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

Numerical simulation of a syngas-fuelled engine
6.3.2 RCM
As shown in chapter 5, RCM simulates a single engine cycle and some adaptations to
the model presented above are needed in order to take into account the dynamic and
geometrical specificness of the RCM. Three main aspects should be considered, the
instantaneous volume, heat transfer and burning rate. Two distinctive cases are
considered in the code: single compression, and compression and expansion strokes.
6.3.2.1 Flame propagation
tel-00623090, version 1 - 13 Sep 2011
The flame development in the combustion chamber of a RCM was shown above for the
compression and expansion strokes. In order two verify the assumption frequently used
for engine combustion models, where the flame area is a spherical flame front
truncated by the cylinder walls and the piston, centered at the spark plug adopted in
this work, the flame images are used in an image treatment Matlab code developed by
Strozzi, (2008), which allows visualizing the flame contours.
Figures 6.5 show the flame contours in a RCM combustion chamber for downdraft
syngas-air stoichiometric mixture. The window has 613×337 pixels with resolution of
2.835 pixels/mm. The frequency of the each contour is kept to 1.4 KHz.
Figure 6.5 - RCM flame contours of stoichiometric downdraft syngas-air mixture with ignition at
12.5 ms BTDC.
The earlier stage of flame kernel with influence of the spark plug was removed from the
contours due to lack of definition. After around 5.0 ms (the duration of the spark), the
flame contours are well defined and shows that the propagation is spherical. At this
moment the piston is reaching TDC and the flame shows a remarkable slow down due
to piston deadening, which is felt on the pressure signal by a decreasing gradient. After
TDC, the flame contour shows to near double the displacement due to expansion.
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