Toward Low-Carbon Diesel Mobility: Experimental Evaluation of a Hydrogen–Diesel Dual-Fuel Passenger Car

This study investigated the effects of partial substitution of diesel fuel with hydrogen in dual-fuel operation on the engine operating characteristics, energy performance, and exhaust emissions of a compression-ignition passenger car engine. Hydrogen was supplied into the intake manifold, and the vehicle was tested on a chassis dynamometer at a constant vehicle speed under varying load conditions. To avoid the onset of abnormal combustion, the maximum stable H2 mass fraction under diesel–hydrogen dual-fuel operation had to be reduced from 19% to 11% as engine load increased over the brake mean effective pressure (BMEP) range of 0.38–0.88 MPa, while the corresponding H2 volume fraction in the intake air increased from 4.2% to 6.3%. Hydrogen addition reduced diesel fuel consumption and CO2 emissions, although its effect depended strongly on engine load. At a 10% H2 mass fraction, diesel fuel consumption decreased by 20–25%, and CO2 emissions decreased by 17–21%. At low load, hydrogen addition improved brake thermal efficiency (BTE) and reduced NOx emissions. At higher loads, reaching the hydrogen flammability limit reduced the excess-air ratio, deteriorated diesel combustion quality, and increased NOx emissions and the exhaust smoke absorption coefficient. Higher H2 concentrations reduced combined NOx + HC emissions at low load but increased them at medium and high loads. Overall, hydrogen enrichment was most effective at low and medium loads, below the abnormal combustion onset limit, indicating that load-sensitive hydrogen dosing is required for efficient and environmentally favourable diesel–hydrogen dual-fuel operation.