Numerical-Experimental Optimization of the Common-Feeding Injection System Concept for Application to Light-Duty Commercial Vehicles

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 to allow easy installation on the engine, compared with a common rail (CR) system. In the CF apparatus, an additional delivery chamber is mechanically fixed at the high-pressure pump outlet, and the rail is removed from the hydraulic circuit. Experimental tests have been carried out on a hydraulic test rig in order to compare the general performance of the prototypal CF system with those of a CR system equipped with different rail volumes. In the cases of the double injections, the fluctuations of the injected mass pertaining to the second injections have been investigated during dwell time (DT) sweeps, and design solutions have been provided to minimize such oscillations. Moreover, an injection system numerical diagnostic model has been validated, and the reduced accumulation volumes linked phenomena have been analyzed. In general, the performance of the injection systems with different hydraulic capacitances or shapes of the accumulator are similar. One difference is that the injection rate features slightly different slopes during the rising phases; furthermore, cycle-to-cycle dispersions in the injected mass increase to some extent when the hydraulic capacitance is dramatically decreased. Finally, the frequencies of the free pressure waves, due to the water hammer occurring at the end of a hydraulic injection, are different when the shape of the accumulation volume changes, whereas these frequencies are independent of the accumulation volume sizes.