Performance Analysis of Rail-Pressure Supply Pumps of Common-Rail Fuel Systems for Diesel Engines

This paper discusses the performance of the radial plunger pump used in the contemporary diesel common-rail fuel systems for rail-pressure supply. On the ground of the pump mechanism, the transient flow, drive torque, and efficiency of the pump are analyzed for various operation conditions. The analysis shows that the number of plungers and utilization of the pump capacity govern fluctuations in the pump discharge. The pump flow can be characterized by a discharge function which applies to both full- and part-capacity pump flows. At the full pump capacity, the discharge fluctuation is determined solely by the number of plungers: a pump with an odd number of plungers has more ripples and lower amplitudes in its discharge than a pump with an even number of plungers does. A pump operates at a part capacity has more fluctuations in the discharge than when at the full capacity. If the pump speed is not very low, then a critical flow exists for any given pump speed, at which the pump discharge becomes fully pulsatile and increase in the pump speed will lead to a discontinuous pump flow, which generates pressure fluctuations in the common rail. This pump discharge induced rail-pressure fluctuation becomes significant when the engine is operated with a multiple-injection strategy: large rail-pressure fluctuations may result in a poor control in the non-primary injections. To mitigate the effect of the rail pressure fluctuation on injections, the pump size and the volume of common rail should be designed according to both the engine fuel demands and the injection control strategy.