normally.

This is repeated until air dem and is increased and stable

conditions are achieved. However, during surging, air supply to

the engine cylinders continues without any interruption.

Surging Symptoms

These are noises at the turbocharger, gulping air sounds at the

compressor intake, repeated violent pressure fluctuations, sudden

quick surges in scavenge pressure, and howling or banging noises.

100

101


Surging Causes

♦ Any factor which causes a change in air mass flow rate.

♦ Excess fouling in the system like intake air filter, compressor

or turbine wheel, turbine blades, nozzle ring, exhaust gas

economizer, or even a blockage o f air filters as in the case of

a cloth covering it.

♦ Sudden load changes during maneuvering, rough seas, overloading,

or crash astern conditions.

♦ The changes in engine rpm which cause vibration in the air flow

rates.

♦ Fuel starvation; dirty fuel filter; and fuel system component defects

lik e fau lty fuel pum p, fu el h ig h p re ssu re pip e

damage, or severely wrong timings.

Surging remedy and action

♦ Reduce engine speed which, in turn, reduces scavenge air

pressure and there is less tendency o f reverse flow from

scavenge air manifold to the turbocharger diffuser.

♦ Dirty o r fouled components to be checked and cleaned.

♦ Proper matching o f turbocharger to the engine with respect to

the com pressor m ap characteristics, com pressor impeller,

diffuser and nozzle area design.

♦ Regular gas and air side washing o f turbocharger.

CHAPTER 4

AIR COMPRESSORS

Isotherm al Compression

It is the compression of a gas under constant temperature conditions.

Adiabatic Compression

It is the compression o f a gas under constant enthalpy conditions.

♦ There is no heat transfer to or from the gas through the cylinder

walls.

♦ As seen in the figure, it is more advantageous to compress the gas

isothermally (curve A), rather than adiabetically (curve B) as less

work is done (shaded area) in isothermal compression.

1 Suction and discharge valve shut

1- 2 Compression

2 Discharge valve is open

2- 3 Discharge of pressurized air

3 Discharge valve shut

3- 4 Re-expansion of residual air

4 Suction valve is open

4- 1 Intake of air.

102 103


Air Compressors

M ulti Stage Com pression

Compression done in stages has

the advantage o f work saved by

inter-cooling between stages.

The figure shows the actual

compression (Curve C ) with inter

co o lin g A betw een stages.

Isothermal compression (Curve

B ) is shown in ‘dash’ lines. The

w ork saved is show n as the

shaded area.

C om pressor Types

Reciprocating Compressors

♦ In marine use, mosdy single crank, tandem piston reciprocating

type compressors are used.

♦ The pressure ratio between the stages of compression is limited by

the final temperatures after compression.

♦ Reciprocating types can be easily arranged for multi-staging.

♦ These types provide better positive sealing.

♦ Valve maintenance is increased.

Rotary Compressors

♦ These are either vane or screw type.

♦ They have a higher mass flow capacity.

♦ Each stage pressure rise is limited to 7 bar due to leakages of

the rotor.

♦ Proper lubrication of the rotor is important for sealing as well as

to prevent wear.

♦ It requires a high speed drive.

Volumetric Efficiency

♦ It is the ratio of the volume o f air taken in during each stroke to the

swept volume of the cylinder.

♦ A loss in volumetric efficiency o f the compressor can be due to

poor valve condition, dirty intake filter, increased bumping

clearance, discharge line blocked, or restrictions in the inter cooler.

Bum ping Clearance

♦ It is the clearance given to avoid the chance of mechanical bumping

o f the piston and the cylinder head cover.

♦ It is the distance between the top of the piston and the cylinder

cover when the piston isatTD C .

♦ It is approximately between 0.5% to 1 % o f the cylinder bore.

♦ It is checked by placing a lead metal piece on the top o f the piston

and then turning the compressor manually to obtain a lead

impression.

♦ It can be adjusted by placing additional shims between the cylinder

head cover and cylinder block, or under the connecting rod.

Compressor Valves

♦ Mostly plate type valves are used.

♦ They have a low inertia o f moving parts and good flow

characteristics.

Valve Materials

Body - Steel (0.4 % C) with hardened seat area.

Plates - Steel (Ni or Cr or M o-A lloy)

Springs - Haldened alloy steel.

Valve Defects

♦ Worn or damaged seats, plates or springs.

♦ Dirt or lube oil deposits on the valve parts.

♦ Incorrect assembly.

104

105


♦ Overheating caused by air leakage back to suction side (recycling)

or cooler problems.

2-Stage C om pressor Faults

1. First stage suction valve leakage causes loss of air back to the

suction filter side during compression. Hence, running time is

increased with less air being delivered at every stroke, and the

second stage suction pressure is reduced.

2. First stage delivery valve leakage causes loss of air back to the

first stage cylinder, instead o f delivering this air to the second

stage. Hence, less fresh air can be drawn in during the next suction

stroke. This recycling o f a part of the air meant to be delivered

causes an increase in first stage and second stage temperatures.

A ir delivery is thereby reduced.

3. Second stage suction valve leakage causes second stage

compressed air to leak into the second stage suction line between

the two stages, increasing its pressure and temperature. The first

stage shows increased delivery pressure since there is additional

back pressure from the second stage air leaking back. Air delivery

.capacity is reduced and the compressor runs for a longer time.

4. Second stage delivery valve leakage causes the second stage

delivery air to leak back to the cylinder during the second stage

suction process. Hence, the second stage shows an increased

suction pressure. Air suction and delivery o f the second stage is

reduced and the compressor runs for a longer time with increased

second stage temperatures.

5. Compressor capacity reduces or full pressure not achieved, is

due to:

♦ Dirty, damaged or worn valves.

♦ Oil coking on valves due to defective piston scraper rings.

106

♦ Worn or seized piston rings.

♦ Increased bumping clearance due to worn bearings.

♦ Blocked suction filters.

Air Compressors

6. ' Low pressure safety valve blows due to second stage suction or

delivery valve leaking back to the second stage suction line

between the stages.

7. High pressure safety valve blows in case the isolation stop valve

in the compressor outlet delivery line is shut.

8. Valves require frequent attention due to :

♦ Overheating due to poor quality water circulation or air leaking

into the water side in the cooler tubes.

♦ Impurities being sucked in when the suction filter is damaged.

♦ Too much moisture carried in the air. Check tightness of gaskets

between cylinder block and cover. Pressure test the cooler to

1.5 times its working pressure.

9. Overheating or knocks in the crankcase caused b y :

♦ Defective bearings or blockage of lubrication oil channels.

♦ Longitudinal bearing clearances of the crankshaft is not correct

due to a bent piston rod or an edge pressure on the bearing.

10. Overheated piston caused b y :

♦ Piston o r crosshead bearing being wrongly fitted. Inspect

piston rings, crosshead bearing, cylinder lubrication, piston

bumping clearance and side clearances.

♦ Ineffective cooling due to poor cooling water circulation, cooler

leakage, cavitation, or an air lock in the cooling water.

11. Low lube oil pressure caused by low oil level, dirty oil filter,

blocked oil piping or channels, and a defective oil pump or

bearings.

107


12. Blocked intake filter or suction : It can cause the discharge

temperature to increase to the auto ignition point of the lube oil.

13. Compressor running unloaded, caused by a problem in the

unloader:

♦ Check timer relay of electrical activation.

♦ Check all air piping to unloader.

♦ C heck u nloader piston or 0 -ring assem bly fo r dirt

or stickiness.

CHAPTER 5

FUEL SYSTEM

Fuel Types

Crude Oil is the source o f fuel from the earth. It is a viscous oily

liquid, yellowish-green to dark black in appearance. It consists of a

complex mixture of liquid hydrocarbons with organic compounds

containing oxygen, nitrogen and sulphur. Petroleum products are

obtained after straight-run vacuum distillation in a refinery. Distillation

produces low boiling fractions, free of unwanted by-products.

Separation during distillation provides the following fuels at different

temperatures:

♦

♦

♦

♦

♦

♦

♦

♦

Petroleum ether

Aviation gasolene

Motor gasolene

Naphtha

Turbine fuel

Diesel fuel

Gas oil

Burner fuel

( 40 to 95 deg.C)

( 40 to 180 deg.C)

( 40 to 200 deg.C)

(120 to 240 deg.C)

(150 to 315 deg.C)

(190 to 350 deg.C)

(230 to 360 deg.C)

(300 to 400 deg.C).

109


Fuel System

M arine Fuels

These are pure distillate fuels or their blends. They are low viscous

diesel fuels and heavy residual fuels. ISO 8217 is the only standard

for fuel specifications. To reduce costs in modem engines, cheaper

residual fuels are used.

Fuel Properties

D ensity

It is the ratio o f the mass to the volume of the fuel. Units are

kg/cub.m.

Viscosity

It is the frictional resistance between layers o f the fluid to resist a

change in shape due to an applied force. It is the resistance to fluid

flow due to shear resistance between adjacent layers in a moving fluid.

Specific Viscosity

It is the ratio o f the efflux time o f 200 cubic cms o f fuel at 20 to

50 deg.C, and that o f200 cubic cms of distilled water at 20 deg.C as

measured by a viscometer with a 2.8 mm orifice. The unit is ‘degree

o f specific viscosity’.

D ynam ic Viscosity

It is the viscosity o f a fluid in a laminar stream lined flow containing

layers spaced one centimeter apart, which require a tangential force

of one dyne per square centimeter to be moved at velocities differing

by one centimeter per second.

The unit of dynamic viscosity is poise, centi-poise or poiseulle.

I P = 1 Poise = 0.1 N-Sec/sq.m.

1 cP = 1 Centi-Poise = 0.001 N-Sec/sq.m.

Kinematic Viscosity

It is the ratio of the dynamic viscosity and the density of the fluid at the

same temperature.

The units are Stokes, Centi Stokes, Saybolt Seconds, or Redwood

Seconds.

1 Stoke = 1 St = 0.0001 sq.m./sec

1 Centi Stoke = 1 cSt = 0.000001 sq.m./sec

Viscosity Index

It is the index of an oil which measures the change of viscosity due to

a change in temperature. It has no units.

Carbon Residue

It is the tendency of a fuel to form carbon residue deposits. Its unit is

coke value which should not exceed 0.05 to 0.1 %.

It affects piston rings, liner wear, plugging of injectors, fouling of gas

passages, etc.

The testing for carbon residue is done by Conradson Test or Micro

Carbon Residue Test.

Conradson Carbon Residue

It is the residue quantity of carbon measured as a percentage of the

original mass of the fuel, after carrying out the Conradson Test.

Sulphur

It is an undesirable corrosion-inhibiting constituent o f fuel. It forms

sulphur dioxide which combines with water vapour at low temperature,

resulting in the formation of sulphuric acid.

110

ill


Fuel System

F lash P oint

It is the minimum temperature that an oil has to be heated, to produce

sufficient volatile vapours capable of ignition when in contact with an

open flame. It is the main fire hazard classification o f oil. All diesel

fuels on the ship should have a flash point greater than 66 deg.C. The

two types o f flash points are open flash point and closed flash point.

Closed Flash Point

It is the minimum temperature for enough flammable mixture to give a

flash when a test lamp source o f ignition is introduced in a closed

container. Closed flash point is measured in a Pensky-Martin closed

tester where the outside atmosphere does not influence the oil vapours.

Open Flash Point

Here, there is no lid on the container. Therefore no vapour is lost, but

the temperature is sufficient to give a flash, when a test lamp source of

ignition is introduced in an open container. Open flash point is

approximately 15 deg.C higher than closed flash point.

Flash P oint examples

For temperatures above 15 deg.C , the test used is the Pensky-Martin

closed flash point test, o r else the A bel test is used. Flash

point examples are:

Less than 22 deg.C

22 to 66 deg.C

Above 66 deg.C

Diesel Oil

Heavy Fuel Oil

Lube oil

Petrol

Gasolene, Benzene (dangerous liquids)

Kerosene, Vapourising Oils.

Oils safe for marine use.

95 deg.C

100 deg.C

230 deg.C

17 deg.C

Fire Point

It is the temperature that an oil has to be heated to produce sufficient

volatile vapours, capable of ignition by a flammable application and

continuing to bum thereafter. It is approximately 40 deg.C higher than

the closed flash point.

Self-Ignition Point

It is the minimum temperature at which a fuel is capable of ignition on

its own accord, without an external application o f heat or flame. It is

used when the choosing the compression ratio to match the fuel grade.

Pour Point

It is the lowest temperature at which an oil ceases to flow, or can be

poured. It is important when considering storing, heating, pumping,

wax crystallization, or solidification of an oil.

Calorific Value

It is the amount of heat produced by complete combustion of one unit

mass o f fuel. For one kg burnt, diesel fuels have a high calorific value

i.e 10,100 to 10,300 Kcal, while heavy residual fuels produce 9500

to 10,000 Kcal. It is used while measuring the thermal efficiency of an

engine.

Cetane Num ber

It is an index of the ignition quality (ignition delay characteristics) of

the diesel fuel which defines the way combustion proceeds in the engine.

It is determined by comparing the ignition quality of a standard solution

(which is a mixture o f two hydrocarbons called cetane and alphamethyl

naphthalene) with the ignition quality of the fuel tested.

It is the percentage of cetane contained in the standard solution which

has an ignition delay equaling the ignition delay of the fuel tested. Cetane

112

113


Fuel Sigg”

which has very good ignition quality is assigned the number of ‘ 100’.

Alpha-Methyl Naphthalene is assigned the number of ‘O’, due to it’s

poor ignition quality. The higher the cetane number, better is the fuel,

shorter is the ignition delay, and easier is the starting o f combustion.

The cetane number o f diesel fuels vary from 35 to 55. If the density

increases, the cetane number also increases.

Octane Num ber

It is a measure o f the knock rating of the fuel combustion in the engine.

Iso-Octane is assigned a number o f ‘ 100’, because o f its excellent

anti-knock characteristics. Heptane is assigned a number o f ‘O’,

because o f its poor antiknock characteristics. Better the fuel, higher

is the octane number.

Specific Gravity

It is used for denoting the weight of the oil while handling or storage.

A sh

It is the quantity of inorganic incombustible impurities in the fuel. It

mainly consists of sand and metal oxides like vanadium or sodium. It

causes abrasive wear.

Vanadium

It is an undesirable impurity in the fuel. During combustion of fuel,

vanadium products like vanadium pentoxide are formed, which are

deposited on the surrounding surfaces. These deposits are highly

corrosive above 700 deg.C.

Vanadium and Sodium

When both these impurities are presentinaNa:Varatio of 1:3, vanadium

pentoxide which is formed combines with sodium to a form a very

hard compound whose melting point is around 630 deg.C. This

compound eats into the metal surface, leaving the surface e x p o ^ to

corrosion.

Catalytic Fines

After vacuum distillation, catalytic cracking is often carried ou .

Catalytic cracking is done to crack the oil vapours by reheating W1

silica and alumina as catalysts. These catalysts are used in poW ®r

form in an oil vapour. Some of these catalysts break up to form a us

known as catalytic fines. They cause abrasion wear in the engibes-

A ir/F uel Ratio

The stoichiometric ratio for proper combustion is 14.5 kg air t° 8

fuel.The actual air ratio is 30 to 44 kg per 1 kg fuel. Excess air I3*101S

36.5 kg per lk g fuel.

Other F uel Impurities .

Other impurities in the fuel include water, iron, phosphorus, e ’

lead, calcium, etc.

Total Sedim ent Test

It measures the stability of the asphaltene phase o f the fuel- e

sediment accumulates at the bottom o f the storage tank and l138 a

very high asphaltness content. This affects filters and componei118-

Wax

It is a residue formed due to high paraffinic content. It is soluble*11 a

petroleum oil base. It crystallizes at it’s cloud point which may ^ 38

high as 35 deg.C.

Calculated Carbon Aromacity Index (CCAI)

It is a rating of the fuel which indicates ignition quality, because is?utl0n

directly depends on the aromatic content in the fuel. AromaticS 31:6

114

115


Fuel System

compact benzene ring structures present in the fuel which affect the

ease o f which a hydrocarbon fuel molecule can bum. A low CCAI

rating means better ignition, better fuel quality and less ignition delay.

Low ratings are upto a CCAI ratio of 850. High ratings are from 850

to 950, and 870 is the limit for its use. It does not affect ignition in

modem 2-stroke low speed marine engines, but it mostly affects ignition

in medium speed engines.

Fuel system line diagram

Fuel Specifications

Given below are the maximum limits for Heavy Fuel Oil and Marine

Diesel Oil:

Heavy Fuel Oil

Marine Diesel Oil

(1) Density at 15 deg.C 991 kg/cub.m. 840 to 920 kg/cub.m.

(2) Knematic Viscosity

at 50 deg.C

700 cSt

at 40 deg.C

14cSt

(3) Sulphur 5% 2%

(4) Conradson Carbon Residue 10 %

2.5%

(Micro Carbon Residue)

Combustion Phases

There are 4 phases in the combustion process:

1. Injection delay

(5) Ash 0.2% 0.02 %

(6) Water 1 to 2 % 0.25%

(7) CCAI 880

(8) Sodium lOOmg/kg

(9) Vanadium 600mg/kg

(10) Aluminium + Silicon 80mg/kg

(11) Sediment 0.1 %m/m

116

117


Fuel System

1. Injection delay o r la g : It is the time delay between the closing of

the spill ports/ valve and the opening of the fuel injector. It depends

on the pressure rise in the fuel pump and the pressure ,in the injector

line.

2. Ignition delay o r lag : It is the time delay between the start of

injection and the start of combustion. Factors affecting ignition delay

are a rise in scavenge air or cooling water temperatures, retarded

fuel injection timing, ignition quality o f fuel, low load and low

speeds.

3. Combustion of the already injected fuel and fuel still beinginjected: '

Ignition delay directly affects the combustion in this phase. In case

o f a large ignition delay, a large pressure rise can cause a diesel

‘knock’,

4. After burning: It is the burning o f fuel after injection is finished.

Afterburning is considerable in case of a large ignition delay, since

heat is now given out in the expansion stroke and cannot be utilized

efficiently.

K nock

It is the phenomenon of a high sudden pressure and temperature rise

due to the detonation of fuel. It sends heavy shock waves, an increased

flame front speed, an increase in noise and vibration and a shock

loading to engine components like bearings, piston rings, cylinder, etc.

In case of a ‘knocking’ sound, check whether it is a mechanical or a

fuel knock by cutting out the fuel. Mechanical knock is due to worn

out bearings; broken or loose components; or an excessive play

between the piston and the liner (worn rings or a worn liner). Diesel

knocking depends on engine speed, load, com pression ratio,

turbulence, mixture strength, fuel characteristics, ignition delay, injection

timings, cetane number and octane number.

Factors Affecting Combustion

A tom isation

It is the breakup of the liquid fuel into a minute vapour mist, so that

these fuel vapour particles possess a very high surface area to self

ignite with hot compressed air. Atomisation depends on the small orifices

of the injector; the pressure difference between the fuel line and

cylinder; and the temperature, mass flow rate and viscosity of the fuel.

If too much atomization takes place, then very small particles will not

have enough kinetic energy to go through the whole combustion space.

They will gather near the injector due to resistance from the dense

compressed air. Hence, they will be starved during combustion and

afterburning will take place. If too little atomization takes place, larger

particles will possess more kinetic energy and get deposited on the

liner wall. This causes after burning and poor combustion. Carbon

deposits will be seen on the liner walls, the side o f the piston crown

and the piston rings.

Penetration

It is the distance traveled by the fuel particles into the combustion

space before ignition takes place. A fuel je t should penetrate well into

the combustion space without impingement onto the liner or piston

crown. Normally, penetration is up to 60% of the liner bore for liquid

fuel, with only fuel vapour being allowed to impinge on liner wall.

Penetration depends on nozzle diameter size, length o f nozzle hole,

fuel particle size and atomisation.

118

119

M arine Diesel Engines

Fuel System

F u e l D istribution

Fuel shouldbedistributedevenly throughout thecombustionspace

without overlapping, for goodcombustiontotakeplace.

m bustion Chamber a nd Piston Crown Designs

pious designs o f the combustion space chambers with respect to

Mon crown shape are shown in the figure.

S w ir l

It is the motion given to the incoming air charge entering the combustion

space. This is done by the shape o f the combustion space and the

direction of entry of the air charge.

Turbulence

It is a factor that has already been designed during manufacture and

can only be influenced by fouling of inlet ports or exhaust ports; and

scavenge or exhaust pressures. It is given to improve the air fuel mixing.

It is done by giving a swirl to the intake air by means of the inlet valve

passage shape o r angle; changing the size o f scavenge ports; the

positioning and alignment of the fuel injectors; the burning of fuel; and

the squish from the piston shape.

A ir F uel M ixing

T he fuel is injected into the cylinder at a velocity o f 150 to 500 m/s

forming a cone-shaped spray with a greater density at the center. Its

penetration length depends o n the injection pressure i.e. 120 to

500 kg/sq.cm for slow speed engines. To ensure proper combustion

especially during overloaded conditions or poor air-fuel intermixtures,

excess air is provided.

Excess A ir Coefficient

It is the ratio o f the actual amount o f air to the theoretical amount

required to bum 1 kg o f fuel. On diesel engines, it varies between 1.3

and 2.2 to achieve complete combustion.

Compression Ratio

It is the ratio of the volume o f air at the start and the finish o f the

compression stroke. For compression ignition engines, it is 12.5 to

13.5. Loss of compression is due to poor sealing or excess clearance

volume. The causes are worn piston rings; w orn liner; or excess

bearing clearances.

Im pingem ent

When there is less atomisation o f the fuel, the fuel particles are larger.

They travel with a higher velocity and get deposited on the liner and

piston crown. This impingement is undesirable as it causes burning at

that area.

120

121


Fuel System

F uel combustion is also influenced by

♦ Scavenge air pressure, temperature, and charge air quality

depending on the scavenging method.

♦ Exhaust gas back pressure due to fouling of exhaust passages which

also affect combustion and proper scavenging.

♦ Fuel parameters i.e. its temperature at the inlet to the engine, its

viscosity, its ignition quality, its fuel ratings and its injection timings.

♦ Fuel pumping faults due to fuel pump internal wear; injector

conditions affecting the maximum pressure delivered; injection

delay; fuel particle size and penetration.

Residual Heavy Fuel Oils

Marine engines use cheaper heavy residual fuels for constant MCR

operations and low viscous diesel fuels for starting, maneuvering,

running-up and stopping. Heavy fuel oil is the residual fraction of a

crude oil source after all other distillation products are extracted in a

refinery. It is also a mixture with lighter distillate fraction oils. In modem

engines, due to escalated fuel oil prices, residual heavy fuel oils are

used to cut on costs. Undesirable properties of the heavy fuel oil are:

high viscosity, increased sulphur, ash, sodium, vanadium, salts, water,

solid particles and sediments. The harmful effects o f these contents

have been discussed earlier.

Residual F uel Treatment

In order to use residual heavy fuel oil for the engine, the oil has to be

treated to reduce the problems faced with these impurities. The

following treatment is carried out:

1. Limiting the impurities when purchasing or bunkering the oil.

Limits for each property and parameters are laid down by

ISO 8217 (1996).

2. Separation of water and sludge in settling and service tanks. The

settling tanks and service tanks have heating coils and bottom

collection space to rem ove sludge and water. Maximum

temperature of the settling or service tank must be 15 deg.Cbelow

the flash point o f the fuel, but not more than 90 deg.C or else,

volatile vapours may form creating an explosive hazard.

3. Filtration is done with filters to remove sediments and particle

impurities; These are commonly fitted (a) at the outlet of die storage

bunker tank i.e. at the inlet to the transfer pump known as cold

filters; and (b) at the inlet to the supply pumps after the heaters

known as hot filters.

4. A mixing tank or column to gradually mix heavy fuel oil and diesel

oil during change over operations. It also serves the purpose of

venting and degasification of trapped air and gases.

5. Purification in centrifugal separators to remove water and some

amount of sediment.

6. Heating to reduce viscosity.

7. Usage of a cylinder lube oil TBN having a high alkalinity to neutralize

acids formed due to sulphur content; and maintaining a low cooling

water temperature.

Bunkering

Bunkering is done to replenish fuel and lube oil supplies required for

mnning the main propulsion plant and auxiliaries. A bunker plan is first

drawn up. This is a written procedure detailing all pipelines and

sequence o f events. It describes in detail the quantities to be filled in

each tank as well as the rate. The Chief Engineer is directly in-charge

and is required to personally supervise all operations. To assist him,

another engineer and an assistant are designated. Before starting, fire

fighting equipment and spillage gear are to be positioned and kept

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123


Fuel System

ready. Communications between ship and bunker barge is to be

checked. Drainage scuppers leading to slop tanks on deck, which

can be filled in case of a large oil spill are to be checked that they are

open. An air operated pump to transfer oil in emergency is set up.

Hoses and seals are to bfe checked at the connections. Smoking is not

allowed. No oil transfers during bunkering is permitted. Explosionproof

tools and lamps to be used. A breathing apparatus is to be

provided in case o f poisonous gas hazard. A fuel sample is to be taken

by a standard approved method. This is then sent for testing (FOB AS).

Initially, oil is supplied at a very low rate. All lines and valves are

checked for leaks and whether the correct quantities are being received

in the designated tanks. O ther tanks are also sounded as a

precautionary measure in case of leaking valves. The bunker line valves

should be open and set under the Chief Engineer’s supervision. After

bunkering, once the fuel quality and quantity are acceptable, then only

will the Chief Engineer sign the receipt forms.

Optimum Injection

♦ Injection o f the fuel is best or optimum if injection is done

immediately after maximum combustion pressure is achieved and

injection supply is very rapid at this point.

♦ Injection tim e is only 20 degrees of crank angle at full load, but

maximum firing load is reached only in the latter half of this period

i.e. latter half o f the injection period. Therefore, w e must inject

more fuel towards the end o f injection after the maximum firing

pressure is reached and supply this remaining fuel as fast as possible.

♦ It is best achieved in the Intelligent Electronically controlled engine

series ( RT-flex or ME engines) for different load conditions.

Fuel Injectors

The fuel injector valve consists of the valve body, valve head, union

nut and atomizer nozzle. In the valve body, there is the thrust spindle,

thrust spring, thrust foot and valve unit.

• 5

1 O-Ring

2 Fuel Valve Head

3 O-Ring

4 Locking Pin

Thrust Foot

6 O-Ring

7 Thrust Spindle

8 Fuel Valve Unit

9 Union Nut

10 Spring

11 Atomiser' Nozzle

12 Valve Body

13 Locating Pin

14 O-Ring

Injector Functions and Requirements

♦ It should inject and disperse the fuel evenly into the engine cylinder

in a finely atomised spray.

♦ The size, position and orientation o f the injector nozzle has the

function of creating a fine atomized spray with good penetration.

♦ The injector also serves as a non-retum valve not allowing any

combustion space gas back into the fuel system.

♦ It should not open till a preset pressure is built up.

♦ At the start of injection, the droplet size should not be too large as

this will encourage ‘slow burning’.

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125


Fuel System

♦ The valve opening should be prompt to prevent pressure loss

through throttling, during the opening process.

♦ It should provide cooling of the valve whilst in use which prevents

softening o f the valve and seat, as well as reduces expansion of the

trapped fuel in the ‘sac’ area.

Injector Types

♦ Cam-operated or Hydraulic-operated types. In marine use, mostly

hydraulic operated type is used.

♦ Open or Closed valve type: Open injectors dispense with a valve

between the fuel line and the combustion chamber, while as closed

type do not do so. Open type are not used in modem marine

engines because they suffer from after-dripping of fuel after the

injection stroke.

Hydraulically Operated F uel Valve

♦ In this type, the operation of opening and closing o f the fuel valve

is performed hydraulically by the fuel pressure delivered by the

fuel pump to the fuel valve. Valve opening is initiated by an oil

pressure shock wave in the oil contained in the high pressure fuel

piping. The shock wave is caused by a sudden very high pressure

increase. This high pressure increase is due to the increasing

acceleration o f the fuel pump plunger and the fuel cam. This

accelerated fuel causes a shock wave when the inlet port or suction

valve is closed during pump delivery.

♦ Fuel pressure from the fuel pumps act on the needle. The needle

opens inwardly. The needle is loaded by a thrust plate, a spring

and a screwed spindle. The thrust plate serves the function of

limiting the needle lift

♦ W hen the fuel oil pressure force overcomes the spring force, the

needle lifts. Oil pressure acts on the annular area at the end o f the

valve spindle where it is machined to a smaller diameter than the

spindle diameter. After opening, the lift exposes the full cross

sectional area of the spindle for quick opening.

♦ Prompt and rapid opening is achieved during opening, because an

extra effective area o f the needle seat is exposed for fuel oil and

pressure to act upon after initial lifting of the needle.

♦ Coolant is circulated through the space around the bottom of the

nozzle cooling oil flow. Passages are drilled in the valve body to

the top.

♦ Leakages of the valve component faces will be seen in the spring

space vent hole.

♦ Atomiser holes vary from a diameter o f0.075 mm to 1 mm.

♦ The valve lift is around 1 mm to 1.5 mm.

Fuel Injector Faults

Improper Cooling

♦ Too much cooling causes sulphur corrosion o f the tip due to the

injector tip temperature falling below the condensation temperature.

This is not seen on modem engines and was only experienced on

older engines. Acorroded atomizing nozzle tip will alter the spray

penetration, atomisation and pattern. Water condensation takes

place at temperatures below 110 deg.C, allowing sulphur oxides

from the fuel to turn into acids.

♦ Too less cooling causes softening of the valve and seat, and allows

expansion of trapped fuel in the ‘sac’ area. This causes carbon

trumpets on the tip, poor combustion and smoky exhausts. A t

temperatures above 180 deg.C, the fuel starts cracking into particles

which clog the nozzle.

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127


Fuel System

Dribbling Nozzle

A dribbling nozzle will result in fuel-burning at the nozzle tip which is

seen as carbon trumpets. Dribbling nozzles are a result of poor seating

o f the fuel valve, which in turn, is caused by the impurities in the fuel

causing abrasive wear to the seat surfaces; poor cooling; increased

banging of the valve needle; poor maintenance and overhaul; and wrong

spring pressures.

Carbon trumpets adversely affect combustion since they influence

the spray pattern of the fuel. This leads to smoky exhaust, higher exhaust

temperatures, poor combustion and loss o f power.

Wrong Spring Pressure

The spring pressure directly influences the size of the fuel particles.

Lower spring pressure leads to the valve opening and closing at a

lower pressure. W hen the injector opens at a lower pressure, larger

fuel particles are formed and these larger fuel particles bum ineffectively,

resulting in a reduced cylinder pressure and smoky exhaust. The causes

of a wrong spring pressure are incorrect overhauling; fatigued material;

or extended life of the spring.

Nozzle hole diameter, depth and number

This will influence the penetration, atomization and overall combustion.

Nozzle holes may be choked due to fuel impurities, carbon trumpet

formation, burning of ‘sac’ area, trapped fuel and prolonged running

of engine at low loads. The length of the nozzle hole is usually thrice

the size o f the diameter of the hole.

Un-Cooled Injectors

These are used in modem engines using residual heavy fuel during

maneuvering operations. In order to run on residual heavy oil during

maneuvering, un-cooled injectors are used on latest engines e.g. MAN

B&W.

Here, hot oil is circulated when

the injector is not injecting.

Once the fuel pressure at the

beginning o f the fuel pump

pressure stroke, increases to

more than 8 bar, the recirculation

line is closed.

During re-circulation, 2 to 8 bar

pressurised fuel oil flow s

through the center bore in the

valve body to a hole in the thrust

spindle; then to the thrust piece

to a circulation hole at the slide

top; and out of the valve housing

through an outlet pipe. Re- n

circulation stops w hen oil

pressure exceeds approximately

Fig-87

10 bar. T his increase in

pressure above 10 bar overcomes the slide valve spring pressure.

The slide pushes the thrust piece, thereby closing the circulation holes

and fuel oil now passes further down to the space above the valve

spindle seat.

Injection System Requirements

♦ The fuel injection system consists of the fuel injector, fuel pump

and metering control.

♦ It should supply a finely atomized spray with correct penetration

and even distribution into the combustion chamber.

♦ The quantity of fuel is to be metered and the same amount is to be

supplied to each cylinder to obtain equal power and balancing of

all units.

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129


Fuel System

♦ Correct timing and quantity of injection corresponding to different

stages in the combustion cycle is important. This is required to

efficiently utilize the heat and energy of combustion and have the

correct cylinder pressure rise to control combustion.

♦ Prompt and rapid opening and closing o f the injector is very

important

Types of Injection Methods

The main types are Blast Injection or Solid Injection methods.

In blast injection, fuel is blown into the cylinder by an air ‘blast’. In

solid or ‘airless’ or ‘mechanical’ injection, fuel is forced into the cylinder

through a fuel valve by a high fuel pump pressure i.e. by the ‘solid’

fuel.

Solid Injection Systems

There are 3 commonly used types:

1. Common rail injection system.

2. Gas compression injection system.

3. Individual unit injection system.

1. Common Rail Injection System

It consists o f fuel pumps, distribution blocks, accumulators, a

common piping or ‘rail’, and camshaft operated spring loaded

injectors. The fuel pumps supply oil pressure to a common pipingor

rail which is connected to an accumulator to damp out pressure

fluctuations. The common rail then supplies the fuel injectors through

a fuel timing valve whose opening and closing is camshaft operated.

It is an outdated system, used earlier in Doxford P and J-type

engines.

However, the latest camshaft-less RT-Flex and ME engines employ

a type of common rail system. Details are discussed under the

engine description chapter.

2. Gas Compression Injection System

In this type, combustion gas pressure from the main engine

combustion chamber is led to drive the fuel pump piston in the fuel

pump chamber. Hence, a camshaft is not required to drive the fuel

pump. Timing o f injection is done by means o f a timing valve

operated by an oscillating lever and eccentric fulcrum. M odem

marine engines do not use this type of injection.

