The effect of dual injection strategy on fuel distribution and combustion characteristics in ammonia/hydrogen rotary engines

Ammonia/hydrogen blended fuel is considered one of the ideal alternative fuels for engines, with significant potential for reducing greenhouse gas emissions. This study combines experimental testing and numerical simulation to systematically investigate the impact of dual injection technology on the fuel distribution and combustion characteristics of ammonia/hydrogen rotary engines. The results indicate that adopting a dual injection strategy can significantly optimize fuel distribution, enhance combustion efficiency, and reduce emissions. As the timing of the dual injection is delayed from 130 degrees CA before the top dead center (BTDC) to 175 degrees CA BTDC, the fuel uniformity within the cylinder is significantly improved, the combustion duration is slightly reduced, and combustion stability is significantly improved. In particular, when the ammonia mass fraction of the dual injection is 70 % and the injection timing occurs between 160 degrees CA and 175 degrees CA BTDC, the combustion and emission performances are enhanced. In this case, the peak pressure for Case 175-70 % reaches 1.84 MPa, an increase of 0.6 bar compared to the single injection strategy. This strategy improves the mixture uniformity of fuel and air by optimizing the timing and proportion of ammonia dual injection, shorten the combustion duration to 11.91 degrees CA, and reduces unburned fuel and nitrogen oxide emissions. Case 175-70 % resulted in a 5.2 % increase in indicated power compared to single injection. This study provides a theoretical basis for the application of ammonia/hydrogen fuel in rotary engines and offers practical guidance for developing efficient, low-emission engine technologies.