A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine.[1] The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the direction of flow:
- a rotating gas compressor
- a combustor
- a compressor-driving turbine.
Additional components have to be added to the gas generator to suit its application. Common to all is an air inlet but with different configurations to suit the requirements of marine use, land use or flight at speeds varying from stationary to supersonic. A propelling nozzle is added to produce thrust for flight. An extra turbine is added to drive a propeller (turboprop) or ducted fan (turbofan) to reduce fuel consumption (by increasing propulsive efficiency) at subsonic flight speeds. An extra turbine is also required to drive a helicopter rotor or land-vehicle transmission (turboshaft), marine propeller or electrical generator (power turbine). Greater thrust-to-weight ratio for flight is achieved with the addition of an afterburner.
The basic operation of the gas turbine is a Brayton cycle with air as the working fluid: atmospheric air flows through the compressor that brings it to higher pressure; energy is then added by spraying fuel into the air and igniting it so that the combustion generates a high-temperature flow; this high-temperature pressurized gas enters a turbine, producing a shaft work output in the process, used to drive the compressor; the unused energy comes out in the exhaust gases that can be repurposed for external work, such as directly producing thrust in a turbojet engine, or rotating a second, independent turbine (known as a power turbine) that can be connected to a fan, propeller, or electrical generator. The purpose of the gas turbine determines the design so that the most desirable split of energy between the thrust and the shaft work is achieved. The fourth step of the Brayton cycle (cooling of the working fluid) is omitted, as gas turbines are open systems that do not reuse the same air.
Gas turbines are used to power aircraft, trains, ships, electrical generators, pumps, gas compressors, and tanks.[2]
Timeline of development
This section needs additional citations for verification. (March 2023) |
- 50: Earliest records of Hero's engine (aeolipile). It most likely served no practical purpose, and was rather more of a curiosity; nonetheless, it demonstrated an important principle of physics that all modern turbine engines rely on.
- 1000: The "Trotting Horse Lamp" (Chinese: 走马灯, zŏumădēng) was used by the Chinese at lantern fairs as early as the Northern Song dynasty. When the lamp is lit, the heated airflow rises and drives an impeller with horse-riding figures attached on it, whose shadows are then projected onto the outer screen of the lantern.[3]
- 1500: The Smoke jack was drawn by Leonardo da Vinci: Hot air from a fire rises through a single-stage axial turbine rotor mounted in the exhaust duct of the fireplace and turns the roasting spit by gear-chain connection.
- 1629: Jets of steam rotated an impulse turbine that then drove a working stamping mill by means of a bevel gear, developed by Giovanni Branca.
- 1678: Ferdinand Verbiest built a model carriage relying on a steam jet for power.
- 1791: A patent was given to John Barber, an Englishman, for the first true gas turbine. His invention had most of the elements present in the modern day gas turbines. The turbine was designed to power a horseless carriage.[4][5]
- 1861: British patent no. 1633 was granted to Marc Antoine Francois Mennons for a "Caloric engine". The patent shows that it was a gas turbine and the drawings show it applied to a locomotive.[6]
- 1872: A gas turbine engine designed by Berlin engineer, Franz Stolze, is thought to be the first attempt at creating a working model, but the engine never ran under its own power.
- 1894: Sir Charles Parsons patented the idea of propelling a ship with a steam turbine, and built a demonstration vessel, the Turbinia, easily the fastest vessel afloat at the time. This principle of propulsion is still of some use.
- 1895: Three 4-ton 100 kW Parsons radial flow generators were installed in Cambridge Power Station, and used to power the first electric street lighting scheme in the city.
- 1899: Charles Gordon Curtis patented the first gas turbine engine in the US ("Apparatus for generating mechanical power", Patent No. US635,919).[7][8][9]
- 1900: Sanford Alexander Moss submitted a thesis on gas turbines. In 1903, Moss became an engineer for General Electric's Steam Turbine Department in Lynn, Massachusetts.[10] While there, he applied some of his concepts in the development of the turbosupercharger. His design used a small turbine wheel, driven by exhaust gases, to turn a supercharger.[10]
- 1903: A Norwegian, Ægidius Elling, built 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.[11]
- 1906: The Armengaud-Lemale turbine engine in France with a water-cooled combustion chamber.
- 1910: Holzwarth impulse turbine (pulse combustion) achieved 150 kW (200 hp).
- 1913: Nikola Tesla patents the Tesla turbine based on the boundary layer effect.[12]
- 1920s The practical theory of gas flow through passages was developed into the more formal (and applicable to turbines) theory of gas flow past airfoils by A. A. Griffith resulting in the publishing in 1926 of An Aerodynamic Theory of Turbine Design. Working testbed designs of axial turbines suitable for driving a propeller were developed by the Royal Aeronautical Establishment, thereby proving the efficiency of aerodynamic shaping of the blades in 1929.[citation needed]
- 1930: Having found no interest from the RAF for his idea, Frank Whittle patented[13] the design for a centrifugal gas turbine for jet propulsion. The first successful use of his engine occurred in England in April 1937.[14]
- 1932: BBC Brown, Boveri & Cie of Switzerland starts selling axial compressor and turbine turbosets as part of the turbocharged steam generating Velox boiler. Following the gas turbine principle, the steam evaporation tubes are arranged within the gas turbine combustion chamber; the first Velox plant was erected in Mondeville, Calvados, France.[15]
- 1934: Raúl Pateras de Pescara patented the free-piston engine as a gas generator for gas turbines.[16]
- 1936: Whittle with others backed by investment forms Power Jets Ltd[citation needed]
- 1937: Working proof-of-concept prototype jet engine runs in UK (Frank Whittle's) and Germany (Hans von Ohain's Heinkel HeS 1). Henry Tizard secures UK government funding for further development of Power Jets engine.[17]
- 1939: First 4 MW utility power generation gas turbine from BBC Brown, Boveri & Cie. for an emergency power station in Neuchâtel, Switzerland.[18]
- 1944: The Junkers Jumo 004 engine enters full production, powering the first German military jets such as the Messerschmitt Me 262. This marks the beginning of the reign of gas turbines in the sky.
- 1946: National Gas Turbine Establishment formed from Power Jets and the RAE turbine division to bring together Whittle and Hayne Constant's work.[19] In Beznau, Switzerland the first commercial reheated/recuperated unit generating 27 MW was commissioned.[20]
- 1947: A Metropolitan Vickers G1 (Gatric) becomes the first marine gas turbine when it completes sea trials on the Royal Navy's M.G.B 2009 vessel. The Gatric was an aeroderivative gas turbine based on the Metropolitan Vickers F2 jet engine.[21][22]
- 1995: Siemens becomes the first manufacturer of large electricity producing gas turbines to incorporate single crystal turbine blade technology into their production models, allowing higher operating temperatures and greater efficiency.[23]
- 2011 Mitsubishi Heavy Industries tests the first >60% efficiency combined cycle gas turbine (the M501J) at its Takasago, Hyōgo, works.[24][25]
Theory of operation
In an ideal gas turbine, gases undergo four thermodynamic processes: an isentropic compression, an isobaric (constant pressure) combustion, an isentropic expansion and heat rejection. Together, these make up the Brayton cycle.
In a real gas turbine, mechanical energy is changed irreversibly (due to internal friction and turbulence) into pressure and thermal energy when the gas is compressed (in either a centrifugal or axial compressor). Heat is added in the combustion chamber and the specific volume of the gas increases, accompanied by a slight loss in pressure. During expansion through the stator and rotor passages in the turbine, irreversible energy transformation once again occurs. Fresh air is taken in, in place of the heat rejection.
If the engine has a power turbine added to drive an industrial generator or a helicopter rotor, the exit pressure will be as close to the entry pressure as possible with only enough energy left to overcome the pressure losses in the exhaust ducting and expel the exhaust. For a turboprop engine there will be a particular balance between propeller power and jet thrust which gives the most economical operation. In a turbojet engine only enough pressure and energy is extracted from the flow to drive the compressor and other components. The remaining high-pressure gases are accelerated through a nozzle to provide a jet to propel an aircraft.
The smaller the engine, the higher the rotation rate of the shaft must be to attain the required blade tip speed. Blade-tip speed determines the maximum pressure ratios that can be obtained by the turbine and the compressor. This, in turn, limits the maximum power and efficiency that can be obtained by the engine. In order for tip speed to remain constant, if the diameter of a rotor is reduced by half, the rotational speed must double. For example, large jet engines operate around 10,000–25,000 rpm, while micro turbines spin as fast as 500,000 rpm.[26]
Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one main moving part, the compressor/shaft/turbine rotor assembly, with other moving parts in the fuel system. This, in turn, can translate into price. For instance, costing 10,000 ℛℳ for materials, the Jumo 004 proved cheaper than the Junkers 213 piston engine, which was 35,000 ℛℳ,[27] and needed only 375 hours of lower-skill labor to complete (including manufacture, assembly, and shipping), compared to 1,400 for the BMW 801.[28] This, however, also translated into poor efficiency and reliability. More advanced gas turbines (such as those found in modern jet engines or combined cycle power plants) may have 2 or 3 shafts (spools), hundreds of compressor and turbine blades, movable stator blades, and extensive external tubing for fuel, oil and air systems; they use temperature resistant alloys, and are made with tight specifications requiring precision manufacture. All this often makes the construction of a simple gas turbine more complicated than a piston engine.
Moreover, to reach optimum performance in modern gas turbine power plants the gas needs to be prepared to exact fuel specifications. Fuel gas conditioning systems treat the natural gas to reach the exact fuel specification prior to entering the turbine in terms of pressure, temperature, gas composition, and the related wobbe-index.
The primary advantage of a gas turbine engine is its power to weight ratio.[citation needed] Since significant useful work can be generated by a relatively lightweight engine, gas turbines are perfectly suited for aircraft propulsion.
Thrust bearings and journal bearings are a critical part of a design. They are hydrodynamic oil bearings or oil-cooled rolling-element bearings. Foil bearings are used in some small machines such as micro turbines[29] and also have strong potential for use in small gas turbines/auxiliary power units[30]
Creep
A major challenge facing turbine design, especially turbine blades, is reducing the creep that is induced by the high temperatures and stresses that are experienced during operation. Higher operating temperatures are continuously sought in order to increase efficiency, but come at the cost of higher creep rates. Several methods have therefore been employed in an attempt to achieve optimal performance while limiting creep, with the most successful ones being high performance coatings and single crystal superalloys.[31] These technologies work by limiting deformation that occurs by mechanisms that can be broadly classified as dislocation glide, dislocation climb and diffusional flow.
Protective coatings provide thermal insulation of the blade and offer oxidation and corrosion resistance. Thermal barrier coatings (TBCs) are often stabilized zirconium dioxide-based ceramics and oxidation/corrosion resistant coatings (bond coats) typically consist of aluminides or MCrAlY (where M is typically Fe and/or Cr) alloys. Using TBCs limits the temperature exposure of the superalloy substrate, thereby decreasing the diffusivity of the active species (typically vacancies) within the alloy and reducing dislocation and vacancy creep. It has been found that a coating of 1–200 μm can decrease blade temperatures by up to 200 °C (392 °F).[32] Bond coats are directly applied onto the surface of the substrate using pack carburization and serve the dual purpose of providing improved adherence for the TBC and oxidation resistance for the substrate. The Al from the bond coats forms Al2O3 on the TBC-bond coat interface which provides the oxidation resistance, but also results in the formation of an undesirable interdiffusion (ID) zone between itself and the substrate.[33] The oxidation resistance outweighs the drawbacks associated with the ID zone as it increases the lifetime of the blade and limits the efficiency losses caused by a buildup on the outside of the blades.[34]
Nickel-based superalloys boast improved strength and creep resistance due to their composition and resultant microstructure. The gamma (γ) FCC nickel is alloyed with aluminum and titanium in order to precipitate a uniform dispersion of the coherent Ni3(Al,Ti) gamma-prime (γ') phases. The finely dispersed γ' precipitates impede dislocation motion and introduce a threshold stress, increasing the stress required for the onset of creep. Furthermore, γ' is an ordered L12 phase that makes it harder for dislocations to shear past it.[35] Further Refractory elements such as rhenium and ruthenium can be added in solid solution to improve creep strength. The addition of these elements reduces the diffusion of the gamma prime phase, thus preserving the fatigue resistance, strength, and creep resistance.[36] The development of single crystal superalloys has led to significant improvements in creep resistance as well. Due to the lack of grain boundaries, single crystals eliminate Coble creep and consequently deform by fewer modes – decreasing the creep rate.[37] Although single crystals have lower creep at high temperatures, they have significantly lower yield stresses at room temperature where strength is determined by the Hall-Petch relationship. Care needs to be taken in order to optimize the design parameters to limit high temperature creep while not decreasing low temperature yield strength.
Types
Jet engines
Airbreathing jet engines are gas turbines optimized to produce thrust from the exhaust gases, or from ducted fans connected to the gas turbines.[38] Jet engines that produce thrust from the direct impulse of exhaust gases are often called turbojets, whereas those that generate thrust with the addition of a ducted fan are often called turbofans or (rarely) fan-jets.
Gas turbines are also used in many liquid fuel rockets, where gas turbines are used to power a turbopump to permit the use of lightweight, low-pressure tanks, reducing the empty weight of the rocket.
Turboprop engines
A turboprop engine is a turbine engine that drives an aircraft propeller using a reduction gear. Turboprop engines are used on small aircraft such as the general-aviation Cessna 208 Caravan and Embraer EMB 312 Tucano military trainer, medium-sized commuter aircraft such as the Bombardier Dash 8 and large aircraft such as the Airbus A400M transport and the 60-year-old Tupolev Tu-95 strategic bomber.
Aeroderivative gas turbines
Aeroderivative gas turbines are generally based on existing aircraft gas turbine engines, and are smaller and lighter than industrial gas turbines.[39]
Aeroderivatives are used in electrical power generation due to their ability to be shut down and handle load changes more quickly than industrial machines.[40] They are also used in the marine industry to reduce weight. Common types include the General Electric LM2500, General Electric LM6000, and aeroderivative versions of the Pratt & Whitney PW4000 and Rolls-Royce RB211.[39]
Amateur gas turbines
Increasing numbers of gas turbines are being used or even constructed by amateurs.
In its most straightforward form, these are commercial turbines acquired through military surplus or scrapyard sales, then operated for display as part of the hobby of engine collecting.[41][42] In its most extreme form, amateurs have even rebuilt engines beyond professional repair and then used them to compete for the land speed record.
The simplest form of self-constructed gas turbine employs an automotive turbocharger as the core component. A combustion chamber is fabricated and plumbed between the compressor and turbine sections.[43]
More sophisticated turbojets are also built, where their thrust and light weight are sufficient to power large model aircraft.[44] The Schreckling design[44] constructs the entire engine from raw materials, including the fabrication of a centrifugal compressor wheel from plywood, epoxy and wrapped carbon fibre strands.
Several small companies now manufacture small turbines and parts for the amateur. Most turbojet-powered model aircraft are now using these commercial and semi-commercial microturbines, rather than a Schreckling-like home-build.[45]
Auxiliary power units
Small gas turbines are used as auxiliary power units (APUs) to supply auxiliary power to larger, mobile, machines such as an aircraft. They supply:
- compressed air for air conditioning and ventilation,
- compressed air start-up power for larger jet engines,
- mechanical (shaft) power to a gearbox to drive shafted accessories, and
- electrical, hydraulic and other power-transmission sources to consuming devices remote from the APU.
Industrial gas turbines for power generation
Industrial gas turbines differ from aeronautical designs in that the frames, bearings, and blading are of heavier construction. They are also much more closely integrated with the devices they power—often an electric generator—and the secondary-energy equipment that is used to recover residual energy (largely heat).
They range in size from portable mobile plants to large, complex systems weighing more than a hundred tonnes housed in purpose-built buildings. When the gas turbine is used solely for shaft power, its thermal efficiency is about 30%. However, it may be cheaper to buy electricity than to generate it. Therefore, many engines are used in CHP (Combined Heat and Power) configurations that can be small enough to be integrated into portable container configurations.
Gas turbines can be particularly efficient when waste heat from the turbine is recovered by a heat recovery steam generator (HRSG) to power a conventional steam turbine in a combined cycle configuration.[46] The 605 MW General Electric 9HA achieved a 62.22% efficiency rate with temperatures as high as 1,540 °C (2,800 °F).[47] For 2018, GE offers its 826 MW HA at over 64% efficiency in combined cycle due to advances in additive manufacturing and combustion breakthroughs, up from 63.7% in 2017 orders and on track to achieve 65% by the early 2020s.[48] In March 2018, GE Power achieved a 63.08% gross efficiency for its 7HA turbine.[49]
Aeroderivative gas turbines can also be used in combined cycles, leading to a higher efficiency, but it will not be as high as a specifically designed industrial gas turbine. 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 the inlet air and increase the power output, technology known as turbine inlet air cooling.
Another significant advantage is their ability to be turned on and off within minutes, supplying power during peak, or unscheduled, demand. Since single cycle (gas turbine only) power plants are less efficient than combined cycle plants, they are usually used as peaking power plants, which operate anywhere from several hours per day to a few dozen hours per year—depending on the electricity demand and the generating capacity of the region. In areas with a shortage of base-load and load following power plant capacity or with low fuel costs, a gas turbine powerplant may regularly operate most hours of the day. A large single-cycle gas turbine typically produces 100 to 400 megawatts of electric power and has 35–40% thermodynamic efficiency.[50]
Industrial gas turbines for mechanical drive
Industrial gas turbines that are used solely for mechanical drive or used in collaboration with a recovery steam generator differ from power generating sets in that they are often smaller and feature a dual shaft design as opposed to a single shaft. The power range varies from 1 megawatt up to 50 megawatts.[citation needed] These engines are connected directly or via a gearbox to either a pump or compressor assembly. The majority of installations are used within the oil and gas industries. Mechanical drive applications increase efficiency by around 2%.
