Turbine | Define Turbine at Dictionary.com turbine [tur-bin, -bahyn] /ˈtɜr bɪn, -baɪn/ Spell noun 1. any of various machines having a rotor, usually with vanes or blades, driven by the pressure, momentum, or reactive thrust of a moving fluid, as steam, water, hot gases, or air, either occurring in the form of free jets or as a fluid passing through and entirely filling a housing around the rotor. Expand 1815-1825 1815-25; < French < Latin turbin-, stem of turbō something that spins, e.g., top, spindle, whirlwind; akin to turbid Dictionary.com Unabridged Examples from the Web for turbine Expand Contemporary Examples Unfortunately for Crist, it will likely take a turbine engine to generate enough wind in his flagging sails to overtake Rubio. Steam Turbines Hubert E. Collins Every throb of the turbine engines was a thrust toward home. Love Stories Mary Roberts Rinehart Are they after some more of dad's inventions because they didn't get his turbine motor? One form of the steam-engine that is coming into general use is the turbine.

Physics Willis Eugene Tower British Dictionary definitions for turbine Expand noun 1. any of various types of machine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate. The moving fluid may be water, steam, air, or combustion products of a fuel See also reaction turbine , impulse turbine , gas turbine Word Origin C19: from French, from Latin turbō whirlwind, from turbāre to throw into confusion Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for turbine Expand n. 1838, from French turbine, from Latin turbinem (nominative turbo) "spinning top, eddy, whirlwind," related to turba "turmoil, crowd" (see turbid ). Originally applied to a wheel spinning on a vertical axis, driven by falling water.

Turbo in reference to gas turbine engines is attested from 1904. Turbocharger is from 1934. Aeronautic turboprop is attested from 1945, with second element short for propeller. Online Etymology Dictionary, © 2010 Douglas Harper Turbine - definition of turbine by The Free Dictionary Turbine - definition of turbine by The Free Dictionary (tûr′bĭn, -bīn′) n. Any of various machines in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder. [French, from Latin turbō, turbin-, spinning top, perhaps from Greek turbē, turmoil.] turbine (ˈtɜːbɪn; -baɪn) n (Mechanical Engineering) any of various types of machine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate. The moving fluid may be water, steam, air, or combustion products of a fuel.

See also reaction turbine , impulse turbine , gas turbine [C19: from French, from Latin turbō whirlwind, from turbāre to throw into confusion] tur•bine (ˈtɜr bɪn, -baɪn) n. any of various machines having a rotor, usu. with vanes or blades, driven by the pressure or thrust of a moving fluid, as steam, water, hot gases, or air, either in the form of free jets or as a fluid filling a housing around the rotor. [1815–25; < French < Latin turbin-, s. of turbō top, spindle, whirlwind; akin to turbid ] turbine An impulse turbine (top) rotates when the force of a stream of water hits cup-shaped buckets that are mounted around the perimeter of a rotor. In a reaction turbine (bottom), the pressure of the water being discharged from the nozzle forces the turbine to rotate in the direction opposite to the water's motion. tur·bine (tûr′bĭn, tûr′bīn′) Any of various machines in which the kinetic energy of a moving fluid, such as water, steam, or gas, is converted to rotary motion.

turbine - Came from Latin turbo, "whirl, whirling thing." See also related terms for whirl . ThesaurusAntonymsRelated WordsSynonymsLegend: Noun 1.

turbine - rotary engine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate vane , blade - flat surface that rotates and pushes against air or water gas turbine - turbine that converts the chemical energy of a liquid fuel into mechanical energy by internal combustion; gaseous products of the fuel (which is burned in compressed air) are expanded through a turbine hydroelectric turbine - turbine consisting of a large and efficient version of a water wheel used to drive an electric generator impulse turbine - a turbine that is driven by jets direct against the blades reaction turbine - a turbine with blades arranged to develop torque from gradual decrease of steam pressure from inlet to exhaust rotary engine - an internal-combustion engine in which power is transmitted directly to rotating components rotor , rotor coil - the rotating armature of a motor or generator stator , stator coil - mechanical device consisting of the stationary part of a motor or generator in or around which the rotor revolves steam turbine - turbine in which steam strikes blades and makes them turn wind turbine - a turbine that is driven by the wind Translations Turbines - definition of Turbines by The Free Dictionary Turbines - definition of Turbines by The Free Dictionary (tûr′

bĭn, -bīn′) n.

Any of various machines in which the kinetic energy of a moving fluid is converted to mechanical power by the impulse or reaction of the fluid with a series of buckets, paddles, or blades arrayed about the circumference of a wheel or cylinder. [French, from Latin turbō, turbin-, spinning top, perhaps from Greek turbē, turmoil.] turbine (ˈtɜːbɪn; -baɪn) n (Mechanical Engineering) any of various types of machine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate. The moving fluid may be water, steam, air, or combustion products of a fuel. See also reaction turbine , impulse turbine , gas turbine [C19: from French, from Latin turbō whirlwind, from turbāre to throw into confusion] tur•bine (ˈtɜr bɪn, -baɪn) n. any of various machines having a rotor, usu. with vanes or blades, driven by the pressure or thrust of a moving fluid, as steam, water, hot gases, or air, either in the form of free jets or as a fluid filling a housing around the rotor.

[1815–25; < French < Latin turbin-, s. of turbō top, spindle, whirlwind; akin to turbid ] turbine An impulse turbine (top) rotates when the force of a stream of water hits cup-shaped buckets that are mounted around the perimeter of a rotor. In a reaction turbine (bottom), the pressure of the water being discharged from the nozzle forces the turbine to rotate in the direction opposite to the water's motion. tur·bine (tûr′bĭn, tûr′bīn′) Any of various machines in which the kinetic energy of a moving fluid, such as water, steam, or gas, is converted to rotary motion. turbine - Came from Latin turbo, "whirl, whirling thing." See also related terms for whirl . ThesaurusAntonymsRelated WordsSynonymsLegend: Noun 1.

turbine - rotary engine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate vane , blade - flat surface that rotates and pushes against air or water gas turbine - turbine that converts the chemical energy of a liquid fuel into mechanical energy by internal combustion; gaseous products of the fuel (which is burned in compressed air) are expanded through a turbine hydroelectric turbine - turbine consisting of a large and efficient version of a water wheel used to drive an electric generator impulse turbine - a turbine that is driven by jets direct against the blades reaction turbine - a turbine with blades arranged to develop torque from gradual decrease of steam pressure from inlet to exhaust rotary engine - an internal-combustion engine in which power is transmitted directly to rotating components rotor , rotor coil - the rotating armature of a motor or generator stator , stator coil - mechanical device consisting of the stationary part of a motor or generator in or around which the rotor revolves steam turbine - turbine in which steam strikes blades and makes them turn wind turbine - a turbine that is driven by the wind Translations How turbines work | Impulse and reaction turbines Tweet by Chris Woodford . Last updated: June 4, 2016.

