Experimental and Numerical Study of a Low-Pressure Hydrogen Jet under the Effect of Nozzle Geometry and Pressure Ratio

Hydrogen (H₂), a potential carbon-neutral fuel, has attracted considerable attention in the automotive industry for transition toward zero-emission. Since the H₂ jet dynamics play a significant role in the fuel/air mixing process of direct injection spark ignition (DISI) engines, the current study focuses on experimental and numerical investigation of a low-pressure H₂ jet to assess its mixing behavior. In the experimental campaign, high-speed z-type schlieren imaging is applied in a constant volume chamber and H₂ jet characteristics (penetration and cross-sectional area) are calculated by MATLAB and Python-based image post-processing. In addition, the Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach is used in the commercial software Star-CCM+ for numerical simulations. The H₂ jet dynamics is investigated under the effect of nozzle geometry (single-hole, double-hole, and multiple-hole (5-hole)), which constitutes the novelty of the present research, and pressure ratio (PR = injection pressure (P_i) / chamber pressure (P_ch)). The results show that the H₂ jet from the single-hole nozzle possesses the fastest penetration and smallest cross-sectional area. On the contrary, the H₂ jet from the double-hole nozzle possesses the slowest penetration and largest cross-sectional area. The H₂ jet from the multiple-hole nozzle shows characteristics between those of the single-hole and double-hole. Overall, since higher pressure ratio and larger jet cross-sectional area lead to higher uniformity of the fuel/air mixture, high-pressure injection with the double-hole nozzle seems more advantageous to attain efficient mixing.