Numerical Simulation Research On The Influence Of Injection Parameters On Internal Flow In Nozzle And Spray-atomization Characteristics Of Biodiesel

As a green,environmental and renewable energy,the research and widespread use of biodiesel can solve the increasingly serious energy crisis and mitigate environmental pollution simultaneously.However,the high viscosity,large density and surface tension of biodiesel combine to result in bad atomization and thus,the advantages of biodiesel are hard to be in full use.In this paper the effect of injection pressure,backpressure,length-diameter ratio and fuel temperature on spray characteristics of biodiesel was investigated by means of numerical simulation method,and the accuracy of cavitating flow model and atomization model was experimentally verified.Firstly,Layering Mesh Methods was applied to simulate the movements of needle valve and the transient flow inside the orifice,and the results of the simulation were used as boundary conditions of the spray field.The effect of injection pressure,backpressure,length-diameter ratio and fuel temperature on spray characteristics of biodiesel was then investigated,which provides theoretical guidance for improving the atomization quality of biodiesel.The numerical results of transient flow inside the orifice show that during the period that needle valve is open,the gaseous phase volume fraction increases rapidly at first and then the uptrend slows down,besides instantaneous increase occurs at the moment the needle valve shuts.Increased injection pressure,reduced backpressure,higher fuel temperature and decreased length-diameter ratio are all stimulatives for cavitation,and also beneficial for increasing the average velocity and average turbulent kinetic energy at the exit of orifice,which can optimize the primary atomization of the fuel.The rules of macroscopical and microcosmic spray characteristics changing with time can be concluded based on the numerical results of spray characteristics that the spray penetration sharply increases at the beginning and then slows down;The sauter mean diameter decreases gradually;The locations of maximum fuel spray velocity and maximum concentration as well as maximum turbulent kinetic energy are all situate in the central area of spray field,the velocity,concentration and turbulent kinetic energy all decrease with the expansion outward along both the axial and radical direction.Increasing the injection pressure as well as reducing the backpressure and length-diameter ratio can lead to an enlarged spray penetration and a reduced sauter mean diameter,the velocity and turbulent kinetic energy in the central area of the fuel spray monotonously increase while the concentration shows an opposite trend;However,an increased fuel temperature can result in a reduced spray penetration and sauter mean diameter,besides,the velocity and concentration in the central area both diminish gradually,whereas turbulent kinetic energy gradually increases.Drop breakage and fuel atomization can be improved by increasing injection pressure and fuel temperature,decreasing backpressure and reducing lengh-diameter ratio.