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103-470: An afterburner (or reheat in British English) 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 ("burner") in the jet pipe behind (i.e., "after") the turbine , "reheating"

206-691: A Rolls-Royce W2/B23 in a Gloster Meteor I in late 1944 and ground tests on a Power Jets W2/700 engine in mid-1945. This engine was destined for the Miles M.52 supersonic aircraft project. Early American research on the concept was done by NACA , in Cleveland, Ohio, leading to the publication of the paper "Theoretical Investigation of Thrust Augmentation of Turbojet Engines by Tail-pipe Burning" in January 1947. American work on afterburners in 1948 resulted in installations on early straight-wing jets such as

309-399: A convergent-divergent nozzle is needed on high-speed aircraft. The engine thrust is highest if the static pressure of the gas reaches the ambient value as it leaves the nozzle. This only happens if the nozzle exit area is the correct value for the nozzle pressure ratio (npr). Since the npr changes with engine thrust setting and flight speed this is seldom the case. Also at supersonic speeds

412-680: A rotating air compressor powered by a turbine , with the leftover power providing thrust through the propelling nozzle —this process is known as the Brayton thermodynamic cycle . Jet aircraft use such engines for long-distance travel. Early jet aircraft used turbojet engines that were relatively inefficient for subsonic flight. Most modern subsonic jet aircraft use more complex high-bypass turbofan engines . They give higher speed and greater fuel efficiency than piston and propeller aeroengines over long distances. A few air-breathing engines made for high-speed applications (ramjets and scramjets ) use

515-486: A supersonic jet's flyby (directly underneath the meteor's path) and as a detonation wave , with the circular shock wave centred at the meteor explosion, causing multiple instances of broken glass in the city of Chelyabinsk and neighbouring areas (pictured). In the examples below, the shock wave is controlled, produced by (ex. airfoil) or in the interior of a technological device, like a turbine . The wave disk engine (also named "Radial Internal Combustion Wave Rotor")

618-488: A turbofan application). The first designs, e.g. Solar afterburners used on the F7U Cutlass, F-94 Starfire and F-89 Scorpion, had 2-position eyelid nozzles. Modern designs incorporate not only variable-geometry (VG) nozzles but multiple stages of augmentation via separate spray bars. To a first order, the gross thrust ratio (afterburning/dry) is directly proportional to the root of the stagnation temperature ratio across

721-407: A component vector analysis of the flow; doing so allows for the treatment of the flow in an orthogonal direction to the oblique shock as a normal shock. When an oblique shock is likely to form at an angle which cannot remain on the surface, a nonlinear phenomenon arises where the shock wave will form a continuous pattern around the body. These are termed bow shocks . In these cases, the 1d flow model

824-408: A compressor ( axial , centrifugal , or both), mixing fuel with the compressed air, burning the mixture in the combustor , and then passing the hot, high pressure air through a turbine and a nozzle . The compressor is powered by the turbine, which extracts energy from the expanding gas passing through it. The engine converts internal energy in the fuel to increased momentum of the gas flowing through

927-642: A configuration in which the rapidly moving material down the chute impinges on an obstruction wall erected perpendicular at the end of a long and steep channel. Impact leads to a sudden change in the flow regime from a fast moving supercritical thin layer to a stagnant thick heap. This flow configuration is particularly interesting because it is analogous to some hydraulic and aerodynamic situations associated with flow regime changes from supercritical to subcritical flows. Astrophysical environments feature many different types of shock waves. Some common examples are supernovae shock waves or blast waves travelling through

1030-456: A counterexample, the SR-71 had reasonable efficiency at high altitude in afterburning ("wet") mode owing to its high speed ( mach 3.2) and correspondingly high pressure due to ram intake . Afterburning has a significant influence upon engine cycle choice. Lowering the fan pressure ratio decreases specific thrust (both dry and wet afterburning), but results in a lower temperature entering

1133-429: A demonstrator engine was run. The duct heater used an annular combustor and would be used for takeoff, climb and cruise at Mach 2.7 with different amounts of augmentation depending on aircraft weight. A jet engine afterburner is an extended exhaust section containing extra fuel injectors. Since the jet engine upstream (i.e., before the turbine) will use little of the oxygen it ingests, additional fuel can be burned after

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1236-702: A distance (not coincidentally, since explosions create shock waves). Analogous phenomena are known outside fluid mechanics. For example, charged particles accelerated beyond the speed of light in a refractive medium (such as water, where the speed of light is less than that in a vacuum ) create visible shock effects, a phenomenon known as Cherenkov radiation . Below are a number of examples of shock waves, broadly grouped with similar shock phenomena: Shock waves can also occur in rapid flows of dense granular materials down inclined channels or slopes. Strong shocks in rapid dense granular flows can be studied theoretically and analyzed to compare with experimental data. Consider

