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A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. While this broad definition can include rocket, water jet, and hybrid propulsion, the term jet engine typically refers to an internal combustion airbreathing jet engine such as a turbojet, turbofan, ramjet, or pulse jet. In general, jet engines are internal combustion engines.
A ramjet, sometimes referred to as a flying stovepipe or an athodyd, is a form of airbreathing jet engine that uses the engine's forward motion to compress incoming air without an axial compressor or a centrifugal compressor. Because 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 and can operate up to speeds of Mach 6.
A turboprop engine is a turbine engine that drives an aircraft propeller.
The turbofan or fanjet is a type of airbreathing jet engine that is widely used in aircraft propulsion. The word "turbofan" is a portmanteau of "turbine" and "fan": the turbo portion refers to a gas turbine engine which achieves mechanical energy from combustion, and the fan, a ducted fan that uses the mechanical energy from the gas turbine to force air rearwards. Thus, whereas all the air taken in by a turbojet passes through the combustion chamber and turbines, in a turbofan some of that air bypasses these components. A turbofan thus can be thought of as a turbojet being used to drive a ducted fan, with both of these contributing to the thrust.
The turbojet is an airbreathing jet engine, typically used in aircraft. It consists of a gas turbine with a propelling nozzle. The gas turbine has an air inlet which includes inlet guide vanes, a compressor, a combustion chamber, and a turbine. The compressed air from the compressor is heated by burning fuel in the combustion chamber and then allowed to expand through the turbine. The turbine exhaust is then expanded in the propelling nozzle where it is accelerated to high speed to provide thrust. Two engineers, Frank Whittle in the United Kingdom and Hans von Ohain in Germany, developed the concept independently into practical engines during the late 1930s.
The Pratt & Whitney JT9D engine was the first high bypass ratio jet engine to power a wide-body airliner. Its initial application was the Boeing 747-100, the original "Jumbo Jet". It was Pratt & Whitney's first high-bypass-ratio turbofan.
An afterburner is an additional combustion component used on some jet engines, mostly those on military supersonic aircraft. Its purpose is to increase thrust, usually for supersonic flight, takeoff, and combat. The afterburning process injects additional fuel into a combustor in the jet pipe behind the turbine, "reheating" the exhaust gas. Afterburning significantly increases thrust as an alternative to using a bigger engine with its attendant weight penalty, but at the cost of very high fuel consumption which limits its use to short periods. This aircraft application of reheat contrasts with the meaning and implementation of reheat applicable to gas turbines driving electrical generators and which reduces fuel consumption.
The bypass ratio (BPR) of a turbofan engine is the ratio between the mass flow rate of the bypass stream to the mass flow rate entering the core. A 10:1 bypass ratio, for example, means that 10 kg of air passes through the bypass duct for every 1 kg of air passing through the core.
The Rolls-Royce RB.80 Conway was the first turbofan engine to enter service. Development started at Rolls-Royce in the 1940s, but the design was used only briefly, in the late 1950s and early 1960s, before other turbofan designs replaced it. However, the Conway engine was used in versions of the Handley Page Victor, Vickers VC10, Boeing 707-420 and Douglas DC-8-40. The name "Conway" is the English spelling of the River Conwy, in Wales, in keeping with Rolls' use of river names for gas turbine engines.
The Rolls-Royce RB.183 Tay is a medium-bypass turbofan engine, developed from the RB.183 Mk 555 Spey core and using a fan scaled directly from the Rolls-Royce RB.211-535E4 to produce versions with a bypass ratio of 3.1:1 or greater. The IP compressor and LP turbine were designed using technology from the RB.211 programme. The engine was first run in August 1984. The Tay 650 had a new HP turbine which incorporated new technology which had been proven with the RB.211-535E4. This engine also had a new combustor for improved durability. The Tay family is used on a number of airliners and larger business jets, including the Gulfstream IV family, Fokker 70 and Fokker 100, with a later version being used to re-engine Boeing 727-100s.
The Pratt & Whitney F119, company designation PW5000, is an afterburning turbofan engine developed by Pratt & Whitney for the Lockheed Martin F-22 Raptor advanced tactical fighter.
A compressor map is a chart which shows the performance of a turbomachinery compressor. This type of compressor is used in gas turbine engines, for supercharging reciprocating engines and for industrial processes, where it is known as a dynamic compressor. A map is created from compressor rig test results or predicted by a special computer program. Alternatively the map of a similar compressor can be suitably scaled. This article is an overview of compressor maps and their different applications and also has detailed explanations of maps for a fan and intermediate and high-pressure compressors from a three-shaft aero-engine as specific examples.
The General Electric F414 is an American afterburning turbofan engine in the 22,000-pound thrust class produced by GE Aviation. The F414 originated from GE's widely used F404 turbofan, enlarged and improved for use in the Boeing F/A-18E/F Super Hornet. The engine was developed from the F412 non-afterburning turbofan planned for the A-12 Avenger II, before it was canceled.
The Tumansky R-25 is a turbojet engine, which is seen as the ultimate development of Tumansky R-11. It was designed under the leadership of Sergei Alekseevich Gavrilov.
The General Electric CJ805 is a jet engine which was developed by GE Aviation in the late 1950s. It was a civilian version of the J79 and differed only in detail. It was developed in two versions. The basic CJ805-3 was a turbojet and powered the Convair 880, while CJ805-23, a turbofan derivative, powered the Convair 990 airliners.
In aeronautical engineering, overall pressure ratio, or overall compression ratio, is the ratio of the stagnation pressure as measured at the front and rear of the compressor of a gas turbine engine. The terms compression ratio and pressure ratio are used interchangeably. Overall compression ratio also means the overall cycle pressure ratio which includes intake ram.
This article briefly describes the components and systems found in jet engines.
An airbreathing jet engine is a jet engine that emits a jet of hot exhaust gases formed from air that is forced into the engine by several stages of centrifugal, axial or ram compression, which is then heated and expanded through a nozzle. They are typically gas turbine engines. The majority of the mass flow through an airbreathing jet engine is provided by air taken from outside of the engine and heated internally, using energy stored in the form of fuel.
The General Electric Passport is a turbofan developed by GE Aviation for large business jets. It was selected in 2010 to power the Bombardier Global 7500/8000, first ran on June 24, 2013, and first flew in 2015. It was certified in April 2016 and powered the Global 7500 first flight on November 4, 2016, before its 2018 introduction. It produces 14,000 to 20,000 lbf of thrust, a range previously covered by the General Electric CF34. A smaller scaled CFM LEAP, it is a twin-spool axial engine with a 5.6:1 bypass ratio and a 45:1 overall pressure ratio and is noted for its large one-piece 52 in (130 cm) fan 18-blade titanium blisk.
The familiar study of jet aircraft treats jet thrust with a "black box" description which only looks at what goes into the jet engine, air and fuel, and what comes out, exhaust gas and an unbalanced force. This force, called thrust, is the sum of the momentum difference between entry and exit and any unbalanced pressure force between entry and exit, as explained in "Thrust calculation".
References
- ↑ Glenn Research Center (NASA). "Pressure variation - EPR" . Retrieved January 2, 2015.
- ↑ http://code7700.com/epr.html [ dead link ]
- The Boeing Company Engine thrust control system US Patent 4248042 Includes Boeing's discussion on EPR or IEPR being a better indicator of thrust.
