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

The adoption of hydrogen as a sustainable replacement of fossil fuels is pushing the development of internal combustion engines to overcome the technical limitations related to its usage. Focusing on the crucial roles played by 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. To these aims, experimental campaigns and computational fluid dynamics simulations can be used as complementary tools to provide a deep understanding of the injector behavior and to drive design modifications in a quick and effective way. In the present work an outward opening piezoelectric injector purposely designed to be fueled with hydrogen is tested in a quiescent vessel 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 single-hole jet caps are placed downstream of 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 caps are then performed both in steady state and transient operation to provide detailed explanations on the flow characteristics. 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 assessments collected by the tests. Thanks to the validation against experimental data, 3D-CFD analyses can be used as a reliable tool for the evolution of both injector and cap designs.