Jet engine definition, an engine, as an aircraft engine, that produces forward motion by the rearward exhaust of a jet of fluid or heated air and gases.

All jet engines, which are also called gas turbines, work on the same principle. The engine sucks air in through the front with a fan.

Once inside, a compressor raises the pressure of the air. The compressor is made up of fans with many blades and attached to a shaft. Once the blades compress the air, the compressed air is then sprayed with fuel and an electric spark lights the mixture. The burning gases expand and blast out through the nozzle at the back of the engine. As the jets of gas shoot out, the engine and the aircraft are thrust forward. A jet engine operates on the application of Sir Isaac Newton's third law of physics.

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It states that for every action, there is an equal and opposite reaction. In aviation, this is called thrust. This law can be demonstrated in simple terms by releasing an inflated balloon and watching the escaping air propel the balloon in the opposite direction. In the basic turbojet engine, air enters the front intake, becomes compressed and is then forced into combustion chambers where fuel is sprayed into it and the mixture is ignited. Gases which form expand rapidly and are exhausted through the rear of the combustion chambers. These gases exert equal force in all directions, providing forward thrust as they escape to the rear. As the gases leave the engine, they pass through a fan-like set of blades (turbine) that rotates the turbine shaft.

This shaft, in turn, rotates the compressor and thereby bringing in a fresh supply of air through the intake. Engine thrust may be increased by the addition of an afterburner section in which extra fuel is sprayed into the exhausting gases which burn to give the added thrust. At approximately 400 mph, one pound of thrust equals one horsepower, but at higher speeds this ratio increases and a pound of thrust is greater than one horsepower. At speeds of less than 400 mph, this ratio decreases.

In one type of engine known as a, the exhaust gases are also used to rotate a propeller attached to the turbine shaft for increased fuel economy at lower altitudes. A is used to produce additional thrust and supplement the thrust generated by the basic turbojet engine for greater efficiency at high altitudes. The advantages of jet engines over piston engines include lighter weight to go with greater power, simpler construction and maintenance, fewer moving parts, efficient operation and cheaper fuel.

Jet engine airflow during take-off ( )A jet engine is a type of discharging a fast-moving that generates. While this broad definition can include, and hybrid propulsion, the term jet engine typically refers to an such as a,. In general, jet engines are combustion engines.Airbreathing jet engines typically feature a powered by a, with the leftover power providing thrust through the – this process is known as the. 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.

They give higher speed and greater fuel efficiency than piston and propeller over long distances. A few air-breathing engines made for high speed applications (ramjets and ) use the of the vehicle's speed instead of a mechanical compressor.The thrust of a typical engine went from 5,000 lbf (22,000 N) ( turbojet) in the 1950s to 115,000 lbf (510,000 N) ( 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 the late 1990s.

This, combined with greatly decreased fuel consumption, permitted routine by the turn of the century, where previously a similar journey would have required multiple fuel stops. See also:A rudimentary form of jet power dates back to the, a device described by in 1st-century. This device directed through two nozzles to cause a sphere to spin rapidly on its axis. It was seen as a curiosity.The first practical applications of appeared with the invention of the -powered by the Chinese in the 13th century. It was initially a type of, and gradually progressed to propel formidable. The principles used by the Chinese to send their rockets and fireworks was similar to that of a jet engine.In 1551, in invented a, driven by a, describing a method for rotating a spit by means of a jet of steam playing on rotary vanes around the periphery of a wheel.

It was the first practical steam jet device. A similar device was later described by in 1648.The earliest report of an attempted jet flight also dates back to the.

In 1633, the Ottoman soldier reportedly used a cone-shaped rocket.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, and the Japanese engine intended to power planes towards the end of were unsuccessful. 's -cannonball from 1915Even 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. If aircraft performance were to increase beyond such a barrier, a different propulsion mechanism was necessary. This 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, extracting power from the engine itself to drive the.

The was not a new idea: the patent for a stationary turbine was granted to in England in 1791. The first gas turbine to successfully run self-sustaining was built in 1903 by Norwegian engineer. 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. His engine was an axial-flow turbojet, but was never constructed, as it would have required considerable advances over the state of the art in compressors. Published An Aerodynamic Theory of Turbine Design in 1926 leading to experimental work at the.