1339-509: A good dry SFC, but a poor afterburning SFC at Combat/Take-off. Often the engine designer is faced with a compromise between these two extremes. The Caproni Campini C.C.2 motorjet , designed by the Italian engineer Secondo Campini , was the first aircraft to incorporate an afterburner. The first flight of a C.C.2, with its afterburners operating, took place on 11 April 1941. Early British afterburner ("reheat") work included flight tests on

1442-493: A good thrust boost. If the aircraft burns a large percentage of its fuel with the afterburner alight, it pays to select an engine cycle with a high specific thrust (i.e. high fan pressure ratio/low bypass ratio ). The resulting engine is relatively fuel efficient with afterburning (i.e. Combat/Take-off), but thirsty in dry power. If, however, the afterburner is to be hardly used, a low specific thrust (low fan pressure ratio/high bypass ratio) cycle will be favored. Such an engine has

1545-427: A higher priority than fuel efficiency, fans tend to be smaller or absent. Because of these distinctions, turbofan engine designs are often categorized as low-bypass or high-bypass , depending upon the amount of air which bypasses the core of the engine. Low-bypass turbofans have a bypass ratio of around 2:1 or less. The term Advanced technology engine refers to the modern generation of jet engines. The principle

1648-406: A jet of water. The mechanical arrangement may be a ducted propeller with nozzle, or a centrifugal compressor and nozzle. The pump-jet must be driven by a separate engine such as a Diesel or gas turbine . All jet engines are reaction engines that generate thrust by emitting a jet of fluid rearwards at relatively high speed. The forces on the inside of the engine needed to create this jet give

1751-426: A large number of different types of jet engines, all of which achieve forward thrust from the principle of jet propulsion . Commonly aircraft are propelled by airbreathing jet engines. Most airbreathing jet engines that are in use are turbofan jet engines, which give good efficiency at speeds just below the speed of sound. A turbojet engine is a gas turbine engine that works by compressing air with an inlet and

1854-402: A loud "crack" or "snap" noise. Over longer distances, a shock wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air and loses energy. The sound wave is heard as the familiar "thud" or "thump" of a sonic boom , commonly created by the supersonic flight of aircraft. The shock wave is one of several different ways in which a gas in

1957-435: A particular engine design that if some bumps in a bypass duct are smoothed out the air will flow more smoothly giving a pressure loss reduction of x% and y% less fuel will be needed to get the take-off thrust, for example. This understanding comes under the engineering discipline Jet engine performance . How efficiency is affected by forward speed and by supplying energy to aircraft systems is mentioned later. The efficiency of

2060-759: A powerplant for the world's first jet- fighter aircraft , the Messerschmitt Me 262 (and later the world's first jet- bomber aircraft, the Arado Ar 234 ). A variety of reasons conspired to delay the engine's availability, causing the fighter to arrive too late to improve Germany's position in World War II , however this was the first jet engine to be used in service. Meanwhile, in Britain the Gloster E28/39 had its maiden flight on 15 May 1941 and

2163-548: A practical use. Jet engine A jet engine is a type of reaction engine , discharging a fast-moving jet of heated gas (usually air) that generates thrust by jet propulsion . While this broad definition may include rocket , water jet , and hybrid propulsion, the term jet engine typically refers to an internal combustion air-breathing jet engine such as a turbojet , turbofan , ramjet , pulse jet , or scramjet . In general, jet engines are internal combustion engines . Air-breathing jet engines typically feature

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2266-418: A process of destructive interference. The sonic boom associated with the passage of a supersonic aircraft is a type of sound wave produced by constructive interference . Unlike solitons (another kind of nonlinear wave), the energy and speed of a shock wave alone dissipates relatively quickly with distance. When a shock wave passes through matter, energy is preserved but entropy increases. This change in

2369-424: A shock wave. It is assumed the system is adiabatic (no heat exits or enters the system) and no work is being done. The Rankine–Hugoniot conditions arise from these considerations. Taking into account the established assumptions, in a system where the downstream properties are becoming subsonic: the upstream and downstream flow properties of the fluid are considered isentropic. Since the total amount of energy within

2472-455: A short distance and causes visible banding where pressure and temperature are highest. Thrust may be increased by burning fuel in a turbofan's cold bypass air, instead of the mixed cold and hot flows as in most afterburning turbofans. An early augmented turbofan, the Pratt & Whitney TF30 , used separate burning zones for the bypass and core flows with three of seven concentric spray rings in

2575-530: A strong thrust on the engine which pushes the craft forwards. Jet engines make their jet from propellant stored in tanks that are attached to the engine (as in a 'rocket') as well as in duct engines (those commonly used on aircraft) by ingesting an external fluid (very typically air) and expelling it at higher speed. A propelling nozzle produces a high velocity exhaust jet . Propelling nozzles turn internal and pressure energy into high velocity kinetic energy. The total pressure and temperature don't change through

