CIMAC Congress - Schiff & Hafen

CIMAC CONGRESS | BERGEN 2010
between Particulate Matter (PM) and NOx. The paper will first tell
about previous studies in Helsinki University of Technology TKK and
emission reduction in a standard heavy duty diesel engine. Then the
studies in a corresponding single-cylinder research engine “EVE” will
be presented. In the single-cylinder EVE engine advanced cycles like
Miller cycle and interrnal exhaust gas recirculation (EGR) have been
studied. Also the possible benefits of blending oxygenates with the
fuels have been considered. The first part of the paper concentrates
on high cetane number paraffinic diesel fuels and their oxygenate
blends: previous studies on their properties and effect on engine
emissions. The second part describes the ongoing research in Aalto
University School of Science and Technology (previously TKK,
Helsinki University of Technology). In the studies, potential for
emission reduction has been estimated to be 70% or more and
promising preliminary results have been reached in the first test runs.
This study is part of “ReFuel”–project, which is an IEA collaborative
task of IEA Combustion Agreement program and a collaboration
framework between IEA Combustion Agreement and IEA AMF
(Advance Motor Fuels) Agreement.
EMI MIN – a government funded research
program to reduce emissions
U. Schlemmer-Kelling, S. Watzek, Caterpillar
Motoren GmbH & Co. KG, Germany
There is an ongoing worldwide legislative trend to reduce the
emissions of medium speed diesel engines [1]. For this reason, a
joint research program was established in 2002. Partners of the socalled
EMI MINI program were AVL Germany, L’Orange, University
of Rostock, WTZ and Caterpillar Motoren. The program was funded
by the German Ministry of Economics. The development target was
to reduce the emission of diesel engines by 50% without using aftertreatment
solutions. Meanwhile, the second phase of this program
(EMI MINI II) is nearly finished. The team worked to define the
strategy [2] and the final solution was demonstrated on a multicylinder,
turbocharged 6 M 32C engine in Kiel. Using the strategy,
Caterpillar Motoren was able to reach the emissions target by tuning
the combustion process. The fuel and air systems were modified to
reduce NOx and soot emission for both steady state and transient
operation. The major building blocks of the concept were a common
rail fuel system which was able to operate under heavy fuel conditions
and a flexible valve drive which allowed the Miller cycle to be turned
on and off. A DoE tool was used to find the optimal settings for the
injection system at each load point. With the strategy, a 50 % NOx
reduction was achieved with invisible soot emission. However, a
slight loss in fuel efficiency was also measured. A two-stage turbo
charging system could be used to improve efficiency, but this was not
within the program scope and was not tested. The simulation results
have shown that the target of constant fuel efficiency can be achieved
with the addition of two-stage turbo charging.
10:30 June 17th Room Troldtog
(2–4) Fundamental Engineering –
Piston Engines – Thermodynamics
Advanced heat transfer modelling with
application to CI engine CFD simulations
M. Nuutinen, O. Kaario, M. Larmi, Aalto
University School of Science and Technology,
Finland
The purpose of the work is to implement and further develop an
advanced wall function formalism in conjunction with a modified
low Reynolds number turbulence model in Star-CD, a CFD
software suitable for in-cylinder flow and conjugate heat transfer
simulations. This advanced method has already been demonstrated
to give predictions superior to standard methods when compared
to measured heat transfer values and DNS data in strongly heated
compressible flows, Nuutinen et al. [1]. Besides superior accuracy,
the advanced method has a desirable feature of being free from
the near wall grid resolution restrictions associated with the low
and high Reynolds number turbulence models. The acquired
computational tool is then used to simulate conjugate heat
transfer in realistic compression ignition (CI) engines. The
manufacturers of large CI engines are striving for increasing
cylinder pressures which in turn results in elevated heat transfer
rates and surface temperatures. As a consequence, accurate heat
transfer simulation is becoming increasingly important. With the
new computational tool it is possible to obtain more accurate
results on heat transfer that can be utilized in engineering
processes, e.g., in material choices and geometry design. In
addition to improving the overall accuracy of simulations (energy
balance) the more accurate temperature and heat flux predictions
may be further utilized, e.g., to simulate thermal stresses in solid
engine parts and heat transfer to the coolant.
Piston surface heat transfer during
combustion in large marine diesel engines
M. V. Jensen, J. H. Walther, Technical University
of Denmark, Denmark
In the design process of large marine diesel engines information
on the maximum heat load on the piston surface experienced
during the engine cycle is an important parameter. The peak heat
load occurs during combustion when hot combustion products
impinge on the piston surface. Although the maximum heat
load is only present for a short time of the total engine cycle, it
is a severe thermal load on the piston surface. At the same time,
cooling of the piston crown is generally more complicated than
cooling of the other components of the combustion chamber.
This can occasionally cause problems with burning off piston
surface material. In this work the peak heat load on the piston
surface of large marine diesel engines during combustion was
investigated. Measurements of the instantaneous surface
temperature and surface heat flux on pistons in large marine
engines are difficult due to expensive instrumentation and high
engine running costs compared to automotive engines. Therefore
the investigation in this work was carried out numerically with
the use of a computational fluid dynamics (CFD) code. At the
same time, numerical work on detailed in-cylinder wall heat
transfer in engines has been quite limited. The numerical
investigation focused on the simulation of a hot turbulent gas
jet impinging on a wall under very high pressure, thus
approximating the process of the actual impingement of hot
combustion gasses on the piston surface during combustion.
The surface heat flux at the wall was calculated under different
conditions in the numerical setup in order to obtain information
of the actual peak heat flux experienced at the piston in large
marine diesel engines during combustion. The variation of
physical parameters influencing the heat transfer during
combustion included a variationof pressure, temperatures, jet
velocity and jet turbulence intensity. The variation in heat flux
predictions resulting from application of different turbulence
models was also investigated by performing calculations with
three different models: the V2F model, a k-ε RNG model and a
low-Re k-ε model. The obtained results indicate peak heat fluxes
in the order of 5−10MW/m 2 on the piston surface during the
combustion phase of the engine cycle.
92 Ship & Offshore | 2010 | No. 3