Abstract
The control valve determines the fuel offloading process of the high-pressure fuel system in diesel engines. During the fuel offloading process, when the control valve instantaneously opens, the inlet pressures and the outlet pressures of the valve change quickly, and the inner flow of the control valve is transient and unsteady. This study presents an investigation into the flow characteristics in the control valve region during the fuel-offloaded process of a diesel unit pump fuel system, studies the reasons for unsteady-flow conditions and further analyses the effects on the flow capacity of the valve based on the computational fluid dynamics method. The results reveal that the key reason for unsteady flow in the control valve is the dynamic movement of the valve needle, which induces changes in the inlet pressure and the outlet pressure so that the fluid in the conical region accelerates. In comparison with steady flow, unsteady flow in the control valve has different pressures in the conical region and at the conical outlet, different cavitation intensities and different locations of the bubbles. Moreover, the differences between unsteady flow and steady flow become greater, particularly for small valve needle openings. Unsteady flow in the control valve greatly influences the fuel offloading process of the unit pump fuel system.
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