Numerical study of the effect of NH3 addition on CH4/air combustion characteristics under gas turbine operating conditions

NH3 has recently gained attention as a carbon neutrality fuel and an energy carrier for H-2 or a carbon-free alternative fuel, which has led to renewed interest in studying the combustion characteristics of NH3/CH4/air mixtures. This is crucial for the development of gas turbine combustion chambers for ammonia/methane fuel. Therefore, this study investigated the effects of different NH3 additions on the laminar premix combustion characteristics of CH4/air flame, including laminar combustion velocity, ignition delay time, four important free radicals and NO emission. The results revealed that the increase in ammonia content led to an increase in NH2 free radical content, which, in turn, reduced the concentrations of H, O, and OH free radicals, thus contributing to the decrease in laminar burning velocity. Through quantitative analysis, it is found that the laminar combustion velocity is positively correlated with max(H + O + OH), and the laminar combustion velocity is linearly correlated with the ignition delay time. HNO pathway is the most significant pathway for NO production during ammonia combustion, and N2H2 intermediate pathway has the least effect on NO production.