Question: What does a windmill standing on a sandcastle have in common with a massive ocean liner, a hydroelectric dam, or a transatlantic jet? Answer: They all use turbines—machines that capture energy from a moving liquid or gas. In a sandcastle windmill, the curved blades are designed to catch the wind's energy so they flutter and spin. In an ocean liner or a jet, hot burning gas is used to spin metal blades at high speed—capturing energy that's used to power the ship's propeller or push the plane through the sky. Turbines also help us make the vast majority of our electricity: turbines driven by steam are used in virtually every major power plant, while wind and water turbines help us to produce renewable energy . Wherever energy's being harnessed for human needs, turbines are usually somewhere nearby. Let's take a closer look at these handy machines and find out how they work! Photo: A cutaway model of a steam turbine used to generate electricity in a power plant. This one is an exhibit at the Think Tank science museum in Birmingham, England. What is a turbine?

A windmill is the simplest kind of turbine: a machine designed to capture some of the energy from a moving fluid (a liquid or a gas) so it can be put to use. As the wind blows past a windmill's sails, they rotate, removing some of the wind's kinetic energy (energy of movement) and converting it into mechanical energy that turns heavy, rotating stones inside the mill. The faster the wind blows, the more energy it contains; the faster the sails spin, the more energy is supplied to the mill. Adding more sails to the windmill or changing their design so they catch the wind better can also help to capture more of the wind's energy. Although you may not realize it, the wind blows just a bit more slowly after it's passed by a windmill than before—it's given up some of its energy to the mill! The key parts of a turbine are a set of blades that catch the moving fluid, a shaft or axle that rotates as the blades move, and some sort of machine that's driven by the axle. In a modern wind turbine , there are typically three propeller-like blades attached to an axle that powers an electricity generator .

In an ancient waterwheel, there are wooden slats that turn as the water flows under or over them, turning the axle to which the wheel is attached and usually powering some kind of milling machine. Photo: A prototype gas turbine produced for a high-efficiency power plant. Each of the metal wheels is a separate turbine stage designed to extract a bit more energy from a high-speed gas. You can see how big this turbine is by looking at the little man dressed in white sitting on the middle of the machine. Photo taken at the National Energy Technology Laboratory, Morgantown courtesy of US Department of Energy . Impulse and reaction turbines Turbines work in two different ways described as impulse and reaction—terms that are often very confusingly described (and sometimes completely muddled up) when people try to explain them. So what's the difference? Impulse turbines In an impulse turbine, a fast-moving fluid is fired through a narrow nozzle at the turbine blades to make them spin around. The blades of an impulse turbine are usually bucket-shaped so they catch the fluid and direct it off at an angle or sometimes even back the way it came (because that gives the most efficient transfer of energy from the fluid to the turbine).

In an impulse turbine, the fluid is forced to hit the turbine at high speed. Imagine trying to make a wheel like this turn around by kicking soccer balls into its paddles. You'd need the balls to hit hard and bounce back well to get the wheel spinning—and those constant energy impulses are the key to how it works. The law of conservation of energy tells us that the energy the wheel gains, each time a ball strikes it, is equal to the energy that the ball loses—so the balls will be traveling more slowly when they bounce back. Also, Newton's second law of motion tells us that the momentum gained by the wheel when a ball hits it is equal to the momentum lost by the ball itself; the longer a ball touches the wheel, and the harder (more forcefully) it hits, the more momentum it will transfer. Water turbines are often based around an impulse turbine (though some do work using reaction turbines). They're simple in design, easy to build, and cheap to maintain, not least because they don't need to be contained inside a pipe or housing (unlike reaction turbines). Photo: Left: A Pelton water wheel is an example of an impulse turbine.

It spins as one or more high-pressure water jets fire into the buckets around the edge. This one was originally used in a power plant. Photo courtesy of Wonderferret, published on Flickr under a Creative Commons licence . Artwork: Right: An impulse turbine like this works when the incoming fluid hits the buckets and bounces back again. The exact shape of the buckets and how the fluid hits them makes a big difference to how much energy the turbine can capture. Reaction turbines In a reaction turbine, the blades sit in a much larger volume of fluid and turn around as the fluid flows past them. A reaction turbine doesn't change the direction of the fluid flow as drastically as an impulse turbine: it simply spins as the fluid pushes through and past its blades. Wind turbines are perhaps the most familiar examples of reaction turbines. If an impulse turbine is a bit like kicking soccer balls, a reaction turbine is more like swimming —in reverse. Let me explain! Think of how you do freestyle (front crawl) by hauling your arms through the water, starting with each hand as far in front as you can reach and ending with a "follow through" that throws your arm well behind you.

What you're trying to achieve is to keep your hand and forearm pushing against the water for as long as possible, so you transfer as much energy as you can in each stroke. A reaction turbine is using the same idea in reverse: imagine fast-flowing water moving past you so it makes your arms and legs move and supplies energy to your body! With a reaction turbine, you want the water to touch the blades smoothly, for as long as it can, so it gives up as much energy as possible. The water isn't hitting the blades and bouncing off, as it does in an impulse turbine: instead, the blades are moving more smoothly, "going with the flow." Photo: Left: A typical reaction turbine from a geothermal power plant. Water or steam flows past the angled blades, pushing them around and turning the central shaft to which they're attached. The shaft spins a generator that makes electricity. Photo by Henry Price courtesy of US Department of Energy/National Renewable Energy Laboratory (DOE/NREL) . Artwork: Right: A reaction turbine like this is much more like a propeller.

The main difference is that there are more vanes in a turbine (I've just drawn four blades for simplicity) and often multiple sets of vanes (multiple stages), as you can see in the photos of the steam and gas turbines at the top of this page. Thinking backwards You might have noticed that wind turbines look just like giant propellers —and that's another way to think of turbines: as propellers working in reverse. In an airplane , the engine turns the propeller at high speed, the propeller creates a backward-moving draft of air, and that's what pushes—propels—the plane forward. With a propeller, the moving blades are driving the air; with a turbine, the air is driving the blades. Turbines are also similar to pumps and compressors . In a pump, you have a spinning paddle wheel that sucks water in through one pipe and throws it out from another so you can move water (or another liquid) from one place to another. If you take a water pump apart, you can see the internal paddle wheel (which is called an impeller) is very similar to what you'd find inside a water turbine.

The difference is that a pump uses energy to make a fluid move, while a turbine captures the energy from a moving fluid. Photo: Turbines and propellers work in exactly opposite ways. Propellers use energy to make a fluid move (air, in the case of a plane, or water, in a ship or submarine ); turbines harness energy when a moving fluid flows past them. Left: Propeller photo by Tech. Sgt. Justin D. Pyle courtesy of US Air Force . Right: Turbine blades are shaped in a similar way to propeller blades but are typically made from high-performance alloys because the fluid flowing past them can be very hot. Photo of a turbine blade exhibited at Think Tank, the science museum in Birmingham, England. Turbines in action Broadly speaking, we divide turbines into four kinds according to the type of fluid that drives them: water, wind, steam, and gas. Although all four types work in essentially the same way—spinning around as the fluid moves against them—they are subtly different and have to be engineered in very different ways. Steam turbines, for example, turn incredibly quickly because steam is produced under high-pressure.

