Hydraulic Simulation and Experimental Analysis of Needle Response and Controlled Injection Rate Shape Characteristics in a Piezo-driven Diesel Injector

The More precise control of the multiple-injection is required in common-rail injection system of direct injection diesel engine to meet the low NOx emission and optimal PM filter system. The main parameter for obtaining the multiple-injections is the mechanism controlling the injector needle energizing and movement. In this study, a piezo-driven diesel injector, as a new method driven by piezoelectric energy, has been applied with a purpose to develop the analysis model of the piezo actuator to predict the dynamics characteristics of the hydraulic component (injector) by using the AMESim code and to evaluate the effect of this control capability on spray formation processes. Aimed at simulating the hydraulic behavior of the piezo-driven injector, the circuit model has been developed and verified by comparison with the experimental results. We found that the input voltage exerted on piezo stack is the dominant factor which affects on the initial needle behavior of piezo-driven injector than the hydraulic force generated by the constant injection pressure. And the piezo-driven injector has more degrees of freedom in controlling the injection rate with the high pressure than a solenoid-driven injector. The piezo-electric characteristics of a piezo-driven diesel injector, which was manufactured as prototype version was experimentally examined to confirm the injection driving principle based on the inverse piezo-electric effect and to ensure the operating performance of a prototype piezo-driven injector. The injection duration is proportional to the external input pulse duration for driving the piezo-driven injector. The higher the output current (voltage) applied to piezo-driven injector's controller, the longer the hold time on the injection duration is. The charging time decreases rapidly as the output current increase. And the needle's response of a piezo-driven injector by using an accelerometer has been investigated together with the evaluation of the injection rate employing Bosch's method. Results were compared between a conventional solenoid-driven injector and the piezo-driven injector, both equipped with the same micro-sac multi-hole injection nozzle. The experimental results show that the piezo-driven injector has a higher injection flow rate by a fast needle response time and it is possible to control the injection rate slope by altering the induced current. Also these experimental results showed favorable agreement with the predicted simulation results by AMESim environment.