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冲压式喷气和超燃冲压发动机原理..docx

发布:2016-12-30约3.31万字共18页下载文档
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RamjetA ramjet, sometimes referred to as a flying stovepipe or an athodyd (an abbreviation of aero thermodynamic duct), is a form of airbreathing jet engine that uses the engines forward motion to compress incoming air without an axial compressor. Ramjets cannot produce thrust at zero airspeed; they cannot move an aircraft from a standstill. A ramjet powered vehicle, therefore, requires an assisted take-off like a rocket assist to accelerate it to a speed where it begins to produce thrust. Ramjets work most efficiently at supersonic speeds around Mach 3 (2,284 mph; 3,675 km/h). This type of engine can operate up to speeds of Mach 6 (2,041.7 m/s; 7,350 km/h).Ramjets can be particularly useful in applications requiring a small and simple mechanism for high-speed use, such as missiles or artillery shells. Weapon designers are looking to use ramjet technology in artillery shells to give added range; a 120 mm mortar shell, if assisted by a ramjet, is thought to be able to attain a range of 35 km (22 mi). They have also been used successfully, though not efficiently, as tip jets on the end of helicopter rotors.Ramjets differ from pulsejets, which use an intermittent combustion; ramjets employ a continuous combustion process. They are similar to scramjets, a system designed for higher speeds that uses a supersonic airflow in its combustion chamber. While a scramjet works with the same technology, the combustion process differs slightly, resulting in a higher cruise speed.Engine cycleThe Brayton cycle is a thermodynamic cycle that describes the workings of the gas turbine engine, the basis of the airbreathing jet engine and others. It is named after George Brayton (1830–1892), the American engineer who developed it, although it was originally proposed and patented by Englishman John Barber in 1791. It is also sometimes known as the Joule cycleDesignA ramjet is designed around its inlet. An object moving at high speed through air generates a high pressure region upstream. A
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