Oil and gas platforms require these engines to drive compressors to inject gas into the wells to force oil up via another bore, or to compress the gas for transportation. They are also often used to provide power for the platform. These platforms do not need to use the engine in collaboration with a CHP system due to getting the gas at an extremely reduced cost (often free from burn off gas). The same companies use pump sets to drive the fluids to land and across pipelines in various intervals.
Compressed air energy storage
One modern development seeks to improve efficiency in another way, by separating the compressor and the turbine with a compressed air store. In a conventional turbine, up to half the generated power is used driving the compressor. In a compressed air energy storage configuration, power, perhaps from a wind farm or bought on the open market at a time of low demand and low price, is used to drive the compressor, and the compressed air released to operate the turbine when required.
Turboshaft engines
Turboshaft engines are used to drive compressors in gas pumping stations and natural gas liquefaction plants. They are also used to power all but the smallest modern helicopters. A primary shaft carries the compressor and its turbine which, together with a combustor, is called a Gas Generator. A separately-spinning power-turbine is usually used to drive the rotor on helicopters. Allowing the gas generator and power turbine/rotor to spin at their own speeds allows more flexibility in their design.
Radial gas turbines
Scale jet engines
Also known as miniature gas turbines or micro-jets.
With this in mind the pioneer of modern Micro-Jets, Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67.[44] This engine can produce up to 22 newtons of thrust, and can be built by most mechanically minded people with basic engineering tools, such as a metal lathe.[44]
Microturbines
Evolved from piston engine turbochargers, aircraft APUs or small jet engines, microturbines are 25 to 500 kilowatt turbines the size of a refrigerator. Microturbines have around 15% efficiencies without a recuperator, 20 to 30% with one and they can reach 85% combined thermal-electrical efficiency in cogeneration.[51]
External combustion
Most gas turbines are internal combustion engines but it is also possible to manufacture an external combustion gas turbine which is, effectively, a turbine version of a hot air engine. Those systems are usually indicated as EFGT (Externally Fired Gas Turbine) or IFGT (Indirectly Fired Gas Turbine).
External combustion has been used for the purpose of using pulverized coal or finely ground biomass (such as sawdust) as a fuel. In the indirect system, a heat exchanger is used and only clean air with no combustion products travels through the power turbine. The thermal efficiency is lower in the indirect type of external combustion; however, the turbine blades are not subjected to combustion products and much lower quality (and therefore cheaper) fuels are able to be used.
When external combustion is used, it is possible to use exhaust air from the turbine as the primary combustion air. This effectively reduces global heat losses, although heat losses associated with the combustion exhaust remain inevitable.
Closed-cycle gas turbines based on helium or supercritical carbon dioxide also hold promise for use with future high temperature solar and nuclear power generation.
In surface vehicles
Gas turbines are often used on ships, locomotives, helicopters, tanks, and to a lesser extent, on cars, buses, and motorcycles.
A key advantage of jets and turboprops for airplane propulsion – their superior performance at high altitude compared to piston engines, particularly naturally aspirated ones – is irrelevant in most automobile applications. Their power-to-weight advantage, though less critical than for aircraft, is still important.
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. In series hybrid vehicles, as the driving electric motors are mechanically detached from the electricity generating engine, the responsiveness, poor performance at low speed and low efficiency at low output problems are much less important. The turbine can be run at optimum speed for its power output, and batteries and ultracapacitors can supply power as needed, with the engine cycled on and off to run it only at high efficiency. The emergence of the continuously variable transmission may also alleviate the responsiveness problem.
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 gas turbine engines are rarities; however, turbines are mass-produced in the closely related form of the turbocharger.
The turbocharger is basically a compact and simple free shaft radial gas turbine which is driven by the piston engine's exhaust gas. The centripetal turbine wheel drives a centrifugal compressor wheel through a common rotating shaft. This wheel supercharges the engine air intake to a degree that can be controlled by means of a wastegate or by dynamically modifying the turbine housing's geometry (as in a variable geometry turbocharger). It mainly serves as a power recovery device which converts a great deal of otherwise wasted thermal and kinetic energy into engine boost.
Turbo-compound engines (actually employed on some semi-trailer trucks) are fitted with blow down turbines which are similar in design and appearance to a turbocharger except for the turbine shaft being mechanically or hydraulically connected to the engine's crankshaft instead of to a centrifugal compressor, thus providing additional power instead of boost. While the turbocharger is a pressure turbine, a power recovery turbine is a velocity one.[citation needed]
Passenger road vehicles (cars, bikes, and buses)
A number of experiments have been conducted with gas turbine powered automobiles, the largest by Chrysler.[52][53] More recently, there has been some interest in the use of turbine engines for hybrid electric cars. For instance, a consortium led by micro gas turbine company Bladon Jets has secured investment from the Technology Strategy Board to develop an Ultra Lightweight Range Extender (ULRE) for next-generation electric vehicles. The objective of the consortium, which includes luxury car maker Jaguar Land Rover and leading electrical machine company SR Drives, is to produce the world's first commercially viable – and environmentally friendly – gas turbine generator designed specifically for automotive applications.[54]
The common turbocharger for gasoline or diesel engines is also a turbine derivative.
Concept cars
The first serious investigation of using a gas turbine in cars was in 1946 when two engineers, Robert Kafka and Robert Engerstein of Carney Associates, a New York engineering firm, came up with the concept where a unique compact turbine engine design would provide power for a rear wheel drive car. After an article appeared in Popular Science, there was no further work, beyond the paper stage.[55]
- Early concepts (1950s/60s)
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 (87 mph), at a turbine speed of 50,000 rpm. After being shown in the United Kingdom and the United States in 1950, JET1 was further developed, and was subjected to speed trials on the Jabbeke highway in Belgium in June 1952, where it exceeded 240 km/h (150 mph).[56] The car ran on petrol, paraffin (kerosene) or diesel oil, but fuel consumption problems proved insurmountable for a production car. JET1 is on display at the London Science Museum.
A French turbine-powered car, the SOCEMA-Grégoire, was displayed at the October 1952 Paris Auto Show. It was designed by the French engineer Jean-Albert Grégoire.[57]
The first turbine-powered car built in the US was the GM Firebird I which began evaluations in 1953. While photos of the Firebird I may suggest that the jet turbine's thrust propelled the car like an aircraft, the turbine actually drove the rear wheels. The Firebird I was never meant as a commercial passenger car and was built solely for testing & evaluation as well as public relation purposes.[58] Additional Firebird concept cars, each powered by gas turbines, were developed for the 1953, 1956 and 1959 Motorama auto shows. The GM Research gas turbine engine also was fitted to a series of transit buses, starting with the Turbo-Cruiser I of 1953.[59]
Starting in 1954 with a modified Plymouth,[60] the 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.[61] Each of their turbines employed a unique rotating recuperator, referred to as a regenerator that increased efficiency.[60]
In 1954 Fiat unveiled a concept car with a turbine engine, called Fiat Turbina. This vehicle, looking like an aircraft with wheels, used a unique combination of both jet thrust and the engine driving the wheels. Speeds of 282 km/h (175 mph) were claimed.[62]
In the 1960s, Ford and GM also were developing gas turbine semi-trucks. Ford displayed the Big Red at the 1964 World's Fair.[63] With the trailer, it was 29 m (96 ft) long, 4.0 m (13 ft) high, and painted crimson red. It contained the Ford-developed gas turbine engine, with output power and torque of 450 kW (600 hp) and 1,160 N⋅m (855 lb⋅ft). The cab boasted a highway map of the continental U.S., a mini-kitchen, bathroom, and a TV for the co-driver. The fate of the truck was unknown for several decades, but it was rediscovered in early 2021 in private hands, having been restored to running order.[64][65] The Chevrolet division of GM built the Turbo Titan series of concept trucks with turbine motors as analogs of the Firebird concepts, including Turbo Titan I (c. 1959, shares GT-304 engine with Firebird II), Turbo Titan II (c. 1962, shares GT-305 engine with Firebird III), and Turbo Titan III (1965, GT-309 engine); in addition, the GM Bison gas turbine truck was shown at the 1964 World's Fair.[66]
- Emissions and fuel economy (1970s/80s)
As a result of the U.S. Clean Air Act Amendments of 1970, research was funded into developing automotive gas turbine technology.[67] Design concepts and vehicles were conducted by Chrysler, General Motors, Ford (in collaboration with AiResearch), and American Motors (in conjunction with Williams Research).[68] Long-term tests were conducted to evaluate comparable cost efficiency.[69] Several AMC Hornets were powered by a small Williams regenerative gas turbine weighing 250 lb (113 kg) and producing 80 hp (60 kW; 81 PS) at 4450 rpm.[70][71][72]
In 1982, General Motors used an Oldsmobile Delta 88 powered by a gas turbine using pulverised coal dust. This was considered for the United States and the western world to reduce dependence on middle east oil at the time[73][74][75]
Toyota demonstrated several gas turbine powered concept cars, such as the Century gas turbine hybrid in 1975, the Sports 800 Gas Turbine Hybrid in 1979 and the GTV in 1985. No production vehicles were made. The GT24 engine was exhibited in 1977 without a vehicle.
- Later development
In the early 1990s, Volvo introduced the Volvo ECC which was a gas turbine powered hybrid electric vehicle.[76]
In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1 series hybrid. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator. In 2006, GM went into the EcoJet concept car project with Jay Leno.
At the 2010 Paris Motor Show Jaguar demonstrated its Jaguar C-X75 concept car. This electrically powered supercar has a top speed of 204 mph (328 km/h) and can go from 0 to 62 mph (0 to 100 km/h) in 3.4 seconds. It uses Lithium-ion batteries to power four electric motors which combine to produce 780 bhp. It will travel 68 miles (109 km) on a single charge of the batteries, and uses a pair of Bladon Micro Gas Turbines to re-charge the batteries extending the range to 560 miles (900 km).[77]
Racing cars
The first race car (in concept only) fitted with a turbine was in 1955 by a US Air Force group as a hobby project with a turbine loaned them by Boeing and a race car owned by Firestone Tire & Rubber company.[78] The first race car fitted with a turbine for the goal of actual racing was by Rover and the BRM Formula One team joined forces to produce the Rover-BRM, 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 (173.5 km/h) and had a top speed of 142 mph (229 km/h). American Ray Heppenstall joined Howmet Corporation and McKee Engineering together to develop their own gas turbine sports car in 1968, the Howmet TX, which ran several American and European events, including two wins, and also participated in the 1968 24 Hours of Le Mans. The cars used Continental gas turbines, which eventually set six FIA land speed records for turbine-powered cars.[79]
For open wheel racing, 1967's revolutionary STP-Paxton Turbocar fielded by racing and entrepreneurial legend Andy Granatelli and driven by Parnelli Jones nearly won the Indianapolis 500; the Pratt & Whitney ST6B-62 powered turbine car was almost a lap ahead of the second place car when a gearbox bearing failed just three laps from the finish line. The next year the STP Lotus 56 turbine car won the Indianapolis 500 pole position even though new rules restricted the air intake dramatically. In 1971 Team Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney STN 6/76 gas turbine. 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.
Buses
General Motors fitted the GT-30x series of gas turbines (branded "Whirlfire") to several prototype buses in the 1950s and 1960s, including Turbo-Cruiser I (1953, GT-300); Turbo-Cruiser II (1964, GT-309); Turbo-Cruiser III (1968, GT-309); RTX (1968, GT-309); and RTS 3T (1972).[80]
The arrival of the Capstone Turbine has led to several hybrid bus designs, starting with HEV-1 by AVS of Chattanooga, Tennessee in 1999, and closely followed by Ebus and ISE Research in California, and DesignLine Corporation in New Zealand (and later the United States). AVS turbine hybrids were plagued with reliability and quality control problems, resulting in liquidation of AVS in 2003. The most successful design by Designline is now operated in 5 cities in 6 countries, with over 30 buses in operation worldwide, and order for several hundred being delivered to Baltimore, and New York City.
Brescia Italy is using serial hybrid buses powered by microturbines on routes through the historical sections of the city.[81]
Motorcycles
The MTT Turbine Superbike appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a turbine engine – specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 283 kW (380 bhp). Speed-tested to 365 km/h or 227 mph (according to some stories, the testing team ran out of road during the test), it holds the Guinness World Record for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.
Trains
Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain.
Tanks
The Third Reich Wehrmacht Heer's development division, the Heereswaffenamt (Army Ordnance Board), studied a number of gas turbine engine designs for use in tanks starting in mid-1944. The first gas turbine engine design intended for use in armored fighting vehicle propulsion, the BMW 003-based GT 101, was meant for installation in the Panther tank.[82]
The second use of a gas turbine in an armored fighting vehicle was in 1954 when a unit, PU2979, specifically developed for tanks by C. A. Parsons and Company, was installed and trialed in a British Conqueror tank.[83] The Stridsvagn 103 was developed in the 1950s and was the first mass-produced main battle tank to use a turbine engine, the Boeing T50. Since then, gas turbine engines have been used as auxiliary power units in some tanks and as main powerplants in Soviet/Russian T-80s and U.S. M1 Abrams tanks, among others. They are lighter and smaller than diesel engines at the same sustained power output but the models installed to date are less fuel efficient than the equivalent diesel, especially at idle, requiring more fuel to achieve the same combat range. Successive models of M1 have addressed this problem with battery packs or secondary generators to power the tank's systems while stationary, saving fuel by reducing the need to idle the main turbine. T-80s can mount three large external fuel drums to extend their range. Russia has stopped production of the T-80 in favor of the diesel-powered T-90 (based on the T-72), while Ukraine has developed the diesel-powered T-80UD and T-84 with nearly the power of the gas-turbine tank. The French Leclerc tank's diesel powerplant features the "Hyperbar" hybrid supercharging system, where the engine's turbocharger is completely replaced with a small gas turbine which also works as an assisted diesel exhaust turbocharger, enabling engine RPM-independent boost level control and a higher peak boost pressure to be reached (than with ordinary turbochargers). This system allows a smaller displacement and lighter engine to be used as the tank's power plant and effectively removes turbo lag. This special gas turbine/turbocharger can also work independently from the main engine as an ordinary APU.
A turbine is theoretically more reliable and easier to maintain than a piston engine since it has a simpler construction with fewer moving parts, but in practice, turbine parts experience a higher wear rate due to their higher working speeds. The turbine blades are highly sensitive to dust and fine sand so that in desert operations air filters have to be fitted and changed several times daily. An improperly fitted filter, or a bullet or shell fragment that punctures the filter, can damage the engine. Piston engines (especially if turbocharged) also need well-maintained filters, but they are more resilient if the filter does fail.
Like most modern diesel engines used in tanks, gas turbines are usually multi-fuel engines.
Marine applications
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. Metropolitan-Vickers fitted their F2/3 jet engine with a power turbine. The Steam Gun Boat Grey Goose was converted to Rolls-Royce gas turbines in 1952 and operated as such from 1953.[84] The Bold class Fast Patrol Boats Bold Pioneer and Bold Pathfinder built in 1953 were the first ships created specifically for gas turbine propulsion.[85]
The first large-scale, partially gas-turbine powered ships were the Royal Navy's Type 81 (Tribal class) frigates with combined steam and gas powerplants. The first, HMS Ashanti was commissioned in 1961.
The German Navy launched the first Köln-class frigate in 1961 with 2 Brown, Boveri & Cie gas turbines in the world's first combined diesel and gas propulsion system.
The Soviet Navy commissioned in 1962 the first of 25 Kashin-class destroyer with 4 gas turbines in Combined gas and gas propulsion system. Those vessels used 4 M8E gas turbines, which generated 54,000–72,000 kW (72,000–96,000 hp). Those ships were the first large ships in the world to be powered solely by gas turbines.
The Danish Navy had 6 Søløven-class torpedo boats (the export version of the British Brave class fast patrol boat) in service from 1965 to 1990, which had 3 Bristol Proteus (later RR Proteus) Marine Gas Turbines rated at 9,510 kW (12,750 shp) combined, plus two General Motors Diesel engines, rated at 340 kW (460 shp), for better fuel economy at slower speeds.[86] And they also produced 10 Willemoes Class Torpedo / Guided Missile boats (in service from 1974 to 2000) which had 3 Rolls-Royce Marine Proteus Gas Turbines also rated at 9,510 kW (12,750 shp), same as the Søløven-class boats, and 2 General Motors Diesel Engines, rated at 600 kW (800 shp), also for improved fuel economy at slow speeds.[87]
The Swedish Navy produced 6 Spica-class torpedo boats between 1966 and 1967 powered by 3 Bristol Siddeley Proteus 1282 turbines, each delivering 3,210 kW (4,300 shp). They were later joined by 12 upgraded Norrköping class ships, still with the same engines. With their aft torpedo tubes replaced by antishipping missiles they served as missile boats until the last was retired in 2005.[88]
The Finnish Navy commissioned two Turunmaa-class corvettes, Turunmaa and Karjala, in 1968. They were equipped with one 16,410 kW (22,000 shp) Rolls-Royce Olympus TM1 gas turbine and three Wärtsilä marine diesels for slower speeds. They were the fastest vessels in the Finnish Navy; they regularly achieved speeds of 35 knots, and 37.3 knots during sea trials. The Turunmaas were decommissioned in 2002. Karjala is today a museum ship in Turku, and Turunmaa serves as a floating machine shop and training ship for Satakunta Polytechnical College.
