FEM modeling of the piezoelectric driving system in the design of direct-acting diesel injectors

Abstract

A detailed mathematical model of a direct-acting prototypal piezo-injector has been developed to help experimentation, design and component optimization. The thermo-fluid dynamics of the hydraulic circuit components, including the injector feeding pipe, injector drilled pipes and nozzle, was modeled in conjunction with the mechanics of the mobile elements in the injector. A Finite Element Method (FEM) model of the piezo-stack has been developed to predict the temporal distribution of the elongation of the piezo-actuator. The piezoelectric submodel was based on the experimental trace of the current provided to the piezo-stack and was verified to correctly reproduce the dynamic response of the injector piezoelectric driving system.The complete numerical tool was then validated through an extensive comparison with experimental data taken for different injector working conditions. Finally, the validated model was applied to help develop the direct-acting prototypal injector through a better understanding of the cause and effect relationships in the analysis of the performance of the injection system. An upgraded version of the injector has been set up on the basis of the indications of the model and tested on the hydraulic test rig. The hydraulic performance of the modified injector has proved satisfactory and to be in line with the model predictions.