Hydrogen jet characteristics with an outwardly opening piezo injector

Hydrogen is a promising renewable energy vector for decarbonizing transportation, offering high energy density and clean combustion. In this study, experimental investigation of hydrogen jets discharged from an outwardly opening piezo injector (Bosch HDEV4) was conducted. The HDEV4 injector was suggested by the Engine Combustion Network (ECN) to investigate hydrogen injection and jet mixing dynamics for hydrogen spark-ignition direct injection engines. This choice was based on the injector's compatibility with hydrogen, its comprehensive characterization in literature, and its suitability for open-access research. High-speed z-type Schlieren imaging was employed to visualize jet structure and time-resolved evolution within a constant pressure flow vessel. The injector needle lift was measured using high-magnification, high-speed photography. The needle lift shows a positive correlation with increased driving voltage and some fluctuations after reaching a fully opened position. Jet-projected area and tip penetration decrease monotonically with ambient pressure. The comparison of the theoretically predicted and experimentally measured injected mass across varying injection pressures enabled estimating a discharge coefficient between 0.6 and 0.8. Increasing the injection pressure speeds up penetration due to the higher mass flow injected and increased jet momentum. However, the jet penetration pattern remained almost unaltered across various injector heating temperatures. The jet self-similarity parameter enables scaling correlations for non-dimensional penetration across voltages, revealing a two-phase linear relationship between needle damping and stable stages. This study provides valuable experimental data for the ECN community, supporting comparative studies and serving as a reference for validating computational fluid dynamics simulations.