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 ship was the U.S. Coast Guard's Point Thatcher, a cutter commissioned in 1961 that was powered by two 750 kW (1,000 shp) turbines utilizing controllable-pitch propellers.[89] The larger Hamilton-class High Endurance Cutters, was the first class of larger cutters to utilize gas turbines, the first of which (USCGC Hamilton) was commissioned in 1967. Since then, they have powered the U.S. Navy's Oliver Hazard Perry-class frigates, Spruance 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 amphibious assault ship powered by gas turbines. The marine gas turbine operates in a more corrosive atmosphere due to the presence of sea salt in air and fuel and use of cheaper fuels.
Civilian maritime
Up to the late 1940s, much of the progress on marine gas turbines all over the world took place in design offices and engine builder's workshops and development work was led by the British Royal Navy and other Navies. While interest in the gas turbine for marine purposes, both naval and mercantile, continued to increase, the lack of availability of the results of operating experience on early gas turbine projects limited the number of new ventures on seagoing commercial vessels being embarked upon.
In 1951, the Diesel-electric oil tanker Auris, 12,290 deadweight tonnage (DWT) was used to obtain operating experience with a main propulsion gas turbine under service conditions at sea and so became the first ocean-going merchant ship to be powered by a gas turbine. Built by Hawthorn Leslie at Hebburn-on-Tyne, UK, in accordance with plans and specifications drawn up by the Anglo-Saxon Petroleum Company and launched on the UK's Princess Elizabeth's 21st birthday in 1947, the ship was designed with an engine room layout that would allow for the experimental use of heavy fuel in one of its high-speed engines, as well as the future substitution of one of its diesel engines by a gas turbine.[90] The Auris operated commercially as a tanker for three-and-a-half years with a diesel-electric propulsion unit as originally commissioned, but in 1951 one of its four 824 kW (1,105 bhp) diesel engines – which were known as "Faith", "Hope", "Charity" and "Prudence" – was replaced by the world's first marine gas turbine engine, a 890 kW (1,200 bhp) open-cycle gas turbo-alternator built by British Thompson-Houston Company in Rugby. Following successful sea trials off the Northumbrian coast, the Auris set sail from Hebburn-on-Tyne in October 1951 bound for Port Arthur in the US and then Curacao in the southern Caribbean returning to Avonmouth after 44 days at sea, successfully completing her historic trans-Atlantic crossing. During this time at sea the gas turbine burnt diesel fuel and operated without an involuntary stop or mechanical difficulty of any kind. She subsequently visited Swansea, Hull, Rotterdam, Oslo and Southampton covering a total of 13,211 nautical miles. The Auris then had all of its power plants replaced with a 3,910 kW (5,250 shp) directly coupled gas turbine to become the first civilian ship to operate solely on gas turbine power.
Despite the success of this early experimental voyage the gas turbine did not replace the diesel engine as the propulsion plant for large merchant ships. At constant cruising speeds the diesel engine simply had no peer in the vital area of fuel economy. The gas turbine did have more success in Royal Navy ships and the other naval fleets of the world where sudden and rapid changes of speed are required by warships in action.[91]
The United States Maritime Commission were looking for options to update WWII Liberty ships, and heavy-duty gas turbines were one of those selected. In 1956 the John Sergeant was lengthened and equipped with a General Electric 4,900 kW (6,600 shp) HD gas turbine with exhaust-gas regeneration, reduction gearing and a variable-pitch propeller. It operated for 9,700 hours using residual fuel (Bunker C) for 7,000 hours. Fuel efficiency was on a par with steam propulsion at 0.318 kg/kW (0.523 lb/hp) per hour,[92] and power output was higher than expected at 5,603 kW (7,514 shp) due to the ambient temperature of the North Sea route being lower than the design temperature of the gas turbine. This gave the ship a speed capability of 18 knots, up from 11 knots with the original power plant, and well in excess of the 15 knot targeted. The ship made its first transatlantic crossing with an average speed of 16.8 knots, in spite of some rough weather along the way. Suitable Bunker C fuel was only available at limited ports because the quality of the fuel was of a critical nature. The fuel oil also had to be treated on board to reduce contaminants and this was a labor-intensive process that was not suitable for automation at the time. Ultimately, the variable-pitch propeller, which was of a new and untested design, ended the trial, as three consecutive annual inspections revealed stress-cracking. This did not reflect poorly on the marine-propulsion gas-turbine concept though, and the trial was a success overall. The success of this trial opened the way for more development by GE on the use of HD gas turbines for marine use with heavy fuels.[93] The John Sergeant was scrapped in 1972 at Portsmouth PA.
Boeing launched its first passenger-carrying waterjet-propelled hydrofoil Boeing 929, in April 1974. Those ships were powered by two Allison 501-KF gas turbines.[94]
Between 1971 and 1981, Seatrain Lines operated a scheduled container service between ports on the eastern seaboard of the United States and ports in northwest Europe across the North Atlantic with four container ships of 26,000 tonnes DWT. Those ships were powered by twin Pratt & Whitney gas turbines of the FT 4 series. The four ships in the class were named Euroliner, Eurofreighter, Asialiner and Asiafreighter. Following the dramatic Organization of the Petroleum Exporting Countries (OPEC) price increases of the mid-1970s, operations were constrained by rising fuel costs. Some modification of the engine systems on those ships was undertaken to permit the burning of a lower grade of fuel (i.e., marine diesel). Reduction of fuel costs was successful using a different untested fuel in a marine gas turbine but maintenance costs increased with the fuel change. After 1981 the ships were sold and refitted with, what at the time, was more economical diesel-fueled engines but the increased engine size reduced cargo space.[citation needed]
The first passenger ferry to use a gas turbine was the GTS Finnjet, built in 1977 and powered by two Pratt & Whitney FT 4C-1 DLF turbines, generating 55,000 kW (74,000 shp) and propelling the ship to a speed of 31 knots. However, the Finnjet also illustrated the shortcomings of gas turbine propulsion in commercial craft, as high fuel prices made operating her unprofitable. After four years of service, additional diesel engines were installed on the ship to reduce running costs during the off-season. The Finnjet was also the first ship with a Combined diesel-electric and gas propulsion. Another example of commercial use of gas turbines in a passenger ship is Stena Line's HSS class fastcraft ferries. HSS 1500-class Stena Explorer, Stena Voyager and Stena Discovery vessels use combined gas and gas setups of twin GE LM2500 plus GE LM1600 power for a total of 68,000 kW (91,000 shp). The slightly smaller HSS 900-class Stena Carisma, uses twin ABB–STAL GT35 turbines rated at 34,000 kW (46,000 shp) gross. The Stena Discovery was withdrawn from service in 2007, another victim of too high fuel costs.[citation needed]
In July 2000 the Millennium became the first cruise ship to be powered by both gas and steam turbines. The ship featured two General Electric LM2500 gas turbine generators whose exhaust heat was used to operate a steam turbine generator in a COGES (combined gas electric and steam) configuration. Propulsion was provided by two electrically driven Rolls-Royce Mermaid azimuth pods. The liner RMS Queen Mary 2 uses a combined diesel and gas configuration.[95]
In marine racing applications the 2010 C5000 Mystic catamaran Miss GEICO uses two Lycoming T-55 turbines for its power system.[citation needed]
Advances in technology
Gas turbine technology has steadily advanced since its inception and continues to evolve. Development is actively producing both smaller gas turbines and more powerful and efficient engines. Aiding in these advances are computer-based design (specifically computational fluid dynamics and finite element analysis) and the development of advanced materials: Base materials with superior high-temperature strength (e.g., single-crystal superalloys that exhibit yield strength anomaly) or thermal barrier coatings that protect the structural material from ever-higher temperatures. These advances allow higher compression ratios and turbine inlet temperatures, more efficient combustion and better cooling of engine parts.
Computational fluid dynamics (CFD) has contributed to substantial improvements in the performance and efficiency of gas turbine engine components through enhanced understanding of the complex viscous flow and heat transfer phenomena involved. For this reason, CFD is one of the key computational tools used in design and development of gas[96][97] turbine engines.
The simple-cycle efficiencies of early gas turbines were practically doubled by incorporating inter-cooling, regeneration (or recuperation), and reheating. These improvements, of course, come at the expense of increased initial and operation costs, and they cannot be justified unless the decrease in fuel costs offsets the increase in other costs. The relatively low fuel prices, the general desire in the industry to minimize installation costs, and the tremendous increase in the simple-cycle efficiency to about 40 percent left little desire for opting for these modifications.[98]
On the emissions side, the challenge is to increase turbine inlet temperatures while at the same time reducing peak flame temperature in order to achieve lower NOx emissions and meet the latest emission regulations. In May 2011, Mitsubishi Heavy Industries achieved a turbine inlet temperature of 1,600 °C on a 320 megawatt gas turbine, and 460 MW in gas turbine combined-cycle power generation applications in which gross thermal efficiency exceeds 60%.[99]
Compliant foil bearings were commercially introduced to gas turbines in the 1990s. These can withstand over a hundred thousand start/stop cycles and have eliminated the need for an oil system. The application of microelectronics and power switching technology have enabled the development of commercially viable electricity generation by microturbines for distribution and vehicle propulsion.
Advantages and disadvantages
This section contains a pro and con list, which is sometimes inappropriate. (June 2022) |
The following are advantages and disadvantages of gas-turbine engines:[100]
Advantages include:
- Very high power-to-weight ratio compared to reciprocating engines.
- Smaller than most reciprocating engines of the same power rating.
- Smooth rotation of the main shaft produces far less vibration than a reciprocating engine.
- Fewer moving parts than reciprocating engines results in lower maintenance cost and higher reliability/availability over its service life.
- Greater reliability, particularly in applications where sustained high power output is required.
- Waste heat is dissipated almost entirely in the exhaust. This results in a high-temperature exhaust stream that is very usable for boiling water in a combined cycle, or for cogeneration.
- Lower peak combustion pressures than reciprocating engines in general.
- High shaft speeds in smaller "free turbine units", although larger gas turbines employed in power generation operate at synchronous speeds.
- Low lubricating oil cost and consumption.
- Can run on a wide variety of fuels.
- Very low toxic emissions of CO and HC due to excess air, complete combustion and no "quench" of the flame on cold surfaces.
Disadvantages include:
- Core engine costs can be high due to use of exotic materials.
- Less efficient than reciprocating engines at idle speed.
- Longer startup than reciprocating engines.
- Less responsive to changes in power demand compared with reciprocating engines.
- Characteristic whine can be hard to suppress.
Major manufacturers
- Siemens
- Ansaldo
- Mitsubishi Heavy
- Rolls-Royce
- General Electric
- Silmash
- ODK
- Pratt & Whitney
- P&W Canada
- Solar Turbines
- Alstom
- Zorya-Mashproekt
- MTU Aero Engines
- MAN Turbo
- IHI Corporation
- Kawasaki Heavy
- HAL
- BHEL
- MAPNA
- Techwin
- Doosan Heavy
- Shanghai Electric
- Harbin Electric
- AECC
Testing
British, German, other national and international test codes are used to standardize the procedures and definitions used to test gas turbines. Selection of the test code to be used is an agreement between the purchaser and the manufacturer, and has some significance to the design of the turbine and associated systems. In the United States, ASME has produced several performance test codes on gas turbines. This includes ASME PTC 22–2014. These ASME performance test codes have gained international recognition and acceptance for testing gas turbines. The single most important and differentiating characteristic of ASME performance test codes, including PTC 22, is that the test uncertainty of the measurement indicates the quality of the test and is not to be used as a commercial tolerance.
See also
- List of aircraft engines
- Centrifugal compressor
- Gas turbine modular helium reactor
- Pneumatic motor
- Pulsejet
- Steam turbine
- Turbine engine failure
- Wind turbine
References
'For trotting horse lamp, make paper-cut as wheel-like objects and the candle will heat the air which will rise and push the paper-cut to move, and the shadows of paper-cut will be cast by the candle light on the screen.' ...Judgment from the records of the Song dynasty shows that invention of China's trotting horse lamp was not later than 1000 AD. ...Obviously, the trotting horse lamp has already had the rudiment of a gas turbine.
- Brain, Marshall (1 April 2000). "How Gas Turbine Engines Work". Science.howstuffworks.com. Retrieved 13 March 2016.
Further reading
- Stationary Combustion Gas Turbines including Oil & Over-Speed Control System description
- "Aircraft Gas Turbine Technology" by Irwin E. Treager, McGraw-Hill, Glencoe Division, 1979, ISBN 0-07-065158-2.
- "Gas Turbine Theory" by H.I.H. Saravanamuttoo, G.F.C. Rogers and H. Cohen, Pearson Education, 2001, 5th ed., ISBN 0-13-015847-X.
- Leyes II, Richard A.; Fleming, William A. (1999). The History of North American Small Gas Turbine Aircraft Engines. Washington, DC: Smithsonian Institution. ISBN 978-1-56347-332-6.
- R. M. "Fred" Klaass and Christopher DellaCorte, "The Quest for Oil-Free Gas Turbine Engines," SAE Technical Papers, No. 2006-01-3055, available at sae.org
- "Model Jet Engines" by Thomas Kamps ISBN 0-9510589-9-1 Traplet Publications
- Aircraft Engines and Gas Turbines, Second Edition by Jack L. Kerrebrock, The MIT Press, 1992, ISBN 0-262-11162-4.
- "Forensic Investigation of a Gas Turbine Event" by John Molloy, M&M Engineering
- "Gas Turbine Performance, 2nd Edition" by Philip Walsh and Paul Fletcher, Wiley-Blackwell, 2004 ISBN 978-0-632-06434-2
- Advanced Technologies for Gas Turbines (Report). Washington, DC: The National Academies Press. 2020. doi:10.17226/25630. ISBN 978-0-309-66422-6.
External links
- Gas turbine at Curlie
- Armagnac, Alden P. (December 1939). "New Era In Power To Turn Wheels". Popular Science. p. 81.
- Technology Speed of Civil Jet Engines
- MIT Gas Turbine Laboratory Archived 21 July 2010 at the Wayback Machine
- MIT Microturbine research
- California Distributed Energy Resource guide – Microturbine generators
- Introduction to how a gas turbine works from "how stuff works.com" Archived 16 June 2008 at the Wayback Machine
- Aircraft gas turbine simulator for interactive learning
- An online handbook on stationary gas turbine technologies compiled by the US DOE. Archived 1 July 2017 at the Wayback Machine
https://en.wikipedia.org/wiki/Gas_turbine
Centrifugal compressors, sometimes called impeller compressors or radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.[1]
They achieve pressure rise by adding energy to the continuous flow of fluid through the rotor/impeller. The equation in the next section shows this specific energy input. A substantial portion of this energy is kinetic which is converted to increased potential energy/static pressure by slowing the flow through a diffuser. The static pressure rise in the impeller may roughly equal the rise in the diffuser.
Components of a simple centrifugal compressor
A simple centrifugal compressor stage has four components (listed in order of throughflow): inlet, impeller/rotor, diffuser, and collector.[1] Figure 1.1 shows each of the components of the flow path, with the flow (working gas) entering the centrifugal impeller axially from left to right. This turboshaft (or turboprop) impeller is rotating counter-clockwise when looking downstream into the compressor. The flow will pass through the compressors from left to right.
Inlet
The simplest inlet to a centrifugal compressor is typically a simple pipe. Depending upon its use/application inlets can be very complex. They may include other components such as an inlet throttle valve, a shrouded port, an annular duct (see Figure 1.1), a bifurcated duct, stationary guide vanes/airfoils used to straight or swirl flow (see Figure 1.1), movable guide vanes (used to vary pre-swirl adjustably). Compressor inlets often include instrumentation to measure pressure and temperature in order to control compressor performance.
Bernoulli's fluid dynamic principle plays an important role in understanding vaneless stationary components like an inlet. In engineering situations assuming adiatice flow, this equation can be written in the form:
Equation-1.1
where:
- 0 is the inlet of the compressor, station 0
- 1 is the inlet of the impeller, station 1
- p is the pressure
- ρ is the density and indicates that it is a function of pressure
- is the flow speed
- γ is the ratio of the specific heats of the fluid
Centrifugal impeller
The identifying component of a centrifugal compressor stage is the centrifugal impeller rotor. Impellers are designed in many configurations including "open" (visible blades), "covered or shrouded", "with splitters" (every other inducer removed), and "w/o splitters" (all full blades). Figures 0.1, 1.2.1, and 1.3 show three different open full inducer rotors with alternating full blades/vanes and shorter length splitter blades/vanes. Generally, the accepted mathematical nomenclature refers to the leading edge of the impeller with subscript 1. Correspondingly, the trailing edge of the impeller is referred to as subscript 2.
As working-gas/flow passes through the impeller from stations 1 to 2, the kinetic and potential energy increase. This is identical to an axial compressor with the exception that the gases can reach higher energy levels through the impeller's increasing radius. In many modern high-efficiency centrifugal compressors the gas exiting the impeller is traveling near the speed of sound.
