Parametric analysis of ammonia as a drag reducer in the scramjet combustor

Using ammonia film in the boundary layer for combustion to reduce drag in scramjet engines is an emerging clean energy technology. As a drag reducer, the effects of ammonia inlet parameters on engine performance differ from traditional fuels. Beyond drag reduction, ammonia also has more complex effects on the engine. Therefore, this paper employs a validated numerical model to parametrically investigate the effects of ammonia inlet decomposition ratio and injection thickness on drag reduction, cooling, combustion, and NO emissions characteristics. The results show that changes in inlet parameters affect momentum, energy, and species transport near the wall. Thinner injection thicknesses or higher inlet decomposition ratios enhance cooling performance and reduce NO emissions. However, thicker injection thickness is more beneficial for drag reduction. A moderate inlet decomposition ratio is optimal for drag reduction. The optimal total drag reduction efficiency is 47.6 %. The optimal wall average temperature reduction efficiency reaches 43.3 %. The maximum differences in drag reduction effect, cooling effect and NO emissions among different injection strategies are >2 times, 1.5 times and 6.5 times, respectively. This research contributes to scramjet performance improvements and emissions reduction.