Preston Meadow's Height Enhancement Blog

Jet engine

History
More information: Timeline of jet power
Jet engines can be traced back to the invention Eolípila before the first century AD. This device uses steam power directed through two nozzles so that cause a sphere to spin rapidly on its axis. As is known, was not used for the supply of mechanical energy, and the possibility of practical applications of this invention is not recognized. It was considered as a curiosity.
Jet Propulsion literally and figuratively just went with the invention of the rocket by the Chinese in the 13th century. Rocket exhaust was initially used in a modest form of fireworks but gradually progressed to boost formidable weaponry, and there the technology stalled for hundreds of years.
Archytas, the founder of mathematical mechanics, as described in the writings of Aulus Gellius five centuries after him, was known for having designed and built the first artificial, self-propelled flying device. This device is a bird-shaped model propelled by a jet of what was probably steam, said to have flown 200 meters.
Lagarias Ottoman elebi Hasan is said to have taken in 1633, which was described as a cone-shaped rocket and then glided with wings have a landing with success, winning a position in the Ottoman army. However, this was essentially a trick. The problem was that rockets are simply too inefficient at low speeds to be useful for general aviation.
The first attempts of the reactors were hybrid designs in which a first external power supply of compressed air which was mixed with fuel and burned for propulsion. In one such system, called thermojet by Secondo Campini but more commonly, motorjet, the air was compressed by a fan driven by a conventional piston engine. Examples of this type of design Coanda Henri Coanda-1910 aircraft (first jet-propelled aircraft ever built, with the first flight on December 16, 1910) and much later Campini N.1 Caproni, and the Japanese Tsu-11 engine for Ohka kamikaze planes towards the end of the Second World War. None was a complete success and ended up being CC.2 slower than the same design with a traditional engine and propeller.
Albert ramjet bullet Funds 1915 barrel
The Coanda-1910, first jet-propelled aircraft ever built
In 1913, Lorin Ren came up with a form of jet engine the pulsejet subsonic, which would have been more efficient, but had no way to reach high speeds sufficient for its operation, and the theoretical concept maintained for some time.
Even before the onset of World War II, engineers began to realize that the piston engine is self-limiting in terms maximum yield could reach, the time is due to issues related to the efficiency of the propeller blade was reduced tips approached the speed sound. If the motor, and therefore the aircraft, performance to increase beyond this barrier, a way should be found to dramatically improve the design piston engine, or an entirely new type of engine that would have to be developed. This was the motivation behind the development of gas turbine engine, commonly called a "jet" engine, which would become almost as revolutionary as the aviation flight of the Wright brothers first.
German patent Albert Fon engines for reaction (January 1928 – awarded 1932). The third illustration is a turbojet
The key to a practical jet engine was the gas turbine used to extract energy from the engine itself to drive the compressor. The gas turbine was not an idea developed in the 1930s: the patent for a stationary turbine was granted John Barber in England in 1791. The first gas turbine to successfully run self-built in 1903 by Norwegian engineer gidius Elling. Limitations in the design and practical engineering and metallurgy prevented such engines reaching production. The main problems were safety, reliability, weight and, especially, sustained operation.
In Hungary, Albert Fon in 1915 devised a solution to increase the range of artillery, consisting of a firearm projectile, which was released to be united with a ramjet propulsion unit. This was to make it possible to obtain a long-range with low initial muzzle velocity, allowing deposits heavy to be fired from relatively lightweight guns. Fon presented his invention to the Austro-Hungarian army, but the proposal was rejected. In 1928 he requested a German patent on aircraft supersonic ramjet driven, and this was awarded in 1932.
The first patent for the use of a gas turbine to power an aircraft was filed in 1921 by Frenchman Maxime Guillaume. His engine was an axial flow turbojet.
In 1923, Edgar Buckingham of the U.S. National Bureau Standard published a report that cast doubt on the jet engines would be economically competitive with prop driven aircraft at low altitudes and speeds of the time: "does not seem be, at present, any prospect that the Jet Propulsion species here was never considered a practical value, even for military purposes. "
Instead, by the 1930s, the piston engine in its many different forms (rotary and static radial, air cooling and liquid cooling online) was the only engine type available to aircraft designers. This was acceptable as long as only low performance aircraft were required, and indeed all that were available.
Whittle's engine blew up in the E.28/39 W.2/700 Gloster, the first British aircraft to fly with a turbojet engine, and Gloster Meteor
In 1928, the RAF Cadet College Cranwell Frank Whittle formally submitted his ideas for a jet to his superiors. In October 1929 he developed his ideas. . On January 16, 1930 in England, Whittle submitted his first patent (granted in 1932). The patent showed a two-stage axial compressor feeding a centrifugal compressor on one side. practices axial compressors were made possible by AAGriffith ideas in a seminal work in 1926 ("A Theory of aerodynamic turbine projects). Whittle then will focus on the simple centrifugal compressor only, for a variety of practical reasons. Whittle had his first engine running in April 1937. Era fuel oil, and included a separate fuel pump. Whittle's team experienced almost panic when the engine did not stop accelerating even after that the fuel was switched off. It turned out that fuel had leaked into the engine and accumulated in pools. So the engine would not stop until all the fuel discharge had burned. Whittle could not the government's interest in his invention, and development continued at a slow pace.
Heinkel He 178, first aircraft in the world to fly purely on turbojet power
Jendrassik C-1, the first turboprop engine. Hungarian Ganz works built in 1938
In 1935 Hans von Ohain started work in a similar design in Germany, apparently unaware of the work of Whittle. His first device was strictly experimental and could only run on Power external, but was able to demonstrate the basic concept. Ohain was then introduced to Ernst Heinkel, one of the larger aircraft industrialists of the time, who immediately saw the promise of 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 motor HeS a centrifuge operating in September 1937. Unlike Whittle's design, uses hydrogen Ohain as fuel, supplied under external pressure. Their subsequent designs culminated in the gasoline HeS 3 of 1,100 lb (5 kN), which followed a simple and compact Heinkel He 178 airframe and flown by Erich Warsitz on the morning of August 27, 1939, from Rostock-Marienehe airfield, an impressive short time for development. The He 178 was the airplane in the world, first jet plane.
