Detailed Kinetic Modelling of Chemistry and Temperature Effects on Ammonia Oxidation

Abstract

An extensive set offlat laminar premixedNH3/H2/O2,NH3,/NO/H2/O2 and NH3O2 flames have been investigated by detailed chemical kinetic modelling to facilitate the construction of a reaction mechanism capable of satisfactory predictions for a wide range of flames. Available information for the rate coefficients of all the reactions in the detailed mechanism has been reviewed. An extensive sensitivity analysis has been performed to distinguish the reactions of greatest importance to the formation and destruction of nitric oxide. The relative significance of the different NO formation channels is found to depend entirely on the flame conditions: (i) for all flames the reaction of NH2 with the O radical is found to be significant; (ii) in pure ammonia flames the reaction of the NH radical with OH becomes important; (iii) in hydrogen flames with ammonia and ammonia with nitric oxide dopants the Zel'dovich mechanism becomes increasingly significant with increasing fuel concentrations. The conversion of NO to N2 is dominated by reactions involving the NH2 and N radicals with NH providing a secondary path. In pure ammonia and doped lean hydrogen flames the reaction of NO with NH2 becomes the major NO conversion path. In doped stoichiometric and rich hydrogen flames the reaction of NO with N is dominant.