Combustion and Emissions Characteristics of a Dual-Fuel CI Engine under Varying Hydrogen Energy and Equivalence Ratios: A Computational Study

Hydrogen is widely recognized as a promising zero-carbon fuel for internal combustion engines due to its zero carbon emissions, high laminar flame speed, and wide flammability limits. In dual-fuel compression ignition engines, substituting part of the diesel fuel with hydrogen can significantly reduce carbon-based emissions while maintaining or improving ther-mal efficiency. This study investigates the combined effects of hydrogen substitution ratio (HSR) and equivalence ratio (Φ) on combustion characteristics, engine performance, and emissions in a diesel-hydrogen dual-fuel engine. Three HSR levels (50, 70, and 90) are examined across equivalence ratios ranging from 0.5 to 0.8. A three-dimensional computational fluid dynamics (CFD) model is developed using ANSYS Forte. The model employs an Eulerian-Lagrangian framework, incorpo-rating the unsteady Reynolds-averaged Navier–Stokes (URANS) equations for flow resolution and the G-equation for turbu-lent flame propagation. Spray breakup dynamics are modeled using the Kelvin–Helmholtz/Rayleigh–Taylor approach, while turbulence is captured with the RNG k-ε model. Results indicate that increasing both the HSR and equivalence ratio reduces CO₂ emissions. At HSR 70, unburned hydrocarbon (UHC) emissions decrease by up to 82% as Φ increases from 0.5 to 0.8. Furthermore, the indicated specific fuel consumption (ISFC) decreases, particularly at high HSR, reflecting improved fuel economy. These findings highlight the potential of diesel-hydrogen dual-fuel operation for achieving cleaner and more efficient engine performance.