Simulation Study Of Fuel Wall-wetting Process Based On Surface Wettability

The increasing attention paid by governments around the world to the development of green and clean energy and the increasingly strict laws and regulations on energy conservation and emission reduction in various industries have led to the birth of new models such as homogeneous pressure combustion(HCCI),premix pressure combustion(PCCI),low temperature combustion(LTC),and reaction controlled pressure combustion(RCCI).Although these combustion modes achieve the purpose of energy saving and emission reduction to a certain extent,they are easy to cause problems such as spray wet walls and uneven mixture formation due to their technical characteristics.In order to solve these problems,in addition to the improvement of spray characteristics,the optimization and study of combustion chamber wall parameters is particularly important.At present,CFD models often ignore the basic wetting characteristic parameters of the wall(such as contact Angle,spread rate,etc.),so the existing CFD models are not perfect enough to be widely used in the calculation of engine spray.Therefore,based on the project of national natural science foundation of China(5167060406),this study takes the wettability of metal material surface as the starting point and numerical simulation as the main research method,aiming at the process and controllability of fuel oil droplets’ wet wall.It provides technical reference for the design of new combustion chamber.For fuel oil single droplet impact wall simulation.In this paper,the shape development of fuel oil droplets,the distribution of fuel oil vapor generated by fuel oil droplets evaporation and the difference of fuel oil evaporation rate were studied when a single droplet impinged on a metal wall with different microstructure,a metal wall with different hydrophobic properties,and a metal wall with different wettability under different environmental pressures.The simulation results of the micro-morphologies of different metal walls show that the arrangement and scale of the micro-morphologies will directly affect the wettability of the metal walls,and the droplet motion and evaporation process will change after the droplet impacts the wall.The simulation results of the hydrophobic metal wall surface show that the hydrophobic metal wall surface will cause the droplets to have different degree of rebound trend,which will increase with the enhancement of the hydrophobic characteristics of the wall surface.In a certain range,the rise of wall temperature will reduce the oil-trap property of the wall and affect the rebound movement of the droplets,which also changes the form of droplet evaporation and speeds up the evaporation speed of the droplets.The simulation results of different environmental pressures show that the environmental pressure will reduce the evaporation rate of droplets and affect the wettability performance of wall surface.For fuel spray impact wall simulation.The effects of wall wettability,wall temperature and ambient pressure on spray morphology,steam distribution and fuel evaporation rate were studied.The simulation results of spray impact on different temperature and wettability of wall surface show that the increase of wall temperature will change the evaporation form of spray and accelerate the evaporation rate,which will affect the wettability of wall surface.When the wall temperature is the same,the wettability of the wall will increase,and the scale of spray spreading and entrapping will decrease,which will affect the evaporation of spray particles and the distribution of fuel gas.The simulation results of spray impingement on different wettability metal wall surface under different environmental pressure show that the increase of environmental pressure will inhibit the movement of spray particles and reduce the evaporation speed of spray particles.Under the same environmental pressure,the enhanced wettability of the wall will reduce the motion scale of spray particles and speed up the spray evaporation rate.