The gas turbine has been used since 1939 for electricity generation. Today, it is one of the most widely used power-generating technologies. Gas turbines are known to be internal combustion (IC) engines that allow air-fuel mixtures to produce hot gases that spin a turbine to produce power. The process is common in jet engines, automobile internal combustion engines, ships, locomotives, etc.
Today you’ll get to know the definition, applications, function, components, diagram, types, and working principles of a gas turbine. You’ll also get to know the advantages and disadvantages of this gas turbine.
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What is a gas turbine?
A gas turbine is a mechanical device that transforms the chemical energy of a fuel, i.e., natural gas or similar fuel into mechanical energy. The mechanical energy generated by the turbine shaft is then transferred through a gearbox to the generator’s shaft. Thus, electrical power is generated. Gas turbines are not named so because of the fuel, but because of the production of hot gas during fuel combustion. Different fuels including fuel oils, natural gas, and synthetic fuels can be utilized. In its process, combustion occurs intermittently, that is, it is a continuous process.
A gas turbine is also called a combustion turbine and is a type of continuous and internal combustion engine. Its main functional elements include an upstream rotating gas compressor, a combustor, a downstream turbine on the same shaft as the compressor. A component is often used in gas turbines to increase its efficiency and to convert power into mechanical or electrical form. It also helps to achieve a greater thrust-to-weight ratio in an afterburning engine.
In addition, a gas turbine can be said to be an internal combustion engine that uses gas as its working fluid in order to rotate a turbine. The end power may be used to drive a generator pump, propeller, or in the case of a pure jet aircraft engine.
Applications of a gas turbine
A gas turbine can be used to power aircraft, trains, ships, electrical generators, pumps, gas compressors, tanks, etc. Now let go deep into the various applications of a gas turbine.
- Electric power generation – Apart from aviation, electrical power industries widely make use of gas turbines. Although steam turbines can also be used.
- Industrial uses
- Marine propulsion
- Locomotive propulsion
- Automotive propulsion
Gas turbine engines are used as medium-sized “peak load” plants to run intermittently during short durations of high-power demand on an electric system.
Gas turbines are used for pumping natural gas through pipelines, where a small part of the pumped gas is used as the turbine fuel.
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The oil refining process also makes use of this system. Small portable gas turbines with centrifugal compressors are used to operate pumps.
Note: the primary function of a gas turbine is to produce mechanical and electrical power.
Components of gas turbine
Below are the components of a gas turbine:
The compressor used as gas turbine components is of different types, the earlier ones employed centrifugal compressors. Its design is relatively simple and inexpensive. They are limited to low-pressure ratios and cannot be compared with modern axial-flow compressors when it comes to efficiency. centrifugal compressors are still employed today in small industrial units.
In this system, there are two streams of air coming from the compressor. The smaller stream is fed centrally into a region where atomized fuel is injected and burned with a flame held in place by a turbulence-generating obstruction. The other stream which is known as a cooler stream is then fed into the chamber through holes along with a “combustion liner” (a sort of shell). This helps to reduce the overall temperature to a level suitable for the turbine inlet.
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These gas turbine components are normally based on the reaction principle with the hot gases expanding through up to eight stages. It uses one- or -two-spooled turbines. In this turbine external load is driven, part of the expansion takes place in a high-pressure turbine. This high-pressure turbine drives only the compressor while the remaining expansion takes place in a separate, free turbine connected to the load.
Control and start-up:
A gas turbine engine driving an electric generator, the speed is required to be controlled and must be constant regardless of the electrical load. Reducing fuel flow in this system will lower the exit temperature of the combustion chamber. Because of this, enthalpy drop available to the turbine even though the turbine efficiency is slightly reduced. Control in aircraft gas turbine engines is more difficult to control.
Other design considerations:
With the designs of modern gas turbine engines, extra functional parts may be added to improve their efficiency.