Wind turbines that make electricity turn relatively slowly (mainly for safety reasons), so they need to be huge to capture decent amounts of energy. Gas turbines need to be made from specially resilient alloys because they work at such high temperatures. Water turbines are often very big because they have to extract energy from an entire river , dammed and diverted to flow past them. They can turn relatively slowly, because is water is heavy and carries a lot of energy (because of its high mass) even when it flows at low speeds. Water turbines Photo: A giant Francis reaction turbine (the orange wheel at the top) being lowered into position at the Grand Coulee Dam in Washington State, USA. Water flows past the angled blades, pushing them around and turning the shaft to which they're attached. The shaft spins an electricity generator that makes power. Photo by courtesy of US Bureau of Reclamation . Water wheels, which date back over 2000 years to the time of the ancient Greeks, were the original water turbines. Today, the same principle is used to make electricity in hydroelectric power plants. The basic idea of hydroelectric power is that you dam a river to harness its energy.

Instead of the river flowing freely downhill from its hill or mountain source toward the sea, you make it fall through a height (called a head) so it picks up speed (in other words, so its potential energy is converted to kinetic energy), then channel it through a pipe called a penstock past a turbine and generator. Hydroelectricity is effectively a three-step energy conversion: The river's original potential energy (which it has because it starts from high ground) is turned into kinetic energy when the water falls through a height. The kinetic energy in the moving water is converted into mechanical energy by a water turbine. The spinning water turbine drives a generator that turns the mechanical energy into electrical energy. Different kinds of water turbine are used depending on the geography of the area, how much water is available (the flow), and the distance over which it can be made to fall (the head). Some hydroelectric plants use bucket-like impulse turbines (typically Pelton wheels); others use Francis, Kaplan, or Deriaz reaction turbines. The type of turbine is chosen carefully to extract the maximum amount of energy from the water. Wind turbines These are covered in much more detail in our separate article on wind turbines . Photo: A typical wind turbine, in Staffordshire, England.

The tower is ~50m (~150ft) off the ground because the wind moves faster when it's clear of ground-level obstructions. The rotor blades are ~15m (50ft) in diameter and, with a huge sweep, capture up to 225kW (kilowatts) of energy. Steam turbines Steam turbines evolved from the steam engines that changed the world in the 18th and 19th centuries. A steam engine burns coal on an open fire to release the heat it contains. The heat is used to boil water and make steam, which pushes a piston in a cylinder to power a machine such as a railroad locomotive. This is quite inefficient (it wastes energy) for a whole variety of reasons. A much better design takes the steam and channels it past the blades of a turbine, which spins around like a propeller and drives the machine as it goes. Steam turbines were pioneered by British engineer Charles Parsons (1854–1931), who used them to power a famously speedy motorboat called Turbinia in 1889. Since then, they've been used in many different ways. Virtually all power plants generate electricity using steam turbines.

In a coal-fired plant, coal is burned in a furnace and used to heat water to make steam that spins high-speed turbines connected to electricity generators. In a nuclear power plant , the heat that makes the steam comes from atomic reactions. Unlike water and wind turbines, which place a single rotating turbine in the flow of liquid or gas, steam turbines have a whole series of turbines (each of which is known as a stage) arranged in a sequence inside what is effectively a closed pipe. As the steam enters the pipe, it's channeled past each stage in turn so progressively more of its energy is extracted. If you've ever watched a kettle boiling, you'll know that steam expands and moves very quickly if it's directed through a nozzle. For that reason, steam turbines turn at very high speeds—many times faster than wind or water turbines. Read more in in main article on steam turbines . Gas turbines Airplane jet engines are a bit like steam turbines in that they have multiple stages. Instead of steam, they're driven by a mixture of the air sucked in at the front of the engine and the incredibly hot gases made by burning huge quantities of kerosene (petroleum-based fuel).

Somewhat less powerful gas turbine engines are also used in modern railroad locomotives and industrial machines. See our article on jet engines for more details. Turbines for kids? How do you explain something as complex as a turbine to a young child? All that stuff up above about reaction versus impulse turbines, stages, swimming backwards, and so on is bound to confuse... isn't it? Actually it's easy to explain turbines very simply—and here's how you do it. Take your child into a bathroom or kitchen and get them to hold their hand under a cold tap. Turn on the water a little bit (just a trickle). Now, to their surprise, turn it on really hard and get them to keep their hand there. "Can you feel the force of the water hitting your hand? The moving water has a lot of energy and power in it. Imagine you are a machine that could catch the energy and use it to do something useful, like making electricity. That's what a turbine is. It's a machine that catches energy from a moving liquid (like water) or gas (like air) and helps us do something useful.

So a wind turbine is just a machine that catches air with its propeller, turns a generator hidden inside, and makes electricity. The more energy there is in the air, the more power a wind turbine can make. It's just like the water. The harder it's hitting your hand, the more energy it has, so the more energy you could catch and turn into power. A wind turbine is built very high up in the air because the wind (the air) moves much faster there. That's like turning the tap on harder. It means the wind turbine can catch and make more power for us. Different types of turbines catch different types of fluids (liquids or gases). So while a wind turbine or a windmill catches air, a steam turbine catches hot steam made from burning something like coal, and a water wheel (which is just a water turbine) catches water. All turbines do the same job: they capture energy (the energy in the moving liquid or gas) and turn it into a form we can use (movement in a machine or electricity). Turbines are energy-catching machines." Turbines—child's play really! Photo: Imagine your hand could capture the energy in running water and your body your transform it into a more useful form.

That would make you a kind of turbine. Wind turbines Books Turbines compressors and fans by S M Yahya. Tata McGraw-Hill Education, 2005. A detailed (913-page) and very wide-ranging textbook covering the use of turbines for power production, fans and propellers, and similar energy-conversion technologies. Energy: A Guidebook by Janet Ramage. Oxford/New York: Oxford University Press, 1997. A more general book about energy concepts—useful for basic background reading. Articles Thirst For Power: Can thousands of small dams solve Africa's power crunch? by G. Pascal Zachary. IEEE Spectrum, May 1, 2007. How small water turbines are proving effective for generating renewable energy in remote parts of Africa. Sponsored links If you liked this article... Turbine Turbine Turbine A turbine is a rotary engine that extracts energy from a fluid or air flow and converts it into useful work. The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum, with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor.

Early turbine examples are windmills and water wheels. Gas, steam, and water turbines usually have a casing around the blades that contains and controls the working fluid. Credit for invention of the steam turbine is given both to the British Engineer Sir Charles Parsons (1854-1931), for invention of the reaction turbine and to Swedish Engineer Gustav de Laval (1845-1913), for invention of the impulse turbine. Modern steam turbines frequently employ both reaction and impulse in the same unit, typically varying the degree of reaction and impulse from the blade root to its periphery. A device similar to a turbine but operating in reverse, ie. driven, is a compressor or pump. The axial compressor in many gas turbine engines is a common example. Here again, both reaction and impulse are employed and again, in modern axial compressors, the degree of reaction and impulse will typically vary from the blade root to its periphery. Claude Burdin coined the term from the Latin turbo, or vortex, during an 1828 engineering competition. Benoit Fourneyron, a student of Claude Burdin, built the first practical water turbine.

