Study On Formation Process Of Fuel Mixture After Impinging The Wall Under Different Wall Wettability

The internal combustion engine is the most extensive type of thermal machinery.In recent years,due to the energy crisis and environmental protection issues,the combustion and emission control of the internal combustion engine has developed rapidly.Spray wet wall phenomenon is almost inevitable.Most researchers use blended alternative fuels with good volatility to reduce the mass of fuel spray impinging walls,design the combustion chamber structure to reduce wet walls and use impacting walls.Some researchers have also studied the distribution of the fuel mixture after impinging by changing the wall characteristics,such as wall temperature and surface roughness,etc.However,there are few studies on the micro-flow process between fuel and the wall of the combustion chamber after the wet wall and its influencing factors.Based on the wettability of the wall,this paper studies the single fuel droplets and spray droplets impacting the wall under different boundary conditions.The material surface processing platform,the single-drop droplet impacting the wall Schlieren optical platform and the spray impacting the wall Schlieren optical platform are set up.Based on the MATLAB image processing function,the methods of quantizing and analyzing the single droplet and spray Schlieren images are given.Finally,the evaporation process of the single droplet impacting the wall and the characteristics of the mixture of the spray impacting the wall are summarized.the main research contents are as follows:In terms of single droplets of fuel impacting the wall,the evaporation process of n-butanol and diesel fuel under different conditions of wall temperature and wall wettability was studied,and the effects of wall temperature and wall wettability on the evaporation were summarized and analyzed.The experimental results show that when the n-butanol droplets impact the smooth wall surface,the gas phase distribution after the droplets impact the wall is different under different heat exchange mode.Diesel is in the interval from the initial boiling point of nuclear boiling to membrane boiling.,after the diesel impacts the wall,it usually evaporates in a compound heat transfer mode.Under the condition of excessive boiling,the coverage of n-butanol with respect to the surrounding environment is relatively large,but the concentration of the mixture is relatively low.Under nuclear boiling,it is easier to form a locally thicker mixture in a short time.Comparing the impact of n-butanol droplets on three different wettability surfaces,the initial temperature point of film boiling is obviously different.The wall wettability affects the gas-liquid morphology of different boiling states after n-butanol and diesel droplets impact the wall.Development plays an important role.In terms of fuel spray impacting the wall,the characteristics of the mixture after the fuel spray impacts the wall under different environmental pressures,wall temperature,and wall wettability were studied for n-butanol.The test results show that:except for 0.1 MPa,the entrainment height of the n-butanol impingement wall spray liquid phase increases first and then decreases with the time.The larger the ambient pressure,the higher the gas phase ratio.After the spray impacts the wall,the entrainment height of the gas phase increases with the increase of the wall surface temperature,and the entrainment height of the liquid phase increases first and then decreases with time,and the higher the wall temperature,the faster the decrease of the entrainment height.As the wall temperature increases,the diffusion area of the gas phase increases after the spray impacts the wall,and the proportion of the gas phase of the spray becomes larger.At an ambient pressure of 0.5 MPa and a wall temperature of 20?,the n-butanol fuel spray has a significant gasification phenomenon when it impacts the laser-etched surface,and whirlpool can be observed at both ends during the spreading process when it impacts a chemically treated surface.Under the conditions of ambient pressure of 0.1 MPa and wall temperature of 20?,the n-butanol fuel spray has the highest entrainment height when it impacts the laser-etched surface.The spray has the largest spread radius when it hits the chemically treated surface,followed by the combined surface,and the smallest spread radius when it hits the laser-etched surface.The n-butanol fuel spray has a larger gas phase when it hits the laser-etched and chemically treated surfaces.