Effects of jet interaction angle on the ignition and combustion characteristics of hydrogen-diesel dual-fuel direct injection

This study investigates the ignition and combustion characteristics of intersecting diesel surrogate (pilot) and hydrogen (H2, main) jets under engine-relevant conditions. The experiments, performed in an optically accessible constant-volume combustion chamber (CVCC), utilised two converging single-hole injectors, with the pilot fuel accounting for 12% of the total injected fuel energy. This study investigated the effects of two key parameters on the ignition process: jet interaction angle (12 degrees to 19 degrees) and ambient O2 concentration (10 to 21 vol.%). The results show that the presence of H2 either advances or delays pilot ignition depending on whether the pilot n-heptane jet ignites before or after interacting with the H2 jet, respectively. The pilot-main ignition transition period is influenced by both jet interaction angle and ambient O2 concentration. Under identical ambient conditions, a smaller jet interaction angle results in a longer transition, while for a constant angle, lower ambient O2 leads to a more prolonged transition. Under 10 vol.% O2 conditions, flame kernels emerge upstream of the main flame body, before eventually merging with the reacting jet downstream, with this phenomenon observed to induce variation in heat and flame stabilisation characteristics. An explanation for the upstream kernel formation is offered based on the entrainment of residual pilot n-heptane-jet fuel into the upstream region of the still-injecting main jet, with the relative jet momentum a likely key contributor influencing this entrainment that impacts kernel formation.