Computational study of injector cap design for optimized mixing and combustion in a high-performance DI hydrogen engine

At high engine speeds, the reduced time available for fuel–air mixing makes charge preparation a critical factor in optimizing combustion performance and emissions in direct-injection high-performance hydrogen engines (DI H2-ICEs). Delaying injection into the compression stroke can help mitigate volumetric efficiency losses and reduce the risk of pre-ignition at high loads. However, achieving a sufficiently homogeneous mixture remains essential for stable and efficient combustion. The use of a multi-hole injector cap presents a promising solution, allowing control over jet orientation within the combustion chamber without redesigning the injector body. Nevertheless, the complex interactions between gas jets, in-cylinder flow structures, and turbulence must be thoroughly understood. This study numerically evaluates the impact of eight different injector cap designs on mixture formation and combustion in a single-cylinder H2-ICE operating at 6000 rpm, high load (>25 bar IMEP), and at stoichiometry. It presents a novel systematic analysis, considering the pent-roof tumble-based combustion chamber, high-revving and stoichiometric operation. The simulations provide injector design guidelines, revealing that injection along the cylinder axis or in favour of the main tumble vortex improves mixture uniformity by up to 5 %, whereas injecting upstream reduces uniformity by 15 %. The best-performing design achieves a 5 % increase in engine output and a 30 % reduction in combustion duration, demonstrating the effectiveness of optimized injector configuration in improving mixing and turbulence.