Combustion and emission characteristics of ammonia–diesel and ammonia–PODE dual fuel engines with multi-time ignition mixed-mode combustion (MIMC) mode

Ammonia dual fuel mode holds promise for enhancing ammonia combustion. In this study, differences in combustion and emission characteristics between ammonia–diesel and ammonia–PODE modes were investigated using multi-time ignition mixed-mode combustion (MIMC) mode. Firstly, the effects of single injection and MIMC modes were compared. Moreover, the effects of outer-inner, inner-outer and outer-inner-outer strategies within MIMC mode were explored. The results demonstrated that MIMC mode has substantial potential to achieve higher indicated thermal efficiency (ITE), lower N2O, NH3 and particle emissions, shorter combustion duration, but increased NOx, CO and THC emissions. In outer-inner strategy, increasing first injection energy ratio (ER1) resulted in different combustion behaviors in AD and AP modes. ITE initially increased and subsequently decreased with increasing ER1. For inner-outer strategy, NOx and NH3 emissions decreased with increasing second injection energy ratio (ER2), while N2O emissions initially increased and then decreased. In outer-inner-outer strategy, NOx and NH3 emissions were lower than those in outer-inner strategy. ITE and maximum apparent pressure rise rate in outer-inner-outer strategy were slightly lower compared to outer-inner strategy, indicating that multi-time multi-zone induced ignition strategy in MIMC mode shows significant potential for enhancing ammonia combustion performance and reducing pollutant emissions.