| 摘要 |
PROBLEM TO BE SOLVED: To suppress ignitability reduction of a plasma jet spark plug after a prolonged time of use.SOLUTION: A plasma jet spark plug 100 comprises: an insulator 20 having a shaft hole 21 extending in an axial direction; a center electrode 10 arranged in the shaft hole 21 in such a manner that its front end surface is positioned on a further rear end side, in the axial direction, than a front end surface 72 of the insulator 20; and a ground electrode 40 which is positioned on a further front end side, in the axial direction, than the front end surface 72 of the insulator 20 so as to cover the front end surface 72 of the insulator 20, and which has a through-hole 41 formed in an area where a central axis OL of the shaft hole 21 is located. The insulator 20 has a monocrystalline portion 70 which is arranged on a further front end side, in the axial direction, than a front end surface 81 of the center electrode 10, and at least part of which is made of a monocrystalline insulator material. |
