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Gas Turbine Engine

From RitchieWiki

(Redirected from Gas turbine engine)
Mechanical Features and Designs

A gas turbine engine consists of a compressor, a combustion section, and a turbine. The compressor compresses the inlet air upstream of a combustion chamber. Fuel is then introduced and ignited, producing a high-temperature, high-pressure gas that expands through the turbine section of the engine and spins the turbine. The turbine also powers both the generator and compressor.[1]

Gas turbines operate according to the Brayton cycle, a cycle based on the principle of thermodynamics consisting of two constant-pressure (isobaric) processes combined with two reversible adiabatic (isentropic) processes that requires the maximum volume of gas for a given power output.[2]

A gas turbine engine is used many industrial applications. A gas turbine is the primary propulsion system for aircraft and jets and is therefore sometimes also called a jet engine. Gas turbines are also used as stand alone units or in conjunction with steam turbine generating electrical power in power plants. The exhaust from the gas turbine is used to heat the steam generated from the steam turbine.[3]

Gas turbines are also used in helicopters, military tanks, marine applications, in power plants, and in the pumping of oil and gas.

Kerosene is the primary fuel used in gas turbine engines. However, they can also run on jet fuel, natural gas, and propane.[4]

Contents

[edit] History

The history of gas turbines can be traced back to 1687 when Sir Isaac Newton first developed his three laws of motion. These three laws would come to form the foundation of modern propulsion theory.

[edit] Early Developments in Turbine Technology

However, the Greeks first invented the first turbine of sorts, when Hero of Alexandria invented a device named the aeolipile. The invention proved that the speeding up of a gaseous fluid through a nozzle could result in the rotation of a sphere.[5]

Other early developments that all contributed in some way to the creation of gas turbines included smoke jacks, windmills, waterwheels, and steam turbines.[6] For example, in 1500 A.D. Leonardo Da Vinci invented a contraption called a chimney jack that was used to turn a roasting skewer. The chimney jack was similar to a type of reaction turbine and operated on the principle of heat raising gases from a roasting fire. As the hot air rose, it passed through fan blades that turned the roast through a series of gears.[7]

In 1629, Giovanni Branca invented the first prototype of an impulse turbine. The device was a stamping mill that was powered by a steam-powered turbine. Steam was directed through a jet nozzle onto a horizontally mounted turbine wheel.[8]

[edit] The First Turbine Engine

The first recorded patent for a gas turbine was given to an Englishman by the name of John Barber in 1791. His gas turbine was the precursor for a modern gas turbine and consisted of a compressor, a combustion chamber, and a turbine. The primary difference with Barber’s gas turbine in comparison with gas turbine engines today was that his turbine was outfitted with a compressor that was reciprocating and chain-driven. He designed his gas turbine for the intent of jet propulsion even though it was close to a century before man would even fly in an aircraft.[9]

In theory, his concept was good but not practical for the day because his device was never able to produce amble power to compress the air and gas and have enough remaining energy or power left to provide useful work. However, it was his ideas that led largely to the development of today’s modern gas turbine.

[edit] The Fire Turbine

In 1872, Dr. F.Stolze designed what can be considered the first real gas turbine engine. Called the “Fire Turbine”[10] his turbine had a multistage turbine section and a flow compressor but failed to operate on its own power. He could not patent his idea but did manage to assemble a prototype. His design incorporated a 10-stage axial flow compressor with a 15-stage axial flow turbine by which air from the compressor was directed to U-shaped heat exchanger.[11]

[edit] Brayton’s Gas Turbine

During the 1870s, an American by the name of George Brayton developed a gas turbine engine that was based on a cycle composed of two reversible constant pressure processes and two adiabatic processes. Even though his engine was a reciprocating type, the cycle upon which his turbine was built formed the basis upon which all gas turbines are built today.[12]

[edit] Other Developments

A man by the name of Aegidus Elling from Norway in 1903 proceeded to build the first successfully operating gas turbine engine with rotary compressors and turbines. It became the first gas turbine that produced excess power.[13]

In 1895, Charles Curtis received the first patent for a gas turbine engine in the United States. He would also receive a patent for a steam turbine in 1896 and upon further development sold off the technology to General Electric Co. in 1901 for $1.5 million.[14]

[edit] The Argmengaud Brothers

In 1905 or 1906, the Argmengaud Brothers produced the very first practical gas turbine engine. They also produced another gas turbine with a very unique feature by which the gases from the combustor flowed through the turbine and then through a heat exchanger that generated steam and then was redirected again into the turbine wheel.[15]

[edit] Frank Whittle

It was an Englishman by the name of Frank Whittle who eventually patented a design for a gas turbine engine that was to be used for jet propulsion. The gas turbine was actually used successfully in flight in 1937. In 1941, he went on to design the first turbojet airplane. During World War II, he worked on improving his jet engine design and by 1942 had established a business relationship with General Electric in the U.S. The partnership yielded the building of America’s first jet plane.[16]

After World War II, the advancement of jet propulsion technology would be spearheaded primarily by large commercial enterprises and jet engines would prevail as the primary means by which aircraft were to be powered.[17]

[edit] Features/How it Works

[edit] Gas Turbines in Power Plants

Gas turbines installed in power plants are fueled by natural gas and feature a compressor, combustion section and turbine. Gas turbines used in power plants are considered land based and consist of a heavy frame and aeroderivative engines. Heavy frame gas turbines are characterized by low-pressure ratios lower than 15 and are larger sized. Aeroderivative gas turbines, as the name suggests, are derived from jet engines and operate at a very high compression ratio in excess of 30. Aeroderivative gas turbines are also compact and produce a smaller output.[18]

