Reduction of PM emissions from a heavy-duty diesel engine with diesel/methanol dual fuel

The effects of diesel/methanol dual fuel (DMDF) combustion, diesel oxidation catalyst (DOC) and intake air temperature on dry-soot and PM (particulate matter) emissions were investigated. Experiments were conducted on a 6-cylinder turbo-charged, inter-cooling HD (heavy duty) diesel engine modified to diesel/methanol dual fuel combustion mode. The pressurized methanol was induced into the intake manifold with six injectors and mixed with boost fresh air to form homogeneous mixtures and then ignited by pilot diesel in the cylinder. The amount of injected methanol was varied in accordance with engine power output while the amount of diesel fuel was remained constant under different operation conditions. Experimental results show that at low and medium loads, there is a significant decrease in the dry-soot emission in DMDF mode before the DOC, but a little increase at high load. An important phenomenon was observed that the mass and number concentrations of particulate matter significantly decrease at low and medium loads, due to the increase in fuel burned in the premixed mode and a reduction in diesel fuel involved, while they increase when the tested engine operates on the high engine condition, due to the spontaneous combustion of methanol and a reduction in oxygen for diesel in cylinder. After the DOC, the particulate mass and number concentrations are significantly reduced at all engine loads. Moreover, the temperature of intake air decreases with the increase of methanol injection, and the particulate number and mass concentrations in DMDF mode decrease with the decrease of the intake air temperature.