The One-Dimension Numerical Simulation Of Dimethyl Ether Supercritical Evaporation

The understanding of droplet evaporation at high pressure and temperature environments is of importance to many industrial applications such as liquid-fueled rocket engines and diesel engines. During spray combustion in such devices, the evaporation process may occur at pressures near or above the critical pressure of the fuel. Therefore, many effects that are assumed negligible at low and moderate ambient pressure need to be re-evaluated. These effects are the transient character of the gas phase, non-ideal gas phase behavior, the real gas effect on the heat of evaporation, and the vapor-liquid equilibrium condition at the droplet interface.A comprehensive analysis of dimethyl ether droplet evaporation at high pressure,high temperature environment has been carried out. The model is based on complete time dependent conservation equation, with a full account of variable properties and vapor liquid interface thermodynamics. The influence of various high phenomena including ambient gas solubility,property variation and thermodynamic non-ideality on the mechanism are examined systemically. Results indicate that the ambient gas pressure has a profound impact on the evaporation process, d2 law behavior became invalid and the droplets can reach theirs critical point in a totally transient process. Coupled diffusion processes are also studied and found to be an important factor in high pressure droplet evaporation. The results of comparative of liquid and gas phase models for DME droplets heating and evaporation, suitable for implementation into CFD codes, are also presented. Among liquid phase models, the analysis is focused on the model based on the assumption that the liquid thermal conductivity is infinitely large, and the so-called effective thermal conductivity model. Two gas phase models are compared, classical film model and Sirignano film model. Results indicate that the ambient gas pressure has a profound impact on the evaporation process. And the droplet surface temperature at the initial stage of evaporation does practically depend on the choice of liquid phase model. A new evaporation model is constructed. This model is based on the assumption of the temperature profile in the droplets. A rigorous numerical solution, without restrictions on temperature profiles inside droplets, is compared with predictions of the temperature profile and isothermal models. The comparison shows the applicability of a temperature profile model to modeling of the heating of fuel droplets in realistic diesel engines. The simplicity of the model makes it convenient for implementation into CFD codes.