Numerical Evaluation of Fuel-Air Mixing in a Direct-Injection Hydrogen Engine using a Multi-Hole Injector

Hydrogen as a chemical energy carrier is considered as one of the most promising options to achieve effective decarbonization of the transportation sector, due to its carbon-free chemical composition. This is particularly true for applications that rely on internal combustion engines (ICEs), although much research is still needed to achieve stable, reliable, and safe operations of the engine. To this purpose, direct injection (DI) of gaseous hydrogen during the compression stroke offers great potential to avoid backfire and largely reduce preignition issues, as opposed to port-fuel injection. Recently, much research has been dedicated, both experimentally and numerically, to understanding the physics and chemistry connected with hydrogen’s mixing and combustion processes in ICEs. This work presents a computational fluid dynamics (CFD) study of the hydrogen DI process in an optical engine operating at relatively low tumble conditions. Gaseous hydrogen pressurized at 86 bar is introduced directly into the combustion chamber via a centrally mounted 13-hole injector. Numerical simulations are carried out with the CONVERGE software. The turbulent flow exchange and in-cylinder charge motion are modeled with an unsteady Reynolds-averaged Navier-Stokes formulation closed by the renormalization group k-ε model. Several configurations of the computational mesh are investigated to evaluate its role in the prediction of the hydrogen jet’s early development and the resulting in cylinder mixture distribution. In the sections that follow, an evaluation of the effect of injector geometry features and start of injection timing on the evolution of the fuel-air mixture is presented. The numerical results are systematically compared against experimental planar laser induced fluorescence data from the literature to assess the performance of the CFD model and establish best practices for modeling relatively high-pressure injection of hydrogen using multi-hole injectors in ICEs.