The adoption of hydrogen as carbon-free fuel for internal combustion engines in both transport and off-road applications could offer a significant contribution towards carbon neutrality. In the technical pathway to the conversion of conventional engines operating with liquid fuels to hydrogen, a key role is played by the injection systems. In particular for direct-injected combustion systems, the achievement of an adequate capability to control the gas jets development and the following mixing with air in the combustion chamber is mandatory in order to govern the heat release rate, so to obtain high efficiency levels while limiting the knock tendency and NOx formation. In order to achieve this complex task, injector caps featuring multiple holes (often non uniform in size) can be installed on the injector nozzle so to properly distribute hydrogen obtaining a proper matching with the combustion chamber design and with the air charge flow structure. To this end, the development of both appropriate simulation capabilities as well as effective diagnostic methodologies for a detailed characterization of high-pressure gas jets are required.
In the present paper, a single-hole GDI-derived prototype injector equipped with a 2-hole cap and fed with hydrogen is analysed with a combined experimental and 3D-CFD numerical methodology. The injector was characterized in terms of mean mass flow rate and global development of the two jets emerging from the cap. Further, the measurement of the momentum flux of the jets, coupled with the results of the 3D-CFD analysis, enabled the evaluation of the mass flow distribution among the two jets. The same 3D-CFD numerical tool, adequately validated with the available experimental data, was used to deepen the development of the flow structures within the injector cap, evidencing how the complex flow pattern inside the cap influences the evolution of the emerging jets. Globally, the combined experimental-numerical approach used was proved to be an effective methodology to support the development of hydrogen injection systems.