The formation of NOx from nitrogen containing materials in diffusion flames

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Abstract
The conversion of fuel‐N species to NOx in diffusion flames has been studied by adding acetonitrile to the fuel flow for a methane–Oxygen–argon diffusion flame burning in excess oxygen. It is shown that the conversion is significantly lower than that obtained in a ‘corresponding’ pre‐mixed flame, although the observed concentrations of NOx are still much higher than the appropriate thermodynamic equilibrium concentrations. The effect of initial concentration of acetonitrile, flame temperature and amount of excess oxygen on the conversion can all be explained in terms of the basic structure of a diffusion flame. This enables molecular nitrogen to be formed in the reducing atmosphere which exists on the fuel side of the flame through reaction of cyanide radicals with nitric oxide. The latter diffuses back from the oxygen side of the flame where it is formed, but the overall result is that a proportion of the fuel‐N is converted to molecular nitrogen before it can be converted to nitric oxide.