3. Individual Unit Injection System

In this type, an individual fuel pump and injector, meter and supply

fuel for combustion in the engine cylinder. Timing is carried out by

means of a camshaft drive to the fuel pump plunger. The governor

linkage also influences the fuel pump rack control. Governor input

is common to all units, but the rack on each pump can be adjusted

to compensate for internal pump leakage. M ost marine engines

use this injection system.

Fuel Pumps

The function of the fuel pump is to control the quantity and timing of

the fuel injected into the combustion space and to provide the high

fuel pressure required to hydraulically operate the fuel injector. Most

commonly used fuel pumps in marine engines are discussed below.

Suction Valve Controlled Pum p

This ‘variable beginning constant end’ type pump uses a push rod

to operate the pump suction valve, which in turn, controls quantity

and timing o f fuel injected. It was used on older Sulzer RD engines

upto the mid 1960s.

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Fuel System

1 Plunger

2 Roller

3 Cam

4 Governor Control Lever

5 Eccentric Rocker Arm

6 Push Rod

7 Barrel

Working

During the downward stroke of

the plunger, the barrel is filled

with fuel oil since the suction valve

is open. During the upstroke,

although the pressure starts z

increasing, no fuel is delivered till

the suction valve closes. Hence,

the ‘beginning’ o f delivery can be ‘varied’, depending on the suction

valve closing ‘early or late’. After the suction valve is closed and the

pressure built up is sufficient to. lift the delivery valve, delivery

commences. Hence, the ‘end’ is ‘constant’. Raising or lowering the

suction valve is used to alter the closing o f the suction valve earlier or

later, thereby changing the fuel timings.

Advantages .

Volumetric efficiency is improved and constant. Adjustment is easy

which enables geometrically correct delivery. The plunger design is

simple without helix edge wear and it has a longer life. Easy

maintenance, lapping, grinding and replacement of suction valve is

possible.

Disadvantages

It is more expensive than the jerk helix type pump. The fuel timing is

not ideal for all load changes. At a low rpm, most of the fuel is delivered

after TDC. This delayed ‘later’ injection causes a drop in maximum

132

peak combustion pressures and thermal efficiency. At low loads, charge

air pressure is lower and with this system, combustion firing pressures

dec rease even further. Cheaper fuels imply longer ignition delay which

add to the already delayed ignition problems o f these pumps.

Suction and Spill Controlled F uel Pump

It is a ‘constant beginning

variable end" type pump, in

which the suction valve is not

connected to the governor and

hence a ‘constant beginning’ is

achieved, while the spill valve

connected to the governor

controls the end of ignition i.e.

a ‘variable end’. It is used in

Sulzer RND onward designs.

Working

During the downward stroke of

the plunger, fuel flows and fills

the barrel since the suction valve

is open. During the upward stroke, the plunger and the spill valve

push rod rise, but the suction valve push rod goes down, which closes

due to the delivery pressure. Delivery now takes place once the suction

valve is closed and the delivery valve opens at its preset pressure. The

133


Fuel System

plunger is still moving up, along with the spill valve push rod and after

the clearance is passed, the spill valve is lifted to open. This shows

thatthe ‘end’ ofinjectionis ‘variable’, depending on the opening of

the spill valve. The spill valve opening depends on the governor input

and corresponds to the engine load. The suction valve opening depends

on the length of the push rod and the eccentric shaft position. It is

initially set and is not variable with the load.

Advantages as compared to ‘Variable Beginning’Pumps

Better peak pressures and better thermal efficiencies are possible.

Fuel is injected at a ‘constant beginning’ i.e. at the same crank angle.

Hence, at low revolutions, fuel would be injected earlier than required

and this would balance the ‘longer ignition delay’ period required by

cheaper fuels.

Disadvantages

The whole quantity of fuel is delivered before TDC even at low

revolutions. This may result in ‘knocking’ effects.

Port-Controlled H elix Jerk Pump

It is commonly used in MAN B&W engines as well as 4-stroke engines.

Working

During the downward stroke, the pump barrel fills

up with oil through the suction port which is

uncovered as in fig. 91-A. During the upward

stroke, the plunger covers the suction and spill

ports as in fig. 91 -B. The beginning of injection is

constant and is achieved by the fuel pressure rising

above the spring loaded delivery valve preset

pressure. The delivery ends when the helical edge

uncovers the spill port as in fig. 91-C. Beginning of

injection is initially set and constant. It starts when

the top edge o f the plunger covers the suction ports and the pressure

is greater than the delivery valve setting. End o f injection is variable

and is controlled by the helical edge uncovering the spill port. (This

can be varied by moving a rack and pinion mechanism which rotates

the plunger and helix). The spill port spills fuel back to the suction

side. ;

Advantages

The port and helix control does not require the use of suction or spill

valves. It is more reliable and most commonly used.

Pilot Injection System

Pilot injection can be done by three w ays:

♦ A Jerk pump is used which has a cam with two lobes, instead of a

delivery valve. The first cam lobe opens the valve at a Iowa: pressure

e.g. 75 bar, and injects a small pilot charge which has a long delay

period. This pilot ignition heats up the combustion space so that

the main charge bums well. The second cam lobe opens the valve

at a higher pressure e.g. 415 bar, and injects the main charge.

This reduces ignition delay for the main charge and gives a slower

rate of pressure rise. The chance o f ‘knocking’ is reduced. It was

used on outdated Polar 2-stroke medium speed engines.

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Fuel System

♦ Pilot ignition by means of a double injection profile jeik pump which

will give two injection pulses.

♦ Pilot ignition by means o f an electronic control of the injector.

Twin Injection System

In this type, two injectors are used i.e. the pilot and the main injector.

It is used on Wartsila Vasa-46 engines. It minimizes ignition delay and

knock. The engine can run on low loads for unlimited periods. It allows

high viscous fuels (380 cSt at 50 deg.C) and highly aromatic fuels

(low cetane no., but CCAI not high) to be burnt more efficiently. The

pilot injector injects a constant volume for different loads. Atomisation

in the pilot injector is better due to finer nozzle holes.

Twin F uel P um p Barrel System

In this type, two fuel pumps in parallel supply fuel to the same injector.

One pump plunger controls the beginning of injection, whilst the other

controls the termination o f injection. They achieve much higher

pressures than that which can be achieved by a single fuel pump. This

system is used on Wartsila’s largest medium speed engine.

Electronic Injection Control

It is used on latest engines by Wartsila-Sulzer and MAN B&W. Here,

the engine rpm, crank angle position, etc. are fed into a microprocessor

which gives an output signal to the injection pumps. More details are

listed in the engine description chapter.

Variable Injection Timings (VIT)

VTT

= Variable Timings

= Variable beginning and Variable end of injection.

Reasons fo r VIT

M odern engines (slow

Hpeed, h ig h p ressu re

charged types) lose too

much combustion pressures

and tem peratures at low

lo ads a n d sp eed s. T h e

Mater’ delayed ignition, as in

the case o f constant end

types, led to lower peak

p ressu res and lo w er f*-INJECTION —

efficiency at low loads. With

Fig-90

costs o f fuel increasing,

cheaper highly viscous residual fuels are now used which have longer

ignition delays, lower peak pressures, delayed combustion, higher

exhaust temperatures and higher fuel consumption. Latest engines

have a high stroke-bore ratio i.e. super long stroke for more power

output and run at a lower rpm. In 1978, Sulzer introduced the VIT on

the ‘RLA’ engines mainly to allow better combustion and maximum

pressure at lower loads (75% load) while using residual fuel.

VIT - Sulzer Engines

It is a type of fuel pump control which allows the engine to achieve the

designed maximum combustion pressure at a range o f 75% to 100%

power. It is done by varying the injection timings to maintain higher

combustion pressures at reduced loads.

VIT Advantages

The thermal efficiency and combustion efficiency are improved, while

Specific Fuel Oil Consumption (SFOC) is reduced i.e. a reduction of

7. gm/kwhr in Sulzer engines.There is no dark smoky exhaust; less

136

137


Fuel System

thermal stresses; improved NOx emissions; improved temperature

control for preventing corrosion; and the strength o f parts like the

crankshaft is betterutilized.

The fuel oil consumption directly depends on the expansion ratio and

thermal efficiency.

Expansion ratio = Ratio o f the maximum combustion pressure

to the pressure at the commencement of

exhaust blowdown.

Heat added

In normal engines, Pmax is achieved only at full load power, whilst in

VIT, Pmax is achieved at lower loads. At lower loads, there will be

less fuel consumption but an increase in Pmax. This leads to an

improved expansion ratio; improved utilization with higher Pmax at

lower loads; and improved thermal efficiency. Therefore, SFOC is

reduced.

VIT Method

In suction and spill valve controlled pumps, injection timings can be

varied by raising or lowering the position of the suction and spill valves.

Raising or lowering of the suction and spill valve positions are done by

changing the position of the eccentric. Raising the valve implies earlier

timings, while lowering the valve implies later timings. The suction

valve controls the beginning of ignition i.e. the timing of injection, while

the spill valve controls the end of injection i.e. the quantity o f fuel.

Advancing

Here, the suction valve is ‘lowered’. Hence, injection commences

earlier. This results in more fuel quantity being delivered, since earlier

injection gives more injection time and more fuel is delivered. To

maintain the same fuel quantity, the spill valve is ‘raised’ to give earlier

end o f injection i.e. decreasing the amount o f fuel delivered. Hence,

quantity o f the fuel delivered does not increase.

Advancing = Suction valve lowered + Spill valve raised.

Retarding

This procedure is just the opposite of advancing.

Retarding = Suction valve raised + Spill valve lowered.

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Fuel System

F uel Quality Setting (FQS)

It is a manually adjustable lever whose setting can be changed to

compensate for various fuel qualities. The ‘FQS’ angle is a user

parameter setting in the engine control and can be adjusted within the

range o f- 2 to + 2 degrees. The governor output shaft is connected

to the VIT control and superimposed on the ‘FQS’ linkage.

Super VIT

It is a VIT method used on B&W ’s larger L/K/S-MC engines.

Super VIT = Adjustable Timings + Adjustable Break Point

It is a means of automatically varying the commencement of injection

In order to maintain the maximum combustion pressure (MCR) Pmax

constant, over a range o f 85% to 100% full load. The break point

normally at 85 % load is a pre-specified part load above which the

maximum combustion pressure is maintained constant. Super VIT is

used on larger L/K/S - MC engines.

The Super VIT mechanism consists o f a jerk type pump with double

thread, a VIT regulation lever, a VIT position servo, a control air

signal, a position servo unit with input from the governor, a FQS lever

and a regulating shaft.

Super V IT Method

In this m ethod, the jerk type fuel pump

does not have a profile i.e. no extra

oblique-cut on the plunger. The vertical

position o f the pump barrel is raised or

lowered to change the commencement of

injection by a rack and pinion mechanism

and a double thread.

1. Upper threads control the suction ports

i.e. commencement of injection by

changing the vertical position o f the

pump barrel with respect to the plunger.

2. Lower threads control the spill port i.e.

the fuel quantity and end o f injection

by rotating the helix scroll of the plunger

with respect to the spill port.

Fig-94

140

141


Fuel Syster.

The VTT-rack setting is

controlled according to

the engine load via th e

regulating shaft and the

governor. The V ITrack

setting position is

done by means o f a

control air signal supply

which pushes the VTTrack'position

servo.

The control air position sensor valve gets its input from the governor,

the FQS lever and th e regulating shaft.

lo w Load Operation

Here, the VIT system is out of operation. As shown in the figure (at

*ero load), the beam is fully lifted and control air pressure is ‘O’.

Delayed injection takes place.

Increasing Load

As the load increases, the VIT is still zro (delayed injection) till point I.

Control air pressure at point I is now 0.5 Bar and the beam A has

made contact with the sensor pickup.

v / 1 /

x . 1 Fuel index

i ' I (Quantify)

{ VIT-index

, , (VIT control pressure!

VIT Start Pt, Break-Point 100% ^0AD

Corn air 0,5 Bat 85%

Run-up till 85% Load

From point I to point n , the control pressure increases further making

the VIT position servo change the VIT index setting. The timing is

now advanced.

A t 85% Load

A t Point n , Pmax is achieved early due to the advancing from point I

to point II. The beam A touches the supporting points. The sensor

pickup is fully depressed.

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143


Fuel System

85% to 100% Load

Above point n , the beam A rotates around the support. Control air

pressure causes the VIT-rack position servo to ‘retard’ the injection

timing in order to maintain Pmax constant at this range.

retard timings. Collective adjustment is done to compensate for two

main reasons, which are (a) different fuel qualities, and (b) worn fuel

pumps.

Break Point and Pmax Adjustment

This is carried out in case the fuel cams have been moved.

Break point values are:

Fixed pitch propeller M K I engines =78% load

Fixed pitch propeller M K II engines = 85% load

Controllable pitch propellers = 85% to 90 % load

New engines will set the break point 2 to 3 % higher to compensate

for an excessive pressure jum p from Pcomp to Pmax, as the engine

becomes older.

Non-Return Throttle Valve

This valve is fitted in the control air line between the position-sensor

valve and the position servo. It prevents excessive combustion pressure

during sudden reduction of load in the upper load range i.e. above the

break point e.g. in rough weather. It prevents rapid fuel rack oscillations

from being transmitted to the VIT-rack i.e. for a stable VIT rack in

case of slight governor jiggling.

Individual Adjustments

These adjustments can be done at the individual pumps to balance

‘Pmax’ for all the engine cylinder units. (Pmax adjusted + o r - 3 Bar).

Adjustment is done by moving the position servo at each VIT-rack,

or by adjusting the threaded connection between the position servo

and the VIT control shaft (similar to balancing the fuel racks).

Conventional VIT

(B & W Engines)

Collective (Overall) Adjustments

These adjustments aredonefor theengine as awholeunit, and common

to all fuel pumps. Adjustment is done by adjusting screws on the

position sensor unit which alters the control air pressure to advance or

F ig-100

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145


Fuel System

It is the mechanism for varying the ignition timings used on smaller

GB, L35MC and L42M C engines. Here, the break point is fixed in

relation to the pump index and not adjustable as in super-VTT. The

fuel pump plunger is profiled i.e. it has an extra oblique-cut.

VIT conventional = Adjustable timings + Fixed Break Point

Fuel Cam

A cam is a means o f providing the

required motion to its follower in

order to operate the opening and

closing o f valves, or regulate the

timings of a fuel pump.

1 Spill valve push rod

2 Suction valve push rod

3 Roller follower

4 Base circle

5 Fuel Cam

6 Camshaft

1 2

K g - 101

Camshaft Drive

Cams are mounted on a camshaft, which in turn is driven by the engine

crankshaft through chain drive or gear drive.

Cam Profile

It is the shape or curvature o f the working surface o f the cam which

drives the follower with arequired motion to regulate the timings of a

fuel pump.

Cam Types

Regular, irregular, internal, external, inverse, single lobe, multi-lobe, etc.

Base Circle

It is the smallest circle of the cam profile which acts as the base of the

cam.

Cam A ngle

It is the angle of the cam for which the follower is lifted.

A ngle o f Dwell

It is the peak section of the cam profile during which the follower is

resting, although it is in a lifted position.The angle of dwell is designed

to take into consideration the follow ing: checking o f the plunger

clearance; allowing the exhaust cam to be fitted on the same camshaft

in case o f reversible 2-stroke engines; and smooth filling and spill of

fuel without pressure changes.

F uel Cam requirements

At the beginning of the injection stroke, a high amount of acceleration

is desirable, but with a smooth transition to prevent shocks. During

the injection stroke, constant velocity should be maintained without

any pressure drop when the fuel valve opens. A t the end of the injection

stroke, sharp deceleration is required to snap shut the fuel valve, but

smoothly in order to avoid bouncing.

High Pressure Pipe Safety

It is the very high pressure line between the fuel pump and the fuel

injector, which is subject to pressure shock waves and vibration. It is

an important fire hazard because pressurized oil leaking from it can

spray over numerous hot surfaces o f the engine and cause a fire.

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Protection and monitoring o f the high pressure fuel line is a class

requirement, especially for UMS ships.

CHAPTER 6

LUBRICATION SYSTEM

Function o f Lubrication

It reduces friction, prevents excessive wear of rubbing on surfaces,

provides corrosion protection, removes some frictional heat, helps in

cooling, and prevents accumulation of unwanted deposits.

This high pressure fuel line has a protective double skin sheathing. It

also has a leak offline from the space between the pipe and the outer

sheath. This line is led to a leak off tank which monitors leakage and

gives off an alarm if the leakage is in excess. In case of minor leakages,

there is a small leak off hole connection which directly drains to the

main overflow tank.

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Lubrication System

Engine L ube O il Applications

The following components of the engine require lubrication: cylinder

liner, piston, crankcase, bearings, centrifugal purifiers, camshaft gear

or chain drive, exhaust valve actuation, crosshead guides, turbocharger

bearings, power generators and power take-in/out units.

Lubrication Feed Types are: full force feed lubrication for bearings,

splash lubrication, combination lubrication, and metered lubrication

by a force feed lubricator.

Friction

It is a rubbing force set up between surfaces in contact with each

other due to relative motion between them. It depends on the normal

load on the rubbing surfaces, the surface finish and the rate o f relative

displacement. It causes wear and loss o f power because s.ome of the

power is used as work to overcome the frictional force. Work done

by frictional forces gets converted to heat energy, resulting in overheating

of the parts, which may lead to fusing or seizure in extreme conditions.

Lubrication reduces this friction and wear. It also provides cooling

and removal of any impurities or products of wear.

Friction Types

Dry Friction

It is caused when solid surfaces move relative to each other without

any lubricant between them. It is totally undesirable and leads to

serious breakdowns.

Boundary Lubrication Failure Friction

It is the friction caused when the lube oil film separating the surfaces in

contact is destroyed and dry friction patches appear. Examples a re :

(1) The lubrication between the piston compression rings and the liner.

(2) The lubrication in the small end bearing of the connecting rod at

the start and stopping of the engine.

(3) The lubrication in bearings running at a very low rotational speed

or a high unit load.

Complete Lubrication Friction

This is the type of friction caused when the moving surfaces in contact

are separated by an adequate thickness of lubricant.

Types of Lubrication

1. Hydrodynamic Lubrication

It is also called full fluid film lubrication. It is the lubrication between

moving surfaces which are separated by a continuous unbroken oil

film of adequate thickness. Oil pressure is self generated due to the

motion of the moving surfaces.

Example: A journal bearing with perfect lubrication due to the oil

wedge formed by the rotating shaft. .

2. Hydrostatic Lubrication

It is similar to hydrodynamic lubrication except that the oil pressure

is supplied by an external source. It is seen in slow-moving heavily

loaded components, where sufficient oil pressure cannot be

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Lubrication System

generated due to its relative motion and hence, external oil pressure

from a pump is required.

3. Boundary Lubrication

It is a thin film lubrication which exists between the robbing surfaces

so that full fluid film is not achieved and some degree o f dry patches

occur with metal to metal contact. It is usually seen in cases of very

high relative movement between the rubbing surfaces.

4. Elasto-hydrodynamic Lubrication

It is also called “squeeze film lubrication”. It is the effect of elastic

deformation o f the metals and the effect o f high pressure on the

lubricant Examples: Rolling contact bearings or meshing gear teeth.

Here, contact is a nominal point or line contact.

Lubrication depends on :

Oil quantity, quality, viscosity, oiliness, dynamic coefficient of friction,

speed of motion, load, surface finish and uninterrupted oil supply.

Lube Oil Properties

Viscosity

It determines the resistance of oil internal cohesive forces and promotes

setting up of certain conditions for the friction between the moving

surfaces. Lower or higher viscosity oils are both unacceptable. Viscosity

depends on the temperature.

Coking Capacity or Carbon Residue

It is the tendency to form carbon residues while burning at elevated

temperatures. High carbon residue causes gumming of piston rings

preventing their movement in the grooves.

Sedim ents

These are grit particles formed due to wear and carbon. Their maximum

allowable content is 1.5%. They cause clogged oil filters and

purification problems.

Corrosiveness »

It is the tendency of the oil to oxidize due to the presence of oxygen in

high temperature gaseous surroundings. The organic acidic products

are very hazardous on lead bearing metals.

Base Num ber

It is the most important property of lube oil for cylinder lubrication in

an engine. It is the capacity o f the oil to neutralize the sulphuric

compounds which are formed, especially in modem engines burning

sulphur rich residual fuel.

Neutralisation Value

It is the measurement o f the acidity or alkalinity of the oil.

Total A cid N um ber (TAN)

It is the measure of the combined organic acids due to oxidation of the

oil, and the inorganic acids due to contamination by the acidic products

of combustion.

Strong A cid N um ber (SAN)

It is the measure of the inorganic acids w hich are formed due to

contamination by the acidic products.

Total Base N um ber (TBN)

It is the measure of the alkalinity of alkaline oils.

Example: TBN = 70 mg KOH/g for crosshead engines

T B N = 3 0 mg KOH/g for trunk engines.

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Lubrication System

The difference is because trunk engines use the same oil for cylinder

liner and crank case lubrication.

Flash Point

It is a measure o f the tendency o f the oil vapours to ignite. It is an

important consideration especially in case of the crankcase oil getting

contaminated with fuel leaks.

P our P oint

It is considered when the operation of the engine component is at low

temperatures. It may have to be preheated, if the oil is to be handled

at temperatures exceeding the pour point by 15 deg.C or less.

D ynam ic C oefficient o f Friction

It is the ratio o f the tangential force to the normal force required to

overcome friction.

O iliness

It is the tendency o f the oil to adhere or w et the moving surfaces.

A n ti- Oxidation

It is the tendency to resist oxidation. Additives are used to improve

this property. Examples: Amines or organo-metallic additives.

Cracking Stability

It is the property o f the oil to be stable and resist cracking at high

temperatures. Cracking is the breakdown o f molecules into smaller

sizes at high temperatures.

Detergency and Dispersancy

It is the tendency to colloidally suspend, disperse and wash away any

harmful combustion products in the oil. Harmful deposits build up in

the piston ring pack area. Additives are usually added to the oil to

154

improve this property o f dispersing these harmful deposits. Additives

are metallic based sulphonates or phenates.

De-Emulsivity

It is the property o f the oil to separate from water in a non-miscible

emulsion. Example: Water ingress into the lube oil requires the water

to be separate (not miscible), so that the water can be removed.

Foam ing

It is the undesirable phenomenon of the oil mixing with air resulting in

cavitation and overheating.

Lube oil additives

These are substances added to the mineral based lube oil to enhance

and improve specifically required properties. Examples are: Anti foam

agents, pour point depressants, extreme pressure agents, viscosity

index enhancers, anti-wear agents, dispersants, detergents, antioxidants

and rust inhibitors.

C loud Point

It is the temperature at w hich a cloud forms, due to wax crystal

formation at low temperatures. Example: Paraffin-base oils.

Water Content

Water reduces the viscosity and therefore, reduces the load carrying

capacity o f the oil. Sea water ingress containing high salt content

increases the acidity and leads to corrosion o f metal. Water reacts

with the additives blended in the oil and nullifies their effect.

Lube O il Deterioration

It is due to a reduction in viscosity, TBN, flash point or dispersancy;

and an increase in oxidation, water content or sediments.

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Lubrication System

Lube Oil Testing

On board testing as well as shore testing is carried out regularly to

monitor lube oil condition, deterioration and whether oil is to be

rejected. Crank case oil is changed after 10,000 running hours in low

speed engines, and 5,000 to 10,000 running hours in medium speed

engines. Oil samples are taken every 500 running hours in low speed

engines and every 150 running hours in m edium speed engines.

A detailed sample-taking and testing procedure is outlined. Sample

points are usually before or after the filter or the pump. These points

are marked and are to be the same for all samples in order to maintain

a standard. A testing file or record book is maintained to monitor and

compare results. Excessive lube oil consumption is also monitored

and the cause is to be ascertained in every case. Company specified

standard testing kits are available on board for testing purposes.

The aim o f testing is to monitor deterioration o f oil, amount of

contamination, oil consumption, replenishment, condition/wear of

lubricated machinery, further use o f oil or oil rejection. If the tests

show satisfactory results, the oil can be used further and it need not be

replaced as per running hours. Hence, a saving in costs is achieved.

Good lube oil monitoring helps maintain the machinery in good

condition, gives a warning in case o f deterioration, and lengthens time

between overhauls and surveys.

Onboard Lube Oil Tests

T B N Test

The TBN valve is ascertained by measuring the ‘resultant pressure

rise’ of a test mixture. The chemical reaction is that of the alkaline lube

oil additive (calcium) with the reagent T.

10 ml oil sample and 10 ml Reagent N are m ixed and placed in a

testing unit cup. 10 ml reactive reagent T is added and the testing unit

cup sealed and properly mixed. The resultant pressure rise in compared

with a chart according to the type of oil used.

Water C ontent Test

The water content is ascertained by measuring the ‘resultant pressure

rise’ o f a test mixture.

5 ml oil sample and 15 ml petroleum reagent A (a paraffin or toluene)

are mixed in the test unit cup. A standard amount in a sealed satchet

of reagent B (calcium carbide) is added and the mixture sealed and

shaken thoroughly. The chemical reaction takes place between water

in the oil and the reagent calcium carbide to form acetylene gas which

gives a resultant pressure rise.

Water Crackle Test

It is done by heating 10 drops of oil in an aluminium foil container over

a flame. A crackling sound confirms the presence of water in lube oil.

Viscosity Test

Viscosity is usually measured using a flowstick comparator method.

The relative flow rate is measured between a new oil and the used oil.

3 ml new oil and 3 ml used oil at the same temperature are placed in

the flowstick reservoir respectively. The flowstick is tilted allowing

both the oils to flow through separate channels. When the new oil has

reached the reference mark, the position of the used oil is checked.

Markings on the flowstick give the conditions o f the oil.

Alkalinity Test

A ‘pH ’ paper indicator can be used to check the reserve alkalinity in

the oil sample.

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Lubrication System

Flash Point

This can be done if a Pensky-Martens apparatus is available on board.

The flash point will change if there is a fuel oil leak into the lube oil.

Spot Test

It shows the amount of insoluble particles in the oil. A standard oil

sample is taken and mixed thoroughly. A spot of oil is dropped on a

special test ‘blotter’ paper and allowed to dry. After a few hours, the

spot is compared with the standard spot reference.

Sea water content

It tests the chlorine content of the oil sample. 5 m l oil sample and 5 ml

distilled water are mixed and the water separates. 3 to 5 drops of

mercuric thiocyanate and an iron salt are added to 1 m l o f the water

from the earlier mixture. Chlorine ions react to form a reddish orange

mixture o f chloromercurate and ferric thiocyanate. This colour is

compared to a scale chart calibrated from 0 to 300 ppm.

Shore Testing

Standard samples are sent ashore for testing at regular intervals e.g.

every three months. The sample point should be marked and taken at

the same point every time. The sample is to be taken when engine is

running at normal speed, so that oil is circulated. It is taken at the

closest supply point into the engine. Before collecting the sample,

drain the line. The sample is taken at a very slow rate i.e. decanted

over 5 minutes. The sample container label should have the following

details: ship’s name, date, oil purpose and equipment, running hours

oil type and sample point location. Samples are not to be taken from

purifier lines, sumps or drain cocks. Shore testing involves the following

tests:

158

Spectro-Analysis

This test determines the contamination by metal and additives.

The following metals can be found by this test:

Ti n. Lead, Copper, Aluminium - from bushes or bearings.

Vanadium

- from heavy fuel oil contamination.

Sodium

- from sea water salt ingress,

HFO contamination.

Chrome

- from piston rings.

Iron

- from lubricated moving parts of

the engine like piston crown,

liner, camshaft, etc.

Method

Spectro-Analysis is done by Plasma Atomic Emission procedure for

particles o f 10 micron (or less) in size. The quantity o f these particles

can be determined by a particle quantifier which gauges the quantity in

terms of ‘PR index’. Separation of the particles is done by a rotary

particle depositor.

Flash P oint Test

It is done by using the Pensky Martens standard apparatus. The test

sample is slowly heated in a closed apparatus at a constant rate and

an external flame is introduced at different temperature intervals through

an open shutter. For new lube oils, flash point should be at least

220 deg.C.

Base N um ber

Oil sample + (Anhydrous chloro benzene + Glacial acid) is titrated

with ( perchloric acid + glacial acid). Accurate titration is done by

using an electrical potential bridge arrangement which gives a current

reading proportional to the titrating rate.

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Lubrication System

Kinematic Viscosity

It is done by measuring the time required for a specific quantity o f oil

at a certain temperature to flow under a fixed gravitational head in a

capillary. This time measurement is directly proportional to the

kinematic viscosity.

Density

It is measured by means of a glass hydrometer with its temperature

controlled. It is an important parameter when choosing the correct

size gravity disc in a centrifuge.

Insoluble Content

It is a measurement o f the Pentane or Toluene insolubles.

♦ For Pentane insolubles: A mixture of the oil sample and pentane is

centrifuged. It is decanted and the precipitate washed with pentane

twice. The dried weight gives the pentane insolubles i.e. insolubles

due to wear, carbon or dirt particles.

♦ For Toluene insolubles: Amixture of the oil sample and pentane is

centrifuged. It is decanted and the precipitate washed off with

pentane twice. It is then washed once with a toluene alcohol solution,

and again with toluene. The dried weight gives the toluene insolubles

i.e. dirt and inorganic particles.

Water C ontent

It can be measured by the distillation method. Oil is heated under

reflux with a water-immiscible solvent. The condensed water is

separated from the solvent in a trap.

M icro Biological Test

This test is only carried out if the lube oil is suspected o f microbial

degradation. Anutritive gel is applied over a glass slide and immersed

in the oil sample. It is allowed to incubate for 12 hours. Bacteria

manifests itself by red spots on the slide which is then compared with

a reference guide.

Microbial Degradation of Lube Oil

It is the degradation that takes place due to microorganisms thriving in

the lube oil. Micro-organisms are bacteria, yeasts or moulds. They

require phosphorous, nitrogen, carbon and water. They require water

to grow in the beginning, but later they can self-sustain themselves at

20 to 40 deg.C in stagnant conditions. The danger is that they multiply

at a very rapid rate i.e. double in size and divide into two every half

hour. Once the aerobic bacteria have consumed the dissolved oxygen,

the sulphate reducing bacteria is activated. Ib is bacteria attacks the

metal and forms hydrogen sulphide. It results in corrosion of steel.

The properties of the lube oil and its additives are also affected,

enhancing corrosion and reducing the load bearing capacity. Acids

are formed which cause corrosion especially at oxygen depleted zones.

This microbial degradation is mostly seen in distillate fuels and not

residual fuels.

Indications

Rotten egg smells, sliminess of the oil in the crankcase painted surfaces,

increased acidity and water content, filter choking more frequently,

poor heat exchanger performance, black staining o f white metal

bearings and corrosion of exposed steel surfaces.

Prevention

Crankcase water content to be weekly monitored and within limits.

Lube oil bearing surfaces, exposed steelwork and crankcase painted

surfaces is to be visually inspected during every crankcase inspection.

Regular circulation o f oil is to be carried out by pumps to avoid

stagnant conditions. Lube oil temperature at the purifier is to be at

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Lubrication System

least 75 deg.C as the bacteria perish above 70 deg.C. Purification

and re-circulation o f crankcase oil is to be continued even when the

engine is stopped at port. Regular testing at various sample points is

to be done. Inspection of sludge from purifiers or choked filters also

indicates any degradation o f lube oil.

Treatment

Use o f biocides or fungicides is carried out. Heating and continuous

purification above 75 deg.C is done and the entire sump to be purified

within a period o f 12 hours. Heating is done to a temperature of

80 deg.C, but not exceeding the supplier’s lim it. This kills the bacteria.

M anual cleaning o f the sump, filters and pipelines is carried out.

Replenishment o f the sump oil is done in case the lube oil is badly

-infected.

Cylinder Lubrication

Requirem ents

♦ to provide a lube oil film at the liner and the piston ring surface

♦ to separate the surfaces and reduce friction between them

♦ to neutralize the combustion and acidic products especially due to

sulphur content in the fuel providing corrosion protection.

♦ to disperse the carbon particles which tend to accumulate at the

piston rings.

♦ to help in the sealing of the piston ring to the liner surface.

♦ to bum without leaving hard deposits.

♦ to cater to the problems associated with cheap residual fuel and

running-in requirements

♦ to provide the correct feed rate i.e. quantity per feed

♦ to lubricate and neutralize the combustion products under different

load conditions

♦ to inject the lube oil at the correct timing for optimum use o f cylinder

lube oil.

Cylinder Oil Types

Crosshead Engines

Cylinder oil has aTBN value of 70 mg KOH/g and a S AE 50 viscosity.

Crankcase oil has a TBN value o f between 5 and 30, and a SAE 30

viscosity.

Trunk-Type Engines

Cylinder oil has a TBN value o f 30 mg KOH/g and a SAE 30,40,or

50 viscosity.

The difference in the oil is because trunk-type engines use the same oil

for the crankcase as well as cylinder lubrication, while crosshead type

engines use separate oils. Crosshead engines use higher TBN oil

because only a limited small consumable quantity is injected into the

cylinder. In Trunk engines, a great amount of oil is present. Hence,

TBN level required is lower.

T B N versus Sulphur Selection

Selection o f TBN is done with respect to sulphur content to ensure

low wear rates of cylinder liner.

Sulphur Content in Fuel

Less than 0.25 %

0.25 to 1.0%

1.0 to 3 .0%

Above 3.5 %

TBN Value

10 m g KOH/g

10 to 20 m g KOH/g

70 m g KOH/g

More than 70 m g KOH/g

O ptimum Cylinder Lube O il Injection

The best timing for lube oil injection into the cylinder liner is between

the top two piston rings, when the piston is on its upward stroke. The

correct feed rate would be judged during overhauls o f the engine, if

the piston rings are slightly damp and rings move freely in the grooves

without much accumulation of deposits. Another indication is the liner

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163

Marine Diesel Engirt*

Lubrication System

wear rates which should be less than 0.1 mm/1000 running hours. 1

The oil feed quantity depends on the type and specifications of the 1

lube oil, the quality and sulphur content o f the fuel, and the engine 1

loading conditions. Oil feed rates range from 0.3 to 0.8 gm/bhp/hr.