The world first was the Jendrassik turboprop C-1 designed by the Hungarian György Jendrassik mechanical engineer. It was produced and tested in the Ganz factory in Budapest between 1938 and 1942. It was expected to adapt to the Varga RMI-1 X / H "twin-engine reconnaissance aircraft designed by Lszl Varga in 1940, but the program was canceled. Jendrassik had also designed a 75 kW turboprop on a small scale in 1937.
Whittle engine starts to appear useful, and his Power Jets Ltd. started receiving Air Ministry money. In 1941 a flyable version of the engine called the W.1 capable of 1,000 pounds (4 kN) of thrust, is fitted to the Gloster E28/39 specially built for the cell, and its first flight on May 15, 1941 at RAF Cranwell.
A photo of an early centrifugal engine (DH Goblin II) sectioned to show internal components
A designer of aircraft engines of Scotland, Frank Halford, working from ideas developed Whittle a "Straight" version jet centrifugal design became the de Havilland Goblin.
One problem with these first two designs, which are called centrifugal-flow engines, was that the compressor works by "throwing" (accelerating) air outward from the main entrance to the outer periphery engine, which compresses the air then by a divergent duct setup, converting its velocity into pressure. One advantage of this design was that it was good known, having been implemented in centrifugal compressors, then widely used in piston engines. However, given the technological limitations in early speed of the motor shaft, the compressor needed to have a very large diameter to produce the required power. This meant that the engines had a large area front, which made less useful as an aircraft engine due to friction. Another disadvantage is that the air flow had to be "bent" to flow back through the combustion section and turbine and tailpipe, adding complexity and lowering efficiency. However, this engine had the highest advantages of lightness, simplicity and reliability, and development progressed rapidly to implement the designs of airworthiness.
A cross section of the engine Junkers Jumo 004.
Austrian Anselm Franz of Junkers engine division (Junkers Motoren or Jumo) address these problems with the introduction of axial flow compressor. In essence, is a turbine in reverse. The air in front of the engine is blown in the rear of the engine fan stage (convergent ducts), where he is beaten against a set of non-rotating blades called stators (divergent ducts). The process is not as powerful as the centrifugal compressor, so a number of these pairs of fans and stators are placed in series to obtain the necessary compression. Even with all the added complexity, the resulting engine is much smaller in diameter and therefore more streamlined. Jumo were assigned the next engine number in the RLM numbering sequence, 4, and the result was the Jumo 004 engine. After much less difficulty techniques were solved, mass production of this engine began in 1944 as an engine for the world's first airplane jet fighter, the Messerschmitt Me 262 (and later the first airplane in the world of jet-bomber, the Arado Ar 234). A variety reasons conspired to delay the availability of the engine, this delay led to the fight too late to decisively impact Germany's position in the Second World War. However, as will be remembered as the first use of jet engines in service.
In the UK, its first axial flow engine, the F.2 Metrovick, ran in 1941 and first flew in 1943. Although more powerful than the centrifugal designs at the moment, the Ministry considered that the complexity and unreliability of a disadvantage in time of war. The work carried Metrovick the engine Armstrong Siddeley Sapphire to be built in the U.S. as the J65.
After the end of the war, German aircraft and jet engines were studied extensively by the victorious Allies and contributed to work in the early Soviet and U.S. fighters jet. The legacy of axial flow engine is seen in the fact that practically all jet engines on aircraft Fixed wing have had a bit of inspiration for this design.
centrifugal flow engines have improved since their introduction. With improvements in bearing technology motor shaft speed was increased, which reduces the diameter of the centrifugal compressor. The short engine length remains an advantage of this design, in particular for use in helicopters where overall size is more important than frontal area. Moreover, engine and components are more robust than are less vulnerable to foreign object damage to engine axial flow compressor.
Although German designs were more advanced aerodynamically, the combination of simplicity and lack of requirement rare metals necessary advanced metallurgy (as tungsten, chromium and titanium) for highly stressed components, such as turbine blades and bearings, etc) means that the German was later engines had a short shelf life and had to be changed after 1025 hours. British engines were also widely manufactured under license in the U.S. (See Tizard Mission), and were sold to Soviet Russia investing is designed with the Nene in power the famous MiG-15. American and Soviet designs, independent of axial flow rates for the most part, will strive to achieve superior performance until 1960, although General Electric J47 excellent service provided in the F-86 Sabre in the 1950s.
In the 1950s the jet engine was almost universal in combat aircraft, with the exception of loading, linking and other specialties. At this point some of the British designs were already cleared for civilian use, and had appeared in the Early models like the De Havilland Comet Airliner Avro Canada. In the 1960s all civil aircraft, also the great reaction, leaving the engine piston in roles that low-cost niche, such as cargo flights.
improvements in the relentless turboprop pushed the piston engine (internal combustion engine), outside the mainstream completely, leaving only for the smallest general aviation designs and some use in unmanned aircraft. The ascent engine almost universal reaction to the aircraft was well to twenty years.
However, the story was not entirely over, for the efficiency of turbojet engines was still much worse than piston engines, but by the 1970s with the advent of high bypass engines of the jet, an innovation not foreseen by commentators as early Edgar Buckingham, at high speeds and high altitudes, which seemed absurd, then only fuel efficiency, which ultimately exceeds that of best piston engine and propeller, and the dream of fast, safe, cheap travel around the world finally arrived, and his grim, if well founded Currently, the predictions that jet engines would not therefore lost their lives forever.
Type
There are a number of different types of engines reaction, all of which achieve forward thrust from the jet principle.
Type
Description
Advantage
Disadvantages
Water jet
Rocket propulsion of water and jetboats; jets of water from the rear through a nozzle
On ships, you can run in shallow water, high acceleration, no risk of engine overload (unlike propellers), less noise and vibration, highly maneuverable at any speed, efficiency, high-speed less vulnerable to damage from the debris, very reliable, load flexibility, less harmful to wildlife
It may be less efficient than a propeller at low speed, more expensive, more weight in the boat because the water drawn, will not perform well if the boat is heavier than the jet is the size of
Motorjet
Works like a jet, but instead of a turbine driving the compressor piston engine driving.
