The proposed solution relates to a combustion chamber assembly of an engine (T), in which an overrun of a spark plug is defined with a specific outer cone and a specific inner cone, and mixing air holes of a first arrangement and of at least one second arrangement that lie at least partially in a partial region of the overrun of the spark plug, said overrun being defined by the outer cone and the inner cone and extending downstream of the spark plug as far as an inner apex point (Si) of the inner cone, are formed with a flow cross section which is different from a flow cross section which the mixing air holes adjoining in the circumferential direction (U) of the respective arrangement have.

A spark plug is provided that ensures that a ground electrode is positioned in a predefined, precise orientation when installed in a spark plug hole of an engine head. The spark plug is configured for axial insertion into the plug hole, and has a non-axisymmetric ground shield that fits into the plug hole, wherein the ground shield has an outer shield surface with a non-axisymmetric shape and the plug hole is also provided with a complementary non-axisymmetric shape. The spark plug includes a central insulator, which has an inner end surrounding a central electrode and supporting the ground shield, which is mounted on the insulator to support a ground strap adjacent the electrode for forming a spark therebetween. The insulator and ground shield are axially slidable into the plug hole, and the spark plug includes a jamb nut which is rotatable to fix the spark plug in position in a predefined orientation. Preferably, an outer surface of the insulator and an inner surface of the ground shield have complementary shapes wherein the ground shield fits closely on the insulator. For example, the outer insulator surface and the inner shield surface may have a complementary axisymmetric shape, such as cylindrical, or a non-axisymmetric shape, which may conform to the non-axisymmetric shape of the outer shield surface.

A spark plug is provided that ensures that a ground electrode is positioned in a predefined, precise orientation when installed in a spark plug hole of an engine head. The spark plug is configured for axial insertion into the plug hole, and has a non-axisymmetric ground shield that fits into the plug hole, wherein the ground shield has an outer shield surface with a non-axisymmetric shape and the plug hole is also provided with a complementary non-axisymmetric shape. The spark plug includes a central insulator, which has an inner end surrounding a central electrode and supporting the ground shield, which is mounted on the insulator to support a ground strap adjacent the electrode for forming a spark therebetween. The insulator and ground shield are axially slidable into the plug hole, and the spark plug includes a jamb nut which is rotatable to fix the spark plug in position in a predefined orientation. Preferably, an outer surface of the insulator and an inner surface of the ground shield have complementary shapes wherein the ground shield fits closely on the insulator. For example, the outer insulator surface and the inner shield surface may have a complementary axisymmetric shape, such as cylindrical, or a non-axisymmetric shape, which may conform to the non-axisymmetric shape of the outer shield surface.

A spark plug includes a tubular metallic shell having an attachment screw portion having an external thread, an insulator disposed inside the metallic shell and having an axial hole, and a center electrode disposed in the axial hole. The attachment screw portion has a pitch diameter local maximum portion at which the external thread has a locally maximum pitch diameter. The pitch diameter local maximum portion is located on the forward end side of a rear end of the center electrode in a direction along an axial line of the metallic shell.

A spark plug includes a tubular metallic shell having an attachment screw portion having an external thread, an insulator disposed inside the metallic shell and having an axial hole, and a center electrode disposed in the axial hole. The attachment screw portion has a pitch diameter local maximum portion at which the external thread has a locally maximum pitch diameter. The pitch diameter local maximum portion is located on the forward end side of a rear end of the center electrode in a direction along an axial line of the metallic shell.

Spark plug assemblies and turbomachines are provided. A spark plug assembly includes a monolithic hollow cylinder extending along a longitudinal axis between a first end and a second end, the monolithic hollow cylinder including a sidewall defining an interior, a first end wall, and a second end opening. The first end wall defines a first end opening at the first end. The second end opening is defined at the second end. The spark plug assembly further includes an igniter assembly extending along the longitudinal axis into the interior through the first end opening and from the interior through the second end opening. The spark plug assembly further includes a piston surrounding the igniter, the piston disposed within the interior and extending from the interior along the longitudinal axis through the second end opening.

Spark plug assemblies and turbomachines are provided. A spark plug assembly includes a monolithic hollow cylinder extending along a longitudinal axis between a first end and a second end, the monolithic hollow cylinder including a sidewall defining an interior, a first end wall, and a second end opening. The first end wall defines a first end opening at the first end. The second end opening is defined at the second end. The spark plug assembly further includes an igniter assembly extending along the longitudinal axis into the interior through the first end opening and from the interior through the second end opening. The spark plug assembly further includes a piston surrounding the igniter, the piston disposed within the interior and extending from the interior along the longitudinal axis through the second end opening.

A spark plug is provided that includes an improved jamb nut configuration, which provides improved torque transfer and prevents inadvertent separation of the jamb nut from the remaining components of the spark plug, particularly during removal from the engine head. The spark plug is configured for axial insertion into the plug hole, and may have a non-axisymmetric ground shield that fits into the plug hole, wherein the plug hole is also provided with a complementary non-axisymmetric shape. The spark plug includes a central insulator, which has an inner end surrounding a central electrode and supporting the ground shield, which is mounted on the insulator to support a ground strap adjacent the electrode for forming a spark therebetween. The insulator and ground shield are axially slidable into the plug hole, and the jamb nut is rotatable to fix the spark plug in position in a predefined orientation. The insulator includes a retaining clip outwardly of the jamb nut that permits rotation of the jamb nut relative to the insulator but prevents axial separation of the jamb nut during removal of the spark plug from the engine head. An improved tool is also provided which better distributes torque transfer to the jamb nut and includes a catch to facilitate pulling of the spark plug from the engine head.

A spark plug is provided that includes an improved jamb nut configuration, which provides improved torque transfer and prevents inadvertent separation of the jamb nut from the remaining components of the spark plug, particularly during removal from the engine head. The spark plug is configured for axial insertion into the plug hole, and may have a non-axisymmetric ground shield that fits into the plug hole, wherein the plug hole is also provided with a complementary non-axisymmetric shape. The spark plug includes a central insulator, which has an inner end surrounding a central electrode and supporting the ground shield, which is mounted on the insulator to support a ground strap adjacent the electrode for forming a spark therebetween. The insulator and ground shield are axially slidable into the plug hole, and the jamb nut is rotatable to fix the spark plug in position in a predefined orientation. The insulator includes a retaining clip outwardly of the jamb nut that permits rotation of the jamb nut relative to the insulator but prevents axial separation of the jamb nut during removal of the spark plug from the engine head. An improved tool is also provided which better distributes torque transfer to the jamb nut and includes a catch to facilitate pulling of the spark plug from the engine head.

A spark plug has a housing of a cylindrical shape, an insulator of a cylindrical shape fitted into the inside of the housing, a center electrode and a ground electrode. No male screw part is formed on an outer peripheral surface of the housing. A housing support surface is formed on an inner peripheral surface of the housing. An outer peripheral surface of the insulator has an insulator support surface which is supported by the housing support surface in an axial direction of the spark plug. The housing has a pressure fitting part to be presses to a cylinder head of an internal combustion engine. A part of the pressure fitting part and a part of at least one of the housing support surface and the insulator support surface are arranged to be overlapped with each other in a radial direction of the spark plug.