Spark plug for internal combustion engine

摘要

A spark plug includes a ground electrode formed with a flat region and a convex curved region on an outer peripheral surface thereof. The flat region is located on a front end of the ground electrode and has a length of 0.2 mm or more from a front end face of the ground electrode in a longitudinal direction of the ground electrode. The ground electrode satisfies the following dimensional condition (1) with respect to first and second cross sections of the ground electrode taken through the convex curved region and the flat region in directions perpendicular to the longitudinal direction of the ground electrode, 0.950 ‰¤ S �¢ 2 / L �¢ 2 / S �¢ 1 / L �¢ 1 ‰¤ 0.995
where S 1 is the area of the first cross section; L 1 is the perimeter of the first cross section; S2 is the area of the second cross section; and L2 is the perimeter of the second cross section.