Flow and combustion process investigation of a hydrogen-ammonia rotary engine under ammonia premixed plus hydrogen direct injection mode

The development of zero-carbon fuel engines is crucial for the transportation industry to achieve carbon reduction goals. Hydrogen and ammonia-fueled engine power systems are becoming attractive research directions since their perfectly complementary combustion characteristics. Thus, a hydrogen-ammonia dual-fuel combustion means for rotary engines is proposed, and a numerical model based on parametric modeling and chemical reaction kinetics characterization is established. Then, the influence of the hydrogen energy ratio (HER), ranging from 5 % to 45 %, on mixture formation and combustion processes of the hydrogen-ammonia engine under the ammonia premixed plus hydrogen direct-injection mode is investigated. Results show that the hydrogen combustion-enhanced effect on ammonia is obvious with HER increases, however, when HER is less than 5 %, an ignition failure phenomenon is observed. As HER increases, the combustion performance improves with higher fuel utilization rate and fast heat release. At ignition timing, a higher HER will lead to more hydrogen concentration near the spark plug, which can reduce flame quench probability due to high ammonia concentrations. Blending hydrogen is a promising combustion enhancement means for ammonia combustion, and suggests designing HER higher than 35 % for parametric applications, whose peak pressure and fuel utilization rate are higher than 5.5 MPa and 97 %, respectively.