Flame Structure Studies of Neat and NH3-Doped Low-Pressure H2/N2O/Ar Flames by Molecular Beam Mass Spectroscopy.

An experimental and chemical modeling study of neat and NH3-doped H2N2OAr flames is conducted in order to understand the fundamental mechanism for NO formation and destruction and to predict the efficacy of NH3 on the rate of conversion of NO to N2. Species concentration and temperature profiles are measured with molecular-beam-mass spectrometer and thin-wire thermocouple, respectively. Species profiled include H2,N2O, NH3, N2, NO, and Ar. The experimental mole fractions are compared to both equilibrium and one-dimensional premixed laminar flame code PREMIX calculations. The PREMIX code employs a chemical mechanism consisting of 87 reactions and 20 species with rate constants obtained from a critical literature review. Equilibrium calculations are in very good agreement with both experimental and PREMIX calculations for N2O, N2, and H2O in the postflame region of both neat and doped flames, but underpredict the H2and NO mole fractions. The PREMIX profiles of the majority species agree very well with the experiment for the neat flame and reasonably well for the doped flame. A 55 reduction in the NO mole fraction for 4 dopant is predicted in the post-flame region, in good agreement with that observed experimentally. The flame calculations overpredict, however, the NH3 mole fractions in the post-flame region, suggesting that refinements in the model are necessary. Rate and sensitivity analyses reveal that the decrease in NO mole fraction results from less NO formation by the reactions involving N2OH and more of its consumption to N2 by reactions involving NONH2.