Read more: Understanding wind turbine
Diagram of gas turbine engine:
Types of gas turbine
Below are the various types of gas turbine out there:
These types of gas turbines are less complex than all aircraft turbine engines. In its working, four-section is attained: compressor, combustion chamber turbine section, and exhaust. Turbojets have been available for decades now, developed in Germany and England before World War II. In turbojet types of gas turbine, the air is passed at a high rate of speed into the combustion chamber. This chamber allows fuel into it and contains an igniter. The turbine is driven by expanding air, which thrust from accelerated exhaust gases.
In turboprop types of gas turbine engines, propellers are driven through a reduction gear, which provides optimum propeller performance at slower rpm speeds. This helps to achieve greater fuel efficiency and performance at slower airspeeds, making turboprops a better choice for aircraft engines including, small, commuter aircraft, cargo planes, and agricultural use. Note, the propellers are less efficient as the aircraft speed increases, making them suitable for planes that do not travel at higher speeds.
Turbofan is an aircraft turbine engine that diverts a secondary flow of air around the combustion chamber, making additional trust to be created. Turbofan types of gas turbine engines are modern versions found on high-speed transport and fighter planes.
Turboshaft (afterburning turbojet):
These types of gas turbine engines are used predominately in fighter jets. It includes an afterburner in a core turbojet so that some of the energy from the exhaust can be used to turn the turbine. Additional fuel is injected into the exhaust stream whenever the afterburner is on, producing extra thrust. This does not produce additional speed for the aircraft and it burns more fuel than traditional turbojet aircraft.
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Working principle of gas turbine
The working of a gas turbine is less complex and can be easily understood. It operates with intake, compression, expansion, and exhaust cycle. Normally, in any gas turbine, the air is compressed by a compressor and then driven through a combustion chamber. Fuel is continuously burned for high-temperature and high-pressure gas processing. The air/fuel gas is burned (ignited) and expansion occurs, therefore, generating rotary energy that is used by the compressor on the preceding stage. The remaining energy is used by an output shaft.
Watch the below to learn more on the working of gas turbine:
In few steps let me explain how gas turbines produce electricity. Well, it undergoes the same process stated above but still needs to clarify how electricity is created. For electricity to be generated, the gas turbine heats the air/fuel mixture at very high temperatures, causing the turbine blades to spin. The spinning turbine drives a generator that converts the energy into electricity. Gas turbines can be combined with steam turbines, in a combined-cycle power plant in order to generate extremely efficient power. Easy right! Here are the steps:
- Air-fuel mixture ignites.
- Hot gas spins turbine blades.
- The driveshaft spin along with the blades.
- Turbine rotation powers the generator.
- Generator magnet causes electrons to move and creates electricity.
Advantages and disadvantages of gas turbine
Below are the benefits of the gas turbine engine in their various applications:
- The power-to-weight ratio is very high compared to reciprocating engines.
- Smaller than most reciprocating engines of the same power rating.
- Fewer moving parts
- Smooth rotation of the main shaft
- Less vibration than reciprocating engines.
- Waste heat is dissipated almost entirely in the exhaust.
- Low peak combustion pressures the reciprocating engines.
- Low lubricating oil cost and consumption.
- A variety of fuels can be used for operation.
- Warm-up is not required after starting.
- The initial cost is less.
- Requires less space.
Despite the good advantages of gas turbine engines, some limitations still occur. Below are the disadvantages of a gas turbine in its various applications.
- Engine cost is high due to exotic materials.
- Longer startup
- Less responsive to changes in power demand.
- Inherent efficiency is lower.
Gas turbine engines are widely known for aviation applications, in fact, the various types of turbines listed above are used in aviation. Gas turbine offers good benefits in most situations and it uses chemical energy for its working. That is all for this article, where we explained the definition, applications, function, components, diagram, types, and working of a gas turbine. We also discussed its advantages and disadvantages.
I hope you enjoyed the reading, if so, kindly share with other students. Thanks for reading, see you next time!