Dynamic behaviors of fuel droplets impacting on the wall surfaces with different wettability and temperatures

• Surfaces with different microstructures and special wettability are fabricated. • Heat transfer performance of fuel droplets on different surfaces is evaluated. • The comprehensive effects of microstructures and wettability on the Leidenfrost temperature are revealed. • The influences of surface wettability and wall temperature on the morphological developments of droplets are investigated. To improve the controllability of combustion and reduce the emissions of HC and CO of the newly developed combustion modes, such as the HCCI, PCCI and RCCI, the evaporation processes and morphological developments of diesel droplets impacting on the aluminum alloy surfaces with different wettability and temperatures are experimentally investigated. The results show that the oleophilic surface is conducive to evaporation of diesel droplets, while the oleophobic surface promotes the formation of the vapor film between the fuel droplets and the test surface at a high surface temperature and reduces the Leidenfrost temperature of the fuel droplets. Also, stronger oleophobicity of the surface is beneficial to the rebound and secondary breakup of the droplets, thereby promoting the evaporation of the droplets in the gas-phase space of the cylinder and improving the air–fuel mixing. Moreover, the stronger the surface oleophobicity, the smaller the spreading factor and the larger the rebound factor of the droplets. At a higher wall temperature, the ability for enhancing the surface oleophobicity of the convex domes, grooves and protrusions structures on the laser-etched surface is better than that of the boss/pits and needle-like structures on the chemically etched surface. Under the conditions of lower surface temperatures, the evaporation rate of the droplet after hitting the wall is closely related to the spreading area of the droplet. As the wall temperature increases, when the droplet is in transition boiling regime, the large heat transfer rate makes the diffusion width, height and diffusion area of ​​the vapor phase region are obviously large.