Benefits of hydraulic layout over driving system in piezo-injectors and proposal of a new-concept CR injector with an integrated Minirail

The prediction capability of an advanced Common Rail (CR) piezoelectric injection-system mathematical model has been upgraded and applied to the analysis of transient flows inside injectors. The predicted time histories of the sac-, delivery- and control-chamber pressures, of the pilot- and needle-valve lifts, and of the mass flow-rates through the Z and A holes, as well as through the bypass, have been analyzed to explain the differences in performance between piezoelectric and solenoid injectors. The objective was to study the influence exerted by the different hydraulic and mechanical setups in order to assess the effective benefits that could be obtained from the replacement of the solenoid driving system with the piezoelectric one. Then, the upgraded mathematical model has been applied to the design of new-concept injectors. First, specific attention was given to the effects that variations in the peak current values could have on the injected flow-rate. Furthermore, numerical simulations were performed to comprehend the effects that remarkable increments in the injector internal accumulation volume could have on injection system performance. A prototype of the new-concept injector with a small integrated accumulator (Minirail) has also been tested on the hydraulic rig.

► A model is applied to explain the different performance of piezo and solenoid injectors.
► The piezo-injector internal dynamics is shown and the effect of the bypass on NCD is clarified.
► Pressure waves in piezo-actuated injection systems are analyzed.
► Effects of the current time-history on injected flow-rate are investigated.
► A new injector with an integrated accumulator is designed on the basis of the model predictions.