NastyaK27

11.04.2021 05:57 •  Английский язык

Что такое дизельный двигатель. Написание аннотации к тексту. Diesel engine
Diesel engines are a class of internal combustion engine in which the fuel is burned internally and the combustion products are used as the working fluid. Unlike the spark-ignited (SI) engines found in the majority of today's automobiles in which the premixed fuel-air mixture is ignited by an electric spark, diesel engines are characterized by a spontaneously initiated combustion process where the ignition is brought about by very high temperature compressed air. A small amount of diesel fuel is injected at the end of the compression stroke into the cylinder where the fuel auto-ignites. Because of their higher actual operating efficiencies, as compared with SI engines that require pre-ignition, diesel engines are primarily used in heavy-duty vehicles such as trucks, ships, locomotives, etc.
Diesel engines were first developed by Rudolf Diesel (1858-1913) in the late nineteenth century. The original concept was to build a multifuel engine and to use coal as a primary fuel. However, for some reason, coal-fueled diesel engines so far have gained only occasional interest from the industry (e.g., when fuel-oil prices are high), most of the diesel engines currently being used rely on petroleum fuels. They are four-stroke cycle engines, and operate from several hundred up to around one thousand rpm. In addition to pistons, cylinders, crankshaft, and various valves, diesel engines are also equipped with controlled fuel injection systems, exhaust systems, cooling systems, and so on. Sufficient lubrication is required to prevent excessive wear of various parts in engines. Since pre-ignition is not required, the compression step can be continued to reach a higher pressure or a higher compression ratio than that in SI engines. This results in compressed air with a temperature exceeding the ignition point of the injected fuel for auto-ignition. To achieve high combustion efficiency, the fuel jets must draw in and mix well with air, ignite, and burn, all within less than one millisecond, when they impact on the cold combustion chamber walls. Engine performance is closely related to compression ratio, piston speed, supercharging, turbo-charging, etc., and engine size is normally in terms of power rating (i.e., horsepower; for instance, 20,000 hp applicable for ship propulsion). In principle, the same engine frame can be designed for different output by varying the number of cylinders (10, 12, 16 cylinders, and so on).