Bewise Inc. www.tool-tool.com Reference source from the internet.
A gas turbine extracts energy from a flow of hot gas produced by combustion of gas or fuel oil in a stream of compressed air. It has an upstream air compressor (radial or axial flow) mechanically coupled to a downstream turbine and a combustion chamber in between. "Gas turbine" may also refer to just the turbine element.
Energy is released when compressed air is mixed with fuel and ignited in the combustor. The resulting gases are directed over the turbine's blades, spinning the turbine, and mechanically powering the compressor. Finally, the gases are passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure.
Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, electrical generators, and even tanks.
[edit] History
- 60: Hero's Engine (aeolipile) - apparently Hero's steam engine was taken to be no more than a toy, and thus its full potential not realized for centuries.
- 1500: The "Chimney Jack" was drawn by Leonardo da Vinci which was turning a roasting spit. Hot air from a fire rose through a series of fans which connect and turn the roasting spit.
- 1629: Jets of steam rotated a turbine that then rotated driven machinery allowed a stamping mill to be developed by Giovanni Branca.
- 1678: Ferdinand Verbeist built a model carriage relying on a steam jet for power.
- 1791: A 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.
- 1872: The first true gas turbine engine was designed by Dr F. Stolze, 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). 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.
- 1903: A Norwegian, Ægidius Elling, was able to build the first gas turbine that was able to produce more power than needed to run its own components, which was considered an achievement in a time when knowledge about aerodynamics was limited. Using rotary compressors and turbines it produced 11 hp (massive for those days). His work was later used by Sir Frank Whittle.
- 1914: The first application for a gas turbine engine was filed by Charles Curtis.
- 1918: One of the leading gas turbine manufacturers of today, General Electric, started their gas turbine division.
- 1920. The then current gas flow through passages was developed by Dr A. A. Griffith to a turbine theory with gas flow past airfoils.
- 1930. Sir Frank Whittle patented the design for a gas turbine for jet propulsion. His work on gas propulsion relied on the work from all those who had previously worked in the same field and he has himself stated that his invention would be hard to achieve without the works of Ægidius Elling. The first successful use of his engine was in April 1937.
- 1934. Raúl Pateras de Pescara patented the free-piston engine as a gas generator for gas turbines.
- 1936. Hans von Ohain and Max Hahn in Germany developed their own patented engine design at the same time that Sir Frank Whittle was developing his design in England.
[edit] Theory of operation
Gas turbines are described thermodynamically by the Brayton cycle, in which air is compressed isentropically, combustion occurs at constant pressure, and expansion over the turbine occurs isentropically back to the starting pressure.
In practice, friction, and turbulence cause:
- non-isentropic compression: for a given overall pressure ratio, the compressor delivery temperature is higher than ideal.
- non-isentropic expansion: although the turbine temperature drop necessary to drive the compressor is unaffected, the associated pressure ratio is greater, which decreases the expansion available to provide useful work.
- pressure losses in the air intake, combustor and exhaust: reduces the expansion available to provide useful work.
As with all cyclic heat engines, higher combustion temperature means greater efficiency. The limiting factor is the ability of the steel, nickel, ceramic, or other materials that make up the engine to withstand heat and pressure. Considerable engineering goes into keeping the turbine parts cool. Most turbines also try to recover exhaust heat, which otherwise is wasted energy. Recuperators are heat exchangers that pass exhaust heat to the compressed air, prior to combustion. Combined cycle designs pass waste heat to steam turbine systems. And combined heat and power (co-generation) uses waste heat for hot water production.
Mechanically, gas turbines can be considerably less complex than internal combustion piston engines. Simple turbines might have one moving part: the shaft/compressor/turbine/alternative-rotor assembly (see image above), not counting the fuel system.
More sophisticated turbines (such as those found in modern jet engines) may have multiple shafts (spools), hundreds of turbine blades, movable stator blades, and a vast system of complex piping, combustors and heat exchangers.
As a general rule, the smaller the engine the higher the rotation rate of the shaft(s) needs to be to maintain tip speed. Turbine blade tip speed determines the maximum pressure that can be gained, independent of the size of the engine. Jet engines operate around 10,000 rpm and micro turbines around 100,000 rpm.
Thrust bearings and journal bearings are a critical part of design. Traditionally, they have been hydrodynamic oil bearings, or oil-cooled ball bearings. This is giving way to foil bearings, which have been successfully used in micro turbines and auxiliary power units.
[edit] 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. Jet engines that produce thrust primarily from the direct impulse of exhaust gases are often called turbojets, whereas those that generate most of their thrust from the action of a ducted fan are often called turbofans or (rarely) fanjets.
