Effects of Jet Caps on Hydrogen Piezoelectric Injectors for DI Applications: Experiments and 3D-CFD Simulations

The adoption of hydrogen as a sustainable replacement for fossil fuels is pushing the development of internal combustion engines (ICEs) to overcome the technical limitations related to its usage. Focusing on the fuel injector in a DI configuration, it must guarantee several targets such as the adequate delivery of hydrogen mass for the given operating condition and the proper mixture formation in the combustion chamber playing a primary role in reaching the target performance in H2-ICEs. Experimental campaigns and computational fluid dynamics simulations can be used as complementary tools to provide a deep understanding of the injector behaviour and to drive design modifications in a quick and effective way. In the present work an outward opening, piezo-actuated injector purposely designed to be fuelled with hydrogen is tested on several operating conditions to evaluate its performance in terms of delivered mass flow and jet morphology using the Schlieren imaging technique. To highlight the modification of the jet shape and its interaction with the surrounding air, two different configurations of a single-hole jet caps are placed downstream to the poppet valve. Being one of them optically accessible, some flow features arising inside the cap are seized. 3D-CFD simulations of the tested injector with and without the cap are then performed in transient operation to provide a detailed analysis of the main flow features. Using realistic CAD models, derived from the tested injector and jet caps, together with the poppet lift measurements, the simulations are fully coherent with the tests. A validation study is performed comparing 3D-CFD results with the experiments proving the validity of the developed approach that can be used as a reliable tool to study different injector and injector cap configurations.