A spark plug, including a central electrode, a first ground electrode, which is situated in a curved shape having a horizontal area and an essentially vertical area, and at least one second ground electrode, which is situated adjacent to the central electrode in such a way that a distance between the first ground electrode and the central electrode is less than a distance between the second ground electrode and the central electrode.

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.

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.