The compressor The compressor is the powerhouse of the engine. Its job is to raise the pressure of the air entering the engine and the higher it can raise the pressure, the greater the thrust that can be achieved from the engine. There are two basic types of compressor.The Centrifugal Compressor.The centrifugal compressor draws in air through the centre of its impeller from where the centrifugal motion of the spinning compressor throws the air outwards, raising its velocity in the process. The air is then directed through a series of fixed divergent ducts which convert this high velocity into high pressure. This type of compressor will typically raise the pressure of the air by a ratio of 4:1

Reproduced with kind permission of Rolls-Royce plc

A centrifugal compressor impeller

Airflow passing from impeller through divergent vanes

The advantages of the centrifugal compressor are its ruggedness and its relatively low cost of manufacture. The disadvantages are its large frontal area and its relatively poor pressure ratio when compared with:- The Axial Flow Compressor. The axial flow compressor consists of rows of alternate rotating (rotor) and fixed (stator) blades. A row of rotors followed by a row of stators is known as a stage and there may be many stages attached to a single shaft. As the air is draw in through the engine, the rotor blades accelerate the air rearwards on to the stator vanes. The stator vanes convert this velocity into pressure before directing the air rearwards onto the next set of rotors and stators where the pressure is raised again in each stage the air passes through.

Reproduced with kind permission of Rolls-Royce plc

Each compressor stage raises the pressure by a small amount, typically 1.2:1 but an axial flow compressor can have many stages, which can boost the pressure to a figure much higher than would be capable with a centrifugal compressor. More about compressors Back to "How they work" Index Back to "Home"