These gas turbines work in a similar manner to the gas turbines used in aircrafts. The compressor draws air into the engine and pressurizes it. The air is then fed to the combustion chamber at speeds of hundreds of miles per hour. A ring of fuel injectors then directly injects a steady stream of fuel into the combustion chamber where it mixes with the air. The fuel and air mixture is burned at temperatures of up to 2000 degrees Fahrenheit. This produces a very high temperature, high-pressure gas stream that enters and expands throughout the engine’s turbine section. As the hot gas expands through the turbine, it spins the turbine’s rotating blades. These blades are an array of alternating stationary and rotating aerofoil-section blades. The turbine’s rotating blades are dual functioning in that they continually work to draw more pressurized air into the combustion chamber while at the same time spinning a generator that produces electricity.[19]

[edit] Combined Cycle or Cogeneration Power Plants

The key to a gas turbine’s fuel-to-power efficiency is the temperature at which it operates. There are a number of ways that the efficiency of gas turbines in power plants can be increased. One way is to install what is known as a heat recovery steam generator (HRSG) that recovers energy from the turbine’s exhaust. A recuperator captures excess heat from the turbine’s exhaust and uses it to preheat the compressor discharge air before it enters the combustion chamber. Heat recovery steam generators thereby produce steam by capturing heat from turbine exhaust. The high-pressure steam from these units can also be used to produce electrical power in combination with steam turbines. This configuration is known as a combined cycle.[20] Another device known as waste heat recovery boiler (WHRB) is also used for combined cycle power plant operation and operates similar to a HRSG unit.[21]

[edit] Gas Turbines in Aircraft

There are four types of gas turbine engines used in aircraft or jets today. A turbojet and a turbofan are what are called reaction engines in that power is derived from a reaction to the jet stream. On the contrary, the turboprop and turboshaft use the exhaust stream to power an additional turbine that then drives a propeller to an output shaft.[22]

[edit] Turbojet

The turbo jet is a gas turbine engine in its simplest form. It is dependent on the high velocity of hot gas exhaust to provide thrust. Two drawbacks are that turbo jets generate a lot of noise pollution and are not extremely fuel-efficient.[23]

[edit] Turbofan

A turbofan is the most modern version of a gas turbine engine, and is also known as a bypass engine.[24] In a turbofan engine, partly compressed airflow is divided—some goes back into the central part of the engine consisting of the gas generator and core, and the other part passes into the surrounding casing or a bypass duct.[25]

Incoming air gets caught in an inlet. Some of this incoming air passes through a fan before traveling into a core compressor and then into a combustion section where the air becomes mixed with fuel and leads to combustion. The hot exhaust generated by combustion passes through the engine core and turbines and then out a nozzle. This airflow is called the core airflow. The remaining incoming air passes through a fan and bypasses the engine. The air through the fan has a velocity that is increased from free stream. This airflow is called the fan flow or bypass flow.[26]

[edit] Turboprop

A turboprop relies on a gas turbine to turn a propeller instead of a fan. The turboprop generates thrust by moving a large amount of air through a small change in velocity. The core engine and propeller are therefore the two components of a turboprop propulsion system. The core of a turboprop is similar to a turbo jet with the exception that the energy use from expanded hot exhaust is used to turn the turbine and not to produce thrust.[27]

[edit] Turboshaft

The turboshaft is a power plant used in helicopters. Similar to a turboprop, the turboshaft uses a power turbine and gearbox, but the power is transmitted to the helicopter’s rotors. This version of a gas turbine is also often used in industrial and marine applications.[28]

[edit] References

  1. Gas Turbine. Encyclopedia. 2008-09-29.
  2. Brayton Cycle. Answers.com. 2008-09-29.
  3. Brayton Cycle. Web. 2008-09-29.
  4. Turbine. Howstuffworks.com. 2008-09-29.
  5. History. Turbo Machine. 2008-09-29.
  6. History. Turbo Machine. 2008-09-29.
  7. History of the Turbine. Airca. 2008-09-29.
  8. History of the Turbine. Aircav. 2008-09-29.
  9. History of the Turbine. Aircav. 2008-09-29.
  10. History. Turbo Machine. 2008-09-29.
  11. History. Turbo Machine. 2008-09-29.
  12. History. Turbo Machine. 2008-09-29.
  13. History. Turbo Machine. 2008-09-29.
  14. History. Turbo Machine. 2008-09-29.
  15. History. Turbo Machine. 2008-09-29.
  16. History. Turbo Machine. 2008-09-29.
  17. History. Turbo Machine. 2008-09-29.
  18. How It Works. Fossil Energy. 2008-09-29.
  19. Hot It Works. Fossil Energy. 2008-09-29.
  20. How It Works. Fossil Energy. 2008-09-29.
  21. Combined Cycle Cogeneration. Cogeneration. 2008-09-29.
  22. Gas Turbines. Rolls-Royce. 2008-09-29.
  23. Gas Turbines. Rolls-Royce. 2008-09-29.
  24. Gas Turbines. Rolls-Royce. 2008-09-29.
  25. Gas Turbines. Rolls-Royce. 2008-09-29.
  26. Turbine Fan. NASA. 2008-09-29.
  27. Turbine Fan. NASA. 2008-09-29.
  28. Gas Turbines. Rolls-Royce. 2008-09-29.