Cylinder Lubrication Systems

The two important systems used in modem engines a re :

1. Accumulation and Quill System -Sulzer engines

2. Cylinder lubricator units pumping to orifices in the liner

-M A N B&Wengines.

A ccum ulator a n d Q uill System

This system is used on Sulzer Engines. It consists of a lubricator pump '

supplying oil pressure to a quill fitted with an accumulator.

1 Accumulator cylinder 12 Passage for lubricating quill

2 Spring , 13 Filling pin

3 Accumulator piston 14 Steel ball

4 Cap nut 15 Non-return valve housing

5 Diaphragm 16 Flange ring

6 Accumulator casing 17 Screw

7 Cap nut IS Support ring

H Backing screw 19 Flange

9 Copper sealing rings 20 Joint

10 Cylinder liner 21 Protecting bush

II Lubricating quill 22 O-ring

In this system, the accumulator gets charged by the lubricator pump

for every 10 to 15 revolutions. This oil under pressure is stored in the

accumulator and enters the cylinder whenever the cylinder pressure

falls below the accumulator oil pressure. The cylinder pressure is less

than the accumulator twice for every revolution, (a) when the piston is

moving down in its expansion stroke, and (b) when the piston is moving

up, as th e piston rings pass the feed grooves.

- ^ - K EXPN.

_____

; . ^ . | X - p r r ^ --------------

Fig-106

If

CRANK ANGLE —

B0C

In the figure, the shaded portion shows lubrication while the cylinder

pressure falls below the accumulator oil pressure ( A - A ), with

respect to the crank angle.

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Lubrication System

Q uills

Quills are non-retura valves fitted at the liner oil grooves by screwing

into the liner. They help to dampen the pressure pulsations in the

supply line; prevent cylinder combustion gases or products entering

back into the oil line; and provide storage of pressurized oil in the

accumulator section. Direct contact with the quill and cooling water is

prevented by a sealing pipe which allows easy removal of the quill.

Lubricator Pum p Unit

This lubrication pumping unit gets a rotary drive from the driving shaft

by means of a gear and ratchet mechanism. This rotational drive is

converted into reciprocating motion of the lubricator plunger. Checking

the pumping action can be done through the sight glass which shows a

steel ball lifted and pushed up when the oil is pumped. Acylindrical oil

non-flow alarm is also fitted. The oil feed ratio can be adjusted for

different load conditions. In modem engines, the lubricator pump drive

is by a frequency controlled electric motor which varies with the load

changes i.e. it is load-dependent. Som e modem units have a prelubrication,

post-lubrication and emergency lubrication option by a

switch in the control room, which starts an electric m otor for the

lubricator drive. This is during slow turning o f the engine for one

complete revolution. Manual cranking of the lubricator is also possible.

Lubricator Units

One of the latest types of lubrication systems is the Alpha lubrication

system used in MAN B&W engines. Here, a high pressure lubricator

pump supplies oil to an injector to inject a fixed volume into the engine

cylinder once in 4 revolutions. Acomputer control unit gets input from

engine speed, load index and LCD signals. It sends an ‘on’ signal for

lubrication to the solenoid valve to control the oil injection. The

computer sends an ‘off’ signal to the solenoid valve to allow the oil

back to the return line. The feed rate is adjustable by adjusting the

interval between injection i.e. every 5* and 6th revolution. More details

on this system is given in the chapter on Engine Descriptions.

Advantages

Lower lube oil consumption, lower wear rates of the liner, increased

time between overhauls; and better timing and utilization of the

expensive cylinder lube oil is possible. In case of failure of the solenoid

valve or transducer, the other lubricator automatically changes to

maximum setting. If the air pressure fails, the standby pump will

automatically start. The computer unit too has a backup computer to

ensure lubrication is continued.

Load Dependent Cylinder Lubrication

Modem engines employ load dependent cylinder lubrication where

the amount o f cylinder lube oil to each lubricating point can be

individually adjusted and controlled as per the load changes, via the

remote control system.

The specific oil feed rate increases with the decreasing engine load.

For example, at 20% engine load, the specific cylinder oil amount will

also be 25% more than at 100% engine load. The desired increase in

the specific liibe oil quantity can be programmed in the control unit.

Whenever there is a sudden load increase or a load fluctuation of the

engine, correspondingly the cylinder lube oil flow rate will be increased

automatically. The input signal for the oil increase is initiated from the

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Lubrication System

Specific Cylinder Lube Oil Consumption

According to power,

Specific cylinder lube oil consumption in g/kw-hr or g/bhp-hr.

- Cylinder lube oil consumption in kg/hr x 1000

Effective engine power in kw or bhp

According to fuel consumption,

Specific cylinder lube oil consumption in g/kw-hr or g/bhp-hr

«=K _ x Assumed S.F.O.C. for the engine in g/kw -hr or g/bhp-hr

1000

where K in kg/t =

Cvl. lube oil consumption in kg per 24 hrs

Fuel oil consumption in tons per 24 hrs

Frequency Controlled Electric M otor Lubricator

M ost m odern engines use this type o f lu bricator drive for

load-dependent cylinder lubrication.

load indicator transmitter. This input signal from the load indicator

transmitter is sent to the remote control unit, which sends an output

signal to change the speed of the frequency-controlled electric motor

drive to the lubricator. Below 20 % load, the oil feed rate is not reduced

anymore i.e. the speed o f the electric m otor remains constant. In

‘emergency lubrication’ mode i.e. when the normal cylinder lubrication

control fails, the cylinder lubrication can be adjusted manually by

adjusting the knob on the lubricator. In this mode, the regulation of

lube oil quantity is no more load-dependent, but independent of the

engine load. The remote control signals the electric motor to run with

its nominal frequency.

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Lubrication System

Multi Level Cylinder Lubrication

In this type, cylinder lube oil is injected into

the liner through quills at different levels

(usually 2 levels).

The position of quills can be one o f the

following:

1. A t 10% stroke from TDC: In this case,

although the cylinder lube oil feed rate

is more, there is poor circumferential

spreading due to oil flow breaking down

at high temperatures.

2. A t 20% stroke from TDC : In this

case, lubrication is m ost effective

especially for a single level of quills.

3. Combination of a ‘no groove’ row of

quills at 20 % stroke from TDC, and a

‘continuous groove’ row o f quills at 30

% stroke from TDC.

4. Above the exhaust ports, in case of

loop scavenging engines.

F ig -109

Usually, quills are 250 mm apart from each other around the liner

bore. Grooves are angled downwards. The combustion gas pressure

differential across the rings assist in pushing the oil downwards in the

groove. The disadvantage o f grooves is that they increase the area

into which oil flows. Hence the velocity and pressure o f the oil

decreases, thereby reducing its spreadability.

( 'rosshead Lubrication

K 1 Piston rod stuffing gland box

W 2 Crosshead bearing

p 3 Crosshead guides

|t-| 4 Crosshead pin

5 Lube oil articulated arm

6 Lube oil inlet

E C ro ssh ea d L u b ricatio n

\ Difficulties

The requirements for effective

lubrication are pumping action,

tunple of oil feed supply and an

oil film creation strong enough

to separate m etal surfaces.

Pumping action of acomponent

to produce oil pressure is

difficult in the crosshead, since

th e cro ssh ead m o tio n is

oscillatory with a high sliding

velocity. The speed of rubbing

is not sufficient to supply ample

oil feed, n o r to pro m o te

pum p in g actio n . U n like

F ig -110

4-stroke engines, there is no

load relief in 2-stroke engines

which would allow oil feed to be supplied and the bearing lubricated.

Rupture of the thin oil film which separates the rubbing surfaces is

caused by cyclic unidirectional loads during firing, in large super

charged 2-stroke engines.

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Crosshead Lubrication M ethods

Method (1)

As shown in the figure, oil is supplied at a m uch higher pressure

(16 bar in RTA engines). Here, the generation o f high oil pressure is

done by hydrodynamic m eans . A s the oil under pressure is now

confined to the small clearance area, its elasticity comes into play which

assists in maintaining the oil film for the momentarily instantaneous

loading. This is called Elasto-Hydrodynamic lubrication.

Oil supply is the same as bearing lubrication oil, whose main pressure

is now boosted to 16 b a r and supplied via the lube oil articulated arm.

As shown in the figure, there is a second lube oil supply inlet for oil

supply to the crosshead system in case of crosshead pump failure.

Method (2)

Providing a hydrostatic oil lift of the crosshead pin through hydraulic

pil pumps.

CHAPTER 7

COOLING SYSTEMS

Function of the cooling system

The function of the cooling system of a marine diesel engine is to cool

down the engine components, the lubricating oil and the scavenging

air to a point where optimum operating conditions are achieved. Cooling

is required for the piston, cylinder head, cylinder liner, exhaust valves,

turbochargers, injectors, etc. According to the heat balance chart,

only a fraction of the heat liberated by the engine is converted into

useful work, the rest being wasted within the exhaust into the

atmosphere or absorbed by the engine components in contact with

the hot combustion gases. The loss o f heat energy to the cooling

water is 20% at the cylinder head, 10% through the piston and 5 to

8% through the exhaust manifold and turbocharger. Trouble-free

functioning is essential for the cooling system, not only during running

o f the engine, but also during warming up before starting and

manoeuvring conditions. Lack of cooling causes non uniform heating

of the components inducing thermal stresses. An overheated piston

or liner causes evaporation and burning o f cylinder lube oil and

deposition of lacquer and carbon. This deprives the piston rings of

elasticity and causes failures due to sticking o f rings. Under-cooling

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173


reduces the cylinder clearance causing distortion and scuffing o f the

piston and liner. Thermal stresses trigger off cracks in the piston crown

which lead to combustion blow-by. Pistons were earlier water-cooled

using telescopic pipes, but m odem engines use oil as the cooling

medium.

Bore Cooled Liners

Bore-cooled liners provide intensive cooling at the working surface

and also retain the strength of the liner. Bores are drilled at a tangential

angle or cooling pipes are inserted during the casting process. Insulated

tubes are used in the bore holes to manipulate the desired control of

the cooling required at various sections. The liner temperature should

be within 150 to 220 deg.C. Over-cooling or under-cooling causes

problems and is undesirable. Piston ring region temperature is limited

to 220 deg.C, otherwise ring lubrication is adversely affected. This is

achieved by bore cooling as well as keeping a high top land where the

position of die top piston ring is much below the hot crown top surface.

Load Dependent Liner Cooling

In this system, the liner cooling rate is varied with respect to the load

on the engine. In order to achieve less cooling, some of the cooling

water flow is by-passed away from the liner to maintain the liner wall

temperatures when load decreases. Maintaining the liner temperature

above the dew point has the advantage of preventing cold sulphur

corrosion. The mass flow rate o f cooling water is reduced when the

load decreases. Latest developments in liner material and lubrication

allows a majority o f the liner portions to go without cooling. The

minimum cooling required is achieved from the scavenge air entering

the lower section o f the liner. The maximum admissible temperature

fluctuations for cooling water outlet temperature is + /-2deg.C for

constant load, and + /- 4 deg.C during load changes. This avoids

174

Cooling System

undue tension in the combustion chamber parts especially in the liner

and cylinder head region.

Piston Oil Cooling System

Oil is preferred in modem engines for cooling of the piston due to the

absence of water corrosion, or scaling, or water leaks into the

crankcase; simpler designs of glands; and the absence of telescopic

pipes. The same oil and pressure can be used from the main lube oil

system, thereby avoiding the necessity o f separate piston cooling

pumps. Oil has the drawbacks o f coking at high temperatures; a

reduced specific heat capacity compared to water; and a larger lube

oil system size required in order to allow air release.

Cooling Water Treatment

The cooling water used for engine cooling should be properly treated

with an approved cooling water inhibitor and alkaline agents to avoid

corrosion attack, sludge formation and scale deposits. The following

treatments are used:

1. Sodium Nitrite or Sodium Borate

They are safe for handling, non-toxic, not dangerous if over-dosed

and contain a pH buffer to provide protection against acidic

corrosion. They form a thin passive oxide surface layer on the metal.

Sodium Borate is used when the material to be protected involves

zinc or soft solder material.

2. Chromates

It is not preferred since it is highly toxic and unsafe during handling

and disposal. It is an anodic inhibitor, so pitting is caused if its

concentration is low. It is not to be used if the engine jacket water

is used for evaporator heating.

175


3. Soluble Emulsion Oil

It is not preferred due to foaming problems, bacterial contamination,

disposal problems, and no control over the film thickness. It forms

a greasy film on the metal surface and prevents corrosion. CHAPTER 8

STARTING, REVERSING

AND MANOEUVRING

Starting System

Marine diesel engines are started and reversed with the aid of

compressed air at a pressure o f around 30 kg/sq.cm. Pressurised

starting air is supplied from air compressors and stored in two air

bottle cylinders.

Starting Torque

The starting torque is achieved by the compressed air acting on the

top of the piston to push it down. This reciprocating motion o f the

piston is converted into a torque at the crank shaft. The amount of

starting torque required is the amount of torque needed to rotate the

crankshaft at a speed that will produce the desired self ignition

temperature to ignite the fuel in the cylinders.

Starting is in three step s:

♦ Cranking the engine by compressed air to produce sufficient starting

torque until some of the cylinders fire.

♦ Picking up the combustion cycle on fuel w ithout the engine’s

misfires.

177


♦ Acceleration to a speed in accordance with the fuel injection pump

setting.

The time period which elapses before the engine is under its own

power after being cranked by compressed air is between 2 to 8

seconds. During this period, the engine running is irregular, combustion

improper and exhaust is smoky. The irregular running is because some

of the cylinders misfire initially, while the engine speed increases in

jerks as each cylinder fires one after the other.

Start A ir Timing

The start air timing position should consider that the engine is started

in either direction. The best timing considering a reversible engine

would be when the start air is admitted at TDC, to utilize the positive

starting torque from the beginning of the stroke. In practice, starting

air is admitted slightly before TDC in order to take care o f the time

lag for pilot valve activation, start air valve opening and full pressure

availability to produce the desired starting torque. The start air should

be admitted after the firing dead center to provide a positive torque in

the correct direction at the start of the working stroke.

Ideal F iring Speed

It is the ideal speed of rotation of the crankshaft created by

‘compressed starting air’ cranking to compress the ‘combustion air’

in the cylinder to a temperature sufficient enough to self ignite the fuel

when injected. Usually, the speed is achieved at 8 to 12% o f the MCR

speed.

Firing Interval

It is determined by dividing the number o f degrees in the engine cycle

by the number of cylinder units of the engine.

Example:

For a 3 cylinder 2 stroke engine, firing interval = 360 / 3 = 120 deg.

Starting, Reversing and Manoeuvring

Start A ir Period

It is the minimum cranking period plus an overlap period to provide

sufficient starting torque to start the engine in any direction at any

position. It depends on the exhaust valve opening, as the start air

should shut before the exhaust valve opens, or else the pressurized

compressed starting air is wasted as it will just be blown out of the unit

through the exhaust valve. In 2-stroke pulse turbocharged engines,

the exhaust valve normally opens at 65 degrees before BDC or 115

degrees after TDC. This gives a maximum starting air angle of 115

degrees.

Overlap

Overlap is a period when two (or more) cylinder units are receiving

starting air, where one unit is ‘phasing out’ while the other is ‘phasing

into’ the start air period. It is essential to satisfy the requirement that

the engine be started in any crank position. Overlap is reduced in case

there are more number of cylinder unite, but necessary for engines

with less units to assist the starting torque for cranking. Overlap ensures

that at every crank angle position, there is sufficient air turning moment

to enable positive starting. It depends on the start air period, exhaust

timings and the number of cylinders.

M inim um N um ber o f Units fo r Overlap

1. 3 cylinder engine (2 stroke):

Firing interval = 360 deg = 120 degrees

3 unite

Since maximum start air period is 115 degrees, no overlap'is

possible. For overlap to occur in this case, the start angle

should be greater than 120 degrees which is not possible.

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179



2. 4 cylinder engine (2 stroke):

Firing interval = 360 deg = 90 degrees

4 units

If the start air period is 115 degrees,

then Total Overlap Period

The firing sequence is 1 - 4 - 3 - 2.

Start Air System Components

= Startairperiod-Firinginterval

= 115 deg - (360 / 4) deg.

= 115 deg - 90 deg = 25 deg.

Start A ir Compressors

Two or more start air compressors are to be provided having sufficient

capacity to pressurize both the start air bottles to the working pressure

from the atmosphere pressure in one hour.

Start A ir Receiver

For reversible engines, two air bottles o f equal capacity are required,

sufficient for 12 cold starts of the engine (without simultaneous

replenishment by the start air compressors) in' alternate ahead and

astern directions respectively. For non-reversible engines, 6 starts

are sufficient

The capacity of the air bottles are designed according to the swept

volume o f the engine cylinders, the specified number of cold starts (6

or 12) and the air required per start. Usually, this air requirement is

10 to 12 litres per litre of swept volume for cold engine starting and 5

to 8 litres for a warmed up engine.

Air Receiver Capacity

= (Total air mass in receiver at maximum pressure)

- (Air mass in receiver at minimum start pressure)

where, Total air mass in the receiver at maximum pressure

= 12 starts x 2 x Total displacement volume to give the

required air mass per start.

A ir Bottle Description

The start air bottle is of welded steel type with the following components:

♦ A relief valve to limit accumulation of pressure upto 10% with the

compressor filling the bottle and the outlet valves closed.

♦ A fusible plug, in case the relief valve can be isolated. The fusible

plug vents directly out of the engine room to atmosphere via a

separate piping, in case of an excessively high engine room

temperature (engine room fires). Usually, the melting pointofthe

fusible plug is 150 deg.C.

♦ Outlet valves of slow opening type to avoid sudden pressure surges

in the start air lines. The main stop valve provided allows for manual

isolation of the entire start air system during overhaul.

♦ Manhole door for internal inspection.

♦ Drain valves to drain water from the air bottle receiver from the

lowest point in the receiver without choking.

Start A ir Receiver Inspection

Inspection is done when there is adequate time during which the air

bottle will not be required. The air bottle is isolated and,all valves

lashed and tagged with notices. The air botde is de-pressurized through

the drain valve and then checked through another opening like the

pressure gauge connection in case the drain line gets clogged. The

manhole door is opened and ventilation for the interior is provided.

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181



Visual inspection is to be carried out for the interior coating and paint.

A horoscope can be used where access is not possible. Inspection is

carried out at stress concentration areas like welding seams,

penetrations, drain holes, support points, sludge collection area,

condensation areas, valve connection openings, etc. The internal

corrosion prevention coating layer is to be inspected. In case o f

deterioration, a coat of Copal Varnish can be applied after properly

preparing the internal surface to be coated. The fitting connections for

draining valves are to be cleaned. The relief valve is to be tested

hydraulically to the stamped working pressure and checked for lifting

in actual service after fitting back. In case of serious deterioration e.g.

severe corrosion or pitting, the receiver can be de-rated along with

the compressor settings and relief valves to provide for a lower safer

capacity.

Start A ir Pilot Valve

1 To and from cylinder air start valve

2 Venting to atmosphere

3 From automatic valve to pilot valve

4 Spring to lift roller off the cam

5 Cam

6 Clearance between roller and cam.

It is operated by the start air lever or button in the control room. It’s

function is to operate the opening and closing o f the automatic start

valve and to operate the air distributor by loading up the distributor

slide valve.

♦ In the figure, the pilot start air valve is shown shut since the spring

lifts the roller off the cam.

♦ On starting the engine, the automatic valve sends air to the pilot

valve which pushes the roller onto the cam. As the cam turns, the

negative peak comes into play allowing air to pass through, to the

automatic starting valve piston causing it to open. The shutting of

the valve happens when the roller comes onto the idle surface of

the cam.

Automatic Master Air Start Valve

Function

♦ To act as a stop valve which supplies or shuts off main starting air

into the main start air line at the engine cylinders only during the

starting period.

♦ To act as a non-return valve preventing any blow back of

combustion gases in case an air start valve leaks back, and also

preventing a flame by use o f a flame trap incorporated in the

assembly.

♦ To shut off starting air supply automatically to the start air line ahead

of the stop valve, once the engine is on fuel or when the engine is

shut down, thereby saving on air consumption and providing

additional safety.

Types

They are classified into two types on the basis of the operating

principle:

1. Unbalanced type, where the valve is opened due to relieving the

pilot piston of air pressure.

2. Balanced type, where the valve is opened due to an air pressure

applied to the pilot piston.

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183



1 Tapping for pilot valve

2 Vent, when valve is shut

3 Valve

4 Spring pushing the pilot

piston down

5 Pilot piston

6 Pilot air to open valve

7 Valve body

A Start air inlet

B Start air outlet to start air line

at cylinders.

T h e fig u re show s a

balanced type automatic

m aster start air valve,

which is more reliable than

the unbalanced type. It

consists of the valve closed

by the downward force of

the spring pressure along

w ith air p ressu re ‘A’.

When the starting lever is

sh ifted to ‘STA R T ’

position, the pilot air valve

open s and sends air

pressure to the space ‘a’.

The upward force due to

this air pressure on die pilot

piston is greater than the

downward force and the

Fig-112

valve opens. As soon as

the engine is on fuel or shut down, the pilot valve closes, stopping air

pressure supply to the pilot piston of the automatic valve, thereby

shutting it. Air is then vented via vent pipe connection ‘2’.

A ir Start Valve

An air start valve is fitted to each cylinder head o f the engine and is

operated by the starting air distributor control valve. It is operated by

the start air lever or button in the control room. It’s function is to

operate the opening and closing of the automatic start valve and to

operate the air distributor by loading up the distributor slide valve.

1 Nut

2 Cover

3 Intermediate ring

4 Casing

5 Casing o-ring

6 Cylinder head

7 Self-locking nut

8 Pilot piston

9 Valve spindle

10 Allen screw

11 Spring

A Piston rings

B Control valve

M Air gap

The start air valve is shut

compression spring force acting on

the pilot piston. If the cylinder

pressure is higher than the starting

air pressure, the valve cannot open.

Hence, blow back o f combustion

gas into the starting air manifold is

avoided. The start air valve is opened

pneumatically by air supplied from

the respective start air control valve.

This air pressure acts on the pilot piston causing it to overcome the

spring force and open the valve.

184

185



Start A ir Distributor

Function

♦ To admit pilot air to operate the cylinder air start valves with proper

timing and sequence for starting in ahead and astern directions.

♦ To vent the lower chamber of the cylinder start air valves, which

are not being supplied with starting air.

♦ During reversing, the distributor cam is also turned by the same

angle.

♦ During running, the distributor piston valve is kept off the cam with

the help o f a return spring, with start air supply being shut off. On

pushing the starting lever, air is supplied to the distributor which

pushes all the respective control valves onto the cam.

♦ The distributor sends pilot air in a proper sequence to each cylinder

air start valve until the minimum cranking rpm is reached, after which

start air admission is stopped and fuel is injected to self-ignite.

Start A ir Cam

The start air cam is usually o f inverse type as it has the following

advantages:

♦ Wear is reduced on the cam working edge because the roller is off

the cam during normal running, as there is a definite clearance

between them, when the engine is running. This ensures that the

air distributor functions correctly inspite of the spring failure.

♦ It allows more flexibility to position the control valve of the distributor

so that it does not touch the cam when the engine is running.

♦ The distributor is driven by a cam connected to the fuel camshaft,

which provides the correct sequence o f starting. Starting control

valves are radially fitted around the distributor cam.

186

Starting Interlocks

♦ Thesearemechanicallinkagesordevices which willnotallowfurther

operation until they receive an input signal that the predetermined

conditions are fulfilled.

♦ The following interlocks are placed in the starting system:

. (1) Turning gear is disengaged

(2) Complete reversing is achieved

(3) Correct running direction is done

(4) Lube oil pressure is sufficient

(5) Spring air pressure is sufficient

(6) Auxiliary blower is o n ‘auto’.

187


Starling, Reversing and Manoeuvring

Slow Turning

♦ Its function is to avoid fluid lock in case of fluid accumulation in the

combustion chamber, during engine stand stills for long periods

(similarto ‘blow through’).

♦ This is a ‘mode’ o f the engine control system where the engine is

turned slowly for one complete revolution at a slow speed of 5 to

8 rp m .

♦ During manouevring, while the engine is on Bridge Control, the

‘slow turning’ m ode automatically starts, if there is no telegraph

movement for 30 minutes.

♦ In order to achieve slow turning, the flow of start air to the engine

is limited.

For 2-stroke the firing interval is 360 / Z, and for 4-stroke it is

720 /Z , where Z is the number of cylinders.

Scavenge A ir Lim iter

♦ It is a means o f governor control of the fuel released depending on

the availability of scavenge air in the desired ratio required for good

combustion.

♦ It is im portant while increasing the engine speed so that a

proportional amount of fuel is released as the scavenge air pressure

increases.

♦ The scavenge air limiter can be over-ridden, in case of failed start

attempts so as to provide a better chance for starting with more

fuel available. This is done by sending a false scavenge air

pressure signal to the governor from the control air line.

Firing Order o f Cylinders

♦ The purpose o f a firing order is to relieve the crankshaft journals

between adjacent cylinders from excessive loads, unavoidable if

these cylinder loads would fire in succession.

♦ It provides better and regular crankshaft rotation when firing in

equal intervals.

Reversing

Requirements

Repositioning of the following cams are required for the correct firing

sequence according to the reverse direction:

1. Fuel Cam 2. Air Distributor Cam 3. Exhaust Cam.

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189



F iring Order Reversed

The firing order sequence in the

reverse direction can be as follows:

6-Cylinder 2-stroke engine:

Ahead Firing Order 1-5-3-4-2-6

Astern Firing Order 1-6-2-4-3-5

Reversing Methods

(A)

(B)

(C)

(D)

Camshaft is rotated with respect to crankshaft

Example: R D & RNDEngines

Camshaft is stationary but cams are turned

Example: RTAengines

Camshaft is displaced in the axial direction

Example: 4-stroke engines

Shift in the contact position of the fuel pump roller

Example: SMC engines.

RD Engine Reversing

Fig-105

1. Fuel and Start air distributor cams get repositioned by a common

hydraulic servomotor which turns the camshaft by 98 degrees in

the opposite direction relative to the crankshaft Here, the engine

is stationary and the camshaft physically rotates by 98 degrees.

2. Exhaust rotary valve cams get repositioned by another hydraulic

servomotor connected to the camshaft drive, which turns the rotary

valve cam by 160 degrees in the opposite direction. In RD engines,

since rotary exhaust valves are used, the timing is asymmetric

about BDC and repositioning of exhaust cams is required.

RND Engine Reversing

Fuel and Start air distributor cams get repositioned by a common

hydraulic servomotor, which turns the camshaft by 98 degrees in the

opposite direction relative to the crankshaft.

3 2 Fig-116

r~i Gear train 2 To interlock systems

| 3 To/from reversing control valve._______ ._______________________ 1

RTA Engine Reversing

In these engines, the fuel, air and exhaust cams are fitted on the main

camshaft. Hence the camshaft cannot be repositioned, as this will not

provide the correct repositioning of all three types of cams i.e. fuel, air

and exhaust cams. Hence, the solution is to reposition only the cams,

whilst the camshaft is stationary.

1. Fuel Cams are turned by 70 degrees in the opposite direction

while the camshaft is stationary. The cams are mounted on a

reversing servomotor, which is mounted on the main camshaft.

One servomotor is used to reposition two fuel cams.

190

191

2. Start A ir Distributor Cams are

turned by 98 degrees in the

opposite direction by a separate

servomotor, while the camshaft is

stationary.

98*

2 3 Fig-117

1 Fuel Cam 2 Oil drained ‘out’ for astern direction

3 Oil ‘in’ for ahead direction.

RTA Reversing Servomotor fo r Fuel Cam

It is a mechanism to turn and reposition cams for the reversal sequence

of firing. As shown in the figure, each reversing servomotor has three

pipe connections:

a) for sending oil pressure ‘in’ for ahead direction.

b) for draining oil ‘out’ for astern direction.

c) for control pressure, which gets pressurized only when the

flap is in the end position.

The control air pressure is ‘nil’ during reversal as it is connected to the

side o f the flap where pressure to relieve is acting. This control air

pressure can be used as a signal to cut off fu el.

Fig-118

3. Exhaust cams are symmetrical about BDC (since exhaust valves

are used and not exhaust rotary valves). Hence, no repositioning

is required. Exhaust cams are on the same shaft as the fuel cams.

MC Engine Reversing

1. Air Distributor

The engine drives a rotary disc (distributor) which can be turned

by the reversing angle by means of areversing pneumatic cylinder.

2. Fuel Cam

The fuel pump roller (not the cam) is shifted by a pneumatic cylinder.

Fuel cam is of inverse type. Each fuel pump roller has an individual

pneumatic cylinder. During reversing, the cylinder gets pressurized

pneumatically and moves the pump roller position. After completion,

the cylinder is depressurized and vented. The rollers are o f selflocking

type in their end position. The shift of all fuel pump rollers

take place during the first revolution of the engine while still on air.

After shifting of rollers is done, this end position of the rollers is

sensed by limit switches which gives an indication in the control

room that reversal has taken place.

192

193



Gain M otion

It is the gain in motion caused due to the camshaft turning in the same

direction as the required direction when the engine is being reversed.

It is used in B & W engines.

Governor Booster

It serves the purpose to boost the hydraulic pressure required for the

governor to push the fuel racks when starting.

Running Direction Interlock

It is an interlock which prevents

admission of fuel to the engine, if the

running direction of the engine does

not match with the telegraph lever.

It is fitted at the forward end o f the

fuel pumps.

1 Fork lever

2 Angle of rotation.

3. Exhaust cams are symmetrical about BDC and are on the same

camshaft as the fuel cams. Repositioning is not required for exhaust

cams.

Lost Motion

It is the loss in motion caused due to the camshaft turning opposite to

the required direction when the engine is being reversed. It is used in

Sulzer engines.

Crash Manoeuvring

Crash manoeuvring is the application of brake air, whilst the engine is

still turning in the opposite direction.

In B & W engines

♦ Acknowledge the bridge request for reversal of direction.

♦ The start air cam gets reversed due to telegraph acknowledgment.

However, the fuel is cut off by the running direction interlock,

since telegraph is opposite to the turning direction o f the engine.

194

195



♦ Now put the fuel lever at ‘O’ setting.

♦ When rpm reduces to 20% to 40% MCR rpm, put the fuel lever

to minimum start setting.

♦ Astern rpm is much less than the ahead rpm as the engine is

tremendously overloaded due to increased propeller slip.

♦ Start air becomes braking air because the start air cam reversal

allows air supply inforastem timings, when theengine is still moving

with ahead timings.

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

♦

Manoeuvring Flow Chart

Control is from bridge, engine control room, or local manoeuvring stand.

Safety interlock and pressure conditions are met.

Only in emergency conditions, safety devices can be overridden.

Telegraph lever is put to ahead or astern.

Reversing of cams takes place.

Camshaft is in end position (either in ahead or astern).

Running direction interlock senses that correct reversal is completed.

Fuel lever is set to minimum setting.

Start button pressed or starting lever put to ‘start position'._______

\

Turning gear interlock check is done.

Pilot valve opens automatic valve and distributor control valves.

Automatic valve sends start air to cylinder start air valves.

1

\

Engine turns on air to the minimum firing speed.

Minimum fuel is injected and cylinders fire.

Start air is shut off.

Engine speed is gradually increased.

Critical speed is overridden.

I

Engine speed is brought upto MCR revolutions and parameters checked.



Manoeuvring

F ig -121

I

Running direction interlock

3 Fuel ptimp

5 Automatic valve

7 Start- air distributor cam

9 Fuel pump cam being turned by

1 i Turning gear interlock

13 Control slide valve

15 Engine room telegraph lever

17 Fuel cut out servomotor

19 Oil pressure supply at 6 bar

21 Fuel speed setting lever

23 Reversing control valve

6

8

10

12

14

16

18

20

22

Reversing servomotor

Cylinder start air valve

Governor

Start air distributor

Air cam being turned by the

reversing servomotor

Air start bottle

Starting lever interlock block valve

Starting lever

Pilot air valve

Automatic oil and water low

pressure cut out

Load indicator

Starting, reversing and manoeuvring are explained with reference to a

RND manoeuvring diagram.

Mediums a re:

♦ Start air at 30 bar pressure is supplied from the start air bottle

when the main bottle isolating valve is opened. Start air reaches

the automatic valve (in closed position) and the pilot valve through

the turning gear interlock block valve.

♦ Lube oil at 6 bar pressure.

198

199



Starting

Telegraph lever action to free start lever

The Bridge gives a telegraph order which is acknowledged with the

telegraph lever 15 in the engine control room. The telegraph lever

sets the required running direction by turning the reversing control

valve 23 to either ahead V, stop U or astern R positions via linkage J.

Lube oil at 6 bar pressure 19 now passes through the reversing valve

to the cam shaft reversing servomotor oil passages 2 and turns the

camshaft. Only when the camshaft has reached its end position, the

running direction interlock 1 w ill allow oil pressure to the starting

lever blocking device 14 vialineA . T hisfreesup the starting lever

16 for movement.

Freeing up o f fu e l lever

Simultaneously with the above operation, the lube oil pressure supply

goes along line B to the slide valve 13 and then to the fuel cut out

cylinder 17 to free up the fuel control linkage along line C, so as to

take up the position as per the load indicator setting 22, which is set

up by the fuel lever 21. This freeing up o f the fuel lever assumes that

the safety cut out pressures are met.

