Instantaneous torque, energy saving and flow rate ripple analysis of a common rail pump equipped with different delivery-pressure control systems

Abstract

A mechanical model of a high-pressure pump of a common rail fuel injection system is presented and validated by comparison with experimental instantaneous pump shaft torque and pump piston lift data. The instantaneous torque has been measured with a high-performance torque meter installed on a hydraulic rig for testing pieces of injection apparatus. In the model, the mechanics of the piston plunger and the forces exchanged between pistons and cam are simulated, and friction losses between mobile parts are taken into account. The numerical tool is used to investigate the dynamical performance of the high-pressure pump and to analyse the impact of the rail pressure control strategy on instantaneous torque, energy saving and flow rate ripple. The rail pressure control strategy, based on the application of a fuel metering valve at the pump inlet, gives rise to an improved hydraulic efficiency of the injection system at part loads and to a moderate rate of pressure increase in the pumping chamber at part loads. However, the rail pressure control strategy based on the installation of a pressure control valve at one rail extremity leads to a reduction in the pump flow rate ripple and to a diminution in the fatigue stress. Furthermore, cavitation problems can occur during intake and early compression phases of the pump cycle when the fuel metering unit is working.