Experimental And Numerical Study On The Single Multicomponent Droplet Evaporation

With the energy problem and vehicle emission problem arises,meanwhile,recognizing the disadvantage of the traditional combustion process,the internal combustion engine researchers have explored new combustion modes to find the way to improve the fuel economy and control the formation processes of pollutants.The key to organize the internal combustion process is the multi-component fuel droplet evaporation process and the vapor distribution.So it is necessary to base on the two phase flow method to study the fuel droplet evaporation process.In this paper,based on the OpenFOAM,an open source CFD software package,a three dimensional droplet evaporation model which droplet interface is captured by the VOF method is setted up.A single energy conservation equation is derived from the gas and liquid energy conservation equation.The convection term and diffusion term of specie conservation equation have been modified for fitting the VOF method.To take into account the non-physical value of vapour mass fraction gradient at the liquid-gas interface due to discontinuity in the droplet interface.A modified gradient calculation method which is based on gas-liquid interface normal direction is used in the gas-liquid interface mass fraction gradient calculation.The interfacial Stefan flow effect has brought into the interfacial mass transfer model which is based on the Fick diffusion law.Finally,a OpenFOAM solver of droplet evaporation is implemented.A experiment study of fuel droplet evaporation process have been done with the use of high speed camera.The droplet inside temperature is collected by the suspension which is made by the thermocouple wire.In the experiments,a higher ambient temperature cause a faster evaporation process.In the bi-component droplet evaporation experiment study,a higher proportion of butanol cause a slower droplet heating process,and the two stage of droplet evaporation process is more obvious.The evaporation experiment data of dodecane droplet experiment is used to validate the numerical model.The additional thermal conductivity caused by suspension has been introduced into the evaporation numerical model.And then,the effect of suspension on the droplet evaporation has been study.The results show that the effect of additional thermalconductivity can significantly accelerate the droplet evaporation process,and increase the droplet equilibrium temperature.When the surface of the droplet contact with the thermocouple node,the evaporation process is significantly speed up.In this paper,the evaporation characteristics of single-component and multi-component droplet are also studied.The results show that,the higher ambient temperature,the droplet equilibrium temperature is greater and the droplet lifetime is shorter.The droplet initial temperature mainly affects the transient heating stage of the droplet evaporation process,the droplet initial temperature is higher,the transient heating stage is shorter.The numerical study on evaporation of droplet which composed of difference proportion of butanol and dodecane have been done too.The results show that,the concentration of butanol has little influence on the final droplet equilibrium temperature.However,as the concentration of butanol is increased,the droplet lifetime is shortened.