2678-439: A substantial initial forward airspeed before it can function. Ramjets are considered the simplest type of air breathing jet engine because they have no moving parts in the engine proper, only in the accessories. Scramjets differ mainly in the fact that the air does not slow to subsonic speeds. Rather, they use supersonic combustion. They are efficient at even higher speed. Very few have been built or flown. The rocket engine uses

2781-421: A supersonic afterburning engine or 2200 K with afterburner lit. The pressure entering the nozzle may vary from 1.5 times the pressure outside the nozzle, for a single stage fan, to 30 times for the fastest manned aircraft at Mach 3+. Convergent nozzles are only able to accelerate the gas up to local sonic (Mach 1) conditions. To reach high flight speeds, even greater exhaust velocities are required, and so

2884-458: A supersonic flow can be compressed. Some other methods are isentropic compressions, including Prandtl –Meyer compressions. The method of compression of a gas results in different temperatures and densities for a given pressure ratio which can be analytically calculated for a non-reacting gas. A shock wave compression results in a loss of total pressure, meaning that it is a less efficient method of compressing gases for some purposes, for instance in

2987-402: A test stand, sucks in fuel and generates thrust. How well it does this is judged by how much fuel it uses and what force is required to restrain it. This is a measure of its efficiency. If something deteriorates inside the engine (known as performance deterioration ) it will be less efficient and this will show when the fuel produces less thrust. If a change is made to an internal part which allows

3090-461: A two-stage axial compressor feeding a single-sided centrifugal compressor . Practical axial compressors were made possible by ideas from A.A.Griffith in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design"). Whittle would later concentrate on the simpler centrifugal compressor only. Whittle was unable to interest the government in his invention, and development continued at a slow pace. In Spain, pilot and engineer Virgilio Leret Ruiz

3193-572: Is a kind of pistonless rotary engine that utilizes shock waves to transfer energy between a high-energy fluid to a low-energy fluid, thereby increasing both temperature and pressure of the low-energy fluid. In memristors , under externally-applied electric field, shock waves can be launched across the transition-metal oxides, creating fast and non-volatile resistivity changes. Advanced techniques are needed to capture shock waves and to detect shock waves in both numerical computations and experimental observations. Computational fluid dynamics

Afterburner - Misplaced Pages Continue

3296-402: Is an airshow display feature where fuel is jettisoned, then intentionally ignited using the afterburner. A spectacular flame combined with high speed makes this a popular display for airshows , or as a finale to fireworks . Fuel dumping is used primarily to reduce the weight of an aircraft to avoid a heavy, high-speed landing. Other than for safety or emergency reasons, fuel dumping does not have

3399-407: Is at maximum power, while an engine producing maximum thrust dry is at military power . The first jet engine with after-burner was the E variant of Jumo 004 . Jet-engine thrust is an application of Newton's reaction principle, in which the engine generates thrust because it increases the momentum of the air passing through it. Thrust depends on two things: the velocity of the exhaust gas and

3502-481: Is commonly used to obtain the flow field with shock waves. Though shock waves are sharp discontinuities, in numerical solutions of fluid flow with discontinuities (shock wave, contact discontinuity or slip line), the shock wave can be smoothed out by low-order numerical method (due to numerical dissipation) or there are spurious oscillations near shock surface by high-order numerical method (due to Gibbs phenomena ). There exist some other discontinuities in fluid flow than

3605-507: Is documented in the story of Ottoman soldier Lagâri Hasan Çelebi , who reportedly achieved flight using a cone-shaped rocket in 1633. The earliest attempts at airbreathing jet engines were hybrid designs in which an external power source first compressed air, which was then mixed with fuel and burned for jet thrust. The Italian Caproni Campini N.1 , and the Japanese Tsu-11 engine intended to power Ohka kamikaze planes towards

3708-451: Is highest when combustion occurs at the highest pressure and temperature possible, and expanded down to ambient pressure (see Carnot cycle ). Since the exhaust gas already has a reduced oxygen content, owing to previous combustion, and since the fuel is not burning in a highly compressed air column, the afterburner is generally inefficient in comparison to the main combustion process. Afterburner efficiency also declines significantly if, as

3811-408: Is not valid and further analysis is needed to predict the pressure forces which are exerted on the surface. Shock waves can form due to steepening of ordinary waves. The best-known example of this phenomenon is ocean waves that form breakers on the shore. In shallow water, the speed of surface waves is dependent on the depth of the water. An incoming ocean wave has a slightly higher wave speed near

3914-443: Is that a turbine engine will function more efficiently if the various sets of turbines can revolve at their individual optimum speeds, instead of at the same speed. The true advanced technology engine has a triple spool, meaning that instead of having a single drive shaft, there are three, in order that the three sets of blades may revolve at different speeds. An interim state is a twin-spool engine, allowing only two different speeds for

