Development of novel dimethyl ether – Glycerol blends with improved viscosity and miscibility for potential compression-ignition engine application

Abstract

Dimethyl Ether is a promising diesel alternative fuel due to its significantly low well-to-wheels greenhouse gas emissions from certain renewable pathways and soot-free combustion characteristic. However, in a compression-ignition engine, the fuel injection system exhibits decreased durability due to the dimethyl ether’s extremely low viscosity (i.e., 0.15 cSt @ 40 °C). In this study, the viscosity of dimethyl ether is improved to the level of No.2 diesel fuel (i.e., 1.9 cSt @ 40 °C) via glycerol blending. To prevent the phase separation between glycerol and dimethyl ether, effective co-solvents are determined based on different selection criteria: Hansen Solubility Parameter-based “averaged solubility distance”, viscosity, oxygen mass content, health and environmental impacts, and renewable production capability. As a result, propylene glycol and di-propylene glycol are selected as the final co-solvents and are used to form the two final dimethyl ether blends: i) Michigan DME blend I (i.e., dimethyl ether/dipropylene glycol/glycerol); and ii) Michigan DME blend II (i.e., dimethyl ether/propylene glycol/glycerol). The minimum mass ratio of co-solvent to glycerol to prevent the phase separation is measured to be 1.5 and 1.65 for Michigan DME blend I and II, respectively, at 40 wt% dimethyl ether content. The kinematic viscosity of the two final blends was successfully improved to the level of No. 2 diesel fuel at around 40–43 wt% dimethyl ether content, a higher dimethyl ether content than any previous blends reported. A preliminary engine demonstration result with one of the final dimethyl ether blends (i.e., Michigan DME blend I) is also briefly presented here with suggestions for future improvement. While the current article covers the blend development part of the current research, its companion article covers the life-cycle greenhouse gas emissions assessment for one of the final dimethyl ether blends (i.e., Michigan DME blend II).