Experimental investigation of hydrogen jet impingement from different nozzle orifices in an engine combustion chamber

Direct injection hydrogen engines enable precise fuel jets development control for high-efficiency, low-emission combustion systems. However, performance depends on fuel–air mixing quality affected by wall-impinging hydrogen jets. Current studies lack systematic investigation of jet-wall interactions under engine-representative confined conditions. This study experimentally investigates hydrogen jet impingement in an engine-dimensioned combustion chamber using high-speed schlieren imaging under injection pressures ranging from 0.5 to 1.0 MPa, nozzle diameters between 1.0 and 2.5 mm, and impingement distances from 20.6 to 42.6 mm at ambient conditions of 298 K and 1 atm. Results reveal that elevated injection pressure significantly enhances spreading radius, entrainment height, and projected area by accelerating momentum conversion into radial flows and promoting faster impingement stabilization with improved mixing efficiency. Shorter impingement distances intensify radial momentum conversion through earlier wall interaction at higher axial momentum, whereas longer distances weaken impingement intensity due to turbulence-induced momentum decay and reduced spatial utilization. Larger nozzle diameters substantially improve post-impingement behavior through higher momentum flux and enhanced turbulence, promoting more vigorous wall interaction and broader radial dispersion with complex vortex dynamics. Interestingly, for a given cumulative injected mass, smaller-diameter nozzles can produce larger projected areas due to longer injection durations, which allow more time for axial and lateral spreading before reaching the measurement plane. This work specifically addresses low-pressure direct injection systems, and the findings provide critical insights for optimizing injection parameters and combustion chamber geometry for direct-injection hydrogen engines.