The dependence of chemistry on the inlet equivalence ratio in vortex-flame interactions

The interaction of a vortex pair with a premixed flame serves as an important prototype for premixed turbulent combustion. In this study, we investigate the interaction of a counter-rotating vortex pair with an initially flat premixed methane flame. We compare computational solutions obtained using a time-dependent, two-dimensional adaptive low Mach number combustion algorithm that incorporates GRI-Mech 1.2 for the chemistry, thermodynamics, and transport of the chemical species. We discuss the mechanical nature of the flame-vortex interaction and the features of the interaction that are strongly affected by fuel equivalence ratio, phi. We find that the circulation around the vortex scours gas from the preheat zone in front of the flame, making the interaction sensitive to equivalence ratio. For cases with phi approximate to 1, the peak mole fraction of CH across the flame is relatively insensitive to the vortex, whereas for richer flames we observe a substantial and rapid decline in the peak CH mole fraction, commencing early in the flame-vortex interaction. The peak concentration of HCO is found to correlate, in both space and time, with the peak heat release across a broad range of equivalence ratios. The model also predicts a measurable increase in C2H2 as a result of interaction with the vortex and a marked increase in the low-temperature chemistry activity.