Hydrocarbon/nitric oxide interactions in low-pressure flames

Abstract

We have studied a low-pressure (25 Torr), rich, H2/O2 — Ar flame and added to it various combinations of C2H2, HCN, and NO. Our objective is to investigate interactions between the hydrocarbon and nitrogen chemistry in flames, particularly the kinetics of the “recycle” mechanism that produces hydrogen cyanide from nitric oxide. Major stable species concentrations are determined by mass spectrometric techniques, and relative CN and CH concentrations and temperature are measured by laser-induced fluorescence. The experimental results are analyzed by comparing them to complete flame structure computations. The kinetic model is discussed in some detail. The flame model predicts, accurately the NO removal, the intermediate production of HCN and CN, and the eventual production of N2 observed in the flames to which NO and C2H2 are added. Formal sensitivity analysis is used to help identify the most important kinetic steps. The analysis indicates that in these flames NO is converted to cyanides primarily by reaction with C and CH; reaction with CH2 is somewhat less important. The HCN produced in these flames is converted to N2 by the mechanism described previously by Miller, et al. (Twentieth Combustion Symposium).