Most modern high-efficiency impellers use "backsweep" in the blade shape.[2][3][4]
A derivation of the general Euler equations (fluid dynamics) is Euler's pump and turbine equation, which plays an important role in understanding impeller performance. This equation can be written in the form:
Equation-1.2 (see Figures 1.2.2 and 1.2.3 illustrating impeller velocity triangles)
where:
- 1 subscript 1 is the impeller leading edge (inlet), station 1
- 2 subscript 2 is the impeller trailing edge (discharge), station 2
- E is the energy added to the fluid
- g is the acceleration due to gravity
- u is the impeller's circumferencal velocity, units velocity
- w is the velocity of flow relative to the impeller, units velocity
- c is the absolute velocity of flow relative to stationary, units velocity
Diffuser
The next component, downstream of the impeller within a simple centrifugal compressor may the diffuser. [5] [4] The diffuser converts the flow's kinetic energy (high velocity) into increased potential energy (static pressure) by gradually slowing (diffusing) the gas velocity. Diffusers can be vaneless, vaned, or an alternating combination. High-efficiency vaned diffusers are also designed over a wide range of solidities from less than 1 to over 4. Hybrid versions of vaned diffusers include wedge (see Figure 1.3), channel, and pipe diffusers. Some turbochargers have no diffuser. Generally accepted nomenclature might refer to the diffuser's lead edge as station 3 and the trailing edge as station 4.
Bernoulli's fluid dynamic principle plays an important role in understanding diffuser performance. In engineering situations assuming adiatice flow, this equation can be written in the form:
Equation-1.3
where:
- 2 is the inlet of the diffuser, station 2
- 4 is the discharge of the diffuser, station 4
- (see inlet above.)
Collector
The collector of a centrifugal compressor can take many shapes and forms. [5] [4] When the diffuser discharges into a large empty circumferentially (constant area) chamber, the collector may be termed a Plenum. When the diffuser discharges into a device that looks somewhat like a snail shell, bull's horn, or a French horn, the collector is likely to be termed a volute or scroll.
When the diffuser discharges into an annular bend the collector may be referred to as a combustor inlet (as used in jet engines or gas turbines) or a return-channel (as used in an online multi-stage compressor). As the name implies, a collector's purpose is to gather the flow from the diffuser discharge annulus and deliver this flow downstream into whatever component the application requires. The collector or discharge pipe may also contain valves and instrumentation to control the compressor. In some applications, collectors will diffuse flow (converting kinetic energy to static pressure) far less efficiently than a diffuser.[6]
Bernoulli's fluid dynamic principle plays an important role in understanding diffuser performance. In engineering situations assuming adiatice flow, this equation can be written in the form:
Equation-1.4
where:
- 4 is the inlet of the diffuser, station 4
- 5 is the discharge of the diffuser, station 5
- (see inlet above.)
Historical contributions, the pioneers
Over the past 100 years, applied scientists including Stodola (1903, 1927–1945),[7] Pfleiderer (1952),[8] Hawthorne (1964),[9] Shepherd (1956),[1] Lakshminarayana (1996),[10] and Japikse (many texts including citations),[2][11][citation needed][12] have educated young engineers in the fundamentals of turbomachinery. These understandings apply to all dynamic, continuous-flow, axisymmetric pumps, fans, blowers, and compressors in axial, mixed-flow and radial/centrifugal configurations.
This relationship is the reason advances in turbines and axial compressors often find their way into other turbomachinery including centrifugal compressors. Figures 1.1 and 1.2 illustrate the domain of turbomachinery with labels showing centrifugal compressors.[13][14] Improvements in centrifugal compressors have not been achieved through large discoveries. Rather, improvements have been achieved through understanding and applying incremental pieces of knowledge discovered by many individuals.
Aerodynamic-thermodynamic domain
Figure 2.1 (shown right) represents the aero-thermo domain of turbomachinery. The horizontal axis represents the energy equation derivable from The first law of thermodynamics.[1][14] The vertical axis, which can be characterized by Mach Number, represents the range of fluid compressibility (or elasticity).[1][14] The Z-axis, which can be characterized by Reynolds number, represents the range of fluid viscosities (or stickiness).[14] Mathematicians and physicists who established the foundations of this aero-thermo domain include:[15][16] Isaac Newton, Daniel Bernoulli, Leonhard Euler, Claude-Louis Navier, George Stokes, Ernst Mach, Nikolay Yegorovich Zhukovsky, Martin Kutta, Ludwig Prandtl, Theodore von Kármán, Paul Richard Heinrich Blasius, and Henri Coandă.
Physical-mechanical domain
Figure 2.2 (shown right) represents the physical or mechanical domain of turbomachinery. Again, the horizontal axis represents the energy equation with turbines generating power to the left and compressors absorbing power to the right.[1][14] Within the physical domain the vertical axis differentiates between high speeds and low speeds depending upon the turbomachinery application.[1][14] The Z-axis differentiates between axial-flow geometry and radial-flow geometry within the physical domain of turbomachinery.[1][14] It is implied that mixed-flow turbomachinery lie between axial and radial.[1][14] Key contributors of technical achievements that pushed the practical application of turbomachinery forward include:[15][16] Denis Papin,[17] Kernelien Le Demour, Daniel Gabriel Fahrenheit, John Smeaton, Dr. A. C. E. Rateau,[18] John Barber, Alexander Sablukov, Sir Charles Algernon Parsons, Ægidius Elling, Sanford Alexander Moss, Willis Carrier, Adolf Busemann, Hermann Schlichting, Frank Whittle and Hans von Ohain.
Partial timeline of historical contributions
<1689 | Early turbomachines | Pumps, blowers, fans |
1689 | Denis Papin | Origin of the centrifugal compressor |
1754 | Leonhard Euler | Euler's "Pump & Turbine" equation |
1791 | John Barber | First gas turbine patent |
1899 | A. C. E. Rateau | First practical centrifugal compressor |
1927 | Aurel Boleslav Stodola | Formalized "slip factor" |
1928 | Adolf Busemann | Derived "slip factor" |
1937 | Frank Whittle and Hans von Ohain, independently | First gas turbine using a centrifugal compressor |
>1970 | Modern turbomachines | 3D-CFD, rocket turbo-pumps, heart assist pumps, turbocharged fuel cells |
Turbomachinery similarities
Centrifugal compressors are similar in many ways to other turbomachinery and are compared and contrasted as follows:
Similarities to axial compressor
Centrifugal compressors are similar to axial compressors in that they are rotating airfoil-based compressors. Both are shown in the adjacent photograph of an engine with 5 stages of axial compressors and one stage of a centrifugal compressor.[10][citation needed] The first part of the centrifugal impeller looks very similar to an axial compressor. This first part of the centrifugal impeller is also termed an inducer. Centrifugal compressors differ from axials as they use a significant change in radius from inlet to exit of the impeller to produce a much greater pressure rise in a single stage (e.g. 8[19] in the Pratt & Whitney Canada PW200 series of helicopter engines) than does an axial stage. The 1940s-era German Heinkel HeS 011 experimental engine was the first aviation turbojet to have a compressor stage with radial flow-turning part-way between none for an axial and 90 degrees for a centrifugal. It is known as a mixed/diagonal-flow compressor. A diagonal stage is used in the Pratt & Whitney Canada PW600 series of small turbofans.
Centrifugal fan
Centrifugal compressors are also similar to centrifugal fans of the style shown in the neighboring figure as they both increase the energy of the flow through the increasing radius.[1] In contrast to centrifugal fans, compressors operate at higher speeds to generate greater pressure rises. In many cases, the engineering methods used to design a centrifugal fan are the same as those to design a centrifugal compressor, so they can look very similar.
For purposes of generalization and definition, it can be said that centrifugal compressors often have density increases greater than 5 percent. Also, they often experience relative fluid velocities above Mach number 0.3[20] when the working fluid is air or nitrogen. In contrast, fans or blowers are often considered to have density increases of less than five percent and peak relative fluid velocities below Mach 0.3.
Squirrel-Cage fan
Squirrel-Cage fans are primarily used for ventilation. The flow field within this type of fan has internal recirculations. In comparison, a centrifugal fan is uniform circumferentially.
Centrifugal pump
Centrifugal compressors are also similar to centrifugal pumps[1] of the style shown in the adjacent figures. The key difference between such compressors and pumps is that the compressor working fluid is a gas (compressible) and the pump working fluid is liquid (incompressible). Again, the engineering methods used to design a centrifugal pump are the same as those to design a centrifugal compressor. Yet, there is one important difference: the need to deal with cavitation in pumps.
Radial turbine
Centrifugal compressors also look very similar to their turbomachinery counterpart the radial turbine as shown in the figure. While a compressor transfers energy into a flow to raise its pressure, a turbine operates in reverse, by extracting energy from a flow, thus reducing its pressure.[citation needed] In other words, power is input to compressors and output from turbines.
Turbomachinery using centrifugal compressors
Standards
As turbomachinery became more common, standards have been created to guide manufacturers to assure end-users that their products meet minimum safety and performance requirements. Associations formed to codify these standards rely on manufacturers, end-users, and related technical specialists. A partial list of these associations and their standards are listed below:
- American Society of Mechanical Engineers:BPVC, PTC.[21][22]
- American Petroleum Institute: API STD 617 8TH ED (E1), API STD 672 5TH ED (2019).[23][24]
- American Society of Heating, Refrigeration, and Airconditioning Engineers: Handbook Fundamentals.[25]
- Society of Automotive Engineers[26]
- Compressed Air and Gas Institute[27]
- International Organization for StandardizationISO 10439, ISO 10442, ISO 18740, ISO 6368, ISO 5389[28]
Applications
Below, is a partial list of centrifugal compressor applications each with a brief description of some of the general characteristics possessed by those compressors. To start this list two of the most well-known centrifugal compressor applications are listed; gas turbines and turbochargers.[10]
- In gas turbines and auxiliary power units.[29] Ref. Figures 4.1–4.2 In their simple form, modern gas turbines operate on the Brayton cycle. (ref Figure 5.1) Either or both axial and centrifugal compressors are used to provide compression. The types of gas turbines that most often include centrifugal compressors include small aircraft engines (i.e. turboshafts, turboprops, and turbofans), auxiliary power units, and micro-turbines. The industry standards applied to all centrifugal compressors used in aircraft applications are set by the relevant civilian and military certification authorities to achieve the safety and durability required in service. Centrifugal impellers used in gas turbines are commonly made from titanium alloy forgings. Their flow-path blades are commonly flank milled or point milled on 5-axis milling machines. When running clearances have to be as small as possible without the impeller rubbing its shroud the impeller is first drawn with its high-temperature, high-speed deflected shape and then drawn in its equivalent cold static shape for manufacturing. This is necessary because the impeller deflections at the most severe running condition can be 100 times larger than the required hot running clearance between the impeller and its shroud.
- In automotive engine and diesel engine turbochargers and superchargers.[30] Ref. Figure 1.1 Centrifugal compressors used in conjunction with reciprocating internal combustion engines are known as turbochargers if driven by the engine's exhaust gas and turbo-superchargers if mechanically driven by the engine. Standards set by the industry for turbochargers may have been established by SAE.[26] Ideal gas properties often work well for the design, test and analysis of turbocharger centrifugal compressor performance.
- In pipeline compressors of natural gas to move the gas from the production site to the consumer.[31] Centrifugal compressors for such uses may be one- or multi-stage and driven by large gas turbines. Standards set by the industry (ANSI/API, ASME) result in thick casings to achieve a required level of safety. The impellers are often if not always of the covered style which makes them look much like pump impellers. This type of compressor is also often termed an API-style. The power needed to drive these compressors is most often in the thousands of horsepower (HP). The use of real gas properties is needed to properly design, test, and analyze the performance of natural gas pipeline centrifugal compressors.
- In oil refineries, natural-gas processing, petrochemical and chemical plants.[31] Centrifugal compressors for such uses are often one-shaft multi-stage and driven by large steam or gas turbines. Their casings are termed horizontally split if the rotor is lowered into the bottom half during assembly or barrel if it has no lengthwise split-line with the rotor being slid in. Standards set by the industry (ANSI/API, ASME) for these compressors result in thick casings to achieve a required level of safety. The impellers are often of the covered style which makes them look much like pump impellers. This type of compressor is also often termed API-style. The power needed to drive these compressors is usually in the thousands of HP. Use of real gas properties is needed to properly design, test and analyze their performance.
- Air-conditioning and refrigeration and HVAC: Centrifugal compressors quite often supply the compression in water chillers cycles.[32] Because of the wide variety of vapor compression cycles (thermodynamic cycle, thermodynamics) and the wide variety of workings gases (refrigerants), centrifugal compressors are used in a wide range of sizes and configurations. Use of real gas properties is needed to properly design, test and analyze the performance of these machines. Standards set by the industry for these compressors include ASHRAE, ASME & API.
- In industry and manufacturing to supply compressed air for all types of pneumatic tools.[33] Centrifugal compressors for such uses are often multistage and driven by electric motors. Inter-cooling is often needed between stages to control air temperature. Road-repair crews and automobile repair garages find screw compressors better adapt to their needs. Standards set by the industry for these compressors include ASME and government regulations that emphasize safety. Ideal gas relationships are often used to properly design, test, and analyze the performance of these machines. Carrier's equation is often used to deal with humidity.
- In air separation plants to manufacture purified end product gases.[33] Centrifugal compressors for such uses are often multistage using inter-cooling to control air temperature. Standards set by the industry for these compressors include ASME and government regulations that emphasize safety. Ideal gas relationships are often used to properly design, test, and analyze the performance of these machines when the working gas is air or nitrogen. Other gases require real gas properties.
- In oil field re-injection of high-pressure natural gas to improve oil recovery.[31] Centrifugal compressors for such uses are often one-shaft multi-stage and driven by gas turbines. With discharge pressures approaching 700 bar, casings are of the barrel style. Standards set by the industry (API, ASME) for these compressors result in large thick casings to maximize safety. The impellers are often if not always of the covered style which makes them look much like pump impellers. This type of compressor is also often termed API-style. The use of real gas properties is needed to properly design, test, and analyze their performance.
Theory of operation
In the case where flow passes through a straight pipe to enter a centrifugal compressor, the flow is axial, uniform, and has no vorticity, i.e. swirling motion. As the flow passes through the centrifugal impeller, the impeller forces the flow to spin faster as it gets further from the rotational axis. According to a form of Euler's fluid dynamics equation, known as the pump and turbine equation, the energy input to the fluid is proportional to the flow's local spinning velocity multiplied by the local impeller tangential velocity.
In many cases, the flow leaving the centrifugal impeller is traveling near the speed of sound. It then flows through a stationary compressor causing it to decelerate. The stationary compressor is ducting with increasing flow-area where energy transformation takes place. If the flow has to be turned in a rearward direction to enter the next part of the machine, e.g. another impeller or a combustor, flow losses can be reduced by directing the flow with stationary turning vanes or individual turning pipes (pipe diffusers). As described in Bernoulli's principle, the reduction in velocity causes the pressure to rise.[1]
Performance
While illustrating a gas turbine's Brayton cycle,[15] Figure 5.1 includes example plots of pressure-specific volume and temperature-entropy. These types of plots are fundamental to understanding centrifugal compressor performance at one operating point. The two plots show that the pressure rises between the compressor inlet (station 1) and compressor exit (station 2). At the same time, the specific volume decreases while the density increases. The temperature-entropy plot shows that the temperature increases with increasing entropy (loss). Assuming dry air, and the ideal gas equation of state and an isentropic process, there is enough information to define the pressure ratio and efficiency for this one point. The compressor map is required to understand the compressor performance over its complete operating range.
Figure 5.2, a centrifugal compressor performance map (either test or estimated), shows the flow, pressure ratio for each of 4 speed-lines (total of 23 data points). Also included are constant efficiency contours. Centrifugal compressor performance presented in this form provides enough information to match the hardware represented by the map to a simple set of end-user requirements.
Compared to estimating performance which is very cost effective (thus useful in design), testing, while costly, is still the most precise method.[12] Further, testing centrifugal compressor performance is very complex. Professional societies such as ASME (i.e. PTC–10, Fluid Meters Handbook, PTC-19.x),[34] ASHRAE (ASHRAE Handbook) and API (ANSI/API 617–2002, 672–2007)[31][33] have established standards for detailed experimental methods and analysis of test results. Despite this complexity, a few basic concepts in performance can be presented by examining an example test performance map.
Performance maps
Pressure ratio and flow are the main parameters[15][31][33][34] needed to match the Figure 5.2 performance map to a simple compressor application. In this case, it can be assumed that the inlet temperature is sea-level standard. This assumption is not acceptable in practice as inlet temperature variations cause significant variations in compressor performance. Figure 5.2 shows:
- Corrected mass flow: 0.04 – 0.34 kg/s
- Total pressure ratio, inlet to discharge (PRt-t = Pt,discharge/Pt,inlet): 1.0 – 2.6
As is standard practice, Figure 5.2 has a horizontal axis labeled with a flow parameter. While flow measurements use a variety of units, all fit one of 2 categories:
Mass flow per unit time
Mass flow units, such as kg/s, are the easiest to use in practice as there is little room for confusion. Questions remaining would involve inlet or outlet (which might involve leakage from the compressor or moisture condensation). For atmospheric air, the mass flow may be wet or dry (including or excluding humidity). Often, the mass flow specification will be presented on an equivalent Mach number basis, .[35] It is standard in these cases that the equivalent temperature, equivalent pressure, and gas is specified explicitly or implied at a standard condition.
Volume flow per unit time
In contrast, all volume flow specifications require the additional specification of density. Bernoulli's fluid dynamic principle is of great value in understanding this problem. Confusion arises through either inaccuracies or misuse of pressure, temperature, and gas constants.
