Radical species profiles in low-pressure methane flames containing fuel nitrogen compounds

Abstract

Relative concentration profiles of CN, NH, NCO, NH 2, and NO are recorded for a 10 torr, premixed CH 4/O 2/Ar flame doped with the following compounds: 0.35% NH 3, CH 3NH 2, and CH 3CN, and 0.86% NO. Profiles were measured by laser-induced fluorescence and compared between the different dopants. The experimental data are compared to detailed kinetic calculations based on the Gas Research Institute Mechanism 2.11 for the NH 3 and NO dopants, with added submechanisms for CH 3CH and CH 3NH 2. The kinetic model underpredicts the amount of CN and NCO formed from the ammonia dopant; if we postulate a reaction between CH 3 and NH, these discrepancies are largely resolved. Comparison of CN and NCO profiles between the NO and NH 3 dopants indicates that HCN is the primary product of the CH + NO reaction. Extrapolation of measured rates for CH 3CN destruction reactions to combustion temperatures predicts a rate of CH 3CN removal which is far too slow. Previously published mechanisms for methylamine combustion overpredict the amount of NH 2 produced, indicating that cleavage of the CN bond is less likely in the initial attack than the kinetic mechanisms predict. We propose modifications to the CH 3CN and CH 3NH 2 submechanisms which correct these deficiencies and lead to good agreement with the measured intermediate profiles for all dopants.