Types of turbines Steam turbines are used for the generation of electricity in thermal power plants, such as plants using coal or fuel oil or nuclear power. They were once used to directly drive mechanical devices such as ships' propellers (eg the Turbinia), but most such applications now use reduction gears or an intermediate electrical step, where the turbine is used to generate electricity, which then powers an electric motor connected to the mechanical load. Turbo electric ship machinery was particularly popular in the period immediately before and during WWII, primarily due to a lack of sufficient gear-cutting facilities in US and UK shipyards. Gas turbines are sometimes referred to as turbine engines. Such engines usually feature an inlet, fan, compressor, combustor and nozzle (possibly other assemblies) in addition to one or more turbines. Transonic turbine. The gas flow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a transonic turbine the gas flow becomes supersonic as it exits the nozzle guide vanes, although the downstream velocities normally become subsonic. Transonic turbines operate at a higher pressure ratio than normal but are usually less efficient and uncommon. Contra-rotating turbines.

With axial turbines, some efficiency advantage can be obtained if a downstream turbine rotates in the opposite direction to an upstream unit. However, the complication can be counter-productive. A contra-rotating steam turbine, usually known as the Ljungström turbine, was originally invented by Swedish Engineer Fredrik Ljungström (1875-1964), in Stockholm and in partnership with his brother Birger Ljungström he obtained a patent in 1894. The design is essentially a multi-stage radial turbine (or pair of 'nested' turbine rotors) and met with some success, particularly in marine applications, where its compact size and low weight lent itself well to turbo-electric applications. In this radial arrangement, the overall efficiency is typically less than that of Parsons or de Laval turbines. Statorless turbine. Multi-stage turbines have a set of static (meaning stationary) inlet guide vanes that direct the gas flow onto the rotating rotor blades. In a statorless turbine the gas flow exiting an upstream rotor impinges onto a downstream rotor without an intermediate set of stator vanes (that rearrange the pressure/velocity energy levels of the flow) being encountered. Ceramic turbine.

Conventional high-pressure turbine blades (and vanes) are made from nickel based alloys and often utilise intricate internal air-cooling passages to prevent the metal from overheating. In recent years, experimental ceramic blades have been manufactured and tested in gas turbines, with a view to increasing Rotor Inlet Temperatures and/or, possibly, eliminating air-cooling. Ceramic blades are more brittle than their metallic counterparts, and carry a greater risk of catastrophic blade failure. This has tended to limit their use in jet engines and gas turbines, to the stator (stationary) blades. Shrouded turbine. Many turbine rotor blades have shrouding at the top, which interlocks with that of adjacent blades, to increase damping and thereby reduce blade flutter. In large land-based electricity generation steam turbines, the shrouding is often complemented, especially in the long blades of a low-pressure turbine, with lacing wires. These are wires which pass through holes drilled in the blades at suitable distances from the blade root and the wires are usually brazed to the blades at the point where they pass through. The lacing wires are designed to reduce blade flutter in the central part of the blades.

The introduction of lacing wires substantially reduces the instances of blade failure in large or low-pressure turbines. Shroudless turbine. Modern practice is, wherever possible, to eliminate the rotor shrouding, thus reducing the centrifugal load on the blade and the cooling requirements. Bladeless turbine uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine. Water turbines Pelton turbine, a type of impulse water turbine. Francis turbine, a type of widely used water turbine. Kaplan turbine, a variation of the Francis Turbine. Voith, water turbine. Wind turbine. These normally operate as a single stage without nozzle and interstage guide vanes. An exception is the Éolienne Bollée, which has a stator and a rotor, thus being a true turbine. Tide Turbine Other Velocity compound "Curtis". Curtis combined the de Laval and Parsons turbine by using a set of fixed nozzles on the first stage or stator and then a rank of fixed and rotating blade rows, as in the Parsons or de Laval, typically up to ten compared with up to a hundred stages of a Parsons design.

The overall efficiency of a Curtis design is less than that of either the Parsons or de Laval designs, but it can be satisfactorily operated through a much wider range of speeds, including successful operation at low speeds and at lower pressures, which made it ideal for use in ships' power plant. In a Curtis arrangement, the entire heat drop in the steam takes place in the initial nozzle row and both the subsequent moving blade rows and stationary blade rows merely change the direction of the steam. It should be noted that the use of a small section of a Curtis arrangement, typically one nozzle section and two or three rows of moving blades is usually termed a Curtis 'Wheel' and in this form, the Curtis found widespread use at sea as a 'governing stage' on many reaction and impulse turbines and turbine sets. This practice is still commonplace today in marine steam plant. Pressure Compound Multistage Impulse or Rateau. The Rateau employs simple Impulse rotors separated by a nozzle diaphragm. The diaphragm is essentially a partition wall in the turbine with a series of tunnels cut into it, funnel shaped with the broad end facing the previous stage and the narrow the next they are also angled to direct the steam jets onto the impulse rotor.

Uses of turbines Almost all electrical power on Earth is produced with a turbine of some type. Very high efficiency steam turbines harness about 40% of the thermal energy, with the rest exhausted as waste heat. Most jet engines rely on turbines to supply mechanical work from their working fluid and fuel as do all nuclear ships and power plants. Turbines are often part of a larger machine. A gas turbine, for example, may refer to an internal combustion machine that contains a turbine, ducts, compressor, combustor, heat-exchanger, fan and (in the case of one designed to produce electricity) an alternator. However, it must be noted that the collective machine referred to as the turbine in these cases is designed to transfer energy from a fuel to the fluid passing through such an internal combustion device as a means of propulsion, and not to transfer energy from the fluid passing through the turbine to the turbine as is the case in turbines used for electricity provision etc. Reciprocating piston engines such as aircraft engines can use a turbine powered by their exhaust to drive an intake-air compressor, a configuration known as a turbocharger (turbine supercharger) or, colloquially, a "turbo".

Turbines can have very high power density (ie the ratio of power to weight, or power to volume). This is because of their ability to operate at very high speeds. The Space Shuttle's main engines use turbo pumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The liquid hydrogen turbo pump is slightly larger than an automobile engine (weighing approximately 700 lb) and produces nearly 70,000 hp (52.2 MW). Turbo expanders are widely used as sources of refrigeration in industrial processes. Turbines could also be used as powering system for a remote controlled plane that creates thrust and lifts the plane of the ground. They come in different sizes and could be as small as soda can, still be strong enough to move objects with a weight of 100kg. T U R B O K A R T :: Home WHAT IS A GAS TURBINE? A gas turbine engine is an internal combustion engine, designed to convert latent energy in a fuel (kerosene, jet fuel, diesel, gasoline, etc.) into mechanical energy or kinetic energy to do work.

This energy can be used in the form of thrust, or mechanical horsepower to drive a propeller, a rotor, a transmission, a generator, or just about anything else. The definition of a turbine is a device which converts the kinetic energy of a fluid into a rotational energy through the reaction or impluse of the moving fluid upon paddles, buckets, or blades. A common example of a turbine is a windmill. A windmill, or wind turbine, converts kinetic energy present in moving air into a rotation. In a wind turbine, the working fluid is air. In a gas turbine, the working fluid is gas. Hot combustion gases, at high dynamic pressure and temperature, pass through one or more turbine wheels, causing them to rotate, typically at very high speed. This gas turbine wheel forms the basis for what are known as gas turbine engines. There is more to a gas turbine engine than the turbine wheel, however. Every gas turbine engine has three fundamental elements in common; the compressor, the combustor, and the turbine. These three elements form the basis of what is known as the gas producer, also referred to as the gasifier, the gas generator, or the core.

