PowerPedia:Gas turbine

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A gas turbine, also called a combustion turbine, is a rotary engine that extracts energy from a flow of combustion gas. A Gas turbine may also refer to just the Turbine element.


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!Gas Turbine Timeline



1500: The 'Chimney Jack' was drawn by Leonardo da Vinci which was turning a roasting spit. Hot air from a fire rose through a series of fans which connect and turn the roasting spit.

1629: Jets of steam rotated a turbine that then rotated driven machinery allowed a stamping mill to be developed by Giovanni Branca.

1678: Ferdinand Verbeist built a model carriage relying on a steam jet for power.

1791: A basic turbine engine was patented with all the same elements as today's modern gas turbines. The turbine was designed to power a horseless carriage.

1872: The first true gas turbine engine was designed by Dr F. Stolze, but the engine never ran under its own power.

1897: A steam turbine for propelling a ship was patented by Sir Charles Parson. This principle of propulsion is still of some use.

1903: A Norwegian, Ægidius Elling, was able to build the first gas turbine that was able to produce more power than needed to run its own components, which was considered an achievement in a time when knowledge about aerodynamics was limited. Using rotary compressors and turbines it produced 11 hp(massive for those days). His work was later used by Sir Frank Whittle.

1914: The first application for a gas turbine engine was filed by Charles Curtis.

1918: One of the leading gas turbine manufacturers of today, General Electric, started their gas turbine division.

1920: The then current gas flow through passages was developed by Dr A. A. Griffith to a turbine theory with gas flow past airfoils.

1930: Sir Frank Whittle patented the design for a gas turbine for jet propulsion. His work on gas propulsion relied on the work from all those who had previously worked in the same field and he has himself stated that his invention would be hard to achieve without the works of Ægidius Elling. The first successful use of his engine was in April 1937.

1936: Hans von Ohain and Max Hahn in Germany developed their own patented engine design at the same time that Sir Frank Whittle was developing his design in England.


Gas turbines have an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. Energy is released when air is mixed with fuel and ignited in the combustor. A common mistake is that combustion increases the pressure of the gasses flowing through a turbine. In fact the heat addition stage of a gas turbine cycle incurs a slight pressure drop to facilitate flow through the engine. For all intents and purposes, however, the combustion process can be considered as occuring at constant pressure, with an increasing volume to accommodate the temperature rise, as explained by the ideal gas law. This in turn results in an increase in the velocity of the gas flow (see gas laws). This is directed over the turbine's blades, spinning the turbine and powering the compressor, and finally is passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks.

Operation theory

Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.

In practice, friction and turbulence cause:

#non-isentropic compression - for a given overall pressure ratio, the compressor delivery temperature is higher than ideal.

#non-isentropic expansion - although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work.

#pressure losses in the air intake, combustor and exhaust - reduces the expansion available to provide useful work.

As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (co-generation) uses waste heat for hot water production.

Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft/compressor/turbine/alternator-rotor assembly (see image above), not counting the fuel system. More sophisticated turbines (such as those found in modern jet engines) may have multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast system of complex piping, combustors and heat exchangers. As a general rule, the smaller the engine the faster the shaft(s) rotate to maintain tip speed jet engines operate around 10,000 rpm and micro turbines around 100,000 rpm. Thrust bearings and journal bearings are a critical part of design. Traditionally, they have been hydrodynamic oil bearings, or oil-cooled ball bearings. This is giving way to hydrodynamic foil bearings, which have become common place in micro turbines and APU's (auxiliary power units.)

Electrical gas turbines


The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated building. They can be particularly efficient — up to 60% — when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling or refrigeration. Simple cycle gas turbines in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for baseload plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40 % thermal efficiency.

Jet Engines

A Jet engine is an engine that discharges a fast moving jet of fluid to generate thrust in accordance with Newton's third law of motion. This broad definition of jet engines includes turbojets, turbofans, rockets and ramjets and water jets, but in common usage, the term generally refers to a gas turbine used to produce a jet of high speed exhaust gases for special propulsive purposes.


The components of a jet engine are standard across the different types of engines, although not all engine types have all components. The parts include:

Air Intake (Inlet):The standard reference frame for a jet engine is the aircraft itself. For subsonic aircraft, the air intake to a jet engine presents no special difficulties, and consists essentially of an opening which is designed to minimise drag, as with any other aircraft component. However, the air reaching the compressor of a normal jet engine must be travelling below the speed of sound, even for supersonic aircraft, to sustain the flow mechanics of the compressor and turbine blades. At supersonic flight speeds, shockwaves form in the intake system and reduce the recovered pressure at inlet to the compressor. So some supersonic intakes use devices, such as a cone or ramp, to increase pressure recovery, by making more efficient use of the shock wave system.

Compressor or Fan:The compressor is made up of stages. Each stage consists of vanes which rotate, and stators which remain stationary. As air is drawn deeper through the compressor, its heat and pressure increases. Energy is derived from the turbine (see below), passed along the shaft.