Higher exhaust velocity of a propeller, offering better direction at high speed
Heavy, inefficient and underpowered. Examples include: Coanda-1910 Campini Caproni N.1.
Turbojet
A tube with a compressor and turbine share a common axis with a burner in the middle and a propulsion tube exhaust. Use a high exhaust gas velocity to produce thrust. It has a flow much higher than central type motors bypass
The simplicity of design, efficient at supersonic speeds (~ M2)
A basic design, misses many improvements in efficiency and power of subsonic flight, relatively noisy.
Low-bypass turbofan
One or two-stage fan added in front omitted part of the air through a bypass line directly to the nozzle / afterburner, avoiding the combustion chamber, with the remainder heated in the combustion chamber and passing through the turbine. Compared with its predecessor turbojet, this allows a more efficient operation with a little less noise. This is engine high-speed military aircraft, some small, private aircraft, civil aircraft and more like the Boeing 707, McDonnell Douglas DC-8 and its derivatives.
As with the turbojet, the design is streamlined, with only a slight increase in diameter in the jet fans needed to accommodate branch and the camera. It is capable of supersonic speeds with a minimum of down thrust at high speeds and altitudes and more efficient than the subsonic jet in operation.
Noisier and less efficient than high-bypass turbofan, with less static (Mach 0) of thrust. Added complexity to accommodate dual-axis designs. More inefficient for a turbojet around M2 due to increased cross-sectional area.
High-bypass Turbofan
First stage compressor dramatically enlarged provide bypass airflow around engine core, providing significant amounts of thrust. Compared with the low pressure turbine bypass and without bypass-turbojets, high bypass turbine operates on the principle of moving a large amount of air a bit quicker, but a very small amount fast. Most common form of civil jet engine use today are used in aircraft like the Boeing 747, most of the 737, and all Airbus aircraft.
About 10 to 20 percent quieter than the turbojet engine due to greater mass flow and lower total exhaust speed. It is also more efficient for a range subsonic airspeeds useful for the same reason, cooler exhaust temperature. Exhibit less noise and greater efficiency of low-bypass turbofans.
Greater complexity (additional lines, usually multiple shafts) and the need to contain heavy blades. Fan diameter can be extremely large, especially in high-bypass turbofans and the GE90. More subjects of DU and ice damage. Top speed is limited due to the possibility of shock waves of engine damage. Lapse thrust at higher speeds, which require large diameters and introduces additional friction.
Rocket
Carries all propellants and oxidizer on board, jet propulsion issue
Very few moving parts, Mach 0 to Mach 25 +, efficient at very high speed (> Mach 5.0 or so) thrust / weight ratio of more than 100, no complex air intake, high compression ratio, very high speed (hypersonic) exhaust, good value cost-push, rather easy to prove, in a vacuum-in fact it works better exoatmospheric kinder on vehicle structure at high speed, fairly small area to keep cool, not hot turbine exhaust stream.
Needs a lot of very low-specific impulse fuel normally 100,450 seconds. Extrema thermal stresses of combustion chamber can make reuse harder. Normally required to be carried oxidant increases the risks. Extraordinarily noisy.
Ramjet
Intake air is compressed entirely by speed and air approaches canal shape (convergent), then passes through a section of the burner where it is heated and then passes through a nozzle propulsion
Very few moving parts, Mach 0.8 to Mach 5 +, efficient at high speed (> Mach 2.0 or so) lightest of all air breathing aircraft (thrust / weight of up to 30 at optimum speed), cooling much easier than turbojets as no blades turbine to cool.
Must have a high initial speed to function, inefficient at low speeds due to poor compression ratio, difficult organize the shaft power for accessories, usually limited to a small range of speeds, intake flow must be slowed to subsonic speeds, noisy quite difficult to prove, careful to keep alight.
Turboprop (similar Turboshaft)
Strictly not a reaction throughout a gas turbine engine is used as an engine to drive a propeller shaft (or rotor in the case of a helicopter)
High efficiency at lower subsonic airspeeds (300 knots), high shaft power to weight
Limited top speed (aircraft), a bit noisy, complex transmission
Propfan / Unducted Fan
Turbojet engine that also drives one or more propellers. Similar to a turbofan without the fan cowl.
The greater fuel efficiency, potentially less noise of turbofans, could lead to higher speed commercial aircraft, popular in the 1980s during fuel shortages
development of turboprop engines has been very limited, usually noisier turbofans, complexity
Pulsejet
The air is compressed and burned intermittently rather than continuously. Some designs use valves.
Very simple design, commonly used in model airplanes
Noisy, inefficient (low compression ratio), malfunctioning large-scale, the valves in valve designs wear out quickly
Pulse detonation engine
Similar to a pulsejet, but combustion occurs as a detonation instead of a deflagration, may or may not need valves
Maximum theoretical engine efficiency
Very noisy, parts subject to extreme mechanical fatigue, hard to start detonation, not practical for current use
air-augmented rockets
Essentially a ramjet where it is compressed intake air and burned by the exhaust of a rocket
Mach 0 to Mach 4.5 + (you can also run exoatmospheric), good efficiency at Mach 2-4
efficiency similar to rockets at low speed or exoatmospheric difficulties from the outset, a relatively undeveloped and unexplored, cooling difficulties, very noisy, thrust / weight is similar to the ramjet.
Scramjet
Similar to a ramjet without a diffuser, air flow through the whole engine remains supersonic
Few mechanical parts can operate at very high Mach number (Mach 8-15) with a good efficiency
Still in development stages, should have a speed very high initial to function (Mach> 6), cooling difficulties, very poor thrust / weight (~ 2), the extreme aerodynamic complexity, airframe difficulties, testing difficulties / expense
Turborocket
A turbojet where an additional oxidizer such as oxygen is added to the airstream to increase maximum altitude
Very close to existing designs, operates at high altitude, wide range of altitude and speed
airspeed range is limited to the same jet, leading oxidant like LOX can be dangerous. Much heavier than simple rockets.
precooled jets / LACE
Intake air is cooled to very low temperatures in the entry of a heat exchanger before passing through a ramjet and / or jet aircraft and / or rocket engine.
