Experimental and Numerical Investigation of Hydrogen Jet-Wall Impingement

Decarbonization of the automotive industry is one of the major challenges in the transportation sector, according to the recently proposed climate neutrality policies, e.g., the EU 'Fit for 55' package. Hydrogen as a carbon-free energy career is a promising alternative fuel to reduce greenhouse gas emissions. The main objective of the present study is to investigate non-reactive hydrogen jet impingement on a piston bowl profile at different injection angles and under the effect of various pressure ratios (PR), where PR is the relative ratio of injection pressure (IP) to chamber pressure (CP). This study helps to gain further insight into the mixture formation in a heavy-duty hydrogen engine, which is critical in predicting combustion efficiency. In the experimental campaign, a typical high-speed z-type Schlieren method is applied for visualizing the jet from the lateral windows of a constant volume chamber, and two custom codes are developed for post-processing the results. In particular, the jet's major characteristics i.e., penetration, width, and cross-sectional area are calculated at different PRs (25, 10, 5, and 2.5). The results show that higher pressure ratios lead to faster penetration and larger cross-sectional areas of the hydrogen jet. In addition, the jet-piston interaction at different angles as well as the flow around the piston towards the liner and back to the main cylinder volume are studied considering the optimization of mixture formation in the cylinder. By changing the injection angle (10°, 15°, and 20°), jet-piston impingement occurs near the edges, which results in greater hydrogen concentration around those areas, adversely affecting mixture formation. The measurements are further used to validate a numerical model for hydrogen injection and mixing in a similar jet-piston geometry, applying an unsteady Reynolds-averaged Navier-Stokes simulation approach in the commercial software Star-CCM+.