The /700 engine flew in the, the first British aircraft to fly with a turbojet engine, and theIn 1928, cadet 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 a two-stage feeding a single-sided. Practical axial compressors were made possible by ideas from 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. The world's first aircraft to fly purely on turbojet powerIn 1935, started work on a similar design 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 was able to demonstrate the basic concept. Ohain was then introduced to, 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 were set up there as a new division of the Hirth company. They had their first centrifugal engine running by September 1937. Unlike Whittle's design, Ohain used as fuel, supplied under external pressure.

Their subsequent designs culminated in the -fuelled of 5 kN (1,100 lbf), which was fitted to Heinkel's simple and compact airframe and flown by in the early morning of August 27, 1939, from -Marienehe, 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 in May 31, 1939; patent number US2256198, with M Hahn referenced as inventor. A cutaway of the Junkers Jumo 004 engineof ' engine division ( Junkers Motoren or 'Jumo') introduced the in their jet engine.

Jumo was assigned the next engine number in the 109-0xx numbering sequence for gas turbine aircraft powerplants, '004', and the result was the engine. After many lesser technical difficulties were solved, mass production of this engine started in 1944 as a powerplant for the world's first jet-, the (and later the world's first jet- aircraft, the ). A variety of reasons conspired to delay the engine's availability, causing the fighter to arrive too late to improve Germany's position in, however this was the first jet engine to be used in service.

Gloster Meteor F.3s. The was the first British jet fighter and the only jet aircraft to achieve combat operations during World War II.Meanwhile, in Britain the had its maiden flight on 15 May 1941 and the finally entered service with the 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.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 and US jet fighters. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on have had some inspiration from this design.By 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. By the 1960s, all large civilian aircraft were also jet powered, leaving the in low-cost niche roles such as flights.The efficiency of turbojet engines was still rather worse than piston engines, but by the 1970s, with the advent of (an innovation not foreseen by the early commentators such as, at high speeds and high altitudes that seemed absurd to them), fuel efficiency was about the same as the best piston and propeller engines.

A turbofan jet engine installed on a aircraft.Jet engines power,. In the form of they power, and military.Jet engines have propelled high speed cars, particularly, with the all-time record held by a. A turbofan powered car, currently holds the.Jet engine designs are frequently modified for non-aircraft applications, as. 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 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 HP.Jet engines are also sometimes developed into, or share certain components such as engine cores, with and engines, which are forms of gas turbine engines that are typically used to power and some propeller-driven aircraft.Types of jet engine There are a large number of different types of jet engines, all of which achieve forward thrust from the principle of jet propulsion.Airbreathing. Turbojet engineA engine is a engine that works by compressing air with an inlet and a compressor (, or both), mixing fuel with the compressed air, burning the mixture in the, and then passing the hot, high pressure air through a and a. 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 kinetic energy in the exhaust, producing thrust. All the air ingested by the inlet is passed through the compressor, combustor, and turbine, unlike the engine described below.

Turbofan. Main article: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.Turbofans are usually more efficient than turbojets at subsonic speeds, but at high speeds their large frontal area generates more. Therefore, in supersonic flight, and in military and other aircraft where other considerations have a higher priority than fuel efficiency, fans tend to be smaller or absent.Because of these distinctions, turbofan engine designs are often categorized as or, depending upon the amount of air which bypasses the core of the engine. Low-bypass turbofans have a of around 2:1 or less.Ram compression.

Further information:Ram compression jet engines are airbreathing engines similar to gas turbine engines and they both follow the. Gas turbine and ram powered 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 through the inlet or diffuser.

A ram engine thus requires a substantial initial forward airspeed before it can function. Ram powered engines are considered the most simple type of air breathing jet engine because they can contain no moving parts.Ramjets are ram powered jet engines. They are mechanically simple, and operate less efficiently than turbojets except at very high speeds.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. Further information: Non-continuous combustion TypeDescriptionAdvantagesDisadvantagesWorks like a turbojet but instead of a turbine driving the compressor a drives it.Higher exhaust velocity than a propeller, offering better thrust at high speedHeavy, inefficient and underpowered. Example:.Air is compressed and combusted intermittently instead of continuously. Some designs use valves.Very simple design, used for the and more recently on model aircraftNoisy, inefficient (low compression ratio), works poorly on a large scale, valves on valved designs wear out quicklySimilar to a pulsejet, but combustion occurs as a instead of a, may or may not need valvesMaximum theoretical engine efficiencyExtremely noisy, parts subject to extreme mechanical fatigue, hard to start detonation, not practical for current useOther types of jet propulsion Rocket. A pump jet schematic. Main article:The propelling nozzle is the key component of all jet engines as it creates the exhaust. Propelling nozzles turn internal and pressure energy into high velocity kinetic energy.