The purpose of the gas producer is simply to create gas at high dynamic pressure and temperature. What is done with this high energy gas determines what specific type of gas turbine engine is being used. TOP Types of Gas Turbines Gas turbine engines generally fall into one of four categories. These are turbojet, turbofan, turboprop, and turboshaft; Although a fifth category would cover alternative uses for a gas producer core, such as a turbogenerator, turbo water pump, a jet dryer or snow melter, turbocompressor, etc. A turbojet is the simplest form of gas turbine engine. In a turbojet, the hot gas produced is channelled through a jet pipe and jet nozzle, which increase the exhaust velocity tremendously. This gas is then expelled from the rear of the engine, creating reaction force that is referred to as thrust. This thrust was used to power the earliest jet aircraft, as well as older fighter aircraft. Turbojet engines are now almost exlusively used in small engine applications such as model jet aircraft, and various other specialized or recreational applications. The Concorde is an example of a modern aircraft that utilizes turbojet engines, although the Concorde is no longer in service.

A turbofan is similar to a turbojet, except that instead of using the hot gas produced to exclusively provide high velocity thrust, some of the gas energy is expanded through a second set of turbine wheels, often referred to as a low pressure turbine, to drive a large ducted fan in front of the engine. The low pressure turbine rotates completely independent of the gas producer, allowing the fan to turn at a slower speed than the engine core. The fan draws air in from the front of the engine, accelerates it, and feeds some of the air into the gas producer core, while the rest of it actually travels around the engine core, helping to cool the engine and quiet it as well. The air that travels through this bypass duct mixes with the core engine exhaust, where it is expelled out of the rear of the engine in the form of thrust. Depending upon the bypass ratio of the engine, the fan can contribute as much as 90% of the overall engine thrust. The bypass ratio is the ratio of air drawn in by the fan that is distributed to the bypass duct rather than the engine core. The bypass ratio can vary from as little as .2:1 on modern military fighter aircraft, to as much as 9:1 on modern commercial aircraft.

Turbofans are much more efficient at high subsonic aircraft speeds, and have almost totally replaced turbojets in modern aircraft. Specific fuel consumption of a large commercial jet liner engine is dramatically lower than a turbojet engine in a fighter aircraft. Turbofans range in power output from as little as 600 lbs of thrust, to as much as 115,000 lbs of thrust as in the General Electric GE90 ultra high bypass turbofan. A turboprop is similar to a turbofan, except that instead of turning a ducted fan, the engine turns a traditional aircraft propeller through a gearbox. Also, while in a turbofan, a significant portion of the core engine exhaust is often used to produce thrust, the core exhaust of a turboprop produces very little thrust, typically no more than around 20%. In most cases, the propeller is driven by a separate turbine wheel, usually referred to as the free power turbine. The free power turbine spins completely independent of the gas producer, so that the propeller can turn at a constant speed while the compressor rpm can be varied to increase or decrease power.

However, some turboprop engines are referred to as a single spool design, where there is no free power turbine. The propeller is driven via a reduction gear by the gas producer. In most turboprops, the reduction gear is integral with the engine, although some turboprops require a separate propeller reduction gearbox. A turboshaft engine is similar to a turboprop, exept that instead of turning a propeller, it is used to turn some other type of load. Turboshafts are most commonly used in helicopters. In a turboshaft, the hot gas produced by the gasifier is used to drive a separate free power turbine wheel that spins independently from the gas producer. The engine is designed so that the free power turbine extracts as much energy from the combustion gas as possible, and the remaining exhaust is expanded through a diffuser so that the engine exhaust produces no thrust. A turboshaft could theoretically be used to drive any load, and works equally well when running with a constant output shaft speed as it does with a variable output shaft speed.

Some turboshaft engines have integrated reduction gearboxes, which convert the high speed/low torque of the free power turbine into low/speed high torque, which is more suitable to drive a load, while some engines are direct drive; output is taken off at free power turbine speed. Auxiliary power units are a type of turboshaft engine that are used in aircraft to drive the accessories when the main engines are shut down. They can drive generators, pumps, air compressors, and any number of other ancillary loads. APUs can either be single shaft, or free shaft engines. TOP HOW DOES IT WORK? As stated above, a gas turbine consists fundamentally of three elements; a compressor, a burner, and a turbine. These elements work together to produce usable power. A gas turbine is a heat engine. It produces power basically in two steps. First, it converts fuel energy into heat energy, and then it harnesses as much of that heat as possible and converts it into mechanical energy. The more heat the engine can produce, combined with the larger mass of air it can flow through the combustor, the more power it can extract. The heat is produced by burning fuel in the burner, or combustion chamber.

The more fuel that is burned per unit time, the more heat is produced. Under ambient pressure, fuel will only burn at a certain rate. This would not be sufficient to produce enough power to drive the engine cycle. In order to increase the fuel burn, air under high pressure must be forced into the burner. This is the first job of the compressor. The compressor draws in ambient air, increases its pressure, and feeds this pressurized air to the burner, where the air and fuel are mixed to provide a very high temperature combustion. In combustion, the fuel's potential energy is converted to heat energy through a chemical reaction. It should be noted that the hotter the combustion temperature, the more complete the burning of the fuel is. The second job of the compressor is to flow large quantities of air, referred to as the air mass flow, through the combustor. The air mass serves two purposes: It cools the gas temperature of combustion down, to a value that is safe for the materials downstream of the primary combustion zone, by absorbing the combustion heat; Then, by absorbing that heat, the large mass of air expands and increases its dynamic pressure dramatically.

The rapid increase in temperature due to combustion, combined with the large mass of air, creates a tremendous flow of high energy gas which provides the power to drive the turbine. This hot gas under high pressure seeks to escape the burner, and finds its exit via the burner nozzle. The burner nozzle has vanes that accelerate the gas and direct it onto the turbine wheel, or wheels, causing the turbine to spin at a high rate of speed. The turbine drives the compressor via a fixed shaft, and the cycle is complete, and self sustaining. The cycle that governs the operation of a gas turbine engine is referred to as the Brayton constant pressure cycle. The engine compressor typically requires about 2/3 of the usable heat energy produced in the burner to turn at maximum speed; the remaining energy can then be used to produce thrust or mechanical power, or a combination of the two. TOP Compressor The purpose of the compressor is twofold; It is to provide the burner with high pressure air at large air mass flows. A compressor will increase the pressure ratio anywhere from 3:1 on some of the smallest engines, to as much as 50:1 on the largest commercial turbofan engines.

The compressor is probably the single most important component in a gas turbine engine, because its performance governs how powerful and how efficient the complete engine can be. Thermal efficiency of the engine is almost directly related to the pressure ratio, and engine power is very closely linked to the compressor's air mass flow. A General Electric GE90 turbofan's fan and compressor can pull in around 3,000 lbs. of air every second. There are two basic types of compressors; axial and centrifugal. Centrifugal compressors are generally used on smaller engines. They are compact and rugged, and have a high pressure ratio increase per stage, up to 9:1 on some of the newer engines. However, very high compression ratios become difficult to accomplish with a centrifugal compressor because having multiple stages becomes awkward from a packaging and airflow standpoint. And because of the centrifugal compressor's lower efficiency, using more than one or two stages requires too much of the power produced in the burner to drive. A centrifugal compressor consists of an impeller, a diffuser, and a compressor manifold.

