Performance and emission characteristics of ammonia fueled scramjet engine

Climate change and energy crisis are driving green aviation. The carbon emissions from scramjet engines cannot be overlooked in the future. Ammonia emerges as a potential alternative fuel. However, there is still a lack of sufficient research on ammonia fueled scramjets. We developed a thermodynamic model to explore the theoretical performance and emission characteristics of ammonia fueled scramjets. The combustion was calculated by chemical equilibrium. The perfectly stirred reactor model was also used to calculate NO_x emissions for comparison. Ammonia fueled scramjets have higher thrust than traditional fuels. At Ma₀ = 9, the specific thrust of ammonia is 54.5 % higher than that of hydrocarbon, but the specific impulse is only 64.3 % of hydrocarbon. The NO_x emission of ammonia in the scramjet is more complex than that of traditional engines. From thermodynamic analysis, ammonia theoretically has the lowest NO_x emission. However, considering the kinetic effects, ammonia usually has higher NO_x than other fuels. Nevertheless, as the Mach number increases, ammonia exhibits lower NO_x emissions than other fuels. In addition, hydrogen from ammonia decomposition in regenerative cooling channels can effectively enhance engine performance. To improve the specific impulse of the ammonia engine, we proposed to blend fuel and add boron. The effects of NH₃/Jet-A or NH₃/H₂ blends on engine performance present an interesting trade-off. The addition of boron greatly enhances the engine performance, especially the volume specific impulse. Overall, ammonia is a promising fuel for scramjets. It is more suitable for high-speed and high-thrust aircraft. And the higher the speed, the more obvious the advantage of ammonia in performance and emissions.