Also as is standard practice, Figure 5.2 has a vertical axis labeled with a pressure parameter. There is a variety of pressure measurement units. They all fit one of two categories:
- A △pressure, ie increase from inlet to exit (measured with a manometer)
- A discharge pressure
The pressure rise may alternatively be specified as a ratio that has no units:
- A pressure ratio (exit/inlet)
Other features common to performance maps are:
Constant speed-lines
The two most common methods for producing a map for a centrifugal compressor are at constant shaft speed or with a constant throttle setting. If the speed is held constant, test points are taken along a constant speed line by changing throttle positions. In contrast, if a throttle valve is held constant, test points are established by changing speed and repeated with different throttle positions (common gas turbine practice). The map shown in Figure 5.2 illustrates the most common method; lines of constant speed. In this case, we see data points connected via straight lines at speeds of 50%, 71%, 87%, and 100% RPM. The first three speed-lines have 6 points each while the highest speed line has five.
Constant efficiency islands
The next feature to be discussed is the oval-shaped curves representing islands of constant efficiency. In this figure we see 11 contours ranging from 56% efficiency (decimal 0.56) to 76% efficiency (decimal 0.76). General standard practice is to interpret these efficiencies as isentropic rather than polytropic. The inclusion of efficiency islands effectively generates a 3-dimensional topology to this 2-dimensional map. With inlet density specified, it provides a further ability to calculate aerodynamic power. Lines of constant power could just as easily be substituted.
Design or guarantee point(s)
Regarding gas turbine operation and performance, there may be a series of guaranteed points established for the gas turbine's centrifugal compressor. These requirements are of secondary importance to the overall gas turbine performance as a whole. For this reason, it is only necessary to summarize that in the ideal case, the lowest specific fuel consumption would occur when the centrifugal compressor's peak efficiency curve coincides with the gas turbine's required operation line.
In contrast to gas turbines, most other applications (including industrial) need to meet a less stringent set of performance requirements. Historically, centrifugal compressors applied to industrial applications were needed to achieve performance at a specific flow and pressure. Modern industrial compressors are often needed to achieve specific performance goals across a range of flows and pressures; thus taking a significant step toward the sophistication seen in gas turbine applications.
If the compressor represented in Figure 5.2 is used in a simple application, any point (pressure and flow) within the 76% efficiency would provide very acceptable performance. An "End User" would be very happy with the performance requirements of 2.0 pressure ratio at 0.21 kg/s.
Surge
Surge - is a low flow phenomenon where the impeller cannot add enough energy to overcome the system resistance or backpressure.[36] At low flow rate operation, the pressure ratio over the impeller is high, as is back system backpressure. Under critical conditions, the flow will reverse back over the tips of the rotor blades towards the impeller eye (inlet).[37] This stalling flow reversal may go unnoticed as the fraction of mass flow or energy is too low. When large enough, rapid flow reversal occurs(i.e., surge). The reversed flow exiting the impeller inlet exhibits a strong rotational component, which affects lower radius flow angles (closer to the impeller hub) at the leading edge of the blades. The deterioration of the flow angles causes the impeller to be inefficient. A full flow reversal can occur. (Therefore, surge is sometimes referred to as axisymmetric stall.) When reversed flow reduces to a low enough level, the impeller recovers and regains stability for a short moment at which point the stage may surge again. These cyclic events cause large vibrations, increase temperature and change rapidly the axial thrust. These occurrences can damage the rotor seals, rotor bearings, the compressor driver, and cycle operation. Most turbomachines are designed to easily withstand occasional surging. However, if the machine is forced to surge repeatedly for a long period of time, or if it is poorly designed, repeated surges can result in a catastrophic failure. Of particular interest, is that while turbomachines may be very durable, their physical system can be far less robust.
Surge line
The surge-line shown in Figure 5.2 is the curve that passes through the lowest flow points of each of the four speed-lines. As a test map, these points would be the lowest flow points possible to record a stable reading within the test facility/rig. In many industrial applications, it may be necessary to increase the stall line due to the system backpressure. For example, at 100% RPM stalling flow might increase from approximately 0.170 kg/s to 0.215 kg/s because of the positive slope of the pressure ratio curve.
As stated earlier, the reason for this is that the high-speed line in Figure 5.2 exhibits a stalling characteristic or positive slope within that range of flows. When placed in a different system those lower flows might not be achievable because of interaction with that system. System resistance or adverse pressure is proven mathematically to be the critical contributor to compressor surge.
Maximum flow line versus choke
Choke occurs under one of 2 conditions. Typically for high speed equipment, as flow increases the velocity of the flow can approach sonic speed somewhere within the compressor stage. This location may occur at the impeller inlet "throat" or at the vaned diffuser inlet "throat". In contrast, for lower speed equipment, as flows increase, losses increase such that the pressure ratio eventually drops to 1:1. In this case, the occurrence of choke is unlikely.
The speed-lines of gas turbine centrifugal compressors typically exhibit choke. This is a situation where the pressure ratio of a speed line drops rapidly (vertically) with little or no change in flow. In most cases the reason for this is that close to Mach 1 velocities have been reached somewhere within the impeller and/or diffuser generating a rapid increase in losses. Higher pressure ratio turbocharger centrifugal compressors exhibit this same phenomenon. Real choke phenomena is a function of compressibility as measured by the local Mach number within an area restriction within the centrifugal pressure stage.
The maximum flow line, shown in Figure 5.2, is the curve that passes through the highest flow points of each speed line. Upon inspection it may be noticed that each of these points has been taken near 56% efficiency. Selecting a low efficiency (<60%) is the most common practice used to terminate compressor performance maps at high flows. Another factor that is used to establish the maximum flow line is a pressure ratio near or equal to 1. The 50% speed line may be considered an example of this.
The shape of Figure 5.2's speed-lines provides a good example of why it is inappropriate to use the term choke in association with a maximum flow of all centrifugal compressor speed-lines. In summary; most industrial and commercial centrifugal compressors are selected or designed to operate at or near their highest efficiencies and to avoid operation at low efficiencies. For this reason there is seldom a reason to illustrate centrifugal compressor performance below 60% efficiency.
Many industrial and commercial multistage compressor performance maps exhibits this same vertical characteristic for a different reason related to what is known as stage stacking.
Other operating limits
- Minimum operating speed
- The minimum speed for acceptable operation, below this value the compressor may be controlled to stop or go into an "idle" condition.
- Maximum allowable speed
- The maximum operating speed for the compressor. Beyond this value stresses may rise above prescribed limits and rotor vibrations may increase rapidly. At speeds above this level the equipment will likely become very dangerous and be controlled to lower speeds.
Dimensional analysis
To weigh the advantages between centrifugal compressors it is important to compare 8 parameters classic to turbomachinery. Specifically, pressure rise (p), flow (Q), angular speed (N), power (P), density (ρ), diameter (D), viscosity (μ) and elasticity (e). This creates a practical problem when trying to experimentally determine the effect of any one parameter. This is because it is nearly impossible to change one of these parameters independently.
The method of procedure known as the Buckingham π theorem can help solve this problem by generating 5 dimensionless forms of these parameters.[1][citation needed][16] These Pi parameters provide the foundation for "similitude" and the "affinity-laws" in turbomachinery. They provide for the creation of additional relationships (being dimensionless) found valuable in the characterization of performance.
For the example below Head will be substituted for pressure and sonic velocity will be substituted for elasticity.
Buckingham Π theorem
The three independent dimensions used in this procedure for turbomachinery are:
- mass (force is an alternative)
- length
- time
According to the theorem each of the eight main parameters are equated to its independent dimensions as follows:
Flow | ex. = m3/s | ||
Head | ex. = kg·m/s2 | ||
Speed | ex. = m/s | ||
Power | ex. = kg·m2/s3 | ||
Density | ex. = kg/m3 | ||
Viscosity | ex. = kg/m·s | ||
Diameter | ex. = m | ||
Speed of sound | ex. = m/s |
Classic turbomachinery similitude
Completing the task of following the formal procedure results in generating this classic set of five dimensionless parameters for turbomachinery.[1] Full-similitude is achieved when each one of the 5 Pi-parameters is equivalent when comparing two different cases. This of course would mean the two turbomachines being compared are similar, both geometrically and in terms of performance.
1 | Flow-coefficient | ||
|
Head-coefficient | ||
3 | Speed-coefficient | ||
4 | Power-coefficient | ||
5 | Reynolds-coefficient |
Turbomachinery analysts gain tremendous insight into performance by comparisons of the 5 parameters shown in the above table. Particularly, performance parameters such as efficiencies and loss-coefficients, which are also dimensionless. In general application, the Flow-coefficient and Head-coefficient are considered of primary importance. Generally, for centrifugal compressors, the Speed-coefficient is of secondary importance while the Reynolds-coefficient is of tertiary importance. In contrast, as expected for pumps, the Reynolds-coefficient becomes of secondary importance and the Speed-coefficient of tertiary importance. It may be found interesting that the Speed-coefficient may be chosen to define the y-axis of Figure 1.1, while at the same time the Reynolds coefficient may be chosen to define the z-axis.
Other dimensionless combinations
Demonstrated in the table below is another value of dimensional analysis. Any number of new dimensionless parameters can be calculated through exponents and multiplication. For example, a variation of the first parameter shown below is popularly used in aircraft engine system analysis. The third parameter is a simplified dimensional variation of the first and second. This third definition is applicable with strict limitations. The fourth parameter, specific speed, is very well known and useful in that it removes diameter. The fifth parameter, specific diameter, is a less often discussed dimensionless parameter found useful by Balje.[38]
1 | Corrected mass flow coefficient | ||
2 | Alternate#1 equivalent Mach form | ||
3 | Alternate#2 simplified dimensional form | ||
4 | Specific speed coefficient | ||
5 | Specific diameter coefficient |
It may be found interesting that the specific speed coefficient may be used in place of speed to define the y-axis of Figure 1.2, while at the same time, the specific diameter coefficient may be in place of diameter to define the z-axis.
Affinity laws
The following affinity laws are derived from the five Π-parameters shown above. They provide a simple basis for scaling turbomachinery from one application to the next.
From flow coefficient | |||
From head coefficient | |||
From power coefficient |
Aero-thermodynamic fundamentals
The following equations outline a fully three-dimensional mathematical problem that is very difficult to solve even with simplifying assumptions.[10][39] Until recently, limitations in computational power, forced these equations to be simplified to an Inviscid two-dimensional problem with pseudo losses. Before the advent of computers, these equations were almost always simplified to a one-dimensional problem.
Solving this one-dimensional problem is still valuable today and is often termed mean-line analysis. Even with all of this simplification it still requires large textbooks to outline and large computer programs to solve practically.
Conservation of mass
Also termed continuity, this fundamental equation written in general form is as follows:
Conservation of momentum
Also termed the Navier–Stokes equations, this fundamental is derivable from Newton's second law when applied to fluid motion. Written in compressible form for a Newtonian fluid, this equation may be written as follows:
Conservation of energy
The first law of thermodynamics is the statement of the conservation of energy. Under specific conditions, the operation of a Centrifugal compressor is considered a reversible process. For a reversible process, the total amount of heat added to a system can be expressed as where is temperature and is entropy. Therefore, for a reversible process:
Since U, S and V are thermodynamic functions of state, the above relation holds also for non-reversible changes. The above equation is known as the fundamental thermodynamic relation.
Equation of state
The classical ideal gas law may be written:
The ideal gas law may also be expressed as follows
where is the density, is the adiabatic index (ratio of specific heats), is the internal energy per unit mass (the "specific internal energy"), is the specific heat at constant volume, and is the specific heat at constant pressure.
With regard to the equation of state, it is important to remember that while air and nitrogen properties (near standard atmospheric conditions) are easily and accurately estimated by this simple relationship, there are many centrifugal compressor applications where the ideal relationship is inadequate. For example, centrifugal compressors used for large air conditioning systems (water chillers) use a refrigerant as a working gas that cannot be modeled as an ideal gas. Another example are centrifugal compressors design and built for the petroleum industry. Most of the hydrocarbon gases such as methane and ethylene are best modeled as a real gas equation of state rather than ideal gases. The Wikipedia entry for equations of state is very thorough.
Pros and cons
- Pros
- Centrifugal compressors offer the advantages of simplicity of manufacturing and relatively low cost. This is due to requiring fewer stages to achieve the same pressure rise.
- Centrifugal compressors are used throughout industry because they have fewer rubbing parts, are relatively energy efficient, and give higher and non-oscillating constant airflow than a similarly sized reciprocating compressor or any other positive displacement pump.
- Centrifugal compressors are mostly used as turbochargers and in small gas turbine engines like in an APU (auxiliary power unit) and as main engine for smaller aircraft like helicopters. A significant reason for this is that with current technology, the equivalent airflow axial compressor will be less efficient due primarily to a combination of rotor and variable stator tip-clearance losses.
- Cons
- Their main drawback is that they cannot achieve the high compression ratio of reciprocating compressors without multiple stages. There are few one-stage centrifugal compressors capable of pressure ratios over 10:1, due to stress considerations which severely limit the compressor's safety, durability and life expectancy.
- Centrifugal compressors are impractical, compared to axial compressors, for use in large gas turbines and turbojet engines propelling large aircraft, due to the resulting weight and stress, and to the frontal area presented by the large diameter of the radial diffuser.
Structural mechanics, manufacture and design compromise
Ideally, centrifugal compressor impellers have thin air-foil blades that are strong, each mounted on a light rotor. This material would be easy to machine or cast and inexpensive. Additionally, it would generate no operating noise, and have a long life while operating in any environment.[clarification needed]
From the very start of the aero-thermodynamic design process, the aerodynamic considerations and optimizations [29,30] are critical to have a successful design. during the design, the centrifugal impeller's material and manufacturing method must be accounted for within the design, whether it be plastic for a vacuum cleaner blower, aluminum alloy for a turbocharger, steel alloy for an air compressor or titanium alloy for a gas turbine. It is a combination of the centrifugal compressor impeller shape, its operating environment, its material and its manufacturing method that determines the impeller's structural integrity.[40][41]
See also
- Angular momentum
- Axial compressor
- Centrifugal force
- Centripetal force
- Coandă effect
- Computational fluid dynamics
- Compressibility
- Compressor map
- Coriolis force
- Darcy–Weisbach equation
- Enthalpy
- Entropy
- Euler equations (fluid dynamics)
- Finite element method
- Fluid dynamics
- Gas laws
- Gustaf de Laval
- Ideal gas law
- Kinematics
- Mach number
- Multiphase flow
- Navier–Stokes equations
- Real gas
- Reynolds-averaged Navier–Stokes equations
- Reynolds transport theorem
- Reynolds number
- Rossby number
- Three-dimensional losses and correlation in turbomachinery
- Turbulence
- Viscosity
- von Karman Institute for Fluid Dynamics
References
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- Xu, C., Design experience and considerations for centrifugal compressor development., J. of Aerospace Eng. 2007
External links
- MIT Gas Turbine Laboratory
- (1948), First Marine Gas Turbine in Service. Journal of the American Society for Naval Engineers, 60: 66–86. doi:10.1111/j.1559-3584.1948.tb02754.x
- A history of Chrysler turbine cars
- To find API codes, standards & publications
- To find ASME codes, standards & publications
- To find ASHRAE codes, standards & publications
- Glenn Research Center at NASA
- Hydrodynamics of Pumps, by Christopher Earls Brennen
- Ctrend website to calculate the head of centrifugal compressor online
https://en.wikipedia.org/wiki/Centrifugal_compressor
A pneumatic motor (air motor), or compressed air engine, is a type of motor which does mechanical work by expanding compressed air. Pneumatic motors generally convert the compressed air energy to mechanical work through either linear or rotary motion. Linear motion can come from either a diaphragm or piston actuator, while rotary motion is supplied by either a vane type air motor, piston air motor, air turbine or gear type motor.
Pneumatic motors have existed in many forms over the past two centuries, ranging in size from hand-held motors to engines of up to several hundred horsepower. Some types rely on pistons and cylinders; others on slotted rotors with vanes (vane motors) and others use turbines. Many compressed air engines improve their performance by heating the incoming air or the engine itself. Pneumatic motors have found widespread success in the hand-held tool industry,[1] but are also used stationary in a wide range of industrial applications. Continual attempts are being made to expand their use to the transportation industry. However, pneumatic motors must overcome inefficiencies before being seen as a viable option in the transportation industry.
Classification
Linear
In order to achieve linear motion from compressed air, a system of pistons is most commonly used. The compressed air is fed into an air-tight chamber that houses the shaft of the piston. Also inside this chamber a spring is coiled around the shaft of the piston in order to hold the chamber completely open when air is not being pumped into the chamber. As air is fed into the chamber the force on the piston shaft begins to overcome the force being exerted on the spring.[2] As more air is fed into the chamber, the pressure increases and the piston begins to move down the chamber. When it reaches its maximum length the air pressure is released from the chamber and the spring completes the cycle by closing off the chamber to return to its original position.
Piston motors are the most commonly used in hydraulic systems. Essentially, piston motors are the same as hydraulic motors except they are used to convert hydraulic energy into mechanical[3] energy.[4]
Piston motors are often used in series of two, three, four, five, or six cylinders that are enclosed in a housing. This allows for more power to be delivered by the pistons because several motors are in sync with each other at certain times of their cycle.
