Combustion and emission characteristics for an ammonia engine based on the reactivity-controlled turbulent jet ignition (RCTJI)

The regulation of pre-chamber (PC) mixture reactivity controls the formation and development of the jet flame, subsequently affecting the combustion process in the main combustion chamber (MC) of the ammonia (NH3) engine. In this study, a reactivity-controlled turbulent jet ignition (RCTJI) mode with hydrogen-enhanced combustion was performed to achieve the different PC mixture reactivities and produce the jet with varying performances, which involves three types of PC systems, including Active PC, Scavenging PC, and Double scavenging PC. The PC fuel reactivity factor coefficient, RPC, was defined to evaluate the PC fuel reactivity quantitatively, and the effects of the key engine parameters on the PC fuel reactivity were analyzed. The results showed that the RCTJI mode with Double scavenging PC obtains the highest reactivity in the PC. It promotes the ignition and combustion processes within the PC, resulting in a more intense jet flame with higher velocity and temperature, as well as a higher OH concentration. Further, the enhanced jet flame promotes the combustion process of the ammonia engine, the improved flame development is obtained in the MC. NOx and N2O emissions are relatively higher in the RCTJI modes with Scavenging PC and Double scavenging PC, while the concentration of unburned NH3 is significantly lower. In contrast, Double scavenging PC has greater potential for reducing emissions from the ammonia engine.