| 摘要 |
Projecting portions (61-65) extended in an axis (—‹) direction and projecting forward are formed on a front end face (57) of a cylindrical portion (60) provided on a front end side of a metal shell (50). The projecting portions (61-65) are disposed at an equal interval therebetween in a circumferential direction revolving around a center S of a firing portion (70). No matter what the mounting state of a spark plug (100) on an engine head (shifted in the circumferential direction that is caused by a difference in tightening an fitting screw) may be, a side face or an end face of any one of projecting portions faces at an upstream side of a fuel (combustible air-fuel mixture layer) flow direction which flows with an air current in a combustion chamber. Therefore, the combustible air-fuel mixture layer colliding with the projecting portion includes the flow direction directed to the firing portion (70) as its reflective direction and is adrift around the firing portion (70). |
