Research On Steady And Transient Flow Characteristics Of Gas-Liquid Two-Phase Flow In Diesel Engine Intersection Hole Nozzles

With the increasing demand for energy and more stringent emission regulations,higher requirements for energy saving and emission reduction of diesel engines have been put forward.As the last part of the fuel into the combustion chamber,the internal flow characteristics of the nozzle play a decisive role in the atomization effect of the fuel into the combustion chamber,and then affect the combustion and emission effect in the diesel engine.Because the intersecting hole can be maintained good mass flow characteristics at low pressure,so it is started to put into use.However,the effect of the structural parameters of the intersection hole is not clear about the flow characteristics inside the nozzle.Therefore,the influence of the structure parameters and pressure boundary conditions on the internal flow is studied in this paper.On the one hand,three-dimensional numerical simulation software Fluent is used to simulate the effect of structural parameters on the flow characteristics of nozzles.A mathematical model for the additional cavitation of multiphase flow is established,the flow process of gas liquid two phase flow in the nozzle is simulated and compared with the experimental results,the results shows that the mass flow error between simulation and experiment is within 5%,which is in good agreement.On this basis,the influence of the jet pressure and back pressure,the ratio of the nozzle holes length to diameter,the contraction coefficient and the cross angle on the internal flow characteristics of the intersecting nozzles are analyzed,which is compared with the single nozzles.The results show that: Increasing the injection pressure and reducing the back pressure can increase the mass flow rate,the velocity and the turbulent kinetic energy at the outlet of the nozzle;The intersecting nozzle structure and the sub nozzle shrinkage structure can effectively suppress the cavity generation inside the nozzle;With the ratio increased of length to diameter,the mass flow and velocity at the outlet of the nozzle decreased,and the turbulent kinetic energy increases first and then decreased.As the cross angle increases,the mass flow and velocity at the outlet of the nozzle decreased,and the turbulent kinetic energy increased.With the increase of nozzle shrinkage coefficient,the mass flow rate and velocity at the outlet increase,and the turbulent kinetic energy decreases.On the other hand,the influence of pressure fluctuation on the internal flow characteristics of different cross nozzle structures is studied.It is assumed that the pressure fluctuation at the entrance is sinusoidal,the effects of pressure fluctuation amplitude,pressure fluctuation frequency and nozzle structure parameters on the flow characteristics of the nozzle with time are analyzed.The results show that: The mass flow rate,velocity and the size of turbulent kinetic energy at the outlet of the nozzle are consistent with the form of inlet pressure fluctuation,but there is a certain delay phenomenon.The fluctuation amplitude and frequency of the flow parameters at the outlet of the nozzle can be increased with the increase of the amplitude and frequency of the inlet pressure fluctuation.As the ratio of length to diameter decreases,the mass flow rate,velocity and turbulent kinetic energy at the outlet of the nozzle are more sensitive to the pressure fluctuation.With the increase of the cross angle of the nozzle,the size of the turbulent kinetic energy at the outlet of the nozzle is more sensitive to the reaction of the pressure fluctuation,and the sensitivity of mass flow and velocity are relatively lower.As the shrinkage coefficient increases,the mass flow rate and velocity at the outlet of the nozzle are more sensitive to pressure fluctuation and the sensitivity of turbulent kinetic energy decreases.