Experimental characterisation of hollow-cone hydrogen jet behaviour under engine-like conditions

Abstract

Internal combustion engines equipped with direct injection (DI) of hydrogen represent a promising pathway toward carbon-neutral transportation. This work presents a systematic experimental investigation of hollow-cone hydrogen jet dynamics generated by an outward-opening injector using high-speed schlieren imaging, integrating jet momentum measurements. The hydrogen jet evolution is identified as a two-stage process, i.e., near-nozzle underexpanded structures dominated by pressure-ratio effects and a subsequent self-similar dense-jet stage governed by momentum. The pressure-ratio-dominant and momentum-dominant scaling laws are evaluated for these two stages, clarifying the governing mechanisms of hollow-cone hydrogen jet development. Furthermore, a quantitative evaluation of hydrogen mixing behaviour is conducted with a constant injected mass under different injection pressures (Pinj). The results show that Pinj has a limited influence on jet shapes during injection, whereas higher Pinj improves spatial mixture homogeneity. The difference in homogeneity can be reduced by allowing a longer mixing time after the end of injection.