| 摘要 |
A spark plug comprising a cylindrical portion which projects into a combustion chamber from an inner wall face of an engine head when the spark plug is fixed to the engine head, wherein the cylindrical portion has one or more ventilating portion comprised of a through hole or a notch in an outer circumferential face thereof. An igniting portion projecting into the combustion chamber improves ignitability. Further, because an air-fuel mixture fed from an inlet of the internal combustion engine flows to inside of the cylindrical portion through the ventilating portion, heat of an insulator is taken away and cooled down, whereby an occurrence of pre-ignition is prevented.
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