The practical mechanical efficiencies attained by a piston air motor are between 40%-50%.[5]
Rotary vane motors
A type of pneumatic motor, known as a rotary vane motor, uses air to produce rotational motion to a shaft. The rotating element is a slotted rotor which is mounted on a drive shaft. Each slot of the rotor is fitted with a freely sliding rectangular vane.[4] The vanes are extended to the housing walls using springs, cam action, or air pressure, depending on the motor design. Air is pumped through the motor input which pushes on the vanes creating the rotational motion of the central shaft. Rotation speeds can vary between 100 and 25,000 rpm depending on several factors which include the amount of air pressure at the motor inlet and the diameter of the housing.[2]
One application for vane-type air motors is to start large industrial diesel or natural gas engines. Stored energy in the form of compressed air, nitrogen or natural gas enters the sealed motor chamber and exerts pressure against the vanes of a rotor. This causes the rotor to turn at high speed. Because the engine flywheel requires a great deal of torque to start the engine, reduction gears are used. Reduction gears create high torque levels with the lower amounts of energy input. These reduction gears allow for sufficient torque to be generated by the engine flywheel while it is engaged by the pinion gear of the air motor or air starter.
Turbine motors
Air turbines spin the burr in high-speed dental handpieces, at speeds over 180,000 rpm, but with limited torque. A turbine is small enough to fit in the tip of a handpiece without adding to the weight.
Application
A widespread application of pneumatic motors is in hand-held tools, impact wrenches, pulse tools, screwdrivers, nut runners, drills, grinders, sanders and so on. Pneumatic motors are also used stationary in a wide range of industrial applications. Though overall energy efficiency of pneumatics tools is low and they require access to a compressed-air source, there are several advantages over electric tools. They offer greater power density (a smaller pneumatic motor can provide the same amount of power as a larger electric motor), do not require an auxiliary speed controller (adding to its compactness), generate less heat, and can be used in more volatile atmospheres as they do not require electric power [6] and do not create sparks. They can be loaded to stop with full torque without damages.[7] The efficiency of a rotary piston engine is highly dependent on mechanical energy losses. The value of mechanical losses, according to various estimates, can be 20 % of the energy supplied to the engine.[8]
Historically, many individuals have tried to apply pneumatic motors to the transportation industry. Guy Negre, CEO and founder of Zero Pollution Motors, has pioneered this field since the late 1980s.[9] Recently Engineair has also developed a rotary motor for use in automobiles. Engineair places the motor immediately beside the wheel of the vehicle and uses no intermediate parts to transmit motion which means almost all of the motor's energy is used to rotate the wheel.[10]
History in transportation
The pneumatic motor was first applied to the field of transportation in the mid-19th century. Though little is known about the first recorded compressed-air vehicle, it is said that the Frenchmen Andraud and Tessie of Motay ran a car powered by a pneumatic motor on a test track in Chaillot, France, on July 9, 1840. Although the car test was reported to have been successful, the pair didn't explore further expansion of the design.[11]
The first successful application of the pneumatic motor in transportation was the Mekarski system air engine used in locomotives. Mekarski's innovative engine overcame cooling that accompanies air expansion by heating air in a small boiler prior to use. The Tramway de Nantes, located in Nantes, France, was noted for being the first to use Mekarski engines to power their fleet of locomotives. The tramway began operation on December 13, 1879, and continues to operate today, although the pneumatic trams were replaced in 1917 by more efficient and modern electrical trams.
American Charles Hodges also found success with pneumatic motors in the locomotive industry. In 1911 he designed a pneumatic locomotive and sold the patent to the H.K. Porter Company in Pittsburgh for use in coal mines.[12] Because pneumatic motors do not use combustion they were a much safer option in the coal industry.[11]
Many companies[who?] claim to be developing compressed air cars, but none are actually available for purchase or even independent testing.
Tools
Impact wrenches, pulse tools, torque wrenches, screwdrivers, drills, grinders, die grinders, sanders, dental drills, tire changers and other pneumatic tools use a variety of air motors. These include vane type motors, turbines and piston motors.
Torpedoes
Most successful early forms of self-propelled torpedoes used high pressure compressed air, although this was superseded by internal or external combustion engines, steam engines (driven by the catalytic decomposition of hydrogen peroxide), or electric motors.
Railways
Compressed air engines were used in trams and shunters, and eventually found a successful niche in mining locomotives, although in the end they were replaced by electric trains, underground.[13] Over the years designs increased in complexity, resulting in a triple expansion engine with air-to-air reheaters between each stage.[14] For more information see Fireless locomotive and Mekarski system.
Pneumatic Locomotive with attached pressure container used during the construction of the Gotthard Rail Tunnel 1872-1880.[15]
A compressed air locomotive by H.K. Porter, Inc., in use at the Homestake Mine, South Dakota, between 1928 and 1961
Flight
Water rockets use compressed air to power their water jet and generate thrust, they are used as toys.
Air Hogs, a toy brand, also uses compressed air to power piston engines in toy airplanes (and some other toy vehicles).
Automotive
There is currently some interest in developing air cars. Several engines have been proposed for these, although none have demonstrated the performance and long life needed for personal transport.
Energine
The Energine Corporation was a South Korean company that claimed to deliver fully assembled cars running on a hybrid compressed air and electric engine. The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car. The CEO was arrested for fraudulently promoting air motors with false claims.[16]
EngineAir
EngineAir, an Australian company, is making a rotary engine powered by compressed air, called The Di Pietro motor. The Di Pietro motor concept is based on a rotary piston. Different from existing rotary engines, the Di Pietro motor uses a simple cylindrical rotary piston (shaft driver) which rolls, with little friction, inside the cylindrical stator.[17]
It can be used in boats, cars, burden carriers and other vehicles. Only 1 psi (≈ 6,8 kPa) of pressure is needed to overcome the friction.[18][19] The engine was also featured on the ABC's New Inventors programme in Australia on 24 March 2004.[20]
K'Airmobiles
K'Airmobiles vehicles were intended to be commercialized from a project developed in France in 2006-2007 by a small group of researchers. However, the project has not been able to gather the necessary funds.
People should note that, meantime, the team has recognized the physical impossibility to use on-board stored compressed air due to its poor energy capacity and the thermal losses resulting from the expansion of the gas.
These days, using the patent pending 'K'Air Generator', converted to work as a compressed-gas motor, the project should be launched in 2010, thanks to a North American group of investors, but for the purpose of developing first a green energy power system.[21]
MDI
In the original Nègre air engine, one piston compresses air from the atmosphere to mix with the stored compressed air (which will cool drastically as it expands). This mixture drives the second piston, providing the actual engine power. MDI's engine works with constant torque, and the only way to change the torque to the wheels is to use a pulley transmission of constant variation, losing some efficiency. When vehicle is stopped, MDI's engine had to be on and working, losing energy. In 2001-2004 MDI switched to a design similar to that described in Regusci's patents (see below), which date back to 1990.
It has been reported in 2008 that Indian car manufacturer Tata was looking at an MDI compressed air engine as an option on its low priced Nano automobiles.[22] Tata announced in 2009 that the compressed air car was proving difficult to develop due to its low range and problems with low engine temperatures.
Quasiturbine
The Pneumatic Quasiturbine engine is a compressed air pistonless rotary engine using a rhomboidal-shaped rotor whose sides are hinged at the vertices.
The Quasiturbine has demonstrated as a pneumatic engine using stored compressed air [23]
It can also take advantage of the energy amplification possible from using available external heat, such as solar energy.[24]
The Quasiturbine rotates from pressure as low as 0.1 atm (1.47psi).
Since the Quasiturbine is a pure expansion engine, while the Wankel and most other rotary engines are not, it is well-suited as a compressed fluid engine, air engine or air motor.[24]
Regusci
Armando Regusci's version of the air engine couples the transmission system directly to the wheel, and has variable torque from zero to the maximum, enhancing efficiency. Regusci's patents date from 1990.[25]
Team Psycho-Active
Psycho-Active is developing a multi-fuel/air-hybrid chassis which is intended to serve as the foundation for a line of automobiles. Claimed performance is 50 hp/litre. The compressed air motor they use is called the DBRE or Ducted Blade Rotary Engine.[26][27]
Defunct air engine designs
Conger motor
Milton M. Conger in 1881 patented and supposedly built a motor that ran off compressed air or steam that using a flexible tubing which will form a wedge-shaped or inclined wall or abutment in the rear of the tangential bearing of the wheel, and propel it with greater or less speed according to the pressure of the propelling medium.[28]
See also
- Angelo Di Pietro (inventor)
- Compressed air energy storage
- Compressor
- Proe's Ericsson cycle engine;[29] a variation of a compressed air motor that uses a fuel to compress the air which is then immediately injected to the motor
- Chicago Pneumatic
- Simon Ingersoll
- Atlas Copco
References
- "Proe Ericsson Cycle Engine". Archived from the original on 2013-04-29.
External links
- Media related to Pneumatic motor at Wikimedia Commons
https://en.wikipedia.org/wiki/Pneumatic_motor
A turbine engine failure occurs when a turbine engine unexpectedly stops producing power due to a malfunction other than fuel exhaustion. It often applies for aircraft, but other turbine engines can fail, like ground-based turbines used in power plants or combined diesel and gas vessels and vehicles.
Reliability
Turbine engines in use on today's turbine-powered aircraft are very reliable. Engines operate efficiently with regularly scheduled inspections and maintenance. These units can have lives ranging in the thousands of hours of operation. However, engine malfunctions or failures occasionally occur that require an engine to be shut down in flight. Since multi-engine airplanes are designed to fly with one engine inoperative and flight crews are trained to fly with one engine inoperative, the in-flight shutdown of an engine typically does not constitute a serious safety of flight issue.
The Federal Aviation Administration (FAA) was quoted as stating turbine engines have a failure rate of one per 375,000 flight hours, compared to of one every 3,200 flight hours for aircraft piston engines.[1] Due to "gross under-reporting" of general aviation piston engines in-flight shutdowns (IFSD), the FAA has no reliable data and assessed the rate "between 1 per 1,000 and 1 per 10,000 flight hours".[2] Continental Motors reports the FAA states general aviation engines experience one failures or IFSD every 10,000 flight hours, and states its Centurion engines is one per 20,704 flight hours, lowering to one per 163,934 flight hours in 2013-2014.[3]
The General Electric GE90 has an in-flight shutdown rate (IFSD) of one per million engine flight-hours.[4] The Pratt & Whitney Canada PT6 is known for its reliability with an in-flight shutdown rate of one per 333,333 hours from 1963 to 2016,[5] lowering to one per 651,126 hours over 12 months in 2016.[6]
Emergency landing
Following an engine shutdown, a precautionary landing is usually performed with airport fire and rescue equipment positioned near the runway. The prompt landing is a precaution against the risk that another engine will fail later in the flight or that the engine failure that has already occurred may have caused or been caused by other as-yet unknown damage or malfunction of aircraft systems (such as fire or damage to aircraft flight controls) that may pose a continuing risk to the flight. Once the airplane lands, fire department personnel assist with inspecting the airplane to ensure it is safe before it taxis to its parking position.
Rotorcraft
Turboprop-powered aircraft and turboshaft-powered helicopters are also powered by turbine engines and are subject to engine failures for many similar reasons as jet-powered aircraft. In the case of an engine failure in a helicopter, it is often possible for the pilot to enter autorotation, using the unpowered rotor to slow the aircraft's descent and provide a measure of control, usually allowing for a safe emergency landing even without engine power.[7]
Shutdowns that are not engine failures
Most in-flight shutdowns are harmless and likely to go unnoticed by passengers. For example, it may be prudent for the flight crew to shut down an engine and perform a precautionary landing in the event of a low oil pressure or high oil temperature warning in the cockpit. However, passengers in a jet powered aircraft may become quite alarmed by other engine events such as a compressor surge — a malfunction that is typified by loud bangs and even flames from the engine's inlet and tailpipe. A compressor surge is a disruption of the airflow through a gas turbine jet engine that can be caused by engine deterioration, a crosswind over the engine's inlet, ice accumulation around the engine inlet, ingestion of foreign material, or an internal component failure such as a broken blade. While this situation can be alarming, the engine may recover with no damage.[8]
Other events that can happen with jet engines, such as a fuel control fault, can result in excess fuel in the engine's combustor. This additional fuel can result in flames extending from the engine's exhaust pipe. As alarming as this would appear, at no time is the engine itself actually on fire.[citation needed]
Also, the failure of certain components in the engine may result in a release of oil into bleed air that can cause an odor or oily mist in the cabin. This is known as a fume event. The dangers of fume events are the subject of debate in both aviation and medicine.[9]
Possible causes
Engine failures can be caused by mechanical problems in the engine itself, such as damage to portions of the turbine or oil leaks, as well as damage outside the engine such as fuel pump problems or fuel contamination. A turbine engine failure can also be caused by entirely external factors, such as volcanic ash, bird strikes or weather conditions like precipitation or icing. Weather risks such as these can sometimes be countered through the usage of supplementary ignition or anti-icing systems.[10]
Failures during takeoff
A turbine-powered aircraft's takeoff procedure is designed around ensuring that an engine failure will not endanger the flight. This is done by planning the takeoff around three critical V speeds, V1, VR and V2. V1 is the critical engine failure recognition speed, the speed at which a takeoff can be continued with an engine failure, and the speed at which stopping distance is no longer guaranteed in the event of a rejected takeoff. VR is the speed at which the nose is lifted off the runway, a process known as rotation. V2 is the single-engine safety speed, the single engine climb speed.[11] The use of these speeds ensure that either sufficient thrust to continue the takeoff, or sufficient stopping distance to reject it will be available at all times.[citation needed]
Failure during extended operations
In order to allow twin-engined aircraft to fly longer routes that are over an hour from a suitable diversion airport, a set of rules known as ETOPS (Extended Twin-engine Operational Performance Standards) is used to ensure a twin turbine engine powered aircraft is able to safely arrive at a diversionary airport after an engine failure or shutdown, as well as to minimize the risk of a failure. ETOPS includes maintenance requirements, such as frequent and meticulously logged inspections and operation requirements such as flight crew training and ETOPS-specific procedures.[12]
Contained and uncontained failures
Engine failures may be classified as either as "contained" or "uncontained".
- A contained engine failure is one in which all internal rotating components remain within or embedded in the engine's case (including any containment wrapping that is part of the engine), or exit the engine through the tail pipe[13] or air inlet.[14]
- An uncontained engine event occurs when an engine failure results in fragments of rotating engine parts penetrating and escaping through the engine case.
The very specific technical distinction between a contained and uncontained engine failure derives from regulatory requirements for design, testing, and certification of aircraft engines under Part 33 of the U.S. Federal Aviation Regulations, which has always required turbine aircraft engines to be designed to contain damage resulting from rotor blade failure.[14] Under Part 33, engine manufacturers are required to perform blade off tests to ensure containment of shrapnel if blade separation occurs.[15] Blade fragments exiting the inlet or exhaust can still pose a hazard to the aircraft, and this should be considered by the aircraft designers.[14] Note that a nominally contained engine failure can still result in engine parts departing the aircraft as long as the engine parts exit via the existing openings in the engine inlet or outlet, and do not create new openings in the engine case containment. Fan blade fragments departing via the inlet may also cause airframe parts such as the inlet duct and other parts of the engine nacelle to depart the aircraft due to deformation from the fan blade fragment's residual kinetic energy.
The containment of failed rotating parts is a complex process which involves high energy, high speed interactions of numerous locally and remotely located engine components (e.g., failed blade, other blades, containment structure, adjacent cases, bearings, bearing supports, shafts, vanes, and externally mounted components). Once the failure event starts, secondary events of a random nature may occur whose course and ultimate conclusion cannot be precisely predicted. Some of the structural interactions that have been observed to affect containment are the deformation and/or deflection of blades, cases, rotor, frame, inlet, casing rub strips, and the containment structure.[14]
Uncontained turbine engine disk failures within an aircraft engine present a direct hazard to an airplane and its crew and passengers because high-energy disk fragments can penetrate the cabin or fuel tanks, damage flight control surfaces, or sever flammable fluid or hydraulic lines.[16] Engine cases are not designed to contain failed turbine disks. Instead, the risk of uncontained disk failure is mitigated by designating disks as safety-critical parts, defined as the parts of an engine whose failure is likely to present a direct hazard to the aircraft.[16]
Notable uncontained engine failure accidents
- National Airlines Flight 27: a McDonnell Douglas DC-10 flying from Miami to San Francisco in 1973 had an overspeed failure of a General Electric CF6-6, resulting in one fatality.[17]
- Two LOT Polish Airlines flights, both Ilyushin Il-62s, suffered catastrophic uncontained engine failures in the 1980s. The first was in 1980 on LOT Polish Airlines Flight 7 where flight controls were destroyed, killing all 87 on board. In 1987, on LOT Polish Airlines Flight 5055, the aircraft's inner left (#2) engine, damaged the outer left (#1) engine, setting both on fire and causing loss of flight controls, leading to an eventual crash, which killed all 183 people on board. In both cases, the turbine shaft in engine #2 disintegrated due to production defects in the engines' bearings, which were missing rollers.[18]
- The Tu-154 crash near Krasnoyarsk was a major aircraft crash that occurred on Sunday, December 23, 1984 in the vicinity of Krasnoyarsk. The Tu-154B-2 airliner of the 1st Krasnoyarsk united aviation unit (Aeroflot) performed passenger flight SU-3519 on the Krasnoyarsk-Irkutsk route, but during the climb, engine No. 3 failed. The crew decided to return to the airport of departure, but during the landing approach a fire broke out, which destroyed the control systems and as a result, the plane crashed to the ground 3200 meters from the threshold of the runway of the Yemelyanovo airport and collapsed. Of the 111 people on board (104 passengers and 7 crew members), one survived. The cause of the catastrophe was the destruction of the disk of the first stage of the low pressure circuit of engine No. 3, which occurred due to the presence of fatigue cracks. The cracks were caused by a manufacturing defect – the inclusion of a titanium-nitrogen compound that has a higher microhardness than the original material. The methods used at that time for the manufacture and repair of disks, as well as the means of control, were found to be partially obsolete, which is why they did not ensure the effectiveness of control and detection of such a defect. The defect itself arose probably due to accidental ingestion of a titanium sponge or charge for smelting an ingot of a piece enriched with nitrogen.
