Combined experimental and numerical investigation of the turbulent mixing of hydrogen jets issued from a hollow cone injector

Injection processes play a crucial role in hydrogen-fueled direct-injection propulsion systems and must be thoroughly studied to improve efficiency and reduce pollutant emissions. In this context, the current study proposes a combined experimental and numerical characterization of hydrogen jets for use in advanced combustion systems. The injector under investigation was the Bosch HDEV-4, which produces a hollow-cone jet. We conducted an experimental campaign to investigate jet morphology using the Schlieren optical technique and measure the mass flow rate under various operating conditions with a purposely developed tool. To numerically reproduce the injection process under attention, we adopted a multi-scale modeling approach to simulate the in-nozzle and external flows for three different pressure ratios. The CFD simulations yielded promising results that closely align with experimental observations, enabling a detailed analysis of jet morphology across various pressure ratios (PR) and providing insights into the flow-field structure. We found that the flow field created by the hollow-cone jet structure keeps the mass fraction below 0.2 in most of the injection environment. Finally, we also characterized the mixture quality using a probability density function, providing a quantitative evaluation of the turbulent mixing obtained in the different injection conditions studied. The statistical distributions observed for the three investigated PRs are quite similar, peaking around Y = 0.08. The only notable difference occurs at PR = 25, where the distribution declines rapidly at Y 0.4.