Computed structure of low strain rate partially premixed CH4/air counterflow flames:: Implications for NO formation

Results from computations of low strain rate, partially premixed methane/air counterflow flames are reported. The Oppdif computer code was used with GRI-Mech 2.11 to obtain the results. When the fuel-side equivalence ratio (Phi(B)) is above 2.5, the present flame structure can be described as a CH4/air premixed flame merged with a CO/H-2/air nonpremixed flame. When Phi(B) is below 2.5, the two flame zones exist on opposite sides of the stagnation plane, and the CO/H-2/air nonpremixed flame is characterized by hydrocarbon concentration peaks on its fuel-side edge. Broad NO destruction regions, caused primarily by CHi + NO reactions, exist between the resulting double hydrocarbon concentration peaks. The fuel-side equivalence ratio is the most important indicator of how rapidly NO is destroyed relative to how rapidly it is formed, and NO destruction reactions are more important in pure diffusion flames than in partially premixed flames for the present low strain rate computations. (C) 1998 by The Combustion Institute.