Comprehensive effects of ammonia substitution rate, compression ratio, and ignition timing on knock, NOx emissions and indicated thermal efficiency in a hydrogen fuel engine

To reduce knock and keeping low NOx emissions and high indicated thermal efficiency (ITE) in a hydrogen fuel engine, the comprehensive effects of ammonia substitution rate (ASR), compression ratio (CR), and ignition timing (IT) on its combustion and its NOx emissions were studied numerically. Based on a four-cylinder gasoline direct injection (GDI) engine, it was modified into an ammonia/hydrogen dual-fuel (AHDF) spark ignition (SI) engine. The simulation was conducted by GT-Power software, and simulation data were validated through experiments. 2500 rpm_50% load was selected for the research. ASR, CR and IT vary from 0% to 20%, 10.5 to 8.5, and −24 to 0°CA ATDC, respectively. The findings indicate that increasing ASR decreases the maximum pressure rise rate (MPRR) and the knock index (KI), improving the ITE, but increasing NOx emissions. Based on 20% ASR, CR was optimized. The findings indicate that decreasing CR reduces the MPRR and KI, but increasing NOx emissions and decreasing the ITE. Finally, based on CR of 9, IT was optimized. The findings indicate that delaying IT reduces the MPRR and KI, but also has a certain impact on NOx emissions and ITE. After compromise consideration, the optimal IT in this study was selected as −9°CA ATDC.