Abstract: A spark plug has a base with a bottom end portion adapted to be received and retained by a cylinder head of an internal combustion engine. An insulator retains a central electrode within the base with a combustion chamber end of the electrode extending into a combustion chamber of the engine when the plug is installed in the cylinder head. The central electrode combustion chamber end includes a combustion chamber end face with a hole having the physical characteristics of an acoustically tuned pipe with an open and a closed end formed in its surface. A ground electrode is attached to the base and defines a spark gap between its inner surface and the central electrode face. The ground electrode has a hole passing through it which has the physical characteristics of an acoustically tuned pipe with two open ends.

Abstract: A spark plug having a cylindrical rod-shaped high voltage electrode and a metal sleeve press-fitted on the main body of the plug concentrically surrounding the electrode and having an inwardly projecting annular throat rib with a cylindrical inner surface concentrically completely surrounding the electrode and defining an annular firing space. The bottom end of the electrode extends down to at least the bottom of the cylindrical throat inner surface. Above the throat rib there is thus defined a resonating acoustical cavity, with the dimensions of the parts being such that the acoustic fundamental frequency is above ten thousand Hertz. The metal sleeve has an annular shoulder spaced from the bottom rim of the spark plug body to define an annular recess serving to induce high-multiple harmonics in the acoustic wave generated by the resonating cavity system.