A spark plug includes a cylindrical metallic shell having a ground electrode at a forward end of the cylindrical metallic shell, a cylindrical insulator held in the metallic shell, a center electrode disposed in the insulator, a resistor element disposed in the insulator and having a forward end located rearward of a rear end of the center electrode, a forward-end-side electrically conductive seal layer disposed in the insulator to be located between the center electrode and the resistor element, and a rear-end-side electrically conductive seal layer disposed in the insulator to be located rearward of the resistor element. The forward end of the resistor element is located forward of the rear end of the metallic shell, and the rear end of the resistor element is located rearward of the rear end of the metallic shell.

The spark plug has a shaft shaped center electrode, insulator, terminal fitting, ground electrode and resistor. The insulator has an axially penetrating shaft hole, and the center electrode is held in a tip end side of the shaft hole. The terminal fitting has a shaft and a terminal part. The shaft is held in a base end side of the shaft hole. The terminal part is projected from a base end of the shaft hole to a base end side of the spark plug. The ground electrode faces the center electrode in a tip end side of the shaft hole. The resistor is disposed between the center electrode and the terminal fitting in the shaft hole. An axial length L of the resistor is 15 mm≦L≦22.5 mm. An axial length T of the shaft satisfies a relation of 1.25≦T/L.

The spark plug has a shaft shaped center electrode, insulator, terminal fitting, ground electrode and resistor. The insulator has an axially penetrating shaft hole, and the center electrode is held in a tip end side of the shaft hole. The terminal fitting has a shaft and a terminal part. The shaft is held in a base end side of the shaft hole. The terminal part is projected from a base end of the shaft hole to a base end side of the spark plug. The ground electrode faces the center electrode in a tip end side of the shaft hole. The resistor is disposed between the center electrode and the terminal fitting in the shaft hole. An axial length L of the resistor is 15 mm≦L≦22.5 mm. An axial length T of the shaft satisfies a relation of 1.25≦T/L.

A spark plug having a spark plug body and an insulator arranged therein, in which insulator a passage is provided in which a center electrode, an ignitor and a glass seal connecting the center electrode to the ignitor and acting as an interference-suppression resistor are arranged. At least one additional interference-suppression element is arranged in the passage of the insulator.

A spark plug having a spark plug body and an insulator arranged therein, in which insulator a passage is provided in which a center electrode, an ignitor and a glass seal connecting the center electrode to the ignitor and acting as an interference-suppression resistor are arranged. At least one additional interference-suppression element is arranged in the passage of the insulator.

An ignition system that uses a technique capable of restraining radiation of noise caused by discharge of a spark plug in the ignition system. The ignition system includes a spark plug and a power supply section. The spark plug is attached to an engine head. The power supply section has a battery having a ground terminal, and an ignition coil which transforms a voltage of the battery and supplies a transformed voltage to the spark plug. In the ignition system, a metallic shell of the spark plug is fixed to the engine head while being electrically insulated from the engine head through an insulator an electrically conductive path is connected to the metallic shell, and the electrically conductive path is electrically connected to the ground terminal of the battery while being electrically insulated from the engine head.

A spark plug for a gas-powered internal combustion engine, having a center conductor, an insulator surrounding the center conductor, a body surrounding the insulator, a center electrode connected in an electrically conductive manner to the center conductor, and at least one ground electrode that is connected in an electrically conductive manner to the body and forms a spark air gap with the center electrode. A shield that shields the spark air gap in the radial direction of the spark plug is located at the front end of the body. The shield includes multiple shield components that are attached to the front end of the body adjacent to one another in the circumferential direction of the spark plug.

A spark plug for a gas-powered internal combustion engine, having a center conductor, an insulator surrounding the center conductor, a body surrounding the insulator, a center electrode connected in an electrically conductive manner to the center conductor, and at least one ground electrode that is connected in an electrically conductive manner to the body and forms a spark air gap with the center electrode. A shield that shields the spark air gap in the radial direction of the spark plug is located at the front end of the body. The shield includes multiple shield components that are attached to the front end of the body adjacent to one another in the circumferential direction of the spark plug.

The spark plug includes: an insulator having a through hole that penetrates therethrough along an axial direction; a center electrode disposed on one end side of the through hole; a metal terminal disposed on the other end side of the through hole; and a conductive seal layer connected to at least one of the center electrode and the metal terminal. The conductive seal layer contains glass and a Cu—Zn alloy. A volumetric percentage of the Cu—Zn alloy in the conductive seal layer is greater than or equal to 44% and not greater than 55%.

A spark plug includes an insulator body and a central electrode having a spark-end and a terminal-end. The central electrode is disposed within the insulator body, with the spark-end and the terminal-end protruding from the insulator body at opposite ends thereof. A metal electrode surrounds the insulator body and extends to form a gap with the central electrode at the spark-end. A capacitor with metalized inner and outer surfaces is provided, with the metalized inner surface being connected to the central electrode and the metalized outer surface being connected to the metal electrode. A first resistive component is embedded within the central electrode between the capacitor and the terminal-end, and a second resistive component embedded within the central electrode between the capacitor and the spark-end.