Shopping on line can be easy, simple and save you lots of money. It can also take a lot of your time, frustrate you, and result in unwanted purchases. Now the same can be said for regular high street shopping, but with the vast opportunity presented by the Internet it will pay you to spend a few minutes reading this and understanding how to better optimize your Gas Turbine shopping experience:

1. Compare - without doubt the biggest advantage that the Gas Turbine offers shoppers today is the ability to compare thousands of Gas Turbine at a time. This is a great thing, but not necessarily all the time! Too much can be daunting at times so take advantage of the great comparison sites and where possible let them do the hard work for you.

2. Research - if it has been said it will be on the internet. Ignorance is no longer a justifiable reason for buying the wrong thing. Take the time to research in detail everything that you could possible want to know about

3. Testimonials - don't know anybody that has bought a Gas Turbine? Wrong! If the Gas Turbine is good the internet will let you know. Use the Internet as a friend and get testimonials before you buy.

4. Questions - Got a question about Gas Turbine then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....

5. Reputation - Never heard of the company selling Gas Turbine? Don't worry, no reason why you should know every company in the world, but you know someone that does! Use the internet to find out what people are saying about Gas Turbine and build up a picture of their reputation for sales, returns, customer service, delivery etc.

6. Returns - still worried that even after all of the above your Gas Turbine wont be what you want? Check out the returns policy. There is so much competition now that someone, somewhere is bound to offer the terms that you are comfortable with.

7. Feedback - happy with your Gas Turbine then let people know, after all you are depending on others people input in your buying decision, so why not give a little back.

8. Security - check for the yellow padlock on the Gas Turbine site before you buy, and the s after http:/ /i.e. https:// = a secure site

9. Contact - got a question about Gas Turbine, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.

10. Payment - ready to pay for your Gas Turbine, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.

and turbine, a recuperator, and foil bearings.

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 ignition system 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.

History

Theory of operation Gas turbines are described thermodynamics 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:

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

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

c) 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 fuel 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 turbofan) 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 plain bearing are a critical part of design. Traditionally, they have been Fluid bearing, or oil-cooled ball bearings. This is giving way to foil bearings, which have been successfully used in micro turbines and auxiliary power units.

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.

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.

Gas turbines for electrical power production unit has a rated Thermodynamic efficiency of 60% in combined cycle configurations.

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 gas-absorption refrigerator 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 Revolutions per minute to match the alternating current 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 plant 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 to 40% thermodynamic efficiency. The most efficient turbines have reached 46% efficiency.

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.

Radial Gas Turbines 1963, Norway, Jan Mowill initiated the development at Kongsberg Våpenfabrikk. The turbine had a unique, all radial configuration, originally rated at 1200 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 privatised, 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 / 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 servicability, a four can combustion systems was favoured 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 degrees Celsius 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 / multifuel capabilities.

The generator sets can be installed as single or multiple units effectively covering installation requirements from 2 MW to 10 MW.

Scale jet engines Also known as:

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. 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.

Microturbines by M-Dot Also known as:

Microturbines are becoming wide spread for distributed generation and cogeneration applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts.

Part of their success is due to advances in electronics, which 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. 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 1990's 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.

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 (car) unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car, and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum (London). 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 (car) 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 1989's filmed Batman, the production department built a working turbine vehicle for the Batmobile prop. Its fuel capacity, however, was reportedly only enough for 15 seconds of use at a time. Hall of Fame Museum, with the Pratt & Whitney gas turbine shown.American car manufacturer Chrysler Corporation demonstrated several Chrysler Turbine engines-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 Corporation introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the General Motors EV-1#EV1 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 Turbine Corporation 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 engine 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 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 103. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See Tank#Gas turbines for more details.

Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See gas turbine-electric locomotive for more information.

Naval use Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Tribal class frigate frigates, the first of which (HMS Ashanti (F117)) was commissioned in 1961.

The Swedish Navy produced 6 Spica class torpedoboats between 1966 and 1967 powered by 3 Bristol Siddeley Bristol Proteus, 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 gunboat 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 Iroquois class destroyer 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 United States Coast Guard's Hamilton class cutter USCG high endurance cutter the first of which (USCGC Hamilton (WHEC-715)) commissioned in 1967. Since then, they have powered the United States Navy's Oliver Hazard Perry class frigate, Spruance class destroyer and Arleigh Burke class destroyer destroyers, and Ticonderoga class cruiser. USS Makin Island (LHD-8), a modified Wasp class amphibious assault ship, is to be the Navy's first amphibious assault ship powered by gas turbines.

Commercial Use 900 class gas turbine powered ferry.Three Rolls-Royce plc gas turbines power the 118 WallyPower, a super-yacht. These engines combine for a total of 16,800 hp allowing this boat to maintain speeds of 60 Knot (speed) 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 High-speed Sea Service fastcraft ferries. HSS 1500-class Stena Explorer, Stena Voyager and Stena Discovery vessels use combined gas and gas (COGAG) setups of twin General Electric General Electric LM2500 plus GE LM1600 power for a total of 68,000 kW. The slightly smaller HSS 900-class Stena Charisma, uses twin Asea Brown Boveri–:sv: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 of 2000, the Millennium (ship) became the first cruise ship to be propelled by gas turbines, in a COGAS configuration. The RMS Queen Mary 2 uses a CODAG configuration.

