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Monday, May 13th
Tuesday, May 14th
Wednesday, May 15th
Thursday, May 16th
optical line of sight diagnostics and hence the in-situ measurements
of temperature and soot concentrations. Effects of diffusion
and turbulence are minimised here and efforts are therefore
paid on the modelling of combustion chemistry, radiation and
soot formation. For improved computational runtime, a two-step
chemical reaction scheme proposed by Westbrook and Dryer is
used together with a steady-state solver. The steady-state solver is
developed by modifying an existing solver, Local Time Stepping
(LTS) ReactingParcelFoam. Akin to reactingFoam, which has been
widely used in combustion simulations, LTSReactingParcelFoam is
also applicable for laminar and turbulent reacting flow but it is a
local time stepping solver for steady-state simulations. The modified
version is henceforth addressed as radiationReactingLTSFoam
(rareLTSFoam). In order to simulate the radiative heat loss, P1 radiation
model is used. The model validation uses two test cases of
laminar premixed flames with different equivalence ratios. In the
first case, a stoichiometric flame is produced in which soot radiation
process can be omitted; while in the second case, a rich flame
with equivalence ratio of 2.15 is used. The results generated by the
integrated CFD chemistry model are validated against temperature
measurements at different heights along the axial direction. For
the radiative heat transfer, a parametric study is conducted using
P1 model. The absorption coefficients are modeled using RADCAL
and WSGGM models. Implementation of the steady-state solver
has been proved to simulate the stabilised, laminar premixed
flame accurately with an expedited calculation. This serves as a
useful platform when comprehensive radiation model such as inite
Volume Discrete Ordinate Method (fvDOM) radiation model
is implemented. Understanding and further improvements on the
robustness of numerical models achieved at this phase are critical
prior to computationally investigating the radiative heat transfer
process in turbulent diffusion flame and diesel engine combustion
that have higher levels of complexity.
Flow and pressure simulation of cooling water,
lubricating oil and fuel supply systems
Andreas Hjort, Wärtsilä, Finland
Juhani Ervasti, Wärtsilä, Finland
Jaakko Koivula, Wärtsilä, Finland
Lars Ola Liavag, Wärtsilä, Finland
Alexandre Pereira, Wärtsilä, Finland
Antonino Di Miceli, Wärtsilä, Finland
When designing fluid systems for four-stroke medium-speed diesel
engines, it is beneficial to use modern simulation tools to achieve
an optimised design in an early phase. Today’s engines have become
very compact and typically have a high degree of integration
of fluid channels into castings. Therefore, changes to address flow
problems after design is complete will require big re-design efforts
and should be avoided. The heat balance of the engine determines
the needed cooling water flow to achieve sufficient cooling without
excessive temperature increase in the water. As the pumps used
are of centrifugal type the flow in the system is determined by the
system pressure drop. CFD simulation of complicated channelling
as part of the design phase will ensure unnecessary pressure drop
is avoided and thus the water flow through the system will be increased.
A well-designed cooling system will have the majority of
the pressure drop in coolers and as little as possible in the channels
and piping. Oil pumps for four-stroke diesel engines must be
dimensioned to ensure sufficient pressure is available in the critical
components at all conditions. Over-dimensioning of the oil pump
will lead to unnecessary oil flow wasted through the pressure control
valve. To determine the exact oil flow through the engine in
the design phase is difficult, as the oil system has many consumers
with different characteristics. 1D flow simulation of a complete oil
system gives a sufficiently accurate prediction of the needed flow
to avoid over- or under-dimensioning of the oil pump and avoid
excessive pressure drop in any part of the oil system. Pressure pulsation
from mechanical fuel pumps to the fuel supply line can be
a source for vibration both on the engine itself but also in the external
fuel piping of the installation, e.g. ship. By 1D simulations
of the fuel supply system, the pulsation can be predicted and the
need for damping can be determined. This paper presents successful
simulation projects of all the above mentioned systems.
Turbulence during the compression stroke
Eero Antila, VTT Technical Research Centre of Finland, Finland
Mika Nuutinen, Aalto University, Finland
Ossi Kaario, Aalto University, Finland
Normally, diesel combustion simulations are started from bottom
dead centre before combustion. Initial values of pressure and temperature
are taken from experimental results or 1D-simulations.
As initial turbulence values (k and ε), some correlation, intake
flow simulation or just best practise values are used. All those values
are initialised to be constant for whole simulation volume. In
the previous study, intake channel simulations were done. Authors
found that the level of turbulence values at TDC were different if
the intake stroke was simulated or if average values were initialised
at IVC. In this paper three different engines are simulated. For each
engine intake and compression strokes are simulated to get the
best possible knowledge about the real turbulence values. From
those results the average values of p, T, k, ε and swirl number at
IVC are captured and used as initial values of compression simulation.
Finally, a better method to initialise turbulence values is
described and tested.
Wednesday May 15th / 13:30 – 15:00 Room B
Environment, Fuel & Combustion
Gas and Dual-Fuel Engines – Abnormal Combustion
Understanding the influence of heat transfer and
combustion behaviour on end gas knock in heavyduty
lean burn engines
Joel Hiltner, Hiltner Combustion Systems, USA
The onset of end gas knock remains one of the primary factors
limiting the thermal efficiency, fuel flexibility, specific power output,
and transient capability of lean burn natural gas engines. In
the past two decades, huge strides have been taken to improve the
performance of these engines, based largely on a fundamental
understanding of the impact of thermodynamic design and fuel
properties on the resistance of a given combustion platform to engine
knock. Simulation tools based on this knowledge have led to
optimised designs as regards expansion ratio, Miller cycle utilisation,
and other design approaches aimed at limiting end gas temperatures.
Two basic engine phenomena whose impact on knock
is less well understood are in-cylinder heat transfer and overall
combustion rate, phasing, and stability. In-cylinder heat transfer
has a profound impact on charge temperatures and can lead either
to increased or decreased knock tolerance for a given design,
depending on a number of factors. Combustion chamber surface
temperatures are a function of detail design, engine load, and engine
operating condition and have a direct impact on heat transfer
rates during compression and the early part of combustion. Incylinder
bulk flow and turbulence level induced, for example, by
swirl and squish also impact the heat transfer rate and thus the unburned
gas temperature. The influence of these heat transfer effects
May 2013 | Schiff&Hafen | Ship&Offshore SPECIAL 55