Etude de la combustion de gaz de synthèse issus d'un processus de ...

Conclusions
conditions, therefore single compression tests were also performed in the RCM
operating with and without combustion in order to identify different parameters related
with its operation, namely the heat transfer to the walls.
tel-00623090, version 1 - 13 Sep 2011
Higher pressures are obtained with methane-air mixture followed by downdraft-syngas
and lastly by updraft-syngas. These results could be endorsed to the heat of reaction of
the fuels and air to fuel ratio under stoichiometric conditions, but also to burning
velocities. Updraft and downdraft syngas compositions have similar burning velocities
in laminar conditions but the same is not found in turbulent conditions, where the
difference in peak pressure is higher by about 25%. As the turbulent burning velocity is
proportional to the laminar burning velocity, analysing the correlations for laminar
burning velocity of the typical syngas compositions developed on this work show that
the effect of pressure is very significant (coefficient β for updraft is 40% higher in
relation to downdraft syngas coefficient). The higher pressure used on RCM also
makes temperature to increase due to compression but the effect of temperature on
burning velocity for typical syngas compositions is irrelevant since the coefficient α is of
the order. Another major finding is that syngas typical compositions are characterized
by high ignition timings due to their low burning velocities.
A simulation code for the power cycle of syngas-fuelled engines has been developed,
using a quasi-dimensional model with ‘standard’ modeling assumptions. Model testing
has been carried on over detailed experimental data available in literature for hydrogen
and methane, two of the main constituents of syngas. The very good agreement found
allows validating the developed model and applied it to typical syngas compositions. An
attempt to adapt the model to the RCM is made by changing several aspects of the
model namely the in-cylinder volume function and burning rate model. The comparison
with experimental results obtained in this work in the RCM shows that the adapted
code is able to reproduce fairly well the in-cylinder pressure and that the Woschni
model works well in its original formulation and represent the heat transfer of the RCM
compression stroke.
The validated model is then applied to a syngas-fuelled engine in order determine its
performance. Conclusions can be drawn that typical syngas compositions besides its
lower heat value and burning velocities can be used on SI engines even at elevated
rotation speeds.
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