COMPARATIVE SPECIES CONCENTRATIONS IN CH4 O2/AR FLAMES DOPED WITH N2O, NO, AND NO2/

Laser-induced fluorescence is used to monitor the relative concentrati ons of the species OH, CH, NH, CN, NCO, and NO in a 10-torr premixed s toichiometric methane/oxygen/argon flame dope with N2O, NO, and NO2 at 0.0086 mole fraction. The relative yields of combustion intermediates for equivalent mole fractions of the different dopants are measured, and comparisons are made with PREMIX calculations based on currently a ccepted reaction rates. This procedure allows the chemical pathways fo llowed by the different dopants to be compared under nearly identical conditions. Comparison of radical concentrations between the NO- and N 2O-doped flames shows that CN and NCO are underpredicted for the N2O-d oped flame, while NO is overpredicted. Conversely, NH is underpredicte d for the NO-doped flame. These findings suggest that reburn consumpti on of NO is roughly 50% higher than predicted by current models. Never theless, the fraction of NO that reacts with hydrocarbon radicals in t he reburn reactions is found to be fairly minor (less-than-or-equal-to 20%). Under the present conditions, NO2 is rapidly converted to NO, l eading to quantitatively similar behavior for these two dopants.