An experimental study of jet-wall and jet-jet interactions of directly injected hydrogen and methane in a wave-piston geometry

This study investigates the interactive dynamics of directly injected (DI) hydrogen and methane jets with wall and neighboring jets in a non-reactive environment, focusing on the influence of wave-shaped piston geometry. Experiments were conducted in a high-pressure optical chamber using a custom 2-hole DI injector, with Schlieren imaging employed to capture the temporal evolution of jet structures for varying injection durations and injection pressure ratios. Comparative analyses between conventional flat and wave-shaped wall geometries reveals that the wave geometry significantly alters post-impingement jet behavior, particularly enhancing jet guidance toward the center and promoting early detachment from the wall. For both hydrogen and methane, jets impinging on the wave wall exhibited accelerated formation of a central flow structure akin to the radial mixing zone (RMZ) observed in reactive diesel combustion. This effect was most pronounced after end of injection, where the trailing edge of the impinged jets in the wave geometry detached earlier and exhibited inward momentum, forming U-shaped flow patterns indicative of efficient mixing. Quantitative jet area analysis further showed that the wave geometry confined and redirected the jets more effectively than the flat wall, especially for hydrogen at shorter injection durations. These results demonstrate that the wave-piston concept, originally developed for soot reduction in diesel engines, also enhances jet-jet and jet-wall interaction efficiency in gaseous DI systems by promoting structured recirculation. Moreover, these results suggest that wave-based piston geometries can substantially influence fuel-air mixing dynamics even in the absence of combustion, providing a foundation for optimizing combustion chamber designs for low-carbon and high-diffusive gaseous fuels. • Jet-wall and jet-jet interactions of H 2 and CH 4 studied with wave piston geometry in a chamber. • Wave walls redirected jets inward, detached earlier, and formed U-shaped RMZ-like flow. • H 2 jets spread faster and mixed more broadly than CH 4 despite lower Reynolds numbers. • Jet speed and mixing improved with PR, but gains diminished beyond PR ≈ 10. • Wave piston geometry enhanced post-impingement mixing for low-carbon DI gas engines.