Biodiesel–Natural gas/Hydrogen Dual Direct-Injection Engine Optimization via Fuel Energy Matching

This study numerically investigates fuel-energy matching in a biodiesel–natural gas (NG)/hydrogen dual direct-injection engine by examining the coupled effects of biodiesel energy ratio (BER), hydrogen energy ratio (HER), and biodiesel start of injection (BSOI) on combustion, thermal efficiency, and emissions. A moderate BER improves ignition and combustion, whereas an excessive BER prolongs combustion and reduces efficiency, especially under retarded BSOI. Hydrogen addition promotes earlier heat release, but its benefit depends strongly on BER and BSOI because it also changes the NOx–soot trade-off. The BER associated with favorable performance is therefore not fixed, but shifts with HER and BSOI. Under HERs of 0–10%, the favorable condition occurs at BER = 15% with BSOI = −18°CA ATDC. At HER = 20%, it shifts to BER = 10% with BSOI = −10°CA ATDC, yielding an indicated thermal efficiency of 43.76%, NOx of 12.8 g/kWh, and soot of 5.34 × 10 ⁻6 g/kWh. These results show the importance of coordinated fuel-energy matching for balancing efficiency improvement with emissions control.