Hydrogen and ICEs: validation of a 3D-CFD approach for in-cylinder combustion simulations of ultra-lean mixtures with a focus on the combustion regime

This paper proposes a numerical setup for 3D-CFD in-cylinder simulations of H2-fuelled internal combustion engines. The flamelet G-equation model, based on Verhelst and Damköhler-like correlations for laminar and turbulent flame speeds respectively, is used to reproduce the flame propagation. The validation against experimental data from a homogeneous-mixture port-injection engine enables a focus on combustion simulation by minimising stratification uncertainties. Accurate flame propagation modelling is identified as the main challenge. The results on different operating conditions confirm the predictive capabilities of the framework, thanks to the agreement with the experimental pressure traces, combustion indicators and flame imaging. Notably, combustion rate predictions remain accurate even without considering the flame thermo-diffusive instability, as the turbulence effect dominates at the investigated conditions. The combustion regime is analysed by a modified Borghi-Peters diagram and it ranges from flamelet to thin reaction zones. This highlights the numerical setup flexibility, which accurately simulates combustion across different regimes.