Method for operating a four stroke diesel engine

The method involves injecting water into a cylinder (2) in which a piston (3) moves reciprocally and which has at least one exhaust outlet (7) for carrying away gases and at least one air inlet (8). The outlet is closed during the exhaust cycle of the piston so that the outlet is already closed before the piston reaches top dead center at the end of the exhaust cycle and water is injected into the cylinder when the piston is near top dead center. Independent claims are also included for the following: a four-stroke diesel engine.