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In recent studies the possibility of emission reduction through
high-pressure fuel injection was shown. By changing the nozzle
configuration (number of holes, hole diameter and conicity of the
holes) it is possible to reach very low emission levels by using high
rail pressures (approx. 3,000 bar and above). For that investigation
different nozzles with different configuration were manufactured
and investigated. The huge potential for the reduction of emissions
was presented. However, changing the nozzle design changes
the hydraulical behaviour of the injector. With decreasing diameter
of the nozzle holes (down to 91m) certain oscillation effects
start to occur which are amplified with increasing rail pressure.
These effects can be observed in injection rate measurements and
apparently have a positive effect on the combustion process. The
description, characterisation and the impact of these injection rate
oscillations are the main focus of this study. The research focuses
on experimental investigations with modern techniques. For that
the injection rate of different injectors will be investigated. It can
be shown that for different nozzle configurations the injection rate
either shows a chattering and instability effect or not. The nozzles
with distinct oscillations will be investigated in an optical highpressure
vessel. A high-speed camera will be used to observe which
impact the changed hydraulic behaviour has on the spray pattern.
For this investigation a high-speed Mie Scattering Technique will
be used. In order to get a better understanding of this effect and
the impact on the spray pattern, a long-distance microscope will
be used for the investigations of the near nozzle field. With the
long-distance microscope it is possible to zoom to the nozzle hole
outlet and investigate whether needle chattering has an effect on
the fuel atomisation or not. The study will close with an outlook
on ongoing research, especially a possibility to calculate the effects
with coupled CFD and 1D-hydraulic simulation methods.
An approach for dimensioning case hardened
components through utilisation of sophisticated
fatigue analysis with the finite element method
Matti Savolainen, Wärtsilä Finland Oy, Finland
Roger Rabb, Wärtsilä Finland Oy, Finland
Anton Leppaenen, Wärtsilä Finland Oy, Finland
Aulis Silvonen, Wärtsilä Finland Oy, Finland
Sylvia Leever, Wärtsilä Netherlands BV, The Netherlands
Wolfgang Luft, Wärtsilä Switzerland Ltd, Switzerland
Component design procedures have developed significantly during
the last decades. As a part of the process, the prediction of accurate
stresses using the finite element method (FEM) as well as the
calculation of fatigue strength with specific codes, have become
common practice. Due to ever increasing computational power,
different surface treatments, which contribute to the formation of
the local microstructure and stress situation, such as heat treatment
or shot peening, can also be integrated in the FE model. The
determination of the fatigue life of a component can be automated
to some extent for the sake of decreased design time by using
numerical methods. When the outcome of a surface treatment is
taken into account in such an analysis, it naturally gives the analyst
an opportunity to optimise not only the geometry but also the desired
surface treatment influence on the component. This in turn
leads to the fact that the parameters of the surface treatment procedure
in manufacturing can be defined more precisely already in
the designing phase leading to obvious cost savings. Case hardening
is a surface treatment process in which the surface of a metal is
hardened by infusing elements into the material. More specifically
carburisation, where the component is introduced to a carbon-rich
environment at an elevated temperature and afterwards quenched
so that the carbon stays in the structure, is a commonly used method
for improving the wear and fatigue resistance of several engineering
components. The advantage from the fatigue point of view
of this procedure is naturally the increase in hardness as well as
the compressive residual stresses in the surface of the component.
The disadvantage, on the other hand, can be found underneath
the surface in a form of balancing tensile residual stresses, which
in turn may be a source location for a possible failure initiation.
This paper introduces an approach for dimensioning a component,
which has been hardened by carburisation. The focus of
the exercise is on defining the correct case hardening profile in
order to meet the required probability of survival. As an example,
a gear from a thruster manufactured by Wärtsilä Netherlands BV
is investigated, where the teeth of the gear wheels are treated. The
examination is conducted through the component surface until a
certain depth in order to also take into account the influence of
the tensile part of the residual stresses. Those are then combined
with the working stresses during operation, and based on the result,
the fatigue analysis is performed. That is done by adapting
existing Wärtsilä tools including the multiaxial damage models of
Findley and Dang Van together with the concept of local fatigue
strength, which defines local fatigue limits through depth based
on the hardness variation. The material parameters used are obtained
by testing and finally the calculated results are compared to
available real world data.
The valve seat ring shrink fit simulation methods in
the finite element modelling of the cylinder head
Xuyang Guo, Beijing Institute of Technology, China
Ying Cheng, Beijing Institute of Technology, China
In this paper, the uniform pressure method, the contact model
method and the temperature method are used to simulate the
shrink fit of the valve seat ring. Based on theories and calculation
results, it is concluded that the contact model method can reflect
the real contact condition. In order to investigate the influence of
the valve seat ring on the fire deck stresses, the contact model is
used. The mechanical stress, thermal stress and thermomechanical
stress are calculated. With the valve seat ring, the mechanical
stresses increase while the thermal stresses and thermomechanical
stresses decrease in the valve bridge areas. Therefore, the influence
of the valve seat ring can not be ignored when calculating the
stresses of the cylinder head.
Visualisation of the combustion in Wärtsilä’s 34SG
pre-chamber ignited lean-burn gas engine
Jeudi Duong, Wärtsilä, Finland
Jari Hyvonen, Wärtsilä, Finland
Rikard Wellander, Lund University, Sweden
Oivind Andersson, Lund University, Sweden
Mattias Richter, Lund University, Sweden
An experimental study is carried out to investigate the combustion
process in a Wärtsilä 34SG spark ignited lean-burn four-stroke
large-bore engine (cylinder bore of 340mm and stroke of 400mm)
by means of passive optical diagnostics when operated with natural
gas. The main focus of this work is to gain qualitative and quantitative
knowledge about the in-cylinder combustion phenomena
when igniting a lean air/fuel mixture, i.e. lambda about 2, with
pre-chamber induced igniting jets The work consists of two-dimensional
imaging of the combustion process in single cylinder
research engine with optical access to the combustion chamber
under relevant operating condition. To gain further knowledge
of the ignition and combustion process in the SG optical engine,
May 2013 | Schiff&Hafen | Ship&Offshore SPECIAL 49