| 摘要 |
An object of the present invention is to effectively restrain rapid erosion of a side surface of a ground electrode resulting from skewing of spark discharge and to reliably prevent separation of a tip from the ground electrode. A spark plug 1 includes a ceramic insulator 2; a center electrode 5; a metallic shell 3; a ground electrode 27 disposed at a forward end portion of the metallic shell 3 and adapted to form a gap 33 in cooperation with a forward end portion of the center electrode 5; and a tip 32 at least a portion of which is joined to at least the one of two side surfaces 27S1 and 27S2 of the ground electrode 27 which is disposed downstream with respect to fuel gas flow. In a first imaginary plane VS1 which contains a forward end surface 5F of the center electrode 5 and on which a discharge surface 32A of the tip 32 is projected, at least a portion of a projected image PR1 of the discharge surface 32A is located within a range of 2.5G from the outer circumference of the forward end surface 5F of the center electrode 5, where G (mm) is the size of the gap 33. |