Air is draw in at the center of the rotating impeller, known as the inducer, and is accelerated radially toward the outside of the wheel by vanes on the face of the impeller. This air is collected in the diffuser and compressor manifold, where it is allowed to slow down, converting its velocity into static pressure. The air is then directed to the burner. An axial compressor is more commonly used on larger engines, which require greater air flows and pressure ratios. Large commercial turbofan engines are typically axial flow engines. Axial compressors have a lower pressure rise per stage, more along the lines of 1.2-1.5:1, although some large fans have pressure rises of 3:1, but for the most part, an axial compressor is much more efficient, meaning that for the amount of compression it provides, it uses a lot less engine power than a centrifugal compressor. Also, an axial compressor is much more amenable to multi-stage use. Axial compressors with ten stages or more are very common. The General Electric J79 turbojet engine has a 17 stage axial compressor with a pressure ratio of 13:1.

An axial compressor is like a fan with many thin, angled blades along its hub. Each set of blades makes up one stage. Each compressor stage must be followed by a set of similar, stationary blades called stators, which slow down the airflow, increasing its static presssure, while directing the airflow to the next set of rotating blades. Many axial compressors feature variable geometry stator vanes, for more fine control of the airflow, especially during acceleration and deceleration of the compressor. The airflow travels from stage to stage, increasing its pressure as it goes. The compressor blades and stator vanes get subsequently shorter in length to assure the pressure increases as the air mass tries to fill a smaller volume. The high velocity airflow after the final compressor stage is converted into static pressure in the diffuser before it enters the burner. Axial-Centrifugal and Split Compressors It is also possible to combine both types of compressors into an engine design. In just about every case, an axial compressor of any number of stages is followed by a single centrifugal stage. The Lycoming T53 as well as the Allison T63 both feature a multi-stage axial compressor followed by a single stage centrifugal.

This design takes advantage of the strong points of both compressor designs. To further improve efficiency, some engines use a split compressor, where there are actually two separate compressors, spinning on completely independent spools. Each compressor spins at its own optimum speed, driven by a separate set of turbine blades. The compressors are then usually referred to as a low and high pressure compressors. The Rolls Royce Gem has a four stage axial low pressure compressor, followed by a single stage centrifugal high pressure compressor. The Rolls Royce Olympus , which powers the Concorde, also features a split compressor, although it is completely axial. Finally, the Pratt & Whitney PW100 series of engines feature a two stage split compressor that is completely centrifugal. TOP Burner The burner is the section of the engine where air and fuel are mixed and ignited to create heat energy to drive the turbine and to provide usable power. A gas turbine engine is a continuous combustion device. As long as the engine is running, fuel is continually being burned.

During engine start up, some outside ignition source, such as a spark or a pilot burner, must be present to start the combustion process, but once the engine has accelerated up to self sustaining speed, the flame will keep itself lit as long as there is fuel flow, and the ignition source can be deactivated. The burner consists of an outer combustion liner and an inner combustion liner. Compressor discharge air first enters the outer combustor, surrounding the inner combustor in a blanket of air that is designed to conduct heat away from the metal parts of the combustion chamber, which would otherwise melt from the extreme combustion temperatures, which can get as high as 4,000 degrees F or more. Since thermal efficiency and specific power are directly related to combustion temperature, engineers are constantly striving to make the burner run hotter, increasing the requirements for cooling and increasing the need for exotic, high temperature materials. Actually, only a very small portion of the compressor discharge air gets used in the combustion reaction; typically around 20%. The rest is used to cool the combustor and turbine. Air enters the inner combustor via a number of holes in the liner. The combustor is divided into three sections; the primary zone, the secondary zone, and the dilution zone.

Fuel is continuously injected at the front of the burner. In the primary zone, air is admitted and recirculated to create a stable low pressure area that acts as a continuous pilot for the whole combustor. Air that enters through the secondary holes feeds the flame to accelerate the reaction and increases the temperature to the highest levels, to assure the most complete combustion of the fuel and reduced hydrocarbon formation. The dilution zone is where the large air mass is mixed with the combustion gas, to put out the flame in the rear part of the burner and cool the gases down to a lower localized temperature which is around half the maximum temperature in the primary and secondary zone, assuring that the turbine nozzle and blades don't melt, at the same time increasing the average temperature of the air mass flow to create the high volume gases to drive the turbine. The high energy gases are accelerated through the turbine nozzle where they will impinge on the turbines. There are essentially four types of burners. The can type burner, the annular burner, the can-annular burner, and the toroidal, or scroll type burner. The can burner consists of one or more cylindrical "cans" with an outer wall and an inner wall which features the combustion holes.

An annular burner is a continuous dual walled ring surrounding the engine rotor shaft. The combustion holes are on the inner wall, which surrounds the inner combustor. A can annular burner features multiple can burners for the inner combustion chambers, sitting inside of an annular outer combustion chamber. These burners can be what is referred to as through-flow or reverse-flow. The through flow design is favorable for aircraft because it allows the engine to have a smaller frontal area, but it also takes up more engine length. Much shorter and compact packaging can usually be realized by utilizing a reverse flow layout, with attendant increases in efficiency under most circumstances, due to more favorable mixing of air and fuel due to the counter-flow. The toroidal burner is a somewhat unique design; one which was used to good effect on many of the automotive turbine designs of the late 60's and 70's. The combustor is a round scroll or ring that sits around the gas producer shaft in between the compressor and turbine. The burner is fed air from holes in the scroll, in a reverse flow manner, while fuel is actually sprayed out through tiny nozzles in the rotating gas producer shaft. The hot gas is ducted 90 degrees out to the turbine nozzle.

Advantages of the scroll combustor is an ultra compact design and slightly higher efficiency, due to the excellent atomization of the fuel by the spinning action of the gas producer shaft and the natural reverse flow effect of the airflow and the fuel flow opposing one another. A major disadvantage is the complexity of plumbing the fuel from the fuel controller to the center of the rotating engine shaft. The Textron Lycoming AGT 1500 Engine in the M1A1 Abrams Main Battle Tank is an example of an engine with a scroll combustor. TOP Turbine The turbine is the section of the engine where the heat energy is converted into mechanical energy, to drive the compressor, the engine accessories, and the engine load on a turboprop or turboshaft. A turbine can be single stage or multi-stage, depending on how much power it is required to absorb from the gas stream, but typically a gas turbine engine will have far fewer turbine stages for a given number of axial compressor stages, due to the fact that the high energy gas expands across a turbine stage much more naturally than the air can be compressed by a single compressor stage. There are basically two types of turbines; the axial flow and radial flow turbine.