[edit] Auxiliary power units
Auxiliary power units (APUs) are small gas turbines designed for auxiliary power of larger machines, such as those inside an aircraft. They supply compressed air for aircraft ventilation (with an appropriate compressor design), start-up power for larger jet engines, and electrical and hydraulic power. These are not to be confused with the auxiliary propulsion units, also abbreviated APUs, aboard the gas-turbine-powered Oliver Hazard Perry-class guided-missile frigates. The Perrys' APUs are large electric motors that provide maneuvering help in close waters, or emergency backup if the gas turbines are not working.
[edit] Gas turbines for electrical power production
Industrial gas turbines range in size from truck-mounted mobile plants to enormous, complex systems. They can be particularly efficient——up to 60%——when waste heat from the gas turbine is recovered by a heat recovery steam generator to power a conventional steam turbine in a combined cycle configuration. They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling or refrigeration. A cogeneration configuration can be over 90% efficient. The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the AC power grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated enclosure.
Simple cycle gas turbines in the power industry require smaller capital investment than either coal or nuclear power plants and can be scaled to generate small or large amounts of power. Also, the actual construction process can take as little as several weeks to a few months, compared to years for base load power plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Since they 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 couple 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, a gas turbine power plant may regularly operate during most hours of the day and even into the evening. A typical large simple cycle gas turbine may produce 100 to 300 megawatts of power and have 35–40% thermal efficiency. The most efficient turbines have reached 46% efficiency. [1]
[edit] 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.
[edit] Turboshaft engines
Turboshaft engines are often used to drive compression trains (for example in gas pumping stations or natural gas liquefaction plants)and are used to power almost all modern helicopters. The first shaft bears the compressor and the high speed turbine (often referred to as "Gas Generator" or "N1"), while the second shaft bears the low speed turbine (or "Power Turbine" or "N2"). This arrangement is used to increase speed and power output flexibility.
[edit] Radial Gas Turbines
1963, Norway, Jan Mowill initiated the development at Kongsberg Våpenfabrikk. The turbine had a unique, all radial configuration, originally rated at 1,200 kW. The turbine proved very successful and was generally sold in electric generating packages. The major markets for the units were in the maritime, offshore oil and gas and communications industries. During the following years, more than a thousand units were delivered world wide. Kongsberg Våpenfabrikk was privatized, split up and sold off in the late nineteen eighties and development of the original turbine business was discontinued under the new ownership. As a result, Jan and Hiroko Mowill founded OPRA in Hengelo in 1991.
Consequently the first 1.6 MW OP16 was designed as a single shaft, all-radial machine. NOx emissions were developed to a very low level for both diesel fuel and natural gas. This was achieved with a unique, patented fuel and air pre-mixer in connection with an annular combustor.
The current production model, OP16-3 features both single and dual fuel operation as well as low emissions on natural gas. For improved maintenance and serviceability, a four can combustion systems was favored rather than the annular combustor used on the prototype.
For a single stage radial turbine the pressure ratio of 6.7: 1 is relatively high, which entails a high turbine impeller tip speed of 700 m/s (equal to the velocity of a rifle bullet).
Since this is nearly the same as the velocity of the gas entering the impeller tip from the nozzle guide vanes, an "impact" between the hot gas and the turbine impeller is avoided.
It could be said that this phenomenon constitutes "dynamic" cooling gaining about 100°C compared to a temperature increase in an axial turbine. OPRA’s radial turbine is able to take this high tip speed due to it's "Eiffel Tower" shape with a strong base and a thinner blade tip region with low stresses. Having low stresses in the hot tip region and higher stresses in the cold, "fat" hub region makes OPRA work with nature rather than against it.
The OPRA radial turbine stage has an advanced aerodynamic design with an efficiency of 90% from the inlet of the guide vanes to the exhaust diffuser exit.
The efficient centrifugal compressor has a very good "match" with the turbine as their optimal running speeds are similar.
Since both compressor and turbine are close coupled via a Hirth-type teeth connection, an overhung rotor suspension is possible. This system provides balance integrity despite the differential thermal expansions between the compressor and turbine.
A ball bearing is placed in the front of the rotor support housing taking the combined thrust- and radial load. The rear, tilting pad bearing takes the main radial load. The cantilever, or overhung suspension of the rotor places the bearings in the cold section of the engine, avoiding oil supply to hot bearings. This system has considerable positive impact on engine reliability and maintenance.
