INFLUENCES OF FLAME-VORTEX INTERACTIONS ON FORMATION OF OXIDES OF NITROGEN IN CURVED METHANE-AIR DIFFUSION FLAMELETS

Previous work has identified a parabolic flamelet in a uniform flow as a useful model for studying flame-vortex interactions and has present ed an asymptotic analysis of this flamelet structure for two-step redu ced chemistry of the methane-air system. The present paper addresses p roduction rates of oxides of nitrogen in this flamelet by one-step red uced-chemistry descriptions of both thermal and prompt mechanisms, for both two-step and three-step methane-air reduced chemistry, and also reports some results of calculations of production rates with a full-c hemistry description of planar counterflow flames, for purposes of com parison. The comparisons suggest that the asymptotic approximations si gnificantly overestimate production rates and fail as extinction is ap proached but give qualitatively correct trends away from extinction. T hese trends show that increasing the tip curvature of the flamelet inc reases the prompt contribution while decreasing the thermal contributi on. It is concluded that more research is needed on both elementary ra tes and asymptotic descriptions, especially for the prompt mechanism.