Mechanism of Enhanced Heat Release in Spray Combustion of a Methanol–DME Blended Fuel

This paper investigates the spray combustion characteristics of a methanol–DME blended fuel with a DME mole fraction of 0.57 in a constant volume vessel. The rate of heat release (ROHR) was evaluated using pressure-based heat release analysis. The results show that the methanol–DME blended fuel requires a longer injection duration due to the lower LHV (lower heating value), but it exhibits a shorter combustion duration than conventional diesel fuel, together with a higher ROHR normalized by the injection LHV rate and a shorter afterburning duration. To elucidate the relationship between the spray combustion processes and the ROHR characteristics, the spray flame was visualized using schlieren and OH chemiluminescence imaging techniques. In addition, a one-dimensional simulation based on a diesel jet model was conducted to evaluate the distributions of the equivalence ratio. These analyses reveal that the lower theoretical air–fuel ratio, attributed to the oxygenated nature of the methanol–DME blended fuel, reduces the equivalence ratio within the spray, promoting earlier formation of near-stoichiometric mixtures. As a result, the ROHR reaches and sustains its maximum earlier during mixing-controlled combustion, and fuel consumption is enhanced during afterburning.