Experimental and numerical characterization of a single-hole LPDI Hydrogen injector: identification of a suitable inert replacement for Hydrogen jet studies

In recent years, climate change has exerted great pressure for the development of both existing and new technologies to reduce green-house gases emissions. The transportation sector has been, and is still, heavily impacted by this green revolution, which is driving the automotive world towards electrification, at least for light- and mid-duty vehicles. In parallel, the development of Hydrogen powertrains, both as Internal Combustion Engines (ICEs) and Fuel Cells (FCs) has found new impulse, being it a solution to help the transportation sector, for heavy- as well for light-duty applications, to reach carbon neutrality. Conversion of conventional thermal engines into carbon free fuelled ones could speed up the achievement of the goals set by COP21 for the 2030–2050 agenda. The result would be environmentally effective and cost sustainable, avoiding obsolescence for the internal combustion engine technology. For the fossil-to-Hydrogen conversion, a key role is played by the injection system, which is responsible for both the fuel mass delivery rate and the fuel jet morphology in the combustion chamber, thus highly impacting air–fuel mixing, heat release rate and pollutant formation. For these reasons, a detailed understanding of the Hydrogen injector is mandatory to achieve an efficient and “clean” engine operation. In this work, a detailed numerical and experimental characterization of a single-hole gas injector is presented using Argon (Ar), Helium (He), and Nitrogen (N2) as substitutes for Hydrogen (H2). The use of inert gases is a common practice in the literature to reduce experimental costs and enhance safety. However, the influence of gas properties on measured quantities is not yet fully understood. The experimental data are used to develop and validate a CFD methodology to simulate gas jets and to numerically extrapolate the injector's behaviour when using Hydrogen. This combined experimental–numerical approach enables definitive conclusions regarding the substitution of H2 with inert gases. Strong similarities between He and H2 confirm helium as the most suitable surrogate gas to characterize jet cone angle and penetration while near nozzle flow details are well reproduced by using a bi-atomic gas such as N2.