Numerical Study On The Evaporation Characteristics Of The Multi-Component Fuel Droplet

Mixing different fuels together as new fuels so as to realize energy-saving and emission reduction, become one of the popular research fields. Right now, the mixture of gasoline(diesel) and ethanol had been widely used in petrol(diesel) engines, both of the applications turned out to be useful. During the working processes of engines, the evaporation of droplets affects the space distribution of fuel-vapor and the formation of fuel-air mixture gas, and the overall combustion and emission processes. Thus, it is necessary to study the evaporation process of mixture fuels.Nowadays, both at home and abroad, the study on applying DME to diesel engines has got certain process, but the application of DME on petrol engines is a new project. Owing to the lower octane number, if petrol engines fueled DME solely, it would easily result in engine-knocking; on the other hand, the low heat value of DME could hardly meet the need of practical uses. Take liquefied petroleum gas(LPG) as the neutralizer of boosting the octane number and heat value of DME, and obtained the mixture fuels, turned out to be a new solution.In this paper, the methods of calculating the gas-liquid equilibrium were simply introduced, and the Raoult’s law related with equilibrium constant, e.g. K, was chosen to obtain the gas-liquid equilibrium, in order to simplify the phase-equilibrium calculation under subcritical conditions. Under subcritical conditions, the physical properties of each component at gas phase and liquid phase were inconstant; different mixing-rules were used for the calculation of mixture densities, viscosity of fuel mixture vapor, etc. Since then, the whole system of calculation method for mixture properties was established.Based on the model for the evaporation of simple-component droplets, the physical mathematical model for the multiple-component droplets was established. With the calculation procedure compiled by Fortran code, the subcritical evaporation processes of DME/LPG mixture droplets was numerically simulated. In the model, the diffusion between the components were neglected, the diffusion of the fuel components vapor in the ambient gas surrounding the drop is simplified to the binary diffusion between the fuel components and ambient air. It was founded that the temperature of droplets would reach up to the wet bulb temperature after being heated. The wet bulb temperatures of each component depend on the ambient temperature and pressure. And the wet bulb temperature of mixture-droplet closely relate with the mole friction of each component. The subcritical evaporation processes of mixture-droplets agreed with the d2law. Higher temperature or lower ambient pressure would promote the evaporation of droplet. The relative motion between the droplets and the ambient gas advanced the heat transfer from ambient gas to droplets, which accelerated the evaporation. With the same mass of droplets, the life-time would be longer as the initial mole friction of the difficult-volatile component was more.