A Numerical Study On Supercritical Evaporation Of Dimethyl Ether Droplets

Due to the physical and chemical special properties of dimethyl ether (DME) and in-creasing enhancement of in-cylinder conditions, a deeply study on supercritical evaporation process of DME is more necessary for the application and theory research of this widely concerned alternative fuel in internal combustion engine (ICE).Based on the in-cylinder evaporation conditions of DME, the limitations for the stud-ies of moderate and low pressure evaporation process are analyzed. A review of an array of studies on fuel evaporation in high-pressure and supercritical environments is presented, based on which the characteristics of supercritical evaporation and the crucial problems in its numerical simulation are concluded.Theory and calculation methods of high-pressure vapor-liquid equilibrium (VLE) are discussed. Binary interrelation coefficients are fitted by the experimental data. A FORTRAN program is developed to solve the high-pressure VLE using a method of equation of state (EOS). Based on the results of cal-culation, the dissolvability of ambient gas in droplets under supercritical conditions and the migration of critical mixing temperature are discussed. The results from different EOS are compared. The differences and relationship between Raoult's law and VLE calculation are analyzed theoretically.Characteristics and theory of supercritical fluid are introduced. A detailed research of selection and calculation of thermophysical and transportation parameters under supercriti-cal condition are carried out. Thermophysical parameters such as density and isobaric heat capacity of gas and liquid and partial molar heat of phase change, while transportation pa-rameters such as binary diffusion coefficient and heat conductivity and viscosity of gas mixture are calculated. Calculated results are compared with experimental data based on the theories concerned. A set of calculation methods for Nusselt and Sherwood number is ob-tained by the review of documents.Finally, a mathematical model is established for supercritical evaporation of DME droplets in nitrogen, and numerical simulation of which is performed by using a FORTRAN program. The effects of ambient pressure and temperature as well as droplet motion on droplet heating-up; droplet radius changing ratio and droplet lifetime are then discussed.