Comprehensive optical and numerical investigation of hydrogen jet formation for a commercial gasoline hollow-cone injector

Hydrogen produced from renewable sources offers the opportunity to reduce future emissions and enable CO2-neutral mobility by both adapting existing internal combustion engines (ICE) and developing new combustion engine systems. One challenge of hydrogen direct injection (DI) ICE is to optimize the mixture formation to ensure low engine out emissions as well as high efficiencies. In the study presented in this paper, a conventional piezo hollow-cone gasoline injector, commonly used in passenger car series, was adapted for high-pressure hydrogen direct injection applications. Therefore, optical measurements within a low pressure chamber (LPC) were conducted using a high-speed Schlieren imaging measurement technique to visualize the injection behavior and jet pattern at various injection conditions. The visualization of density gradients during the injection process showed a slightly decreased relative gaseous penetration length (GPL) of 4% for hydrogen in comparison to helium while the gas area of the jet was comparable. Consequently, helium can be considered a suitable surrogate for hydrogen injection applications. The effect of hydrogen diffusivity on the GPL is visible after the end of the injection duration. To improve the mixture formation, different recess positions of the injector were investigated. For a more detailed analysis of the injection, a 3D CFD (Computational Fluid Dynamics) model was developed using a Reynolds-averaged Navier-Stokes (RANS) approach and validated using the macroscopic injection properties of the experimental measurements from different operating points. Additionally, several Large Eddy Simulations (LES) cycles of one operating point were performed to gain a comprehensive understanding of the hydrogen jet formation and to evaluate its statistical behavior. Both the RANS and the time-averaged LES simulations are capable of accurately reproducing the contour and penetration depth of the hydrogen jet. Furthermore, LES identified transient revolving structures near the injector, which were also observed in the experiment.