Experimental Investigation of Dynamics Effects on Multiple-Injection Common Rail System Performance

Fundamental aspects of Common Rail (CR) fuel-injection-system dynamics were investigated, paying specific attention to the wave propagation induced pressure oscillations and to their relationships with the system control parameters and multiple-injection performance. A detailed experimental analysis of the pressure-wave propagation phenomena in a last-generation CR Multijet equipment of the solenoid type was carried out on a high performance new test-bench Moehwald-Bosch MEP2000-CA4000 under real engine simulated conditions. The experimental results include pressure time histories in the rail and at the injector inlet, as well as flow-rate patterns, for both single and multiple injection events. The measured volume of fuel injected at each injection pulse is also reported. The analysis of the system oscillating behavior was carried out with the support of a simple lumped parameter model. Such a model was shown to be capable of predicting the main frequencies of the hydraulic circuit and their dependence on the geometrical parameters. The good agreement between the outcome of this simple model and the experimental data also substantiated the reliable authors’ interpretation of the primary cause and effect relations underlying the complex flow phenomena occurring in the system. A refined computational model was developed and validated in a parallel work, providing a hydrodynamic analysis tool that is complementary to experimentation and also a means of hydraulic-system layout design and optimization. Finally, the mutual fluid-dynamic interactions taking place between consecutive injection events by distinct injectors of the same system are investigated in addition to the difference in dynamics of valve covered orifice and Minisac-nozzle injectors. Cycle-to-cycle variations in system performance were also investigated.