Effect of hydrogen injection timing in a compression ignition engine operating in hydrogen diesel dual fuel mode

Stringent European CO2 emission regulations have stimulated the development of alternative technologies such as Dual Fuel (DF), which involves partially replacing fossil fuel with a low-carbon alternative. Hydrogen represents an ideal candidate for DF due to its properties, including the absence of carbon, high flame propagation speed, and high diffusivity. This study analyzes the combustion and performance of a 1L, naturally aspirated, three-cylinder in-line compression ignition off-road engine with a 17.5:1 compression ratio, originally equipped with a conventional diesel system and modified for diesel-hydrogen dual fuel operation. The conversion involved installing three PFI injectors in the intake manifold for hydrogen injection, attempting to minimize the volume between the intake valve and injector tip. Tests were conducted at a fixed engine speed of 2000 rpm, varying the engine load from 30% to 85% of maximum torque. The diesel contribution was maintained at 10%, while hydrogen provided the remaining energy, achieving a substitution ratio of up to 72%. The analysis showed that hydrogen without diesel doesn't burn efficiently, and the combustion of the air-hydrogen mixture is influenced by diesel injection and excess air in the engine. Subsequently, with the load fixed at 70%, the effect of hydrogen injection timing (SOI) on the engine's air intake flow was studied. The injection window was shifted by 112°CA, avoiding injection near the intake valve closing. The results showed that injection too close to the compression phase, (end of injection equal to 163 crank angle degree before top dead center), can cause irregular combustion problems.