Gas turbines are machines that convert the heat and kinetic energies of hot, high pressure jets of gas into mechanical energy through the use of rotary blades. The blades catch some of the energy of the gas in motion, in the same way that the blades of a windmill do, causing the rotary blades to turn, which then turns the turbine's other machinery. Many gas turbines have a device called a compressor for creating the hot gas stream for turning the turbine blades, but some do not. Gas turbines have an outstanding power-to-weight ratio, and are usually reliable in that they have fewer moving parts compared to a reciprocating engine design. However, they are also very fuel inefficient in some roles.
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Jet engines are gas turbines that are optimised to create and accelerate the flow of air through them, creating thrust. Fans draw air and partly compress air into the first stage of these engines, the compressor, where jet fuel is injected into a chamber with the air and ignited. This combustion has the effect of making the air very hot, expanding its volume rapidly and increasing its pressure. The now larger and pressurised volume of air rushes out of the compressor, through a nozzle and over the turbine blades. Jet engine turbines provide power for the compressor and the electrical systems of the aeroplane, but most of the energy is directed out the back as thrust for the aeroplane.
Gas turbines are used to generate electricity, either as primary or secondary units. The best example of this is in natural gas-fired power plants, where they are combined with steam turbines. The burning of natural gas can produce a hot stream of gas in and of itself. A simple cycle gas turbine in this role may have no need for a compressor at all, as the gas stream is already hot and fast enough to turn the turbine blades. The mechanical energy created by the turbine is transferred to a generator, which creates electricity. Other gas turbines used in power generation are secondary units, placed to capture waste heat produced in some other industrial process. These usually need a little extra boost, and will therefore have a compressor stage, but the net power output more than pays for the fuel used by the compressor.
Gas Turbines in Ships and Vehicles
Gas turbines are used in some custom-built cars, in a few models of tanks and frequently aboard warships. Vehicular gas turbines are used in place of piston engines to provide power motive power. Like jet engines, they have a substantial compressor and rely entirely upon it for creating the hot stream of gas for the turbine. However, like the power plant turbine, they are optimised for creating mechanical power, not thrust.
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