CALCULATIONS OF NOX FORMATION PATHWAYS IN PROPAGATING LAMINAR, HIGH-PRESSURE PREMIXED CH4/AIR FLAMES

Nitric oxide formation in laminar, adiabatic, stoichiometric, premixed CH4-air flames was calculated over a range of pressures from 0.1 to 20 atmospheres. The detailed kinetics model (46 species and 212 reversible reactions) included four chemical pathways to NO formation, and the relative import- ance of 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 substantially by the presence of superequilibrium O atoms. The Fenimore mechanism also contributed substantial amounts of NO. In the postflame gases, the calculations suggested that most of the NO was formed from the Zeldovich mechanism, but the N20 intermediate mechanism became important at high pressures where it contributed as much as 10% of the postflame NO. Experimental measurements of superequilibrium radical concentrations and flamefront NO formation are clearly essential to confirm the suggested import- ance of superequilibrium (O) concentrations and the N2O mechanism for NO formation in high pressure flames. © 1991, Taylor & Francis Group, LLC. All rights reserved.