Diesel engine

英文Diesel engine

中文 (征集中)


A type of internal combustion engine which ignites fuel by injecting it into hot, high-pressure air in a combustion chamber. It has neither carburettor nor ignition system. The fuel is injected in the form of a very fine spray, by means of a nozzle, into the combustion chamber. There it is ignited by the heat of compressed air which the chamber has been charged with. The diesel engine operates within a fixed sequence of events, which may be achieved either in four or two strokes. The low-speed (i.e. 70 to 120 rev/min) two-stroke diesel is used for main propulsion units, since it can be directly coupled to the propeller and shafting. The medium speed four-stroke engine (250 – 1200 rev/min) is used for the auxiliaries such as alternators and also for main propulsion with a gearbox. A four-stroke diesel engine resembles a gasoline engine as it works on the four-stroke cycle, that is: admission, compression, power and exhaust. When the piston gets down on the air admission stroke, the lower pressure in the cylinder allows a charge of air into the cylinder through the inlet valve which opens just before top dead centre. Once the piston has passed the bottom dead centre and is beginning to ascend, the inlet valve closes and the upward movement of the piston compresses the air charge in the cylinder causing a quick rise of temperature. Before the second stroke is over, the charge of fuel oil is gradually injected into the cylinder by an injector. The burning of the air-fuel charge makes the gases expand. They push the piston downwards and create the power stroke. Before the piston reached the bottom dead centre, the exhaust valve opens and, as the piston goes up again, the burnt gases are forced out through the exhaust valve. Just before top dead centre the inlet valve opens and the cycle begins again



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