The structure of the reaction zones of ammonia-oxygen and hydrazine-decomposition flames

The reaction zones of 40%, 57%, and 65% ammonia-oxygen flames have been investigated at 20 mm Hg on an 8-cm-diameter burner. Mass-spectrometric analyses, employing a specially designed dynamic sampling system, yielded concentration profiles of NO, H2O, N2, NH3, H2, and N2O in the reaction zones. Optical spectrophotometric analyses gave OH-concentration and NH-absorption profiles as well as emission profiles of the excited species NH2, NO, NH, and OH. Temperature profiles were measured with thermocouples, by sodium-line reversal or by means of the OH-rotation spectra. End products of the reaction were, in order of importance, H2O, N2, H2, and NO. The H2 concentration passed through a maximum in lean and near-stoichiometric flames, but did not react further in ammonia-rich flames. Maximum NO concentrations of about 4 mole per cent were found in 40% and 57% flames, whereas only 0.5 mole per cent appeared in the 65% flame, and this decayed slowly but completely. Intermediate products measured were N2O, OH, and NH. N2O appeared early in the reaction zone, ran through a maximum of approximately 1 mole per cent just beyond the middle of the zone, and then disappeared completely. OH concentrations of up to 2.3 mole per cent were found in the middle of the reaction zones of 40% and 57% flames, but only 0.22 mole per cent appeared in ammonia-rich flames. Up to 30% absorption was measured for NH in ammonia-rich flames. Maximum temperatures of 2200°K were observed in near-stoichiometric flames. Hydrazine-decomposition flames were studied at a pressure of 14 mm Hg. Concentration profiles for N2H4, N2, H2, and NH3 were measured. The initial temperature of the N2H4 vapor had little effect on the profiles. A small but distinct maximum was observed in every NH3 curve near the end of the reaction zone. The implications of this data for the reaction kinetics is discussed.