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On the basis of the molecular thermodynamics for fluids, the thermodynamic properties of DME are developed for pressure p ≤ 500 bar and temperature T ≤ 200 °C, which covers pressures and temperatures that a DME fuel system for the CI-engine application would experience. The properties cover subcooled, two-phase, and superheated/supercritical regions, including p-v-T properties, enthalpy, entropy, latent heat, heat capacity, speed of sound in vapor, liquid and two-phase mixtures, bulk modulus, and surface tension. A volume-cubic equation of state for DME also is developed, which allows calculating the DME density at any given pressure and temperature analytically. All the properties are given in equations as well as in charts. For convenience in two-phase-flow applications, e.g., design of the fuel tank and cavitation analysis, the saturated properties are also given in tables, listed in both pressure and temperature up to the critical point.

A novel fuel tank for storing liquid dimethyl ether (DME) has been developed. This fuel tank was made of cast aluminum with a water capacity of 40 liters. It contains two fluids: liquid DME and a vapor-liquid mixture of propane. A diaphragm separates the two fluids. The propane in the tank is a pressurizing fluid that pressurizes DME into a subcooled-liquid state; and, it also functions as a driving fluid that pumps the liquid DME from the tank to the injection pump using its vapor pressure. These features characterize the tank as a thermodynamic pump. Several hundred hours of tank tests at various temperatures have been conducted. Results of tank filling-discharge cycles simulating those in vehicle applications demonstrated that the concept of the two-fluid thermodynamic pump works and that the tank design is successful.

This paper analyzed chemical and thermophysical properties of dimethyl ether (DME) as an alternative fuel for compression-ignition engines. On the basis of the chemical structure of DME and the molecular thermodynamics of fluids, equations have been developed for most of the DME thermophysical properties that would influence the fuel-system performance. These equations are easy to use and accurate in the pressure and temperature ranges for CI engine applications. The paper also pointed out that the DME spray in the engine cylinder would differ significantly from that of diesel fuel due to the thermodynamic characteristics of DME. The DME spray pattern will affect the mixing and combustion processes in the engine cylinder, which, in turn, will influence emissions from combustion.