SPARK PLUG, IGNITION DEVICE AND METHOD FOR IGNITING AIR-FUEL MIXTURE

摘要

This spark plug is provided with: an insulator; a center electrode; a main metal fitting; and a floating electrode. An exposed area of the floating electrode is relatively close to an exposed area of the center electrode, and the main metal fitting is relatively far away from the exposed area of the center electrode. A capacitance formed between the floating electrode and the center electrode is relatively small. A capacitance formed between the floating electrode and the main metal fitting is relatively large. Alternatively, the exposed area of the floating electrode is relatively close to the exposed area of the main metal fitting, and the center electrode is relatively far away from the exposed area of the main metal fitting. The capacitance formed between the floating electrode and the center electrode is relatively large. The capacitance formed between the floating electrode and the main metal fitting is relatively small. A capacitor is externally attached to the insulator when so required due to the capacitance of the main body of the spark plug.