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

Chapter 5
TDC 1.25 ms 2.5 ms 3.75 ms 5.0 ms
6.25 ms 7.5 ms 8.75 ms 10.0 ms 11.25 ms
12.5 ms 13.75 ms 15.0 ms 16.25 ms 17.5 ms
(a)
tel-00623090, version 1 - 13 Sep 2011
-12.5 ms -11.25 ms -10.0 ms -8.75 ms -7.5 ms
-6.25 ms -5.0 ms -3.75 ms -2.5 ms -1.25 ms
TDC 1.25 ms 2.5 ms 3.75 ms 5.0 ms
6.25 ms 7.5 ms 8.25 ms 10.0 ms
(b)
Figure 5.12 –Direct visualization of stoichiometric updraft syngas-air mixtures combustion in a
RCM. (a) Ignition at TDC; (b) ignition at 12.5 ms BTDC.
When the ignition is made at TDC the combustion occurs at constant volume, in the
clearance volume. Direct visualizations show an explosion with fast and turbulent flame
propagation with combustion duration of about 17.5 ms. In opposite, the initial phase of
combustion shows a quasi-spherical relatively smooth flame kernel specially for ignition
timing of 12.5 ms BTDC. The flame kernel propagation is laminar and at some point
experience flattening due to piston movement reaching the TDC. After that, a change
to constant volume combustion occurs. The whole combustion duration is around 22.5
ms, a remarkable increase compared with the full constant volume combustion. This is
due to the deviation from TDC ignition that allows lower initial pressure and
temperature for combustion in the compression stroke, lower turbulence intensity as
seen in 3.2.5 and higher heat transfer areas.
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