ASPECTS OF THE STRUCTURE AND EXTINCTION OF DIFFUSION FLAMES IN METHANE OXYGEN NITROGEN SYSTEMS

Methods for simplifying descriptions of methane diffusion flames, with detailed chemical kinetics taken into account, are identified and compared with respect to their predictions of flame structure and of extinction conditions. Attention is focused on methane-air flames, both with and without nitrogen dilution, at atmospheric pressure and with reactants at temperatures near room temperature. Deficiencies are noted in earlier schemes for simplification on the basis of concepts of asymptotic analysis. Methods for correcting these deficiencies are discussed, and influences of selection of different sets of data for elementary rate constants are evaluated. Tradeoffs between fidelity and complexity of descriptions are addressed. It is shown that extinction is a more severe discriminant than structure (as measured by zone arrangement, major species, and temperature) in the evaluation of alternatives. A relatively simple procedure is identified that yields results in reasonable agreement with experiment concerning flame structure, but extinction predictions remain in sufficient disagreement to motivate further study along avenues identified here. © 1990.