Study On Effects Of Different Conditions To Wall Wettability And Wall-Wetting Process

During these years governments increasingly attach importance to energy conservation and emissions reduction and low carbon economy.Under the huge pressure which bought by the emerging field of new energy vehicles,because the internal combustion engine is the main source of the pollution of enviroment and energy consumption,it has to further speed up the implementation of efficient and clean combustion technology of internal combustion engine for the most severe challenges which the future of traditional fuel cars will face.Although new combustion modes such as HCCI,PCCI and low-temperature combustion have been the focus of worldwide combustion research,the problem of combustion and emission deterioration caused by spray wall-wetting phenomenon cannot be ignored.Therefore,based on the project of national natural science foundation of China(5167060406)and the latest research progress in the field of internal combustion engine and materials science,this study takes the surface wettability of solid materials as the entry point to conduct research on the development process and controllability of wall-wetting on combustion chamber walls.For investigating the control of spray wall-wetting phenomenon and the process,the laser engraving method and chemical etching-low surface energy modification method were taken to obtain different extreme metal surface wettability.Under the condition of different wall temperature,the visualization experimental study on the physical development process of droplet impacting was conducted.Analyzing how the wall temperature,microstructure,surface wettability and different metal effect the spreading coefficient and the rebounding coefficient.At the same time by using numerical simulation method,the model of single drop impacting is established based on experimental data for further exploring movement and heat transfer process of the experiment.According to the explanation of the surface wettability based on Young equation,the three-phase interface tension between junction interfaces is the main factor that changes the wettability,the change of the surface wettability has a great influence on droplet wall-wetting.Spreading always happens on the oleophilic wall and rebounce happens on the oleophobic wall.Meanwhile different wall temperatures transfer droplet into different states of boiling and evaporation with the action of rapid evaporation,rebounce and crushing.Under the influence of wettability,droplet on the oleophilic wall easily evaporate and droplet on the oleophobic wall more likely boil.Different evaporation states of droplets also affect this process,when it is in the state of convection heat transfer,the increase of surface roughness in the process of wall collision is accompanied by the advance of droplet shrinkage process and the acceleration of the conversion between surface energy and kinetic energy,so that it can reach the equilibrium state earlier.When the droplet is nucleate boiling,the increase of lipophilicity will reduce the boiling intensity and increase the spreading coefficient.The wettability of different wall surfaces has little effect on the spreading process of membrane boiling droplets due to the presence of vapor layer.