As the name suggests, gas turbine engine compressors provide the compression part of the gas turbine engine thermodynamic cycle. There are three basic categories of gas turbine engine compressor: axial compressor, centrifugal compressor and mixed flow compressor. A fourth, unusual, type is the free-piston gas generator, which combines the functions of compressor and combustion chamber in one unit. Axial compressor Most high-compression jet engine use axial compressors for their high efficiency. In the axial compressor the air flows parallel to the axis of rotation. Axial compressor are made to be multi-staged. A stage consists of a row of rotating blades called the rotor, which are connected to the central shaft and a row of stationary or fixed blades called stator. In axial flow compressor, the air flows from stage to stage. The role of the rotor blades is the accelerate the incoming air for increasing the kinetic energy of the air. Then the fluid is decelerated across the stators and as a consequence the kinetic energy is converted into the pressure rise by the stators. Through the compressor, the flow area decreases and the blades get smaller and smaller from stage to stage and this compensates for the increase of air pressure and density, creating a constant axial velocity. In a axial compressors, there may be up to 20 stages between the air inlet and compressor outlet. Centrifugal compressor The very first jet engines used centrifugal compressors and they are still used on small turbojets and turbo shaft engines. The key component that makes a compressor centrifugal is the centrifugal impeller which contains a rotating set of blades. In a centrifugal compressor the airflow goes perpendicular to the axis of rotation. When the air passes through the rotating impeller it experiences a centrifugal force. Air is pushed toward the center and this radial movement of air results in a pressure rise and the generation of kinetic energy. Then the air passes through another key component of centrifugal compressor called diffuser section which responsibility is to convert the kinetic energy of the air into pressure rise by gradually slowing the air velocity. The diffuser is a fixed or static component that escorts the air flow after leaving the impeller. The impeller and the diffuser contributes about 65% and 35% of the total pressure produced in the centrifugal compressor respectively. Comparison between Axial and Centrifugal Compressor A typical, single-stage, centrifugal compressor can