section_path: Combustion turbines/Gas turbines
section_name: Gas turbines
paragraph_text: Gas turbines
  
  A gas turbine compresses air and uses it to turn a turbine. It is essentially a jet engine which directs its output to a shaft. There are three stages to a turbine: 1) air is drawn through a compressor where the temperature rises due to compression, 2) fuel is added in the combuster, and 3) hot air is exhausted through turbine blades which rotate a shaft connected to the compressor.
  
  A gas turbine is a rotary machine similar in principle to a steam turbine and it consists of three main components: a compressor, a combustion chamber, and a turbine. The temperature of the air, after being compressed in the compressor, is increased by burning fuel in it. The heated air and the products of combustion expand in a turbine, producing work output. About 2 ⁄ 3 of the work drives the compressor: the rest (about 1 ⁄ 3) is available as useful work output.
  
  Gas turbines are among the most efficient internal combustion engines. The General Electric 7HA and 9HA turbine combined cycle electrical plants are rated at over 61% efficiency.