The potential of hydrogen, generated by renewable sources, to reduce future emissions and develop new internal combustion engine (ICE) systems in combination with adapting existing engines for hydrogen operation offers the ability for CO2 neutral mobility solutions. 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 this study, a conventional piezo hollow-cone gasoline injector, commonly used in passenger car series, was adapted for high-pressure hydrogen direct injection (DI) applications. Therefore, optical measurements within a low pressure chamber (LPC) are conducted with a high-speed Schlieren imaging measurement technique to visualize the injection behavior and spray 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 spray 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 are investigated. 
 

For detailed analysis of the injection a 3D computational fluid dynamics (CFD) model using a RANS approach was developed and validated using the macroscopic injection properties of the experimental measurements from different operating points. Additionally, multiple Large Eddy simulations (LES) cycles of one operating point are performed to offer a comprehensive understanding of the hydrogen spray formation for hollow-cone injectors and evaluate their 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, the LES identified transient revolving structures near the injector, which were also observed in the experiment.