Cylinder head structure of internal combustion engine

A cylinder head structure of an internal combustion engine in which a spark plug is installed to a through hole penetrating to an inner wall surface of a cylinder head, the spark plug including:

• a ground electrode having a cylindrical shape;
• an insulator being held inside the ground electrode and protruding to a tip side than a tip of the ground electrode;
• and
• a center electrode being held inside the insulator and protruding to a tip side than a tip of the insulator,
• wherein in a case where a first position of a surface of the ground electrode exposed to a side of the inner wall surface of the cylinder head is a most downstream position in an air flow direction between the center electrode and the ground electrode, and a second position of the inner wall surface of the cylinder head is a position closest to the center electrode on a downstream side of the center electrode in an air flow direction, the spark plug is installed at a position where the first position and the second position are on a same air flow line, or at a position where the first position is recessed to a side where the first position recedes from the inner wall surface than the second position, and
• wherein in a downstream side of the center electrode in the air flow direction, the cylinder head includes a stepped portion protruding from the inner wall surface of a periphery.

A cylinder head structure of an internal combustion engine in which a spark plug is installed to a through hole penetrating to an inner wall surface of a cylinder head, the spark plug including:

• a ground electrode having a cylindrical shape;
• an insulator being held inside the ground electrode and protruding to a tip side than a tip of the ground electrode;
• and
• a center electrode being held inside the insulator and protruding to a tip side than a tip of the insulator,
• wherein in a downstream side of the center electrode in an air flow direction flowing between the center electrode and the ground electrode, the cylinder head includes a stepped portion protruding from the inner wall surface of a periphery.