Premixed flat flames of acetylene-nitrous oxide were stabilized on a perforated, water cooled burner, 3 in. in diameter. A rich flame (C2H2: 27%, N20: 73%) was stabilized at 20 mm Hg and a lean flame (C2H2: 9%, N20:91%) at 45 mm Hg. Temperature profiles and concentration profiles of free radicals and of stable products of reaction were determined in the reaction and postreaction zones using spectroscopic techniques. NO, CN. NH, C.,, CH, and OH were measured by absorption using single rotational lines of their molecular spectra in the visible or uv regions. H20 and CO2 were measured using the integrated emission intensities of their infrared spectra.
Results indicated that the combustion of acetylene-nitrous oxide flames occurs in two steps: decomposition of nitrous oxide into O2, N2, and NO followed by combustion of acetylene with oxygen. The presence of NO is responsible for the reactions C2(a TIu) + NO--'CN(B 2~; ") + CO. CH(X"I I) + NO-'NH(A ~H) + CO. These reactions are extremely fast so that NO acts as a free radical ~avenger for C2 and CH in this reaction system. This permits estimating the total amount of C2 produced in the combustion process from the analysis of the C2 and NO profiles. In the rich C2Hz-NO flame it was found that at least 13% of acetylene is reacting via C2 radicals. In the lean flame C2 was too small to be measured and no estimation of the percent conversion of C2H2 into C, could be made.
I. INTRODUCTION
Although the acetylene-nitrous oxide flame is widely used in analytical flame spectroscopy, its properties have been little investigated. Previous workers in this area have generally dealt with physical characteristics, emission spectra, and flame structure [1][2][3][4][5]. With only one exception [6], little attempt has been made to measure the concentrations of intermediates observed in C2H2-N20 flames (e.g. NH, CN, OH, CH, C2) or to speculate on their origins and subsequent reactions.
The purpose of the present work is to gain some understanding of the reaction mechanism of the C2H2-N20 flames. Concentration profiles in the reaction zone and in the burnt gases of fiat flames