Analysis of nitrogen-oxide formation mechanisms in filtration combustion of methane–air mixtures

The kinetics of nitrogen-oxide formation under conditions of filtration combustion of lean and rich methane–air mixtures is analyzed. Intense interphase heat exchange in the wave of filtration combustion of gases leads to a drastic decrease in the gas residence time in the high-temperature region and also to a decrease in the maximum temperatures in the reaction zone. As a result, the processes of filtration combustion of gases are characterized by reduced emission index of nitrogen oxides as compared to diffusion flames. Under these conditions, the thermal mechanism does not make any significant contribution to NO formation, and the dominating channels are the NNH channels for lean mixtures and the Fenimore mechanism for rich mixtures. Nitrogen oxides in lean mixtures are mainly represented by NO and N$_2$O, whereas nitrogen-containing components HCN and NH$_3$ are typical of rich mixtures. NO decomposition in rich mixtures occurs in “afterburning” reactions with participation of HCCO, CH$_3$, and CH$_2$ radicals.