Easily tested on ground. Very high thrust / weight ratios are possible (~ 14) with good fuel efficiency over a wide range of airspeeds, Mach 0 to 5.5 +, this combination of efficiencies may permit launch to orbit, single stage, or very fast, very long distance intercontinental travel.
Exists only in the laboratory prototype stage. Examples are RB545, SABRE Reaction Engines, Atrex. Requires liquid hydrogen fuel which has a very low density and requires insulated tanks.
Uses
Motors reaction are usually used as aircraft engines for jet aircraft. They are also used for cruise missiles and unmanned aerial vehicles.
In the form of rocket motors used for fireworks, model rockets, space flight and military missiles.
Jet engines have also been used to drive high speed cars, including drag racers, with their numbers on a car to rocket. A turbofan powered car holds the record ThrustSSC land speed.
Jet engine designs are frequently modified to convert them into gas turbine engines used in a wide variety of industrial applications. These include power generation, water supply, natural gas, or oil pumps, and provide propulsion for ships and locomotives. turbines Industrial gas can create up to 50,000 shaft horsepower. Many of these engines from more military jets such as the Pratt & Whitney J57 J75 and models. There is also a derivative of the P & W JT8D low-bypass turbofan that creates up to 35,000 HP.
The main components
Main article: Components jet engine
The main components of a jet engine are similar in all the major different types of engines, although not all engine types all components. The main parts are:
Cold section:
Air inlet (entrance) For subsonic aircraft, the air intake of an engine reaction consists essentially of an opening that is designed to minimize drag. The air reaching the compressor of a normal jet engine must travel the speed of sound, even for supersonic aircraft, to allow smooth flow through the compressor and turbine blades. A supersonic flight speeds, waves shock in the intake circuit, they help to compress the air, but there is also some inevitable reduction of recovered pressure at the inlet to the compressor. Some supersonic consumer devices use as a cone or ramp, to increase pressure recovery.
Compressor or fan compressor consists of stages. Each stage consists of vanes which rotate, and stators which remain stationary. When air is drawn through deep the compressor, heat and pressure increases. The energy is derived turbine (see below), passed along the axis.
Bypass ducts Much of the thrust of almost all modern jet engines comes compressor air that passes in front of the combustion chamber and turbine section of gas that leads directly to the afterburner nozzle or (if exists.)
Common:
Shaft The shaft connects the turbine to the compressor and runs most of the length of the motor. You can have up to three concentric shafts, rotating at independent speeds, with many sets of turbines and compressors. Other services, such as a purge of fresh air, you can also go down the shaft.
diffuser section: – This section is a divergent duct using the Bernoulli principle to decrease the rate of compressed air to allow easy ignition. And at the same time, it continues increasing the air pressure before entering the combustion chamber.
Hot section:
Or combustion chamber or chamber may or Flameholders It's combustion chamber where fuel is continuously burned in compressed air.
A blade with internal cooling is applied in high-pressure turbine
The turbine of the turbine is a series of leaf discs, which act as a windmill, gaining energy from the hot gases leaving the combustion chamber. Part of this energy is used to drive the compressor, and in some turbine engines (turboprop is, turboshaft or turbofan engines), energy is extracted by Additional drives turbines to drive and use devices such as propellers, fans referral or helicopter rotors. One type, a free turbine, is configured so that the disc turbine driving the compressor rotates independently of the disks that external power components. relatively cool air, bled from the compressor can be used to cool the turbine blades and vanes, to prevent melting.
Of Afterburner or reheat (chiefly UK) (in particular push military) Produces extra by burning extra fuel, usually inefficiently, to significantly increase the inlet nozzle to the discharge temperature. Because flow greater volume (ie lower density) in the output of the afterburner, an area of the nozzle flow longer needed to maintain the consistency of motor satisfactory, when the afterburner is on.
Exhaust nozzle or hot gases leaving the engine exhaust to atmospheric pressure through a nozzle, with the aim of producing a high-velocity jet. In most cases, the nozzle is convergent and of fixed flow area.
If the pressure supersonic nozzle Ratio nozzle (nozzle inlet pressure and ambient pressure) is very high, to maximize thrust it may be worthwhile, despite the extra weight, to fit a convergent-divergent (De Laval) nozzle. As its name suggests, initially this type of nozzle is convergent, but beyond the throat (smallest flow area) the flow area starts to increase to form the divergent. The expansion of the atmospheric pressure and supersonic gas velocity continues downstream of the throat, while in a converging nozzle expansion beyond sonic velocity occurs externally, in the exhaust plume. The first process is more efficient than second.
The various components mentioned above are restrictions on how they combine to generate greater efficiency and performance. The performance and efficiency of an engine can never be taken in isolation, for example, fuel efficiency and distance of a supersonic jet engine maximizes at a speed of Mach 2, while the drag carrying vehicle is increasing as a square law and has much extra drag in the transonic region. The greater fuel efficiency for your vehicle is therefore typically ~ 0.85 Mach.
For the optimization of engines for its intended use is important here is air intake design, total area, the number of compressor stages (sets of blades), fuel type, number of exhaust stages, metallurgy of components, amount of bypass air used, where it enters the air bypass, and many other factors. For example, consider the design of the air intake.
Terminology
A description of the jet engine RPM, Abbreviations are commonly used:
For a turboprop engine, Np refers to the RPM of the propeller shaft. For example, a common Np would be approximately 2200 RPM for a constant speed propeller.
N1 or natural gas refers to gas generator speed (producer gas) in section (RPM). Each engine manufacturer will choose between these two acronyms N1, but is used mainly for turbofan engines Ng, while mainly used for turboprop and turboshaft engines. For example, a common Np would be around 30,000 RPM.
Or Nf N2 refers to the speed of the turbine section of power. Each engine manufacturer will choose between these two abbreviations N2, but is used mainly for turbofan engine where Nf is mainly used for turboprop and turboshaft engines. In many cases, even free turbine engine, the N1 and N2 may be very similar. [Citation needed]
Ns refers to the speed of the reduction gearbox (RGB) in the output shaft for turbo engines.
In many cases, Instead of expressing the rates of N-(N1, N2) as a pure RPM displays cockpit, pilots are provided with the N-speed, expressed as a percentage of value nominal or maximum. For example, at full power, the N1 could be 101.5% or 100%. This user interface decision has been made as of human factors, as the drivers are more likely to notice a problem with a rate of two or three digits (where 100% implies a nominal value) that a large number, scale without limits.
