A pre-chamber spark plug. The pre-chamber spark plug includes a housing, a pre-chamber, a cap that closes the pre-chamber on the housing and that has one or more through-openings, and an ignition device situated in the pre-chamber. The cap has a cap base and a cap jacket. The cap jacket and a housing inner wall of the housing defines a pre-chamber inner wall. The pre-chamber is defined by the pre-chamber inner wall and the cap base. At least one rib projects into the pre-chamber is formed in the region of the pre-chamber inner wall.

A pre-chamber spark plug. The pre-chamber spark plug includes a housing, a pre-chamber, a cap that closes the pre-chamber on the housing and that has one or more through-openings, and an ignition device situated in the pre-chamber. The cap has a cap base and a cap jacket. The cap jacket and a housing inner wall of the housing defines a pre-chamber inner wall. The pre-chamber is defined by the pre-chamber inner wall and the cap base. At least one rib projects into the pre-chamber is formed in the region of the pre-chamber inner wall.

A spark ignition device includes a ceramic insulator with a metal shell surrounding at least a portion of the ceramic insulator. A ground electrode is attached to the shell. The ground electrode has a ground electrode sparking tip spaced from a central sparking tip by a spark gap. A first terminal is arranged in electrical communication with the central sparking tip and is configured for electrical connection with a power source. The device further includes a second terminal configured for electrical connection with the power source. The second terminal is spaced from the first terminal, with the second terminal being arranged in electrical communication with the first terminal. A heater element brings the first terminal in electrical communication with the second terminal and completes an electrical circuit. The heater element has a resistance greater than the first and second terminals thereby producing a significant source of heat.

A spark ignition device includes a ceramic insulator with a metal shell surrounding at least a portion of the ceramic insulator. A ground electrode is attached to the shell. The ground electrode has a ground electrode sparking tip spaced from a central sparking tip by a spark gap. A first terminal is arranged in electrical communication with the central sparking tip and is configured for electrical connection with a power source. The device further includes a second terminal configured for electrical connection with the power source. The second terminal is spaced from the first terminal, with the second terminal being arranged in electrical communication with the first terminal. A heater element brings the first terminal in electrical communication with the second terminal and completes an electrical circuit. The heater element has a resistance greater than the first and second terminals thereby producing a significant source of heat.

A spark plug includes an insulator, a center electrode, a metallic shell, and a ground electrode. The insulator contains not less than 90.0 mass % and not greater than 98.1 mass % of Al.sub.2O.sub.3 with respect to a total mass of elements, as reduced to oxides, contained in the insulator, and has a porosity not greater than 5%. Assuming that a porosity of the insulator after a heat treatment is B, a difference (BA) of the porosities before and after the heat treatment is not greater than 3.5%. In the heat treatment, the insulator is placed in a furnace, and a temperature in the furnace is increased from a room temperature to 1400 C. at a temperature increase rate of 7 C./min and is held at 1400 C. for 30 minutes, and thereafter, the temperature is decreased from 1400 C. to 400 C. at a temperature decrease rate of 10 C. or less per 5 minutes and is decreased to the room temperature.

A spark plug includes an insulator, a center electrode, a metallic shell, and a ground electrode. The insulator contains not less than 90.0 mass % and not greater than 98.1 mass % of Al.sub.2O.sub.3 with respect to a total mass of elements, as reduced to oxides, contained in the insulator, and has a porosity not greater than 5%. Assuming that a porosity of the insulator after a heat treatment is B, a difference (BA) of the porosities before and after the heat treatment is not greater than 3.5%. In the heat treatment, the insulator is placed in a furnace, and a temperature in the furnace is increased from a room temperature to 1400 C. at a temperature increase rate of 7 C./min and is held at 1400 C. for 30 minutes, and thereafter, the temperature is decreased from 1400 C. to 400 C. at a temperature decrease rate of 10 C. or less per 5 minutes and is decreased to the room temperature.

A multipoint spark plug includes side electrodes provided in a pair so as to extend in a lengthwise direction of a tip end portion via a gap, and an intermediate electrode provided in the gap between the pair of side electrodes such that a plurality of ignition gaps are formed in the lengthwise direction of the tip end portion. An electrode holding portion is formed from separate parts that hold the side electrodes and the intermediate electrode, respectively, so as to insulate the side electrodes and the intermediate electrode from the main body portion, and the respective parts thereof project into the combustion chamber from the tip end portion.

A spark plug includes an insulator, a center electrode, a metallic shell, and a ground electrode. The insulator contains not less than 90.0 mass % and not greater than 98.1 mass % of Al.sub.2O.sub.3 with respect to a total mass of elements, as reduced to oxides, contained in the insulator, and has a porosity not greater than 5%. Assuming that a porosity of the insulator after a heat treatment is B, a difference (BA) of the porosities before and after the heat treatment is not greater than 3.5%. In the heat treatment, the insulator is placed in a furnace, and a temperature in the furnace is increased from a room temperature to 1400 C. at a temperature increase rate of 7 C./min and is held at 1400 C. for 30 minutes, and thereafter, the temperature is decreased from 1400 C. to 400 C. at a temperature decrease rate of 10 C. or less per 5 minutes and is decreased to the room temperature.

A spark plug includes an insulator, a center electrode, a metallic shell, and a ground electrode. The insulator contains not less than 90.0 mass % and not greater than 98.1 mass % of Al.sub.2O.sub.3 with respect to a total mass of elements, as reduced to oxides, contained in the insulator, and has a porosity not greater than 5%. Assuming that a porosity of the insulator after a heat treatment is B, a difference (BA) of the porosities before and after the heat treatment is not greater than 3.5%. In the heat treatment, the insulator is placed in a furnace, and a temperature in the furnace is increased from a room temperature to 1400 C. at a temperature increase rate of 7 C./min and is held at 1400 C. for 30 minutes, and thereafter, the temperature is decreased from 1400 C. to 400 C. at a temperature decrease rate of 10 C. or less per 5 minutes and is decreased to the room temperature.