Effect of Stoichiometry and Strain Rate on Transient Flame Response

The interaction of a premixed methane/air flame with a counter-rotating vortex pair is analyzed using a parallel low-Mach-number computational model that is based on a detailed C1C2 chemical mechanism. Attention is focused on the transient response of the heat release rate and the flame structure at the centerline of the vortex pair. Results are obtained for vortex pairs of different strengths under lean, stoichiometric, and rich conditions. For the range of vortex strengths considered, the computations indicate that the heat release rate in the rich flame decays significantly faster than in the stoichiometric flame; this behavior is consistent with recent experimental measurements. Meanwhile, the heat release rate in the lean flame decays at a slightly slower rate than in the stoichiometric flame. The transient response of flame radicals such as H, CH, OH, and HCO is also analyzed. The analysis reveals a complex nonlinear dependence of the transient structure on both the vortex strength and the stoichiometry.