Category:United States Department of Defense agencies and Gas turbine: Difference between pages
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[[Image:GasTurbine.jpg|thumb|right|400px|This machine has a single-stage radial [[compressor]] and turbine, a [[recuperator]], and [[foil bearings]]. ]]
A '''gas turbine''' is a rotary [[engine]] that extracts energy from a flow of [[combustion]] gas. It has an upstream [[compressor]] coupled to a downstream [[turbine]], and a combustion chamber in-between. ('''Gas turbine''' may also refer to just the [[turbine]] element.)
[[Energy]] is added to the gas stream in the [[combustor]], where [[air]] is mixed with [[fuel]] and [[ignition system|ignited]]. Combustion increases the [[temperature]], [[velocity]] and [[volume]] of the gas flow. This is directed through a diffuser ([[nozzle]]) over the turbine's blades, spinning the turbine and powering the compressor.
Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power [[aircraft]], [[train]]s, [[ship]]s,[[generator]]s, and even [[tank]]s.
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==Theory of operation==
Gas turbines are described [[thermodynamics|thermodynamically]] by the [[Brayton cycle]], in which air is compressed [[isentropic]]ally, [[combustion]] occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.
In practise, friction and turbulence cause:
a) non-isentropic compression - for a given overall pressure ratio, the compressor delivery temperature is higher than ideal
b) 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.
a) a pressure loss in the combustor - reduces the expansion available to provide useful work.
[[Image:Brayton cycle.png]]
As with all cyclic [[heat engine]]s, 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. [[Recuperator]]s are [[heat exchanger]]s 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 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 engine]]s operate around 10,000 rpm and micro turbines around 100,000 rpm.
[[Thrust bearing]]s and [[plain bearing|journal bearings]] are a critical part of design. Traditionally, they have been [[Fluid_bearing|hydrodynamic oil bearings]], or oil-cooled [[Ball_bearing|ball bearings]]. This is giving way to hydrodynamic [[foil bearing]]s, which have become common place in micro turbines and APU’s (auxiliary power units.)
==[[Jet engine]]s==
See [[jet engine]] page.
== Gas turbines for electrical power production ==
[[Image:GE_H_series_Gas_Turbine.jpg|thumb|left|350px| GE H series power generation gas turbine. This 400-[[megawatt]] unit has a rated [[Thermodynamic_efficiency|thermal efficiency]] of 60% in [[combined cycle]] configurations.]]
Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems.
The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 [[rpm]] to match the [[alternating current|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 percent—when waste heat from the gas turbine is recovered by a conventional steam turbine in a [[combined cycle]] configuration.
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 percent [[Thermodynamic_efficiency|thermal efficiency]].
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==Micro turbines==
[[Image:Micro turbine.jpg|thumb|right|200px|A micro turbine designed for [[DARPA]] by M-Dot]]
Also known as:
*Turbo alternators
*Gensets
*MicroTurbine® (registered trademark of [[Capstone Turbine Corporation]])
*Turbogenerator® (registered tradename of [[Honeywell Power Systems]], Inc.)
'''Micro turbines''' are becoming wide spread for [[Distributed generation|distributed power]] and [[cogeneration|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 percent. When in a combined heat and power [[cogeneration]] system, efficiencies of greater than 80 percent are commonly achieved.
==Auxiliary power units==
[[Auxiliary power unit]]s (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 engine]]s, and electrical and hydraulic power. (These are not to be confused with the auxiliary propulsion units, also abbreviated APUs, 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.)
==Gas turbines in vehicles==
Gas turbines are used on [[ship]]s, [[locomotive]]s, [[helicopter]]s, and in [[tank]]s. A number of experiments have been conducted with gas turbine powered [[automobile]]s.
In 1950, designer F. R. Bell and Chief Engineer Maurice Wilks from British car manufacturers [[Rover (car)|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 (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). American car manufacturer [[Chrysler]] demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. [http://www.aardvark.co.nz/pjet/chrysler.shtml A history of Chrysler turbine 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 [[turboprop]]s for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly [[natural aspiration|naturally-aspirated]] ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important. Their use in hybrids reduces the second problem. Capstone currently lists on their website a version of their turbines designed for installation in hybrid vehicles.
