Evaporation Characteristics and Morphological Evolutions of Fuel Droplets After Hitting Different Wettability Surfaces

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 ( R a), 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 R a leads to a higher Leidenfrost temperature ( T_Leid ). The low T_Leid 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.