Study Of Evaporation Mechanism And Atomization Characteristics Of Biomass Blended Oil

As a renewable and clean energy source,biodiesel is one of the alternative fuels to achieve the carbon peak and carbon neutral targets in the 14 th Five-Year Plan and to achieve green and low carbon.Biodiesel from a wide range of sources is one of the best available resources due to its similarity to diesel in physical parameters,but it has low energy density,the addition of nanoparticles with high thermal conductivity is one of the main means to improve its combustion performance.Methyl palmitate and Methyl oleate are typical representatives of two types of fatty acid methyl esters of biodiesel,of which methyl oleate is a typical unsaturated fatty acid methyl ester,which will undergo chain breaking and phase change to generate gas at high temperature,which is one of the main reasons for micro-explosion when the fuel droplets evaporate at high temperature.Blending nanoparticles can improve the physical properties of fuel such as thermal conductivity and mass diffusivity,so the mechanism of the effect of adding nanoparticles on the evaporation behavior of biodiesel droplets needs further study.To address the above issues,this thesis investigates the evaporation characteristics of the methyl palmitate/methylethyl oleate fuel blend and its nano-fuel droplets,and simulates the atomization characteristics of the fuel blend in the injector TS16949 nozzle outfield.The main work is as follows:First,the evaporation characteristics of methyl palmitate/methylethyl oleate fuel blends at 773 K and 973 K were investigated experimentally,and the test fuel was formulated and the feasibility of the data processing method was verified.The results showed that the droplets at 773 K and 973 K were subjected to micro-explosions due to bubbles generated by the phase change due to unsaturated long chain cleavage and the large difference in boiling points between the fuel droplet components.In addition,due to the internal circulation of the droplet,bubbles accumulate near the liquid film,and when the bubble pressure overcomes the surface tension of the droplet,the film breaks and microbursts occur.Meanwhile,a two-dimensional evaluation of the evaporation characteristics of single-droplet mixed fuel with obvious differences in boiling points from micro-explosion intensity SI and micro-explosion number MT was proposed,and the relationship equations of three factors,namely,ambient temperature,micro-explosion intensity SI and evaporation rate K,were constructed to obtain the optimal evaporation performance ratios of two types of fatty acid methyl esters,and a conceptual model of microburst of saturated and unsaturated fatty acid methyl esters was established.Secondly,the effect law of blending different concentrations of nanoparticles on the evaporation characteristics of fuel blends at two ambient temperatures of 773 K and 973 K was experimentally investigated.Firstly,the irrelevance of surfactants was verified,and the evaporation characteristics of the four concentrations of nanofuel were investigated from the characterization perspectives of normalized diameter squared,evaporation time in each phase,time share in each phase,volume change amount,evaporation lifetime and evaporation rate.The results show that due to the high thermal conductivity of nanoparticles promoting the heat transfer effect between the fuel and the surrounding environment,the low concentration of nanoparticles will promote the evaporation of fuel droplets and accelerate the evaporation of fuel,while the addition of higher concentration of nanoparticles inhibits the evaporation of droplets due to the aggregation of nanoparticles into a shell in the liquid film,which prevents the heat transfer between the droplets and the ambient temperature.Finally,the simulation investigated the nano-fuel atomization characteristics of the injector nozzle external field.For the effect of long-chain unsaturated fatty acid methyl ester cracking,an expression for the thermal cracking of unsaturated fatty acids was constructed,and the controlling equation was established according to the gas-liquid phase equilibrium by substituting the physical parameters to simulate the evaporation characteristics of droplets at an ambient temperature of 773 K and to validate the evaporation model.Further,the blended fuel evaporation model was embedded into the atomization model and the nozzle external field atomization characteristics,including spray cone angle,penetration distance and sot mean diameter(SMD),were simulated and investigated.The results show that blending nanoparticles with higher concentration will reduce the spray cone angle and penetration distance and other characteristic parameters,which will decrease the atomization effect of the fuel.The addition of suitable proportion of nanoparticles to the base oil can improve the physical parameters of the fuel,increase the energy density of the fuel,and thus improve the atomization quality of the fuel.