| 摘要 |
PROBLEM TO BE SOLVED: To maintain excellent ignitability over a long period of time.SOLUTION: A plasma jet ignition plug 1 includes an insulator 2 having an axial hole 4 extending therethrough in the direction of an axis CL1, a center electrode 5 inserted into the axial hole 4, and a ground electrode 27 disposed frontward of the front end of the insulator 2. The insulator 2 has a cavity 31 defined by the inner circumferential surface of the axial hole 4 and the front end surface of the center electrode 5 and opens frontward. The ground electrode 27 has a through-hole 28 for establishing communication between the cavity 31 and an outside. A front end portion of the center electrode 5 is formed into a taper portion 51 whose diameter reduces frontward in the direction of the axis CL1. The outside diameter of a front end of the taper portion 31 is smaller than the diameter of the through-hole 28. The cavity 31 has a substantially constant inside diameter along the direction of the axis CL1. Assuming that the inside diameter of the cavity 31 is DC (mm) and the length of the cavity 31 in the direction of the axis CL1 is LC (mm), the expression 0.5≤LC/DC<1.0 is satisfied. |