4017-400: Is the propellant flow in kg/s, A e {\displaystyle A_{e}} is the cross-sectional area at the exit of the exhaust nozzle, and p {\displaystyle p} is the atmospheric pressure. Combined-cycle engines simultaneously use two or more different principles of jet propulsion. A water jet, or pump-jet, is a marine propulsion system that uses

4120-570: Is used for launching satellites, space exploration and crewed access, and permitted landing on the Moon in 1969. Rocket engines are used for high altitude flights, or anywhere where very high accelerations are needed since rocket engines themselves have a very high thrust-to-weight ratio . However, the high exhaust speed and the heavier, oxidizer-rich propellant results in far more propellant use than turbofans. Even so, at extremely high speeds they become energy-efficient. An approximate equation for

4223-404: Is usually the case, the inlet and tailpipe pressure decreases with increasing altitude. This limitation applies only to turbojets. In a military turbofan combat engine, the bypass air is added into the exhaust, thereby increasing the core and afterburner efficiency. In turbojets the gain is limited to 50%, whereas in a turbofan it depends on the bypass ratio and can be as much as 70%. However, as

Afterburner - Misplaced Pages Continue

4326-607: The Concorde was developed by Snecma . Afterburners are generally used only in military aircraft, and are considered standard equipment on fighter aircraft. The handful of civilian planes that have used them include some NASA research aircraft, the Tupolev Tu-144 , Concorde and the White Knight of Scaled Composites . Concorde flew long distances at supersonic speeds. Sustained high speeds would be impossible with

4429-903: The Gloster Meteor finally entered service with the RAF in July 1944. These were powered by turbojet engines from Power Jets Ltd., set up by Frank Whittle. The first two operational turbojet aircraft, the Messerschmitt Me 262 and then the Gloster Meteor entered service within three months of each other in 1944; the Me 262 in April and the Gloster Meteor in July. The Meteor only saw around 15 aircraft enter World War II action, while up to 1400 Me 262 were produced, with 300 entering combat, delivering

4532-590: The Pirate , Starfire and Scorpion . The new Pratt & Whitney J48 turbojet, at 8,000 lbf (36 kN) thrust with afterburners, would power the Grumman swept-wing fighter F9F-6 , which was about to go into production. Other new Navy fighters with afterburners included the Chance Vought F7U-3 Cutlass , powered by two 6,000 lbf (27 kN) thrust Westinghouse J46 engines. In

4635-500: The aeolipile , a device described by Hero of Alexandria in 1st-century Egypt . This device directed steam power through two nozzles to cause a sphere to spin rapidly on its axis. It was seen as a curiosity. Meanwhile, practical applications of the turbine can be seen in the water wheel and the windmill . Historians have further traced the theoretical origin of the principles of jet engines to traditional Chinese firework and rocket propulsion systems. Such devices' use for flight

4738-664: The gasoline -fuelled HeS 3 of 5 kN (1,100 lbf), which was fitted to Heinkel's simple and compact He 178 airframe and flown by Erich Warsitz in the early morning of August 27, 1939, from Rostock -Marienehe aerodrome , an impressively short time for development. The He 178 was the world's first jet plane. Heinkel applied for a US patent covering the Aircraft Power Plant by Hans Joachim Pabst von Ohain on May 31, 1939; patent number US2256198, with M Hahn referenced as inventor. Von Ohain's design, an axial-flow engine, as opposed to Whittle's centrifugal flow engine,

4841-402: The ram effect of the vehicle's speed instead of a mechanical compressor. The thrust of a typical jetliner engine went from 5,000 lbf (22 kN) ( de Havilland Ghost turbojet) in the 1950s to 115,000 lbf (510 kN) ( General Electric GE90 turbofan) in the 1990s, and their reliability went from 40 in-flight shutdowns per 100,000 engine flight hours to less than 1 per 100,000 in

4944-805: The 1950s, several large afterburning engines were developed, such as the Orenda Iroquois and the British de Havilland Gyron and Rolls-Royce Avon RB.146 variants. The Avon and its variants powered the English Electric Lightning , the first supersonic aircraft in RAF service. The Bristol-Siddeley/ Rolls-Royce Olympus was fitted with afterburners for use with the BAC TSR-2 . This system was designed and developed jointly by Bristol-Siddeley and Solar of San Diego. The afterburner system for

5047-482: The 1950s, the jet engine was almost universal in combat aircraft, with the exception of cargo, liaison and other specialty types. By this point, some of the British designs were already cleared for civilian use, and had appeared on early models like the de Havilland Comet and Avro Canada Jetliner . By the 1960s, all large civilian aircraft were also jet powered, leaving the piston engine in low-cost niche roles such as cargo flights. The efficiency of turbojet engines

