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

Laser-induced fluorescence is used to monitor the relative concentrations of the species OH, CH, NH, CN, NCO, and NO in a 10-torr premixed stoichiometric 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 accepted reaction rates. This procedure allows the chemical pathways followed by the different dopants to be compared under nearly identical conditions. Comparison of radical concentrations between the NO- and N2O-doped flames shows that CN and NCO are underpredicted for the N2O-doped flame, while NO is overpredicted. Conversely, NH is underpredicted for the NO-doped flame. These findings suggest that reburn consumption of NO is roughly 50% higher than predicted by current models. Nevertheless, the fraction of NO that reacts with hydrocarbon radicals in the reburn reactions is found to be fairly minor (less-than-or-equal-to 20%). Under the present conditions, NO2 is rapidly converted to NO, leading to quantitatively similar behavior for these two dopants.