CIMAC Congress - Schiff & Hafen

CIMAC CONGRESS | BERGEN 2010
over the top piston ring. Further, Ansys CFX is used for predicting
the 3-dimensional gas flow field past the top ring and the
3-dimensional temperature field in the top piston ring in a set of
steady-state simulations at different engine crank angles. The timeaveraged,
3-dimensional temperature field in the top piston ring is
then predicted through a weighted average over the various crank
angles. Finally the circumferential ring-liner contact pressure is
predicted through the Ansys Simulation package, taking into account
the computed time-averaged, 3- dimensional temperature field in
the top piston ring. There are different design concepts for piston
rings aiming to reduce thermal load and contact pressure variation.
The above model was applied to compare a traditional straight-cut
piston ring design against MAN Diesels’ Controlled Pressure Release
(CPR) design for the K90MC large bore, low- speed marine diesel
engine. The results show that the ring with the straight-cut opening
is heated on the inside near the opening due to the blow-by gas
flow. This generates a strong thermal gradient which in turn reduces
the ring-liner contact pressure near the ring opening and creates
hard contact at the opening. This effect is significantly reduced for
the CPR design since the blowbygas flow is then restricted to grooves
resulting in a more even temperature field and a more even ringliner
contact pressure. The predicted 3-dimensional temperature field
was validated against piston-ring mounted thermo-plug
measurements made by MAN Diesel for the CPR design. The
simulation results were found to compare reasonably well with
measured values. A set of hypothetical temperature fields were
applied in Ansys Simulation in order to improve the understanding
of factors affecting the ring-liner contact pressure. The results show
that the most important factor is the temperature difference between
the inside and the outside of the ring. The average temperature of
the piston ring was found to be of minor importance to the ringliner
contact pressure.
Cylinder condition analysis in relation to
large bore engines
J. W. Fogh, C. L. Felter, MAN Diesel & Turbo SE,
Denmark
The present design of piston ring packs and cylinder liners is a result
of an ongoing development driven by environmental regulations,
reliability issues and operating costs of our two-stroke engines. The
use of low sulphur fuels, now a reality in several SECA areas, an
increasing demand from shipowners to be able to operate the
engines without major overhauls between dockings and the cost of
lube oil are some of the elements which have led to the present
piston ring pack design, maintaining the good cylinder condition
for our two-stroke engines. This paper is focused on the development
of the piston ring pack. The design and performance of the latest
piston ring configuration for our large bore engines will be discussed.
A short description of the development of the other components
relating to cylinder condition will also be given. A general description
of the service experience over the years will be given. The conclusion
which can be drawn from this service experience is used to motivate
the introduction of Ceramic coating (Cermet) on the top and fourth
ring in the standard ring pack. Different designs of the piston ring
pack are correlated to service experience with a view on reliability.
An analysis of the oil film thickness, pressures and asperity contact
has been carried out using our in-house piston ring programme
showing the performance of piston ring/liner contact. The theoretical
results are compared with the results from the service experience.
Furthermore, tribological tests of different piston ring designs have
been carried out, using a novel test rig and test procedure for
evaluating piston ring/cylinder liner contact. The results from these
tests are compared with service experience and simulation results
from our in-house piston ring programme. The main conclusion
from this work is that the introduction of Cermet coating on the top
and forth piston rings is in fact supported by service experience as
well as by the theoretical simulation results and the test rig results..
Development of bearing wear monitoring
system using automatic calibration
technique, B-WACS
J. K. Kim, U. Duk Hyung, K. Sok Ha, K. Sang Jin,
Doosan Engine, Korea
In this paper, bearing wear monitoring system (BWMS) that detects
abnormal wear in power train bearings of marine diesel engines is
developed based on automatic calibration technique. BWMS
provides continuous measurement of bearing wear status from the
power train bearings consists of three bearings such as main bearing,
crank-pin bearing and crosshead bearing. The primary aim of BWMS
is to detect a bearing failure before it develops to an extent where
heat is causing damage to other parts than the bearing shell. The
working principle of BWMS is based on the fact that any change in
bearing wall thickness in the loaded part of one of these bearings
will result in a corresponding change of bottom dead center level of
one or more of the crossheads relative to the engine structure.
Doosan BWMS, B-WACS(bearing warning and control system), is
consists of signal capture unit (SCU), signal analysis unit (SAU) and
date monitoring unit (DMU). The SCU is the processing unit for
sensing distance data from inductive proximity sensor and finding
BDC distance and sending data to SAU that analyzes the data from
SCUs and determines the wear status. DMU shows bearing wear
status in real time and other information such as wear data trend,
system status, alarm status and temperature ets.
In this paper, for achieving high accuracy of SCU, the automatic
calibration technique is proposed. The idea of automatic calibration
technique is compensating contactless sensor value with regards to
temperature and precision laser distance sensor at once. It can realize
the accuracy of SCU up to ±5μm.
Development of a new evaluation method
for the influences of catalyst fines on
abrasive wears of marine diesel engines
burning heavy fuel oil
T. Yamada, H. Ukai,
T. Fujii, Diesel United, Japan
Catalyst fines in the marine heavy fuel oil may cause abrasive wear
in the engines. In order to prevent problems resulting from use of so
called FCC (Fluid Catalytic Cracking) fuel, content of catalyst fines
must be put under control during whole process from refinery to
the ship. For this purpose, as a practical solution to represent the
main components Al 2
O 3
and SiO 2
, quantitative analysis of Al
(Aluminum) and Si (Silicon) by ICP (Inductively Coupled Plasma)
method is generally adopted. The upper limit of Al + Si content in
the fuel is specified by engine makers and DU (Diesel United, Ltd.)
specifies 15 ppm at engine inlet. Our field experiences show
correlation between wear figures and Al + Si content in the fuel,
however, with some exceptions. There are cases of high abrasive
wear even with low Al + Si content. On the contrary, there are cases
of normal wear with higher Al + Si content than our specification.
Investigations have been conducted to make clear why exceptional
cases happen and our attention was focused to catalyst fines particle
size distribution in the fuel. Meantime, attempts to develop a new
evaluation method for the influence of catalyst fines on abrasive
wears have been made. The new evaluation method being developed
consists of two steps. The first step is to produce worn particles by
80 Ship & Offshore | 2010 | No. 3