Safety cut out device

A safety cut out device 20 is set to ensure that the lube oil, jacket

cooling and piston cooling water pressures are above the predetermined

setting.

♦ In case any o f the pressures are not upto the values set, then the

slide valve 13 moves down due to a decrease in pressure at line D.

This causes the slide valve to vent the fuel cut out cylinder, thereby

bringing the fuel rack back to zero through line C.

♦ In an emergency, the automatic cut-out devices can be overridden

as in the case of reduced pressures.

Starting operation

♦ Start lever 16 is put to ‘start’ position.

♦ This leverage raises the pilot air valve 18 opening it.

♦ Pilot air now passes to open the automatic valve 5 through line E

by venting its underside and also to the start air distributor 8 control

valves along line F to force them onto the cam 7.

♦ The start air distributor cam 7has already been positioned for the

firing sequence by the reversing servomotor turning the camshaft in

either ahead or astern end positions 10.

♦ Pilot air passes through the air distributor and goes to open the

cylinder start air valve 4 via line G i.e. to the top of the cylinder

start air valve piston to push it down. The underside of the cylinder

start air valve piston is vented via line H.

♦ Starting air from the automatic valve is admitted to the engine

cylinders, after each cylinder start air valve is opened b y the

distributor in the correct sequence via line 1.

♦ The fuel lever 21 is already set to around 3.5 setting.The engine

turns on air and then fires on fuel.

♦ Once the engine starts, the starting lever 16 is released to its normal

position by a spring fitted. This action makes the leverage to

lower the pilot valve 18, thereby shutting it and shutting pilot air to

the distributor 8 and the automatic valve 5. Start air is now shut

and the air in the start air manifold line is relieved through small

leakage points in the starting air valves.

Reversing operation

♦ The telegraph lever 15 is brought back from ‘ahead’ to ‘stop’

position.

♦ The fuel lever 21 is brought back to minimum setting around 3.5,

so as to prevent excessive fuel injection when the engine is restarted.



♦ Bringing the telegraph lever 15 to ‘Stop’, puts the reversing control

valve 23 to stop position U via linkage J. This relieves the oil

pressure supply from the reversing control valve 23 to the reversing

servomotor 2. This pressure drop causes the slide valve 13 to

move down, thereby bringing back the fuel cut-out cylinder 17 to

cut fuel injection.

♦ Telegraph lever 15 is put to ‘astern’, thereby pushing the reversing

control valve 23 to astern V position via link J. The oil pressure

from the reversing control valve 23 is supplied to the reversing

servomotor 2 to turn the camshaft to astern position. O h reaching

its end position, the running direction interlock will allow oil pressure

to the starting lever blocking device 14 via line A, to free up the

starting lever 16 for movement.

♦ The start lever 16 is now put to ‘start’ position and the starting

sequence is repeated as per the starting operation described earlier.

Bridge Control System

Bridge Control Unit

It consists of the following:

1. A telegraph lever handle for ahead / astern movement with speed

positions like dead slow, slow, half ahead, full ahead and navigational

full ahead.

2. A speed sensing unit getting a signal directly from the engine

flywheel.

3. A control unit on the bridge.

4. A load programme unit either on the bridge or in the engine control

room.

5. Bridge control solenoid system in the engine control room.

6. Alarm unit for alarms like low start air pressure remote system

failure.

Bridge Control Procedure

♦ Once the engine is blown through and tested on fuel, controls are

handed ova: to the bridge by pressing a button in the ‘engine control

room’, which must be acknowledged on the bridge.

♦ Starting will be blocked, in case any of the pre-set conditions are

not met, such as: starting air pressure low, turning gear engaged,

lube oil pressure low, cooling water pressure low, reversing running

direction interlock, etc.

♦ Starting operation is the same as the engine control room starting

sequence.

♦ In case o f a failed start attempt, start air will be automatically kept

on.

♦ Three to four starts are allowed in case of start failures, after which

a false scavenge air pressure from the control air line is supplied to

the scavenge air limiter, so that more fuel can be injected for a

better start attempt.

♦ Start air is always kept open in the engine room even after the

engine is full away.

♦ Once the engine is started, the speed is increased as per the bridge

telegraph lever position.

♦ Speeds with each speed range can be varied by pressing a button

or a fine setting knob.

♦ Automaticjumping over the critical speed range (around 8 to 12%

o f the M CR speed) is done by releasing more fuel.

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203

♦ In case o f any deviation in critical parameters, the engine is

automatically slowed down or stopped.

♦ Emergency manoeuvring is possible by overriding the safety devices J

CHAPTER 9

ENGINE STRESSES,

VIBRATION AND DYNAMICS

In a single cylinder engine; during the expansion stroke, a force is

applied onto the piston due to the gas pressure and an inertia force of

the reciprocating parts. While the former varies with the crank angle,

205


Engine Stresses, Vibration and Dynamics

the latter equaling the product o f the acceleration of the parts and their

mass varies directly w ith crankshaft speed. The mass o f the

reciprocating parts equals the mass o f the piston assembly and

30-40 % o f the mass o f the connecting rod. The resultant o f these

forces, referred to as the motive force P is applied to the centre of the

piston pin and transmitted to the crankshaft through the connecting

rod. The motive force is resolved into two components N and S. The

normal component force N presses the piston against the cylinder

liner in a trunk-type engine or it presses the shoe against the

corresponding guide in a crosshead engine. This force, varying in both

direction and magnitude, produces a recurrent piston thrust against

the opposite sides of the cylinder liner. It also gives rise to an overturning

moment about an arm equal to the distance between the axis o f the

piston pin and the crankshaft axis. The moment opposing the direction

of the crankshaft rotation is taken up by the bolts holding down the

engine to the bedplate.

The second component force S is brought down the line of its action

and applied to the crank pin center. It can be resolved into two

components : a force T tangential to the crankpin and a force Z

coinciding with the crankpin radius. The force T produces a torque

which varies with the crank angle from a maximum to a minimum

within a certain period. This torque causes the crankshaft to rotate

irregularly. The force Z bends the crankpin and creates wear in the

bearing.

In a multi-cylinder engine, the crankshaft is set to rotate by the torques

produced by all the cylinders in succession. It w ill operate more

regularly than the crankshaft of a single cylinder engine. However, the

torques will not coincide in time, because the cranks are arranged at

certain angles to each other, rather than in the same plane. This implies

that the recurrence of torque alterations increases directly with the

number of cylinders and the irregularity of the crankshaft rotation

decreases. The continuously changing engine torque is compared with

the moment caused by the force resisting the crankshaft rotation. The

torque exceeds the moment at the instance of cylinder firing and is less

than the moment during the intermissions. Hence, the two conditions

are extra torque and torque deficiency, causing ‘irregularity’ in

crankshaft rotation.

Irregularity Factor

It is the ratio of the difference between the maximum and minimum

angular velocities o f the crankshaft and the mean angular velocity

throughout a cycle of torque alterations.

Flyw heel

A flywheel is fitted to the aft end o f the crankshaft to help reduce the

irregularity o f crankshaft rotation. It is an accumulator which stores

the energy o f the gyrating masses when there is extra torque, and

supplying the stored energy during torque deficiency. Increasing the

number of engine cylinders also decreases the irregularity of crankshaft

rotation. Example: Adiesel engine with more than 12 cylinders does

not require a flywheel.

Static Loads

These are loads caused by the weights of the engine components and

the bolt loads.

Dynamic Loads

These are loads caused by the cylinder gas fluctuating pressure and

inertia loads o f the reciprocating and rotating masses.

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207



Static Balancing

♦ It implies that the shaft is stationary or stops at a different position,

if rotated when supported between centres.

♦ The sum of all moments taken about its centre of rotation should

be zero at any angular position.

♦ It is done by placing counter weights to balance the moments so

that their sum becomes zero.

Primary a nd Secondary Imbalance

D ynam ic Balancing

Although a shaft may be statically balanced, imbalance is caused while

it is rotating, due to rotating and reciprocating masses producing inertia

forces, couples and moments. Dynamic balancing is balancing of the

unbalanced inertia forces together with their moments.

An inertia force is set up due to the translating (reciprocating) masses

o f the connecting rod-crank mechanism, and due to unbalanced

gyrating (rotating) masses. Both forces cause foundation vibration.

The forces due to translating (reciprocating) masses of the connecting

rod-crank mechanism tend to either tear the engine off the foundation

or to press it against the foundation, depending on the direction of

action.

The unbalanced gyrating (rotating) masses act along the crank web

and are constant at any angle on the crankshaft at a given engine speed.

They tend to shift the engine off the foundation or overturn it.

Moments caused by these two inertia forces :

♦ The gyrating (rotating) masses cause moments to act in the vertical

and horizontal planes.

♦ The translating (reciprocating) masses cause moments only in the

vertical plane.

♦ Primary and secondary forces are set up due to the inertia force

caused by reciprocating masses.

♦ The variation in these forces are in the form o f a sine w ave of

simple harmonic motion.

♦ Considering one revolution of360degrees, the variation of primary

. forces (Curve 1) and secondary forces (Curve 2) is shown.

Vibration

♦ It is the oscillation caused due to a disturbing force.

♦ It can be longitudinal, axial, transverse or torsional.

E ngine Vibration Causes

-♦ Constantly changing firing pressures.

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209



♦ U nbalanced forces, couples and moments due to reciprocating

and rotating masses.

♦ Pulsations due to gas forces including exhaust gases.

♦ Guide force moments.

♦ Axial forces due to in-plane bending of crank webs.

♦ Torsional vibration caused by varying torque and propeller thrust.

A m plitude

It is the m axim um displacement of vibration from the point of

equilibrium.

Node

It is the point in the vibrating system at which the amplitude of vibration

is zero.

Order o f Vibration

It is the num ber o f vibration ‘cycles’ in one revolution of the engine.

Vibration M o d e

It is designated by the number of nodes in a system.

N atural Vibration

It is the vibration caused by the elastic forces of the crankshaft material

and the inertia o f its masses in the absence of external forces.

Forced Vibration

It is the vibration o f the crankshaft and the shafting coupled to it, which

is induced by a variable engine torque.

Resonance

♦ It is the coincidence o f the frequency of the natural vibration and

the frequency of the forced vibration.

♦ It results in vibration, local overheating and overstressing o f the

shafting.

Vibrations D uring Starting

♦ Balanced engines tend to vibrate during starting, and gradually the

vibrations die out as more cylinders develop their own power.

♦ This is due to intermittent fuel delivery and misfiring o f some

cylinders giving rise to unbalanced inertia forces and moments. After

a while, the combustion pressures in the cylinders level up and the

imbalance is reduced.

Torsional Crankshaft Vibration

♦ The engine crankshaft, its flywheel gears and the different elements

of the propeller shafting form an elastic system, incapable of being

absolutely stiff.

♦ Application of a torque to the crankshaft causes it to ‘twist’ within

elastic limits. Removal or reduction o f the torque causes the

crankshaft to twist or untwist in the opposite direction. This state

will recur, for the crankshaft will be urged by the elastic forces of

its material and the inertia forces of its masses to vibrate at a certain

frequency.

♦ Torsional vibration is the relative vibration of the masses o f the

elastic system causing it to twist and untwist.

Critical Speed

♦ It is the crankshaft speed at which resonance may occur.

♦ There may be more than one critical speed range for an engine.

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211



♦ It manifests itself by a shaxp increase in the amplitude o f torsional

shaft vibration.

♦ Critical speed can be measured by a torsiograph, which automatically

records the torsional vibration on a paper tape.

Barred Zone Range

♦ It is a range of operational speed which is ‘barred’ i.e. overridden.

This is a critical speed range which must be passed as soon as

possible.

♦ Under Bridge control, the Bridge control unit programme

automatically increases the speed setting so that more fuel can

enable the engine to cross over this speed range as fast a possible.

♦ It is specified for a given engine.

♦ The means of avoiding these resonant frequencies is to adjust the

speed of the engine or the mass of the flywheel or the engine firing

order.

♦ The most effective means o f reducing the amplitude o f torsional

vibration is the sectionalizing of the shafting and interposing special

couplings between the sections.

♦ Another method is to use vibration absorbers which are fitted to

the crankshaft to dissipate the energy o f vibration in a given

range of engine speeds.

Reduction o f E ngine Vibration

1. The vibrations due to reciprocating and rotating masses can be

countered by compensating masses rotating at the engine speed

for first order frequency, and twice the engine speed for second

order frequency. These compensators or balancers can be

positioned in the chain drive.

2. Axial vibration due to in-plane bending o f crank webs can be

countered by fitting an axial vibration damper at the free end of the

crankshaft.

3. Torsional vibration due to varying torque and propeller thrusts is

countered by detuning or damping.

4. Vibration due to guide force moments is countered by detuning, by

using top bracing to increase the stiffness.

Detuners

They are frequency control devices used to change the frequency of

the system.

Examples:

1. Top bracing supporting the engine:

The bracing increases the stiffness and raises the natural frequency

beyond the operating range.

2. Flexible couplings:

These couplings sectionalise the system. The flexible element

absorbs part o f the vibrational energy and hence, decreases its

amplitude. The flexible element can be either rubber or a spring

element

3. Hydraulic oil-filled mechanical detuners:

Here, the oil gets passed to and fro past the springs, causing detuning

as well as damping.

Dampers

These are devices which absorb part of the vibrational energy.

Examples:

1. Rubber damper using the elasticity of rubber to absorb part o f the

vibrational energy.

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213


2. Viscous damper using a viscous silicone fluid.

It is made up o f two masses i.e. a light outer casing and a heavy

inner ring. The inner heavy ring rotates at a lesser speed than the

light outer ring separated by viscous silicone fluid. This heavier

ring is driven by the viscous shear o f the silicone. The energy

required for the viscous shear (relative oscillating motion) is

provided from the vibration energy, thus giving a damping effect.

CHAPTER 10

ENGINE OVERHAULS AND

MAINTENANCE

Unit Decarbonisation

Safety Precautions to be observed:

♦ The port authorities are to be informed that immobilization of the

engine is to take place.

♦ In case of turning the propeller, propeller clearance is to be taken

from the Bridge.

♦ Spare parts, tools, lifting devices, gaskets, 0-rings, hydraulic jacks,

special tools, gauges, operational crane, etc. are to be kept ready.

♦ Engine is to be isolated:

A t Finished With Engines (FWE), bring the telegraph lever and

fuel lever to zero. Take over the controls from the Bridge to the

ECR. Stop pumps and shut valves for fuel, exhaust valve air, start

air, lube oil and jacket water systems. Use ‘Do not operate’ tags

and signs, or lash valves. Engage die turning gear. Usually die turning

gear is engaged and run for a few revolutions before stopping the

lube oil pumps. Drain the jacket water for that unit.

214

215


Engine Overhauls and Maintenance

Cylinder Head Removal

Tools required

Hydraulic tensioning device, suspension lifting device and special eye

bolt screws.

Procedure

♦ Remove the cooling water piping for the exhaust valve; high pressure

fuel oil pipes to the injectors; air piping to the cylinder start air

valve; lube oil hydraulic pipe for exhaust valve actuation; drain

pipe between exhaust valve and hydraulic actuator; and exhaust

valve bellow.

♦ Clean the threads o f the cylinder head studs after removing the

stud caps. Place the hydraulic device to remove the hydraulic nuts

on the cylinder head studs.The hydraulic pressure to be applied

by the hydraulic pump is given in the manufacturer’s manual.

Example:

600 bar pressure for RTA engines;

700 bar pressure for LGF engines.

Hydraulic nut removal

♦ Hydraulic pressure is used to elongate the stud. The nut is then

opened by a turn, by a tommy bar inserted into holes on the side

of the n ut Hydraulic pressure is then released and the nut unscrewed

easily.

♦ Hydraulic pressure can be supplied to one point as shown in the

fig-124 and vented before applying full pressure. Example shown

is as per a ‘LGF’ engine.

♦ Other engines use a hydraulic tensioning device consisting of a pump

and a single flexible hose branching out to each nut itself. Example

shown in fig-125 is as per a ‘RTA’ engine.

Fig-125

F ig -124

1 Stud 2 Nut

3 Pin 4 Vent screw

5 Hydraulic nut piston 6 Hydraulic nat cylinder

7 Sealing ring

8 Hole to insert tommy bar

9 Oil pressure inlet

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217



►Once the hydraulic nuts are removed, lifting eye bolts are screwed

on to lift the cylinder head cover (along with the small water jacket)

by the crane.

►Land the cylinder cover onto wooden

blocks placed on the platform floor

plates.

• D iscard the sealing m etal gasket

between the cylinder cover and liner.

’ Remove the mountings and clean the

cylinder head cover.

■ Lap the fuel, start air and exhaust valve

bores.

’ Use new seal rings and cooling water

connection gaskets while assembling

back.

■ After assembling, air supply to the

exhaust valve is opened first so that

the exhaust valve spring air closes the

exhaust valve, after which camshaft lube

oil pump is started.

Exhaust Valve Removal

♦ The procedure is similar to cylinder head removal. Only the exhaust

valve can be removed while the head is still in place.

♦ The necessary exhaust valve piping connections like hydraulic

actuation pipe, exhaust bellow and expansion piece are removed.

♦ The hydraulic nuts which secure the exhaust valve to the cylinder

head are removed.

♦ With the help o f a suspension device, eye bolts and the engine

room crane, the valve is removed and placed on woodenblocks.

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219



Piston Removal

1. Cleaning o f the liner top and

the piston crown hole threads

After the cylinder head is removed,

clean the carbon deposits from the

upper part o f the liner. Clean the

lifting holes in the piston crown top.

Tap the threads o f the holes in the

crown to enable the fixing o f the

lifting tool. Fitthe lifting tool into the

threaded holes of the piston crown.

2. Removal o f the piston rod palm

nut

The piston rod palm nut is removed

hydraulically. The weight o f the

piston is now taken by the engine

room crane.

3. S epara te th e c ro ssh ead

bearing

Turn the engine with the turning gear

and lower the crosshead bearing so

that it is separated and clear from

the piston rod. In some engines, the

stuffing box is taken out along with

the piston, whilst in other engines it

is taken out after the piston is

removed.

Fig-128

Piston Withdrawal

♦ Remove the piston and land it in the space provided, through the

engine room platforms. Supporting devices in two halves are

provided for the purpose.

♦ A rubber sheet or a wooden board is placed over the crosshead

to protect it from dirt falling from the top.

Piston Inspection

♦ Check the crown surface for any traces o f fuel, water or cracks.

♦ The piston crown is cleaned and the bum-away on the surface is

checked with the help of a template. For cracks, use a simple

white chalk test or dye penetrant

test.

Mok. permiuible burn-away

♦ The ring area and liner surface * pi,,on ,af>

should be seen as slightly damp

with lube oil to confirm whether

cylinder lubrication is correct.

♦ R em ove the rings w ith the

expander tool.

F ig -129

FITTING OF TENSION SPRING

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♦ Clean the grooves and measure the groove / ring clearances. The

groove inner comers should be cleaned o f deposits.

Piston Ring Clearances

(1) Ring gap o r butt clearance

It is taken where the liner is least

worn, usually at the lower part, or in

a new liner. The used ring is inserted

into the liner and the ring gap (or butt

clearance) is taken , by making an

impression of the gap on a paper.

(2) Groove axial clearance

It is taken using a feeler gauge inserted

horizontally in the gap between the top

of the ring and the groove.

Wear rate = Ring wear x 1000

Running hrs.

where Pi = 3.14

Piston Mounting

♦ The rings are fitted correctly by checking the ‘top’ marking on

each ring.

♦ Coat the piston ring, piston rod, and liner with lube oil; and mount

the lifting tool.

♦ Use new 0-rings on the outside of the stuffing box and smear a

coat o f lube oil.

♦ Remove the protective rubber sheet for crosshead protection.

♦ Remove the stuffing box hole cover.

♦ Mount the piston guide ring piece (bell mouth) and lower the piston

with the crane.

♦ The piston rod foot is to be guided into the stuffing box opening.

♦ Lower the complete piston in the liner leaving a gap between the

guide ring and the lifting tool.

♦ Turn the engine with the turning gear to put the piston rod centre

hole into the crosshead bearing section.

♦ Remove the guide ring and the lifting tool.

♦ Tighten the piston rod screws and the stuffing box screws.

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223



L in er Removal

♦ Drain the jacket w ater from the

cylinder unit after isolating it

♦ Remove the cylinder head, piston and

stuffing box.

♦ Remove two screws which locate the

liner on the support ring.

♦ Remove the quills, protecting devices

and oil connections.

♦ Lower the beam tool 1 from the top

and fasten it with screws 2 at the

bottom of the liner.

♦ Turn the engine to TDC and place a

support piece 5 along with a hydraulic

jack 4 on to the crosshead pin 3. .

♦ A bridge lifting tool dism ounted on

the top of the liner 7 with the help of

screws 8.

♦ Jack up slightly w ith hydraulic

pressure and check that the two 0-

rings are detached and liner is loose.

♦ Pull the liner out with the help of the

crane.

L iner Inspection

Check and clean the corrosion layer o f the jacket.Use new 0-rings

when fitting back. Lubricate guide areas with lube oil.Clean landing

faces and quill holes. When using a new liner, the protection coating

layer should not be scraped out. Remove the coating with diesel oil to

prevent any damage of the surface. Check the cylinder liner lubrication

after fitting of the quills

L iner Calibration

♦ Once the cylinder head and piston are

removed, the liner is cleaned before

calibration.

♦ A straight edge tool 1 is supplied to

provide the points at w hich the

measuring gauge is put.

Main Bearing Removal

Example Sulzer RTA:

Upper H alf

♦ Turn the engine so that the respective

crank web is approximately horizontal.

♦ Disconnect the lube oil pipes at 6.

♦ Som e engines have jack bolts 2

securing the top half of the bearing,

while other engines have thrust bolts

or wasted stud bolts. Slacken them

hydraulically and remove the nuts.

♦ Lift the top cover vertically w ith a

lifting tackle 6, wire slings and a chain

block.

♦ Now take the top cover outside the

crankcase horizontally with another

lifting tackle, wire sling and chain

block.

♦ Fit an eyebolt 3 on the top half bearing

4 and take it out.

Fig-134

Fig-135

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The figure 136 shows the removal o f the

main bearing top cover 1, upper bearing

shell 2 and lower bearing shell 3 as in a

B&W engine.

Bottom H alf

♦ T he engine is turned so that the

respective crank web is parallel to the

bedplate separating face.

♦ Mount the support cross-piece 2 and jacks 3 below the adjoining

crank 4. Jack up 6 the crankshaft by 0.1 to 0.15 m m (max 0.2

mm). Check the lift with a dial gauge 1.

♦ The shims 8 are removed and a rope support piece 9 is fitted.

♦ A steel rope 7 is passed around the lower shell 5 and pulled out

with a rope pulley.

226

Crosshead Bearing Removal

The crosshead bearing is the same as the

connecting rod top end bearing. Example

given is as per ‘RTA’ engines.

First, take the crosshead clearances.

1. Suspend the lube oil articulate arm

♦ Loosen the screws o f the lube oil

articulate linkage arm.

♦ M ount the suspending tool.

♦ Turn the engine to TDC to suspend the

arm.

Fig-138

2. Suspend the piston

♦ Turn the engine to allow access to the piston rod screws and

remove them hydraulically.

♦ To suspend the piston, first turn the engine to TDC to take the

piston up. Fit two eyebolts to either side of the piston rod foot,

and suspend with two chain blocks to the hook provisions at

the top comer of the crankcase (port and

starboard).

♦ Take the crosshead down with the turning

gear so that the piston is suspended

(hanging) by the two chain block

attachments.

3. Remove the con-rod top end upper half

cover with shell

♦ Remove the four hydraulic nuts which

secure the top end upper half cover.

♦ M ount the lifting attachment to the top

cover o f the con-rod.

227

Fig - 139

Marine Diesel Er\gir,


♦ Using two chain blocks and two eye

bolts, remove the upper half cover to

inspect the shell.

. Suspend the crosshead

♦ Take the crosshead up towards TDC.

♦ Secure the crosshead by fitting 4 nos

guide supports (or by lifting tackles in

some engines or retaining pins).

F ig -140

Support the co n -ro d a n d tu rn th e en g in e to in sp ect the

bottom h a lf bearing

♦ The con-rod is to be supported on either side by chain blocks.

♦ By turning the engine shaft with the turning gear, the bottom half

can be inspected.

Connecting Rod Bearing Removal

The con-rod bottom end bearing is the

same as the crank pin bearing.

Bottom h a lf o f the bottom end bearing

♦ The crank case doors are opened for

access.

♦ T\im the engine to TDC.

♦ Support the lower half o f the bottom

end bearing with chain blocks, tackles,

wire slings, etc. as shown in 1.

♦ Remove the securing nuts hydraulically.

♦ Lower the bottom half with a chain,

block.

Top h a lf o f the bottom end bearing

♦ Take the bottom end bearing section

out with the help of chain blocks and

wire slings.

♦ Suspend the crosshead with guide

supports or retaining pins or lifting

tackles, etc. (as explained earlier in

crosshead bearing removal) as shown

in 2.

♦ Turn the engine till the top half of the

bottom end bearing is clear fo r

inspection as shown in 3.

Crosshead Pin Removal

Fig-142

This is very rarely done, except in case o f damage to the crosshead

pin. A brief removal procedure is described below.

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♦ Remove the working piston, crosshead

lubrication toggle lever and crosshead

bearing top cover exposing the

crosshead pin top side.

♦ Mount a special lifting plate 2 onto the

crosshead pin and take its weight with

the engine room crane 1.

♦ Secure the con-rod and raise the

crosshead head pin.

♦ Remove the guide rails (fuel pump side)

leading to the neighbouring cylinder,

both guide shoes and the middle

piece 3 on each side of the pin. Fig -141

♦ The crosshead pin can now be removed from the middle piece.

Thrust Bearing Transmission

The thrust transmission is from the engine crankshaft to the thrust collar

to the thrust pads to the thrust block housing to the bedplate to the

holding down bolts to the foundation plate and to the ship’s hull.

Thrust Bearing Pad Removal

Connecting Rod Removal

The connecting rod can be removed, even without removing the

working piston and crosshead pin.

♦ Remove top-end and bottom-end bearing

covers as described in earlier procedures.

♦ Suspend the crosshead with retaining

pins 1 or guide supports.

♦ Remove the con-rod with chain blocks

and wire slings 2 as shown.

♦ The crosshead pin must be carefully

wrapped for protection.

Fig-145

♦ Remove the top bearing cover 1.

♦ Remove the retainer 2 and its screws.

♦ Insert a ‘turning out’ device at the gear wheel.

♦ Turn the crankshaft so that an eyebolt can be screwed into a

pad 3 which can be lifted and removed one b y one.

♦ All pads are numbered.

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Bearing Clearances

The following table gives an approximate idea of clearance values:

Crosshead B earing Clearances

Bearing

Clearance Value

Main bearing

Crank pin bearing

(Conrod bottom end)

Crosshead bearing

(Conrod top end)

Thrust bearing

Camshaft bearing

Procedures for taking Clearances

M ain Bearing Clearances

Method 1

After removing the bearing top

cover and shell, a special ‘Bridge’

is placed. The clearance is taken

by placing a feeler gauge between

the bridge gauge and the journal.

Method 2

The bearing lube oil pipe and insert

are removed, and a special feeler

gauge is inserted to take the

reading.

0.3 to 0.4 mm

0.4 to 0.6 mm

Pin and Shoe - 0 .1 to 0.3 mm

Shoe and Rail - 0.4 mm

Plate and Rail - 1.5 mm

0 .5 to 1.0mm (m ax2 mm)

0.1 to 0.2 mm

♦ The crank pin should stand in a horizontal position 90 degrees

towards the fuel pump side. Hence, the crosshead is automatically

pressed by the con-rod against the rail surfaces on the exhaust

side and the clearance is taken on the fuel pump side.

♦ The crosshead bears on one side fully. However, clearances are

to be taken on both exhaust and fuel pump sides. One side should

give a ‘zero’ value or else, the piston is not aligned or the liner is

worn.

1. Pin and Shoe

The radial clearance between the crosshead ‘pin’ and ‘shoe’ is

very difficult to measure when the pin is fitted in the engine. It can

only be taken by measuring the pin outside diameter and the shoe

inner diameter by a micrometer.

2. Shoe and Rail

It is measured w ith a long feeler gauge inserted at the top and

bottom of each guide shoe.

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3. Plate and Rail

The complete crosshead must be pressed axially to one side with

suitable hardwood edges or similar aids. This side pressure should

be exerted onto the shoe and not the pin. Clearances are taken

with a feeler gauge.

Method 1

(Example: B & W engines):

♦ Turn the engine so that the aftermost crank is at BDC. This ensures

that the thrust bearing collar rests on the forward (foremost) thrust

bearing pads. Hence, the value 'B ’ =0.

♦ A feeler gauge is inserted at ‘A’ between the side o f the aftermost

bearing and the crank throw.

♦ Maximum thickness of gauge entering ‘A’ should be 2 mm.

♦ If the gauge entering ‘A’ is less than [2 mm - (B + C)], then clearance

is within limits.

♦ I f the gauge en te rin g ‘A’ is eq u al to o r g re a te r than

[2 mm - (B + C)], then clearance is more than the limit.

♦ Clearance is 0.5 to 1.0 mm for new engines and its maximum

value is 2 mm.

234

Method 2

(Example : Sulzer engines)

The total displacement which

results from pushing the

crankshaft axially both ways

until it touches the thrust

pads 1 in ahead and astern

is measured with a ‘clock

gauge’.

It is com pared w ith the

engine manual guide. Incase

of increase, there could be

possible wear of thrust pads.

Example:

Axial clearance fl = 0.8 to 1.3

M axim um f l value due to w ear

= 2.5 mm

Connecting Rod Clearances

These are taken with feeler gauges at the

crosshead pin (top end) and the crank pin

(bottom end).

235

\ r

I F ig-152

II



F uel P um p Setting /A djustm ents

It is carried out in suction and spill type fuel pumps. Example: Sulzer

engines

It's purpose:

♦ To check if the fuel pump setting is correct for the injection

timings.

♦ To compare with the original data fo r:

(1) Idle Stroke = ‘a’ in mm.

(2) Beginning of injection angle, before or after TDC.

(3) Total injection stroke = ‘b ’ in mm.

(4) End o f injection angle, after TDC.

(5) Effective plunger stroke = b - a .

Procedure

Initializing Suction Valve Dial Gauge

♦ Rotate the engine in ahead direction.

♦ Cam roller to be on the peak.

♦ Fit dial gauge 7 with 1 mm pretension

over the suction valve (now closed)

and set to ‘O’.

Initializing Spill Valve and the Plunger %

♦ R otate th e engine in the astern

direction.

♦ Cam roller to be on the base.

♦ Fit dial gauges 2 with 1 mm pretension

over the spill valve (now closed) and

plunger.

♦ Set both gauges to ‘O’.

C hecking B eg in n in g o f In jectio n

i.e. Closing o f Suction Valve

♦ R otate the engine in the ahead

direction till die suction valve gauge 3

shows 0.02 mm.

♦ Note the plunger gauge 4 reading= ‘a’.

♦ Also note the flywheel angle.

F ig -153

F ig-155

236

Marine Diesel Engir


Checking E nd o f Injection' i.e.

Opening o f the Spill Valve

4 Rotate the engine in ahead

direction till the spill valve

gauge 5 shows 0.02 mm.

♦ Note the plunger gauge reading

= ‘b \

♦ Also note the flywheel angle.

♦ Plunger stroke = ‘b-a’.

4 Carry out cut-out checks.

Fuel Pump Cut Out Checks and Zero Setting Checks

1. A t zero position o f the governor, the load indicator and cut-out

servomotor should coincide for ‘zero’ fuel injection.

2. W hen the governor is tripped by hand, the suction valves of the

fuel pump should be lifted by at least 6 mm.

3. When the governor and speed adjusting lever is at ‘zero’, the fuel

pump eccentric shaft should also be at zero.

4. When the fuel pump is manually cut-out, the clearance between

the cam and rollers should be at least 0.5 mm.

5. A t zero setting shield position, the suction and spill valves must

never be closed at the same time i.e. when one is open, the other is

closed.

Fuel Pump Cut-Out

♦ W hen the cut-out lever

at the fuel pum ps is

turned by 180 degrees,

the mechanism lifts the

rollers from the cams.

H ence, there are no

Fig-157

plunger movements.

♦ When the fuel pump is cut out by hand, the clearance between the

rollers of the plunger and the cam must have at least 0.5 mm

clearance.

Fuel Pump Lead

It is carried out in jerk type fuel

pumps e.g. ‘B&W ’ engines.

♦ It is the distance that the

plunger top is lifted above

the upper cut-off holes in

the barrel, when the unit’s

piston is at TDC.

4 F u el pum p lead = Y

= X + D5

4 D5 is a correction factor. It

is the distance between the

plunger top and upper cuto

ff holes top, w hen the

plunger top reaches the

exact position at which light

can be seen through the

lower cut-off holes in the

barrel and plunger.

Fig-158

238

239



3. Adjust the measuring tool dial gauge to ‘zero’.

4. Turn the engine ahead till the engine piston is at TDC.

5. Note the dial gauge reading = ‘X ’.

6. Fuel pump lead = Y = X +D 5.

4 - Stroke Medium Speed Engine Fuel Pump Timings

In a 4-stroke engine, the fuel camshaft rotates at half the speed of the

crankshaft. Hence, during the two revolutions o f the crankshaft,

injection takes place only once. In order to make sure that it is the

injection stroke, check the fuel cam.

Preparation

Turn the unit to TDC, shut the fuel oil inlet and drain from the bottom.

Disconnect the air pipe to the puncture valve. Remove the protection

cover and the puncture valve. Remove the erosion plugs from the

pump housing. Remove the connecting pin and disconnect the VIT

index arm. Pull out the VIT index arm to ‘zero’ index. Align the cross

bore in the plunger with the lower cut-off holes in the barrel. Put the

fuel oil index to 21.5 or 93.5. Verify the alignment by shining a torch

through the put-off holes.