Production gas turbine motorcycle first appeared in [[MTT Turbine SUPERBIKE]] in 2000. This high-priced machine is produced in miniscule numbers.
Use of gas turbines in military tanks has been more successful. In the 1950s, a [[Conqueror tank | Conqueror heavy tank]] was experimentally fitted with a [[Parsons]] 650-hp gas turbine, and they have been used as [[auxiliary power unit]]s in several other production models. Today, the Soviet/Russian [[T-80]] and U.S. [[M1 Abrams]] tanks use gas turbine engines. See [[Tank#Gas turbines |tank]] for more details.
===Naval use===
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 [[Tribal class frigate|Type 81 (Tribal class)]] [[frigate]]s, the first of which ([[HMS Ashanti (F117)|HMS ''Ashanti'']]) was commissioned in [[1961]].
The first U.S. gas-turbine powered ships were the [[United States Coast Guard|U.S. Coast Guard]]'s [[Hamilton class cutter|''Hamilton''-class]] [[USCG high endurance cutter|High Endurance Cutters]] the first of which ([[USCGC Hamilton (WHEC-715)|USCGC ''Hamilton'']]) commissioned in [[1967]]. Since then, they have powered the [[United States Navy|U.S. Navy]]'s [[Oliver Hazard Perry class frigate|''Perry''-class frigates]], [[Spruance class destroyer|''Spruance''-class]] and [[Arleigh Burke class destroyer|''Arleigh Burke''-class]] [[destroyer]]s, and [[Ticonderoga class cruiser|''Ticonderoga''-class guided missile cruisers]]. [[USS Makin Island (LHD-8)|USS ''Makin Island'']], a modified [[Wasp class amphibious assault ship|''Wasp''-class amphibious assault ship]], is to be the Navy's first [[amphibious assault ship|amphib]] powered by gas turbines.
==Amateur gas 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 amature. See external links for resources.
==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 bearing]]s 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.
==See also==
*[[turbine]]
*[[jet engine]]
*[[Brayton cycle]]
==Further reading==
* ''Gas Turbine Engines for Model Aircraft'' by [[Kurt Schreckling]], ISBN 0 9510589 1 6 Traplet Publications
==External links==
* [http://web.mit.edu/aeroastro/www/labs/GTL/gtl_about.html MIT Gas Turbine Laboratory]
* [http://www.memagazine.org/backissues/october97/features/turbdime/turbdime.html MIT Microturbine research]
* [http://www.sciencemuseum.org.uk/collections/treasures/margas.asp First Marine Gas Turbine 1947]
'''Amature groups and small manufacturers'''
* [http://groups.yahoo.com/group/DIYGasTurbines DIY Gas Turbines Yahoo Group]
* [http://www.power.alstom.com/home/equipment___systems/turbines/gas_turbines/7323.EN.php?languageId=EN&dir=/home/equipment___systems/turbines/gas_turbines/ ALSTOM Gas Turbines]
* [http://www.nyethermodynamics.com Nye Thermodynamics Corporation]
* [http://www.Innodyn.com Innodyn]
* [http://www.m-dot.com/page8.html M-Dot Microturbines]
'''Large turbine manufacturers'''
* [http://www.rolls-royce.com/energy/products/oilgas/gasturb.jsp Rolls-Royce Gas Turbines]
* [http://www.mpshq.com/products_gasturbines.htm Mitsubishi Gas Turbines]
* [http://www.gepower.com/prod_serv/products/gas_turbines_cc/en/index.htm GE Gas Turbines]
* [http://www.siemenswestinghouse.com/en/gasturbinesitem/index.cfm Siemens Gas Turbines]
* [http://www.microturbine.com/ Capstone Microturbines]
* [http://mysolar.cat.com/cda/layout Solar Turbines]
[[Category:Engines]]
[[Category:Turbines]]
[[Category:Gas turbines]]
[[Category:Marine propulsion]]
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