Shaft:This carries power from the turbine to the compressor, and runs most of the length of the engine. There may be as many as three concentric shafts, rotating at independent speeds, with as many sets of turbines and compressors. Other services, like a bleed of cool air, may also run down the shaft.

Combustor or Can or Flameholders or Combustion Chamber: This is a chamber where fuel is continuously burned in the compressed air.

Turbine: The turbine acts like a windmill, extracting energy from the hot gases leaving the combustor. This energy is used to drive the compressor through the shaft, or bypass fans, or props, or even (for a gas turbine-powered helicopter) converted entirely to rotational energy for use elsewhere. Relatively cool air, bled from the compressor, may be used to cool the turbine blades and vanes, to prevent them from melting.

Afterburner or reheat: Produces extra thrust by burning extra fuel, usually inefficiently, to significantly raise Nozzle Entry Temperature at the exhaust. Owing to a larger volume flow (i.e. lower density) at exit from the afterburner, an increased nozzle flow area is required, to maintain satisfactory engine matching, when the afterburner is alight.

Exhaust or Nozzle:Hot gases leaving the engine exhaust to atmospheric pressure via a nozzle, the objective being to produce a high velocity jet. In most cases, the nozzle is convergent and of fixed flow area.

Supersonic Nozzle:If the Nozzle Pressure Ratio (Nozzle Entry Pressure/Ambient Pressure) is very high, to maximize thrust it may be worthwhile, despite the additional weight, to fit a convergent-divergent (de Laval) nozzle. As the 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 portion. The expansion to atmospheric pressure and supersonic gas velocity continues downstream of the throat, whereas in a convergent nozzle the expansion beyond sonic velocity occurs externally, in the exhaust plume. The former process is more efficient.

Scale jet engines

Known as "Minature Gas Turbines" and "Micro-jets", model engineers relish the challenge of re-creating the grand engineering feats of today as tiny working models. Naturally, the idea of re-creating a powerful engine such as the jet, fascinated hobbyists since the very first full size engines were powered up by Hans von Ohain and Frank Whittle back in the 1930s. Re-creating machines such as engines to a different scale is not easy. The laws of physics governing the behaviour of many machines do not always scale up or down at the same rate as the machine's size (and often not even in a linear way), usually at best causing a dramatic loss of power or efficiency, and at worst causing them not to work at all. An automobile engine, for example, will not work if re-produced in the same shape as the size of a human hand. With this in mind the pioneer of modern Micro-Jets, Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67. This amazing little engine can give out 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe.

Micro turbines


Micro turbines (also known as Turbo alternators, Gensets, MicroTurbine® (registered trademark of Capstone Turbine Corporation), and Turbogenerator® (registered tradename of Honeywell Power Systems, Inc.)) are becoming wide spread for distributed power and combined heat and power applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts. Part of their success is due to advances in electronics, which allow unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows, for example, the generator to be integrated with the turbine shaft, and to double as the starter motor.

Micro turbine systems have many advantages over piston engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. However, piston engine generators are quicker to respond to changes in output power requirement. They accept most commercial fuels, such as natural gas, propane, diesel and kerosene. The are also able to produce renewable energy when fueled with biogas from landfills and sewage treatment plants.

Micro turbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy. Typical micro turbine efficiencies are 25 to 35 %. When in a combined heat and power cogeneration system, efficiencies of greater than 80 % are commonly achieved.

Auxiliary power units


Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, usually aircraft. They are well suited for supplying compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power. (These are not to be confused with the auxiliary propulsion units aboard the gas-turbine-powered Oliver Hazard Perry-class guided-missile frigates. The Perrys' APUs are large electric motors that provide maneuvering help in close waters, or emergency backup if the gas turbines are not working.)

The APU is a relatively small self-contained generator used in aircraft to start the main engines, usually with compressed air, and to provide electrical power, hydraulic pressure and air conditioning while the aircraft is on the ground. In many aircraft, the APU can also provide electrical power in the air. APU's are also fitted to some tanks to provide electrical power when stationary, without the high fuel consumption caused by running the main engine. A gasoline piston engine APU was first used on the Pemberton-Billing P.B.31 Night Hawk Scout aircraft in 1916. The Boeing 727 in 1963 was the first jetliner to feature a gas turbine APU, allowing it to operate at smaller, regional airports, independent from ground facilities. Although APUs have been installed in many locations on various military and commercial aircraft, they are usually mounted at the rear of modern jet airliners. The APU exhaust can be seen on most modern airliners as a small pipe exiting at the aircraft tail.

