Abstract: A spark plug for internal combustion engines having a center electrode, a ceramic insulator body and metal sleeve around the body. The sleeve defines an annular outside electrode around the center electrode with a concave depression in the insulator between the electrodes. The plug is operated at high current and voltage so that a high intensity spark will burn off any combustion residue on the relatively small insulator area between the electrodes. A process for removing combustion residues using this spark plug is also disclosed.

Abstract: An ignition system for an internal combustion engine is disclosed including an ignition timing pulse generator for providing an output pulse which is a function of the angular position of the engine cylinder, and a control circuit, responsive to such output pulse, including another pulse generator comprising an astable multivibrator for turning on and off at least one switching transistor coupling a DC voltage source to the ignition transformer. The switching frequency of the transistor is determined by the control circuit to control the start, end and duration of the ignition power. The control circuit can vary, in a continuous manner, the duration of the ignition power and the switching frequency as a function of the characteristics of the internal combustion engine and its environment.