A flexible coupling connects the turbine to the two stage planetary gearbox, reducing the turbine speed from 26000 to 1500 or 1800 rpm, depending on generator speed requirements
The OP16-3 has an ISO rating of 1.9 MW. The engine efficiency of nominally 27% is at the highest level in the below 2 MW power range. Past competitors (no longer active) in this range have been at the 23–25% level.
Utilising proven radial gas turbine technology, the OP16 gas turbine is a compact, efficient and reliable industrial gas turbine designed for supplying power generation applications to both the Oil and Gas and Industrial markets.
The OP16 generator sets can be provided in a variety of configurations to meet customer specific requirements. The engineering design, component selection and maintenance accessibility of the generator sets enhance high reliability and long product life. The generator sets can be provided with low emission and dual and multifuel capabilities.
Single or multiple OP16 units can effectively cover installations from 1.5 to 10 MW electric power demand.
OPRA provides gas turbine generating sets for customers world-wide within the oil & gas and industrial sectors. OPRA's 2 MW class OP16 gas turbine is of an industrial, all-radial design which provides robustness, reliability and class leading efficiency and emissions. Dual fuel and off-specification fuel options are also available. Complete gas turbine generating sets are engineered to meet customer specific requirements both for land based and offshore applications.
[edit] Scale jet engines
Also known as miniature gas turbines or micro-jets.
Many model engineers relish the challenge of re-creating the grand engineering feats of today as tiny working models. Naturally, the idea of re-creating a powerful engine such as the jet, fascinated hobbyists since the very first full size engines were powered up by Hans von Ohain and Frank Whittle back in the 1930s.
Recreating machines such as engines to a different scale is not easy. Because of the square-cube law, the behaviour of many machines does not always scale up or down at the same rate as the machine's size (and often not even in a linear way), usually at best causing a dramatic loss of power or efficiency, and at worst causing them not to work at all. An automobile engine, for example, will not work if reproduced in the same shape at the size of a human hand.
With this in mind the pioneer of modern Micro-Jets, Kurt Schreckling, produced one of the world's first Micro-Turbines, the FD3/67.[1] 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. Its radial compressor, which is cold, is small and the hot axial turbine is large experiencing more centrifugal forces, meaning that this design is limited by Mach number. Guiding vanes are used to hold the starter, after the compressor and before the turbine, but not after that. No bypass within the engine is used.
[edit] Microturbines
Also known as:
- Turbo alternators
- MicroTurbine® (registered trademark of Capstone Turbine Corporation)
- Turbogenerator® (registered tradename of Honeywell Power Systems, Inc.)
Microturbines are becoming wide spread for distributed power and combined heat and power applications. They range from hand held units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts.
Part of their success is due to advances in electronics, which allows unattended operation and interfacing with the commercial power grid. Electronic power switching technology eliminates the need for the generator to be synchronized with the power grid. This allows the generator to be integrated with the turbine shaft, and to double as the starter motor.
Microturbine systems have many advantages over reciprocating engine generators, such as higher power density (with respect to footprint and weight), extremely low emissions and few, or just one, moving part. Those designed with foil bearings and air-cooling operate without oil, coolants or other hazardous materials. Microturbines also have the advantage of having the majority of their waste heat contained in their relatively high temperature exhaust, whereas the waste heat of recriprocating engines is split between its exhaust and cooling system. [2] However, reciprocating engine generators are quicker to respond to changes in output power requirement and are usually slightly more efficient, although the efficiency of microturbines is increasing. Microturbines also lose more efficiency at low power levels than reciprocating engines.
They accept most commercial fuels, such as natural gas, propane, diesel and kerosene. They are also able to produce renewable energy when fueled with biogas from landfills and sewage treatment plants.
Microturbine designs usually consist of a single stage radial compressor, a single stage radial turbine and a recuperator. Recuperators are difficult to design and manufacture because they operate under high pressure and temperature differentials. Exhaust heat can be used for water heating, drying processes or absorption chillers, which create cold for air conditioning from heat energy instead of electric energy.
Typical microturbine efficiencies are 25 to 35%. When in a combined heat and power cogeneration system, efficiencies of greater than 80% are commonly achieved.
MIT started its millimeter size turbine engine project in the middle of the 1990s when Professor of Aeronautics and Astronautics Alan H. Epstein considered the possibility of creating a personal turbine which will be able to meet all the demands of a modern person's electrical needs, just like a large turbine can meet the electricity demands of a small city. According to Professor Epstein current commercial Li-ion rechargeable batteries deliver about 120-150 Wh/kg. MIT's millimeter size turbine will deliver 500-700 Wh/kg in the near term, rising to 1200-1500 Wh/kg in the longer term[3].
