Research On Evaporation Characteristics And Micro-explosion Mechanism Of Nanofluid Fuel Droplets

The development of high energy density and clean emission fuel is the main way to improve the combustion and emission performance of diesel engines.Nanofluid fuel containing metal or non-metallic nanoparticles,it can improve the fuel energy density,and the droplets will breakup in the cylinder of the diesel engine,producing secondary atomization and promoting the combustion.However,the evaporation characteristics and micro explosion mechanism of nanofluid fuel are not clear.In this dissertation,the nanofluid fuel(diesel/nano-cerium oxide)is used as the research object.The evaporation characteristics,puffing characteristics and parameter influence rule of nanofluid fuel were studied by single pendent droplet evaporation apparatus.The characteristic conditions of the micro-explosion of nanofluid fuel were obtained,and the mechanism of nanoparticle micro-explosion in diesel fuel was obtained.Meanwhile,one dimensional single component nanofluid fuel evaporation model was established,which provides a theoretical reference for further study on the evaporation mechanism of high temperature,high pressure and micro-small fuel droplets in the actual cylinder of diesel engine.First of all,the morphological image processing method is applied to droplet image processing,and batch image processing program is developed.MATLAB software combined with morphological image processing method were used to batch automatic extraction the droplet evaporation process diameter data.And the image processing uncertainty was calculated.The results show that the calculated uncertainty of droplet squared diameter is 4.35%,which does not affect the law of droplet evaporation.Secondly,the droplet evaporation characteristics of nanofluid fuel were systematically studied by single pendent droplet evaporation apparatus.The evaporation characteristics and micro-explosion mechanism of droplets at low temperature and high temperature were obtained,and the influence of nanoparticle concentration,initial droplet volume and ambient temperature on droplet evaporation were also obtained.The consistency and repeatability of experimental apparatus were verified through repeated experiments,and the independence of the surfactant was also verified.On the basis,the evaporation rate curve of nanofluid fuel at low temperature and high temperature were studied with the boundary temperature of 800K in the diesel engine,and the instantaneous evaporation rate/equivalent evaporation rate,the evaporation stage time and the phase of droplet evaporation were analyzed.The evaporation characteristics of various stages of nanofluid fuel were obtained.The results show that the evaporation of nanofluid fuel is slower than that of pure diesel at low temperature,this is mainly because the formation of porous spherical shells in evaporation process inhibits evaporation.However,at high temperature,the evaporation of nanofluid fuel is faster than that of diesel.This is mainly due to the formation of different nucleation sites within the droplets.The formation of heterogeneous nucleation sites causes a large number of bubbles in the droplets,then lead to droplet micro-explosion and accelerate droplet evaporation.Finally,based on the theory of classical D~2 law,n-hexadecane was chosen as a substitute for diesel fuel,one-dimensional single component nanofluid fuel evaporation model was proposed to calculate droplet evaporation rate,and the feasibility of the model was used the pendent droplet evaporation test data to verify.Which provides a theoretical basis for revealing the mechanism of micro-explosion and the influence of the atomization characteristics.