The most common types
The types of jet engines
There are two types of jet engine commonly observed today, the turbine is used in almost all commercial aircraft and rocket engines are used for space flight and other land uses such as ejection seats, flares, fireworks, etc.
Turbofan engines
Main article: Turbofan
a turbofan engine animation
Most modern jet engines are actually turbofans, where acts of low-pressure compressor and a fan, supplying supercharged air not only to the core engine, but to a bypass line. The air flow bypass or pass to an 'independent of the cold nozzle' or mixed with low-pressure turbine exhaust gases, before expanding through a " mixed flow pipe. "
Turbofans used for airlines because they provide an escape rate that is better suited for subsonic aircraft. A speed flight of aircraft, conventional turbojet engines generate exhaust just travel very fast backwards, and this wastes energy. By issuing the exhaust gases so that ends traveling more slowly, better fuel consumption is achieved and greater thrust at low speeds. In addition, the lowest rate escape gives much lower noise.
In the 1960 s there was little difference between the engines of civil and military aircraft, besides the use of afterburning in some applications (supersonic). Civil turbofans today have a low exhaust speed (low specific thrust net thrust divided by airflow) to maintain noise to a minimum of reaction and improve fuel efficiency. Consequently, the pass ratio (bypass flow divided by the base flow) is relatively high (ratio of 4:1 to 8:1 are common). Only a single fan stage is required, for a special purpose low ratio implies a low pressure fan.
Today's military turbofans, however, be targeted relatively high, to maximize the thrust front of a particular area, jet noise to be minor in relation to military applications for civilian purposes. Multistage fans are normally needed to reach the ratio of relative pressure ventilator high for the specific high-momentum needed. Despite the high temperatures of turbine inlet are often used, the pass ratio is generally low, usually significantly lower than 2.0.
Rocket engines
Main article: Rocket engine
A common form of jet engine is the rocket engine.
Rocket engines are used for high altitude flights because they give very high thrust and lack of confidence in atmospheric oxygen they can operate at altitudes of arbitrary.
This is used launching of satellites, manned space exploration and access, and allowed to land on the moon in 1969.
However, the exhaust gases, high-speed the heavier, fuel-oxidant rich results in using more of the jet fuel and its use is restricted to high altitudes, very high speeds, or when very high accelerations are needed as rocket engines have a relationship thrust / weight very high.
An approximate equation for net thrust of a rocket engine is:
Where F is the thrust, Isp (VAC) is the specific impulse, g0 is a standard gravity, is the flow of fuel into kg / s, Ae is the area of gas hood exhaust exit, and P is atmospheric pressure.
Physical principles
All jet engines are reaction engines generate thrust by issuing a stream of fluid back to relatively high speeds. The forces inside the engine needed to create this jet to give a strong impetus the engine that pushes the boat forward.
Jet engines of a jet fuel tanks attached to the engine (as in a "rocket") and in the engine duct (The commonly used in aircraft) by the ingestion of an external fluid (air typical) and drive them out faster.
Push
The momentum of movement of the motor is equal to the mass of the liquid multiplied by the speed at which the engine emits this mass:
I = mc
where m is the mass of liquid per second, c is the speed of escape. In other words, a vehicle gets the same thrust, if the exhaust pipes of very, very slowly, or a bit of escape very quickly. (In some places the practice of exhaust gases can be faster than others, but the momentum is the average that matters, and therefore the important quantity is called speed effective exhaust – c here.)
However, when a vehicle is moving with velocity v determined, the fluid moves, creating a ram drive to oppose the entry:
mv
Most types of jet engine have a consumption that provides most of the liquid coming from the exhaust. Conventional rocket motors, however, does not have an intake, both oxidant and fuel are carried in the vehicle. Therefore, rocket motors has no ram drag, the gross thrust nozzle is the net thrust of the engine. Consequently, the thrust characteristics of a rocket engine are different to those of a jet engine air to breathe, and the thrust is independent of speed.
The jet engine with an intake duct is only useful if the velocity of the gases from the engine, c, is greater than the speed vehicle, v, given that the net economic engine is the same as if the gas is delivered with the speed c v. So the idea is actually equal to
S = m (cv)
This equation shows that as vc approaches, a greater mass of fluid must pass through the engine to continue to accelerate at the same pace, but all engines have a limit designed in this regard. Moreover, the equation implies that the vehicle can not accelerate the rate of escape from his past as they have negative thrust.
Energy efficiency
Dependence on energy efficiency () to the vehicle speed / ratio of escape velocity (v / c) for air-jet and rocket breathing engines
Energy efficiency () of units installed in vehicles has two main components, the efficiency of the cycle (c) – the efficiency of the engine can accelerate the reaction, and propulsive efficiency (p)-the amount of energy of the jet ends in the bodywork of the vehicle instead of being carried as kinetic energy of the reaction.
Although the overall energy efficiency is simply:
= Pc
For all jet propulsion engines efficiency is greater when the emits a jet engine exhaust at a speed that is the same as, or nearly identical to the speed of the vehicle as this gives the smallest residual kinetic energy. (Note:) The exact formula for the engines to breathe the air moving at a speed V c of escape is given in the literature as the speed: it is
And a rocket:
In addition to propulsive efficiency, another factor is the efficiency of the cycle, essentially a jet engine is usually a form of heat engine. engine efficiency heat is determined by the ratio of the temperatures reached in the engine to be exhausted in the nozzle, which in turn is limited by the pressure ratio can be achieved overall. Cycle efficiency is the highest in rocket motors (~ 60 +%), and that can reach very high combustion temperatures and can be very large, energy-efficient jets. Cycle efficiency and similar jet is closer to 30%, the combustion temperatures and the practical effectiveness nozzle are much lower.
