Characterizing and visualizing the direct injection of hydrogen into high-pressure argon and nitrogen environments

Using argon as the working fluid in an internal combustion engine holds the potential of substantially enhancing thermal efficiency because of its high specific heat ratio. Burning hydrogen, not with air but with pure oxygen, in a closed-loop argon power cycle would lead to an emission-free exhaust composition, effectively containing only water and argon, which can be separated by condensation. One of the current challenges is the high-pressure direct injection of both fuel and oxidizer, which directly controls the combustion process. To support the development of such an injection strategy, high-pressure injections of hydrogen into pressurized argon and nitrogen are investigated using high-speed Schlieren and pressure transducers in a non-heated constant-volume chamber at varying conditions. In this work it is shown that hydrogen mass flow increases linearly with injection pressure and that it is unaffected by chamber pressure as expected based on choked flow theory, while jet penetration and cone angle are determined by the pressure ratio between the fuel line and the ambient. A correlation is presented between jet penetration and pressure ratio for argon or nitrogen environments at room temperature.