Thermodynamic Properties of Dimethyl Ether - An Alternative Fuel for Compression-Ignition Engines 2004-01-0093

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. Because they are derived on the basis of the general thermodynamic theories, these properties have a reasonable accuracy; thus, they can be used as reliable estimations when the experimental data are unavailable. For the two-phase regions, the calculated properties are compared with available experimental data reported in the literature and excellent agreements are observed. Comparisons between diesel fuel and DME are conducted on the properties affecting the engine fuel management. Thermochemical properties for the DME-air mixture and characteristics of the exhaust from DME combustion are also analyzed. Finally, to facilitate the DME fuel system design and modeling, the transport properties from the authors' previous work, such as viscosity, thermal conductivity and Prandtl number for liquid DME, are included in the paper, making this paper a rich source for DME properties.