A center electrode is electrically coupled with a main terminal. A ground electrode is opposed to the center electrode to form a gap therebetween. A piezo actuator changes in length on application of a voltage. The piezo actuator actuates one of the center electrode and the ground electrode to manipulate the gap.

A center electrode is electrically coupled with a main terminal. A ground electrode is opposed to the center electrode to form a gap therebetween. A piezo actuator changes in length on application of a voltage. The piezo actuator actuates one of the center electrode and the ground electrode to manipulate the gap.

Fuel injector-igniters with variable gap electrodes. A fuel injector-igniter comprises a housing, an actuator disposed in the housing, and a valve including a valve head operative to open and close against a valve seat in response to activation of the actuator. A valve seat electrode including at least one aperture surrounds the valve head and valve seat and at least one rocker electrode is pivotably mounted to the housing to form a variable gap between the electrode and a portion of the valve seat electrode. The rocker electrode is positioned to move relative to the valve seat electrode in response to a fuel flow through the aperture, thereby varying the gap.