Effect of intake pre-heating and injection timing on combustion and emission characteristics of a methanol fumigated diesel engine at part load

Diesel–methanol dual fuel (DMDF) engines at light loads suffer from low thermal efficiency and high unburned percentages of fuel. Pilot fuel injection timing and intake temperature are two important parameters which affect the combustion process in DMDF engines. In present experimental work, the combined effects of intake temperature and injection timing on the performance of a DMDF engine have been studied. The experiments were conducted on a methanol-fumigated diesel engine at 25% of full load and the results concerning performance, combustion characteristics and emissions were analyzed. Results show that the low efficiency at light loads can be improved significantly by raising the intake temperature and advancing the injection timing of direct-injected diesel. Increasing the intake temperature also significantly decreases the heat release rate of premixed combustion and increases the combustion rate of methanol burned by flame propagation. Flame propagation of the methanol–air mixture disappears gradually and DMDF combustion transforms into single stage combustion as the injection timing is retarded. When injection timing is retarded after 4.6° crank angle, misfire occurs at higher methanol substitute percent (MSP) and lower intake temperature, while the auto-ignition of methanol occurs at lower MSP and higher intake temperature. Under DMDF operation, soot and nitrogen oxides trade-off dilemma is completely broken at lower intake temperature and higher MSP.