Numerical Analysis of Lean Hydrogen Combustion in an SI Internal Combustion Engine Using G-Equation Model

Hydrogen represents a promising fuel for spark-ignition internal combustion engines, particularly under lean operating conditions, where high combustion efficiency can be combined with very low NOx emissions. In this work, experimental measurements and three-dimensional CFD simulations are used to investigate hydrogen combustion in a port-fuel-injected single-cylinder research engine operating at 1000 rpm and three relative air–fuel ratios, λ = 1.7, 2.0, and 2.3. RANS simulations are performed using the G-equation combustion model in CONVERGE, with hydrogen laminar flame speed supplied through a tabulated approach based on detailed chemical kinetics. Different values of the turbulent flame-speed model constant b1 are assessed over the complete set of operating conditions, and b1=3.0 is selected as the best overall compromise and retained for all simulations. The model reproduces the experimentally observed slowing of combustion with increasing λ, while differences in the combustion-rate profile and late combustion become more pronounced towards the leanest condition. The CFD overpredicts the maximum in-cylinder pressure by 4.1–9.9%, while its crank-angle location is reproduced within approximately 1.2 CAD. Increasing mixture dilution substantially reduces the predicted in-cylinder temperature and NOx formation, with NOx reductions of 84% and 98% at λ = 2.0 and 2.3, respectively, relative to λ = 1.7, consistently with the strong experimental reduction. Overall, the results indicate that a single G-equation calibration can provide a consistent description of the main changes in hydrogen combustion behavior across the investigated lean operating range, without condition-specific adjustment of the turbulent flame-speed parameter.