The specific impulse depending on the reaction rate for different types with kerosene (Isp hydrogen would be approximately twice). Although efficiency plummets with speed, greater distance covered, is that the efficiency per unit distance (per km or miles) is more or less independent speed for jet engines as a group, however airframes become inefficient at supersonic speeds
Fuel / fuel consumption
A close relationship (But different) concept to energy efficiency is the consumption rate of propellant mass. propellant consumption in jet engines is measured by the specific fuel consumption, the specific impulse and effective exhaust velocity. They all measures as well. The specific impulse and effective exhaust velocity are strictly proportional, while consumption Specific fuel is inversely proportional to each other.
To airbreathing engines as the jet energy efficiency and propellant (fuel) the efficiency are the same thing, because the engine is a fuel and energy source. In rockets, the propellant is also the exhaust gases, and this means that a propeller high energy efficiency gives greater driving but in some cases can actually give a lower energy efficiency.
Engine Type
Stage
SFC in kg / (Lbfh)
SFC in g / KNS ()
The specific impulse (s)
Effective exhaust velocity (m / s)
NK-33 rocket motor
Empty
10.9
309
330
3240
SSME rocket engine
Empty space shuttle
7.95
225
453
4423
Ramjet
Mach 1
4.5
127
800
7877
J-58 turbojet
SR-71 to Mach 3.2 (Wet)
1.9
53.8
1900
18 587
Olympus Rolls-Royce/Snecma 593
Concorde Mach 2 cruise (dry)
1.195
33.8
3012
29 553
CF6 turbofan-80C2B1F
Boeing 747-400 cruise
0.605
17.1
5950
58 400
General Electric CF6 turbofan
Sea level
0.307
8.696
11 700
115 000
It can be seen that the subsonic turbofans such as General Electric CF6 uses much less fuel to generate momentum for a second than the Concorde jet, 593. However, since energy is force times distance and the distance per second is higher in Concordia, the actual power generated by the engine for the same amount of fuel Concordia is higher in the cruise at Mach 2 Concorde's engines are more efficient CF6-thrust for the mile, in fact, the most efficient ever.
Thrust-to-weight
Main article: List thrust / weight
The thrust / weight of jet engines similar principles varies somewhat with scale, but above all is a function engine technology of the construction. It is evident that for a given engine, the engine is lighter, the better the weight is thrust, less fuel is used to compensate for the resistance due to the elevation necessary to support the weight of the engine, to accelerate the mass of the motor.
As can be seen in the table below, rocket engines, generally achieve much higher thrust to weight ratios through engines such as turbojet and turbofan. This is mainly due to the almost universal rockets use liquid density or solid reaction mass which gives a much smaller volume and therefore the pressurization system that supplies the nozzle is much smaller and lighter the same performance. engines have to deal with through the air is 2-3 orders of magnitude less dense and this gives to the pressure on much larger areas, and in turn leads to engineering materials more than necessary to hold together the engine and air compressor.
The reactor or rocket engine
Mass, kg
Jet or push the rocket kN
Thrust-to-weight
RD-0410 nuclear rocket engine
2000
35.2
1.8
J-58 (SR-71 Blackbird jet engine)
5.2
Olympus 593 Concorde Rolls-Royce/Snecma
turbojet with reheat
3175
169.2
5.4
RD-0750 rocket engine, three thrusters mode
4621
1413
31.2
RD-0146 rocket motor
260
98
38.5
Space Shuttle SSME rocket engine
3177
2278
73.2
RD-180 rocket engines
5393
4152
78.6
F-1 (Saturn V first stage)
8391
7740.5
94.1
NK-33 engines rocket
1222
1638
136.8
Rocket axle shafts are vaccuum unless otherwise stated
Comparison of rates
Comparative suitability (of left to right) turboshaft, low bypass and turbojet to fly at 10 km altitude in various speeds. The horizontal axis – speed, m / s. Vertical axis shows the efficiency of motor.
Turbopropulsores get jet thrust some effect, but are useful for comparison. They are the gas turbine engine having a rotating fan that takes and accelerates the mass of air, but by a relatively small change in velocity. This low speed limits the speed of any propeller driven aircraft. When the plane speed exceeds this limit, propellers do not provide any thrust (cv <0). However, due to accelerate a large mass of air, are very efficient turboprops.
Turbo speed up a much smaller mass of air and fuel burned, but emit much higher speeds possible with a Laval nozzle. For this grounds are suitable for supersonic and higher speeds.
Low bypass turbofans have the common gas exhaust of the two air streams at speeds different (c1 and c2). The aim of these engines is
S = m1 (c1 – v) + m2 (c2 – v)
where m1 and m2 are the masses of air that leaks out of both. These engines are effective at low speeds, the pure jets, but at higher speeds than the turboshaft and propellers in general. By example, the altitude of 10 km, is more effective turboshaft at about Mach 0.4 (0.4 times the speed of sound), low bypass turbofans become more effective at about Mach 0.75 and be more effective than jet exhaust mixed engine when the speed approaches Mach 2.3.
Rocket engines have very high exhaust velocity and therefore are best suited for high speed (Hypersonic) and high altitudes. At any given throttle, the thrust and efficiency of a rocket motor improves slightly with increasing altitude (for the back-pressure which increases net thrust falls in the plane of nozzle exit), whereas with a turbojet (or turbofan) the falling density of the air entering the intake (and the hot gases leaving the nozzle) causes the net thrust to decrease with increasing altitude. Rocket engines are more efficient than scramjets even above about Mach 15.
The altitude and speed
With the exception of scramjets, jet engines, deprived of their air intake systems can only accept about half the speed of sound. The work of entry system and transonic supersonic aircraft is to reduce the air and perform some of the compression.
The maximum height limit for motors is fixed by the flammability, high air becomes too thin to burn, or after compression, too hot. For turbojet engines a height of about 40 km seem possible, while for the 55 km ramjet engines may be reachable. Scramjets can theoretically handle 75 km. Rocket engines, of course, have no upper limit.
Flying faster compresses the air in front of the engine, but eventually the engine can not go faster without melting. The limit than is generally believed that a speed of Mach 5.8, with the exception of scramjets that may be able to reach a speed of Mach 15 or more, and stop avoiding the air.
Noise
The noise is caused by shock waves that form when the jet exhaust gases interact with the outside air. The noise intensity is proportional to the orientation and proportional to the fourth power of the jet velocity.Generally then the lower speed streams of exhaust gases emitted by turbofan engines, such as referral high are the quietest, while faster aircraft are the loudest.
