How a turbine engine works

A turbine engine does the same four jobs as a piston engine (intake, compression, combustion, exhaust), but all at once and continuously, in different places along the engine. This is the Brayton cycle. The gas is pushed out the back faster than it came in, and the reaction pushes the engine forward (Newton's third law).

The sections

1. Inlet: brings air to the compressor smoothly.
2. Compressor: raises the air's pressure. Centrifugal compressors fling air outward; they're rugged and give a big rise per stage. Axial compressors have many stages of spinning rotor blades and fixed stator vanes; they handle more air and higher overall pressure ratios.
3. Diffuser: slows the air, raising its pressure further, ready for burning.
4. Combustion chamber (can, can-annular or annular): fuel burns continuously. Only about a quarter of the air is used for burning; the rest cools the chamber and the gas.
5. Turbine: takes energy from the hot gas to drive the compressor and accessories (and a fan or propeller). The highest temperatures are at the turbine inlet.
6. Exhaust: the nozzle speeds up the gas for thrust.

Many engines have two or three spools: separate shafts each joining a compressor to the turbine that drives it. N1 is the low-pressure spool (fan or low-pressure compressor), N2 the high-pressure one. A compressor stall happens when the air over the blades separates, like a wing stalling: a bang or rumble, rising exhaust temperature and falling thrust. Bleed valves and variable stator vanes help prevent it; damaged blades, ice and rough throttle use can cause it.

The types

• Turbojet: all the air goes through the core; loud and thirsty.
• Turbofan: a big fan moves extra air around the core. The bypass ratio is the air around the core divided by the air through it; high bypass engines are quiet and efficient.
• Turboprop: the turbine drives a propeller through a reduction gearbox; many use a separate free power turbine not connected to the compressor.
• Turboshaft: the power goes to a shaft, for helicopters and APUs.