Effect of ammonia/hydrogen dual direct injection positions on fuel distribution and combustion characteristics in a rotary engine

Ammonia and hydrogen are promising carbon-free fuels for rotary engines, but poor mixing reduces combustion efficiency and raises NOx emissions. This study employs a three-dimensional numerical model of a customized Z160F rotary engine equipped with in-cylinder dual direct injection, using an ignition-immediately-after-injection strategy with an extremely short mixing window to systematically investigate how the spatial combinations of ammonia and hydrogen injection positions affect mixture formation, combustion performance, and pollutant emissions. Results show that central hydrogen injection (near the spark plug) produces a mean peak in-cylinder pressure of approximately 1.91 MPa, 11-43% higher than non-central cases, with shorter combustion duration and lower predicted NOx formation than the H2N1 reference case. Hydrogen enrichment near the spark plug accelerates flame propagation, while the shortened high-temperature duration limits NOx formation. These findings provide guidance for optimizing dual-direct-injection arrangements in ammonia–hydrogen rotary engines under the investigated conditions.