Calculations of NOx Formation Pathways in Propagating Laminar, High Pressure Premixed CH4/Air Flames

Abstract

Nitric oxide formation in laminar, adiabatic, stoichiometric. premixed CH4-air flames wascalculated over a range of pressures from 0.1 to 20 atmospheres. The detailed kinetics model (46 speciesand 212 reversible reactions) included four chemical pathways to NO formation, and the relative importanceof these pathways was found to vary with pressure and with position in the flame. In the flamefront,the rates of the Zeldovich mechanism and the N20 intermediate mechanism were increased substantiallyby the presence of superequilibrium °atoms. The Fenimore mechanism also contributed substantialamounts of NO. In the postflame gases, the calculations suggested that most of the NO was formed fromthe Zeldovich mechanism, but the N20 intermediate mechanism became important at high pressures whereit contributed as much as 10% of the postflame NO. Experimental measurements of superequilibriumradical concentrations and ffamefront NO formation are clearly essential to confirm the suggested importanceof superequilibrium (0) concentrations and the N20 mechanism for NO formation in high pressureflames.