Evaporation Characteristics And Experimental Study Of Diesel-Jatropha Biodiesel Fuel Droplet

Diesel engine has been widely used because of its large power and good economy.The quality of fuel spray and evaporation is an important factor affecting the diesel cylinder combustion.As a fossil fuel alternative,biodiesel has good cleanliness and economy and can reduce the emission of harmful substances in diesel engine cylinder combustion.However,the bio-oil by preparing from raw has relatively high density and viscosity,which leads to poor fuel flow characteristics and not conducive to fuel atomization and evaporation.Therefore,it is necessary for bio-oil transesterification to produce biodiesel to enhance the fuel flow characteristics and improve the combustion characteristics.Compared with diesel,biodiesel has a low calorific value.At that conditions,mixing biodiesel with diesel to increase the fuel calorific value,and reduce fuel consumption.Therefore,in order to find out the evaporation process and mechanism of Jatropha methyl esters(JME)-diesel blend fuel,its influence on the atomization and combustion inside the cylinder of diesel engine.In this paper,the characteristics of evaporation and micro-explosion of mixed fuels at different temperatures were studied from two aspects: experimental and theoretical simulations.The main work is as follows:Firstly,Alkaline transesterification method was used to prepare JME fuel and the ratio of binary mixed fuel with diesel.Then,to determine the percentage of major chemical compositions in the fuel,to calculate the fuel properties including density,viscosity et al.based on some literatures.In the condition of meeting the biodiesel standards,JME fuel mixed with diesel by the proportion of 10%,20%,50%,and they can be recorded as JME10,JME20,JME50.Placing at room temperature to retain experimental use.Secondly,the droplet evaporation experimental apparatus was used to carry out experiments.The image processing program was designed based on matlab,by which droplet normalized square diameter can be extracted from the droplet evaporation process images by high-speed camera shooting automatically,get droplet evaporation curve.The evaporation and micro-explosion characteristics of diesel,Jatropha biodiesel and their blends respectively were studied under atmospheric pressure,ambient temperature of 573 K,723K and 873 K.The results showed that,the blend ratio of JME fuel directly affected the evaporation rate and droplet life at the same ambient temperature.With the increase of blend ratio,the evaporation rate of fuel decreases and the evaporation time increases,but the delay time of droplets micro-explosion shortens and the intensity of micro-explosion decreases.Improving the ambient temperature,the evaporation characteristics of blend fuel made the essential changes.The nucleation and puffing of bubbles inside the droplets,and the continuous jet and multiple micro-explosion phenomena were recorded by high-speed camera,which can be attributed to the differences in diesel and biodiesel components and the differences in boiling points.In addition,the intense movement of bubbles inside the droplets at high temperatures can promote droplets to deviate from the center of thermocouple,resulting in a local excessive temperature and frequent micro-explosion.Considering the vaporization and micro-explosion characteristics of droplets,20% JME in diesel oil has good evaporation effect.Finally,this paper established a single droplet evaporation model and simulating the evaporation characteristics of fuel.In order to simplify the construction of the evaporation model and improve the computational efficiency,the infinite heat conduction model,the theoretical equations and empirical formulas of the physical properties of the fuel-air phase were used to build the binary compositions fuel evaporation model.The diesel and Jatropha biodiesel were replaced by n-dodecane and n-hexadecane,and the evaporation characteristics at ambient temperature of 573 K were simulated.Then,this paper studyed the effect of differences between components and interactions on droplet evaporation,and obtained the ideal results compared with the experiment.It provides the guide for the subsequent study of multi-component droplet evaporation.