Study on cyclic variability of dual fuel combustion in a methanol fumigated diesel engine

• Cyclic variability of diesel methanol dual fuel (DMDF) combustion was examined.
• High methanol substitution percent increases the cyclic variations at light loads.
• DMDF combustion stability at high loads is comparable with neat diesel combustion.
• Intake preheating remits cyclic variations at light load and boosts it at high load.
• The effect of diesel injection timing has no effect on cyclic variations.

An experimental study was conducted to investigate into the cyclic variations of diesel methanol dual fuel (DMDF) combustion on a methanol fumigated diesel engine. The effects of engine load, methanol substitution percent (MSP), injection timing and intake temperature on cyclic combustion variation were studied experimentally. In-cylinder pressure of 100 consecutive combustion cycles were recorded for each test case. The coefficient of variation (COV) of maximum in-cylinder pressure (pmax), maximum mass-averaged temperature (Tmax) and the indicated mean effective pressure (IMEP) were used to evaluate the cyclic variations of DMDF combustion. The results showed that the stability of DMDF combustion at high loads is comparable with that of neat diesel combustion. But the magnitude of cyclic DMDF combustion variations increases at light loads and more sensitive to the quantity of fumigated methanol. At light loads, COVpmaxCOVpmax and COVTmaxCOVTmax increase significantly and the crank angles corresponding to pmax and Tmax scatter more around with the increment of MSP. IMEP values show obvious fluctuations and are distributed in a wider range with an increase in MSP. DMDF combustion stability is very sensitive to intake temperature. At light loads the COVs of all combustion parameters decrease with the increment of intake temperature. In contrast, at high loads, the effect of intake temperature on the cyclic variations is quite small while there is a significant increase in the COVs when the intake temperature exceeds over 75 °C. Overall, injection timings does no effect on cyclic variations of DMDF combustion.