Procedure

1. Turn the engine ahead till the upper edge ofthe plunger reaches

the exact position at which light can be seen through the ‘lower

cut-off holes’ in the barrel and plunger.

2. Mount the measuring tool so that it touches lightly against the

top o f the plunger.

♦ Open the cam case doors to see the fuel cams.

♦ During injection stroke, the roller will not be

on the base circle of the cam.

♦ Turn the flywheel to the angle specified by the

manufacturerforfuel delivery commencement.

♦ Check the jerk type fuel pump window

marking.

♦ The start o f delivery should coincide with the

top mark 1.

♦ Turn only in one direction or else, there will

be an error due to play.

TUrbocharger Overhaul

Fig-160

Compressor End

♦ Remove air filter.

♦ Drain lube oil.

♦ Remove the bearing space cover.

♦ Check the true run ‘B 1’ o f the nipple with a dial gauge.

♦ Remove the nipple.

♦ Check the true run ‘B2’ o f the oil slinger with the dial gauge.

240

241



Turbocharger Out of Operation

Fig-161

♦ Remove the cap nut and the locking washer.

♦ Measure dimension K.

♦ Remove oil slinger using an extractor and holding device.

♦ Measure K1 and K2.

♦ K1 is measured at the same place as ‘K ’ while pushing the rotor

towards the compressor.

♦ K2 is measured at the same place as ‘K ’ while pulling the rotor

towards the turbine.

♦ Remove the bearing using the extractor screwed to the inner bearing

bush.

Turbine End

♦ Similarly, remove the turbine-side bearing also.

♦ Using a special pipe and an eye bolt screwed to the shaft, the rotor

can be removed.

♦ The clearances K, K1 and K2 are compared during disassembly

and assembly.

♦ Check the labyrinth seal, binding wire, blades, pitting on the shaft,

casing nozzle ring damage and corrosion.

♦ Clearance L = K - K l , and M = K 2 -K .

Case] : In case one turbocharger is damaged

♦ The following measures are to be taken in

case o f one or more turbochargers are still

in operation. The engine can still be run at

low rpm and with less power.

♦ The charge air pressure, tem perature,

turbocharger rpm, firing pressure, etc. are

to be monitored.

♦ R em ove the expansion piece between

turbocharger and exhaust manifold and fit

the flanges A and B.

♦ F it a b lank flan g e C betw een the

turbocharger air outlet and diffusor.

♦ Isolate the turbocharger cooling system.

Stop the lube oil supply only if the

turbochargers are provided with external

lubrication system.

♦ Block the rotor of the defective turbocharger.

Case2: In case all turbochargers are damaged

♦ Block rotor and stop lube oil supply from

external lubrication.

♦ Open all covers D on the charge air receiver.

♦ Open and remove cover E on the auxiliary

blower.

♦ Start the auxiliary blower and put in use.

♦ M onitor exhaust temperatures before the

turbine, exhaust smoke, charge air pressure,

turbocharger speed, firing pressures, etc.

Run the engine at a reduced rpm.

242

243



Fuel Injector Overhaul

A fuel injector is checked and overhauled for the following:

♦ Condition o f the valve spindle (sticky, etc.).

♦ Opening pressure of the valve.

♦ Functioning of the slide valve.

♦ Oil tightness o f valve seat between valve spindle and spindle guide.

♦ Direction and spray of fuel jet.

♦ Slackness of the needle.

Overhaul

♦ The fuel valve is disassembled by

unscrewing the union nut with a

tommy bar or a spanner, while

retaining the valve in a vice with

soft jaws.

♦ Clean and examine all parts.

♦ Lapping o r grinding of seating

surfaces by grinding mandrels is

done manually or by a slow speed

drill if required.

♦ The nozzle holes are cleaned and

cleared with special needle drills of

diameter size 0.025 mm smaller than

the nozzle.

♦ A test plug gauge is used to ascertain

whether the hole is still proper. If the

test plug enters the hole, then it

should be discarded. The test plug is

10% larger in size than the normal

spray hole size.

♦ The needle should not be too slack in the nozzle. Test it by leaving

it to fall into the nozzle. It should go down smoothly and slowly.

♦ Needles and nozzles are a pair and are to be replaced together.

♦ Atomisation into a fine spray is checked by quick pumping

movement of the test machine handle.

♦ The direction of the spray is checked at its opening pressure. Here,

the oil spray jet direction can be seen through a transparent control

screen.

♦ The correct functioning of the valve is checked by testing the opening

and closing pressures of the spindle guide.

Apply and oil pressure to the valve to a value o f 50 kg/sq.cm

below the opening pressure. This means that the pressure should

not be raised above approximately 200 kg/sq.cm, following which

it will fall relatively slowly towards zero. A t around 8-10 kg/

sq.cm, when the return oil passage has been re-established, the

pressure should fall abruptly.

244



0-Ring Check

Raise the pressure slowly so that the return oil

connection is not closed, until oil flows out o f

‘A’. Then plug the outlet hole, raise the pressure

to 100 kg/sq.cm , and maintain it at this level

for a moment to see that o-ring ‘B ’ seals tight.

Checking Pre-Tension of the Tie Rods

This is done to check if the tension is correct for already tightened tie

rods. If tensioning is incorrect, then there will be fretting which may

permanently misalign the affected components. If fretting is already

present, then even correct tensioning over fretted tie-rods will cause

misalignment. The only remedy is corrective machining.

Pretensioning Check Procedure

Example: (Sulzer RTA)

♦ Remove the thread protection caps and clean contact face of the

intermediate ring.

♦ Screw both pre-tensioning jacks onto the two tie-rods lying opposite

each other, until the hydraulic jack cylinder rests on the intermediate

ring of the n ut

♦ Slightly slacken vent screws o f the hydraulic jack.

♦ Connect operate and vent the high pressure oil pump.

♦ Operate the oil pump till 100 Mpa pressure is obtained and

maintain this pressure.

♦ Use a feeler gauge inserted into the slot, to check that there is no

clearance between tie rod nut and intermediate ring of the nut.

246

♦ If there is clearance, tighten the nut with the round tommy bar.

♦ Release hydraulic press, apply non-acidic grease to the threads

and cap the nut.

Checks D uring Loosening and Tightening

♦ Pinching or clamping screws should be removed.

♦ If the tie-rods are newly tightened, then the wasted studs or jack

bolts o f the main bearings also have to be checked for correct pretensioning.

♦ Tightening is done in the correct sequence.

Tie R o d Tensioning M ethods

M ethod (1) .

Example: (Sulzer RTA)

♦ Slacken the main bearing wasted studs o r jack bolts, i f initial

tensioning is to be done for new fittings.

♦ Slacken the pinching or clamping screws.

♦ Attach a hydraulic pumping unit to opposite nuts.

247



♦ Follow the correct tightening

sequence starting from midengine.

♦ Raise the hydraulic pressure to

350 bar.

♦ With the round bar, tighten the

nuts as per tightening sequence.

♦ Raise the hydraulic pressure to

600 bar.

♦ M easure the elongation o f the

tie-rod and compare w ith the

reference manual values.

♦ Tighten all bolts at 600 bar.

♦ Check w ith a feeler gauge that

there is no clearance between

nut and in term ediate ring

washer.

♦ R e-tighten th e pinching or

clamping screws, so that it just

nips (touches) the tie-bolt.

Method (2)

Example of B&W ‘M C’ Engines

♦ Ensure pinching or clamping screws are slack.

♦ Attach and operate the hydraulic pumping unit to 700 Bar, starting

in the correct tightening sequence.

♦ Tighten the nut with the round tommy bar. ■

Air Compressor Overhaul

♦ Before disassembly, record all temperatures; pressures; and starting

and running current parameters; as a reference for later comparison.

♦ Spare parts and tools to be kept ready.

♦ Compressor to be properly isolated and tagged.

♦ Disassemble the compressor.

♦ Check the piston condition, piston ring clearances, liner wear,

gudgeon pin surface and w ear in the outer diameter, crankshaft

bearings, oil seals, crankcase lube oil condition and renewal, lube

oil strainer, float switches, lubricators for cylinder lubrication, valves,

unloaders, pressure testing of inter and after coolers, cooling pump

safety devices like bursting disc, relief valve testing, alarms and cut

outs, automatic drain valves, etc.

248

249



Testing of Materials

Destructive Tests

1. Tensile Test is done to test the strength and ductility. The specimen

is elongated an<J its elongation measured.

2. Hardness Test is done to test the m aterials’ surface hardness.

Indentation is carried out with a 10 mm diameter steel ball under

load, which gives either Rockwell hardness number or Brinell

hardness number i.e. Load / Indentation area.

Non-Destructive Tests

1. Visual or microscopic lens examination for cracks. . .

2. Chalk test.

3. Fluorescent dye or red dye aerosol method.

4. Magnetic crack detection.

5. Hammer ringing noise test.

6. X-Radiography.

7. Ultrasonic high frequency sound test.

Heat Treatment of Materials

A very brief description is given below.

Tempering : Heating to 250 deg.C + Retain at this temp + Air quenching.

Normalising: Heating to Upper crit. temp + (30 to 40 deg.Q + Air cooling normally.

Annealing : HeatingtoUppercrit.temp +'(30 to 40 deg.C) + Furnace soak+cool.

Quenching : Hearing to Upper crit. temp + (30to40deg.C) + Waterrapid cooling.

Work Hardening

Here, cold working is done e.g. shot blasting with steel balls.

Flame Hardening

An oxy-acetylene flame is used on the surface and later quenching is

carried out with a water spray.

Induction Hardening

Electro-magnetic heating and quenching is done.

Case Hardening or Pack Carburising

Pack the material in a charcoal box, heat to 900 deg.C and retain.

The outer case gets hardened.

Nitriding

The material is placed with NH3 in a gas tight chamber and heated to

500 deg.C and retained.

Hardening

Heating is done to a temperature higher than upper critical range. At

this range, the iron structure gets transformed to a new structure i.e.

martensite. Stresses are to be relieved by tempering, annealing and

normalizing.

250

251

CHAPTER 11

ENGINE DESCRIPTIONS AND

SPECIFICATIONS

Sulzer Com parison: RD / RND / RTA Engines

Parameter BD END RTA

Turbocharger Pulse(no auxiliary blower) Constant pressure Constant pressure

Scavenging

Loop + under piston Uni-flow

[*",

Exhaust valve Rotary Hap valves Exhaust ports Hydraulic operated

S/B ratio 1.7 1.7 3 to 4.2

Piston Convex shape Convex shape Concave shape

Piston cooling Water Water Oil

Fuel pump Suction valve control, Suction valve + spill Suction valve + spill

no spill valve valve introduced valve + VIT

Drive Chain Gear Gear

Cylinder Mechanical drive Mechanical drive Load-dependent,

lubrication

electric motor drive

Cylinder quills No quills at bottom Quills only at upper part Quills at two levels

Crosshead bearing; 2-piece type 2-piece type Continuous bottom

half type

Piston skirt Short Long in order Short

to

blank exhaust ports

SFOC 208 g/bhp/hr 203 to 208 g/bhp/hr 115 g/bhp/hr

MEP 8.6 bar 10.6 to 12.3 bar 17 bar

Peak Pressure 76 bar 84 to 94 bar 140 bar

Power /cylinder 1700 kw 2100 to 2500 kw 3700 kw

Piston speed 6.1 m/s 6.3 m/s 8 m/s _

253


Engine Descriptions and Specifications

Sulzer Engines

RTA Engines

Specifications

7 RTA 84 M Engine:

7 - Numbers of cylinders

R - Welded bedplate

T - Superlong

A - First in series

84 - Boreincm s

M - Modified

Cylinder bore

Piston stroke

Stroke/bore ratio

Total power

Engine speed

MEP

Pmax

S.F.O.C.

Liner wear

Cylinder oil consumption

Specific cylinder oil consumption

840 mm

2800 mm

3 t4 • ■

23,000 BHP (20,552KW)

92 rpm

17.2 bar

135 bar

115gm/bhp/hr

0.05 to 0.7/1000 hrs

e.g. 240 kg = lOkg/hr

24 hrs

0.85 g/kw/hr

Engine features

♦ Superlong stroke.

♦ Uniflow scavenging in a two stroke cycle.

♦ Constant pressure turbo-charging.

254

255



♦ Gear driven camshaft driven by the crankshaft.

♦ Exhaust valves opened by a cam driven hydraulic oil actuator and

closed by spring air.

♦ Welded bedplate o f deep, single-wall, fabricated box type.

♦ Electronically regulated VIT system.

♦ Liner made of alloy cast iron with stiff upper collar to resist heavy

load tangential entry.

♦ Bore cooled liner, with lower end uncooled within the scavenge

space.

♦ Multi-level cylinder lubrication of load dependent type.

♦ Exhaust valve made of Nimonic alloy, rotated by vanes fitted to

the spindle.

♦ Solid forged bore cooled cylinder covers with exhaust valve cage.

♦ Concave shaped piston made o f an alloy-steel crown, short cast

iron skirt, and oil cooled by jet and shaker method.

♦ Piston rings: Top ring is RVK-C (Wear reducing, chromium layer

plasma coated into base metal for high mechanical strength).

♦ Piston cooling oil is supplied and returned through the piston rod

from swinging links at die cross head i.e. the lube oil articulate arm

at crosshead.

♦ Water separator of high efficiency after the scavenge air cooler.

♦ Scavenge ports with reduced height.

♦ Bore polishing ring fitted on the topmost part of liner. It comes out

slighdy from the surface thereby giving a jerking effect to the piston.

This increases the compression ratio. It reduces and removes

carbon particles on topmost piston rings and grooves, thereby saving

lube oil and reducing liner wear.

♦ Vibration damper on the crankshaft. It is a silicon filled damper.

♦ Uncooled turbocharger.

♦ Integrated thrust block.

♦ Crosshead lubrication at 16 bar pressure.

♦ The crosshead is a single piece. It has the piston rod bolted at its

upper surface and a continuous full length lower half bearing.

♦ Thecontinuous crosshead bearing is of large surface Tin Aluminium

white metal thin shell type.

♦ Crankshaft is semi built up i.e. each crank throw is separate and

then shrunk fit onto the journal.

♦ Large surface main bearing is of thin walled white metal type.

♦ M ain bearing caps are secured by jack-bolts from engine frames.

♦ Fuel pump is cam driven and of suction and spill type.

♦ Each cylinder has three un-cooled fuel injectors. Hot fuel circulates

only when the injector valve is not injecting.

♦ Two piece un-cooled injection nozzles with stellite 6 tips.

♦ Crosshead lubrication oil is same as main bearing oil, boosted to

16 bar.

♦ On failure of the crosshead pump, oil is supplied from main bearing

oil supply via another pipe connection to the lube oil articulate arm.

♦ Reversing: Fuel and air distributor cams are to be reversed. Fuel

cams are reversed by supplying oil (control oil line) to the cam

spaces. Therefore, cams change their direction while the camshaft

is stationary. The exhaust cam does not need rotation as it is

symmetrical about BDC. The start air distributor cam is reversed

separately by a separate servomotor.

♦ Safety cut-off device: It is independent of the fuel pump regulating

linkage. It operates in case o f overspeed or emergency stop. It is

a mechanical-pneumatic activation device mounted on each injection

pump between the suction valves.

256

257



R T -F L E X Camshaftless -Intelligent E ngine

♦ Research on the ‘RT-Flex’ design was started in June 1998. It is a

new design which offers distinctive operational benefits which are

not possible with ‘Camshaft’ engines.

♦ The first ‘RT-Flex’ engine went into shipboard service in September

2001.

♦ The first ‘RT-Flex’ 60 C engine was built in 2002.

♦ It is an engine incorporating many o f the design features o f the

previous RTA-T and RTA 96 engines, but without the constraints

imposed by the mechanical drive of fuel injection pumps and valve

actuation pumps.

♦ It provides far greater flexibility and scope in the engine setting to

reach future requirements and operational benefits to the ship

owners. .

♦ These are standard Sulzer low-speed two-stroke m arine diesel

engines, except that, instead of the usual camshaft and its gear

drive, fuel injection pumps; exhaust valve; actuator pumps and

reversing servomotors; it is equipped with a ‘Common-Rail' system

for fuel injection and exhaust valve actuation, and full electronic

control of the engine functions.

♦ It was found to be more cost-effective to achieve the benefits of

the ‘RT-Flex’series by using a completely new design, rather than

adapting to the previous existing engine designs. Hence, a new

design was m ade to optim ise pow er and speeds for ship

applications.

'

♦ They are used as intelligent engines by electronic control and

feedback. Sulzer’s ‘Intelligent Engine’ is a concept on which the

RT-Flex engine provides a fully operational basis.

♦ An Intelligent Engine is one which will monitor its own condition

according to its feedback and pre-set settings and adjust the key

parameters of the engine’s performande, under various conditions

without manual intervention.

♦ The improved control reduces operational costs, exhaust emissions,

fuel consumption and time between overhauls.

♦ This flexibility is provided by electronic control of fuel injection

exhaust valve actuation, starting air and cylinder lubrication.

♦ Using a Common Rail reduces the hydraulic power requirements

and allows fuel and hydraulic pumps to be arranged in a neat setup

driven off the crankshaft.

♦ The WECS 9000 control system electronically controls the function

of starting air, load dependent cylinder lubrication, engine cooling,

electronically driven Lanchester Balancer (ELBA), etc.

♦ Starting air distribution to different cylinders is controlled by

individual solenoid valves controlling the start air valves, rather

than the conventional mechanically-driven start air distributor.

♦ There is no need for the camshaft drive, since all functions are

operated by hydraulic pressure (fuel oil or servo oil) under electronic

control. This allows a net reduction in engine weight, simplifies

engine erection work and removes some physical constraints for

future engine design.

258

259



Specifications

RT-Flex 60 C engine:

Cylinder bore

Piston stroke

Engine speed

M E PatM C R

Pmax

Piston speed

Fuel viscosity specification

Power output/cylinder

Brake specific fuel consumption

At full load

At 85 % load

600 mm

2250 mm

91 to 114rpm

19.5 bar

155 bar

8.5 m/s

730 cst at 50 deg.C

2360 K W or 3210 BHP.

170 g/kw-hr or 127 g/bhp-hr

167 g/kw-hr or 123 g/bhp-hr.

Electronically Controlled. Common-Rail System

260



Common R ail System

The common rail system consists o f:

(1) Common fuel oil rail (1000 bar Heavy fuel or Diesel).

(2) Common servo oil rail (200 bar).

♦ T he‘Common-Rail’ is basically amanifoldrunningalongthelength

of the engine just below the cylinder head level, while its piping is

at the engine top platform.

♦ Highpressurefuelpumpsrunningonmulti-lobecams, supply heated

fuel oil at a pressure o f 1000 bar (ready for injection).

♦ A fuel injection control unit controls the fuel injection valves. Fuel

injection valves are standard valves, hydraulically operated by high

pressure fuel oil.

♦ The fuel control units use quick-acting rail valves which control

fuel injection timing, volume and set the shape o f the injection

pattern.

♦ Each of the three fuel injectors are individually controlled, so that

they can be sequentially cut off or run in unison, according to the

load, although all engine cylinders are firing.

Exhaust Valve Control

♦ Exhaust valves are operated by a hydraulic push rod with hydraulic

actuating pressure supplied from the servo rail at 200 bar pressure.

♦ The hydraulic servo oil pumps are incorporated in the same supply

drive as the fuel oil pumps.

♦ Opening and closing of the exhaust valve is regulated by the

electronic-controlled actuating unit.

Starting A ir Valve Control

Starting air valves are controlled by the electronic control system

through solenoids.

Control Unit

♦ The control unit is an integrated Wartsila WECS-9500 electronic

controlled system, which controls and monitors the functions of

th e ‘RT-Flex’design.

♦ It is a modular system with separate microprocessor control units

for each cylinder and overall control and supervision by duplicated

microprocessor control units.

♦ The microprocessor control unit is an interface for the electronic

governor remote control and alarm systems.

Advantages o f the RT-FLEX System

♦ The lowest fuel consumption over the whole operating range.

♦ Competitive initial cost

♦ Three years’ time between overhauls (TBO).

♦ Lower maintenance costs.

♦ High operating flexibility offers excellent ‘slow running’ capability.

♦ Full compliance with the ‘NOx’ emission regulations (Annex. VI

of Marpol 73/78) due to optimizing of fuel injection and exhaust

valve processes.

♦ Smokeless operation even at lowest speeds and loads.

♦ Lower steady running speeds (10 to 12 % of MCR) can be

smokeless due to sequential shut-off o f injectors, although all

cylinders are firing.

♦ Reduced running costs at part load operations.

262

263



♦ Reduced maintenance requirements with the simpler setting of the

engine. The ‘as new’ running settings are automatically maintained.

♦ Fuel injection control with integrated flow-out security is precise,

leading to reduced maintenance costs and longer time between

overhauls (TBO).

♦ Fuel injection common-rail system provides improved volumetric

control resulting in excellent power-balancing between cylinders

and cycles with precise injection and equal thermal loads.

♦ Reliability o f the common-rail hardware and fuel oil pumps, long

proven in Sulzer’s 4-stroke engines.

♦ Higher availability due to integrated monitoring functions and builtin

redundancy.

♦ Full power can be developed with one fuel pump and one servo oil

pump inactive. The high pressure fuel pipes, servo-oil delivery pipes

and electronic systems are also duplicated for redundancy.

♦ Fuel injection rate, pressure and shape can be changed.

♦ Stable pressure levels in common rail and supply pipes.

♦ Better suited for heavy fuel oil use through clear separation of fuel

oil from the hydraulic pilot valves.

-♦ Highly efficient common-rail fuel pumps.

♦ Freedom to select optimum injection pressure, fuel valve timings

and exhaust valve timings at all engine loads and speeds.

♦ Control o f exhaust valve timing allows the system to keep

combustion air excess high by earlier closing, when load decreases.

This reduces fuel consumption and component temperature at low

loads. Hence it is more advantageous than fixed exhaust valve

timings (in older series) which resulted in low excess combustion

air supply by the turbocharger at low loads.

♦ VTT is easier to arrange in an electronically controlled engine, unlike

. the mechanical arrangements of earlier engines.

♦ Increased exhaust heat recovery further reducing the fuel

consumption, e.g. RT-Flex 60C has an exhaust gas outlet

temperature of 285 deg.C giving a high potential for waste heat

recovery.

♦ Potential for future developments. e.g. Different modes for different

emission regimes. One mode for minimum fuel consumption and

another to comply w ith global NOx limits or local port limits.

Lowering NOx emissions however, increase fuel consumption.

Tribo-Pack Technology

■ Fig-173

264

265



♦ It is a combination of design features which allow the time between

overhauls of cylinder components, including piston ring renewal,

to be extended to at least three years.

♦ It also provides more safety for the piston while operating under

adverse conditions.

♦ It allows standard cylinder lubricating oil feed rates to fall as low as

1 g/kw-hr.

Features o f Tribo-Pack

♦ Pre-profiled piston rings in all piston grooves.

♦ Ghromium-ceramic coating on the top piston ring.

♦ RC (running-in coating) piston rings in all lower piston grooves.

♦ Anti-Polishing Ring (APR) at the top o f the cylinder liner.

♦ Increased thickness of chromium layer in the piston ring grooves.

♦ Multi-level cylinder lubrication.

♦ Liner of the appropriate material, with sufficient hard phase.

♦ Careful turning of the liner running surface and deep-honing of the

liner over the full length of the running surface for ideal running

surface for rings.

♦ Mid-stroke liner insulation.

♦ Liner corrosive wear also depends on water droplets entering the

engine cylinders. Here, ahighly efficient vane-type water separator

after the scavenge air cooler is used for effective water drainage.

♦ Load dependent cylinder lubrication by the multi-level accumulator

system.

♦ Lubricating pumps are driven by frequency controlled electric

motors.

Description o f the Engine a nd its components

♦ The bedplate is of a sturdy type surmounted by very rigid A-shaped

double- walled columns and cylinder blocks, all screwed by pretensional

vertical tie-rods.

♦ The engine structure is very sturdy withlow stresses buthigh stiffness.

♦ The cylinder jacket is a single piece iron casting.

♦ Thethrustbearingisof the tilting pad type, integrated in the bedplate.

The thrust bearing girder has only two Steel cast pieces omitting

welding seams in critical comers. The girder is stiffer than earlier

designs.

♦ The crankshaft is semi-built type with special care taken for the

fillet areas and shrinkfits to cope with compact cylinder distance.

♦ The main bearings are of white metal, thin steel shell type.

♦ The bearing bores are co-machined, mounted and tightened with

the bearing caps.This allows better precision in the geometry of

the mounted bearing shells, thereby improving running safety.

♦ The crosshead has a full width lower bearing. The pin is of uniform

diameter and the two guide shoes are made in single steel castings

with white metal-plated running surfaces. Guide shoes have better

flexibility to adapt to the natural deformation of the guide rails under

load.

♦ The crosshead bearing has a full width shell for the lower half

bearing.

♦ There is a separate elevated pressure o f 16 bar lube oil supply to

the crosshead. This allows hydrostatic lubrication which lifts the

crosshead pin off the bearing at every revolution, ensuring sufficient

oil film thickness at all times.

♦ The piston rod stuffing box gland is a new type (as used in

RTA-68 TB and RTA-84C engines). It reduces the crank case oil

consumption and maintains the oil quality. It consists of a highly

effective dirt scraping top part with an oil scraping bottom part.

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Oil scraping is done by six spring-loaded

grey cast iron segments which run on a

hardened piston rod. Oil can flow back to

the crankcase through many large vertical

holes. It results in practically no flow from

the neutral space. Instead, there is complete

re-circulation o f the scraped off oil to the

crankcase, g iv in g less sy stem oil

consumption.

Combustion Chamber

Fig-175

Fig-174

♦ Combustion chamber conditions influence the time between

overhauls, the engine’s reliability and the NOx emissions.

♦ Piston cooling and fuel injection spray patterns influence the surface

temperatures in the combustion chamber as well as earlier deposit

formation.

♦ Bore cooling is provided for the liner along w ith shaker cooling

effect o f the piston for improved heat transfer, temperature,

'mechanical and thermal stress control of the components.

Cylinder H ead Cover

It is made o f steel material and bore-cooled. It is secured by eight

elastic studs arranged in four pairs. Anti-corrosion cladding is applied

to the head covers, downstream of the injectors to protect the cylinder

head covers from hot corrosive or erosive attacks.

The Exhaust Valve

It is made of ‘Nimonic 80A’ material and is housed in a bolted-on

exhaust valve cage.

Fuel Injector Valves

These are three in number. They are symmetrically distributed on the

cylinder head. This arrangement equalizes the temperature distribution

on the piston crown over the liner and head circumference.

Piston

It has a forged steel crown and a very short skirt.

Piston Rings

These are four in number and of the same height, thickness and

geometry.

Liner

It employs bore-cooling with insulated tubes, to adjust the temperature

distribution in the liner and limit stresses.

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Scavenging

It; is of uniflow type, with air inlet ports in the lower part of the cylinder.

Turbocharging

It is of constant pressure type augmented by electrically-driven auxiliary

blowers.

Scavenge A ir Receiver

It has integral non-return flaps and hanging cooler bundles with tubes

and fins, circulated with fresh water.

Water Separator

It is of vane type. It is a new design of high efficiency. It has ample

drainage provisions to completely collect the condensed water at the

bottom and drain it. To avoid blow-back through the drains from the

high pressure areas, all the drains are collected at the bottom o f a

vertically mounted pot, which is filled with water and kept under

scavenge air pressure. Drain water then leaves from the top of the

pot into an orifice controlling the discharge.

Engine Seating

It is simple with a modest number o f holding down bolts and side

stoppers. N o end stoppers,

thrust brackets or fitted bolts are

needed, as thrust transmission is

provided by ‘thrust sleeves’,

which are applied to a number of

holding down bolts. The holes in

the tank top for the thrust sleeves

are made by drilling or even flame

cutting. Epoxy resin chocks are

used by pouring resin around the

thrust sleeves.

Fig-176

B & W Engines

SM C Engines

Specifications

6 SMC 60 engine:

Cylinder bore

600 mm

Piston stroke

2300 mm

Stroke bore ratio 3.8

Total power

16680 BHP (12240 KW)

Engine speed

105 rpm

MEP

18 bar

Pmax

140 bar

S.F.O.C.

118gm/bhp/hr

Scavenge air pressure

3 bar

Mean piston speed

8m/s

Specific cylinder oil consumption 0.6 to 1.0 g/bhp/hr

Features

♦ Superlong stroke.

♦ Uniflow scavenging in a two-stroke cycle.

♦ Constant pressure turbocharging.

♦ The piston crown has chromium plated grooves for four piston

rings. The top-most piston ring is of controlled pressure relief (CPR)

type. Piston rings 2 ,3 ,4 have oblique cuts. Piston ring no. 3 has a

right-hand cut. Piston ring nos. 2 and 4 have left-hand cuts. An

Aluminium coating is given for running-in.

♦ The piston rod has a through-going bore for the cooling oil pipe,

which is secured to the piston rod top.

♦ Cooling oil is supplied through a telescopic pipe connection on the

guide-shoe or on the crosshead and passed through a bore in the

piston rod foot and, through the cooling oil pipe in the piston rod,

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to the piston crown. The oil is passed on, through a number of

bores in the thrust part o f the piston crown, to the space around

the cooling oil pipe in the piston rod. From the bore in the piston

rod foot, the oil is led through the crosshead to a discharge spout

and to a slotted pipe inside the engine framebox as well as through

a control device for checking the flow and temperature.

♦ The piston rod foot rests on a face cut-out in the crosshead pin. A

shim is inserted between the piston rod and the crosshead. The

thickness o f the shim is predetermined to match the actual engine

layout. The piston rod is fastened to the crosshead pin with screws

or studs and nuts. The nuts are tightened with hydraulic tools.

♦ The cylinder cover is made o f steel.

♦ The cylinder frame has a bolted-on or integrated camshaft housing.

The cylinder section is tightened together with the engine framebox

and the bedplate by means o f stay bolts.

♦ The scavenge air ports are bored at an oblique angle to the axis of

the cylinder liner so as to give the scavenge air a rotary movement

in the cylinder.

♦ The crosshead is equipped with steel shells with bearing metal.

The lower shell is provided with an overlayer coating.

♦ The crosshead is provided with bores for distributing the oil supplied

through the telescopic pipe, partly as cooling oil for the piston;

partly as lubricating oil for the crosshead bearing and guide shoes;

and through a bore in the connecting rod for lubricating the crankpin

bearing.

♦ The piston cooling oil outlet is led through a control device foi

each cylinder for the purpose o f checking the temperature and

flow before the oil is passed on to the lube oil tank.

♦ The sliding faces of the guide shoes are lined with cast-on bearing

metal. The guide shoes are guided by crosshead shoes in the engine

273



framebox and properly secured against displacement by guide strips

fastened to the guide shoes.

♦ The crankpin bearing is fitted with steel shells lined with bearing

metal and assembled in the same way as the crosshead bearing.

♦ The crankshaft is provided with a chain wheel for the camshaft

drive and a turning wheel. Furthermore, a tuning wheel, a torsional

vibration damper and a chain wheel drive for second order and

fourth order moment compensators are installed.

♦ At the aftmost end of the engine, a thrust bearing is fitted. A thrust

bearing serves the purpose o f transmitting the axial thrust of the

propeller through propeller shaft and intermediate shafts to the

ship’s thrust collar.

♦ The thrust shoes rest on surfaces in the thrust bearing housing and

are held in place by means of stoppers or cross bars. The segments

have white metal cast onto the wearing faces against the thrust

collar.

♦ The thrust bearing is lubricated by the pressure lubrication system

of the engine. The oil is supplied between the segments through

spray pipes and spray nozzles.

♦ The thrust bearing is provided with alarm, slow-down and shutdown

devices for low lube oil pressure and high segment

temperature.

♦ To counteract heavy axial vibrations and any resultant adverse

forces and vibrations, the crankshaft is provided with an axial

vibration damper. The damper consists of a ‘piston’ and a slit-type

housing. The ‘piston’ is made as an integrated collar on one of the

main bearing journals and the housing is mounted on the pertaining

main bearing support. The axial movement is damped as a result of

the ‘restrictions’ incorporated in the bores, which interconnect the

oil-filled chambers on the two sides of the ‘piston’. Lubricating oil

is supplied to both sides of the ‘piston’ from the main system.

♦ The camshaft is made in one or more sections. The sections are

assembled by means of flange couplings. For each cylinder, the

camshaft has a cam for operation o f the fuel pump, a cam for

operation o f the exhaust valve and a cam for operation of the

indicator drive (option).

♦ The fuel pump and exhaust valve cams are shrunk onto the shaft

by heating, whereas the indicator cams are in two parts, which are

assembled with fitted bolts.

♦ After the engine has been test run, the camshaft parts and the cylinder

frame will be provided with pin gauge marks, and the necessary

pin gauges are delivered together with the engine, enabling the

camshaft timing to be checked and readjusted if the parts have

been dismantled.

♦ Moment compensators: On the basis of calculations, the engine

may be provided with flyweights to counteract engine forces and

moments.

♦ The exhaust valve is actuated by a cam on the camshaft through a

hydraulic transmission.

♦ Puncture v alv e: In the top cover o f the fuel pump, a puncture

valve is fitted. The puncture valve consists of a piston which

communicates with the control air system of the engine. In the

event o f actuation o f the shut-down system, and when ‘stop’ is

activated, compressed air is supplied to the top of the piston, causing

the piston with pin to be pressed downward and keep the suction

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valve in the open position. This will ‘puncture’ the oil flow to the

fuel valve. As long as the puncture valve is activated, the fuel oil is

returned through bores to the pump housing, and no injection takes

place.

