Progressive compound injection strategies to combustion improvement and pollutants reduction of an ammonia/hydrogen net-zero rotary engine

The adaptation of fixed/variable ratio compound injection technology and the application of ammonia-hydrogen zero-carbon fuels are key technical paths for high-efficiency and clean rotary engines to break through combustion bottlenecks and support the dual-carbon goals. Ammonia has become an important alternative to fossil fuels due to its full-life-cycle zero-carbon advantage, while hydrogen compensates for ammonia’s ignition delay defect with its high combustion rate and wide flammability limit. Taking gasoline rotary engine as the research object, this study established a CONVERGE multi-physics coupling simulation model, combined with the RNG κ-ε turbulence model and the SAGE detailed chemical reaction kinetics model. The influence of injection strategy on mixture preparation, combustion development, and pollutant formation was examined from two aspects, namely fixed-ratio operation and variable-ratio operation. The former mainly involves the direct injection share and split injection pattern, whereas the latter is characterized by fuel distribution ratio and split injection mode. The results show that, in the fixed-ratio case, maintaining the direct injection proportion within 20%–80% provides a balanced optimization of combustion efficiency and NO x emissions. Furthermore, emission control can be enhanced by split injection: the two-split mode is more favorable for lowering unburned NH 3 , while the three-split mode is more effective in restraining thermal NO x generation. In variable ratio injection, increasing the hydrogen direct injection ratio can improve the indicated thermal efficiency, with H40A60 being the transition operating condition for combustion characteristics; At H40A60, three-split injection maintains a similar ITE and reduces N 2 O emissions relative to continuous injection, although NO x emissions increase. This study clarifies the injection technology adaptation law and combustion control mechanism of ammonia-hydrogen rotary engines, providing theoretical reference for the in-depth integration of zero-carbon fuels with rotary engines and the optimization of injection systems.