Patent ID: 8237342

Claim:
A plasma jet ignition plug comprising: an insulator having an axial bore extending in a direction of an axis; a center electrode inserted in the axial bore in such a manner that a front end thereof is located rearward of a front end of the insulator with respect to the direction of the axis; a metallic shell disposed externally of an outer circumference of the insulator; and a ground electrode fixed to a front end portion of the metallic shell and disposed frontward of the front end of the insulator with respect to the direction of the axis; a cavity being defined by a wall surface of the axial bore and a front end surface of the center electrode; and the ground electrode having a through hole portion for allowing the cavity to communicate with an ambient atmosphere; the plasma jet ignition plug further comprising a support intervening between a front end surface of the insulator and a surface of the ground electrode located on a side toward the insulator; wherein a space formed radially outward of the support and a space formed radially inward of the support communicate with each other, and as viewed on an imaginary plane which is orthogonal to the axis and onto which an opening of the axial bore located on a front side with respect to the direction of the axis and the support are projected, a point A which is on an outline of the support such that a distance to the axis therefrom is the shortest distance between the outline of the support and the axis is located radially outward of an outline of the opening of the axial bore.