Optical Investigation of DI Hydrogen Jet Development and Jet-Wall Interactions Under Engine-Like Conditions

Direct injection (DI) hydrogen internal combustion engines are gaining attention as a promising technology for a sustainable energy transition, particularly in the transport sector. A key factor in improving the performance of these engines is understanding how hydrogen jets behave within the combustion chamber, especially their interactions with the chamber walls. These jet-wall interactions are critical since they have a major influence on fuel-air mixing which directly affects combustion efficiency and emissions. This study investigates the behavior of high-velocity hydrogen jets formed after exiting the injector. These jets propagate through surrounding air and interact with wall surfaces. When they impinge on wall surfaces, they undergo various processes such as radial spreading outward along the wall surface, mixing, and diffusion. These processes are influenced by factors including pressure ratio (PR) - the ratio between injection pressure and chamber pressure - and the geometry of the walls. To examine jet development and jet-wall interactions under high-pressure engine-like conditions, Schlieren video imaging was employed to enable visualization of the jet behavior with high time resolution without interfering with the process. The experiment focused on the behavior of the hydrogen jets with varying PRs as they interacted with flat and curved surfaces positioned at different distances from the injector within a pressurized chamber. Image post-processing techniques were applied to quantify jet properties. The results demonstrate that PR has a significant impact on jet characteristics. Higher PRs lead to faster jet development and greater jet propagation, improving fuel-air mixing. Additionally, wall geometry plays a crucial role in jet dispersion after impingement; a curved wall surface restricts jet volume and velocity. Optimizing PR and chamber wall design is essential for improving combustion efficiency without resorting to excessively high injection pressures. These findings offer valuable insights and guidance for future DI hydrogen engine designs.