- Cameroon Airlines Flight 786: a Boeing 737 flying between Douala and Garoua, Cameroon in 1984 had a failure of a Pratt & Whitney JT8D-15 engine. Two people died.[19]
- British Airtours Flight 28M: a Boeing 737 flying from Manchester to Corfu in 1985 suffered an uncontained engine failure and fire on takeoff. The takeoff was aborted and the plane turned onto a taxiway and began evacuating. Fifty-five passengers and crew were unable to escape and died of smoke inhalation. The accident led to major changes to improve the survivability of aircraft evacuations.[20]
- United Airlines Flight 232: a McDonnell Douglas DC-10 flying from Denver to Chicago in 1989. The failure of the rear General Electric CF6-6 engine caused the loss of all hydraulics, forcing the pilots to attempt a landing using differential thrust. There were 111 fatalities. Prior to this crash, the probability of a simultaneous failure of all three hydraulic systems was considered as low as one in a billion. However, statistical models did not account for the position of the number-two engine, mounted at the tail close to hydraulic lines, nor the results of fragments released in many directions. Since then, aircraft engine designs have focused on keeping shrapnel from puncturing the cowling or ductwork, increasingly utilizing high-strength composite materials to achieve penetration resistance while keeping the weight low.[citation needed]
- Baikal Airlines Flight 130: a starter of engine No. 2 on a Tu-154 heading from Irkutsk to Domodedovo, Moscow in 1994, failed to stop after engine startup and continued to operate at over 40,000 rpm with open bleed valves from engines, which caused an uncontained failure of the starter. A detached turbine disk damaged fuel and oil supply lines (which caused fire) and hydraulic lines. The fire-extinguishing system failed to stop the fire, and the plane diverted back to Irkutsk. However, due to loss of hydraulic pressure the crew lost control of the plane, which subsequently crashed into a dairy farm killing all 124 on board and one on the ground.[21][22]
- On June 8, 1995, a DC-9-32 doing service as, ValuJet Flight 597, suffered an uncontained engine failure of the 7th stage high pressure compressor disk due to inadequate inspection of the corroded disk. The resulting rupture caused jet fuel to flow into the cabin and ignite, and the fire caused the jet to be a write-off.
- Delta Air Lines Flight 1288: a McDonnell Douglas MD-88 flying from Pensacola, Florida to Atlanta in 1996 had a cracked compressor rotor hub failure on one of its Pratt & Whitney JT8D-219 engines. Two died.[23]
- TAM Flight 9755: a Fokker 100, departing Recife/Guararapes–Gilberto Freyre International Airport for São Paulo/Guarulhos International Airport on 15 September 2001, suffered an uncontained engine failure (Rolls-Royce RB.183 Tay) in which fragments of the engine shattered three cabin windows, causing decompression and pulling a passenger partly out of the plane. Another passenger held the passenger in until the aircraft landed, but the passenger blown out of the window died.
- Qantas Flight 32: an Airbus A380 flying from London Heathrow to Sydney (via Singapore) in 2010 had an uncontained failure in a Rolls-Royce Trent 900 engine. The failure was found to have been caused by a misaligned counter bore within a stub oil pipe leading to a fatigue fracture. This in turn led to an oil leakage followed by an oil fire in the engine. The fire led to the release of the Intermediate Pressure Turbine (IPT) disc. The airplane, however, landed safely. This led to the grounding of the entire Qantas A380 fleet.[24]
- British Airways Flight 2276: a Boeing 777-200ER flying from Las Vegas to London in 2015 suffered an uncontained engine failure on its #1 GE90 engine during takeoff, resulting in a large fire on its port side. The aircraft successfully aborted takeoff and the plane was evacuated with no fatalities.[25]
- American Airlines Flight 383: a Boeing 767-300ER flying from Chicago to Miami in 2016 suffered an uncontained engine failure on its #2 engine (General Electric CF6) during takeoff resulting in a large fire which destroyed the outer right wing. The aircraft aborted takeoff and was evacuated with 21 minor injuries, but no fatalities.[26]
- Air France Flight 66: an Airbus A380, registration F-HPJE performing flight from Paris, France, to Los Angeles, United States, was en route about 200 nautical miles (230 mi; 370 km) southeast of Nuuk, Greenland, when it suffered a catastrophic engine failure in 2017 (General Electric / Pratt & Whitney Engine Alliance GP7000). The crew descended the aircraft and diverted to Goose Bay, Canada, for a safe landing about two hours later.[27]
References
a helicopter can be landed safely in the event of an engine failure
- Editorial, Reuters (30 September 2017). "Air France flight with engine damage makes emergency landing in Canada". Reuters. Retrieved 18 April 2018.
{{cite news}}
:|first=
has generic name (help)
- This article contains text from a publication of the United States National Transportation Safety Board. which can be found here [1] As a work of the United States Federal Government, the source is in the public domain and may be adapted freely per USC Title 17; Chapter 1; §105 (see Wikipedia:Public Domain).
https://en.wikipedia.org/wiki/Turbine_engine_failure
The Gas Turbine Modular Helium Reactor (GT-MHR) is a class of nuclear fission power reactor designed that was under development by a group of Russian enterprises (OKBM Afrikantov, Kurchatov Institute, VNIINM and others), an American group headed by General Atomics, French Framatome and Japanese Fuji Electric.[1] It is a helium cooled, graphite moderated reactor and uses TRISO fuel compacts in a prismatic core design. The power is generated via a gas turbine rather than via the more common steam turbine.
A conceptual design was produced by 1997,[1] and it was hoped to have a final design by 2005, and a prototype plant commissioning by 2010.[1]
Construction
The core consists of a graphite cylinder with a radius of 4 metres (13 ft) and a height of 10 metres (33 ft) which includes 1 metre (3 ft 3 in) axial reflectors at top and bottom. The cylinder allocates three or four concentric rings, each of 36 hexagonal blocks with an interstitial gap of 0.2 centimetres (0.079 in). Each hexagonal block contains 108 helium coolant channels and 216 fuel pins. Each fuel pin contains a random lattice of TRISO particles dispersed into a graphite matrix. The reactor exhibits a thermal spectrum with a peak neutron energy located at about 0.2 eV. The TRISO fuel concept allows the reactor to be inherently safe. The reactor and containment structure is located below grade and in contact with the ground, which serves as a passive safety measure to conduct heat away from the reactor in the event of a coolant failure.[2]
Advantages
The Gas Turbine Modular Helium Reactor utilizes the Brayton cycle turbine arrangement, which gives it an efficiency of up to 48% – higher than any other reactor, as of 1995.[3] Commercial light water reactors (LWRs) generally use the Rankine cycle, which is what coal-fired power plants use. Commercial LWRs average 32% efficiency, again as of 1995.
Legacy
Energy Multiplier Module (EM2)
In 2010 General Atomics conceptualized a new reactor that utilizes the power conversion features of the GT-MHR, the Energy Multiplier Module (EM2). The EM2 uses fast neutrons and is a gas-cooled fast reactor, enabling it to reduce nuclear waste considerably by transmutation.[4]
See also
References
- "Energy Multiplier Module (EM²)". Ga.com. Retrieved 2013-09-05.
External links
- "General Atomics GT-MHR Page". Archived from the original on December 11, 2013. Retrieved December 11, 2013.
https://en.wikipedia.org/wiki/Gas_turbine_modular_helium_reactor
https://en.wikipedia.org/wiki/Category:Nuclear_power_reactor_types
https://en.wikipedia.org/wiki/Gas-cooled_fast_reactor
https://en.wikipedia.org/wiki/High-temperature_gas_reactor
A high-temperature gas-cooled reactor (HTGR), is a nuclear reactor that uses a graphite moderator with a once-through uranium fuel cycle. The HTGR is a type of high-temperature reactor (HTR) that can conceptually have an outlet temperature of 750 °C (1,380 °F). The reactor core can be either a "prismatic block" (reminiscent of a conventional reactor core) or a "pebble-bed" core. The high temperatures enable applications such as process heat or hydrogen production via the thermochemical sulfur–iodine cycle.
https://en.wikipedia.org/wiki/High-temperature_gas_reactor
The sulfur–iodine cycle (S–I cycle) is a three-step thermochemical cycle used to produce hydrogen.
The S–I cycle consists of three chemical reactions whose net reactant is water and whose net products are hydrogen and oxygen. All other chemicals are recycled. The S–I process requires an efficient source of heat.
Process description
H2O | ½O2 | |||||
↓ | ↑ | |||||
I2 | → | Reaction 1 | ← | SO2+H2O | ← | Separate |
↑ | ↓ | ↑ | ||||
2HI | ← | Separate | → | H2SO4 | → | Reaction 2 |
↓ |
| |||||
H2 |
|
The three reactions that produce hydrogen are as follows:
- I2 + SO2 + 2 H2O 2 HI + H2SO4 (120 °C (250 °F)); Bunsen reaction
- The HI is then separated by distillation or liquid/liquid gravitic separation.
- 2 H2SO4 2 SO2 + 2 H2O + O2 (830 °C (1,530 °F))
- The water, SO2 and residual H2SO4 must be separated from the oxygen byproduct by condensation.
- 2 HI I2 + H2 (450 °C (840 °F))
- Iodine and any accompanying water or SO2 are separated by condensation, and the hydrogen product remains as a gas.
- Net reaction: 2 H2O → 2 H2 + O2
The sulfur and iodine compounds are recovered and reused, hence the consideration of the process as a cycle. This S–I process is a chemical heat engine. Heat enters the cycle in high-temperature endothermic chemical reactions 2 and 3, and heat exits the cycle in the low-temperature exothermic reaction 1. The difference between the heat entering and leaving the cycle exits the cycle in the form of the heat of combustion of the hydrogen produced.
Characteristics
Advantages
- All fluid (liquids, gases) process, therefore well suited for continuous production
- High thermal efficiency predicted (about 50%)
- Completely closed system without byproducts or effluents (besides hydrogen and oxygen)
- Suitable for application with solar, nuclear, and hybrid (e.g., solar-fossil) sources of heat - if high enough temperatures can be achieved
- More developed than competing thermochemical processes
- Scalable from relatively small scale to huge applications
- No need for expensive or toxic catalysts or additives
- More efficient than electrolysis of water (~70-80% efficiency) using electricity derived from a thermal power plant (~30-60% efficiency) combining to ~21-48% efficiency
- Waste heat suitable for district heating if cogeneration is desired
Disadvantages
- Very high temperatures required (at least 850 °C (1,560 °F)) - unachievable or difficult to achieve with current pressurized water reactors or concentrated solar power
- Corrosive reagents used as intermediaries (iodine, sulfur dioxide, hydriodic acid, sulfuric acid); therefore, advanced materials needed for construction of process apparatus
- Significant further development required to be feasible on large scale
- At the proposed temperature range advanced thermal power plants can achieve efficiencies (electric output per heat input) in excess of 50% somewhat negating the efficiency advantage
- In case of leakage corrosive and somewhat toxic substances are released to the environment - among them volatile iodine and hydroiodic acid
- If hydrogen is to be used for process heat the required high temperatures make the benefits compared to direct utilization of heat questionable
- Unable to use non-thermal or low-grade thermal energy sources such as hydropower, wind power or most currently available geothermal power
Research
The S–I cycle was invented at General Atomics in the 1970s.[1] The Japan Atomic Energy Agency (JAEA) has conducted successful experiments with the S–I cycle in the Helium cooled High Temperature Test Reactor,[2][3][4][5] a reactor which reached first criticality in 1998, JAEA have the aspiration of using further nuclear very high-temperature generation IV reactors (VHTR) to produce industrial scale quantities of hydrogen. (The Japanese refer to the cycle as the IS cycle.) Plans have been made to test larger-scale automated systems for hydrogen production. Under an International Nuclear Energy Research Initiative (INERI) agreement, the French CEA, General Atomics and Sandia National Laboratories are jointly developing the sulfur-iodine process. Additional research is taking place at the Idaho National Laboratory, in Canada, Korea and Italy.
Material challenge
The S–I cycle involves operations with corrosive chemicals at temperatures up to about 1,000 °C (1,830 °F). The selection of materials with sufficient corrosion resistance under the process conditions is of key importance to the economic viability of this process. The materials suggested include the following classes: refractory metals, reactive metals, superalloys, ceramics, polymers, and coatings.[6][7] Some materials suggested include tantalum alloys, niobium alloys, noble metals, high-silicon steels,[8] several nickel-based superalloys, mullite, silicon carbide (SiC), glass, silicon nitride (Si3N4), and others. Recent research on scaled prototyping suggests that new tantalum surface technologies may be a technically and economically feasible way to make larger scale installations.[9]
Hydrogen economy
The sulfur-iodine cycle has been proposed as a way to supply hydrogen for a hydrogen-based economy. It does not require hydrocarbons like current methods of steam reforming but requires heat from combustion, nuclear reactions, or solar heat concentrators.
See also
- Cerium(IV) oxide–cerium(III) oxide cycle
- Copper–chlorine cycle
- Hybrid sulfur cycle
- High-temperature electrolysis
- Iron oxide cycle
- Zinc–zinc oxide cycle
Footnotes
References
- Paul M. Mathias and Lloyd C. Brown "Thermodynamics of the Sulfur-Iodine Cycle for Thermochemical Hydrogen Production", presented at the 68 th Annual Meeting of the Society of Chemical Engineers, Japan 23 March 2003. (PDF).
- Atsuhiko TERADA; Jin IWATSUKI, Shuichi ISHIKURA, Hiroki NOGUCHI, Shinji KUBO, Hiroyuki OKUDA, Seiji KASAHARA, Nobuyuki TANAKA, Hiroyuki OTA, Kaoru ONUKI and Ryutaro HINO, "Development of Hydrogen Production Technology by Thermochemical Water Splitting IS Process Pilot Test Plan", Journal of Nuclear Science and Technology, Vol.44, No.3, p. 477–482 (2007). (PDF).
External links
- Hydrogen: Our Future made with Nuclear (in MPR Profile issue 9)
- Use of the modular helium reactor for hydrogen production (World Nuclear Association Symposium 2003)
https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle
https://en.wikipedia.org/wiki/Hydroiodic_acid
https://en.wikipedia.org/wiki/Nuclear_fuel_cycle
https://en.wikipedia.org/wiki/Nuclear_reactor_core
https://en.wikipedia.org/wiki/Neutron
https://en.wikipedia.org/wiki/Core_shroud
https://en.wikipedia.org/wiki/Pebble-bed_reactor
https://en.wikipedia.org/wiki/Gas-cooled_reactor
https://en.wikipedia.org/wiki/Pressurized_heavy-water_reactor
https://en.wikipedia.org/wiki/Nuclear_fission
https://en.wikipedia.org/wiki/Nuclear_chain_reaction
https://en.wikipedia.org/wiki/Neutron_poison
https://en.wikipedia.org/wiki/Neutron_moderator
https://en.wikipedia.org/wiki/Neutron_moderator
https://en.wikipedia.org/wiki/Fairbottom_Bobs
https://en.wikipedia.org/wiki/Nuclear_cross_section
https://en.wikipedia.org/wiki/Momentum#Special_case:_m1.3Dm2
https://en.wikipedia.org/wiki/Neutron_cross_section#Absorption_cross_section
https://en.wikipedia.org/wiki/Flux
https://en.wikipedia.org/wiki/Uranium
https://en.wikipedia.org/wiki/Thermal-neutron_reactor
https://en.wikipedia.org/wiki/Neutron_temperature#Fast
https://en.wikipedia.org/wiki/Uranium-235
https://en.wikipedia.org/wiki/Pressurized_water_reactor
https://en.wikipedia.org/wiki/Supercritical_water_reactor
https://en.wikipedia.org/wiki/Fast-neutron_reactor
https://en.wikipedia.org/wiki/Spallation
https://en.wikipedia.org/wiki/Corrosion
https://en.wikipedia.org/wiki/Ablation
https://en.wikipedia.org/wiki/Windscale_fire
https://en.wikipedia.org/wiki/Pyrolytic_carbon
https://en.wikipedia.org/wiki/Void_coefficient
https://en.wikipedia.org/wiki/Weapons-grade_nuclear_material#Weapons-grade_plutonium
https://en.wikipedia.org/wiki/Boron
https://en.wikipedia.org/wiki/Loss-of-coolant_accident
https://en.wikipedia.org/wiki/Uranium_hydride_bomb
https://en.wikipedia.org/wiki/Uranium_hydride_bomb
https://en.wikipedia.org/wiki/Fizzle_(nuclear_explosion)
https://en.wikipedia.org/wiki/Deuterium
https://en.wikipedia.org/wiki/Nuclear_weapon_design#Implosion-type_weapon
https://en.wikipedia.org/wiki/Neutron_reflector
https://en.wikipedia.org/wiki/Isotopes_of_hydrogen#Hydrogen-1_(protium)
https://en.wikipedia.org/wiki/Neutron_capture
https://en.wikipedia.org/wiki/Uranium_hydride
https://en.wikipedia.org/wiki/Neutron_temperature
https://en.wikipedia.org/wiki/Paraffin_wax
https://en.wikipedia.org/wiki/Pyrolytic_carbon
https://en.wikipedia.org/wiki/RBMK
https://en.wikipedia.org/wiki/Molten_salt_reactor
https://en.wikipedia.org/wiki/Lithium_fluoride
https://en.wikipedia.org/wiki/Beryllium_fluoride
https://en.wikipedia.org/wiki/Category:Neutron_instrumentation
https://en.wikipedia.org/wiki/Core_shroud
https://en.wikipedia.org/wiki/Heat_shield
https://en.wikipedia.org/wiki/Rail_fastening_system
https://en.wikipedia.org/wiki/Steam_turbine
https://en.wikipedia.org/wiki/Anchor_bolt
https://en.wikipedia.org/wiki/Facade_engineering
https://en.wikipedia.org/wiki/Stud_welding
https://en.wikipedia.org/wiki/Reinforced_concrete
https://en.wikipedia.org/wiki/Prestressed_concrete
https://en.wikipedia.org/wiki/Bearing_pressure
https://en.wikipedia.org/wiki/Concrete_masonry_unit
https://en.wikipedia.org/wiki/Wall_plug#Expansion_anchors
https://en.wikipedia.org/wiki/Torque_wrench
https://en.wikipedia.org/wiki/Friction
https://en.wikipedia.org/wiki/Rebar
https://en.wikipedia.org/wiki/Threaded_rod
https://en.wikipedia.org/wiki/Creep_(deformation)
https://en.wikipedia.org/wiki/Limit_state_design
https://en.wikipedia.org/wiki/Wall_plug#Fibre_and_resin_mixes
https://en.wikipedia.org/wiki/Polyester_resin
https://en.wikipedia.org/wiki/Seismic_loading
https://en.wikipedia.org/wiki/Earthquake_engineering
A hysteretic damper is intended to provide better and more reliable seismic performance than that of a conventional structure by increasing the dissipation of seismic input energy.[27]
Seismic design is carried out by understanding the possible failure modes of a structure and providing the structure with appropriate strength, stiffness, ductility, and configuration[37] to ensure those modes cannot occur.
