| 摘要 |
A ground electrode includes a main body portion and a projecting portion having a width smaller than a width of the main body portion. A spark discharge gap is formed between a discharging surface of the projecting portion and a front end surface of a center electrode. When the front end surface and the ground electrode are projected on a first plane, at least a part of the projection region of the projecting portion overlaps the projection region of the front end surface. A width Le (mm), a width Lc (mm), a cross-sectional area Sg (mm 2 ), a cross-sectional area Sc (mm 2 ), an angle ¸1(°), an angle ¸2(°), an angle ¸3(°), and an angle ¸4(°) satisfy expressions Le < Lc, 2.9 ‰¤ Sc + Sg ‰¤ 4.25, and 0.30 ‰¤ (¸1/¸2) × (¸3/¸4) ‰¤ 0.67. |
