Visual Experimental Study On Single Droplet Evaporation Characteristics Of Emulsified Diesel Blending With Water

With the increasing demand for energy,people are paying more and more attention to environmental issues.Research on renewable energy and alternative fuels has received increasing attention.Due to its unique microstructure,emulsified fuel can generate micro-explosion during its evaporation process.Many small droplets are produced to make combustion better.At the same time,due to the high specific heat value of water,the peak temperature of combustion is reduced,and at the same time reduces nitrogen oxides?NOx?and Soot.At present,many engine researchers have carried out some researches on the characteristics of spray,evaporation,and combustion of emulsified fuel.However,there are few studies on evaporation and combustion of single droplets and the influence of microstructure on the evaporation of droplets.Therefore,it is of great theoretical and practical significance to study the influence of various factors on the evaporation process.This paper studied the evaporation characteristics of emulsified diesel under normal pressure conditions and at ambient temperatures of 300°C,400°C,500°C,and 600°C for W20?mass ratio of 20%water and mass ratio of 80%diesel?.The evaporation process exhibits a three-stage evaporation process,namely the transient heating phase,fluctuation evaporation phase and equilibrium evaporation phase.The single-droplet normalized diameter squared curve keeps stable at four different ambient temperatures during the transient heating phase;micro-explosion occurs mainly in the fluctuation evaporation phase,since the internal water nucleus can fully swell under low temperature conditions,but the energy absorbed by droplets can't be fully utilized under high temperature conditions,so maximum micro-explosion intensity,micro-explosion frequency,and cumulative micro-explosion intensity,first increases with increase ambient temperature and then decreases;the curve of the normalized diameter squared of a single drop at four different ambient temperatures in the equilibrium evaporation phase presents two different laws,namely a linear decrease and a step drop decrease.At the same time,as the temperature increases,the similarity curve changes from a single period to a multi-period overlap,from wavy to dentate,and as the temperature increases,instability of the similarity and deformation degrees increase.Then this paper studied the evaporation characteristics of W0?pure diesel?,W10?mass ratio 10%water and mass ratio 90%diesel?,W20?mass ratio 20%water and mass ratio 80%diesel?,W30?mass ratio 30%water and mass ratio 70%diesel?at an ambient temperature of500°C.And in the fluctuation evaporation phase,due to the increasing of the mass of water added,the energy accumulated in the droplets increases.However,the excessive water content made it easy to break the oil film and causes the droplets to explode prematurely after absorbing enough energy.Therefore,the maximum micro-explosion intensity,the micro-explosion frequency,and the cumulative micro-explosion intensity for the four kinds of single droplets increase first and then decrease with the increase of the water.At the same time,with the increase of the water added,the number of passive broken phenomena increase.The rate of micro-explosion became faster,and multiple water cores happen micro-explosion at the same time.The similarity curve has the phenomenon of period separation,overlapping period,and incomplete period.The similarity curve changes from wavy to dentate.In addition to pure diesel single droplet,the evaporation process of different emulsified diesel single droplets with the same Sauter mean diameter(D₃₂)at the same temperature also have three-stage evaporation.It is found that the size of the discrete water core in the droplet increase,the large-scale micro-explosion phenomenon weaken,the maximum micro-explosion intensity decrease,the entire evaporation duration become longer,the temperature rise slowly,and the temperature drop during the fluctuation evaporation phase is not obvious.The decrease in the size of discrete water cores within the droplets make the micro-explosion phenomenon more rapid and obvious,the large-scale micro-explosion phenomenon increase,and the maximum micro-explosion intensity increase.And different from the droplets with different Sauter mean diameter(D₃₂),the time of micro-explosion of the same Sauter mean diameter(D₃₂)droplets are gradually advanced with the increase of the water.But the maximum micro-explosion intensity,the micro-explosion frequency,and the cumulative micro-explosion intensity for the four kinds of single droplets still increase first and then decrease with the increase of the water.At the same time,it is found that the Sauter mean diameter?D32?,which is the discrete water core inside the droplet,is independent of trend of the similarity curve.It can only affect the stable time during droplet evaporation.But the influence is not more important than the amount of water added.Therefore,when the Sauter mean diameter?D32?changes,the degree of deformation of the droplets still increases with the increase of the water added,but the severity of the change is reduced.In the end this paper studied the evaporation characteristics of W20 which have the Sauter mean diameter(D₃₂)from 2?m-6?m at an ambient temperature of 500°C.The evaporation process of the five emulsified diesel single droplets also have three-phase evaporation process.In the transient heating phase,the evaporation mode changes from the large-scale water nuclear cooperative micro-explosion mode to the small-scale water nuclear coagulation to nuclear micro-explosion mode.Therefore,the time for the transient heating section will decrease first and then increase with the decrease of the Sauter mean diameter,and then decrease slightly and continue to increase.In the fluctuation evaporation phase,the two micro-explosive modes compete with each other,assist each other,and transform each other,causing the maximum micro-explosion intensity to decrease first,then increase,then decrease,and finally slightly increase as the Sauter mean diameter decreases;the frequency of micro-explosion and the cumulative micro-explosion intensity decrease first and then increase and then continue to decline as the Sauter mean diameter decreases.At the same time,with the decrease of the the Sauter mean diameter of the droplets,the curve of similarity changes from large amplitude fluctuating dentate structure to small amplitude fluctuating dentate structure,and then becomes to a wavy structure with multiple complete cycles.Finally,the wavy structure reduces to a single cycle.