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

Abstract

A new-generation common feeding (CF) fuel injection system without rail has been compared with the standard common rail (CR) apparatus for diesel engine passenger cars. The high-pressure 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 flow-rates 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 high-pressure transients. The dynamics of the pressure waves changes because the high-pressure 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 one-dimensional (1D) code for the CF high-pressure 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 injector-integrated Minirail on the CF performance have been investigated by means of the model. Numerical parametrical tests have also been conducted on the pump-to-injector pipe length. The additional orifices that can be installed in the high-pressure 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 flow-rates 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 pump-to-injector 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.