5150-521: The British embassy in Madrid a few years later by his wife, Carlota O'Neill , upon her release from prison. In 1935, Hans von Ohain started work on a similar design to Whittle's in Germany, both compressor and turbine being radial, on opposite sides of the same disc, initially unaware of Whittle's work. Von Ohain's first device was strictly experimental and could run only under external power, but he

5253-465: The Earth's atmosphere. The Tunguska event and the 2013 Russian meteor event are the best documented evidence of the shock wave produced by a massive meteoroid . When the 2013 meteor entered into the Earth's atmosphere with an energy release equivalent to 100 or more kilotons of TNT, dozens of times more powerful than the atomic bomb dropped on Hiroshima , the meteor's shock wave produced damage as in

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5356-534: The Pratt & Whitney J57 and J75 models. There is also a derivative of the P&;W JT8D low-bypass turbofan that creates up to 35,000 horsepower (HP) . Jet engines are also sometimes developed into, or share certain components such as engine cores, with turboshaft and turboprop engines, which are forms of gas turbine engines that are typically used to power helicopters and some propeller-driven aircraft. There are

5459-485: The afterburner (i.e. exit/entry). Due to their high fuel consumption, afterburners are only used for short-duration, high-thrust requirements. These include heavy-weight or short-runway take-offs, assisting catapult launches from aircraft carriers , and during air combat . A notable exception is the Pratt & Whitney J58 engine used in the SR-71 Blackbird which used its afterburner for prolonged periods and

5562-425: The afterburner. Since the afterburning exit temperature is effectively fixed, the temperature rise across the unit increases, raising the afterburner fuel flow. The total fuel flow tends to increase faster than the net thrust, resulting in a higher specific fuel consumption (SFC). However, the corresponding dry power SFC improves (i.e. lower specific thrust). The high temperature ratio across the afterburner results in

5665-406: The afterburner. The mass flow is also slightly increased by the addition of the afterburner fuel. The thrust with afterburning is 16,000 lb f (71,000 N). The visible exhaust may show shock diamonds , which are caused by shock waves formed due to slight differences between ambient pressure and the exhaust pressure. This interaction causes oscillations in the exhaust jet diameter over

5768-400: The air/combustion gases to flow more smoothly the engine will be more efficient and use less fuel. A standard definition is used to assess how different things change engine efficiency and also to allow comparisons to be made between different engines. This definition is called specific fuel consumption , or how much fuel is needed to produce one unit of thrust. For example, it will be known for

5871-427: The approach of the object. In this description, the shock wave position is defined as the boundary between the zone having no information about the shock-driving event and the zone aware of the shock-driving event, analogous with the light cone described in the theory of special relativity . To produce a shock wave, an object in a given medium (such as air or water) must travel faster than the local speed of sound. In

5974-400: The bright timbre of the instruments. While shock formation by this process does not normally happen to unenclosed sound waves in Earth's atmosphere, it is thought to be one mechanism by which the solar chromosphere and corona are heated, via waves that propagate up from the solar interior. A shock wave may be described as the furthest point upstream of a moving object which "knows" about

6077-466: The bypass flow. In comparison, the afterburning Rolls-Royce Spey used a twenty chute mixer before the fuel manifolds. Plenum chamber burning (PCB) was partially developed for the vectored thrust Bristol Siddeley BS100 engine for the Hawker Siddeley P.1154 until the program was cancelled in 1965. The cold bypass and hot core flows were split between two pairs of nozzles, front and rear, in

6180-449: The case of an aircraft travelling at high subsonic speed, regions of air around the aircraft may be travelling at exactly the speed of sound, so that the sound waves leaving the aircraft pile up on one another, similar to a traffic jam on a motorway. When a shock wave forms, the local air pressure increases and then spreads out sideways. Because of this amplification effect, a shock wave can be very intense, more like an explosion when heard at

6283-407: The combustor). The above pressure and temperature are shown on a Thermodynamic cycle diagram. Shock waves For the purpose of comparison, in supersonic flows, additional increased expansion may be achieved through an expansion fan , also known as a Prandtl–Meyer expansion fan . The accompanying expansion wave may approach and eventually collide and recombine with the shock wave, creating

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6386-427: The control surfaces that bound this volume parallel to the shock wave (with one surface on the pre-shock side of the fluid medium and one on the post-shock side). The two surfaces are separated by a very small depth such that the shock itself is entirely contained between them. At such control surfaces, momentum, mass flux and energy are constant; within combustion, detonations can be modelled as heat introduction across

6489-409: The crest of each wave than near the troughs between waves, because the wave height is not infinitesimal compared to the depth of the water. The crests overtake the troughs until the leading edge of the wave forms a vertical face and spills over to form a turbulent shock (a breaker) that dissipates the wave's energy as sound and heat. Similar phenomena affect strong sound waves in gas or plasma, due to

