A spark plug including an insulator and a metallic member such as a metallic shell. In the spark plug, a mark such as a two-dimensional code is provided on the surface of at least one of the insulator and the metallic member. Also, a protective layer covers the mark. The protective layer is optically transparent and contains a fluorescent substance.

A spark plug including an insulator and a metallic member such as a metallic shell. In the spark plug, a mark such as a two-dimensional code is provided on the surface of at least one of the insulator and the metallic member. Also, a protective layer covers the mark. The protective layer is optically transparent and contains a fluorescent substance.

A spark plug 100 of the present disclosure includes a center electrode 20; a metallic member provided to form a tubular shape around an axis AX of the spark plug, holding the center electrode 20 therein in an insulated state, and having a hole 55 formed in a side wall thereof and extending in a radial direction; and a ground electrode 30 supported in the hole 55 and extending from the hole 55 toward the axis AX. The ground electrode 30 has a fixing portion formed of a metal and fixed to the hole 55, and an ignition portion 39 containing a noble metal, disposed on a side toward the axis AX in relation to the fixing portion, and having a discharge surface for forming a gap G between the ignition portion and the center electrode 20. The absolute value of the difference in coefficient of thermal expansion between the metallic member and the fixing portion is smaller than the absolute value of the difference in coefficient of thermal expansion between the metallic member and the ignition portion 39.

A spark plug 100 of the present disclosure includes a center electrode 20; a metallic member provided to form a tubular shape around an axis AX of the spark plug, holding the center electrode 20 therein in an insulated state, and having a hole 55 formed in a side wall thereof and extending in a radial direction; and a ground electrode 30 supported in the hole 55 and extending from the hole 55 toward the axis AX. The ground electrode 30 has a fixing portion formed of a metal and fixed to the hole 55, and an ignition portion 39 containing a noble metal, disposed on a side toward the axis AX in relation to the fixing portion, and having a discharge surface for forming a gap G between the ignition portion and the center electrode 20. The absolute value of the difference in coefficient of thermal expansion between the metallic member and the fixing portion is smaller than the absolute value of the difference in coefficient of thermal expansion between the metallic member and the ignition portion 39.

A spark plug includes a ground electrode facing a distal end surface of a center electrode. In a main body of the ground electrode, a first slanted surface is formed at a portion on a side facing the distal end surface and upstream of the center electrode relative to the airflow, a facing portion, a second slanted surface is formed at a portion on a side opposite to the side facing the distal end surface and upstream of the center electrode relative to the airflow, and when T represents a thickness of the main body of the ground electrode and Su represents a distance from a connection between the first slanted surface and the second slanted surface to the facing portion, 2T/16Su8T/16.

A spark plug includes a ground electrode facing a distal end surface of a center electrode. In a main body of the ground electrode, a first slanted surface is formed at a portion on a side facing the distal end surface and upstream of the center electrode relative to the airflow, a facing portion, a second slanted surface is formed at a portion on a side opposite to the side facing the distal end surface and upstream of the center electrode relative to the airflow, and when T represents a thickness of the main body of the ground electrode and Su represents a distance from a connection between the first slanted surface and the second slanted surface to the facing portion, 2T/16Su8T/16.

A spark plug has a housing of a cylindrical shape and an insulator supported to an inside of the housing. A channel part is formed at a distal end side of the housing. The channel part is open so that the inside of the housing communicates with an outside of the housing through the channel part. The channel part has a channel bottom having a tapered shape oblique relative to a plug central axis. An overall channel bottom is arranged in the housing closer to a proximal end side than to the distal end side of the housing.

A spark plug has a housing of a cylindrical shape and an insulator supported to an inside of the housing. A channel part is formed at a distal end side of the housing. The channel part is open so that the inside of the housing communicates with an outside of the housing through the channel part. The channel part has a channel bottom having a tapered shape oblique relative to a plug central axis. An overall channel bottom is arranged in the housing closer to a proximal end side than to the distal end side of the housing.

A spark plug for generating an axially extending surface spark between a sparking tip of the center electrode and a seal supporting sparking projection located at an internal step portion of the metal shell. In one embodiment, the spark plug is a pre-chamber spark plug having a pre-chamber cap attached to a distal end of the metal shell. The spark plug can allow for unobstructed flame propagation through the pre-chamber, without having the flame obstructed by narrow gaps or a separate ground electrode.

A spark plug for generating an axially extending surface spark between a sparking tip of the center electrode and a seal supporting sparking projection located at an internal step portion of the metal shell. In one embodiment, the spark plug is a pre-chamber spark plug having a pre-chamber cap attached to a distal end of the metal shell. The spark plug can allow for unobstructed flame propagation through the pre-chamber, without having the flame obstructed by narrow gaps or a separate ground electrode.