Hydrogen Jet Characteristics of an Outward-opening Injector based on Schlieren Imaging

Hydrogen was considered as a promising carbon-free fuel for future society. The application of hydrogen in internal combustion engines has drawn more and more attentions. Jet performance of hydrogen injection plays a crucial role in characteristics of the hydrogen fuelled engines, in terms of mixture preparation, combustion and heat release in cylinder. In this research, an outward-opening injector was developed for hydrogen direct injection application. The jet performance was studied using high-speed schlieren imaging in a constant volume chamber and the effects of injection and ambient pressures on jet characteristics were investigated. The results show that, the hydrogen jet exhibits a conical structure in the near-field and overall presents a bell-shaped appearance under relatively low ambient pressure, which differs from irregular structure under relatively high ambient pressure. The pressure ratio, defined as the ratio of injection pressure to chamber pressure, significantly influences the jet characteristics. The increase in the pressure ratio leads to greater axial and radial penetration of the jet, and an increase in the cross-sectional area. Separately, elevating the injection pressure enhances its mass flow and improves mixture formation. While increasing the chamber pressure hinders the development and expansion of the jet, resulting in a reduction in the jet entrainment rate.