Development of a Piezoelectric Fuel Injector

A piezoelectric fuel injector that directly controls the injection process using a piezoelectric actuator is presented. In the design pursued, energizing the actuator initiates the displacement of the injection needle and allows the fuel spray to form. The direct-acting concept is implemented by developing a motion inverter that reverses the direction of the input force and displacement and amplifies the output displacement. A fuel injector prototype was built, consisting of an actuator module that housed the preloaded piezoelectric actuator, a motion inverter module, and a dispensing module consisting of the injection nozzle and needle. Experiments with input voltage signals corresponding to those used in diesel engines verified the performance of the fuel injector prototype. The prototype was successfully tested for 250-, 400-, 600-, and 800-$\mu\mbox{s}$ holding times and only showed a response delay due to hysteresis, which can be reduced using closed-loop control with the integration of the electronic control unit (ECU). Since the prototype takes advantage of direct control of the injection needle, it allows for more precise control of the timing of the injections. The design also has the potential to control the quantity of injected fuel more precisely than currently available commercial injectors.