Experimental Study on Combustion Characteristics of Methane/Gasoline Dual-Fuel in a SI Engine at Different Load Conditions

Methane as an attractive alternative fuel offers the most potential in clean combustion and low CO₂ emissions. In this work, combustion characteristics of methane/gasoline dual-fuel were investigated in a spark-ignited engine with port-injection of methane and direct-injection of gasoline, allowing for variations in methane addition and excess air coefficient. Engine experimental results showed that under low load conditions, as methane mass rate was raised, there was a promotion in methane/gasoline dual-fuel combustion, and this became more obvious at lean conditions. Similar observations were also obtained when the engine was operated at intermediate load conditions, but a prolonged combustion duration was found with the methane addition. Further analysis showed that the promotion of methane/gasoline dual-fuel combustion with methane addition mainly occurred in the early stage of combustion, especially for lean conditions. Under large load conditions, methane addition showed good knocking resistance and the potential of knocking limit extension. Through advancing spark-ignition timing, methane/gasoline dual-fuel combustion was able to provide sufficient torque output with optimized combustion phasing. Current research results shall give insights into combustion optimization of methane (or natural gas) and gasoline dual-fuel engines.