Comparative study on steady and unsteady flow characteristics in control valve for the unit pump

Control valve is one critical component of electronic unit pump fuel system. Control valve controls the pressure build-up within the high-pressure fuel line through rapid opening, which is a dynamic process. On the basis of theoretical analysis, there are two key reasons for the unsteady flow within the control valve:one is the acceleration of fuel which is induced by the valve needle's dynamic movement, and another is the acceleration of fuel flow due to the change of the inlet/outlet pressure, and this acceleration of fuel flow enhances the inertia force. Comparison of the flow field characteristics of the control valve are made under both steady and dynamic conditions by simulation. Results show that with the increase of valve opening, the cavitation becomes stronger under the unsteady condition but cavitation declines under the steady condition. There are significant differences between steady and unsteady conditions on the flow velocity during the whole opening process. In small valve needle opening, the flow capacity of steady condition is higher than that of unsteady condition;however, with the increase of valve opening, the flow capacity of unsteady become greater than that of steady flow.