Effects of Ambient and Injection Conditions on a High-Pressure Hydrogen Jet for Direct Injection in ICE

The transport sector is responsible for about one third of the global CO2 emissions. To align to the net zero emission scenario, the transportation sector needs the implementation of policies aimed to reduce as much as possible the highly emitting transport options and, at the same time, the use of new technologies to reduce the environmental impact of transport methods whose emissions cannot be entirely eliminated. An exploitable solution for the internal combustion engine (ICE), even in the nearest future, would be to use hydrogen as a fuel in these engines. This is supported by the fact that H2-ICE is the only ICE technology currently capable of meeting the standards imposed by the European Union for 2035. Due to the possibility of different injection strategies as well as the variation of in-cylinder back pressure, the comprehensive knowledge of hydrogen injection jet behavior and characteristics is fundamental for improving the combustion process in direct injection H2-ICE. In this context, current study focuses on the characterization of experimental hydrogen jets in terms of mass flow rate and jet morphology under a wide range of engine-like conditions by the use of an injector appropriate for direct injection applications. A measuring system, suitable for gaseous fuels, was used for measuring instantaneous and total flow rates as well as the dynamic behavior of the entire injection system. The spatial and temporal evolution of a highly under-expanded H2 jet was studied by a Z-type schlieren optical setup. H2 fuel was injected into a constant-volume combustion vessel (CVCV) at different injection pressures (up to 50 bar) and ambient back pressures simulating typical engine conditions. Measurements of jet penetrations, jet width, and total areas of the injected gas showed a strong dependence on those parameters.