Numerical investigation on the combustion performance of ammonia-hydrogen spark-ignition engine under various high compression ratios and different spark-ignition timings.

This paper aims to numerically investigate the effects of high compression ratio (CR) on the performance of ammonia-hydrogen engines. In this work, four CRs from 10.7 to 13.7 with scanning spark timing (ST) from 28°CA to 0°CA BTDC were analyzed. The main results are as follows: As the CR increases, there is a trade-off relationship between the dissipation rate of turbulence and the turbulent kinetic energy (TKE). Initially, the TKE rises as the CR increases. As the CR continues to rise, the tendency for an increase in TKE diminishes, while the turbulent dissipation rate consistently rises. Additionally, there is an escalation in heat transfer loss. Therefore, there is a trend of rising and then falling in the flow velocity and turbulence intensity with the increase of the CR. Ammonia-hydrogen flame propagation is susceptible to temperature and flow field, and a high CR can improve ignition stability, shorten combustion duration, minimize cooling loss, and enhance output power. Unfortunately, the emission of NOx gradually rises as the CR increases. At high CR, the combustion performance is optimized by adjusting ST, and the maximum IMEP and ITE are 4 bar and 38.3 %, respectively. The ST for maximum braking torque (MBT) should be gradually delayed toward TDC as the CR increases. • As the compression ratio increases, the flow velocity first rises and then decreases. • The turbulent dissipation rate increases with increasing compression ratio. • A high compression ratio improves ignition stability and combustion velocity. • The NOx gradually increases with the increase of the compression ratio. • A high compression ratio improves the power and economy of NH3-H2 engines. [ABSTRACT FROM AUTHOR]