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Scramjet

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A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to forcefully compress and decelerate the incoming air before combustion (hence ramjet), but whereas a ramjet decelerates the air to subsonic velocities before combustion, airflow in a scramjet is supersonic throughout the entire engine. This allows the scramjet to operate efficiently at extremely high speeds: theoretical projections place the top speed of a scramjet between and . A form of jet engine that has no propellers but the air is compressed into the engine by the sheer speed at which the craft moves. Therefore it must be accelerated to Mach 3 by a "normal" jet engine which uses a propeller to compress air. Once started, howewer, the scramjet can accelerate to Mach 11 and thus escape the Earths gravity. It is a technology for better launches partly because the whole craft can be used many times before service and partly because the use of compressed surrounding air eliminates the need to carry oxidant for the launch. The latter also saves so much weight the amount of fuel can be greatly reduced. The craft can also start and land on normal airports. A scramjet (supersonic combustion ramjet) is a variation of a ramjet where combustion of the fuel air mixture occurs at supersonic speeds. This allows the scramjet to achieve greater speeds than a conventional ramjet which slows the incoming air to subsonic speeds before entering the combustion chamber. Projections for the top speed of a scramjet engine (without additional oxidiser input) vary between Mach 12 and Mach 24. The fastest air-breathing, manned vehicle, the U.S. Air Force SR-71, achieved slightly more than Mach 3.2. The Scramjet is a large custom plane vehicle that holds around 11 people. It has two large jet engines on its wings. Since it is a very large vehicle, it is also difficult to maneuver.

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US Patent & Trademark Office

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Variable geometry inlet design for scram jet engine

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--10-07

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2005

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A scramjet (supersonic combustion ramjet) is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow. As in ramjets, a scramjet relies on high vehicle speed to forcefully compress and decelerate the incoming air before combustion (hence ramjet), but whereas a ramjet decelerates the air to subsonic velocities before combustion, airflow in a scramjet is supersonic throughout the entire engine. This allows the scramjet to operate efficiently at extremely high speeds: theoretical projections place the top speed of a scramjet between and . The scramjet is composed of three basic components: a converging inlet, where incoming air is compressed and decelerated; a combustor, where gaseous fuel is burned with atmospheric oxygen to produce heat; and a diverging nozzle, where the heated air is accelerated to produce thrust. Unlike a typical jet engine, such as a turbojet or turbofan engine, a scramjet does not use rotating, fan-like components to compress the air; rather, the achievable speed of the aircraft moving through the atmosphere causes the air to compress within the inlet. As such, no moving parts are needed in a scramjet. In comparison, typical turbojet engines require inlet fans, multiple stages of rotating compressor fans, and multiple rotating turbine stages, all of which add weight, complexity, and a greater number of failure points to the engine. Due to the nature of their design, scramjet operation is limited to near-hypersonic velocities. As they lack mechanical compressors, scramjets require the high kinetic energy of a hypersonic flow to compress the incoming air to operational conditions. Thus, a scramjet-powered vehicle must be accelerated to the required velocity by some other means of propulsion, such as turbojet, railgun, or rocket engines. In the flight of the experimental scramjet-powered Boeing X-51A, the test craft was lifted to flight altitude by a Boeing B-52 Stratofortress before being released and accelerated by a detachable rocket to near Mach 4.5. In May 2013, another flight achieved an increased speed of Mach 5.1. While scramjets are conceptually simple, actual implementation is limited by extreme technical challenges. Hypersonic flight within the atmosphere generates immense drag, and temperatures found on the aircraft and within the engine can be much greater than that of the surrounding air. Maintaining combustion in the supersonic flow presents additional challenges, as the fuel must be injected, mixed, ignited, and burned within milliseconds. While scramjet technology has been under development since the 1950s, only very recently have scramjets successfully achieved powered flight. A form of jet engine that has no propellers but the air is compressed into the engine by the sheer speed at which the craft moves. Therefore it must be accelerated to Mach 3 by a "normal" jet engine which uses a propeller to compress air. Once started, howewer, the scramjet can accelerate to Mach 11 and thus escape the Earths gravity. It is a technology for better launches partly because the whole craft can be used many times before service and partly because the use of compressed surrounding air eliminates the need to carry oxidant for the launch. The latter also saves so much weight the amount of fuel can be greatly reduced. The craft can also start and land on normal airports. A scramjet (supersonic combustion ramjet) is a variation of a ramjet where combustion of the fuel air mixture occurs at supersonic speeds. This allows the scramjet to achieve greater speeds than a conventional ramjet which slows the incoming air to subsonic speeds before entering the combustion chamber. Projections for the top speed of a scramjet engine (without additional oxidiser input) vary between Mach 12 and Mach 24. The fastest air-breathing, manned vehicle, the U.S. Air Force SR-71, achieved slightly more than Mach 3.2. Like a conventional ramjet, a scramjet consists of a constricted tube through which air is compressed, fuel is combusted, and the exhaust is vented at higher speed than the intake air. Also like a ramjet, there are either few or no moving parts. In particular there are no high speed turbines as found in a turbofan or turbojet engine that can be a major point of failure. The scramjet requires extremely high speed airflow to function and requires acceleration to supersonic speed before it can be started. Recent tests of prototypes have used a booster rocket to obtain the necessary velocity. Theoretically, air breathing engines should have a greater specific impulse while within the atmosphere than rocket engines. The Scramjet is a large custom plane vehicle that holds around 11 people. It has two large jet engines on its wings. Since it is a very large vehicle, it is also difficult to maneuver.