♦ The roller guide o f each fuel pump incorporates an angular

displaceable reversing link. Reversing is achieved by shifting the

roller in the fuel pump drive mechanism at each cylinder. The link

connecting the roller guide and roller is provided with a reversing

arm, and a pivot is mounted at the top end of die reversing arm.

The pivot travels in a reversing guide connected to an air cylinder.

The link is self-locking in either the ahead or astern position without

the aid o f external forces. Each cylinder is reversed individually,

and the reversing mechanism is activated by compressed air.

♦ The fuel valve consists of a valve head and a valve housing. Fitted

within the valve housing is a non-return valve, and a spindle and

spindle guide with a pressure spring and a nozzle. The spindle may

be provided with a cut-off slide. When the fuel valve is fitted in the

cylinder cover, the valve parts are tightened together by the pressure

from the securing nuts.

♦ The functioning of the fuel valve is as follows: The electrical fuel oil

primary pump circulates preheated oil through the fuel pump and

fuel valve. The fuel oil passes through the fuel valve, leaving through

a circulation bore and the return oil pipe on the valve head. When

the pressure at the beginning of the fuel pump’s delivery stroke

has reached the predetermined pressure, the circulating bores are

closed. When the pressure has reached the predetermined opening

value for the fuel valve, the spindle will be lifted and oil injected

through the nozzle into the engine cylinder. On completion of the

fuel pump’s delivery stroke, the valve spindle is pressed against

the seat and injection now ceases. The circulating bore is now

uncovered and oil starts to recirculate through the valve.

♦ The engine is provided with two or more auxiliary blowers. The

suction sides are connected to the space after the water mist catcher.

The discharge sides are connected to the scavenge air receiver.

♦ Separate non-return valves are installed at the suction side or

discharge side of the auxiliary blowers, in order to prevent reversed

air flow. The non-return valves protect the blowers and the engine,

during start-up as well as during the running of the auxiliaiy blowers.

♦ From the exhaust valves, the exhaust gas is led to the exhaust gas

receiver where the pulsatory pressure from the individual exhaust

valves is equalized and led to the turbocharger at a constant

pressure. Inside the exhaust gas receiver, a protective grating is

mounted before the turbocharger.

♦ The charging air cooler insert is o f the block type. The cooler is

designed with an air reversing chamber which incorporates a water

m ist catcher. The water mist catcher is built up o f a number of

lamellas which separate the condensation water from the scavenge

air during the passage of the air flow.

♦ Each cylinder cover is provided with a spring-loaded safety valve

which is set to open at a pressure somewhat higher than the

maximum firing pressure in the cylinder.

♦ On the exhaust side of the engine a number o f spring-loaded relief

valves are fitted, which will open in the event o f excessive pressure

in the crankcase/chain casing, for instance as aresult of the ignition

of oil mist.

♦ The scavenge air receiver is fitted with a safety valve.

♦ The bedplate consists o f two welded, longitudinal girders and a

number of cross girders which support the main bearings. The

main bearings consist of steel shells, lined with bearing metal. The

bedplate is fitted with an axial vibration damper.

♦ A framebox is bolted on to the top of the bedplate. Together, the

bedplate and the framebox constitute the crankcase of the engine.

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ME Intelligent Electronically Controlled Camshaft-less Engines

First generation research was carried out in 1993 to 1997 in

Copenhagen. However it was over-engineered and expensive. Second

generation research was carried out from 1997. It was simpler and

tailormade. It facilitated more production, so costs reduced.

Power Drive Supply

Engine driven multi-piston pumps are used. These axial piston pumps

are very reliable. They pressurize a common rail servo lube oil system.

Lube oil pressure is the working medium to drive fuel, air, exhaust,

lubrication and.start-air systems. The hydraulic power is provided by

hydraulic power supply units placed at the aft end of the engine. Control

is from computer units i.e. an Engine Control Unit (ECU) and a

Cylinder Control Unit (CCU). ‘NC’ valves are used to control the

functions. These are fast acting proportional qontrol valves controlled

by an electric linear motor drive from the CCU.;

Fuel Pumps

The pump plunger has a modified umbrella design to prevent heavy.

fuel oil entering the lube oil system. The beginning and end of plunger

stroke is controlled only by the hydraulic NC valves. The fuel pump

drive is hydraulically operated by lube oil pressure.

Fuel Injectors

1 Injectors

2 Control NC Valves.

Optimum combustion and thermal efficiency

require an optimized fuel injection pattern. In

conventional type, this pattern was dependent

on cams, fuel pumps and injectors. In ME engines,

electronic control with NC valves gives greater

F ig -178

control of the fuel injection. There are more number o f fuel injector

valves usually three in number. Opening of the valves is done in stages

one by one, and progressively. Different amounts in increasing quantities

can be supplied to each of the three valves. This progressive opening

is done so that, the pressure at the injection start will not decrease in

the rail system during injection. This woulcfhappen due to fuel flowing

out o f rail to the injectors, at a much faster rate than the fuel supply to

rail. Double injection increases the specific fuel consumption slightly,

but lowers the NOx by 20%. Electronically Profiled Injection (EPIC)

is carried out. Electronic control ensures fuel injection timing and rate

as well as exhaust valve timing and operation is exactly when and as

desired. Camshaft-less control does not have the lifnitations o f a

mechanical cam, in respect to precise fuel injection pressure and timing

control and variations over the load range. ELFI is the proportional

control valve controlling the servo oil pressure to the fuel oil pressure

booster. It serves to control the fuel oil ‘ cam length’, the ‘cam inclination

and angle’ and also the number of ‘activations per stroke’ which varies

the fuel injection. The fuel oil booster along with the ELFI valve raises

the fuel pressure during injection, from 10 bar supply pressure to the

specified load dependent injection pressure of 600 to 1000 bar.

Permanent high pressure with pre-heated fuel oil on the.top of the

engine is thereby avoided, without losing any advantage o f high

pressure injection.

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Exhaust Valve Actuation

It controls timing o f the opening and the closing of the exhaust valve

using fast acting on-off control NC valves. Here, pressurized control

oil is used to drive the hydraulic actuator. Actuation is in a simple

two-stage design. The first stage actuator piston has a damping collar

to provide damping in both directions. The second stage actuator piston

has no damping collar, and is in direct contact with a gear oil piston

which transforms hydraulic oil pressure into pressure in the oil push

rod. However, this gear oil piston includes a damping collar which

becomes active at the end of exhaust valve opening, when the exhaust

valve movement is stopped by spring air. Changing the ‘cam length’ in

respect to exhaust valve movement, can be done simply by changing

the point in time o f activating the ELVA valve. ELVA is the on-off

electronic valve controlling the exhaust valve actuator. ELVA can be

used to control the energy supplied to the turbocharger, both during

steady as well as transient conditions.

Engine Control System (ECS)

It is a fully integrated computer controlled electro-hydraulic system.

It controls the timing o f the fuel injection through close monitoring of

the crankshaft position via a tacho-system, which is far more accurate

and responsive than any mechanical method. This results in savings in

fuel and lube oil consumption and much greater manoeuvring control.

The ECS consists o f several integrated units: the Engine Control Unit

(ECU), the Cylinder Control Unit (CCU), the Engine Interface Control

Units (EICU) and the Auxiliary Control Unit (ACU).

ECU controls the following :

♦ The engine speed with respect to the set reference.

♦ Governor control and functions.

♦ Engine protection (overload) system and faults.

♦ Optimum combustion requirements for that running condition.

♦ Control of the functions for start, stop and reversing.

♦ Control o f the function of the auxiliary blower and turbocharger.

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Cylinder Pressure Measurement

This is done by a,strain type pressure sensor. It is a.rod sensor,

located at the bottom hole in the cylinder head cover, but it is not in

direct contact with the combustion products. Online assistance and

measurement of pressure is thereby available. There is less work load

for crew. It is reliable and no checking is needed. Compensation for

crankshaft twisting is used without which there would be errors, in

pressure of around 5%.The computer evaluates the indicator card

data. The pressure is transferred directly to COCOS EDS Diagnosis

System.

CCU controls the following :

The functions o f the fuel injection pump, the injector, the exhaust

valve, the start air valve and cylinder lubrication for each cylinder.

E1CU

It handles the interface to the external systems.

A C U

It controls the hydraulic power supply and auxiliary blower pumps.

Failures o f the Control System

Each cylinder has its own CCU. Therefore, failure is limited to

temporary power loss o f that particular cylinder only.. ECU has a

second standby unit for immediate take-over. ECU & CCU have

the same hardware. Therefore, few and identical spares required. A

guidance programme is present to find faults. Testing modes are

incorporated in case o f failure o f the sensors, actuators or wiring.


Here, intermittent lubrication is employed i.e. a large amount of cylinder

lube oil is sent every 4 or 5 revolutions as required. Lube oil is injected

when the top piston ring passes through the lube oil quills. This gives

better utilization o f expensive cylinder lube oil and reduces die

consumption.

Start A ir Valves

The conventional pneumatic control of individual start air valves is

replaced by the electronic control system activating solonoid valves

on the individual start air valves. This allows greater control and more

precision.

The ALPHA Lubricator A C C System

This system has reduced the specific cylinder oil consumption by

0.3 g/bhp-hr. The Alpha ACC (Fig-182 and Fig-183)allows the

cylinder oil dosage in g/bhp-hr to be controlled in such a way that it is

proportional to the amount of sulphur in g/bhp-hr entering the cylinder

with the fuel. This is achieved by making the cylinder oil dosage

proportional to the sulphur percentage in the fuel and to the engine

load ( amount of fuel).

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♦ The main element of cylinder liner wear is o f a corrosive nature,

and the amount of neutralizing alkalinic components needed in the

cylinder, will therefore be proportional to the amount of sulphur

(which generates sulphurous acids) entering the cylinders.

♦ A minimum cylinder oil dosage is set in order to satisfy other

requirements of a lubricant, such as providing an adequate oil film

and detergency properties.

Computer Controlled Surveillance System (CoCoS)

♦ The CocoS system has been specified as the engine monitoring,

diagnostic and maintenance overview system on this engine. It is a

comprehensive collection o f M AN B&W Diesel-developed

software, which is designed to detect various data, determined

through the alarm system as well as other sensors in order to keep

the engine working in its optimum state.

♦ The CoCoS system’s four major programme groups consist of

the Engine Diagnostic System (EDS), a Maintenance Planning

System (MPS), a Stock Handling and Spare Parts Ordering (SPO)

facility, and the Spare Parts Catalogue (SPC).

♦ The EDS continually monitors all stored operating parameters for

the entire lifetime o f the engine, and provides a warning to the

attendant staff if it suspects a problem is developing. If a problem

is likely to occur, the appropriate work can be scheduled through

the MPS, perhaps to coincide with other planned maintenance work.

The MPS normally shows scheduled maintenance work together

with timing instructions, list o f required tools, spare parts and

manpower requirements.

♦ W hile scheduling maintenance, the SPO system automatically

checks whether the spare parts are available (while allowing for a

minimum and safety reserve), and the SPC gives the opportunity

for the staff to display them (either in graphical or textual form).

285



♦ The aim o f the system is to prevent longer than necessary offservice

repair time by increasing the engine’s availability and

reliability, thus reducing operational costs. Additional savings can

also be achieved through the appropriate scheduling o f

maintenance and spare parts ordered.

PM1 System

♦ The PM I system is a computerized tool for evaluating cylinder

pressures in M AN B&W Diesel engines. It consists o f a hand

held transducer and control unit, which interfaces with a PC.

♦ A single operator can collect and display a complete set of

measurements in less than fifteen minutes. It uses a high performance

piezo-electric pressure transducer and an advanced crankshaft

angle trigger system for determining the TDC of each cylinder to

reliably and precisely measure cylinder pressures.

♦ The cylinder pressure data is presented as easy-to-interpret

measurement curves on the PC as well as in tabular form. By

calculating the maximum pressure deviation o f each cylinder and

computing index settings for balanced output from all cylinders,

the engine output can be adjusted for enhanced performance.

♦ The system automatically calculates effective power, mean indicated

pressure, and gives proposals for fuel pump index adjustments.

Alphatronic 2000 Control System

This electronic propulsion control system for ships with CP propellers

enables the navigator to manoeuvre the ship from the bridge. This can

be done without consideration for engine load conditions as the system

automatically enacts an overload protection. The pre-pulsion control

can be transferred at any time to other control areas such as the bridge

wing or control room panel. A separate emergency back-up system,

as required by the major classification societies, maintains a pre-set

engine speed and propeller pitch, and is physically integrated into the

control panel.

Parts omitted in camshaft-less M E engine

♦ Chain drive

♦ Chain wheel frame

♦ Chain box on frame box

♦ Camshaft with cams

♦ Roller guides for fuel pumps and exhaust valves

♦ Fuel injection pumps

♦ Exhaust valve actuators

♦ Starting air distributor

♦ Governor

♦ Regulating shaft

♦ Mechanical cylinder lubricator

♦ Local control stand.

The above-mentioned parts are replaced by

♦ Hydraulic Power Supply (HPS)

♦ Hydraulic Cylinder Units (HCU)

♦ Engine Control System (ECS), controlling the following:

Electronically Profiled Injection (EPIC)

Exhaust valve actuation

Fuel oil pressure boosters

Start and reversing sequences

Governor function

Starting air valves

Auxiliary blowers

♦ Crankshaft position sensing system

♦ Electronically controlled AlphaLubricator

♦ Local Operating Panel (LOP).

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Advantages o f the M E-C range

♦ Lower SFOC and better performance parameters, thanks to

variable electronically controlled timing of fuel injection and

exhaust valves at any load.

♦ Appropriate fuel injection pressure and rate shaping at any load.

♦ Improved emission characteristics, with lower NOx and smokeless

operation.

♦ Easy change of operating mode during operation.

♦ Simplicity of the mechanical system with well-proven traditional

fuel injection technology familiar to any crew.

♦ Control system with more precise timing, giving better engine

balance with equalized thermal load in and between cylinders.

♦ System comprising o f performance, adequate monitoring and

diagnostics of the engine for longer time between overhauls.

♦ Lower rpm possible for manoeuvering.

♦ Better acceleration, astern and crash stop performance.

♦ Integrated Alpha cylinder lubricators.

♦ Up-gradable to software development over the lifetime of the engine.

Fig-184

CHAPTER 12

ENGINE DEVELOPMENTS

Each development topic has already been clearly discussed in the

earlier chapters.

Fuel Injection System

♦ The conventional type fuel valve had asacvolumeof 1700cub.mm.

It was improved to the minimum sac type which had a sac volume

o f520 cub.mm. The latest type in use is the Slide type which has

a sac volume o f 0 cub.mm. This reduced sac volume drastically

reduces the SOx, NOx and unbumt carbon emissions.

CONVENTIONAL MINI-SAC SLIDE

Fig-185

291


Engine Developments

♦ VIT and Super VIT is introduced.

♦ 2 to 3 number o f injectors are used. e.g. in RTA and MC engines.

♦ Dual injection, pilot injection and twin injection systems.

♦ Common rail system is used in camshaft-less engines like RT-Flex

and M E series.

♦ FQS (Fuel Quality Setting) adjustment is possible for bad fuel

quality.

♦ 2 piece uncooled injectors with nozzles using Stellite tips.

♦ Electronically controlled fuel injection to change fuel timings and

rate.

♦ Cutting out of injectors when running at low loads.

TUrbocharger

1. Constant pressure 2-stage turbochargers are used on large slow

speed modem engines. Turbocharger efficiency is improved and

hence the turbocharger needs less energy. Therefore, more energy

is available at the crankshaft. Power Take In (PTI) and Power

Take Out ( PTO) units can be coupled.

2. Use o f two turbochargers rather than one. Standby reliability is

more. One turbocharger can be cut off at low loads which gives

more efficiency than using both turbochargers and less dependency

on auxiliary blowers.

3. UncooledTurbochargers:

♦ Un-cooled turbochargers allow greater heat recovery as there

is less heat loss to the cooling water as in cooled turbochargers.

♦ Thermal efficiency of the overall plant increases.

♦ The gas inlet ducts are totally uncooled.

♦ No contact with cooling w ater at any point for the gas inlet

side.

♦ This allows maximum heat availability to the exhaust gas

economizer for further waste heat recovery.

♦ Bearing housing on the turbine end is cooled with a small amount

of water, thereby controlling the lube oil temperature.

♦ Simultaneous cooling is carried out for the jacket o f the gas

outlet casing to allow some cooling and control o f the entire

casing surface within safety limits i.e. protection against fire

and accidental contact. Example of the latest turbocharger

series is ABB’s TPL-B series used for large 2-stroke diesel

engines. This series gives a much higher turbocharger efficiency

than the earlier VTR-4E and VTR-4D series.

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Engine Developments

♦ Uncooled turbochargers may also totally dispense o f water

cooling, thereby giving the advantages of no water connection,

easy integration, high application flexibility and reduced

corrosion.

4. Compressor noise reduction is done by means o f felt-covered

shaped plates.

5. Improved bearings allow 35,000 running hours before bearing

change. E.g. ABB’s special TPL inboard plain bearings.

6. An emergency oil gravity tank (e.g. TPL91-B series) ensures safe

run-out of the turbocharger rotor in the event of a power blackout

causing failure of the engine lube oil pump. This is for the new

TPL plain bearings designed for direct lubrication by the engine

lube oil system through a 50 micron filter.

7. A simpler, robust design is used.

8. Fewer parts than the earlier series giving lower life cycle costs,

faster overhauls and easier service.

9. Complete dismantling requires minimum additional space. Turbine

parts can be dismantled from the compressor side and hence, there

is no need to disconnect the hot gas pipes allowing easier and

safer handling.

10. Turbine and compressor cleaning i.e. water washing, is possible

under full engine load conditions.

11. The free floating axial bearing disc gives a compensation for

inclination and friction allowing a low wear of the bearing with a

longer life time.

12. Radial bearing bushes w ith squeeze oil damper provide high

reliability and an increased time between overhauls.

13. The inlet and outlet of the oil passages is from the bottom allowing

easy connection for lubrication.

14. Wide compressor map allowing high application flexibility.

15. Stiff construction with a high eigen-frequency mono block silencer.

This lowers the sensitivity to the engine vibration and reduces the

stress on the turbocharger supports.

16. Improved and extensive testing to ensure safe operations under

any circumstance. The tests include: resonance endurance test,

low cycle fatigue test, temperature cycle test, hot shut down test,

oil leakage test, compressor and turbine containment test, blade

vibration test, thrust bearing test and a prototype qualification

test.

17. Different turbine and compressor trims are available for optimized

matching for all applications.

18. Improved pressure ratio and turbocharger efficiency. Peak

efficiencies of more than 87 % are obtainable. High compression

ratios give increased mean effective pressures and less fuel

consumption.

19. Radial com pressor and axial turbine have the following

improvements:

♦ The turbine uses a wide chord blade without a damping wire

for constant pressure use.

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295


Engine Developments

♦ The compressor uses a single piece aluminium alloy wheel with

a splitter-bladed impeller and back-swept blades for high

efficiency and a wide compressor map.

♦ Enlarged compressor diameters further increase the volume of

the flow.

Scavenge System

♦ Uniflow scavenging method is used for large slow speed modem

engines.

♦ A reduced cylinder oil consumption is therefore possible.

♦ Improved air cooler design with a new and very efficient water

separator is introduced.

♦ Scavenge ports have reduced heights.

Exhaust System

Variable Exhaust Closing (VEC) enables the exhaust valve to close

earlier at 70% to 85 % lo ad, giving higher compression and peak

pressures.

Combustion Chamber

♦ Engulfed type combustion chamber with improved material selection

is introduced.

♦ Lower temperatures are possible due to the

piston shape and design.

Liner

♦ Uncooled ceramic fire ring.

♦ Improved m aterials: Outer layer is made of

Cast Steel and inner layer is m ade o f Tark

♦ Honing is carried out of the running surface o f the liner.

♦ Higher jacket temperatures with load dependent cooling.

♦ Anti polishing ring is incorporated at the topmost part of the liner.


♦ Multilevel cylinder liner lubrication for better usage of the cylinder

lube oil.

♦ Alpha lubrication system in B&W ME engines.

♦ Frequency control electric motor drive for the lubricators with

automatic lubrication for pre-lubrication, post-lubrication, slow

turning and emergency modes.

♦ Load dependent cylinder lubrication changing the feed rate with

respect to the engine load.

Piston

A new ‘Oros’ design is provided

for the pisto n . T he average

temperature in the crown region

is 410 deg.C, rather than 480

deg.C as in conventional types.

The injector gets more distance for

fuel penetration, thereby reducing

the temperatures in the crown

region.

A Conventional design

B Oros design

♦ Plasma coated top piston ring.

♦ Constant pressure relief CPR

rings.

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Engine Developments

♦ Sulzer’s SIPWAanalysis and monitoring.

♦ Al-Br coatings for running in purposes.

♦ Concave shaped crowns.

Crosshead

♦ Short, rigid, hollow type with a larger diameter pin.

♦ A continuous bottom half bearing.

♦ Bearing is of thin shell white metal type.

♦ High section modulus with a reduced mass.

♦ Lube oil pressure is increased to 16 bar in RTA engines, unlike

earlier 4.5 bar in older series.

Stroke Bore Ratio

A n increased stroke bore ratio o f 4.2 to 4.4. This allows a greater

ratio for expansion i.e. expansion ratio increases. Thermal efficiency

increases as more heat energy can be utilized. Thus, SFOC and fuel

consumption reduces. SFOC and thermal efficiency depend on the

exhaust blowdown pressure which is much less.

Power to W eight R atio

This is improved with large slow speed engines with a high stroke

bore ratio.

Engine Speed

Slower speeds allow more power extraction. A larger propeller size

can be used with less propeller slip and more efficiency.

Intelligent Engines

These are the latest RT-Flex and ME series o f camshaft-less

electronically-controlled engines. They are a whole new concept and

design change, w hich is exhaustively covered in the engine

description chapter.

Specific Fuel Consumption ( SFOC)

SFOC reduces with VIT, Super VIT, VEC, super long stroke and

improved turbocharger efficiencies.

Engine Components

♦ Semi-built welded type crankshaft.

♦ Fabricated steel bedplate.

♦ Integrated thrust block.

♦ Tie rods terminating at the bearing housing level. The tie rods are

threaded and do not pass through tubes and, therefore easier to

remove.

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CHAPTER 13

ENGINE EMISSIONS

Engine Emissions

The emissions from the engine exhaust consists of sulphur oxides,

nitrogen oxides, carbon monoxide, hydrocarbons, particles, soot and

smoke.

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Engine Emissions

Over 99% o f the emissions generated by a diesel engine consist

of the same elements as a ir: nitrogen, oxygen, carbon dioxide and

water. The sulphur dioxide component can be reduced effectively

by choosing the right engine fuel. The emissions of carbon monoxide

(C O ), c arb o n d io x id e ( C 0 2), h y d ro carb o n s (T H C ) and

particulates, are low due to the superior thermal efficiency o f the

diesel process. M inimising the NOx, SOx, and C 0 2 emissions is

im portant to protect marine environments. N O x form ation in a

diesel engine is prim arily caused by locally high combustion

temperatures in the combustion space.

S O x

These are oxides of sulphur, depending mainly on the sulphur content

in the fuel.

Effects

Sulphur gets oxidized to form S 0 2 and S 0 3in the ratio o f 15:1. The

sulphur oxides emitted from the engine combine with rain in the

atmosphere to form sulphuric acid i.e. acid rain.

SOx Limits

♦ 4.5 % when operating any where in the world.

♦ 1.5% when operating in new SOx emission control areas.

Remedy and control

♦ Low level sulphur fuel to be used which however increases the

costs,

♦ Removingsulphurfromfuel.

♦ Wash the exhaust gases in a scrubber tower and then neutralise it.

♦ Use high alkaline cylinder lube oils to neutralize the sulphur in the

fuel, thereby reducing sulphur corrosion and slightly reducing

emissions.

Measuring

It is done by the following m ethods: Infrared, ultraviolet or electro

chemical sensors.

N ° x

These are oxides of nitrogen, which cause smog formation and local

ozone concentration. Nitrogen is present in the fuel as well as in the

excess air provided for combustion. During combustion, nitrogen

combines with oxygen to form nitrogen oxide. This nitrogen oxide,

then gets converted to nitrogen dioxide N 0 2and nitrus oxide N20 in

the ratio o f 5:1. Nitrus oxide destroys the stratospheric ozone.

NOx limits

For new or converted engines after the year 2000 operating below

130 rpm, the limit is 17 g/kw-hr.

Remedy and control ' .

Basically, if w e reduce the cylinder temperatures, less NOx will be

produced. Modem day engines have a large bore and a slow speed,

both resulting in high gas and cylinder temperatures. Therefore larger

quantities of NOx are produced.

Methods used

♦ Later injection during the combustion process is carried o u t. This

reduces the cylinder temperature, but peak pressures and.specific

fuel consumption increases.

♦ Using fuel-water emulsions: Water present in the fuel absorbs some

of the heat generated during combustion. 1 % water addition reduces

NOx by 1%, but the specific fuel consumption increases by 0.3%

as a penalty.

♦ Fuel injector nozzle adaption as in the Slide valve design.

♦ Water injection or humidification.

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303


Engine Emissions

♦ Exhaust Gas Recirculation (EGR), where exhaust gas is recirculated

back to the scavenge side. This reduces the oxygen content of the

airsupplied to the engine, thereby reducing the amount o f NO

produced.

♦ Increasing the scavenge pressure and compression ratios. This gives

a larger quantity of air to the combustion cylinder, thereby reducing

cylinder temperatures and diluting the N O x already formed.

Although this method improves specific fuel consumption slightly,

it hardly reduces the NOx emissions.

♦ Selective Catalytic Reduction (SCR): Exhaust gas is mixed with

ammonia and a 's e le c tiv e cataly st a t a te m p e ra tu re o f

290 to 450 deg.C. The NOx is converted to nitrogen and water.

NO( reduces to 130 ppm i.e. a 90% reduction, making it the most

cost effective method, but the specific fuel consumption increases

by 2 to 3% and the SCR plant is a bulky one. The reducing agent

is urea ( 40wt-% solution), which is a harmless substance used in

the agricultural sector. The urea solution is injected in to the exhaust

gas directly after the turbocharger. Ureadecays immediately into

ammonium and carbon dioxide. The mixture is passed through the

catalyst, where NOx is converted into nitrogen and water.

Measuring

It is done by the Chemical Luminescence method, where NO is

converted to NO and then measured by a portable Electro Chem

Sensor (ECS) unit.

Carbon Monoxide

The exhaust emissions contain large quantities of carbon monoxide,

because o f the excess oxygen supplied in combustion air. Increase in

the normal operating levels indicate poor atomization of the fuel by

the fuel injectors.

Hydrocarbons

Efficient and correct combustion will allow a very small percentage of

hydrocarbons in the emissions. Hydrocarbons are basically unbumt

fuel particles.

Particle Emission

The particles and soot in the exhaust emission come from partly burnt

lube oil, ash in the fuel or the lube oil which includes unconsumed

calcium additives, and the deposits peeling off from the cylinder

or the exhaust system.

Soot

Soot is the agglomeration of minute partly burnt fuel particles. It is

formed during combustion by very poor burning of the fuel without a

flame. This type of burning called prolysis can bum only the lighter

fractions o f the fuel particle, leaving the partly burnt remainder as

soot. Soot increases with slow burning asphaltene fuels; burning of

fuel impinged on the relatively cooler liner surface; and with large fuel

droplets. Soot is an environment pollutant as well as it fouls the exhaust

uptakes and increases exhaust boiler back pressure, sparking or even

soot fires.

Smoke and Opacity

It is the degree of blackening of a white filter paper or the amount of

light reduction when light is passed through the exhaust plume.

Methods o f measurement

1. Bosch smoke scale 0 - 1 0

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2. Bacharach smoke scale 0 - 9

3. Hartridge smoke scale % Hartridge

4. Ringleman number 0 - 5

CHAPTER 14

ENGINE PERFORMANCE AND

INDICATOR CARDS

M ean Effective Pressure (MEP)

It is the theoretical constant pressure acting on the piston during the

power stroke.

In d ic a te d M ean E ffe c tiv e P ressu re o r M e a n In d ic a te d

Pressure (M IP)

It is the pressure which on acting upon the piston, performs the same

work as the actual pressure in the operating cycle. It is the ratio of

work done during the w orking stroke to the swept volume. It is

determined graphically from a diagram or calculated from engine

parameters.

Measurement o f MIP

It can be done by measuring the area of the indicator diagram.

The various methods are :

1. Planimeter

2. Mid-ordinate method.

3. Counting the number of squares, if the diagram is taken on a special

square type graph sheet.

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Engine Performance and Indicator Cards

On board the ship, the M IP is obtained by measuring the area of the

indicator diagram (in sq.cms) and dividing it by the length o f the

diagram (cms).

Indicated H orse Power

IHP = P x L x A x N

4500

where,

P = M IPinkg/sq.cm

L = Engine stroke, in metres

A = Cross sectional area of one cylinder, in sq.cm

N = Speed of the engine in rpm

= N for 2-stroke & = N/2 for 4-stroke

4500 = The conversion ofkg-m/min to H.P. in metric units.

Brake H orse Power (BHP)

It is the power output measured at the crankshaft by a brakedynamometer

on the manufacturers’ test bed. On board a ship, Bhp

can be determined by a torsiometer which gives shaft horse power.

The Shp is less than the Bhp o f the dynamometer by the frictional

horse power at the thrust block.

M echanical Efficiency

It is the ratio of the brake horse power to the indicated horse power.

It’s value is 0.75 to 0.85.

= Output at the crank shaft .= Brake Horse Power

Input at the cylinder

Indicated Horse Power

Therm al Efficiency

= Heat converted to useful work

Total heat supplied

Its value is approximately 0.60

308

Rated Power

It is a continuous effective power given by the manufacturer for a

certain rated rpm o f the crankshaft, taking into account the auxiliaries

used under normal service conditions, with a provision for overload.

Gross Power

It is a continuous effective power guaranteed by the engine supplier

for an approximate rpm using a certain set of auxiliaries under normal

service conditions without any allowance for overload.

Overload Power

It is a short-time effective power in excess o f the rated power with

the same set o f auxiliaries, under the same service conditions, which

can be used periodically for a limited interval only.

M inim um Power

It is the lowermost effective power guaranteed by the engine supplier

for an appropriate crankshaft rpm.

M inim um Stable E ngine Speed

It is the rate o f crankshaft rotation at a given irregularity factor. Any

speed below the minimum stable speed would result in stalling o f the

engine.-

E ffective Power

It is the power at the output end o f the engine i.e. at the crankshaft

flange position. It is the indicated horse power minus the mechanical

losses.

Actual Efficiency = Heat converted into actual work

Total heat supplied

= Indicated Efficiency x Mech. Efficiency

309



Its value = 0.32 to 0.42 (2-stroke)

= 0.35 to 0.45 (4-stroke)

H eat Balance Diagram

Excess A ir Coefficient

= Actual air supplied

Stoichiometric air

Excess air is supplied to the ensure complete combustion. Power of

the engine also depends on the mass of air supplied.

Continuous Power

It is the brake horse power given by the supplier measured at the

power take off end, under continuous safe operation of the engine

without a time limit

M axim um Continuous Rating

It is the maximum output power for the engine running continuously

under safe conditions. Contractual maximum continuous rating is the

rating according to the contract agreed upon.

N orm al or Standard Rating

It is the output power at normal service speed corresponding to

economical efficiency, thermal efficiency, mechanical efficiency and

easy maintenance.

A stern Output Power

It is the maximum outputpower which theenginecan run whilstrunning

in astern directions.

Testing of Marine Engines

(1) Manufacturers’ Acceptance Test

Here, tests are carried out at the manufacturers’ test bed to check

whether the performance values are within the acceptable

standards of specification.

(2) Sea Trial Test

Here, tests are carried out to check whether the engine and ship’s

performance are as per the contractual agreement supplied by

the manufacturer.

(3) Comparative Testing

This is done after handing over the vessel by the manufacturer to

the ship owner. It is carried out during the service life o f the

vessel to ensure maintenance o f the service standards as

compared to the same engine when it was newly built.

(4) Research Testing

This testing is performed after feedback from the ship’s owner in

case o f problems to be overcome, or m odifications, o r latest

improvements to be incorporated on the engine.

Trials

Marine diesel engines are normally tested by Test-Bed Tests and Sea

Trials.

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311



Test-Bed Tests

These include trials on the engine which is loaded by a water brake.

The following trials are done:

© Consumption trials.

(ii) Starting and reversing trials.

(m) Running astern trials.

(iv) Increased torque trials.

Sea Trials

The following sea trial tests are performed on new ships to check the

ship’s performance conforming to acceptable standards specified by

the manufacturer:

© M ooring Trial

Before testing out in the open sea, a mooring trial is done when

the ship is in a moored condition.

(ii) Running-in Trial

This trial is done during the running-in period of the piston rings

and cylinder liner at a controlled output, only for a short runningin

period.

(iii) Preliminary Trial

This is a trial done to confirm the engine’s performance before

going through the official trial.

(iv) Official Trial

This is done officially in the open sea. The following tests are

carried out:

a) Consumption test.

b) Guarantee speed test between two fixed points at maximum

continuous rated power.

c) A stern ru nning te st w here astern p o w er is lim ited

(50 to 80% o f maximum ‘ahead’ running power rating).

d) Overload T est: The engine is run in an overloaded condition

at a set" controlled overload rating.

e) MinimumStableSpeedTest: The engineminimumstable

speedisconfirmedfor smoothrunningat agivenirregularity

factor. The engineshouldnot stall at thisspeed.

f) Starting and Reversing Test: This test checks the starting and

reversing system for reliability, and also the capacity of the air

reservoir for minimum number of starts and its pressure drop.

g) Vibration Test: Torsion vibrations and transverse vibrations

are checked.

h) Cylinder Cut Out Test.

j) Minimum number of units firing test.

j) Noise measurement test.

k) Stop Trials : To test how quickly the ship can stop for

safety reasons, when sailing under constant propulsion.

