A comprehensive analysis of liquid fuel droplet evaporation at supercritical conditions is performed.The numerical model is based on complete time-dependent conservation equations,with a full account of variable therm...A comprehensive analysis of liquid fuel droplet evaporation at supercritical conditions is performed.The numerical model is based on complete time-dependent conservation equations,with a full account of variable thermophysical properties and vapor-liquid interfacial thermodynamics.And the model employs the Peng-Robinson(PR)equation of state(EOS).As a specific example,problems involving n-heptane droplet in nitrogen gas are investigated.The results indicate that the increase of ambient pressure and temperature results in the increase of surface temperature rise rate and surface regression rate.The transition from subcritical state to supercritical state can occur at the droplet surface when the droplet evaporates in a strongly supercritical environment.展开更多
To solve the wall-wetting problem in internal combustion engines,the physical and chemical etching methods are used to prepare different wettability surfaces with various microstructures.The evaporation characteristic...To solve the wall-wetting problem in internal combustion engines,the physical and chemical etching methods are used to prepare different wettability surfaces with various microstructures.The evaporation characteristics and morphological evolution processes of diesel and n-butanol droplets after hitting the various surfaces are investigated.The results show that the surface microstructures increase the surface roughness(Ra),enhancing the oleophilic property of the oleophilic surfaces.Compared with n-butanol droplets,the same surface shows stronger oleophobicity to diesel droplets.When a droplet hits an oleophilic property surface with a lower temperature,the stronger the oleophilicity,the shorter the evaporation time.For oleophilic surfaces,larger Ra leads to a higher Leidenfrost temperature(TLeid).The low TLeid caused by enhanced oleophobicity,dense microstructures and increased convex dome height facilitates droplet rebound and promotes the evaporation of the wall-impinging droplets into the cylinder.The evaporation rate of the droplets is not only related to the characteristics of the solid surfaces and the fuel droplets but also affected by the heat transfer rate to the droplets in different boiling regimes.The spreading diameter of a droplet on an oleophobic surface varies significantly less with time than that on an oleophilic surface under the same surface temperature.展开更多
To improve the controllability for the evaporation process of fuel spray impinging on the cylinder wall,an experimental study on the development of morphological process of different fuel droplets on aluminium alloy s...To improve the controllability for the evaporation process of fuel spray impinging on the cylinder wall,an experimental study on the development of morphological process of different fuel droplets on aluminium alloy surfaces is carried out.The metal surfaces with different wettability are prepared by laser etching and chemical etching for the experiments.In total,three different fuels are tested and compared under different surface temperatures,including diesel,n-butanol and dimethyl carbonate(DMC).The results show that under a lower wall temperature,the surface wettability,viscosity and surface tension of the fuels have significant effects on spreading and rebounding behaviour of the droplets.As the wall temperature rises over the boiling points of the fuel but below its Leidenfrost temperature,the contact angles between the fuels and surfaces are varying according to the surface wettability,boiling point and Leidenfrost temperature of the fuels.When the temperature of the surface exceeds the Leidenfrost temperature of all the fuels,after impacting the surfaces,different fuel droplets tend to have the same development pattern,regardless of the surface wettability.The rebound level is mainly affected by the amount of fuel vapour generated during the wall-hitting process.Viscosity,surface tension and other properties of the fuel have little effect on post-impacting behaviour of the droplet when the wall temperature is higher than the Leidenfrost temperature of the fuel.展开更多
基金supported by the National Natural Science Foundation of China(Grant No,50376003)
文摘A comprehensive analysis of liquid fuel droplet evaporation at supercritical conditions is performed.The numerical model is based on complete time-dependent conservation equations,with a full account of variable thermophysical properties and vapor-liquid interfacial thermodynamics.And the model employs the Peng-Robinson(PR)equation of state(EOS).As a specific example,problems involving n-heptane droplet in nitrogen gas are investigated.The results indicate that the increase of ambient pressure and temperature results in the increase of surface temperature rise rate and surface regression rate.The transition from subcritical state to supercritical state can occur at the droplet surface when the droplet evaporates in a strongly supercritical environment.
基金the National Natural Science Foundation of China(Project code:51676084)Jilin Province Specific Project of Industrial Technology Research&Development(Project code:2020C025-2)+2 种基金Natural Science Foundation of Jilin Province(Project code:20220101212JC)Free Exploration Project of Changsha Automotive Innovation Research Institute of Jilin University(Project code:JCZT20220202)2021“Interdisciplinary Integration and Innovation”Project of Jilin University(Project code:XJRCYB07).
文摘To solve the wall-wetting problem in internal combustion engines,the physical and chemical etching methods are used to prepare different wettability surfaces with various microstructures.The evaporation characteristics and morphological evolution processes of diesel and n-butanol droplets after hitting the various surfaces are investigated.The results show that the surface microstructures increase the surface roughness(Ra),enhancing the oleophilic property of the oleophilic surfaces.Compared with n-butanol droplets,the same surface shows stronger oleophobicity to diesel droplets.When a droplet hits an oleophilic property surface with a lower temperature,the stronger the oleophilicity,the shorter the evaporation time.For oleophilic surfaces,larger Ra leads to a higher Leidenfrost temperature(TLeid).The low TLeid caused by enhanced oleophobicity,dense microstructures and increased convex dome height facilitates droplet rebound and promotes the evaporation of the wall-impinging droplets into the cylinder.The evaporation rate of the droplets is not only related to the characteristics of the solid surfaces and the fuel droplets but also affected by the heat transfer rate to the droplets in different boiling regimes.The spreading diameter of a droplet on an oleophobic surface varies significantly less with time than that on an oleophilic surface under the same surface temperature.
基金The authors gratefully acknowledge the financial supports from the National Natural Science Foundation of China(Nos.51676084 and 51776086)Specific Project of Industrial Technology Research&Development of Jilin Province(No.2020C025-2)Natural Science Foundation of Jilin Province(No.20180101059JC).
文摘To improve the controllability for the evaporation process of fuel spray impinging on the cylinder wall,an experimental study on the development of morphological process of different fuel droplets on aluminium alloy surfaces is carried out.The metal surfaces with different wettability are prepared by laser etching and chemical etching for the experiments.In total,three different fuels are tested and compared under different surface temperatures,including diesel,n-butanol and dimethyl carbonate(DMC).The results show that under a lower wall temperature,the surface wettability,viscosity and surface tension of the fuels have significant effects on spreading and rebounding behaviour of the droplets.As the wall temperature rises over the boiling points of the fuel but below its Leidenfrost temperature,the contact angles between the fuels and surfaces are varying according to the surface wettability,boiling point and Leidenfrost temperature of the fuels.When the temperature of the surface exceeds the Leidenfrost temperature of all the fuels,after impacting the surfaces,different fuel droplets tend to have the same development pattern,regardless of the surface wettability.The rebound level is mainly affected by the amount of fuel vapour generated during the wall-hitting process.Viscosity,surface tension and other properties of the fuel have little effect on post-impacting behaviour of the droplet when the wall temperature is higher than the Leidenfrost temperature of the fuel.
