Experimental Study On The Dynamic Characteristics Of Interaction Between High-pressure Atomized Fuel Spray And Wall In A Constant Volume Chamber

Spray-wall impingement is a widespread phenomenon applied in the internal combustion engines.Although the impinging spray has been investigated for decades,the mechanisms of the interaction between liquid and wall are still blurred to fully understand.Recently,with the development of the visual technology,a range of interesting behaviors were reported.In gasoline direct injection(GDI),it is difficult to avoid the fuel film on the piston and cylinder walls owing to the compact spatial structure.The wet-wall caused by the liquid impingement affects the air-fuel mixture formation process,which is a possible source of unburned hydrocarbons(UHC)and particulate matters(PM),making it difficult to meet the future requirements of particle number(PN)regulation.Besides,the spray-wall interaction can also be applied in the spray and combustion of marine and aircraft engines.Therefore,it is significantly important to study on the spray and impingement.The novelty of this study lies in the correlation between the impinging spray and fuel film formation together to better understand the spray-wall impinging behaviors.The experimental investigations are performed in a constant volume chamber.Mie scattering is applied to visualize the spray evolution and impingement processes.Meanwhile,the fuel film formed on the wall is measured by refractive index matching(RIM).The research can be divided into two parts: non-evaporation and evaporation conditions.The influences of physical field(wall surface roughness and impingement distance),pressure field(injection and ambient pressures)and temperature field(ambient temperature)are checked and compared in detail.Furthermore,the microscopic characteristics of impinging spray are investigated using particle image analysis(PIA).Firstly,the spray and droplet behaviors at the near-nozzle region are analyzed.Then,droplet sizes before and after impingement are compared and analyzed.Finally,the droplet characteristics after the end of injection are studied to explain the reason for fuel film still increasing after the end of injection.One thing should be noted that owing to the dense number of droplets near the wall,it is still difficult to obtain the microscopic observation at the near wall region or around the spray axis.Therefore,the device named “slicer” is designed and applied to “cut” the spray.Consequently,the multiple drops impacting on the wall and splashing along the wall at the spray tip and quasi-steady state can be characterized.Moreover,the relationships between droplets behaviors and fuel film formation on the wall are discussed.Additionally,the models of single droplet impacting on the wall are mapped with the multiple drops,which can be used to predict the impacting behaviors as well.