The Visualization Experiment And Numerical Simulation For Cavitation Flow In A Injector Nozzle Of Diesel Engine

With the increasing attention to protecting the environment and saving energy all over the world, it is urgent to design a diesel engine with low energy consumption and less emission. In the diesel engine, fuel injection and atomization performance make great contribution to engine combustion and emission. Therefore, domestic and foreign scholars in this field have paid lots of attention, and the fuel jet atomization mechanism were studied. After scholars’ long-term unremitting efforts, people gradually realize that liquid spray atomization is a result of the integrated effects of many factors, aerodynamic, spray hole of cavitation and turbulence are the three basic factors. At present only the researches in aerodynamic instability is more mature, so it is very necessary for further researches in cavitation flow phenomenon of internal orifice.This paper systematically analyzes the development and the development trend of numerical simulation for the fuel injection system, we establish the mathematical model of internal cavitation flow of nozzles, analyze the variable parameters and variable mediums of internal cavitation flow of nozzles by numerical simulation and illustrate the effects of the injection system structure parameters and different mediums on flow. We also analyze the impact of the pressure differential between the inlet and outlet and length to diameter ratio of2D nozzles, and analyze the different flow state corresponding spray flow field of internal orifice. In addition to this, the rules and effect of cavitation on spraying are analyzed. Simulating the internal cavitation flow of soybean biodiesel and diesel with3d modeling based on CFD technology. The result shows that:compare to diesel, under the same injection pressure, soybean biodiesel has higher mass flow because of its high density. Moreover, its larger viscosity makes cavitation more difficult which brings lower cavitation strength. At the same time, soybean biodiesel has smaller orifice export momentum and effective jet velocity. Otherwise, The flow coefficient and coefficient respectively are not significant.This paper systematically studies the internal flow inside the amplifier orifice with the help of X-ray phase-contrast photography technology. In order to observe the internal flow inside the amplifier transparent orifice, a visual platform is built based on Shanghai light source unit. On the premise of not changing the structure of the real orifice, we conduct the research for further study of cavitation flow of internal real orifice using Neutron imaging technology. Images of cavitation flow internal real orifice under the real working condition will be got. Therefore, further study cavitation flow mechanism in the nozzle is expected to make great breakthrough.Through the visual test results, internal orifice flow can be divided into three parts, respectively no cavitation period, cavitation development period and pick flow period; And the shooting images of hole outside indicate that cavitation flow can increase the orifice spray cone angle outside. When the inlet pressure is less than0.22MPa, cavitation number is greater than1.82, the spray hole only has turbulent motion rather than cavitation appearance; And when the inlet pressure between0.22MPa to0.4MPa, cavitation number between1.33and1.82, the cavitation appear and outspread gradually to the orifice exit; When the inlet pressure is higher than0.4MPa, hole number is less than1.33, the internal flow state into the pick flow period; So when spray pressure increases, the internal flow state by no hole flow get into the pick flow period, and the spray cone Angle is increased gradually, when the super cavitation is achieved, the spray cone angle is the greatest; Along with the spray pressure increasing, the spray cone angle will decrease.This article features:(1) Design a new kind of two-dimensional visual orifice to research on flow state of internal orifice;(2) Simulate and analysis internal cavitation flow and spray outside the orifice based on CFD technology, Including the grid independence verification as well as determining the import-export pressure boundary conditions;(3) Using the X-ray phase-contrast imaging technique to build the internal cavitation flow of the orifice and the near field spray visual platform with the help of high-speed photography, analyzing internal cavitation flow and the near field spray in different inlet pressure, different length to diameter ratio respectively;(4) Simulate internal cavitation flow of soybean biodiesel in a real nozzle with3D modeling based on CFD technology, analyzes the flow state and the impact on the injection process.