Numerical Analysis of the Combustion Process in a Hydrogen-Fueled Pre-Chamber Combustion Engine

Direct injection hydrogen internal combustion engine (ICE) has emerged as a promising alternative fuel due to its potential to enable clean and sustainable energy systems. However, the rapid injection of low-density hydrogen leads to strong mixture stratification and strong flame-turbulence-wall interactions. This challenge is exacerbated in the high-performance engine under study operating at a high engine load (indicated mean effective pressure of about 20 bar) and speed (7500 revolutions per minute). Furthermore, to target high efficiencies, restrict abnormal combustion behaviors, and inhibit oxides of nitrogen emissions, a lean-burn combustion strategy with a global equivalence ratio of 0.4 was applied, where diffusive-thermal (DT) instability effects further complicate the flame characteristics. Additionally, to promote engine performance, the pre-chamber (PC) combustion concept was applied, further complicating the turbulent flame dynamics. To address the modeling challenges and accurately predict the physical and chemical characteristics of this high-speed direct-injection hydrogen PC combustion engine, this study intends to establish a well-validated computational framework based on measured engine combustion data. A flamelet-based G-equation model incorporating the DT instability effects was applied and analyzed for flame propagation. Validation against experimental data highlighted the importance of incorporating DT effects to accurately capture turbulent hydrogen combustion dynamics. Further parametric simulations of three jet-forming caps at a fixed start of injection (SOI) showed significantly different combustion performance and identified the cause of the experimentally observed anomalies. The results also revealed key design guidelines, including the need for a locally rich mixture in the PC to ensure rapid ignition and strategies to promote fast, uniform MC combustion. These findings provide a foundation for optimizing jet-cap geometries in conjunction with injection strategies to maximize the performance of high-load hydrogen PC engines.