Numerical Study On Flow And Atomization Characteristics Of Each Hole Of The Unsymmetrical Diesel Injector

In order to obtain the same power and performance,and to develop a more environmentally friendly engine,the structure design of the nozzle and the study of its injection law play a key role in the performance and emission of the diesel engine.In this paper,for a two-valve diesel engine fuel injector were symmetric numerical simulation of internal and external flow atomization.In this paper,the geometric model of the nozzle is set up in the 3D software UG,and then the mesh is divided in the grid division software ICEM,and the Euler-Euler multiphase flow model is selected as the mathematical model of the numerical simulation of the fuel flow inside the nozzle.The numerical simulation of asymmetric injection nozzle is carried out by using different inlet and outlet pressure.The specific values of gas volume fraction,mass flow rate,turbulent kinetic energy,turbulent kinetic energy dissipation rate and velocity parameters at the nozzle section are obtained.The relationship between the flow parameters of each hole and the pressure difference is analyzed.It is found that: for a single nozzle,(1)the greater the pressure difference is,the greater the mass flow rate is and the linear relationship in the case of no super-cavitation;(2)the volume fraction of the gas phase is basically 0 when the cavitation is not produced.When the cavitation occurs,the larger the pressure difference is,and the larger the volume fraction of the gas phase is;(3)the greater the pressure difference,the greater the velocity of the pressure difference;the increase rate of the flow velocity slows down in the presence of cavitation,and the speed increase rate increases after reaching super-cavitation;(4)the greater the pressure difference,the greater the turbulent dissipation rate is,and the turbulent dissipation rate increases when cavitation occurs;(5)the greater the pressure difference,the greater the velocity,the slower the rate of growth of the flow velocity in the presence of cavitation,and the increase in the rate of speed increasing after supercavitation.For each hole,the larger the axial angle,the easier the cavitation is.After the cavitation,the variation curves of the flow parameters and the pressure difference are obvious.In addition,the influence of the structure of the pressure chamber on the flow characteristics of the nozzle is also analyzed.By comparing the asymmetrical nozzle of the pressure chamber and the unsymmetrical nozzle of the pressure free chamber,it is found that the flow of each hole in the pressure chamber of the pressure chamber is larger than that of the non-pressure chamber under the same inlet and outlet pressure;under the lower and middle inlet pressure,the pressure chamber is under the same inlet pressure.The pores of the nonpressure chamber injector are more likely to produce cavitation than that of the pressure chamber nozzle,and the porosity of the two types of injectors at the higher inlet pressure are basically the same.When the inlet pressure is constant,the mass flow and pressure difference are linear with the decrease of the outlet pressure.When the cavitation occurs,the mass flow continues to increase,and the mass flow of the hole is no longer changed when the phenomenon of supercavitation occurs.With the increase of the axial angle of each hole,the smaller the flow,the easier the cavitation is.For these two injectors,only the cavitation of the nozzle hole 3 and the hole 4 in the pressure chamber appears at the upper and lower ends of the hole.The cavitation of the remaining holes is produced only at the upper end.Through the numerical simulation of the flow parameters at the nozzle section of the internal flow,as the initial parameters of the external atomization,a mesh model of the fog field is set up.The atomization model of the HK-RT is used to simulate the atomization of each hole.The three main characteristics of the spray are obtained and analyzed.The spray cone angle,the spray penetration distance and the spray penetration are analyzed.SMD(Sauter mean diameter).The results show that:(1)the larger the pressure difference is,the larger the spray cone angle is,the larger the spray cone angle is,the spray cone angle slows down at the cavitation,and the increase of the spray cone angle increases with the increase of the volume fraction of the gas phase;(2)the greater the pressure difference is,the larger the spray penetration distance is,the greater the spray penetration distance,the greater the pressure difference,and the cavitation is produced;(3)the larger the pressure difference is,the smaller the SMD is,and the rate of SMD decrease after cavitation.For each hole,the larger the axial angle,the easier the cavitation is.After the cavitation,the change curves of the atomization parameters and the pressure difference appear more obvious.