Numerical And Experimental Investigation Of Cavitating Flow In Nozzles

Nowdays,most of liquid fuel engines use a hybrid approach to form mixed gases,such as diesel engines and gasoline engines using GDI technology.The atomization of fuel has a direct impact on the engine performance and exhaust emissions.Therefore,the fuel atomization quality plays a decisive role in high efficiency and low pollution combustion.There are many factors that affect the fuel atomization,among them,the cavitating and turbulent flow in the nozzle are considered to be one of the most important factors.Due to the small length and diameter of actual nozzle,the features of high flow velocity and high turbulence,many cavitating and atomization mechanism has not been fully revealed.Based on domestic and international researches,build a visual test bench which can adjust flash time according to the fuel injection timing signal.The cavitating flow and spray characteristics under conditions such as different injection pressures,nozzles with different structure parameters and different injection fuels are studied using actual size of the transparent nozzles.And on the basis of experiment,a relatively accurate mathematical model is established.Based on this model,numerical simulations are made on the cone nozzles and the expansion and contraction nozzles.The main conclusions are as follows:(1)Built a visual test bench which can observe the cavitating flow and spray characteristics,used MATLAB software process photos,calculating the relative area of cavitating,spray cone angle,spray penetration distance and the spray area.(2)Explain some special phenomenon outside the nozzle,also find that change the position of the nozzle will have some influence on the development of the cavitating.(3)Increasing the injection pressure can effectively promote the development of cavitating in the nozzle,and further promote the diffusion and development of fuel spray.Properly reducing nozzle length to diameter ratio will also promote the cavitating flow and further promote the fuel atomization.The higher the saturation vapor pressure of the fuel,the smaller the kinematic viscosity,the sooner the occurrence of cavitating in the nozzle,the cavitating mobility sooner reached a steady state,a spray droplet is easily broken,the larger the spray angle,the better the atomization effect.(4)Based on the actual nozzle,use PROE,ICEM establish nozzle model,and by comparison with the experimental results verify the accuracy of the model,simulate the fuel flow in and out the cone nozzles and the expansion and contraction nozzles based on the previous model.In this paper,a combination of experimental research and numerical simulation method is used to study fuel flow.It provides theoretical basis for the improvement of the mechanism of cavitating and initial atomization.