The total pressure and temperature don't change through 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 1000K exhaust gas temperature for a supersonic afterburning engine or 2200K 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 a is often used on high-speed aircraft.The nozzle 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 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. Typical combustion stability limits of an aircraft gas turbine.The combustion efficiency of most aircraft gas turbine engines at sea level takeoff conditionsis almost 100%. It decreases nonlinearly to 98% at altitude cruise conditions. Air-fuel ratio ranges from 50:1 to 130:1. For any type of combustion chamber there is a rich and weak limit to the air-fuel ratio, beyond which the flame is extinguished. The range of air-fuel ratio between the rich and weak limits is reduced with an increase of air velocity.

If theincreasing air mass flow reduces the fuel ratio below certain value, flame extinction occurs. As a function of speed for different jet types with kerosene fuel (hydrogen I sp would be about twice as high). Although efficiency plummets with speed, greater distances are covered. Efficiency per unit distance (per km or mile) is roughly independent of speed for jet engines as a group; however, airframes become inefficient at supersonic speeds. Consumption of fuel or propellant A closely related (but different) concept to energy efficiency is the rate of consumption of propellant mass.

Propellant consumption in jet engines is measured by,. They all measure the same thing.

Specific impulse and effective exhaust velocity are strictly proportional, whereas specific fuel consumption is inversely proportional to the others.For airbreathing engines such as turbojets, energy efficiency and propellant (fuel) efficiency are much the same thing, since the propellant is a fuel and the source of energy. In rocketry, the propellant is also the exhaust, and this means that a high energy propellant gives better propellant efficiency but can in some cases actually give lower energy efficiency.It can be seen in the table (just below) that the subsonic turbofans such as General Electric's CF6 turbofan use a lot less fuel to generate thrust for a second than did the 's turbojet. However, since energy is force times distance and the distance per second was greater for the Concorde, the actual power generated by the engine for the same amount of fuel was higher for the Concorde at Mach 2 than the CF6. Thus, the Concorde's engines were more efficient in terms of energy per mile.Specific fuel consumption (SFC), specific impulse, and effective exhaust velocity numbers for various rocket and jet engines.Engine typeScenarioSpecificimpulse (s)(m/s)(lb/lbfh)(g/kNs)rocket engineVacuum3250rocket engineSpace shuttle vacuum7.40Mach 7800turbojetSR-71 at Mach 3.2 (Wet)1.00Reheat1.66–1.7347–40turbojetConcorde Mach 2 cruise (Dry)1.029500Dry0.74–0.8121–20CF6-80C2B1F turbofanBoeing 747-400 cruise0.058400turbofanSea level0.3015000Thrust-to-weight ratio. Main article:The thrust-to-weight ratio of jet engines with similar configurations varies with scale, but is mostly a function of engine construction technology. For a given engine, the lighter the engine, the better the thrust-to-weight is, the less fuel is used to compensate for drag due to the lift needed to carry the engine weight, or to accelerate the mass of the engine.As can be seen in the following table, rocket engines generally achieve much higher thrust-to-weight ratios than such as turbojet and turbofan engines. This is primarily because rockets almost universally use dense liquid or solid reaction mass which gives a much smaller volume and hence the pressurization system that supplies the nozzle is much smaller and lighter for the same performance.

Airbus A340-300 DisplayIn a jet engine, each major rotating section usually has a separate gauge devoted to monitoring its speed of rotation.Depending on the make and model, a jet engine may have an N 1 gauge that monitors the low-pressure compressor section and/or fan speed in turbofan engines. The gas generator section may be monitored by an N 2 gauge, while triple spool engines may have an N 3 gauge as well.

Each engine section rotates at many thousands RPM. Their gauges therefore are calibrated in percent of a nominal speed rather than actual RPM, for ease of display and interpretation. See also.References.