Parameter Observation during Tests

The following parameters are to be observed and noted during the

above tests for different loads: Fuel oil temperature, viscosity, density

and pressure at the inlet to main engine; engine room temperature;

ambient air temperature; relative humidity; rpm; load index; exhaust

temperature for each cylinder; exhaust temperature before and after

the turbochargers; lube oil temperatures before and after the cooler;

piston cooling oil discharge temperature for each cylinder; cooling

fresh water temperature before and after the cooler; cooling water

discharge temperature for each cylinder; lube oil pressure; air pressure

drop across air cooler; cooling fresh water pressure; air temperature

at air inlet; air temperature after air cooler; cooling temperature before

and after air cooler; indicator diagrams; fuel flow m eter and

consumption calculation; cylinder oil flow meter and consumption; and

exhaust gas pressure before and after the turbochargers.

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313



From the above readings o f trials, calculations are don,e and the

propeller graph is plotted.

Load Diagram

A load diagram is one which shows the graph of engine speed

relationship with power over the operating range o f a specific engine.

It is dictated by the Maximum Continuous Rating (MCR) for a specific

rpm and engine load.

Propeller Curve

It is a curve of the propeller characteristics imposed onto a load

diagram. The propeller curve is a curve plotted with the relationship

between the propeller power and the shaft rotational speed.

The numbered lines in the diagram denote the following curves:

Line 1: The Propeller Curve

It intersects the maximum continuous rating o f 100% power

and 100% speed values.

Line 2: Clean Propeller and Hull Line

It is the same as Line 1 assuming engine propeller and hull are

in clean condition.

Line 3: Maximum Engine Speed Line

It is the limiting line drawn at 103.5 to 105 % speed for

continuous operations, depending on the engine builder. The

engine should not be ran at low loads and above 100 % speed

for long periods.

Line4: Ample A ir Available Line

It gives the limit for ample availability of air above which thermal

overload limits the torque and the speed.

A

M

O

$ S Si 3 ot 8 8 8 iS 8 8 3

1 0 0 % reference point

Specified MCR

Optimising point

Point, A = M

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315



Line 5: Mechanical MEP Limit Line

It limits the value of mean effective pressure from the 100%

power-speed point. This line can be extended horizontally

from the M CR point in order to include a 100% power limit

after the 100% speed limit.

Line 6: Fouled Propeller Curve

This is the propeller curve compensation of 2 to 3 % light or

reduced load, so that it takes into account the fouled dirty

propeller or adverse weather.

Line 7: Maximum Power Rating Line

It is the line representing the maximum power output of the

engine at 100% Maximum Continuous Rating (MCR).

Line 8: Thermal Overload Line

This line represents the limit for the engine running thermally

overloaded.

Line 9: Mechanical Overload Line

This line represents the limitfortheengine running mechanically

overloaded.

Propeller curve characteristics with Safety Margins

Engine Power

Safety Margins

There are 4 safety margins used:

1. Sea Margin (approximately. 15% power)

It is the expected increase in power required to maintain the

vessel’s calm weather speed, measured along the propeller curve.

2. Light Running Margin (approximately 5 to 6 %)

This is the compensation for the loss in rpm between dry docks for

constant power operation. It consists o f :

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317



♦ 1.5 to 2% increase in ship’s resistance and wake due to hull

rippling, local fouling and under paint roughness.

♦ 1 % increase in propeller friction losses.

♦ 1.5 to 2% increase due to wind and. weather influence on intake

water flow to the propeller.

♦ 1 % increase to compensate the decrease in engine'efficiency

due to fouled air coolers, piston ring wear, poor fuel

injection, etc.

3. Shaft Generator Margin

It is given in case a shaft generator is fitted.

4. Engine Operational Margin

Contractual speed is 90% of MCR for most engines. This is the

margin which allows the vessel to increase speed above the

contractual speed.

Indicator Diagrams

Purpose

♦ To enable the evaluation of the power developed in each engine

cylinder.

♦ To highlight conditions during fuel injection, combustion and

after-burning.

♦ To highlight conditions prevailing in tire cylinder during the scavenge/

exhaust gas exchange process.

♦ To show the pressure variations in the cylinder with respect to

piston displacements.

Rg-194

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Types of Indicator Diagrams

1. Power Cards (In-Phase)

It plots the pressure variations

in the cylinder ( fig-195) and

can be integrated w ith a

planimeter to calculate the

m ean in dicated pressure

(as shown in fig -194). The

power developed in a cylinder

can b e c alculated by

multiplication o f the engine

sp eed and th e cylin d er

constant. It also highlights

afterburning.

2. D raw Cards (90 degrees

out o f phase)

It is similar to a power card

but taken with the indicator

drum rotation 90 degrees out

of phase. It highlights the fuel

injection process, point of

injection and compression

pressure.

Fig-195

Fig-196

3. Compression Cards

The compression card is only a line on the indicator diagram and

gives the compression pressure and a timing check on the indicator

cam. It is taken at a reduced rpm with the fuel cut-out.

The figure shows an ideal,

compression card with fuel cut

out, w here compression and

e x p ansio n lin es are the

same. This shows correct

synchronizing of the indicator

piston movement with the

engine piston movement.

The figure shows compression

and re-expansion lines not

coinciding. The compression

card is positive in area and

hence, th e indicator cam

should be retarded. This

implies that the indicator cam

setting is wrong. F ig -198

T he fig u re show s the

compression card is negative

in a rea and h ence, the

in d icato r cam sh o u ld be

advanced. This implies that

the indicator cam setting is

wrong. F ig -199

4. L ight Spring Diagrams

It is a diagram taken similar to the power card and in phase with

the engine, but with a light compression spring fitted to the indicator.

It shows the pressure variations during exhaust and scavenge

operations.

Pc o m p

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321



Analysis of Indicator Diagrams

F ig-202 show s norm al

correct combustion.

O b serv e th at the

co m p ressio n pressu re

(Pcom p) and maximum

pressure (Pmax) coincide

with the m anufacturer’s

data.

5. Pressure Derivative Card

It shows the maximum rate of pressure rise and the point of injection.

It is used to highlight ignition delay.

Indicator Instrument

1 Coupling Nut

2 Nut

3 Cylinder

4 Piston

5 Indicator Piston Rod

6 Pen Arm

7 Chart Drum

8 Spring

9 Driving Gear

10 Three-way Indicator Cock •

Fig-203 shows early ignition.

Ignition point starts earlier

resulting in a higher Pmax,

but the Pcomp is the same.

E x h a u st tem p eratu res

decrease and it may cause

knocking. It is corrected by

adjusting theFQS setting for

bad quality fuel or injection Fig -203

timings.

Fig-204 shows late ignition

after-burning. Observe that

the ignition point starts later

and Pm ax is lower but

Pcomp is the same. Exhaust

temperatures decrease as

more fuel is burnt later and

sm oke in creases. The

causes are wrong fuel pump

Fig -204

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323



timings, camshaft drive wear, worn fuel pump plunger, faulty delivery

valve or suction valve spring, injectornozzle trumpets, or worn injector

Fig-205

F ig-205 show s pressu re

o scillatio n s. O bserve th e

oscillations startonly afterignition.

Oscillations are due to the gas

column or indicator drive. To use

this diagram, take the mean of the

oscillation amplitude as shown to

get the curve.

Fig-208 shows leaking exhaust

valve or worn piston rings. Observe

Pcomp is lower and ignition point

is later. P m ax and ex h au st

tem peratures increase, w hile

power decreases.

Fig-209 shows an overloaded

engine. Observe Pcomp is higher

and Pm ax is higher. Exhaust

temperature and smoke increases.

Fig-206

Fig-206 shows high compression pressure. Observe that the Pcomp

is high, resulting in a higher Pmax. Ignition point is higher although

there is late ignition.

Fig-210 shows a leaky injector or a worn fuel pump. Observe Pcomp

is the same while there is a fluctuating pressure in the expansion stroke

after the ignition point. Pmax and power decrease. Injection is done

later and smoke increases.

Fig - 207

- F ig -2 0 7 show s low

I compression pressure.

"1 a rc c Observe Pcomp is lower,

S u j resulting in a lower Pmax

and early ignition.

Rg-210

Fig-211 shows choked intake. Observe that due to a choked intake,

compression pressure is less throughout the curve. It results in a

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325



Kg-211

lower Pcomp and Pmax, while exhaust temperature and smoke

increases. The turbocharger surges.

Analysis of Light Spring Diagram

Fig-212 shows a choked intake. The

‘dashed’ line indicates the ideal curve, while

the dark line indicates the actual curve.

Fig-215 shows a choked exhaust Observe ^

that since the exhaust is choked, there is less

pressure throughout. Exhaust temperatures

and smoke increase. Scavenging efficiency

decreases and and there is a possibility of

turbocharger surging.

Faults with Indicator Instruments.

Fig-216 shows vibrations in the indicator

instrument drive. Only the power card is

affected, w hile the draw card is not

affected.

Fig-216

Fig-213 shows early opening of the exhaust

valve. Observe the exhaust valve opening

point X has shifted to an earlier position. Fi§"213

Power decreases and exhaust temperatures

Fig-217 shows the cord o f the indicator

instrument is too long. Hence, the TDC

section is missing.

Fig-217

Fig-214 shows late opening of the exhaust

valve. Observe the exhaust valve opening

point X has shifted to a later position.

Scavenge efficiency decreases and less

energy is passed to the turbocharger.

Fig-218 shows the cord of the indicator

instrument is too short. Hence, the BDC

partis missing.

Fig-218

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Fig-219 shows friction in the indicator

piston. Observe that both power and

draw cards are affected. It results in an

extra large working diagram area.

Fig-220 shows a weak spring o f the

indicator instrument. It results in the

indicator piston striking the top end of the

cylinder.

Fig-221 shows a leaking indicator cock.

Observe that the atmosphere datum line

is untrue.

Fig-220

Fig-221 -

A ll Indicator Cards Faulty

It indicates that the problem is w ith the instrumentCheck spring

tension, piston freeness, deposits, linkages, drum cord, clear indicator

cock, etc.

Electronic Indicator

It receives its input of the cylinder pressure by a pressure sensor and

also the flywheel position by another sensor. It is used in the latest

intelligent engines. (More details are listed under the ‘Intelligent

Engine' heading in Engine Description chapter).

CHAPTER 15

GOVERNORS AND CONTROL

Governor Function

♦ To control the engine speed within close limits, from no load speed

to full rated speed.

♦ To control either the engine speed or the engine load.

Isochronous Governor

It is a governor which maintains a ‘constant speed’, irrespective of

load and power changes.

Example: Auxiliary engines.

Variable Speed Governors

When there is a facility to adjust the set speed on the governor according

to the load, then the governor is a variable speed governor.

Example: Main engine governor.

Droop

It is the drop in speed from stable ‘no load condition’ to stable ‘full

load’ condition i.e. a fall in speed due to load changes.

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329


Governors and Control

L ine A show s isochronous

c h a ra c te ristic s i.e. speed

(frequency) is same, 60Hz at

0% load and 100% load.

L in e B show s droop

characteristics i.e. a fall in speed

or frequency from 60H z to

58H z at 0% lo ad to 100%

load.

KW LOAD

_ . . . Kg-222

Sensitivity

It is the measure of the smallest change needed for which the governor

responds with the required output signal. It implies that the governor

can control the speed within very narrow limits.

Stability

It is the ability to attain a stable speed for varied load conditions.

Governor E ffort

It is the force applied by the governor onto the fuel pump control,

when there is a change in load or speed.

Mechanical Governor

T h e fig u re show s a basic

m echanical governor. The

engine drive input signal 6 is

transmitted via the gearing 4 to

the governor mechanism. The

governor mechanism consists of

flyweights 3 on a bell crank 7

pivoted 8 to act on a spring

loaded co lla r 9 w h ich is

connected to the fuel pum p

Fig-223

linkage 5. The speed setting control can be adjusted by the screw 1

changing the spring tension. When the engine speed increases if load

is reduced, the flyweights m ove outwards, due to their increased

centrifugal force. This causes the bell cranks to push the spring loaded

collar to reduce fuel. Mechanical governors have the following

drawbacks: Increased wear, friction, mechanical damage, bearing

failures, instability and a limited governor effect

Hydraulic Governor with Compensation

D ead B and

It is a band or range in speed, only after which the governor will

respond.

H unting

It is the fluctuation in the engine speed due to over or under control of

the governor. Too much sensitivity can cause ‘hunting’.

330

331



1 Ball head 2 Centering spring

3 Receiving piston 4 Reservoir

5 Transmitting piston 6 To fuel linkage increase or decrease

7 Needle valve 8 Oil drain

9 Oil supply 10 Pilot valve !

11 Conical speeder spring

♦ This governor can be considered as isochronous (constant speed),

except during the compensation (transient speed drop) period.

♦ It is a ‘stable’ governor.

♦ Compensation or transient speed drop is included in the form of

reset action.

♦ Compensation can be changed by adjusting the needle valve setting.

♦ When load increases, the engine speed decreases along with the

centrifugal force. The spring force becoming greater causes the

pilot valve 10 to move down. This allows oil to flow to the servo.

The servo causes the increase in the fuel racks 6.

♦ The servo simultaneously acts on the transmitting piston 5 which

applies a force onto the receiving piston 3. This receiving piston

pushes the centering spring 2 and causes the closing of the pilot

valve (pilot valve moving up). Thus, equilibrium and stability are

achieved at a lower speed. Once the oil in the compensating system

leaks past the needle valve, the centering spring causes the speeder

spring to return to its original valve, so that equilibrium is brought

about at the original speed, inspite of the increased load.

♦ The hydraulic governor has operational problems in case of low

oil level, dirty oil, incorrect viscosity, air lock, wrong adjustments,

excessive oil operating temperatures, and wear at fine clearances.

Fig-225

It basically consists o f fo u r components

♦ The load sensing input signal 1 which senses the load 12 after

the governor alternator 10 and sends this input signal to the setting

control unit 4.

♦ The speed sensing input signal 2 which senses the speed at the

engine flywheel 11 and sends this input signal to the comparator

amplifier unit 5.

♦ The setting control unit 4 which has settings for droop or

isochronous mode 6, speed setting signal 7 and ramp generator 8.

♦ The Comparator / Amplifier Control unit which compares the

input signals with the reference settings and sends an output signal

to the actuator 3 to change the racks position of the engine fuel

pumps 9.

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333



The advantages o f the electronic governor

Less mechanical components; quick response; no friction; capable of

complex engine speed control; taking into account the engine load

and electrical load; overspeed control; load sharing requirements; easy

installation; and easy adjustments.

The main disadvantages o f the electronic governor is that it can fail

in case there is a failure o f input current to the governor from any

source. The remedy is to combine the electronic governor with a

mechanical hydraulic governor which will act as the back up in case of

electronic governor failure.

Governor Adjustments

Compensation Range

It can be adjusted by changing the fulcrum position on the lever

connection between the servo output linkage and the compensation

transmitter piston.

Compensation Rate

♦ It is done only after the compensation range has been set.

♦ It is done only in case o f sluggish response, excessive hunting or

overspeeding during initial start-up.

♦ The needle valve is opened till the control just becomes unstable,

after which it is shut by 1/4® turn.

Local Speed Setting Knob

♦ During normal operation, the control o f speed setting is done

remotely, via the electric motor mounted on the governor.

♦ This local speed setting knob is used only in case o f failure of the

remote control system or when on local control to test the engine

over-speed trip.

334

♦ Turning the knob clockwise changes the tension o f the speeder

spring and increases the speed of the engine.

♦ The number of turns that the speed setting knob has turned can be

seen on the speed setting indicator, which has a minimum and

maximum fuel setting limit.

Load Lim iter Knob

♦ It limits the fuel and, therefore the load.

♦ It limits the stroke o f the power piston by altering the position of

the droop lever fulcrum point.

♦ It is used only when load on the engine is to be limited, as in cases

of running-in after major overhauls.

Speed Droop Knob

It is used to control the speed droop during load sharing operations

between generators. It is not usually adjusted.

Load Sharing and the N ecessity o f Droop

C o n sid er tw o d iesel

generato rs connected in

parallel.

Fig-226 shows the condition I

just after synchronization has ®

been done to run the

generators in parallel. At

p o in t X , it is seen th at „

g e n erato r/ takes fu ll load 100

(100 % ), w hile g e n e ra to r

takes no load (0%).

335

kwg«52



in case o f a droop i.e. a change in speed (frequency) o f the generator

during transient conditions o f load changes.

In Fig-229 fo r isochronous operation, both generato r; and

generator2 share the same line i.e. at constant speed or frequency of

60Hz. There can be no crossing o f generator; and generator2 lines if

constant speed (isochronous) is to be maintained. Hence, sharing of

load would not be stable.

Fig-227: Generator2 speed (frequency) control increases so as to

take up part o f the load.

Fig-228 : Once generator has taken up some of the load, generator?

will decrease its speed (frequency) as it takes up less load. The

frequency of generator; will now be brought back to 60Hz.

Electronic Digital Governor for Bridge Control

Bridge Control using an electronic digital governor consists of 4 units,

namely (1) Digital Governor, (2) Remove Control Unit on Bridge, (3)

Engine Telegraph and (4) Engine Protection Devices.

1) D igital Governor

Fig-229: By comparing Fig-228 and Fig-229, we can conclude that

for stable operation, droop is

necessary fo r load sharing G ent and <3an2

between generators.

N ecessity o f droop f o r load

sharing

In order to achieve sharing o f

load, the g e n e r a to r l and

g e n e r a to r lin e s sh o u ld ,

intersect, as in the case o f

Fig-228. This is only possible

336

337


The various components are described below :

RPM Command

It is the order from the Bridge requesting a certain speed. This input

signal should meet the safety settings i.e. the rpm should not rise too

fast causing engine overload or the rpm should not be within the

critical speed range.

Measured Command

It is the rpm measured at the engine by means o f two inductance

pick-ups, fitted at the toothed ring. The higher rpm value is chosen

from the two pick-ups.

RPM Comparator

It compares the measured rpm with the rpm command desired by the

Bridge and sends a resultant signal to the regulator amplifier.

Regulator Gain

It regulates the gain or sensitivity of the governor during different

engine load conditions.

Example:

♦ With constant fuel setting, die dead band of the controller output is

increased so that an engine speed change of at least 2 rpm is needed,

before the governor responds.

♦ With rough sea setting, the governor output varies with the engine

speed changes.

Controller Gain

♦ This is a P and I controller.

♦ P-gain is varied between normal and rough sea options. Rough

sea has a slightly lower gain since the dead band of the controller

output is reduced.


♦ I-gain increases in rough sea conditions which slows down the

controller response.

♦ The gain also improves with both P and I functions, as the difference

between the desired and measured rpm value increases to improve

the, controller response and prevent over-speed of the engine.

Fuel Limiters

There are 3 fuel limiters:

a) Maximumfiiellimiter

It is used to limit fuel to avoid mechanical overloading of the engine

(excess firing pressures and excess bearing loads). It can be

overridden from the Bridge using the ‘Cancel Limiter’ button, but

the engine should never be run more than 110 % load for more

than an hour in a 12-hour period.

b) Torque (fuel) limiter

It is used to limit the fuel to avoid excessive torque conditions i.e,high

thermal load on cylinders and high torsional loads on crankshaft

especially at low speeds.

c) Scavenge air limiter

It is used to limit the fuel as per the scavenge air pressure

available to ensure proper combustion.

Actuator Positioner

The actuator gets an input of the desired fuel command signal. It

compares it with the actual position of the actuator and sends a resultant

signal to the actuator which is amplified before being fed into the actuator

motor.

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339



Actuator Speed Pick-Up

It is a feedback link which prevents excessive actuator motor speeds.

It allows the actuator amplifier to position the actuator at the correct

position quickly.

Actuator

It is a brush-less servomotor fitted with a digital encoder for motor

output position.

2) Remote Control Unit

Fig-231

The mimic diagram as shown displays the functioning o f the remote

control unit from the bridge. This mimic diagram has indicator lights

to show the sequence and changes taking place during maneuvering.

The following components in this mimic diagram are described below.

Bridge shows bridge control.

System Sim ulation: It is used during testing and simulation o f the

engine running conditions while the engine is actually stopped.

Stop indicates that the bridge telegraph lever is at ‘stop’ or the

emergency stop button is pressed.

Ahead/Astern Command: It only indicates the bridge command that

has been requested and not the engine or camshaft position.

Start B lock: It indicates that the engine starting is blocked in case of

turning gear engaged, low start air pressure, both ipm detectors’ failure,

engine tripped, automatic start air valve blocked or start air distributor

blocked.

Above Reversing Limit indicates that the engine speed is more than

the maximum level at which brake air can be supplied.

Start Set Point indicates that the governor setting is at its preset start

level to allow sufficient fuel for starting. This signal is maintained for 6

seconds.

Ahead / Astern S.V. indicates the presence of the bridge speed

setting signal.

Stop governor indicates the presence of a signal to the governor to

stop fuel admission. This is not a cut-out device.

Cancel Limiter Governor indicates the scavenge air limiter and

torque limiter are cancelled. This happens in case the engine fails to

start after three automatic starts. A n alarm indicates the repeatedstart

function activation.

Above Start Level indicates that the start system will be activated to

brake the engine before reversing can take place.

Start S. V indicates start air system is activated.

Stop S. V. indicates the starting air has started the engine above the set

point for starting.

Set Point Limiter indicates that the bridge engine speed request has

not been allowed due to the load-up programme being activated above

full ahead rpm, or due to the critical range speed being blocked by the

bridge control system, or a slow down condition has been activated.

This can be cancelled at the bridge panel.

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341



3) E ngine Telegraph System

♦ It conveys the speed anddirection command from the bridge

to the engine control room personnel.

♦ When on bridge control, the engine room telegraph control is

disconnected and becomes a transmitter/recei ver for the bridge

to engine room command communications. It indicates the

following:

• Standard ring o f bell if the bridge and engine telegraph

position do not match.

• Wrong way alarm indicates that the engine room telegraph

and engine rotation are opposite.

• Failure of remote system power supply indicates that bridge

control is no more possible. Emergency control may have

to be done in case of failure from engine room control.

• An internal communication failure between the telegraph

panels.

• Indicators for the FWE, Standby and A t Sea modes.

c) Slowdown to dead slow speed rpm, due to:

♦ Low lube oil pressure (1.5 bar)

♦ Low camshaft oil pressure (2 bar)

♦ Thrust block high temperature (75 deg.C)

♦Pistoncoolant no-flow.

♦ Scavenge air temperature high (65 deg.C)

♦ Oil mist detection high.

♦ Cylinder exhaust temperature high (450 deg.C)

♦ Lube oil inlet temperature high (60 deg.C)

♦ Piston coolant high temperature (75 deg.C).

The Emergency run button on the bridge can over-ride the

shutdown function.

4) E ngine Protection

It is provided to safeguard the engine during:

a) Overspeed i.e. 107 % o f MCR :

It activates the emergency stop solonoid for shutdown of the

engine.

b) Shutdown for:

♦ low lube oil pressure (1 bar)

♦ jacket water .high temperature(96 deg.C)

♦ thrust block high temperature (85 deg.C)

♦ camshaft oil low pressure (1.5 bar).

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343

CHAPTER 16

WATCH KEEPING

AND SAFETY

Taking Over An Engine Room Watch

A proper hand-over of important events and conditions of die machinery

from one watch-keeper to the other is o f utmost importance. The

usual practice is that the relieving watch-keepers should come 15

minutes before the start of the watch. He should come to the engine

room via the staircase starting at the highest entrance point. He should

first take a brief ‘round’ or ‘walk through’ of the engine room before

the start of the watch.

Taking a ‘Walk Through’ or a ‘Round’

A walk-through the engine room is a must, as one can visually see and

check all important parameters and conditions.

The follow ing aspects are checked during a ‘w alk-through’

or a ‘round’ :

♦ When starting around one should always be near the funnel so that

one can check the exhaust smoke colour from outside the engine

room. The smoke colour is checked to see whether it is whitish,

dark black or transparent light grey. Whitish smoke indicates excess

345


Watch Keeping And Safety

of air, while blackish smoke indicates poor combustion usually due

to fuel problems. Atransparent slightly greyish smoke shows good

combustion.

♦ One should also identify the source of the smoke i.e. from which

exhaust piping it is emerging. There is one exhaust funnel pipe for

the main engine, separate ones for each diesel generator and one

for the auxiliary boiler. Blackish smoke from the exhaust is an

offence when the ship is at port. However, some blackish smoke

may emerge initially when starting or maneuvering of the engine or

the auxiliaries.

♦ Check to see if there are sparks emerging from the funnel. This is

due to minute hydro-carbon deposits which self-ignite at the

economizer. This happens either when soot-blowing the economizer

or the boiler, or due to water in the fuel, or due to a very dirty

economizer, or due to running the engine at low loads for a long

time especially during maneuvering, or due to poor combustion.

It is dangerous if the wind direction is blowing the sparks to a

hazardous cargo zone at the forward side o f the ship.

♦ All pumps are to be checked for the follow ing: M otor current

amperes should not be higher than the normal running amperes.

No overheating o f the m otor o r the pump body. Bearing

temperatures and all temperature and pressure gauges should be

showing normal values. N o unusual noise or vibrations. Slight

leakage o f the gland that is required for cooling, b ut excessive

leakage requires tightening of the gland packing.

♦ On the top platform, check the exhaust gas economizer for exhaust,

steam, or water leaks. Check the condition o f the ‘lagging’ on the

pipes and any leakages. Check the engine room ventilation, position

of sky lights and access doors to the engine room. There should

be no restrictions so that they can be quickly closed in emergency

situation.

♦ Check the main engine jacket water expansion tank level and

condition, and monitor the loss in case jacket water level decreases.

♦ Check the presence and condition o f portable fire fighting

appliances, fire hoses and nozzles at their correct locations.

♦ On the upper platform, check the inert gas system, bubbler, fan

and motor bearings, and fan leakages.

♦ Check the boiler flame colour through the sight glass to see if the

combustion is correct.

♦ Check the boiler water level in the gauge glass. Blow through the

gauge glass if required.

♦ Check the generator expansion tank water level, loss and condition.

Also check the exhaust gas economizer circulating pump.

♦ On the control room platform, check the temperature and level of

the fuel oil tanks, drain them for water, and open steam heating if

necessary.

♦ Check the steering gear room, oil level in steering gear tank and

greasing of the rudder.

♦ Check the diesel generators for operating load, exhaust,

temperatures, leakages, all pressures and temperatures, unusual

noise, loose parts, exhaust bellows and sump levels.

♦ At the bottom platform, check all pumps and ascertain which sea

water suction is in use. Check double bottom tanks; sludge tanks;

bilges for oil or water leakages and trace the cause; cofferdam

sounding; stem-tube oil levels and pressure; and the intermediate

bearing and its lubrication.

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347



♦ Check the oily water separator and sample the water being pumped

overboard. All over board pumping procedures should be followed

strictly according to the company’s policies and instructions. Ensure

that weighted cocks on double bottom sounding pipes are in shut

position and caps closed. The main engine is to be checked

thoroughly from the crankcase platform upto the economizer

platform. Feel the crank case and scavenge doors for any increase

in temperatures. Listen to the engine sound and observe any unusual

noise.

♦ Check the piston cooling flow from the sight glass.

♦ Check the scavenge drains to see quality and quantity o f oil or

water leaks.

♦ Check the air cooler air-side drains to make sure that the drained

water is from condensation and not from sea water. Scavenge

temperature must not be too low.

♦ Check the hydraulic governor oil level.

♦ Feel air starting pipes to see if they are hot and touch the high

pressure pipe to feel the pressure pulses of injection.

♦ For hearing machinery sounds, use a metal rod with one end to' the

ear and the other end touching the machinery.

♦ Drain all air bottles of water.

♦ Check all parameters and gauges in the engine control room.

♦ Check that the load is sufficient on the generators. It is preferable

to run the generators at higher loads rather than at low loads which

would cause fouling, especially when running on heavy fuel oil.

♦ Check the engine room log book requirements for any cargo or

maneuvering operations; requirements for adverse conditions; and

any problems encountered during the previous watches. Ensure

proper knowledge of procedures to be followed in the event of a

failure o f any equipment. Read the Standing orders and Chief

Engineer’s instructions.

♦ Check if any operations are being carried out like fuel transfers;

fresh water tank filling; and disposal of oil residues, bilges, sewage

or garbage.

♦ Check all auxiliaries like air compressors and purifiers.

♦ Check the compressor running temperatures; time to press up the

air receiver; lubricator operation and level; sump oil level; and running

current amperes.

♦ Check the purifier inlet oil temperature; overflow pipe for oil

overflow; running current amperes; back pressure, filter pressure;

and leakages.

♦ Check all objects in the engine room in case they have to be lashed,

especially during bad weather conditions.

♦ Check the nature and location o f all w ork being carried out on

various machineries.

♦ Check the work being done by all engine room personnel and

hazards involved.

♦ Check if any system has been isolated or whether any abnormalities

are present with the machinery.

♦ Check proper working of the communication system.

♦ Some companies now require both watch-keepers to sign a hand

over form listing all checks and abnormalities.

♦. Only after the incoming watch-keeper is fully satisfied with the handover,

will he take over charge from the outgoing watch-keeper.

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349


Checks D uring T he W atch

♦ After taking a thorough ‘walk through’ or ‘round’ o f the engine

room, it is imperative that periodic personal checks are made on

all running machinery.

♦ In case o f any abnormal conditions, the watchkeeper should

immediately assess the situation. If it is an emergency, he can call

for help by pressing the engineer’s call alarm.

♦ In case of a ship or fire emergency, he can press the ‘Emergency ’

general alarm.

♦ If he is not in a position to understand the cause or the remedy, he

should inform the Chief engineer or the Second engineer.

♦ In case o f abnormalities which affect the speed or operations of

the main engine, power generators or the cargo plant, the

watchkeeper should also inform the bridge or the cargo control

room watchkeeper.

♦ All starting, stopping and important procedures are listed in the

engine room operation guide book which is now a requirement.

♦ In case the watchkeeper requires more manpower, He should ask

the Chief engineer or Second engineer to provide mote manpower,

rather than compromise on safety.

♦ Priority to be given to the running machinery and operations, rather

than any overhaul work.

♦ A safe working atmosphere is required at all times.

♦ While logging down and recording parameters in the engine room

log book, the watchkeeper should analyse any change and its cause.

350

Problems During The Engine Room Watch


A list of problems occurring during the watch are discussed below

and the action to be taken. Safety and prevention of further damage

should always be the priority.

Crankcase Explosion

Conditions fo r a crankcase explosion

1. A source of heat or ignition which is required to vapourise the oil

into a fine vapour.

2. The correct air to fuel ratio required for explosion.

3. Fine oil vapour with a high surface area to mass ratio.

♦ The source of ignition is mostly a hot spot due to a bearing running

hot. This heat causes the lube oil in contact with the hot surface, to

vapourise into a fine vapour. This oil vapour forms an oil mist in

the presence o f condensation in a relatively cooler section o f the

crankcase.

♦ W hen this fine oil mist ignites in the presence o f a hot surface, a

pressure rise occurs which depends on the weakness or richness

of the oil particle to air ratio. An explosion occurs if this mixture is

in the explosive range.

♦ A primary explosion is relatively slow as the crankcase atmosphere

is too rich with oil vapour, but may cause a rapture of the crankcase

allowing ingress of air. This ingress of air causes a very good air to

oil-particle ratio and a secondary explosion occurs, which is more

violent

♦ A remedy for secondary explosions is the use of crankcase relief

doors, which relieve the crankcase pressure if it exceeds 0.05 bar,

thereby preventing any rapture to the crankcase and ingress of air.

Constant monitoring of the crankcase oil mist is accomplished by

an oil mist detector.

351



Crankcase R elief Valve

♦ Self-closing crankcase relief valves are fitted at various points along

the crankcase 1 to relieve pressure, irrespective of the origin in the

crankcase.

♦ The valve should be self-closing to prevent ingress o f air which

leads to a secondary explosion. Self-closing function is achieved

by the spring 3 which shuts the disc valve 2, if the crankcase pressure

is less than 0.05 bar.

♦ An oil-wetted metallic gauze 5 is fitted on the internal side for

stopping a flame emerging from the relief valve.

♦ A rubber o-ring 6 provides oil tightness and sealing. A deflector 4

is fitted to deflect any flame or pressure wave in case of an

explosion.

Scavenge Fires

It is due to the ignition of carbon or cylinder lube oil deposits.

C auses:

♦ Blow past due to worn or damaged piston rings.

♦ Stuffing box leaks.

♦ Excessive cylinder lubrication.

♦ Inadequate draining of scavenge spaces.

♦ Poor combustion, injector condition, fuel timings or worn liners.

Indications:

♦ Increase in scavenge temperature of one unit as compared to the

others.

♦ Increase in temperatures in scavenge and exhaust systems.

♦ Rough running of the engine with a slight rpm drop and surging of

the turbocharger.

♦ Smoky exhaust.

♦ Flame, smoke or sparks at the scavenge drains.

Prevention

♦ Regular draining, cleaning and monitoring of the scavenge spaces.

♦ Correct rate of cylinder lubrication.

♦ Correct maintenance o f piston rings, cylinder liners and fuel

injection equipment.

Remedy

In Sulzer engines: Slow down the engine, cut-off the fuel, increase

cylinder lubrication; and continue running till the fire bums out. Stop

the engine. After waiting till the scavenge space cools down, open up

for inspection and ascertain the cause.

352

353

Marine D iesel Engines

Watch Keeping A nd Safety

I h B & W engines: C ut-off the fuel, slow down the engine, request

the bridge; and stop the engine and auxiliary blower. Apply extinguishing

m edium , allow the scavenge space to cool, and then open up for

inspection and ascertain the cause. Components affected by scavenge

fires include Piston rod, cylinder liner, stuffing box, piston and rod

alignment, scoring or cracks in the liner, and tie rod tension.

