| 摘要 |
A spark plug according to the invention includes a metal shell, an insulator, a center electrode, a first ground electrode, and a second ground electrode. The metal shell has a threaded portion with an outer diameter in a range of 12 to 14 mm. The first ground electrode is aligned with the center electrode in an axial direction of the spark plug to form a first spark gap across which normal sparks are discharged in normal conditions. The second ground electrode is aligned with the center electrode in a radial direction of the spark plug to form a second spark gap across which side sparks are discharged when the insulator is fouled with carbon deposits. The spark plug has an improved structure ensuring that when the insulator is fouled with carbon deposits, side sparks are discharged without formation of channels on the insulator, thereby recovering the insulation properties of the insulator.
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