Optimizing hydrogen direct injection strategy in a passive pre-chamber turbulent jet ignition NH3/H2 Miller-cycle engine: Analysis of flow, combustion and emission characteristics

Hydrogen and ammonia, as promising zero-carbon fuels, are gaining increasing attention in transportation applications. The passive pre-chamber (PC) can effectively enhance combustion efficiency. This study investigates the impact of hydrogen direct injection strategies on passive PC turbulent jet ignition (TJI) Miller-cycle NH3/H2 engine performance. The flow field and mixture distribution are explored through numerical simulation, while the engine performance is evaluated through experiments. Experiments were conducted at 1600 rpm engine speed with 60 kPa intake manifold pressure under stoichiometric conditions. The research findings that as the start of injection (SOI) timing is delayed, the distribution of the mixture gradually transitions from uniform to stratified. Maximum BMEP and BTE were achieved at 60°CA BTDC SOI. The TJI technology can effectively mitigate the combustion instability induced by the late injection strategy. However, the late injection strategy will lead to an increase in N2O emissions from combustion and unburned NH3 emissions. In addition, an overly early injection timing causes a decrease in the mixture quality, deteriorating the engine power. Adopting a secondary injection strategy counteracts performance degradation from early injection while maintaining mixture homogeneity. The findings suggest that appropriately delaying the SOI represents a viable approach to improve the working performance of the TJI NH3/H2 engine.