6592-401: The dependence of the sound speed on temperature and pressure. Strong waves heat the medium near each pressure front, due to adiabatic compression of the air itself, so that high pressure fronts outrun the corresponding pressure troughs. There is a theory that the sound pressure levels in brass instruments such as the trombone become high enough for steepening to occur, forming an essential part of

6695-411: The design tradeoff is a large size relative to the power output. Generating increased power with a more compact engine for short periods can be achieved using an afterburner. The afterburner increases thrust primarily by accelerating the exhaust gas to a higher velocity. The following values and parameters are for an early jet engine, the Pratt & Whitney J57 , stationary on the runway, and illustrate

6798-599: The divergent area is less than required to give complete internal expansion to ambient pressure as a trade-off with external body drag. Whitford gives the F-16 as an example. Other underexpanded examples were the XB-70 and SR-71. The nozzle size, together with the area of the turbine nozzles, determines the operating pressure of the compressor. This overview highlights where energy losses occur in complete jet aircraft powerplants or engine installations. A jet engine at rest, as on

6901-435: The effective afterburner fuel flow), but a decrease in afterburner exit stagnation pressure (owing to a fundamental loss due to heating plus friction and turbulence losses). The resulting increase in afterburner exit volume flow is accommodated by increasing the throat area of the exit nozzle. Otherwise, if pressure is not released, the gas can flow upstream and re-ignite, possibly causing a compressor stall (or fan surge in

7004-405: The end of World War II were unsuccessful. Even before the start of World War II, engineers were beginning to realize that engines driving propellers were approaching limits due to issues related to propeller efficiency, which declined as blade tips approached the speed of sound . If aircraft performance were to increase beyond such a barrier, a different propulsion mechanism was necessary. This

7107-425: The engine is controlled primarily by the operating conditions inside the engine which are the pressure produced by the compressor and the temperature of the combustion gases at the first set of rotating turbine blades. The pressure is the highest air pressure in the engine. The turbine rotor temperature is not the highest in the engine but is the highest at which energy transfer takes place ( higher temperatures occur in

7210-650: The engine, producing thrust. All the air entering the compressor is passed through the combustor, and turbine, unlike the turbofan engine described below. Turbofans differ from turbojets in that they have an additional fan at the front of the engine, which accelerates air in a duct bypassing the core gas turbine engine. Turbofans are the dominant engine type for medium and long-range airliners . Turbofans are usually more efficient than turbojets at subsonic speeds, but at high speeds their large frontal area generates more drag . Therefore, in supersonic flight, and in military and other aircraft where other considerations have

7313-536: The engine. The combustion products have to be diluted with air from the compressor to bring the gas temperature down to a specific value, known as the Turbine Entry Temperature (TET) (1,570 °F (850 °C)), which gives the turbine an acceptable life. Having to reduce the temperature of the combustion products by a large amount is one of the primary limitations on how much thrust can be generated (10,200 lb f (45,000 N)). Burning all

7416-568: 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 increased fuel consumption (decreased fuel efficiency ) 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. Jet engines are referred to as operating wet when afterburning and dry when not. An engine producing maximum thrust wet

7519-467: The first ground attacks and air combat victories of jet planes. Following the end of the war the German jet aircraft and jet engines were extensively studied by the victorious allies and contributed to work on early Soviet and US jet fighters. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on fixed-wing aircraft have had some inspiration from this design. By

7622-712: The form of rocket engines they power model rocketry , spaceflight , and military missiles . Jet engines have propelled high speed cars, particularly drag racers , with the all-time record held by a rocket car . A turbofan powered car, ThrustSSC , currently holds the land speed record . Jet engine designs are frequently modified for non-aircraft applications, as industrial gas turbines or marine powerplants . These are used in electrical power generation, for powering water, natural gas, or oil pumps, and providing propulsion for ships and locomotives. Industrial gas turbines can create up to 50,000 shaft horsepower. Many of these engines are derived from older military turbojets such as

7725-418: The gas flow has left the turbines. When the afterburner is turned on, fuel is injected and igniters are fired. The resulting combustion process increases the afterburner exit ( nozzle entry) temperature, resulting in a significant increase in engine thrust. In addition to the increase in afterburner exit stagnation temperature , there is also an increase in nozzle mass flow (i.e. afterburner entry mass flow plus

7828-430: The high fuel consumption of afterburner, and the plane used afterburners at takeoff and to minimize time spent in the high-drag transonic flight regime. Supersonic flight without afterburners is referred to as supercruise . A turbojet engine equipped with an afterburner is called an "afterburning turbojet", whereas a turbofan engine similarly equipped is sometimes called an "augmented turbofan". A " dump-and-burn "

7931-411: The high values of afterburner fuel flow, gas temperature and thrust compared to those for the engine operating within the temperature limitations for its turbine. The highest temperature in the engine (about 3,700 °F (2,040 °C)) occurs in the combustion chamber, where fuel is burned (at an approximate rate of 8,520 lb/h (3,860 kg/h)) in a relatively small proportion of the air entering