Despite some variations in the rate of reaction can often be arrange for a jet engine (eg, oppress and adjustment of the nozzle) is difficult to vary the speed of reaction of an engine over a wide range. As well as the engines of vehicles such as Concord supersonic military aircraft and rockets inherent need for high speed supersonic escape, so these vehicles are particularly noisy, even at low speeds.
Advanced design
J-58 turbojet combined ramjet
The SR-71 Blackbird Pratt & Whitney J58 was quite unusual. One could make the flight to be largely a turbojet to being largely a compressor-assisted ramjet. At speeds high (above Mach 2.4), the engine used variable geometry vanes to direct excess air through 6 bypass pipes downstream of the compressor stage fourth post-combustion chamber. 80% of the SR-71 high-speed thrust generated in this way, giving much higher thrust, improving specific impulse by 10-15% and permits continuous operation at Mach 3.2. The name coined for this setup is turbo-ramjet.
Motors hydrogen-powered air-jet breathe
Jet engines can run on almost any fuel. Hydrogen fuel is a very convenient, since, although the energy per mole is not unusual high, the molecule is much lighter than other molecules. The energy per kg of hydrogen is twice as common fuels and this gives twice the specific impulse. In addition, the reaction with hydrogen engines are fairly easy to buildhe first jet was run on hydrogen. Also, although not through engines, hydrogen fuel rocket motors have seen widespread use.
However, in almost all other respects, the hydrogen is problematic. The drawback density of hydrogen is in gaseous form, the tanks are handy for flight, but even in the form of liquid hydrogen has a density fourteenth that of water. Also is deeply cryogenic insulation and requires significant that object to be stored in the wings. The overall vehicle would end up being very large, and difficult for most airports to accommodate. Finally, pure hydrogen is not found in nature, and should be made either through reforming steam or expensive electrolysis. However, the investigation is ongoing and hydrogen-fueled aircraft designs there may be feasible.
engines precooled jet
Main article: precooled jet engine
An idea originated by Robert P. Carmichael in 1955 is that the engines that run on hydrogen could theoretically have a much higher return than oil-fueled engines if a heat exchanger used to cool the incoming air. The low temperature allows lighter materials to be used, a high mass flow through the engine combustion and permits to inject more fuel without overheating engine.
This idea leads to plausible designs like SABRE Reaction Engines, which may allow, from one stage to orbit launch vehicle, and Atrex, what would allow jet engines to be used at hypersonic speeds and high altitudes of reinforcements for the shuttles. The idea is also being investigated by EU for a nonstop concept antipodes supersonic passenger travel at Mach 5 (Reaction Engines A2).
nuclear-powered ramjet
Project Pluto was a nuclear-powered ramjet, intended for use in a cruise missile. Instead of burning fuel in regular jet engines, air is heated by high temperature, unshielded nuclear reactor. This dramatic increase in engine ignition time, and the ramjet was predicted to be able to cover any distance required at supersonic speeds (Mach 3 at tree-top height).
However, there was no obvious way to stop it once it had been removed, what would be a great disadvantage in any application not disposable. In addition, because the reactor was shielded, it was dangerous to be in or around the vehicle's flight path (although exhaust itself radioactive). These drawbacks limit the application of the delivery system of nuclear warhead on a large scale, which was being designed.
Scramjets
Main article: Scramjet
Scramjets are an evolution of ramjet engines that are capable of operating at much higher speeds than any other type of airbreathing motor. They share a similar structure with ramjet, with a specially shaped tube that compresses air with no moving parts through ram-air compression. Scramjets, however, operate with supersonic airflow through the whole engine. Therefore, scramjets do not have the ramjet diffuser required to stem the flow of incoming air at subsonic speeds.
Scramjets start working at a speed of at least Mach 4, and have a maximum speed of about Mach 17. Because aerodynamics heating at these high speeds, cooling poses a challenge for engineers.
Environmental considerations
Jet engines are usually run leading proponents of fossil fuels, and therefore a source of carbon dioxide in the atmosphere. Jet engines can use biofuels or hydrogen although production of the latter is usually made from fossil fuels.
Some scientists believe that jet engines are also a source global dimming due to water vapor in the exhaust gases resulting in the formation of clouds.
Nitrogen compounds are also formed in the combustion process of atmospheric nitrogen. At low altitudes are not thought to be especially harmful, but for supersonic aircraft flying into the stratosphere some destruction of Ozone can be produced.
Sulfates also issued if the fuel contains sulfur.
Safety and reliability
Main article: Air Safety
The jet engines are usually very reliable and have a very good safety record. However, failures sometimes occur.
Compressor blade containment
Article Home: Road Test
The most likely failure compressor blade failure, and modern jet engines are designed with structures that can take these leaves and keep within the motor housing. Verification of a jet engine design which involves the evaluation of this system is working properly.
Bird strike
bird strike is an aviation term for a collision between a bird and a plane. This is a common threat to aircraft safety and has led to a series of fatal accidents. In 1988 an Ethiopian Airlines Boeing 737 sucked pigeons in both engines during takeoff and then crashed in an attempt to return to Bahir Dar Airport, of the 104 people aboard, 35 were killed and 21 wounded. In another incident in 1995, crashed a Dassault Falcon 20 at a Paris airport during an attempted emergency landing after sucking lapwings into an engine, causing engine failure and a fire in the fuselage of the plane, the 10 people aboard were killed. In 2009, U.S. Airways Flight 1549, an Airbus A320 sucked a bird into the engine. The plane landed in the Hudson River after takeoff from the international airport LaGuardia in New York. There were no casualties.
Modern engines have the ability to react to survive ingestion of a bird. Small aircraft fast, such as military combat aircraft, are at greater risk than big heavy multi-engine. This is due to the fact that the fan of a high bypass turbofan engine, typical of transport aircraft, acts as a centrifugal separator to force ingested materials (birds, ice, etc) to the outside of the blower wheel. As a result, these materials relatively free pass through the bypass duct, rather than through the core engine, which contains the smaller and more delicate compressor blades. Military aircraft designed for high speed flight typically have pure turbojet or low bypass turbofan engines, increasing the risk that materials ingested go back into the core engine damage.
