Hydrogen-atom concentrations in hydrogen/oxygen/nitrogen flames

Abstract

Flat flames of premixed hydrogen/oxygen/nitrogen have been stabilized on a low-pressure burner operating between 30 and 100 mm Hg. The flames were all fuel-rich and contained, unburned, up to 80% nitrogen. The burned-gas hydrogen-atom concentrations of nineteen such flames, with final flame temperatures in the limited range, 1000° to 1130°K, were measured. The trend of the results was found to be in agreement with that of data in the literature for flames at higher temperatures and at atmospheric pressure. Measurements have also been made of the hydrogen-atom-concentration profile through the reaction zone, on the assumption that molecular oxygen reacts in such flames only with hydrogen atoms. The values obtained downstream tend to approach quite closely to the burned-gas value obtained by a different method. The reaction-zone and burned-gas results are analyzed in terms of H 2 +OH→H 2 O+H (1) H+O 2 →OH+O (2) O+H 2 →OH+H (3) H+O 2 +M→HO 2 +M. (4) Various reactions for the fate of HO 2 are considered, and several may in fact take part. There seems, however, to be strong evidence for the participation of H+HO 2 →H 2 +O 2 (5c) and perhaps also H+HO 2 (+M)→H 2 O 2 (+M) (5i) involving, apparently, a long life for the “collision complex” H 2 O 2 * . In considering flames at higher pressures, H+H+M→H 2 +M (8) would also have to be included.