Abstract: A heater-equipped spark plug comprises an insulator having an insulator nose which holds thereon a center electrode in the vicinity of a free end of an axial bore, a lead wire arranged along a surface of the insulator, a heater formed on the insulator nose by baking a metal paste and connected to the lead wire; and a high softening-point glass layer covering and holding the heater in place with an alumina layer interposed between the high softening-point glass and the heater. Preferably, the alumina layer can have a thickness of 20-200 .mu.m and the high softening-point glass layer can have a thickness of 30-500 .mu.m.

Abstract: A system for controlling heater mounted on a spark plug which ignites the air-fuel mixture in the combustion chamber of an internal combustion chamber. The heater-on time is determined such that it decreases with increasing engine temperature and increasing alcohol concentration. Current supplied to the heater is also determined such that it increases with increasing alcohol concentration and decreases with increasing engine temperature. Therefore, droplets at the spark plug caused by high alcohol concentration fuel can be removed while eliminating carbon fouling. The engine startablity can thus been improved without shorting the service life of the spark plug. Moreover, fuel injection amount is reduced so as not another fuel be deposited on a droplet fuel which is still being present. The heater is furthermore kept off when a starter motor is turning to supply sufficient power to the motor.

Abstract: An air-fuel ratio control method controls the air-fuel ratio of an air-fuel mixture supplied to an internal combustion engine having spark plugs, and heaters for heating the air-fuel mixture in the vicinity of respective ones of the heaters, the air-fuel mixture containing a fuel which is poor in atomizing characteristic at a low temperature. The method comprises the steps of (1) determining whether or not a temperature of the engine is lower than a predetermined value, (2) determining whether or not the engine is being cranked, (3) detecting an amount of electric current flowing through each of the heaters, and (4) controlling an amount of fuel supplied to the engine based on the detected amount of electric current when it is determined that the temperature of the engine is lower than the predetermined value and at the same time the engine is being cranked.