[edit] Gas turbines in vehicles
Gas turbines are used on ships, locomotives, helicopters, and in tanks. A number of experiments have been conducted with gas turbine powered automobiles.
In 1950, designer F.R. Bell and Chief Engineer Maurice Wilks from British car manufacturers Rover unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car, and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum. Rover and the BRM Formula One team joined forces to produce a gas turbine powered coupe, which entered the 1963 24 Hours of Le Mans, driven by Graham Hill and Richie Ginther. It averaged 107.8 mph (173 km/h) and had a top speed of 142 mph (229 km/h). In 1967, the revolutionary STP Oil Treatment Special four-wheel drive turbine-powered special fielded by racing and entrepreneurial legend Andy Granatelli and driven by Parnelli Jones nearly won the Indianapolis 500; the STP Pratt & Whitney 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. In 1971 Lotus principal Colin Chapman introduced the Lotus 56B F1 car, powered by a Pratt & Whitney 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.
The fictional Batmobile is often said to be powered by a gas turbine or a jet engine. In fact, in 1989s filmed Batman, the production department built a working turbine vehicle for the Batmobile prop[4]. Its fuel capacity, however, was reportedly only enough for 15 seconds of use at a time.
American car manufacturer Chrysler demonstrated several prototype gas turbine-powered cars from the early 1950s through the early 1980s. Chrysler built fifty Chrysler Turbine Cars in 1963 and conducted the only consumer trial of gas turbine-powered cars.
In 1993 General Motors introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the EV-1 series hybrid. A Williams International 40 kW turbine drove an alternator which powered the battery-electric powertrain. The turbine design included a recuperator.
The arrival of the Capstone Microturbine has led to several hybrid bus designs from US and New Zealand manufacturers, starting with HEV-1 by AVS of Chattanooga, Tennessee in 1999, and closely followed by Ebus and ISE Research in California, and Designline in New Zealand. AVS turbine hybrids were plagued with reliability and quality control problems, resulting in liquidation of AVS in 2003. Today, the most successful design by Designline is now operated in 5 cities in 6 countries, with over 30 buses in operation worldwide.
It is worth noting that a key advantage of jets and turboprops for aeroplane propulsion - their superior performance at high altitude compared to piston engines, particularly naturally-aspirated ones - is irrelevant in automobile applications. Their power-to-weight advantage is far less important.
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 hybrids, gas turbines reduce the responsiveness problem, and the emergence of the continuously variable transmission may also help alleviate this. A recent idea is the 'Multi-Pressure' turbine proposed by Robin Mackay of Agile Turbines. This concept is expected to provide three different power level ranges - each of them exhibiting high efficiency and low emission levels. The engine has two compressor spindles and an intercooler. By a system of three-way valves, it can be operated with both 'wings' in super atmospheric pressure mode (high power) or one 'wing' super atmospheric and the other sub atmospheric (cruising power) or both 'wings' in sub atmospheric mode (idling). Since there is no change in direction or speed of gas flow at transition from one power level to another (only mass flow changes) transition is almost instantaneous - thus overcoming the slow throttle response characteristic of gas turbines in land vehicle applications.
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; but turbines are mass produced in the closely related form of the turbocharger.
The MTT Turbine SUPERBIKE appeared in 2000 (hence the designation of Y2K Superbike by MTT) and is the first production motorcycle powered by a jet engine - specifically, a Rolls-Royce Allison model 250 turboshaft engine, producing about 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 Records for most powerful production motorcycle and most expensive production motorcycle, with a price tag of US$185,000.
Use of gas turbines in military tanks has been more successful. In the 1950s, a Conqueror heavy tank was experimentally fitted with a Parsons 650-hp gas turbine, and they have been used as auxiliary power units in several other production models. The first production turbine tank was the Swedish Stridsvagn 103A. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See tank for more details.
Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See gas turbine-electric locomotive for more information.
[edit] Naval use
Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Type 81 (Tribal class) frigates, the first of which (HMS Ashanti) was commissioned in 1961.
The Swedish Navy produced 6 Spica class torpedoboats between 1966 and 1967 powered by 3 Bristol Siddeley Proteus 1282, each delivering 4300 hp. 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.Fast missile boat
The Finnish Navy issued two Turunmaa class corvettes, Turunmaa and Karjala, in 1968. They were equipped with one 16 000 shp Rolls-Royce Olympus TMB3 gas turbine and two Wärtsilä marine diesels for slower speeds. Before the waterjet-propulsion Helsinki class missile boats, they were the fastest vessels in the Finnish Navy; they regularly achieved 37 knot speeds, but they are known to have achieved 45 knots when the restriction mechanism of the turbine was geared off. The Turunmaas were paid off in 2002. Karjala is today a museum ship in Turku, and Turunmaa serves as a flotating 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 ships were the U.S. Coast Guard's Hamilton-class High Endurance Cutters the first of which (USCGC Hamilton) commissioned in 1967. Since then, they have powered the U.S. Navy's Perry-class frigates, Spruance-class and Arleigh Burke-class destroyers, and Ticonderoga-class guided missile cruisers. USS Makin Island, a modified Wasp-class amphibious assault ship, is to be the Navy's first amphib powered by gas turbines.