8034-447: The insufficient aspects of numerical and experimental tools lead to two important problems in practices: (1) some shock waves can not be detected or their positions are detected wrong, (2) some flow structures which are not shock waves are wrongly detected to be shock waves. In fact, correct capturing and detection of shock waves are important since shock waves have the following influences: (1) causing loss of total pressure, which may be

8137-400: The intake of a scramjet . The appearance of pressure-drag on supersonic aircraft is mostly due to the effect of shock compression on the flow. In elementary fluid mechanics utilizing ideal gases , a shock wave is treated as a discontinuity where entropy increases abruptly as the shock passes. Since no fluid flow is discontinuous, a control volume is established around the shock wave, with

8240-402: The interstellar medium, the bow shock caused by the Earth's magnetic field colliding with the solar wind and shock waves caused by galaxies colliding with each other. Another interesting type of shock in astrophysics is the quasi-steady reverse shock or termination shock that terminates the ultra relativistic wind from young pulsars . Shock waves are generated by meteoroids when they enter

8343-458: The late 1990s. This, combined with greatly decreased fuel consumption, permitted routine transatlantic flight by twin-engined airliners by the turn of the century, where previously a similar journey would have required multiple fuel stops. The principle of the jet engine is not new; however, the technical advances necessary to make the idea work did not come to fruition until the 20th century. A rudimentary demonstration of jet power dates back to

8446-411: The mass of the gas exiting the nozzle. A jet engine can produce more thrust by either accelerating the gas to a higher velocity or ejecting a greater mass of gas from the engine. Designing a basic turbojet engine around the second principle produces the turbofan engine, which creates slower gas, but more of it. Turbofans are highly fuel efficient and can deliver high thrust for long periods of time, but

8549-437: The matter's properties manifests itself as a decrease in the energy which can be extracted as work, and as a drag force on supersonic objects ; shock waves are strongly irreversible processes . Shock waves can be: Some other terms: The abruptness of change in the features of the medium, that characterize shock waves, can be viewed as a phase transition : the pressure–time diagram of a supersonic object propagating shows how

8652-394: The net thrust of a rocket engine is: Where F N {\displaystyle F_{N}} is the net thrust, I sp,vac {\displaystyle I_{\text{sp,vac}}} is the specific impulse , g 0 {\displaystyle g_{0}} is a standard gravity , m ˙ {\displaystyle {\dot {m}}}

8755-404: The nozzle but their static values drop as the gas speeds up. The velocity of the air entering the nozzle is low, about Mach 0.4, a prerequisite for minimizing pressure losses in the duct leading to the nozzle. The temperature entering the nozzle may be as low as sea level ambient for a fan nozzle in the cold air at cruise altitudes. It may be as high as the 1000 Kelvin exhaust gas temperature for

8858-551: The oxygen delivered by the compressor stages would create temperatures (3,700 °F (2,040 °C)) high enough to significantly weaken the internal structure of the engine, but by mixing the combustion products with unburned air from the compressor at (600 °F (316 °C)) a substantial amount of oxygen ( fuel/air ratio 0.014 compared to a no-oxygen-remaining value 0.0687) is still available for burning large quantities of fuel (25,000 lb/h (11,000 kg/h)) in an afterburner. The gas temperature decreases as it passes through

8961-424: The same basic physical principles of thrust as a form of reaction engine , but is distinct from the jet engine in that it does not require atmospheric air to provide oxygen; the rocket carries all components of the reaction mass. However some definitions treat it as a form of jet propulsion . Because rockets do not breathe air, this allows them to operate at arbitrary altitudes and in space. This type of engine

9064-544: The same manner as the Rolls-Royce Pegasus , and fuel was burned in the fan air before it left the front nozzles. It would have given greater thrust for take-off and supersonic performance in an aircraft similar to, but bigger than, the Hawker Siddeley Harrier . Duct heating was used by Pratt & Whitney for their JTF17 turbofan proposal for the U.S. Supersonic Transport Program in 1964 and

9167-458: The shock wave. The slip surface (3D) or slip line (2D) is a plane across which the tangent velocity is discontinuous, while pressure and normal velocity are continuous. Across the contact discontinuity, the pressure and velocity are continuous and the density is discontinuous. A strong expansion wave or shear layer may also contain high gradient regions which appear to be a discontinuity. Some common features of these flow structures and shock waves and

9270-539: The state of the art in compressors. Alan Arnold Griffith published An Aerodynamic Theory of Turbine Design in 1926 leading to experimental work at the RAE . In 1928, RAF College Cranwell cadet Frank Whittle formally submitted his ideas for a turbojet to his superiors. In October 1929, he developed his ideas further. On 16 January 1930, in England, Whittle submitted his first patent (granted in 1932). The patent showed

