The combustion of fossil-based fuels in ICEs, resulting in a huge amount of greenhouse gases (GHG) and leading to an immense global temperature rise, are the root causes of the more stringent emission legislations to safeguard health and that encourage further investigations on alternative carbon-neutral fuels.
In this respect, the hydrogen has been considered as one of the potential clean fuels because of its zero-carbon nature. The current development of hydrogen-based ICEs focuses on the direct injection (DI) strategy as it allows better engine efficiency than the port fuel injection one. The behavior of the fuel jet is a fundamental aspect of the in-cylinder air-fuel mixing ratio, affecting the combustion process, the engine performances, and the pollutants emissions.
In the present study, comprehensive investigations on the hydrogen jet behavior, generated by a Compressed Hydrogen Gas (CHG) injector under different operative conditions, were performed. A measuring system, suitable for the gaseous fuels, was used for measuring the flow rate. The fuel jet morphology was studied in a constant volume vessel filled with nitrogen as function of the injection pressure (up to 4.0 MPa) and different backpressure in the vessel, through the measurements of the jet penetrations, total areas, and cone angles showing a strong dependence from the set parameters. The cycle-resolved schlieren imaging technique by a high-speed camera was used to follow the jet spreads while the images were processed by a home-made procedure allowed to identify the contours of the hydrogen jet in the nitrogen gas and hence to measure the main parameters characterizing the jet structure.