The highest risk of bird strike is during takeoff and landing, at low altitudes, which is in the vicinity of airports.
uncontrollable failures
A class of bugs that caused crashes in particular, is overwhelming failures, where the rotating parts of engine off and leave the case. These can be cut for fuel or control lines, and can enter the cockpit. Although the fuel and control lines usually by doubled for reliability, the crash of United Airlines Flight 232 took place when the hydraulic fluid lines for the three independent hydraulic systems were simultaneously cut by shrapnel from an engine failure unstoppable. Before the fall United 232, the probability of a simultaneous failure of all three hydraulic systems considered the height of one billion-to-one. However, the statistical models used to arrive at this figure does not take into account the fact that the number two engine was mounted on the tail close to all the hydraulic lines, or the possibility that an engine failure would release many fragments in many directions. Since then, designs more modern aircraft engines have focused on keeping the shrapnel from entering the casing or the pipe, and increasingly used in high strength composite materials to achieve the necessary penetration resistance, keeping your weight down.
See also
Look up jet engine in Wiktionary, the free dictionary.
Look up through engine in Wiktionary, the free dictionary.
Air turboramjet
Balancing machine
Jet engine performance
Jet aircraft
Boat
Variable cycle engine
Pulse-jet engine
Turborocket
Rocket engine nozzles
Spacecraft propulsion
Water injection (engines)
Turbojet development in the SAR
References
^ Encyclopedia Britannica: Internal Combustion Engine
^ propeller efficiency
^ Patent number 554 906
^ Gyorgy, Istvan Nagy, "Albert Fono: A Pioneer of Jet Propulsion," International Astronautical Congress 1977, IAF / IAA
^ Dugger, Gordon L. (1969). Ramjet. American Institute of Aeronautics and Astronautics, p. 15.
^ Maxime Guillaume, "Propulseur raction par sur l'air" French patent no. 534 801 (filed: May 03, 1921 Published: January 13, 1922). Available online (in French) at: http://v3.espacenet.com/origdoc?DB=EPODOC&IDX=FR534801&F=0&QPN=FR534801 .
^ sod1280.tmp
^ PBS – Chasing the Sun – Frank Whittle
^ BBC – History – Frank Whittle (1907 – 1996)
^ Frank Whittle, "Improvements on the propulsion of aircraft and other vehicles, "British patent no. 347 206 (filed: January 16, 1930). Available online at: http://v3.espacenet.com/origdoc?DB=EPODOC&IDX=GB347206&F=0&QPN = GB347206.
^ The history of the Jet Engine – Sir Frank Whittle – Hans Von Ohain Ohain said he had not read the patent of Whittle and Whittle thought he (Frank Whittle 1907-1996) however, the patent was Whittle in German libraries and the son of Whittle Ohain had suspicions that he had read or heard of it (the story of Jet Engine – Sir Frank Whittle a genius betrayed -)
^ Warsitz, Lutz: FIRST jet pilot – The story of Warsitz German pilot Erich (p. 125), Pen and Sword Books Ltd., England 2009
^ CH10-3
^
^ Ab
^
^
^ The merger of Air and Space
^ PRATT AND WHITNEY CANADA MAINTENANCE MANUAL – PART MANUAL NO. 3017042 – Introduction – Page 6
^ Mail skilled in the art – Mr. Field Support Representative, Pratt & Whitney Canada Support Network Worldwide January 12, 2010
^ In Newtonian mechanics the kinetic energy is part of his office. Kinetic energy is the easiest to calculate when speed is measured in the center of mass of the vehicle and (less obviously) the reaction mass / air is the stationary frame begins before takeoff.
^ K. Honicke, R. Lindner, P. Anders, M. Krahl, H. Hadrich, K. Rohricht. Beschreibung der Konstruktion der Triebwerksanlagen. Interflug, Berlin, 1968
^ Elements of rocket propulsion-seventh edition, page 37-38
Abc ^ "The data on large turbofan engines." Aircraft Aerodynamics and Design Group. Stanford University. http://adg.stanford.edu/aa241/propulsion/largefan.html. Retrieved on December 22, 2009.
^ NOVA transcript
Ab ^ Wade, Mark. "RD-0410." Encyclopedia Astronautica. http://www.astronautix.com/engines/rd0410.htm. Retrieved on 09/25/2009.
^ "Buro Konstruktorskoe Khimavtomatiky – Scientific Research Complex / RD0410. Nuclear Rocket Engine. Advanced launch vehicles." KBKhA – Chemical Automatics Design Bureau. http://www.kbkha.ru/?p=8&cat=11&prod=66. Retrieved on 09/25/2009.
^ Aircraft: SR-71 Blackbird A Lockheed
^ "Rolls-Royce SNECMA Olympus – Jane's Transport News." http://www.janes.com/transport/news/jae/jae000725_1_n.shtml. Retrieved 09/25/2009. "With afterburner, and nozzle investor … 3175 kg of … … 169.2 kN Afterburner"
^
^ "Konstruktorskoe Khimavtomatiky Buro – Scientific Research Complex / RD0750.. KBKhA – Automatic Chemical Design Bureau. Http://www.kbkha.ru/?p=8&cat=11&prod=57. Retrieved on 09/25/2009.
^ SSME
^ "RD-180." http://www.astronautix.com/engines/rd180.htm. Retrieved on 09/25/2009.
http://www.astronautix.com/engines/f1.htm ^
Astronautix ^ NK-33 entry
High Speed Propulsion ^
^ Scramjet
J58 ^
^ NASA history Other Interests in Hydrogen
^ The Skylon Spaceplane
X30 ^ Astronautix
^ Transport Canada – Sharing the Skies
John Golley (1997). Genesis of the Jet: Frank Whittle and the invention the jet engine. Crowood Press. ISBN 1-85310-860-X.
David Brooks S (1997). Vikings at Waterloo: wartime job in the Whittle Jet Engine by the company Rover. Rolls-Royce Heritage Trust. ISBN 1-872922-08-2
Warsitz Lutz (2009): The first pilot of the jet – Warsitz The history of German pilot Erich, Pen and Sword Books Ltd., England, ISBN 9781844158188, English edition
External Links
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