9373-404: The surrounding air. At the region where this occurs, sound waves travelling against the flow reach a point where they cannot travel any further upstream and the pressure progressively builds in that region; a high-pressure shock wave rapidly forms. Shock waves are not conventional sound waves; a shock wave takes the form of a very sharp change in the gas properties. Shock waves in air are heard as

9476-412: The system is constant, the stagnation enthalpy remains constant over both regions. However, entropy is increasing; this must be accounted for by a drop in stagnation pressure of the downstream fluid. When analyzing shock waves in a flow field, which are still attached to the body, the shock wave which is deviating at some arbitrary angle from the flow direction is termed oblique shock. These shocks require

9579-438: The thickness of shock waves in air have resulted in values around 200 nm (about 10 in), which is on the same order of magnitude as the mean free path of gas molecules. In reference to the continuum, this implies the shock wave can be treated as either a line or a plane if the flow field is two-dimensional or three-dimensional, respectively. Shock waves are formed when a pressure front moves at supersonic speeds and pushes on

9682-462: The transition induced by a shock wave is analogous to a dynamic phase transition . When an object (or disturbance) moves faster than the information can propagate into the surrounding fluid, then the fluid near the disturbance cannot react or "get out of the way" before the disturbance arrives. In a shock wave the properties of the fluid ( density , pressure , temperature , flow velocity , Mach number ) change almost instantaneously. Measurements of

9785-468: The turbine (to 1,013 °F (545 °C)). The afterburner combustor reheats the gas, but to a much higher temperature (2,540 °F (1,390 °C)) than the TET (1,570 °F (850 °C)). As a result of the temperature rise in the afterburner combustor, the gas is accelerated, firstly by the heat addition, known as Rayleigh flow , then by the nozzle to a higher exit velocity than that which occurs without

9888-432: The turbines. Ram compression jet engines are airbreathing engines similar to gas turbine engines in so far as they both use the Brayton cycle . Gas turbine and ram compression engines differ, however, in how they compress the incoming airflow. Whereas gas turbine engines use axial or centrifugal compressors to compress incoming air, ram engines rely only on air compressed in the inlet or diffuser. A ram engine thus requires

9991-604: Was able to demonstrate the basic concept. Ohain was then introduced to Ernst Heinkel , one of the larger aircraft industrialists of the day, who immediately saw the promise of the design. Heinkel had recently purchased the Hirth engine company, and Ohain and his master machinist Max Hahn were set up there as a new division of the Hirth company. They had their first HeS 1 centrifugal engine running by September 1937. Unlike Whittle's design, Ohain used hydrogen as fuel, supplied under external pressure. Their subsequent designs culminated in

10094-406: Was built in 1903 by Norwegian engineer Ægidius Elling . Such engines did not reach manufacture due to issues of safety, reliability, weight and, especially, sustained operation. The first patent for using a gas turbine to power an aircraft was filed in 1921 by Maxime Guillaume . His engine was an axial-flow turbojet, but was never constructed, as it would have required considerable advances over

10197-578: Was eventually adopted by most manufacturers by the 1950s. Austrian Anselm Franz of Junkers ' engine division ( Junkers Motoren or "Jumo") introduced the axial-flow compressor in their jet engine. Jumo was assigned the next engine number in the RLM 109-0xx numbering sequence for gas turbine aircraft powerplants, "004", and the result was the Jumo 004 engine. After many lesser technical difficulties were solved, mass production of this engine started in 1944 as

10300-593: Was granted a patent for a jet engine design in March 1935. Republican president Manuel Azaña arranged for initial construction at the Hispano-Suiza aircraft factory in Madrid in 1936, but Leret was executed months later by Francoist Moroccan troops after unsuccessfully defending his seaplane base on the first days of the Spanish Civil War . His plans, hidden from Francoists, were secretly given to

10403-406: Was refueled in-flight as part of every reconnaissance mission. An afterburner has a limited life to match its intermittent use. The J58 was an exception with a continuous rating. This was achieved with thermal barrier coatings on the liner and flame holders and by cooling the liner and nozzle with compressor bleed air instead of turbine exhaust gas. In heat engines such as jet engines, efficiency

10506-427: Was still rather worse than piston engines, but by the 1970s, with the advent of high-bypass turbofan jet engines (an innovation not foreseen by the early commentators such as Edgar Buckingham , at high speeds and high altitudes that seemed absurd to them), fuel efficiency was about the same as the best piston and propeller engines. Jet engines power jet aircraft , cruise missiles and unmanned aerial vehicles . In

10609-409: Was the motivation behind the development of the gas turbine engine, the most common form of jet engine. The key to a practical jet engine was the gas turbine , extracting power from the engine itself to drive the compressor . The gas turbine was not a new idea: the patent for a stationary turbine was granted to John Barber in England in 1791. The first gas turbine to successfully run self-sustaining

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