| 摘要 |
PROBLEM TO BE SOLVED: To provide a spark plug in which the wear or the like of electrodes by a reaction with sulfur constituents is prevented even in an environment generating contact with sulfur of high concentration constituent sand so as to assure a sufficient service life of the electrodes even when adopted for a direct injection engine or the like. SOLUTION: In a spark plug 100, the side to form spark discharge gap g in an axial direction of the central electrode 3 is assumed to be the front side. A distance from the end face of the main fitting 1 at the side of joining with the earthing electrode 4 to the margin of the front side of the earthing electrode 4 in the direction of the axial line should be larger than 6 mm, and at least the surface layer part of the earthing electrode of the spark plug 100 is composed of a corrosion resistant metal against sulfur compounds. The corrosion resisting metal against sulfur compounds may be iron-based alloy containing equal or more than 10 wt.% of chromium or cobalt or both.
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