The innovative Common Feeding (CF) fuel injection system has been designed for a light duty commercial vehicle diesel engine in order to reduce production costs and allow easy installation on the engine, compared to a traditional Common Rail system. In the CF apparatus, a delivery chamber with a volume around 10 cm3 is integrated in the high-pressure pump. The chamber at one side is connected to the pump, and at the other side is linked to the solenoid injectors by means of pipes (the rail is removed from the hydraulic circuit).
Experimental tests have been carried out on a hydraulic test rig at the Politecnico di Torino in order to compare the general performance of the prototypal CF system with that of a Common Rail (CR) system equipped with different rail volume sizes (realized by manufacturing rails of the same length but with different internal diameter). The injected mass flow-rates of single injections as well as of pilot-main injections have been captured by instantaneous flow-rate meters. In the case of the double injection schedules, the dependence of the injected mass pertaining to the second injection shot has been investigated during dwell time sweeps and design solutions have been provided to minimize the oscillations of such injected mass with respect to dwell time for the CF system.
Furthermore, the injector inlet pressure time histories, the static and dynamic injector leakages, the nozzle opening and closure delays and the injected volume cycle-to-cycle dispersion have been evaluated for both CR and CF systems.
In general, the injection performance of the injection systems with different hydraulic capacitances or shapes of the accumulator is similar. One significant difference is that the injection rate feature slightly different slopes during the rising phases. Furthermore, cycle-to-cycle dispersion in the injected mass increase to some extent when the accumulation volume of the high-pressure circuit is dramatically decreased. Finally, the frequencies of the free pressure waves that are originated by the water hammer, which occurs at the end of a hydraulic injection, are different when the shape of the accumulation volume change, whereas these frequencies are basically independent of the accumulation volume size.