PISTON AND ENGINE

A piston is provided in which the amount of uncombusted and discharged air-fuel mixture is small, and agglutination of a piston ring due to heat is prevented. In a piston 2 in which plural peripheral grooves in which piston rings are provided are formed in an outer peripheral surface, as the relation between an inner diameter B of a cylinder 1 and a distance L between an upper surface of the piston and an upper surface of a top peripheral groove 4a, L/B ‰¤ 0.1 holds. A cooling chamber 5a is formed in close vicinity to the top peripheral groove. A dead volume S partitioned with the piston, a cylinder liner 11 and a top piston ring 3a is reduced, and the amount of air-fuel mixture enclosed here and discharged in uncombusted state is reduced. Further, agglutination of the top piston ring to the cylinder due to thermal load can be prevented with the cooling chamber 5a. The thermal efficiency as an engine is improved in comparison with conventional art.