Visualization of hydrogen jet evolution and combustion under simulated direct-injection compression-ignition engine conditions

The evolution and combustion of H-2 jets were investigated in an optically-accessible constant-volume chamber under simulated direct-injection (DI) compression-ignition (CI) engine conditions. The parameters varied include injection pressure (84-140 bar) and ambient temperature (1000-1140 K). A detailed characterization of the injector system and the ensuing jet penetration process is reported first. High-speed schlieren imaging, OH* chemiluminescence imaging and pressure trace measurements were subsequently used to investigate the auto-ignition and combustion of the H-2 jets. The results show that the ignition delay of H-2 jets under such conditions is sensitive to ambient temperature variations, but not to injection pressure. Optical imaging reveals that the combustion of H-2 jets mostly initiated from a localized kernel, before spreading to engulf the whole jet volume downstream of ignition location. The imaging also indicates that after ignition, the flame recesses back towards the nozzle and appears to attach to the nozzle to form a diffusion flame structure. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.