Hydraulic Performance Comparison Between the Newly Designed Common Feeding and Standard Common Rail Injection Systems for Diesel Engines

Abstract

A newgeneration common feeding (CF) fuel injection system without rail has been compared with the standard common rail (CR) apparatus for diesel engine passenger cars. The highpressure pump in the CF apparatus is connected directly to the injectors, and a volume of about 2.5 cm3 is integrated at the pump delivery. Experimental tests on solenoid injectors have been carried out for the CF and CR apparatus at a hydraulic test rig. The dependence of the injected volumes and total injector leakages on the energizing time (ET) of the two systems has been investigated for different rail pressure levels. Furthermore, the measured injected flowrates of the CF and CR systems have been compared for single and pilot–main injection events. In general, the injection performance of the two systems is very similar, even though the differences occur in the highpressure transients. The dynamics of the pressure waves changes because the highpressure hydraulic layouts of the two systems are different, and the propagation and reflection of the rarefaction waves, triggered by the injection events, occur in different ways. A previously developed onedimensional (1D) code for the CF highpressure layout has been further validated by means of a comparison with the experimental data. The effects of either a calibrated orifice installed at the pump delivery or an injectorintegrated Minirail on the CF performance have been investigated by means of the model. Numerical parametrical tests have also been conducted on the pumptoinjector pipe length. The additional orifices that can be installed in the highpressure circuit of the CF are effective, provided their diameter is smaller than the diameter of any other orifice inserted in the injector. Furthermore, the presence of a Minirail within the injector has an impact on the injected flowrates of small injections, such as pilot, pre, after, and post, and also induces a reduction in the energy stored in the pressure waves. Another relevant active damping strategy of the pressure waves for the CF involves shortening the pumptoinjector pipe as much as possible. Finally, the fluid dynamical transients within the solenoid injector have been discussed for the CF and CR systems. The numerical time distributions of the main variables within the injector are shown to be independent of the presence of the rail in the layout.