A parametric study of autoigniting hydrogen jets under compression-ignition engine conditions

This study examines the flame evolution of autoigniting H₂ jets with high-speed schlieren and OH1 chemiluminescence optical methods in a constant-volume combustion chamber over a wide range of simulated compression-ignition engine conditions. Parametric variations include the injector nozzle orifice diameter (0.31–0.83 mm), injection reservoir pressure (100–200 bar), ambient temperature (1000–1140 K), density (12.5–24 kg/m³) and O₂ concentration (10–21 vol.%). The jet ignition delay was found to be highly sensitive to changes in ambient temperature while all other parameter variations resulted in minor ignition delay changes. Optical imaging reveals that in most cases, the reaction front of the H₂ jet initiates from a localised kernel, before engulfing the entire jet volume downstream and recessing towards the nozzle. The flames attach to the nozzle, except at the lowest ambient oxygen condition of 10 vol.% O₂ for which a lifted flame is observed. The H₂ diffusion flame length shows a dependence on both the mass flow rate and the level of O₂ entrainment that follows the same correlations as previously established for atmospheric H₂ jet flames.