Internal combustion engine

摘要

A torch ignition type internal combustion engine has a precombustion chamber formed in a cylinder head in communication with a main combustion chamber through a passage so that a part of a lean air-fuel mixture is forced into the precombustion chamber on compression stroke. A spark plug is mounted on the cylinder head to ignite the lean air-fuel mixture in the precombustion chamber so that the ignited air-fuel mixture is burnt therein to form a torch jet which runs from the precombustion chamber through the passage into the main combustion chamber to ignite the lean air-fuel mixture therein. The spark plug has an insulator extending at one end axially beyond that end face of a metal shell of the spark plug from which grounded electrodes extend. The one end of the insulator supports a center electrode. The spark plug is so positioned that a set of electrodes and the one end of the insulator are disposed in the passage so that the electrodes and the end of the insulator are exposed to successive torch jets running through the passage, whereby deposition of sooty carbon on the electrodes and the end of the insulator is burnt away.