Experimental study on the transient supply consistency for a common rail pump based on impedance theory

Common rail (CR) fuel pumps are characterized by pulsating supply, and instantaneous flow ripple is the main reason for the variation in supply consistency. To analyze the transient supply consistency of CR pump, a test bench for transient supply performance was originally designed and established. The potential effects exerted by pump speed and operating pressure on the pressure ripple were obtained under different fuel metering valve (FMV) openings. On this basis, an approach for the calculation of instantaneous flow ripple was proposed by combining impedance theory and hydraulic transmission line method (TLM). Furthermore, the coefficient of variation (CoV) of flow ripple amplitude was applied to evaluate the cycle-to-cycle consistency in fuel supply process. The results show that the rotational speed together with the plunger number determines the frequency of flow ripple. The pump presents a greater flow ripple amplitude under high speed and low pressure conditions, which further leads to an intense pressure ripple. Besides, in most operating points, the CoV is around 0.15, indicating a good transient supply consistency. When the FMV is partially open, under the coupled effect of FMV operating frequency and plunger movements, the value of CoV shows an oscillating trend as a function of speed.