An injector unit that can use a gaseous fuel such as CNG in an already-existing diesel engine and a spark plug that uses the injector unit, are provided. The injector unit includes an injector, an igniter having a resonance structure configured to boost an inputted microwave and a discharger configured to perform a discharge, and a casing configured to house therein the injector and the igniter. The igniter includes a first part configured to transmit the inputted microwave, a second part configured to perform a capacity coupling to attain an impedance matching between the microwave and the igniter, and a third part configured to transmit the capacity-coupled microwave to the discharger. Moreover, the igniter is bent at a boundary of the first part and the second part, a boundary of the second part and the third part, or inside the first part.

A spark plug 1 includes a tubular housing 2, a tubular insulator 3 held inside the housing 2, a center electrode 4 held inside the insulator 3 such that a distal end portion 41 protrudes, a ground electrode 5 that forms a spark discharge gap G between it and the center electrode 4, and a standing member 6 that stands distalward from a distal end portion 21 of the housing 2. In at least one of a pair of side surfaces 61 of the standing member 6 which face in a plug circumferential direction, there is formed a guide step portion 62 for guiding the flow of an air-fuel mixture in a combustion chamber of an internal combustion engine to the spark discharge gap G.

There are provided a plug built-in type optical measurement probe capable of obtaining a more accurate measurement value, and an optical measurement device provided with the same. A spark section and a light receiving section are held by a plug main body while being arranged next to each other in a protruding manner such that an end face of a holder is arranged at a position where discharge light from the spark section does not enter the field of view of the light receiving section. Accordingly, the light receiving section can be held in a manner protruding from the plug main body, and entering of the discharge light from the spark section can be restricted by the holder of the light receiving section. That is, by arranging the end face of the holder at a position where the discharge light from the spark section does not enter the field of view of the light receiving section, the light receiving intensity of the discharge light from the spark section can be prevented from being added to a measurement value, and it is possible to measure only the light generated at the time of combustion, and thus, a more accurate measurement value can be obtained.

There are provided a plug built-in type optical measurement probe capable of obtaining a more accurate measurement value, and an optical measurement device provided with the same. A spark section and a light receiving section are held by a plug main body while being arranged next to each other in a protruding manner such that an end face of a holder is arranged at a position where discharge light from the spark section does not enter the field of view of the light receiving section. Accordingly, the light receiving section can be held in a manner protruding from the plug main body, and entering of the discharge light from the spark section can be restricted by the holder of the light receiving section. That is, by arranging the end face of the holder at a position where the discharge light from the spark section does not enter the field of view of the light receiving section, the light receiving intensity of the discharge light from the spark section can be prevented from being added to a measurement value, and it is possible to measure only the light generated at the time of combustion, and thus, a more accurate measurement value can be obtained.

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.

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.

A spark plug includes a terminal electrode extending in an axial direction of the spark plug. The terminal electrode has an end in the axial direction, and has a recess formed in the end of the terminal electrode. The recess has a bottom surface and an identifier on the bottom surface. The recess has a side surface parallel to the axial direction.

A spark plug includes a terminal electrode extending in an axial direction of the spark plug. The terminal electrode has an end in the axial direction, and has a recess formed in the end of the terminal electrode. The recess has a bottom surface and an identifier on the bottom surface. The recess has a side surface parallel to the axial direction.

A spark plug includes a terminal electrode extending in an axial direction of the spark plug. The terminal electrode has an end in the axial direction, and has a recess formed in the end of the terminal electrode. The recess has a bottom surface and an identifier on the bottom surface. The recess has a side surface parallel to the axial direction.

A spark plug includes a terminal electrode extending in an axial direction of the spark plug. The terminal electrode has an end in the axial direction, and has a recess formed in the end of the terminal electrode. The recess has a bottom surface and an identifier on the bottom surface. The recess has a side surface parallel to the axial direction.