ramjet


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Related to ramjet: ramjet engine, scramjet

ramjet:

see jet propulsionjet propulsion,
propulsion of a body by a force developed in reaction to the ejection of a high-speed jet of gas. Jet Propulsion Engines

The four basic parts of a jet engine are the compressor, turbine, combustion chamber, and propelling nozzles.
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Ramjet

A member of a class of high-speed air-breathing propulsion systems. These include subsonic combustion ramjets (RAM), supersonic combustion ramjets (SCRAM), dual-mode ram-scramjets (RAM-SCRAM), dual-combustor ramjets (DCR or DCRJ), and air-ducted rockets (ADR). In each case, air collected from the atmosphere is ducted into the engine to serve as the oxidizer for the burning of fuel that is stored on board. All the engines operate on a modified form of the basic Joule or Brayton cycle; that is, the air is compressed in the inlet, burned at near-constant pressure, and accelerated in an expansion nozzle. In accordance with Newton's second law, thrust is produced by the increase in momentum as the gas passes from the inlet to the nozzle exit. Compression is produced by one or a multiplicity of compression waves generated on the inlet surfaces. The level of pressure that can be reached in these waves is insufficient to produce net thrust unless the air speed is greater than about Mach 0.9 (that is, the velocity is 0.9 times the local speed of sound). Thus the ramjet must be launched from a high-speed aircraft or brought up to speed by a booster rocket or another adjunct engine. The latter type are known as combined-cycle engines. A classic example is the combination of a turbojet and a ramjet, which is called a turboramjet. See Brayton cycle, Rocket propulsion, Turbojet, Turboramjet

A subsonic combustion ramjet may be boosted to its operating speed by a solid-fueled rocket (see illustration). After the booster separates, the air entering the inlet is compressed through oblique shocks and a terminal normal shock. The flow aft of the normal shock and in the combustor is subsonic, but the velocity is high and flameholders are needed to anchor the flame and thereby produce high combustion efficiency. Passing from the combustor, the exhaust gases are reaccelerated in a converging-diverging nozzle to supersonic speed at the engine exit. See Nozzle

There are several characteristics that lead to the choice of one of the ramjet cycles for a variety of missions. Foremost are the engine performance as measured by specific impulse, light weight, and low cost. For applications up to about Mach 3, the turbojet has the highest specific impulse among hydrocarbon-fueled engines, which leads to its choice as the power plant for subsonic and supersonic aircraft. Most missile applications demand higher thrust which requires afterburning. For flight speeds between Mach 3 and 5, the subsonic combustion ramjet is optimal, and above Mach 5 the choice is among the supersonic combustion ramjet, the dual-mode ram-scramjet, and the dual-combustor ramjet. The solid rocket has much lower engine performance and is used only when high specific impulse is not the governing factor. Rocket-powered vehicles are used for relatively short-range missions or for near-to-vertical flight.

ramjet

A simple duct or tube of a special shape that collects the air caused by forward speed, or the ram effect; compresses it; makes it flow over some heat source; and then ejects the air at a higher speed than the entry speed. In this arrangement, there is no moving part and the system can work only at a forward speed. Originally called an aerothermodynamic duct

ramjet

, ramjet engine
a. a type of jet engine in which fuel is burned in a duct using air compressed by the forward speed of the aircraft
b. an aircraft powered by such an engine
References in periodicals archive ?
Larger fuel stores also allow a ramjet to sustain high speed during flight, making it harder to shoot down than a solid rocket motor, which exhausts its fuel shortly after launch and then rapidly slows down, he said.
In a nutshell, our new facility is for testing solid fuel ramjet engines and there are a couple of things that distinguish it from most of the others that are available," said Orbital ATK's missile products divisional vice-president and general manager, Pat Nolan.
RAMJET is available on-line in paperback through Amazon and Barnes and Noble and at www.
Conceived more than 50 years ago, it differs from the ramjet in that the latter's inlet slows the air down to subsonic speed, while the scramjet inlet only decelerates the flow to supersonic speeds, which reduces heating.
The final configuration, with moving wings, minimised body rotation in pitch and yaw, both to give better flow into the ramjet intakes and to avoid homing head guidance errors of various sorts.
Braswell is responsible for field support, which includes recommending equipment, product training and technical support for the Marathon Ramjet line of compactors and vertical balers in a territory that consists of South Carolina, northern Georgia, eastern Tennessee and western North Carolina.
The so-called Supersonic Combustion Ramjet - or scramjet - engine was designed to travel at speeds of up to 5,000 mph, or ten times the speed of conventional aircraft, the University of Queensland said.
While a normal jet engine has a fan at the front to suck air in, a ramjet relies on sheer speed to force air into the combustion chamber," wrote the New Scientist Magazine in April 2004.
Wireless content titles include The Adventures of Rocky and Bullwinkle, Casper the Ghost and Roger Ramjet, all of which will be released from June onwards.
With his handsome cartoonish face and Roger Ramjet chin, True-Frost exhibits expert comic timing as the exasperating romantic ditherer: And aside from one or two exceptions (Murray's Irish brogue seems to vanish after his first scene), the accents are remarkably consistent.