Axial flow turbines are much more common, while radial flow turbines are rarely used, and only on very small engines. A radial turbine is similar to a centrifugal compressor working in reverse. High velocity gas flow travels radially from the outside toward the center of the turbine wheel, impinging upon vanes and causing the wheel to rotate. The gas expands and collects at the eye of the radial turbine wheel, where it ultimately travels out of the exhaust duct. An axial flow turbine is similar in appearance to an axial compressor. There are two types of axial turbine blades, although most turbine blades are actually a mixture of the two types. An impulse turbine has concave u-shaped blades often referred to as buckets. High velocity gas passes through a stationary set of blades referred to as the turbine nozzle vanes, which redirect the gas flow so that it strikes the concave section of the buckets almost directly. Each axial turbine stage is preceeded by a stationary set of nozzle vanes, to accelerate and turn the gas flow so that it strikes the buckets with the most force. The other type of blade is the reaction blade. Once again, the gas is turned by the nozzle to strike the blades, but it does so in more of a true axial direction.

The reaction blades are designed so that when the gas strikes them, the gas molecules are deflected in a particular direction. This deflection of gas causes a reaction jet effect, which tends to turn the turbine wheel in the opposite direction to the gas flow, in much the same way a child's pinwheel spins when air is blown through it. Most axial turbines are a combination of the impulse and reaction type. The blades are blended so that the tips are reaction type blades while the roots are impulse type. Some turbine engines feature variable geometry turbine nozzles, which automatically change position to control the way in which the gas strikes the turbine blades, while also controlling the effective nozzle area. Controlling the nozzle area allows for higher turbine inlet temperatures to be maintained as engine power is decreased, which can greatly improve engine part power efficiency. The variable nozzles can also greatly improve engine acceleration and even provide a great degree of engine braking. This feature is particularly useful when using a turboshaft engine to drive a variable speed load, such as an automobile or a tank. In most cases, turbine nozzles and blades must be cooled somehow, or the high temperatures of the engine would melt or damage the blades, especially in modern engines which are running incredibly high burner temperatures.

Cooling air comes from the compressor. As stated earlier, a majority of the air that enters the combustor is used to cool the combustion gas down, as opposed to actually being used in the combustion itself. In active turbine cooling, some of the compressor air is bled off before it reaches the burner and is circulated to the turbine blades, where it can provide additional cooling. Transpiration cooling is one modern technique for cooling the turbine blades and nozzle vanes. Compressor bleed air is actually circulated through the inside of the vanes and blades, and the air is made to escape through thousands of tiny pores in the skin of the blade. As the air escapes, it provides an insulating blanket of air around the blade, directing heat away from the skin and allowing for higher turbine inlet temperatures to be used for greater thermal efficiency. TOP Additonal Gas Turbine Components Apart from the compressor, burner, and turbine, there are many other systems involved that make a turbine work. Like any engine, there are auxiliary systems, such as the fuel system, the lubrication system, and electrical system, a starting system, etc. These systems are almost always driven by the engine's accessory gearbox.

The accessory gearbox is a geartrain which is always driven off the rotation of the gas producer spool. Various gear sets in the accessory gearbox drive output pads to which the accessories are mounted. The oil system can be of either a wet sump or dry sump design. An oil pump will circulate oil to the engine's main bearings. Then, either a scavenger pump or gravity will return the oil back to the oil sump. The fuel system on a gas turbine engine is usually fairly complex. It consists of a number of pumps and some kind of fuel control unit. FCU's can be either mechanical, electronic, or a combination of the two. The FCU controls power output by varying fuel flow to the burner. FCU's are equipped with complicated engine speed governors that are designed to maintain a desired turbine speed based on power setting, engine load, ambient temperature and pressure, and a host of other factors. The electrical system consists of a generator, which sometimes also doubles as an electric engine starter motor, and an ignition system which is designed to begin the continuous combustion cycle. The ignition is typically only needed during engine start. After that, the burner will remain lit on its own.

Hydraulic pumps and external air pumps are also sometimes driven off of the accessory gearbox. TOP Exhaust System The engine exhaust is treated differently depending upon the type of gas turbine engine that is being used. In a turboshaft, the exhaust is essentially just waste heat. Thrust is usually not desirable in a turboshaft, so a diffuser is used to slow down the velocity and kinetic energy, and let it vent to the atmosphere. In some turboshafts, the hot exhaust is channeled through a heat exchanger which is used to pre-heat the compressor discharge air, so that less fuel is required to be burned to achieve a target turbine inlet temperature, thus saving fuel. These heat exhangers are referred to as recuperators or regenerators. In a turboprop, the exhaust is usually ducted so that its energy can contribute some thrust. The exhaust duct is sized to maintain the relatively high exhaust gas velocity. In a turbofan, the core exhaust is also used to provide some portion of thrust, as little as 10% to as much as 90%, depending upon the bypass ratio. At any rate, it is allowed to escape at high velocity and mix with the fan discharge, or bypass air.

Some turbofans mix the hot and cold exhaust streams in a jet pipe before expelling it out of a nozzle, while others exhaust the hot and cold streams individually. In a turbojet, the exhaust gas is collected in a jet pipe, and then forced to accelerate through a nozzle, to maximize thrust. Some turbojet engines have variable area jet nozzles. At low power settings, the nozzle area is large, so that the engine does not produce residual thrust. As power increases, the nozzle area decreases to further increase jet velocity and thrust while maintaining a high turbine inlet temperature. If an afterburner is used, the nozzle area must again increase, to allow the much greater volume flow to escape the jet nozzle unrestricted. Some shaft and prop engines feature exhaust heat recuperators or regenerators. A recuperator is essentially an exhaust heat to intake air heat exchanger. The compressor discharge air is made to circulate through numerous ducts in the recuperator, as exhaust gas is allowed to flow around these ducts. This transfers some of the heat of the exhaust gases to the compressor air.

Because the air is higher in temperature when it enters the burner, less fuel is required to be burned to develop the same burner pressures and turbine inlet temperatures, thus resulting in a fuel savings, especially at part load, where turbine inlet temperature can be maintained near peak while compressor rpm and mass flow decreases. A regenerator is a rotating ceramic honeycomb disc, driven at very low rpm by the high pressure spool. As a given part of the regenerator disc rotates toward the rear of the engine, exhaust is made to pass through the honeycomb elements, heating up the disc. That side of the disc then rotates back toward the intake side, where compressor discharge air is made to circulate through the disc, cooling the disc and heating the air, again improving fuel economy. This type of heat exchanger was favorable in automotive applications because of its more compact size, and its inherent self cleaning capability. TOP STARTING A GAS TURBINE Starting a gas turbine is somewhat different than starting a piston engine, although the basic operations are the same; they are just carried out in a different way. Unlike a piston engine, a gas turbine engine does not spring to life when provoked by the starter and ignition system.

A gas turbine must be spooled up and allowed to accelerate to a particular speed before fuel can be introduced and ignited. Even after ignition, the engine still is not producing enough of its own power to accelerate to idle. Fuel must be carefully metered while the starter continues to accelerate the engine to a point where the engine can then continue to accelerate itself up to a governed idle speed. Requirements for the starter motor are also very different. A piston engine's starter motor requires a quick and sudden burst of starting torque to move the crankshaft and begin the combustion cycle. A turbine engine, on the other hand, should have a very soft initial engagement, and motor torque should then build as rpm builds, to overcome the increasing compressor load. The turbine engine starter must be able to provide steadily increasing and then decreasing power over a longer period of time. Gas turbine engines use many types of starters. The most common starter is the pneumatic starter. The pneumatic starter is basically a compact radial inflow turbine that is spun up to very high rpm through a high volume air source. Reduction gears convert the high rpm into high torque to spool up the engine.

