CFD-supported calibration optimization of a retrofit hydrogen–diesel dual-fuel engine

Dual-fuel (DF) hydrogen–diesel engines could offer a retrofit-compatible pathway for medium-/heavy-duty transport decarbonization. In this study, a 6-cylinder compression ignition engine retrofitted for hydrogen port fuel injection is investigated through a CFD-supported framework. A validated 3D-CFD model, based on an extensive experimental dataset, was applied to investigate injection strategies and calibration parameters in both retrofit and native DF engine modes. The model accurately captures combustion behavior, emissions trends, and the factors limiting hydrogen energy share (HES). Results show that an optimized native DF calibration enables up to 90% CO2 reduction relative to diesel operation while maintaining combustion stability. Particulate matter emissions are nearly eliminated at high HES, whereas low HES combined with non-optimized diesel injection results in PM levels comparable to diesel-only operation. The analysis highlights the decisive role of a coordinated optimization of HES and diesel calibration strategy in governing ignition dynamics, combustion efficiency, and soot formation.