Abstract: A spark plug has a central electrode and a plurality of peripheral electrodes. The central electrode has a proximal portion and a distal portion. The distal portion of the central electrode has a circular cross-section with a longitudinal axis and terminates in a distal end. Each peripheral electrode has a lower portion and an upper portion. Each upper portion has a distal-most point. Each distal-most point is disposed in a central plane within which the longitudinal axis of the distal portion of the central electrode is wholly disposed. The cross-section of each upper portion taken along its central plane defines a convex outer side and a non-convex inner side. Each convex outer side has a curved surface which is tangent to a plurality of tangent planes, all of which intersect the longitudinal axis of the distal portion of the central electrode at points at or above the distal end of the distal point of the central electrode.

Abstract: A spark plug has a central electrode and a plurality of peripheral electrodes. The central electrode has a proximal portion and a distal portion. The distal portion of the central electrode has a circular cross-section with a longitudinal axis and terminates in a distal end. Each peripheral electrode has a lower portion and an upper portion. Each upper portion has a distal-most point. Each distal-most point is disposed in a central plane within which the longitudinal axis of the distal portion of the central electrode is wholly disposed. The cross-section of each upper portion taken along its central plane defines a convex outer side and a non-convex inner side. Each convex outer side has a curved surface which is tangent to a plurality of tangent planes, all of which intersect the longitudinal axis of the distal portion of the central electrode at points at or above the distal end of the distal point of the central electrode.