Influence of wall structure on jet–wall interaction and combustion in an ammonia–hydrogen pre-chamber turbulent jet ignition system: A combined experimental and CFD study

Ammonia–hydrogen blended fuel represents a promising zero-carbon alternative for internal combustion engines. Pre-chamber ignition technology enhances combustion performance; however, jet–wall impingement is inevitable under realistic engine conditions and plays a critical role in ignition and flame development. This study integrates constant volume combustion chamber experiments with three-dimensional computational fluid dynamics simulations to systematically investigate the influence of wall geometry and structural parameters on jet impingement behavior and flame evolution. Results demonstrate that concave wall structures effectively capture and redirect incoming jets, enhancing turbulence intensity and promoting sustained vortex formation near the jet axis. These flow characteristics accelerate the expansion of high Damköhler number regions and intensify flame–turbulence interactions, thereby supporting rapid flame propagation. Compared to convex and flat configurations, concave geometries reduced ignition delay by 65.2 % and combustion duration by 14.9 %. The optimal concave case—with a depth of 5 mm and an apex angle of 60°—achieved the shortest combustion duration due to improved vortex retention. For convex designs, a lower height and wider apex angle (e.g., 5 mm height and 120° apex angle) resulted in over a 26 % reduction in combustion duration compared to taller convex structures.