A numerical model for simulating a Common Rail Piezo Indirect Acting fuel injection-system under steady state as well as transient operating conditions was developed using a commercial code. A 1D flow model of the main hydraulic system components, including the rail, the rail to injector connecting pipe and the injector, was applied in order to predict the influence of the injector layout and of each part of the hydraulic circuit on the injection system performance.
The numerical code was validated through the comparison of the numerical results with experimental data obtained on a high performance test bench of the Moehwald-Bosch MEP2000/ CA4000 type. The developed injection-system mathematical model was applied to the analysis of transient flows in the hydraulic circuit paying specific attention to the fluid dynamics internal to the injector. In particular, numerical results on the time histories of delivery- and control-chamber pressures, pilot- and needle-valve lifts, mass flow rates through Z and A holes as well as through the by-pass, were obtained and analyzed in order to highlight the dependence of main nonstationary events on injector internal geometric features and needle dynamics.
The internal dynamics of the Piezo Indirect Acting fuel injection-system turned out to be very similar to that of a second generation solenoid-actuated Common Rail apparatus. Substantial differences arose from the end of the energizing time onward, leading to reduced values of the Nozzle Closure Delay for the piezo injector. However, such differences can be mainly ascribed to the presence of different hydraulic features in the layout of the indirect acting piezo injector rather than to the high-performance of its driving system. This suggests that comparable values of the Nozzle Closure Delay can also be achieved with solenoid injectors provided that their mechanical and hydraulic setup is conveniently adapted.