外文翻译----柴油机的工作原理(编辑修改稿)

外文翻译----柴油机的工作原理(编辑修改稿)内容摘要：

Methods of starting large engines include the inertia starter, which consists of a flywheel that is rotated by hand or by means of an electric motor until its kiic energy is sufficient to turn the crankshaft, and the explosive starter, which employs the explosion of a blank cartridge to drive a turbine wheel that is coupled to the engine. The inertia and explosive starters are chiefly used to start airplane engines. The ordinary Ottocycle engine is a fourstroke engine。 that is, in a plete power cycle, its pistons make four strokes, two toward the head (closed head) of the cylinder and two away from the head. During the first stroke of the cycle, the piston moves away from the cylinder head while simultaneously the intake valve is opened. The motion of the piston during this stroke sucks a quantity of a fuel and air mixture into the bustion chamber. During the next stroke, the piston moves toward the cylinder head and presses the fuel mixture in the bustion chamber. At the moment when the piston reaches the end of this stroke and the volume of the bustion chamber is at a minimum, the fuel mixture is ignited by the spark plug and burns, expanding and exerting a pressure on the piston, which is then driven away from the cylinder head in the third stroke. During the final stroke, the exhaust valve is opened and the piston moves toward the cylinder head, driving the exhaust gases out of the bustion chamber and leaving the cylinder ready to repeat the cycle. The efficiency of a modern Ottocycle engine is limited by a number of factors, including losses by cooling and by friction. In general, the efficiency of such engines is 本科 生毕业 设计（论文）外文翻译 4 determined by the pression ratio of the engine. The pression ratio (the ratio between the maximum and minimum volumes of the bustion chamber) is usually about 8 to 1 or 10 to 1 in most modern Ottocycle engines. Higher pression ratios, up to about 15 to 1, with a resulting increase of efficiency, are possible with the use of highoctane antiknock fuels. The efficiencies of good modern Ottocycle engines range between 20 and 25 percent— in other words, only this percentage of the heat energy of the fuel is transformed into mechanical energy Theoretically, the diesel cycle differs from the Otto cycle in that bustion takes place at constant volume rather than at constant pressure. Most diesels are also fourstroke engines but they operate differently than the fourstroke Ottocycle engines. The first, or suction, stroke draws air, but no fuel, into the bustion chamber through an intake valve. On the second, or pression, stroke the air is pressed to a small fraction of its former volume and is heated to approximately 440176。 C (approximately 820176。 F) by this pression. At the end of the pression stroke, vaporized fuel is injected into the bustion chamber and burns instantly because of the high temperature of the air in the chamber. Some diesels have auxiliary electrical ignition systems to ignite the fuel when the engine starts and until it warms up. This bustion drives the piston back on the third, or power, stroke of the cycle. The fourth stroke, as in the Ottocycle engine, is an exhaust stroke. The efficiency of the diesel engine, which is in general governed by the same factors that control the efficiency of Ottocycle engines, is inherently greater than that of any Ottocycle engine and in actual engines today is slightly more than 40 percent. Diesels are, in general, slowspeed engines with crankshaft speeds of 100 to 750 revolutions per minute (rpm) as pared to 2500 to 5000 rpm for typical Ottocycle engines. Some types of diesel, however, have speeds up to 2020 rpm. Because diesels use pression ratios of 14 or mo。