[edit] Commercial Use
Three Rolls-Royce gas turbines power the 118 WallyPower, a 118-foot (36 m) super-yacht. These engines combine for a total of 16,800 hp allowing this 118-foot (36 m) boat to maintain speeds of 60 knots or 70mph.
There have been a number of experiments in which gas turbines were used to power seagoing commercial vessels. The earliest of these experiments may have been the oil tanker "Aurus" (Anglo Saxon Petroleum) - circa 1949.
Between 1970 and 1982, Seatrain Container Lines operated a scheduled container service across the North Atlantic with four 26,000 tonne dwt. container ships. Those ships were powered by twin Prat & Whitney gas turbines of the FT 4 series. The four ships in the class were named "Euroliner", "Eurofreighter", "Asialiner" and "Asiafreighter". They operated a transatlantic container service between ports on the eastern seaboard of the United States and ports in north west Europe. Following the dramatic OPEC price increases of the mid-nineteen seventies, 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). The modifications were partially successful. It was proved that particular fuel could be used in a marine gas turbine but, savings made were less than anticipated due to increased maintenance requirements. After 1982 the ships were sold, then re-engined with more economical diesel engines. Because the new engines were much larger, there was a consequential loss of some cargo space.
The first passenger ferry to use a gas turbine was the GTS Finnjet, built in 1977 and powered with two Pratt & Whitney FT 4C-1 DLF turbines, generating 55000 kW 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 just four years of service additional diesel engines were installed on the ship to allow less costly operations during off-season. Another example of commercial usage of gas turbines in a passenger ship are Stena Line's HSS class fastcraft ferries. HSS 1500-class Stena Explorer, Stena Voyager and Stena Discovery vessels use combined gas and gas (COGAG) setups of twin GE LM2500 plus GE LM1600 power for a total of 68,000 kW. The slightly smaller HSS 900-class Stena Charisma, uses twin ABB–STAL GT35 turbines rated at 34,000 kW gross. The Stena Discovery was withdrawn from service in 2007, another victim of too high fuel costs.
In July 2000, the Millennium became the first cruise ship to be propelled by gas turbines, in a COGAS configuration. The RMS Queen Mary 2 uses a CODAG configuration.[5]
[edit] Amateur gas turbines
A popular hobby is to construct a gas turbine from an automotive turbocharger. A combustion chamber is fabricated and plumbed between the compressor and turbine. Like many technology based hobbies, they tend to give rise to manufacturing businesses over time. Several small companies manufacture small turbines and parts for the amateur. See external links for resources.
[edit] Advances in technology
Gas turbine technology has steadily advanced since its inception and continues to evolve; research is active in producing ever smaller gas turbines. Computer design, specifically CFD and finite element analysis along with material advances, has allowed higher compression ratios and temperatures, more efficient combustion, better cooling of engine parts and reduced emissions. On the emissions side, the challenge in technology is actually getting a catalytic combustor running properly in order to achieve single digit NOx emissions to cope with the latest regulations. Additionally, compliant foil bearings were commercially introduced to gas turbines in the 1990s. They can withstand over a hundred thousand start/stop cycles and eliminated the need for an oil system.
On another front, microelectronics and power switching technology have enabled commercially viable micro turbines for distributed and vehicle power.
[edit] Advantages and disadvantages of gas turbine engines
[edit] Advantages of gas turbine engines
- Very high power-to-weight ratio, compared to reciprocating engines (ie. most road vehicle engines);
- Smaller than most reciprocating engines of the same power rating.
- Moves in one direction only, with far less vibration than a reciprocating engine.
- Simpler design.
- Low operating pressures.
- High operation speeds.
- Low lubricating oil cost and consumption.
[edit] Disadvantages of gas turbine engines
- Cost is much greater than for a similar-sized reciprocating engine (very high-performance, strong, heat-resistant materials needed);
- Use more fuel when idling compared to reciprocating engines.
These disadvantages explain why road vehicles, which are smaller, cheaper and follow a less regular pattern of use than tanks, helicopters, large boats and so on, do not use gas turbine engines, regardless of the size and power advantages imminently available.
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