Modelling of ammonia combustion characteristics at preheating combustion: NO formation analysis

In order to improve the combustion characteristics and flame stability of NH3-air flame, preheating the reactants at different temperature was proposed in this study. We focused on the formation of NO at NH3 preheated combustion because NH3 is a typical fuel-nitrogen. The NO formation characteristics of premixed NH3-air mixtures at various preheating temperatures of the reactants were numerically analysed. The Miller and Bowman mechanism was applied in the numerically calculation of all species. The results show that the formation reaction rates of thermal NO from N + O-2 -> NO + O, and N + OH -> NO + H increase with the increase of preheating temperatures of the reactants at fuel lean condition. Higher decomposition reaction rate of N + NO -> N-2 + O at stoichiometric condition finally results in a lower formation of NO comparing to that at fuel lean condition. At fuel rich condition, the reactions of NH2 + NO -> N-2 + H2O, NH + NO -> NNH + OH have grate effect on the decomposition of NO at all preheating temperatures of the reactants, which results in an extremely low formation of NO, showing a potential for reducing NO formation in NH3 combustion.