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.

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 Computational fluid dynamics 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.

Advantages and disadvantages of gas turbine engines Advantages of gas turbine engines http://people.bath.ac.uk/ab2stb/Dis%20or%20Advantages.htm

Disadvantages of gas turbine 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.

See also

References Further reading

External links

and turbine, a recuperator, and foil bearings.

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 ignition system 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.

History

Theory of operation Gas turbines are described thermodynamics 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:

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

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

c) 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 fuel 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 turbofan) 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 plain bearing are a critical part of design. Traditionally, they have been Fluid bearing, or oil-cooled ball bearings. This is giving way to foil bearings, which have been successfully used in micro turbines and auxiliary power units.

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.

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.

Gas turbines for electrical power production unit has a rated Thermodynamic efficiency of 60% in combined cycle configurations.

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 gas-absorption refrigerator 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 Revolutions per minute to match the alternating current 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 plant 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 to 40% thermodynamic efficiency. The most efficient turbines have reached 46% efficiency.

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.

Radial Gas Turbines 1963, Norway, Jan Mowill initiated the development at Kongsberg Våpenfabrikk. The turbine had a unique, all radial configuration, originally rated at 1200 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 privatised, 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 / 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 servicability, a four can combustion systems was favoured 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 degrees Celsius 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 / multifuel capabilities.

The generator sets can be installed as single or multiple units effectively covering installation requirements from 2 MW to 10 MW.

Scale jet engines Also known as:

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. 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.

Microturbines by M-Dot Also known as:

Microturbines are becoming wide spread for distributed generation and cogeneration applications. They range from handheld units producing less than a kilowatt to commercial sized systems that produce tens or hundreds of kilowatts.

Part of their success is due to advances in electronics, which 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. 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 1990's 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.

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 (car) unveiled the first car powered with a gas turbine engine. The two-seater JET1 had the engine positioned behind the seats, air intake grilles on either side of the car, and exhaust outlets on the top of the tail. During tests, the car reached top speeds of 140 km/h, at a turbine speed of 50,000 rpm. The car ran on petrol, paraffin or diesel oil, but fuel consumption problems proved insurmountable for a production car. It is currently on display at the London Science Museum (London). 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 (car) 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 1989's filmed Batman, the production department built a working turbine vehicle for the Batmobile prop. Its fuel capacity, however, was reportedly only enough for 15 seconds of use at a time. Hall of Fame Museum, with the Pratt & Whitney gas turbine shown.American car manufacturer Chrysler Corporation demonstrated several Chrysler Turbine engines-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 Corporation introduced the first commercial gas turbine powered hybrid vehicle—as a limited production run of the General Motors EV-1#EV1 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 Turbine Corporation 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 engine 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 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 103. Today, the Soviet/Russian T-80 and U.S. M1 Abrams tanks use gas turbine engines. See Tank#Gas turbines for more details.

Several locomotive classes have been powered by gas turbines, the most recent incarnation being Bombardier's JetTrain. See gas turbine-electric locomotive for more information.

Naval use Gas turbines are used in many naval vessels, where they are valued for their high power-to-weight ratio and their ships' resulting acceleration and ability to get underway quickly. The first gas-turbine-powered naval vessel was the Royal Navy's Motor Gun Boat MGB 2009 (formerly MGB 509) converted in 1947. The first large, gas-turbine powered ships, were the Royal Navy's Tribal class frigate frigates, the first of which (HMS Ashanti (F117)) was commissioned in 1961.

The Swedish Navy produced 6 Spica class torpedoboats between 1966 and 1967 powered by 3 Bristol Siddeley Bristol Proteus, 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 gunboat 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 Iroquois class destroyer 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 United States Coast Guard's Hamilton class cutter USCG high endurance cutter the first of which (USCGC Hamilton (WHEC-715)) commissioned in 1967. Since then, they have powered the United States Navy's Oliver Hazard Perry class frigate, Spruance class destroyer and Arleigh Burke class destroyer destroyers, and Ticonderoga class cruiser. USS Makin Island (LHD-8), a modified Wasp class amphibious assault ship, is to be the Navy's first amphibious assault ship powered by gas turbines.

Commercial Use 900 class gas turbine powered ferry.Three Rolls-Royce plc gas turbines power the 118 WallyPower, a super-yacht. These engines combine for a total of 16,800 hp allowing this boat to maintain speeds of 60 Knot (speed) 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 High-speed Sea Service fastcraft ferries. HSS 1500-class Stena Explorer, Stena Voyager and Stena Discovery vessels use combined gas and gas (COGAG) setups of twin General Electric General Electric LM2500 plus GE LM1600 power for a total of 68,000 kW. The slightly smaller HSS 900-class Stena Charisma, uses twin Asea Brown Boveri–:sv: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 of 2000, the Millennium (ship) became the first cruise ship to be propelled by gas turbines, in a COGAS configuration. The RMS Queen Mary 2 uses a CODAG configuration.

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.

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 Computational fluid dynamics 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.

Advantages and disadvantages of gas turbine engines Advantages of gas turbine engines http://people.bath.ac.uk/ab2stb/Dis%20or%20Advantages.htm

Disadvantages of gas turbine 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.

See also

References Further reading

External links



 

Gas Turbine



 
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