Experimental and chemical kinetic study on the flame propagation characteristics of ammonia/hydrogen/air mixtures

Carbon-free hydrogen and ammonia have their own drawbacks when used alone. The composite fuel system formed by the combination of hydrogen and ammonia can not only solve the current energy demand and environmental pollution problems, but also effectively overcome the shortcomings of pure fuel application. Laminar flames are the basis for the study of other flame forms. In this paper, the laminar combustion characteristics of hydrogen/ammonia/air mixture were studied in a constant volume combustor. The initial pressures range from 0.5 to 1.5 atm, the equivalence ratios range 0.5 to 1.5, and the hydrogen ratios range from 0 to 1.0. The laminar burning velocity increases monotonously with the increase of hydrogen ratio, while presents an inverted U-shaped relationship with the equivalence ratio. Compared with the hydrogen ratio and the equivalence ratio, the initial pressure has the weakest effect on the laminar burning velocity of hydrogen/ammonia/air mixture. The laminar burning velocity gradually decreases with the initial pressure. This paper also gives an empirical exponential fitting equation for the laminar burning velocity of hydrogen/ammonia/air mixtures, which can well predict the laminar burning velocity of the mixed gas under various equivalence ratios (0.8–1.2) and various hydrogen ratios (0–1.0) at atmospheric pressure. The influence of fuel composition on the laminar burning velocity should be the result of the combined effect of thermal diffusivity and mass diffusivity. The important fuel consumption pathways R3 and R4 generate more key radicals with increasing hydrogen ratio, thereby promoting the combustion process.