Parametric study of nitrogen oxide formation during combustion of uniform methane–air mixtures

With a model for the propagation of normal flame fronts in methane–air mixtures as an example, estimates are made of the contribution of various NO$_x$ formation mechanisms with varying pressure, temperature, and mixture composition. During combustion of near stoichiometric mixtures, the thermal mechanism is found to predominate, while in lean mixtures, the N$_2$O mechanism predominates and in rich mixtures, the “prompt” mechanism. These results are compared with a direct solution of the kinetic problem and it is shown that this simpler model provides a satisfactory description of NO$_x$ formation in lean and nearly stoichiometric flames.