DETAILED CHEMICAL KINETICS STUDIES OF AN NH_3/N_2O/Ar FLAME BY LASER-INDUCED FLUORESCENCE, MASS SPECTROMETRY, AND MODELING

摘要

Experimental and chemical modeling studies of a 60 torr NH_3/N_2O/Ar flame were performed to provide further testing and refinements of a detailed chemical mechanism developed previously in our laboratory. This mechanism, which is denoted as VS, consists of 87 reactions and 20 species. Flame temperatures were measured with a coated, thin-wire thermocouple and by rotational analyses of OH and NH laser-induced fluorescence (LIF) spectra. Species concentration profiles of NH_3, N_2O, N_2, H_2O, NO, O_2, NH, 0, and OH were recorded using molecular beam mass spectrometry (MB/MS), LIF, or both. The experimental species concentrations were compared with those obtained with both equilibrium and PREMIX flame code calculations. The NH_3/N_2O mixture equilibrium calculations agree very well with both the PREMIX and measured postflame N_2 and H_2O concentrations but underpredict the postflame NO concentration and overpredict the O_2 concentration. The PREMIX calculations predict very well the shapes of the experimental NH_3, N_2O, N_2, H_2O, NO, OH, and NH profiles throughout the flame but do not adequately predict the shape of the O-atom profile and overpredict the O_2 concentration by ～60% at 16.25 mm, suggesting that the VS mechanism requires some refinement. A modified mechanism, VS-modified, which provides better agreement with the experimental results, is proposed. In this mechanism the rate constants of the following reactions are altered to the limit of their experimental or calculated uncertainties: (1) N_2O + H = OH + N_2, (2) NH_2 + O = HNO + H, (3) NH_2 + OH = NH + H_2O, (4) NH_2 + H = H_2 + NH, (5) NH_3 + OH = NH_2 + H_2O, and (6) NO + H + M = HNO + M.