In most cases the APU is powered by a small gas turbine engine that provides compressed air from within or drives an air compressor (load compressor). Recent designs have started to explore the use of the Wankel engine in this role. The Wankel offers power-to-weight ratios better than normal piston engines and better fuel economy than a turbine. APUs fitted to ETOPS airplanes are more critical than others, as they supply backup electrical and compressed air in place of the dead engine during emergencies. While most APUs may or may not be startable while the aircraft is in flight, ETOPS compliant APUs must be flight-startable at all altitudes. Recent applications have specified starting up to 43,000ft from a complete cold-soak condition. If the APU or its electrical generator is not available, the airplane cannot be released for ETOPS flight and is forced to take a longer route.

APUs are even more critical for space shuttle flight operations. Unlike aircraft APU's, they provide hydraulic pressure, not electrical power. The space shuttle has three redundant APUs, powered by hydrazine fuel. They only function during powered ascent and during re-entry and landing. During powered ascent, the APUs provides hydraulic power for gimballing of shuttle's engines and control surfaces. During landing, they power the control surfaces and brakes. Landing can be accomplished with only one APU working. On STS-9, two of Columbia's APUs caught fire, but the flight still landed successfully.

A typical gas turbine APU for commercial transport aircraft comprises three main sections:

Power section

Load compressor


The power section is the gas generator portion of the engine and produces all the power for the APU. The load compressor is generally a shaftmounted compressor that provides all pneumatic power for the aircraft. There are two actuated devices, the inlet guide vanes that regulate airflow to the load compressor and the surge control valve that maintains stable or surgefree operation of the turbo machine. The third section of the engine is the gearbox. The gearbox transfers power from the main shaft of the engine to an oil?cooled generator for electrical power. Within the gearbox, power is also transferred to engine accessories such as the fuel control unit, the lube module, and cooling fan. In addition, there is also a starter motor connected through the gear train to perform the starting function of the APU. With the Boeing 787 all electric airplane, the APU delivers only electricity to the aircraft. The absence of pneumatic system simplifies the design, but the demand for hundreds of kW of electricity requires heavier generators and unique system requirements. Two main corporations compete in the aircraft APU market: United Technologies Corporation, through its subsidiaries Hamilton Sundstrand and Pratt & Whitney Canada, and Honeywell International Inc.

Vehicle gas turbines

Gas turbines are used on ships, locomotives, helicopters, and in tanks.

Ground vehicles

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A number of experiments have been conducted with gas turbine powered automobiles. In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km) and had a top speed of 142 mph (229 km/h). In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney gas turbine. Colin Chapman had a reputation of building radical championship-winning cars, but had to abandon the project because there were too many problems with turbo lag. The fictional Batmobile is often said to be powered by a gas turbine or a jet engine.

American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars. In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator. Gas turbines offer a high-powered engine in a very small and light package. However, they are not as responsive and efficient as small piston engines over the wide range of RPMs and powers needed in vehicle applications. Also, turbines have historically been more expensive to produce than piston engines, though this is partly because piston engines have been mass-produced in huge quantities for decades, while small turbines are rarities. It is also worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the responsiveness problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles.

The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a jet engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283kW (380shp). Speed-tested to 365km/h or 227mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000. Use of gas turbines in military tanks has been more successful. In the 1950s, a Conqueror heavy tank was experimentally fitted with a Parsons 650-hp gas turbine, and they have been used as auxiliary power units in several other production models. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See tank for more details. Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See Gas turbine-electric locomotive for more information.

Naval vehicles

Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961. The next series of major naval vessels were the four Canadian Iroquois class helicopter carrying destroyers first commissioned in 1972. They used 2 FT-4 main propulsion engines, 2 FT-12 cruise engines and 3 Solar Saturn 750 KW generators. The first U.S. gas-turbine powered ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines. Three Rolls-Royce gas turbines power the 118 WallyPower, a 118 foot super-yacht. These engines combine for a total of 16,800HP allowing this 118 foot boat to maintain speeds of 60 knots or 70mph. Another example of commercial usage of a gas turbine in a ship is the Stena Discovery, using the GE LM2500.

Amateur turbines

A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur.

Advances in technology

Gas turbine technology has steadily advanced since its inception and continues to evolve research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system.

On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power. An excellent example is the Capstone line of micro turbines, which do not require an oil system and can run unattended for months on end.

External articles and references

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A Practical Forum for the Gas Turbine End-User Community

Larrys Homemade gas turbine jet engines

Model Turbine Engine

MIT Gas Turbine Laboratory

MIT Microturbine research

First Marine Gas Turbine 1947

A history of Chrysler turbine cars

DIY Gas Turbines Yahoo Group

Armor-plated auxiliary power design of a modern gas turbine APU

Kurt Schreckling, Gas Turbine Engines for Model Aircraft, ISBN 0951058916

The Gas Turbine Builders Association,

There was an error working with the wiki: Code[1], Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

"Aircraft Gas Turbine Technology" by Irwin E. Treager, Professor Emeritus Purdue University, McGraw-Hill, Glencoe Division, 1979, ISBN 0-02-801828

Howstuffworks "How Gas Turbine Engines Work"