Electric starters, jet fuel starters, hydraulic starters, hand crank starters, combustion turbine starters, and combination starter generators may also be used. The most basic type of turbine starter is impingement starting. In this method, very high pressure air is injected through special nozzles that allow the air to impinge directly onto the engine's turbine, causing it to spool up. Immense quantities of air at very high pressures are required for impingement starting. An ignition source is also needed during starting. Normally, this ignition source is only active while the starter motor is energized. Once the engine has reached self sustaining speed, the ignition source is no longer needed, as combustion is continuous and self-sustaining. Typically, a high energy spark plug is used as the ignition source, although some engines use glow plugs, or a torch igniter, also referred to as a pilot burner, or any combination of the above. A pilot burner is a very small stream of fuel that is sprayed into the combustor and ignited by a low energy spark or glow plug, as soon as the starter motor is energized.

The fuel spray immediately ignites into a small flame, which then becomes the ignition source to light off the main fuel flow when it is introduced into the burner. In most cases, the igniter is de-energized once the engine is running. However, there are certain applications where a low energy igniter runs continuously to pre-empt a flame out. Some modern engines have an auto-relight feature, which automatically fires the igniter in the even that a sudden loss of combustion temperature or pressure occurs, indicating a flameout. Starting a typical gas turbine engine, such as the Allison T63-A-700 , goes something like this: 1. The electric fuel boost pump must be activated to provide the fuel controller and fuel pump with a source of pressurized fuel. 2. The igniter must be enabled, so that when the starter circuit is closed, the igniter will begin to produce a spark. 3. The starter circuit is closed, and the starter motor and ignition unit are energized. The starter motor begins to accelerate the compressor while the igniter begins to spark continuously. 4.

At lightoff speed, between 12% and 15% N1, about the same time that the starter peaks and cannot accelerate the engine any further on its own, the throttle lever is moved from the cutoff position into the ground idle position. This fully opens the fuel cutoff valve, immediately upstream of the fuel metering valve. The metering valve has been in the minimum flow position, and so it introduces a relatively small amount of fuel to the fuel nozzle in the burner. The atomized fuel spray is immediately ignited by the hot spark of the igniter. 5. The operator continues motoring the starter, and the compressor continues to accelerate beyond lightoff speed. At this point, the combustion gases are contributing minimally to the acceleration of the engine; the starter motor is still providing a bulk of the starting torque. When the engine reaches approximately 25% N1, due to the increase in airflow, the acceleration limiter allows the fuel metering valve to open further than the minimum flow position, and the engine begins to accelerate more quickly. Turbine inlet temperature climbs very rapidly, and must be monitored carefully. At this point, the combustion gases are accelerating the engine, and the starter motor is providing less starting torque. 6.

At around 50% N1, the engine reaches self sustaining rpm, the point at which the starter is no longer needed to continue accelerating the engine. The starter and igniter can be de-energized. The engine will continue to self-accelerate toward governed idle speed. 7. As the engine approaches ground idle, around 58% N1, the governing valve opens which moves the fuel metering valve in a closing direction, reducing fuel flow as rpm settles into an equilibrium, maintaining a governed 58% N1 idle. 8. The engine is allowed to stabilize momentarily before it can be put to use. Shutting down the turbine is simple by comparison. The operator moves the throttle lever from the ground idle position to the cutoff position. This action mechanically closes the cutoff valve, which cuts all fuel flow to the burner. The engine then gradually coasts down to a halt. TOP MODULATING POWER IN A GAS TURBINE Controlling the power output of a gas turbine engine is often compared to a captain controlling the engine power on a large ship. The captain does not directly control engine power; instead, he calls down to an engineer in the engine room.

The engineer then calculates what parameters need to be changed to meet the captain's request while at the same time being sure that those changes will not over exceed any limits put on the engines or the ship. Then the engineer carries out the required engine power change. Similarly, the operator of a gas turbine engine is not directly controlling engine power. When he moves the power lever, he is essentially making a request for a certain level of power. Then, either through a complex mechanical control system, an electronic control system, or a combination of the two, the change is made in such a way that the engine will not exceed certain limits such as temperature, speed, and/or torque. From the most basic standpoint, the amount of engine power being produced is a function of gas producer rpm. The higher the compressor rpm, the higher the air mass flow, pressure ratio, along with an increase in the turbine inlet temperature, and ulitmately, the more power is being produced. Gas producer rpm is modulated by increasing or decreasing fuel flow to the burner. Increase the fuel flow to the burner, and the gas producer rpm will increase.

In some of the earliest jet engines, engine rpm, and therefore power, was controlled by a fuel valve directly connected to the throttle lever inside the cockpit. This arrangement is referred to as a full authority power control, and engineers and pilots alike quickly learned that this wasn't a safe or effective way to control a gas turbine engine. If the pilot moved the throttle lever too quickly in either direction, he could either over temp the engine or cause it to flame out. The pilots had to move the power lever very smoothly and very slowly, which was sometimes difficult in the heat of combat. With a full authority control, it was also very difficult to set a steady engine power setting, as engine rpm would have a tendency to slowly creep upward or downward. These problems led to the development of a system called the fuel control unit, or FCU. The earliest fuel control units consisted of a complex set of mechanical linkages, flyweights, and springs connected to a fuel metering valve. The FCU was incorporated into the engine driven fuel pump, and was driven by the fuel pump drive on the accessory gearbox.

An FCU basically consists of an engine speed governor, to maintain a set speed based on power lever position, and an acceleration limiter, to control the rate at which fuel flow is increased or decreased, to prevent overtemp, flameout, or even compressor surge or stall. As technology developed, Further improvements were incorporated, including bimetallic temperature compensators, and pneumatic bellows systems to compensate for varying ambient pressures and temperatures, as well as to make for more precise governing and acceleration limiting. Eventually these hydromechanical fuel control units were supplemented with electronic systems to sense temperature, compressor discharge pressure, compressor surge, and countless other parameters. This gradual shift toward electronic control finally led to the FADEC systems that are used on just about every modern gas turbine engine in production today. FADEC stands for Full Authority Digital Engine Control, and it is essentially a fully electronic fuel control unit. A full authority fuel metering valve controls all fuel flow to the engine, but the fuel valve is actuated by an electric servomotor, which receives all of its commands from an electronic processor. The electronic processor is constantly monitoring hundreds of engine parameters including rpm, temperatures, pressures, torque, as well as power lever position.

When the operator moves the power lever, the FADEC makes numerous calculations and then increases or decreases fuel flow to modulate engine power. Because so many parameters are constantly monitored, the FADEC can make engine power changes more precisely and more rapidly than the old hydromechanical systems. The incorporation of the FADEC system has improved gas turbine engine response, time between overhaul, and fuel consumption dramatically.

Question: A turbine is essentially a what, driven by water or gas, etc?
Answer: Wheel