Diesel versus DME: Effects of fuel properties, jet momentum, and fuel chemistry on the heat release process in mixing controlled compression ignition combustion

Dimethyl ether (DME) is a high cetane, oxygenated fuel that exhibits strong auto-ignition propensity and inherently low soot formation. However, its physical properties (e.g., density, viscosity, volatility) and chemical kinetics differ substantially from conventional diesel, resulting in spray evolution and combustion behavior that can deviate from typical diesel combustion. In this study, three-dimensional CFD simulations are used to decouple and quantify the roles of liquid-phase physical properties and gas-phase chemical kinetics by systematically swapping diesel and DME liquid fuel properties and reaction mechanisms to determine their effects on combustion. In addition, DME chemistry is replaced with surrogate mixtures of n-heptane and N 2 , as well as n-heptane and O 2 , to further isolate kinetic versus mixing effects. Under comparable injection pressure and injection duration, the DME cases exhibit earlier ignition and faster chemical heat release rates compared to diesel. These differences are linked to the combined influence of injected jet momentum rate and the fuel’s physical/thermochemical characteristics, which primarily govern ignition delay and early heat release. After ignition, the main (mixing-controlled) burn rate for both fuels is dominated by air–fuel mixing, which is mainly driven by the injected jet momentum, and shows comparatively weaker sensitivity to the detailed chemical mechanism or other physical properties like the fuel’s volatility. Nevertheless, the chemical kinetics mechanism remains critical for accurately predicting engine-out emissions. A key takeaway is that the oxygenation of the fuel results in higher injected momentum at matched injection pressure, and the higher momentum results in high mixing rates and heat release rates in mixing-controlled compression ignition combustion.