CIMAC Congress - Schiff & Hafen

CIMAC CONGRESS | BERGEN 2010
felt, to a degree which varies from one individual to another.
Although the matter from a medical point of view is still somewhat
obscure, there is scientific evidence that some people are sensitive to
infra-sound to a degree that can documented objectively. Accordingly,
some noise regulations today stipulate maximum allowable noise
level within a wide frequency spectrum, including values at infrasound
frequencies. Therefore, the acoustic engineer cannot ignore
the issue of infra-sound, apart from disturbance caused by noise
within the audible spectrum. Conventional silencers can indeed
yield satisfactory attenuation at all relevant frequencies, but stringent
demands regarding low-frequency performance tend to call for
ample accommodation space and for an allowance to design for
rather big pressure drops. This is in conflict with the fact that
available space is often narrow, for instance on board ships. Also, a
high backpressure can retract from engine performance and can
cause unwanted increase of thermal loading of combustion
chambers. The paper presents a novel silencer concept that combines
three per se well-known silencer principles in an optimal way. The
first of these principles is the reactive sound-reflection principle; a
silencer according to this principle in acoustic theory is sometimes
referred to as a low-pass filter, since it attenuates noise of frequencies
higher than a lower cut-off frequency. The second principle is the
sound-absorptive principle which provides mainly high frequency
attenuation. The third principle is the Helmholtz resonator principle
in which sound confined to a certain frequency band is being
absorbed. Each principle has its pros and cons: The reactive silencer
can provide noise reduction within a wide frequency spectrum, but
there is a pressure-drop penalty. A resonator, on the other hand, can
be designed for an insignificant pressure drop, but its bandwidth is
rather narrow. Additional problems with a resonator are, that its
resonance frequency is sensitive to temperatur variations, and that
the frequency at which maximum attenuation is needed will change
with rotational speed of the engine, making exact tuning difficult.
The various principles can be combined in such a way that the
attenuation spectrum of a reactive stage is supplemented at the
lower end by a resonator. Automatic tuning of the resonator can be
performed by a robust feed-forward control loop which can
compensate for frequency shifts caused by changed rotational speed
of the engine. The paper presents the theoretical basis for the new
silencer concept, supported by empirical verification, as well as an
evaluation of its fitness from a practical application point of view, as
related to an ongoing field project.
10:30 June 16th Room Klokkeklang
(5–1) Component & Maintenance Technology –
Piston Engines – Components
Recent development in analysis and design
of principal bearings of large two stroke
diesel engines
P. Rønnedal, H. W. Christensen, MAN Diesel & Turbo
SE, Denmark
The two stroke crosshead low speed diesel engine has been a preferred
prime mover in the merchant marine for mostly a century. Although
its basic working principle has not been changed, the demand for
still higher power, produced at the lowest possible fuel consumption,
from a machine occupying a minimum of space, has constantly
increased the demands to its three principal bearings, main bearing,
crank pin bearing, and crosshead bearing. This paper deals with
design techniques for bearings as applied in modern large two stroke
diesel engines. Simulation methodology as well as design verification
techniques by measurements are described. Most important, the
actual design features, as developed using the illustrated techniques,
are shown. Calculation results from in house simulation software
including advanced combinations of loadgeneration and Elasto
Hydro Dynamic (EHD) analysis are demonstrated, in particular for a
newly developed main bearing assembly, and for the Blended- Edge
(BE) main bearing applied in MAN B&W two stroke diesel engines.
Also simulation results for the wide pad crosshead bearing, which
has been introduced in the ME-B engine series, are given. Major
design particulars, bearing application range, and service experience
are illustrated in each case. The actual geometry of a bearing journal,
even when produced within strict tolerances of cylindricity, may
strongly influence the distribution of hydraulic pressure in the oil
film. A method of in situ measuring the shape of a main bearing
journal in detail is presented, and the influence of typical
imperfections discussed. Measurements of the oil film thickness of
the main bearings during full operation, made on the 4T50MX test
engine in Copenhagen, are shown in correlation with the equivalent
simulation results, and illustrating the development on the main
bearing components. In parallel with the mechanical/geometrical
development, also the issue of material properties are addressed.
Traditionally Babbitt has been the preferred bearing material for a
number of reasons. However stronger Tin-Alu bearings have also
been used for decades. MAN B&W diesel engines use both type of
materials, and recent developments aim at merging best properties
for both type of materials in one. MAN has worked on this
development for well over four years now, and the first service trials
are presented.
Trends in engine design and their impact on
engine bearing design and performance
C. Forstner, Miba Gleitlager GmbH, Austria
Latest engine designs are committed to ultimate performance and
low cost of ownership which in turn means high power density and
fuel efficiency combined with engine downsizing and extended
service intervals. The consequences are weight-optimized and hence
more flexible engine components as well as cost reduction at the
expense of material and surface quality. At the same time engine
speed, Brake Mean Effective Pressures and Exhaust Gas Recirculation
rates are increasing to match the performance and emission targets.
All of the above mentioned measures are directly affecting the load
and operating conditions of conrod small end bushings, connecting
rod big end and main bearings. In order to cope with this challenge
new bearing design and material solutions have been developed.
This paper will focus on late-breaking topics like recommended
surface quality of crankshafts, fretting damages at conrod big end
bearings and the influence of crankshaft torsional vibration
optimization on main bearing loads. Finally specific bearing design
changes and adaptations of existing bearing types in order to achieve
the required bearing performance and operational safety will be
presented.
Variable valve timing – a necessity for
future large diesel and gas engines
C. Mathey, ABB Turbo Systems Ltd., Switzerland
Variable Valve Timing (VVT) systems have been used in the
automotive industry for a number of years and very different
techniques, including phase-shifting, variable valve lift and exhaust
valve reopening, can all be found on the market. Beside its positive
impact on emissions and fuel consumption, the main marketing
focus is still on driveability or, in PR language, the “joy to drive”.
While these systems could be described as standard automotive
equipment today, it has been rare in the past for Variable Valve
Timing to be applied to large diesel and gas engines. However, the
74 Ship & Offshore | 2010 | No. 3