Experimental Study And Micro-Explosion Model Of Alcohol-Based Two-Component Blended Fuel Droplet

In the research field of internal combustion engines,the’micro-explosion’of sprayed oil droplets allows the droplets to broke up into smaller droplets,which increases the contact area between fuel and air,resulting in a more homogeneous mixture and improving engine combustion and emission performance.In this paper,Alcohol-octane blended fuels are investigated using a combination method of simulation and experiment.Firstly,the single droplet micro-explosion mechanism is analysed,and the whole process from droplet nucleation to explosion is investigated by establishing a homogeneous nucleation sub-model,a bubble growth kinetic sub-model and a droplet micro-explosion sub-model within the droplet.The experimental study of the evaporation process of a single droplet is then carried out to investigate the evaporation and micro-explosion characteristics of a two-component blended fuel.Firstly,a homogeneous nucleation model for single/dual component fuels is proposed through non-equilibrium thermodynamics,and the nucleation process of single component fuels is analysed.Non-Random Two Liquids(NRTL)and Wilson bubble point pressure models are proposed for methanol-hexadecane and ethanol-hexadecane blended fuels respectively to predict the bubble point pressure under different operating conditions.The critical bubble radius,homogeneous nucleation rate and superheat limit temperature are calculated for fuels with different alcohol blending ratios under different operating conditions.A bubble growth kinetic model for pure/two component fuel droplets is proposed.The bubble growth process is numerically simulated using a program written in MATLAB software,and the heat and mass transfer mechanism inside a single droplet is analysed,and finally a micro-explosion model of the droplet is proposed on the basis of the bubble growth model.The bubble size,the bubble growth rate,the variation of the droplet vapor surface temperature with time and the bubble explosion time scale are discussed in the process from bubble nucleation to droplet explosion in the full cycle of bubble growth.It is found that the bubble growth characteristics in the later stages in single component fuel droplets are entirely determined by heat transfer within the thermal boundary layer,while the bubble growth characteristics in the later stages in two component blended fuel droplets are influenced by heat transfer as well as mass diffusion,which plays a more dominant role.The influence of liquid temperature on the mass diffusion effect in the later stages of droplet growth is more significant than that of ethanol concentration.The evaporation and micro-explosion characteristics of ethanol-hexadecane blended fuels with ethanol blending ratios of 10%,20%,30%,40%and 50%are investigated using a single droplet evaporation experimental setup.Parameters such as the variation of the normalized droplet diameter and the droplet temperature during the evaporation process are obtained for the single/bicomponent fuel droplets,and morphological observations are made on the evaporation and micro-explosion processes of the droplets.It is found that the evaporation process of single component fuels generally satisfies the typical ~2D laws.For two-component blended fuels,there is an acceptable ratio and ambient temperature limit for the droplet to achieve the best micro-explosion effect during evaporation.The micro-explosion intensity of the fuel droplets at low temperatures is also found to have an approximate parabolic relationship with the blending ratio of ethanol.