Investigation On Dynamic Flow Characteristics In Valve Region For Electronic Control Unit Pump Fuel System

To achieve the purpose of efficient combustion and lower emissions,modern diesel engines adopt electronically controlled high pressure fuel injection system.Due to the advantages of high injection pressure,injection quantity and injection timing flexible and adjustable,high reliability,and fuel flexibility,researchers have paid more attention to electronic control unit pump fuel system.The control valve is one critical component of electronic control unit pump fuel system.In the process of control value opens the fuel path from high-pressure to low-pressure,a large number of high-pressure fuel at high velocity in a short period of time through the control value cone flow to the low-pressure fuel line,and the flow in the field of control value is quite complex that can induce turbulent flow and cavitation,and have significant influence on fuel cut-off control.Furthermore,the flow characteristics of the control valve will affect the performance of the fuel system.This study presents investigations into the dynamic flow characteristics of the valve region flow field of the electronic control high-pressure fuel system within the control valve of a unit pump.The control valve flow field transient numerical model was built based on CFD(computational fluid dynamics).The model validation was done according to the test results.Based on the simulation model,the numerical investigations into the flow characteristics within the control valve was done with the boundary conditions of pressure and speed curve that got from experimental results.The results show that:1)During the opening process there are two cavitation regions.One is the conical region and the other is the downstream of the conical region.The cavitation in the conical region occurs first in the valve needle close to the outlet,which is induced by the rapid movement of the valve needle,and then occurs in the valve inlet,which is induced by the local flow velocity increased because of the narrow flow area.The cavitation in the downstream of the conical region is induced by vortex flowing.Both of the cavitation become stronger with the increase of the valve needle lift.The cavitation reduces the flow capacity of the control valve.2)The opening process of the control valve is a dynamic process.The valve needle's dynamic movement and the transient change of the inlet/outlet pressure are two key reasons for the unsteady flow within the control valve.The flow characteristics of the dynamic flow field are obviously different from those of the steady state.3)The valve needle speed has significant effect on the cavitation characteristics,flow capacity,and flow state of the control valve.Under the condition of the same inlet and outlet pressure,with the valve needle speed increases,the cavitation intensity both of the conical region and the downstream of the conical region of the control valve is weakened,the turbulence kinetic energy is also weakened.The valve needle speed has no effect on the mass flow rate of the control valve with small valve needle lifts;under the condition of large valve needle lifts,the higher the valve needle speed is,the larger the mass flow rate is.The influence of the valve needle speed on the chocking flow critical points under large valve needle lifts is obviously bigger than small valve needle lifts.