Numerical Investigation of Injection and Mixture Formation in Hydrogen Combustion Engines by Means of Different 3D-CFD Simulation Approaches

Abstract

For the purpose of achieving carbon-neutrality in the mobility sector by 2050, hydrogen can play a crucial role as an alternative energy carrier, not only for direct usage in fuel cell-powered vehicles, but also for fueling internal combustion engines. This paper focuses on the numerical investigation of high-pressure hydrogen injection and the mixture formation inside a high-tumble engine with a conventional liquid fuel injector for passenger cars. Since the traditional 3D-CFD approach of simulating the inner flow of an injector requires a very high spatial and temporal resolution, the enormous computational effort, especially for full engine simulations, is a big challenge for an effective virtual development of modern engines. An alternative and more pragmatic lagrangian 3D-CFD approach offers opportunities for a significant reduction in computational effort without sacrificing reliability. The detailed and the lagrangian approach are both validated against optical measurements inside a spray chamber, provided by Robert Bosch GmbH to ensure an accurate reproduction of the injection process in the simulation. The investigation shows, that the lagrangian approach enables 30 times bigger time steps, while maintaining comparable results. The effects on jet propagation and mixture formation are examined in a virtual 3D-CFD single cylinder engine test bench under the consideration of a boosted high tumble engine concept and direct injection up to 220 bar. A variation of injection timings and the air-to-fuel ratio are carried out at two load points and validated with the test bench data. By means of the matching simulation results, it is therefore possible to explain trends in engine behavior and make detailed statements about the interaction of the hydrogen high-pressure injection and the mixture formation. Particular attention was hereby paid to the influences on gas exchange losses, NOx emissions and engine efficiency.