Editing Turbojet (section)

=== Compressor ===
The turbine rotates the compressor at high speed, adding energy to the airflow while squeezing (compressing) it into a smaller space.  Compressing the air increases its [[pressure]] and temperature. The smaller the compressor, the faster it turns. The (large) [[General Electric GE90|GE90-115B]] fan rotates at about 2,500 RPM, while a small helicopter engine compressor rotates around 50,000 RPM.

Turbojets supply [[bleed air]] from the compressor to the aircraft for the operation of various sub-systems. Examples include the [[environmental control system]], [[De-icing|anti-icing]], and fuel tank pressurization. The engine itself needs air at various pressures and flow rates to keep it running. This air comes from the compressor, and without it, the turbines would overheat, the lubricating oil would leak from the bearing cavities, the rotor thrust bearings would skid or be overloaded, and ice would form on the nose cone. The air from the compressor, called secondary air, is used for turbine cooling, bearing cavity sealing, anti-icing, and ensuring that the rotor axial load on its thrust bearing will not wear it out prematurely. Supplying bleed air to the aircraft decreases the efficiency of the engine because it has been compressed, but then does not contribute to producing thrust.

Compressor types used in turbojets were typically axial or centrifugal. Early turbojet compressors had low pressure ratios up to about 5:1. Aerodynamic improvements including splitting the compressor into two separately rotating parts, incorporating variable blade angles for entry guide vanes and stators, and bleeding air from the compressor enabled later turbojets to have overall pressure ratios of 15:1 or more. After leaving the compressor, the air enters the combustion chamber.