RADICAL SPECIES PROFILES IN LOW-PRESSURE METHANE FLAMES CONTAINING FUEL NITROGEN-COMPOUNDS

Relative concentration profiles of CN, NH, NCO, NH2, and NO are record ed for a 10 torr, premixed CH4/O-2/Ar flame doped with the following c ompounds: 0.35% NH3, CH3NH2, and CH3CN, and 0.86% NO. Profiles were me asured by laser-induced fluorescence and compared between the differen t dopants. The experimental data are compared to detailed kinetic calc ulations based on the Gas Research Institute mechanism 2.11 for the NH 3 and NO dopants, with added submechanisms for CH3CH and CH3NH2. The k inetic model underpredicts the amount of CN and NCO formed from the am monia dopant; if we postulate a reaction between CH3 and NH, these dis crepancies are largely resolved. Comparison of CN and NCO profiles bet ween the NO and NH, dopants indicates that HCN is the primary product of the CH + NO reaction. Extrapolation of measured rates for CH3CN des truction reactions to combustion temperatures predicts a rate of CH3CN removal which is far too slow. Previously published mechanisms for me thylamine combustion overpredict the amount of NH2 produced, indicatin g that cleavage of the C-N bond is less likely in the initial attack t han the kinetic mechanisms predict. We propose modifications to the CH 3CN and CH3NH2 submechanisms which correct these deficiencies and lead to good agreement with the measured intermediate profiles for all dop ants. (C) 1997 by The Combustion Institute.