O il S pill

In case o f an oil spill, stop the fuel oil transfer operations and raise the

general alarm. Follow the Oil Spill Contingency Plan. Identify the

source o f the spill and immediately restrict any further oil spillage by

isolation- Drain and contain the oil on the ship by putting the oil into a

slop tank or an empty cargo tank. Clean the spill area using an oil spill

dispersant and the gear from the oil spill storage station. Try to recover

as much oil as possible. Log events and communicate with the port

authorities.

Collision

In case o f a collision o f the ship, stop the main engine. Activate the

emergency general alarm. The engine room should be immediately

manned in case ° f UMS mode. Check if there is any ingress of water

into the engine room. Take the soundings o f all double bottom tanks

to check that they are intact. Keep all fire fighting gear on standby.

Check for oil pollution around the ship. Check all machinery to see if

they are affected especially the electrical plant. Report to the bridge

the condition of the engine room , the main engine and the auxiliaries.

The Master will then assess the danger of sinking, capsizing or flooding.

The designated person ashore, the superintendent of the ship and the

port authorities are to be informed.

F looding

In case of flooding, raise the emergency alarm, inform the bridge,

slow down and stop the m ain engine. According to the capacity

needed, designated bilge pumps or sea water pumps using the

emergency bilge injection valve are to be started. Identify and isolate

the cause o f flooding. Once pumping is started make sure the level of

water should be going down and not increasing. Also, give due attention

that the level should not flood any of the pumps or the engine flywheel

bottom level. Take care that no water should fall onto any electrical

starter panel, device or w iring.

G rounding

In case of grounding, immediately stop the main engine and raise the

emergency alarm. Inform the bridge. Change over from low to high

sea suction. Take die soundings of all double bottom tanks in the engine

room as well as the cargo tanks to check for intactness. Report the

condition of the engine room to the Master who will assess the danger

o f sinking, flooding, capsizing, oil pollution and vessel’s stability.

Record the events and status o f the main engine.

Check the following : crank case inspection and deflections if

necessary, stem tube system condition and leakages, steering gear,

and all sea water coolers and filters.

Sudden Overspeeding

Sudden overspeeding can be caused b y :

♦ Fuel racks getting stuck.

♦ A faulty governor.

♦ Racing or jumping of the propeller in bad weather.

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355



Loss o f E ngine Power

A loss o f engine power is due to :

♦ Incorrectly set fuel racks,

♦ Faulty fuel injection pump or timings.

♦ VIT settings.

♦ Afaulty governor.

♦ Fouling in the air system.

♦ Fouling of the hull. .

Detection o f Slack Tie Rods

♦ The cylinder jacket adjacent to the slack tie bolt can be seen lifting

when the piston reaches the end o f compression stroke at TDC.

♦ Press the thumb nail to the tie bolt nut. Small movements which

cannot be seen can be felt this way.

♦ A Dial gauge can be used to detect relative movement between the

bolt and the cylinder jacket.

Too M uch Incorrect F uel Timings

♦ The engine will not start, or it will start in the opposite direction.

♦ Injecting too m uch fuel earlier may cause the engine to move

in the opposite direction.

♦ The engine m ay rock i.e the next unit may fire in the opposite

direction and the effect may be like braking.

E ngine Speed Fluctuation

This is due to presence of water in the fuel, high fuel volatility, fuel gas

lock, injection variation, worn out linkages o f the governor,

bad fuel quality, units not balanced, governor setting too sensitive,

or air in the governor.

Sparks From The F unnel

It can be caused by too m uch after burning or poor combustion.

A dirty economizer should be soot blown (and water washed when

the engine is stopped). In case the exhaust temperature is too high,

there could be a soot fire. Check fuel oil temperature and scavenge

temperatures. Drain the fuel oil tanks.

Too M uch Sparking From The F unnel

If the exhaust gas temperatures are too high in addition to heavy

sparking at the funnel, there is a possibility of a fire at the economizer

or a scavenge fire. Stop the engine, but do not run at low loads since

unbumt fuel is more at low loads. Start the standby economiser water

circulating pump to increase cooling. Provide boundary cooling. Stop

the engine and shut the air inlets at the turbocharger and auxiliary

blowers.

A fter A L ong Voyage

Carry out crankcase inspection; check bearing clearances, crank shaft

deflections, foundation bolts, scavenge port inspection, cleaning of all

filters, etc.

Cylinder R elief Valve Lifting Up

This can be due to excess fuel supplied during starting or manoeuvring;

accumulated or unbumt fuel igniting with excess air; a sudden increase

in load in rough weather; pre-ignition; leaking or sticking air start valves;

water or oil accumulation on the piston crown; or excessive peak

pressures.

Cylinder R elief Valve Lifting D uring Blow Through

Causes :

♦ A choked indicator cock.

♦ An incorrect relief valve setting.

356

357



♦ Water accumulation into the combustion chamber.

♦ Excess water in the starting air.

Reduced Compression Pressure

This is due to worn piston tings, worn liner, worn piston crown, worn

exhaust valve, incorrect exhaust valve timings orinsuffidentscavenging.

Sm oky E xhaust

C auses:

♦ Less air supply to the engine due to fouled gas or air side of the

turbocharger; fouled air cooler; faulty scavenge valves in the air

receiver; fouled scavenge ports; or fouled exhaust gas economizer.

♦ Overloaded running conditions. Check load indicator, exhaust

temperatures and peak pressures.

♦ Excessive cylinder lubrication.

♦ Injection nozzles not atomizing the fuel completely, e.g. due to

carbon trumpet formation and eroded or blocked spray holes.

♦ Incorrect fuel temperature or viscosity, or a shift in the individual

fuel cams.

♦ Compression pressure too low due to leaking piston rings or

exhaust valve.

♦ Too low turbocharger rpm.

♦ Scavenge fire.

A ll Cylinders E xhaust Temperature Increase

This can occur because of fouling in turbocharger, air cooler, intake

air filter, scavenge valves in the air receiver, scavenge ports or exhaust

passages. Incorrect fuel timings, bad quality fuel or inadequate fuel

treatment also result in increased exhaust temperatures.

One Unit E xhaust Temperature Rise

This can occur because o f :

♦ Thermometer defective (local or remote).

♦ Less air supply due to the individual unit scavenge valves in the air

receiver or scavenge ports fouled, or a scavenge fire.

♦ Fuel injector nozzle in a poor condition or the tip broken.

♦ Incorrect fuel timings or a fuel cam shift.

♦ Leaking exhaust valve.

♦ Blow past of piston rings.

Engine Speed Drops


♦ Fuel pressure after the booster pump is too low.

♦ Fuel pump defective or a fuel piping fault.

♦ Incorrect fuel injection.

♦ Fouling o f air or exhaust passages.

♦ Fuel air lock, gassing, water in the fuel, or poor fuel combustion.

♦ Scavenge fire.

♦ Governor problem.

One Unit E xhaust Temperature Drops


♦ Afaulty thermometer.

♦ Less fuel supplied due to faulty fuel injection pump, pipes, injector

or timings; or a shift in the fuel cams.

♦ Exhaust valve does not open due to the actuator pump or piping

being defective.

358

359



Charge A ir Pressure Drops

This occurs due to the fouling of the turbocharger air intake filter,

diffuser, blower, inducer, rotor blades, nozzle ring, air cooler, water

separator or exhaust gas economizer.

E ngine R u n n in g Irregularly, M isfiring or C utting Out

This occurs due to :

♦ Fuel problems like faulty fuel booster pump or fuel pump, wrong

fuel pressure or temperature, air lock or water in fuel, or a defective

fuel valve.

♦ Governor malfunction.

♦ Turbocharger surging.

♦ Running gear components overheated, causing severe alternating

friction.

Jacket Water Pressure Fluctuation


♦ Air pockets in the jacket cooling water, or insufficient venting.

♦ Exhaust gas leaking into jacket cooling water due to a crack

in the liner, cylinder head or valve cage.

♦ A drop in the static pressure at the pump inlet due to throttling

in the return pipe.

Jacket Water Temperature Increase


♦ Valves may be shut or insufficient venting.

♦ Overloaded engine or piston running hot.

♦ Crack in liner, cylinder head or exhaust valve cage.

♦ Temperature controller malfunction.

♦ Jacket cooler setting is wrong:

Running Gear H ot

Running gear like the bearings, piston , liner, etc m ay get

heated due to:

♦ A problem with lubrication or piping.

♦Jpumalsgettingrusted.

♦ Water or dirt in the lube oil.

♦ Lube oil tank level decreases and therefore, the pum p is

drawing air.

♦ Incorrect clearances or component damage.

Engine Fails To Start On A ir


♦ Low air bottle pressure or air line valves may be shut.

♦ Air bottle isolating valve or automatic valve or distributor

malfunction.

♦ Control air valves faulty or less control air pressure.

♦ Start air automatic valve jammed.

♦ Turning gear engaged or limit switch faulty.

♦ Reversing has not taken place completely.

♦ Control valve for fuel or ‘start’ is not in it’s end position.

♦ Bursting diaphragm on start air line damaged.

♦ Fuel lever on maneouvring stand not on remote mode.

♦ N ot sufficient spring air pressure to shut the exhaust valve,

thereby causing loss of compression.

♦ Auxiliary blower not running or not on ‘auto’ mode.

♦ No oil pressure due to the exhaust valve being open or insufficient

spring air pressure.

♦ Start air distributor has not activated its end stop valve.

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361



♦ Start air distributor piston is sticking.

♦ Start air distributor is wrongly adjusted.

♦ Start air distributor control valve is sticking.

♦ Cylinder air start valves are defective or sticky.

E ngine Turns On Air, B u t N ot On Fuel

This can occur because o f:

♦ In B&W engines, the puncture valves are not properly vented.

♦ Fuel regulating linkage jammed or held back by the stop cylinder.

♦ Fuel lever on local maneuvering stand is not on remote mode.

♦ Governor is defective and does not release the fuel linkage, or

there is no boost air to the governor.

♦ Rotary valve of the rotation direction safeguard is sticking.

♦ Shut down of fuel pumps.

♦ Fuel filter is blocked or fuel pump index is too low.

♦ Pre-set control air signal to the governor is too low.

E ngine Does N ot F ire


♦ Less fuel being injected or the speed setting knob is set too low.

♦ Governor does not release the regulating linkage.

♦ VIT & FQS functions are too late.

♦ Start air pressure is insufficient to turn the engine fast enough.

♦ Fuel is unsuitable or it’s viscosity high.

♦ Compression pressure is too low due to faulty piston ring sealing

or exhaust valve closing.

♦ Fuel pump defect. Check the cut-out device, jammed plunger or

clearances.

♦ Injector nozzle needle sticking or holes blocked.

♦ Suction or spill valves leaking or stuck.

♦ Pump push rods jam m ed or fuel cams displaced or incorrect

timings.

♦ Fuel pump relief valve leaking.

Violent Start

This occurs due to:

♦ Speed setting is too high. It injects too much fuel for the start.

♦ Fuel setting or timings are wrong.

♦ Cylinderisexcessivelylubricatedcausinganaccumulationof cylinder

oil.

♦ Auxiliary blowers were not running earlier causing fuel oil

accumulation rather than blowing away fuel vapours (like purging).

N ot Reversing p r Starting In Only One Direction


♦ Start air valve for that unit may be sticking. The remedy is to give a

kick in the opposite direction. Now a different unit will receive

start air due to the change in the crank position.

♦ The reverse control valve is jammed.

♦ The reversing servomotor of the fuel or start air distributor is jammed

or gets stuck before reaching a new end position due to insufficient

oil pressure. Therefore the engine turns on air, but no fuel is released

as the rotation direction safeguard blocks it.

♦ If the engine is running in one direction and reversed, propeller

continues to turn in that direction. Therefore, more air and fuel is

required for starting against the propeller force (first to bring the

propeller to standstill like braking). If the engine still does not start,

the propeller may tend to turn the engine in the original direction

i.e. opposite to the given movement. Therefore the rotational

direction safeguard blocks the fuel.

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363



Checks I f The E ngine Is N ot Reversing

Checks are carried out on the following:

♦ The coil o f the solenoid valve for the desired direction or rotation,

does not get voltage.

♦ Control air signal for desired direction of rotation does not reach

the engine. Loosen piping and check the air route or the defective

valve.

Cracked Piston

Indications:

♦ Fluctuation in piston cooling water or oil flow.

♦ Increase of water or oil from scavenge drains.

♦ Piston cooling water of oil is excessively dirty.

♦ Temperature o f the piston cooling water or oil rises sharply.

♦ Colour of the exhaust is whitish if water cooled, or grey blue if oil

cooled.

♦ Knocking sound.

Reasons:

♦ Thermal stresses caused by too much temperature variation across

a small section of the piston.

♦ Loss of coolant flow due to pump failure or cooling passages

blockage.

♦ Fuel injector needle and valve leaking causing impingement and

burning of the piston crown.

♦ Ineffective cylinder lubrication.

♦ Improper piston ring functioning, seized or broken rings, unbalanced

load or continuous overload operation.

Broken Piston Ring

Causes :

♦ Excessive thermal load, insufficient cooling, or a distorted piston

crown.

♦ Excessive piston ring clearance or distorted grooves.

♦ Sticking of piston rings or incompatible materials.

♦ Excessive lubrication or loss of lubrication.

♦ Collapse of piston rings.

Effects :

♦ Loss of compression.

♦ Blow past of combustion gases.

♦ Scavenge fire.

♦ Scuffing of the cylinder liner.

Cracked L iner Indications

'♦ Gas leak in the jacket cooling water.

♦ Fluctuation in jacket cooling water pressure.

♦ Loss of jacket cooling water and increase in it’s temperature.

♦ Sparks from the funnel or water from the scavenge drains when

•the engine stops.

♦ The cylinder gives a knocking sound.

Piston R unning Hot

Indications:

♦ Knocking sound at both ends o f each piston stroke.

♦ Drop in the engine rpm.

♦ Rise in the piston cooling water or oil temperature, and jacket water

temperature of that cylinder unit.

♦ Smoky exhaust.

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365



A ctio n :

♦ Cut-out the fuel pump, increase cylinder lubrication and stop the

engine.

♦ Continue cylinder lubrication and turning even after engine is

stopped to prevent seizure.

♦ Open and dismantle the piston. If slight scoring is seen on the

piston, then smoothen with an oil stone (carborundium stone) and

an emery cloth. Check cylinder lubrication and piston clearances

after inspection.

Cracked C ylinder H ead

Causes :

♦ Excessive tightening of cylinder head cover studs, combined with

thermal stresses.

♦ Corrosion at the combustion surface o f the cylinder head.

♦ Normal expansion facility for the cylinder head is restricted.

♦ Inflexible structure under firing.

♦ Defect in cylinder head casting.

Indications:

♦ Knocking in the cylinder.

♦ Jacket cooling water temperature increases.

♦ Jacket cooling water pressure fluctuates.

♦ Expansion tank level may drop.

♦ Sparks from funnel.

Crank Case Inspection Checks

♦ White metal particles or foreign particles in the lube oil.

♦ Colour of the lube oil and oil flow.

♦ Check for white metal squeezing at bearings.

♦ Check the crankcase w alls for carbon deposits, leaking from

diaphragm.

♦ Check the crankpin and web alignment mark.

♦ All bolts, nuts and locking marks.

♦ Crankcase relief door.

♦ Any discolourisation signifying hot spots.

♦ Clearances o f bearings.

Individual Piston K nocking A t TDC

C auses:

♦ Early fuel injection due to incorrect fuel pump or fuel cam

adjustment

♦ Overloaded engine unit. Check effective delivery stroke of

respective fuel pump.

♦ Fuel valve nozzle sticking.

♦ Fouled cylinder orunsuitable fuel.

♦ Top piston ring strikes against the ridge worn a t the cylinder

liner top.

♦ Excessive clearances between piston and cylinder.

♦ Excessive bearing clearance of running gear.

♦ Running gear bolts have loosened.

♦ The piston may be striking against the cylinder head cover at TDC.

Bearing Temperature Increase

Causes

♦ Low lube oil pressure supply to bearing or low oil level in supply

tank.

♦ Air lock in the lube oil or lubricating grooves obstructed.

♦ Oil piping defective or lube oil valves shut.

366

367


M arine Diesel Engines

♦ Lube oil contains water or metal impurities.

♦ Excessive bearing clearances, excessive wear or improper

tightening.

L u b e Oil Sum p Level Rising

C a u ses:

♦ Pitching, rolling or changes in cargo loading.

♦ Water leakage from piston cooling or jacket water system.

♦ Lube oil purifier wrongly operated e.g. discharge valves of some

other purifier is wrongly opened thereby filling the sump.

♦ Transfer pump valves wrongly lined up.

♦ Lube oil inlet line valve from the storage tank may be open.

A utom atic Stopping o f the Engine

T his occurs due to :

♦ Activation of safety shut down or overspeed cut-out device.

♦ Control air pressure in the shut-down servomotor too low, causing

pressure to pull the fuel linkage back to zero.

« Governor defective.

♦ Fuel supply stopped due to clogged filter o r empty tank or air

lock.

K nocking in an E ngine Cylinder

♦ Fuel valve nozzle needle stuck open.

♦ Early fuel injection or too much fuel quantity injected, due to wrong

fuel timings or pump settings.

« The ends of the piston rings are knocking against the edges of the

scavenging and exhaust ports due to deformation during fitting.

♦ O ne or more driving gear components have excessive vertical

clearance.

♦ The connection screws on the piston rod o r piston are n ot tight

enough.

♦ Knocking o f all cylinders is due to an incorrectly set camshaft or

unsuitable fuel.

Safeties in the Main Engine

Crank Case

♦ R eliefvalvesetat0.05bar

♦ Oil m ist detector set at 2 to 5 % LEL.

♦ Temperature sensing probes on bearings, and thrust block, which

will shut down the engine.

♦ Flame, spark arrestor and deflector incorporated in the relief valve.

Scavenge

♦ Sight glass.

♦ Drain cocks for monitoring leakages.

♦ Temperature sensing probes.

♦ Fire extinguishing system.

♦ Relief valve set at 1.6 bar in B&W engines.

Cylinder H ead

♦ Relief valve.

♦ Non return air start valve.The pneumatic operated start air valves

are shut by the cylinder pressure once the engine fires.

E xhaust M anifold a n d T runking

♦ Fire extinguishing system.

♦ Drain cock.

♦ Test cocks at individual units.

♦ Flame and spark arrestor.

♦ Protective grid and bellows before turbine.

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368



♦ Drain cock in the trunking of the exhaust gas boiler.

♦ Drain cock at the turbine housing to make sure that no water is

coming to the turbine.

♦ Manometer at inlet and outlet of exhaust gas boiler and a safety

valve.

Piston Cooling System

♦ Low pressure cut out approximately 2 bar.

♦ High inlet temperature slow down alarm at 60 deg.C and shut down

at 65 deg.C.

♦ Low level alarm in the cooling water drain tank.

♦ Sight glass at every unit with a piston cooling non-flow alarm.

Jacket Cooling System

♦ Low inlet pressure shut down at approximately 2 bar.

♦ High outlet temperature slow down at 90 deg C and alarm at 85

degC .

♦ Low level alarm in the expansion tank.

♦ Sight glass in the expansion tank.

♦ Air separator and vent

Lubricating O il System

♦ Sump low and high level alarm.

♦ M ain lube oil pressure low alarm at 2.2 bar and shut down

at 2 bar.

♦ Lube oil outlet temperature alarm at 50 deg.C and slow down at

55 deg.C.

♦ R elief valves at the discharge side of both pumps connecting

the discharge side back to the suction side.

♦ Pressure gauges after cooler and after discharge filter.

♦ Differential pressure low alarm.

♦ Air vent at the cooler.

♦ Air vent at the discharge filter.

F uel O il System

♦ Drains at the service tanks, settling tanks, filters, mixing column

andheaters.

♦ Relief valves at the booster pump discharge, heater, common inlet

manifold to the pump and on the individual fuel pump.

♦ Fuel high temperature alarm at 120 deg.C.

♦ Low Fuel temperature alarm at 85 deg.C.

♦ Viscometer, thermometer and pressure gauges.

Starting A ir System

Bottle

♦ Relief valve set at 32 bar.

♦ Fusible plug.

♦ Drain cock and pressure gauges.

♦ Non return, stop, and isolating valves.

A ir Compressor

♦ Low pressure (first stage) and high pressure (second stage) relief

valves.

♦ Non-return valve at compressor outlet to air bottle.

♦ Corrosion resistant bursting disc o r relief valve in the coolers

on the water side.

♦ Air discharge high temperature cut-out

♦ Cooling water high temperature cut-out.

♦ Low lube oil pressure cut-out.

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371



Start A ir Line

♦ Flame trap, bursting disc cap or a relief valve.

♦ Automatic shut-off master valve.

♦ Non-return start air valves.

♦ Drain cock in the manifold and at other parts.

♦ Drain cock before shut off valve.

♦ Temperature and pressure sensors and gauges.

♦ Running direction and turning gear engaged interlocks to prevent

starting.

Control A ir System

♦ Pressure reducing valve.

♦ Oil separator and moisture separator.

♦ Control air drier.

♦ Manual and auto drain.

♦ Relief valve.

♦ Pressure sensor probe for alarm at 6 bar and shut down at 5.5

bar.

♦ Low pressure alarm for spring air to the exhaust valve.

E xhaust valve actuator

♦ Automatic air venting unit.


♦ Non flow alarm and slowdown.

Leaky Start Air Valves

A t Port

To check whether the air start valves are leaking, disengage the turning

gear and shut off air to distributor. Indicator cocks are to be opened.

Take each unit to TDC and check for air coming out o f the indicator

cock with main air from bottle open, and admitting start air to engine.

The engine does not turn on air, since the air to distributor is shut, but

as a safety measure in case of a leaking start air valve, the turning gear

has to be disengaged.

A t Sea

Feel the start air inlet branch pipes for each unit and see if they are

hot. If the engine fails to start because of a sticking pilot or air start

valve during maneuvering, then give a kick in the opposite direction so

that start air is now admitted to another unit. In case of a generator

engine, manually turn the engine to get it off the blind spot.

Start A ir Line Explosion

This is mainly due to the accumulation of oil due to carry-over of oil

from the starting air compressors. A defective start air valve on the

cylinder head provides heat if it leaks back into the start air line.

Prevention

♦ Good maintenance of the air compressors.

♦ Auto and manual draining o f water and oil in the air line.

♦ J Jh e starting air manifold pipes should be inspected and cleaned.

♦ The start air valves should be overhauled at regular intervals.

Safe Guard A gainst Overspeeding

♦ For slow speed main engines, the speed is sensed by a digital pickup

similar to an induction pick-up. If the engine overspeeds, the

fuel rack is shut down.

♦ In Sulzer engines, a collapsible link is fitted between the governor

and the fuel rack.

372

373


♦ In B & W engines, puncture valves are fitted on the top of each

fuel pump, which spill the high pressure oil back to suction side of

the pump.

♦ In medium speed auxiliary generator engines, fly weights using

centrifugal force activate a stop cylinder to push back the fuel racks.

BIBLIOGRAPHY

1. KANE, A.B.

• ‘Marine Internal Combustion Engines’, 1973.

• ‘Prevention of Crankcase Explosions in Marine Diesels’, 1969.

• ‘Reversing Gears of Marine Diesels’, 1965.

2. VANCHIED, V.A.

• ‘Marine Internal Combustion Engines’, 1957.

3. MASLOV, V.V.

• ‘Slow Speed Diesel Auxiliaries’, 1968.

4. BOWDEN, J.K.

• ‘Marine Diesel Oil Engines’, 1981.

5.M U N TO N R ., M cNAUGHTJ.

• ‘Automation of Highly Powered Diesel Machinery’, 1966.

6. WOOD YARD, DOUG

• ‘Pounder’s Marine Diesel Engines, 2004.

7. CHRISTENSEN, S.G.

• ‘Lamb’s questions and answers on the Marine Diesel Engine’, 1990.

8. COWLEY, J.

• ‘The running and maintenance of Marine Machinery’,1994.

374


A

A-frame, 24

Accumulator, 48,164

Air compressor, overhaul, 249

Alarms, shutdown, slowdown, 342

Alpha lubricator, 283

Annealing, 251

Atomisation, 119

B

Balancing, static, dynamic, 208

Barred zone, 212

Bearing temperature rise, 367

clearance, 232

connecting rod bearing, 72

crosshead bearing, 75

defects, 71

main bearing, 71

materials, 69

pivot pad, 70

plain bush journal, 70

Bedplate, 22

Blowdown, exhaust gas, 84

Bolts, holding down, 25

Bracing, top, 20

Brake horse power, 308

Bridge control, 202

governor, 337

Bunkering, 123

c

Cam, fuel, 146

Camshaft-less engine control, 258,278

Carbon monoxide, 304

Cards

case hardening, 251

light spring diagram, 321

pack carburising, 251

power, draw, compression, 320

INDEX

pressure derivative, 322

Cetane number, 113

Chain drive

camshaft re-adjustment, 68

elongation, 67

inspection, 66

materials, 66

slack, tight, 67

tightening, 64

Chocks

resin, 27

resilient, 28

side, end, 26

Clearance, bumping, 105

Collision, 354

Combustion phases, 117

Common rail system, 261

Compression

faults, 106

isothermal, adiabatic, 103

multi-stage, 104

pressure, reduced, 358

ratio, 121

Compressor

map, 99

reciprocating, 104

rotary, 104

valves, 105

CoCoS, 285

Connecting rod bearing

removal, 228

vConnecting rod

2-stroke, 72

4-stroke, 73

bottom end bolt, 74

clearance, 235

failures, 74

removal, 230

Consumption,



specific cylinder lube oil,’ 169

Conventional VIT, 145

Cooling system

function, 173

piston cooling, 175

treatment. 175

Crankcase explosion, relief valve, 351

inspection, 366

Crankshaft

deflections, 63

failures, 61

fully built up, 58

fully welded, 60

materials, 61

semi-built up, 59

solid single piece, 60

stresses, 62

Crash manoeuvring, 195

Critical speed, 211

Crosshead

bearing clearance, 234

bearing removal, 227

developments, 76

failures, 76

pin removal, 229

Cycles

2-stroke, 9

4-stroke, 12

dual, actual, 7

otto, diesel, 6

Cylinder head

cover, 50

crack, 366

defects, 51

materials, 50

removal, 216

Cylinder lubrication, 283

load-dependent, 167

multi-level, 170

Cylinder oil, types, 163

Cylinder pressure

PMI transducer, 286

sensor, 283

Cylinder relief valve lifting, 357

D

Dampers, 213

Dead band, 320

Decarbonisation, 215

Delay, ignition, injection, 118

Destructive, non-destructive tests, 250

Detuners, 213

Developments,

combustion chamber, 296

crosshead, 298

cylinder lubrication, 297

engine components, 298

exhaust system, 296

fuel system, 291

liner, 296

piston, 297

scavenge system, 296

SFOC, 298

stroke bore ratio, 298

turbocharger system, 292

Droop, 336

E

Efficiency, volumetric, 105

Electronic control, 261, 278

Electronic profiled injection, 279

Emissions, 301

Engine

diagnostic system, 285

forces, 205

knocking, 367, 368

protection, 342

remote control, 340

reversing problems, 363

room watch, round, 345

speed drop, 359

speed fluctuation, 356

starting problems, 361

telegraph, 342

Entabulature, 24

Excess air coefficient, 311

Exhaust gas

grouping, 89

recirculation, 303

temperature rise, drop, 359

Exhaust valve, 51

failures, 57

materials, 152

removal, 218

rotators, 55

seat profile, 54

springs, 53

type, 52

Exhaust, smoky, 358

F

Fatigue failures, 21

Fire ring, 296

Firing

interval, 178

order, 188

Flame hardening, 251

Flash point, fire point, 112

Flooding, 355

Flywheel, 207

Friction, types, 151

Fuel

definitions, 110

specifications, 116

types, 109

Fuel injector valve, 125

overhaul, 244

Fuel limiters, 339

Fuel pump timing, 4-stroke, 241

Fuel pump,

cut-out, lead, 239

cut-out, zero-checks, 238

port control, 134

setting, adjustment, 236

suction and spill control, 133

suction control, 131

Fuel quality setting, 140

Fuel timings, incorrect, 356

Fuel valve

conventional type, 291

functioning, 276

mini-sac type, 291

slide type, 291

Fuel, water emulsion, 303

Funnel sparks, 357

G

Gas exchange process, 84

Governor effect, 320

Governor

compensation range, rate, 334

effect, 320

electric, 333

electronic, 337

function, isochronous, 329

load limiter knob, 335

local speed setting knob, 334

mechanical, hydraulic, 331

speed droop knob, 337

variable speed, droop, 329

Grounding, 355

H

Hardening, 251

Hunting, 320

Hydraulic nut, removal, 217

Hydrocarbon, 305

I

Imbalance, primary, secondary, 209

Indicated horse power, 308

Indicator diagrams, 318

analysis, 323

Indicator instrument, 322



faults, 327

Induction hardening, 251

Injection

electronic, 136

pilot, 135

twin, 136

Intelligent engine, 259, 278

Internal combustion engines, 1

J

Jacket water

K

Knock, 118

pressure, temperature rise, 360

L

Light spring diagram, analysis, 326

Liner, 45

bore-cooled, 174

calibration, 225

crack, 365

failures, 49

inspection, 224

load-dependent cooling, 174

removal, 224

Liner wear

corrosive, abrasive, 47

friction, clover leaf, 47

diagram, 314

sharing, 335

Lubrication

boundary, 152

crosshead, 171

cylinder, 162

elasto-hydrodynamic, 152

function, 149

hydrodynamic, 151

hydrostatic, 151

properties, 152

testing, 156

types, 151

Lubricators, 166, 169

M

Main bearing,

clearances, 232

removal, 225

Maintenance planning system, 285

Manoeuvring

diagram, 198

flowchart, 197

Material

engine, 78

testing, 250

ME engines, 278

Mean effective pressure, 307

Mean indicated pressure, 307

Mean piston speed , 2

Mechanical efficiency, 308

Microbial degradation, 161

Motion, loss, gain, 194

N

Nitriding, 251

Normalising, 251

NOx, 302

o

Octane number, 114

Oil spill, 354

Opposed piston, 82

Over speeding, 355

Over speeding, safeguards, 373

Overlap, 179

P

Penetration, 119

Pinching, clamping screws, 24, 248

Pipe, high pressure, 147

Piston

2-stroke, 4-stroke, 34

composite, 33

crack, 364

hot, 365

inspection, 221

jet-shaker effect, 30

knocking, 367

materials, 31

mounting, 223

oros, 32, 297

removal, 220

defects, 35

rotating, 35

water, oil-cooled, 30, 32-

Piston ring,

anti-polishing ring, 43

broken, 365

cleaning ring, 43

clearance, 222

coatings, 42

collapse, 38

compression type, 36

CPR type, 42

flutter, 38

life, 43

manufacture, 41

oil scraper type, 37

scuffing material, 40

shapes, 41

SIPWA, 44

Planimeter, 319

Power, 310

rated, gross, overload,

minimum, continuous,

maximum continuous,

normal, astern output, ,

Power loss, 356

Power take in, off, 92

Pressure changing, 85

Propeller curve, 314

Puncture value, 275,77

Q

Quenching, 251

Quills, 48, 164

R

RD, RND, RTA engine differences, 253

Residual fuels, 122

Reversing, 189

methods, 190

roller shifting, 276

RT-flex engines, 254

RTA engines, 254

Running direction interlock, 195

Running gear hot, 361

Running-in, 40

s

Safety

cut-out device, 200

margins, 316

Safeties

crankcase, scavenge, 369

cylinder head; manifold, 369

fuel oil system, 371

jacket cooling system, 370

lube oil system, 370

piston cooling system, 370

start air system, 371

Scavenge

air limiter, 188

Scavenging

loop, cross, 82

reverse flow, 82

uniflow, 81

Sea trials, 312

Selective catalytic reduction, 304

Sensitivity, 320

Stuffing gland, 44

Slow turning, 188

SMC engines, 271


Soot, smoke, opacity, 305

SOx, 302

Stability, 320

Start air

automatic master valve, 183

cam, 187

cylinder valve, 185

distributor, 186

interlocks, 187

line explosion, 373

pilot valve, 182

receiver bottle, 180

valve, leak, 372

Starting

air period, 179

torque, timings, 177

Strength

longitudinal, 20

transverse, 19

Stroke, 1

Sump, level rise, 368

Super charging, 85

Super VIT, 140

Surging, 99

Swirl, 120

T

Tempering, 251

Test-bed tests, 312

Testing of marine engines, 311

Thermal efficiency, 308

Thrust bearing pad removal, 231

Tie bolts, rods, 24,25

elongation, 247

pretensioning, 246

slack, 356

tensioning, 247

Tribo-pack, 265

Turbocharger,

faults, 98

inboard plain bearings, 294

out of operation, 243

overhaul, 241

un-cooled, 97, 292

Turbo charging

2-stage, 91

axial, radial flow, 93

constant pressure, 86

materials, 96

pulse, 88

series, parallel, 89

single, multi system, 91

Turbulence, 120

V

Variable exhaust closing (VEC), 56

Variable injection timings (VIT), 136

Vibration, 209

w

Work hardening, 251

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EXHAUSTIVE COVERAGE OF THE FOLLOWING TOPICS

□ Watch Keeping

□ Engine running problems

□ Camshaft-less electronically controlled intelligent engines

□ Indicator card analysis

□ Engine performance and testing

□ Latest developments

□ Engine overhauls

□ Engine emission

□ Starting and reversing

□ Manoeuvring

□ Bridge control

□ VIT and Super-VIT

□ Faults, defects and problems of all engine components.

S H R O F F P U B L IS H E R S &

D IS T R IB U T O R S P V T. LTD .

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