Understanding the role of ammonia combined injection in improving combustion and emissions characteristics for heavy-duty CI engine

In this study, a three-dimensional numerical simulation approach was employed to develop a dual-fuel ammonia-diesel engine model. Subsequently, the impacts of various ammonia energy fractions on engine combustion and emission performance under two injection modes were examined through a comparative analysis: PFI and DI. The results indicate that, in the PFI mode, the IMEP significantly decreased, demonstrating poorer economic performance compared to the neat diesel mode, though it exhibited superior emission characteristics. In contrast, the DI mode notably improved the economic performance, with significantly lower unburned NH3 emissions than the PFI mode. In the DI mode, when the ammonia energy fraction reached 40, the engine displayed optimal performance. Specifically, the in-cylinder fuel mixture was homogeneous, exhibiting greater TKE. The IMEP was 9.40 % higher than the neat diesel mode, at 1.081 MPa. Building upon this, under a combined injection mode, the combustion and emission processes of engine were examined in more detail, with an ammonia energy fraction of 60. Five different DI:PFI ratios (1:4, 2:3, 1:1, 3:2, and 4:1) were considered. The results showed that increasing the DI ratio improved the formation of the air-fuel mixture inside the engine, accelerated flame propagation, and enhanced the economic performance. Notably, when the DI to PFI ratio was 3:2, the IMEP reached its peak at 1.16 MPa, a 7.60 % increase compared to the DI mode. Additionally, the indicated thermal efficiency was 44.61 %, which was 6.14 % higher than the ADI-40 case.