https://en.wikipedia.org/wiki/Earthquake_engineering
https://en.wikipedia.org/wiki/Earthquake_engineering
https://en.wikipedia.org/wiki/Anchor_bolt
https://en.wikipedia.org/wiki/Seismic_loading
https://en.wikipedia.org/wiki/Earthquake_engineering
https://en.wikipedia.org/wiki/Masonry_veneer
https://en.wikipedia.org/wiki/Soil_liquefaction
https://en.wikipedia.org/wiki/Landslide
https://en.wikipedia.org/wiki/Shotcrete
https://en.wikipedia.org/wiki/Shear_wall
https://en.wikipedia.org/wiki/Structural_load#Dead_load
https://en.wikipedia.org/wiki/Hinge
https://en.wikipedia.org/wiki/Abutment
https://en.wikipedia.org/wiki/Sand
https://en.wikipedia.org/wiki/Carapace
https://en.wikipedia.org/wiki/Wind_wave
https://en.wikipedia.org/wiki/Pressure
https://en.wikipedia.org/wiki/Flood
https://en.wikipedia.org/wiki/Epicenter
https://en.wikipedia.org/wiki/Mudbrick
https://en.wikipedia.org/wiki/Limestone
https://en.wikipedia.org/wiki/Framing_(construction)
https://en.wikipedia.org/wiki/Shear_strength
https://en.wikipedia.org/wiki/Grout
https://en.wikipedia.org/wiki/Fiber
https://en.wikipedia.org/wiki/Beam_(structure)
https://en.wikipedia.org/wiki/Tendon
https://en.wikipedia.org/wiki/Nuclear_reactor
https://en.wikipedia.org/wiki/Pier
https://en.wikipedia.org/wiki/Moment-resisting_frame
https://en.wikipedia.org/wiki/Anchor_plate
https://en.wikipedia.org/wiki/Fa%C3%A7ade
https://en.wikipedia.org/wiki/Seismic_intensity_scales
https://en.wikipedia.org/wiki/Soil-structure_interaction
https://en.wikipedia.org/wiki/Spectral_acceleration
https://en.wikipedia.org/wiki/Category:Seismic_vibration_control
https://en.wikipedia.org/wiki/Coulomb_damping
https://en.wikipedia.org/wiki/Stick-slip_phenomenon
https://en.wikipedia.org/wiki/Cold_welding
https://en.wikipedia.org/wiki/Metallic_roller_bearing
https://en.wikipedia.org/wiki/Seismic_hazard
https://en.wikipedia.org/wiki/Nonlinear_system
https://en.wikipedia.org/wiki/Peak_ground_acceleration
https://en.wikipedia.org/wiki/Statics
https://en.wikipedia.org/wiki/Pattern
https://en.wikipedia.org/wiki/Seismic_wave
https://en.wikipedia.org/wiki/Superstructure
https://en.wikipedia.org/wiki/Dissipator_(building_design)
https://en.wikipedia.org/wiki/Seismic_base_isolation
https://en.wikipedia.org/wiki/Substructure_(engineering)
https://en.wikipedia.org/wiki/Ashlar
https://en.wikipedia.org/wiki/Seismic_vibration_control
https://en.wikipedia.org/wiki/Resonance
https://en.wikipedia.org/wiki/Tuned_mass_damper
https://en.wikipedia.org/wiki/Resonance
https://en.wikipedia.org/wiki/Pendulum
https://en.wikipedia.org/wiki/Seismic_loading
https://en.wikipedia.org/wiki/Well_nut
https://en.wikipedia.org/wiki/Sulfur%E2%80%93iodine_cycle
https://en.wikipedia.org/wiki/Continuous_production
https://en.wikipedia.org/wiki/Scalability
https://en.wikipedia.org/wiki/Cogeneration
https://en.wikipedia.org/wiki/Waste_heat
https://en.wikipedia.org/wiki/Glass_production
Tunnel diodes have a heavily doped positive-to-negative (P-N) junction that is about 10 nm (100 Å) wide. The heavy doping results in a broken band gap, where conduction band electron states on the N-side are more or less aligned with valence band hole states on the P-side. They are usually made from germanium, but can also be made from gallium arsenide and silicon materials.
https://en.wikipedia.org/wiki/Tunnel_diode
https://en.wikipedia.org/wiki/Electron_hole
The Bravais lattice concept is used to formally define a crystalline arrangement and its (finite) frontiers. A crystal is made up of one or more atoms, called the basis or motif, at each lattice point. The basis may consist of atoms, molecules, or polymer strings of solid matter, and the lattice provides the locations of the basis.
https://en.wikipedia.org/wiki/Bravais_lattice
For each geometric class, the possible arithmetic classes are
- None: no reflection lines
- Along: reflection lines along lattice directions
- Between: reflection lines halfway in between lattice directions
- Both: reflection lines both along and between lattice directions
https://en.wikipedia.org/wiki/Space_group
https://en.wikipedia.org/wiki/Bravais_lattice
https://en.wikipedia.org/wiki/Screw_axis
https://en.wikipedia.org/wiki/Glide_plane
https://en.wikipedia.org/wiki/Bravais_lattice
https://en.wikipedia.org/wiki/Unit_cell
https://en.wikipedia.org/wiki/Rotation
https://en.wikipedia.org/wiki/Reflection_(mathematics)
https://en.wikipedia.org/wiki/Improper_rotation
https://en.wikipedia.org/wiki/Crystallographic_point_group
https://en.wikipedia.org/wiki/Crystal_system
https://en.wikipedia.org/wiki/Rank_of_a_group
https://en.wikipedia.org/wiki/Wallpaper_group
https://en.wikipedia.org/wiki/Line_group
https://en.wikipedia.org/wiki/Rod_group
https://en.wikipedia.org/wiki/Layer_group
https://en.wikipedia.org/wiki/Affine_transformation
https://en.wikipedia.org/wiki/Semidirect_product
https://en.wikipedia.org/wiki/Chirality_(mathematics)
https://en.wikipedia.org/wiki/Affine_space
https://en.wikipedia.org/wiki/Antiferromagnetism
https://en.wikipedia.org/wiki/Neutron_diffraction
https://en.wikipedia.org/wiki/Space_group
https://en.wikipedia.org/wiki/Magnetic_structure
https://en.wikipedia.org/wiki/Magnetic_space_group
https://en.wikipedia.org/wiki/One-dimensional_symmetry_group#Point_group
https://en.wikipedia.org/wiki/Neutron_scattering
https://en.wikipedia.org/wiki/Neutron_temperature
https://en.wikipedia.org/wiki/Spallation
https://en.wikipedia.org/wiki/Crystal_monochromator
https://en.wikipedia.org/wiki/Powder_diffraction
https://en.wikipedia.org/wiki/Neutron_radiation
https://en.wikipedia.org/wiki/Neutron_activation
https://en.wikipedia.org/wiki/Elementary_particle
https://en.wikipedia.org/wiki/Diffraction
https://en.wikipedia.org/wiki/Atomic_form_factor
https://en.wikipedia.org/wiki/Amorphous_solid
https://en.wikipedia.org/wiki/Rietveld_refinement
https://en.wikipedia.org/wiki/ISIS_Neutron_and_Muon_Source
https://en.wikipedia.org/wiki/Magnetic_nanoparticles
https://en.wikipedia.org/wiki/Pipeline_transport#Oil_and_natural_gas
https://en.wikipedia.org/wiki/Solvation_shell
https://en.wikipedia.org/wiki/Transition_metal_hydride
https://en.wikipedia.org/wiki/Bragg%27s_law
https://en.wikipedia.org/wiki/Neutron_scattering#Inelastic_neutron_scattering
https://en.wikipedia.org/wiki/Dynamic_structure_factor
https://en.wikipedia.org/wiki/Condensed_matter_physics
https://en.wikipedia.org/wiki/Neutron_triple-axis_spectrometry
https://en.wikipedia.org/wiki/Neutron_spin_echo
https://en.wikipedia.org/wiki/Neutron_resonance_spin_echo
https://en.wikipedia.org/wiki/Neutron_flux
https://en.wikipedia.org/wiki/Wave_vector
https://en.wikipedia.org/wiki/Neutron_research_facility
https://en.wikipedia.org/wiki/Neutron_reflectometry
https://en.wikipedia.org/wiki/Neutron_transport
https://en.wikipedia.org/wiki/LARMOR_neutron_microscope
https://en.wikipedia.org/wiki/Category:Neutron-related_techniques
https://en.wikipedia.org/wiki/Bonner_sphere
https://en.wikipedia.org/wiki/Category:Neutron-related_techniques
https://en.wikipedia.org/wiki/Engineering_diffraction
https://en.wikipedia.org/wiki/Momentum_transfer
https://en.wikipedia.org/wiki/Racemic_crystallography
https://en.wikipedia.org/wiki/Reciprocal_lattice
https://en.wikipedia.org/wiki/Texture_(chemistry)
https://en.wikipedia.org/wiki/Transfer-matrix_method_(optics)
https://en.wikipedia.org/wiki/Neutron-velocity_selector
https://en.wikipedia.org/wiki/Neutron_moisture_gauge
https://en.wikipedia.org/wiki/Neutron_depth_profiling
https://en.wikipedia.org/wiki/Semiconductor_detector
https://en.wikipedia.org/wiki/Category:Crystallography
https://en.wikipedia.org/wiki/Grazing_incidence_diffraction
https://en.wikipedia.org/wiki/Grazing-incidence_small-angle_scattering
https://en.wikipedia.org/wiki/Angle_of_incidence
https://en.wikipedia.org/wiki/Evanescent_field
https://en.wikipedia.org/wiki/Antenna_(radio)
The NSLS experimental floor consisted of two electron storage rings: an X-ray ring and a VUV (vacuum ultraviolet) ring which provided intense, focused light spanning the electromagnetic spectrum from the infrared through X-rays. The properties of this light and the specially designed experimental stations, called beamlines, allowed scientists in many fields of research to perform experiments not otherwise possible at their own laboratories.
https://en.wikipedia.org/wiki/National_Synchrotron_Light_Source
Neutron depth profiling (NDP) is a near-surface analysis technique that is commonly used to obtain profiles of concentration as a function of depth for certain technologically important light elements in nearly any substrate. The technique was first proposed by Ziegler et al. to determine the concentration profiles of boron impurities in silicon substrates, and later improved by Biersack and coworkers to much of its existing capabilities.
Neutron depth profiling
In NDP, a thermal or cold neutron beam passes through a material and interacts with isotopes that emit monoenergetic charged particles upon neutron absorption; either a proton or an alpha, and a recoil nucleus. Since the charged particles are equally likely to be emitted in any direction, reaction kinematics are straightforward. Because low-energy neutrons are used, there is no significant momentum transfer from the neutron beam to the substrate, and the analysis is practically non-destructive. As charged particles move towards the surface, they are rapidly slowed down, primarily by interacting with the electrons of the substrate. The amount of energy loss is directly related to the thickness penetrated by the particle. The depth of the reaction site can be found by stopping power correlations.
Profiling
Conventionally, the residual energies of charged particles and recoil nuclei have been measured by a silicon charged-particle detector; most commonly either a surface barrier detector (SBD) or a passivated implanted planar silicon (PIPS) detector. In this configuration, the semiconductor detector is placed opposite to the surface of the sample being analyzed, and an energy spectrum of charged particles emitted by the neutron-induced reaction is acquired.
See also
https://en.wikipedia.org/wiki/Neutron_depth_profiling
Because of the large surface area to volume ratio of MEMS, forces produced by ambient electromagnetism (e.g., electrostatic charges and magnetic moments), and fluid dynamics (e.g., surface tension and viscosity) are more important design considerations than with larger scale mechanical devices. MEMS technology is distinguished from molecular nanotechnology or molecular electronics in that the latter two must also consider surface chemistry.
https://en.wikipedia.org/wiki/MEMS
https://en.wikipedia.org/wiki/Magnetic_lattice_(accelerator)
https://en.wikipedia.org/wiki/MEMS
https://en.wikipedia.org/wiki/Actuator
https://en.wikipedia.org/wiki/Deposition_(chemistry)
https://en.wikipedia.org/wiki/Silicon_nanowire
https://en.wikipedia.org/wiki/Thermal_oxidation
https://en.wikipedia.org/wiki/Photovoltaics
https://en.wikipedia.org/wiki/Orders_of_magnitude_(numbers)#1012
https://en.wikipedia.org/wiki/Hooke%27s_law
https://en.wikipedia.org/wiki/Injection_moulding
https://en.wikipedia.org/wiki/Embossing_(manufacturing)
https://en.wikipedia.org/wiki/Microfluidics
https://en.wikipedia.org/wiki/Silicon_carbide
https://en.wikipedia.org/wiki/Ceramic
https://en.wikipedia.org/wiki/Sputtering
https://en.wikipedia.org/wiki/Biosensor
https://en.wikipedia.org/wiki/Elastic_modulus
https://en.wikipedia.org/wiki/Piezoelectricity
https://en.wikipedia.org/wiki/Plasma-enhanced_chemical_vapor_deposition
https://en.wikipedia.org/wiki/Electron-beam_lithography
https://en.wikipedia.org/wiki/Maskless_lithography
https://en.wikipedia.org/wiki/Diffraction-limited_system
https://en.wikipedia.org/wiki/Photolithography
https://en.wikipedia.org/wiki/Ion_beam_lithography
https://en.wikipedia.org/wiki/Dry_etching
https://en.wikipedia.org/wiki/X-ray_lithography
https://en.wikipedia.org/wiki/Crystallography
https://en.wikipedia.org/wiki/Hydrofluoric_acid
https://en.wikipedia.org/wiki/Xenon_difluoride
https://en.wikipedia.org/wiki/Plasma_etching
https://en.wikipedia.org/wiki/Deep_reactive-ion_etching
https://en.wikipedia.org/wiki/Wafer_backgrinding
https://en.wikipedia.org/wiki/Wafer_dicing#Stealth_dicing
https://en.wikipedia.org/wiki/Wafer_dicing
https://en.wikipedia.org/wiki/Pressure_sensor
https://en.wikipedia.org/wiki/Surface_micromachining
https://en.wikipedia.org/wiki/Analog_Devices
https://en.wikipedia.org/wiki/Accelerometer
https://en.wikipedia.org/wiki/Electronic_stability_control
https://en.wikipedia.org/wiki/Vibrating_structure_gyroscope#MEMS_gyroscopes
https://en.wikipedia.org/wiki/MEMS_magnetic_field_sensor
https://en.wikipedia.org/wiki/Autopilot
https://en.wikipedia.org/wiki/Virtual_reality
https://en.wikipedia.org/wiki/Barometer#MEMS_Barometers
https://en.wikipedia.org/wiki/Pressure_sensor
https://en.wikipedia.org/wiki/Real-time_clock
https://en.wikipedia.org/wiki/Optical_transistor
https://en.wikipedia.org/wiki/Lab-on-a-chip
https://en.wikipedia.org/wiki/Micropump
https://en.wikipedia.org/wiki/Chemoreceptor
https://en.wikipedia.org/wiki/Interferometric_modulator_display
https://en.wikipedia.org/wiki/Energy_harvesting
https://en.wikipedia.org/wiki/Ultrasonic_transducer
https://en.wikipedia.org/wiki/Microelectromechanical_system_oscillator
https://en.wikipedia.org/wiki/Scanning_probe_microscopy
https://en.wikipedia.org/wiki/Atomic_force_microscopy
https://en.wikipedia.org/wiki/Lidar
https://en.wikipedia.org/wiki/3D_modeling
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