How Jet Engines Work

Most jet propelled airplanes use a turbofan design.

The turbofan can be thought of as a high tech propellor inside of a duct called a diffuser,

driven by a gas generator.

The Core

The core of a jet engine is a gas generator that creates high pressure gas to power a

turbine.

This setup has compressor, combustor, and turbine sections.

The Compressor

Compressed air makes for a much more powerful combustion reaction relative to engine size.

Compression happens in stages that force incoming air into an increasingly narrow chamber.

A single compressor stage is comprised of a spinning rotor paired with a ring of stationary

stator vanes which are attached to the core casing.

Rotor blades swirl the air as they force it through the compressor.

Stator vanes slow this swirling momentum in exchange for increased air pressure.

This compressor has four low pressure and ten high pressure stages.

The Combustor

Air is mixed with fuel and ignited as it passes through the combustor, releasing a jet of

super high powered gas.

The design shown here is an annular combustor, meaning "ring shaped."

Compressed air enters the inlet nozzles.

Each nozzle is coupled with a fuel injector, and is designed to swirl the incoming fuel

and air for an even mix.

A couple of ignitor plugs, not unlike the spark plugs found in car engines, ignite this

mixture and the reaction spreads evenly around the ring.

Once started, combustion continues as long as air and fuel are supplied.

The turbine

Turbines at the rear of the jet engine are powered by exhaust gasses exiting the combustor.

Much of the turbine power is used to turn the fan while a smaller percentage powers

the compressor stages.

Turbine fins get extremely hot.

Some air from the compressor is diverted for cooling, and special coatings are used to

keep temperatures down.

The exhaust cone is specially shaped to mix

and accelerate exhaust streams.

It also covers sensitive internal engine parts.

The fan

Early jet engines were turbojets, where all incoming air flows through the core.

Most modern winged aircraft engines are turbofans, where only a fraction of air enters the core

or gas generator, and the resulting power turns a specially designed fan.

Again, the fan can be thought of as a high-tech propeller inside of a duct.

Air that does not enter the core is called bypass air.

High bypass engines are designed to move large quantities of air at slower cruising speeds

(a range of about 310 to 620 mph).

The exchange for high efficiency is engine size – high bypass engines can be very large,

with massive fans compared to core size.

Commercial airliners or military transport aircraft are example applications.

Exhaust velocity is a major factor in jet engine noise.

High bypass engines surround fast-moving core exhaust with large quantities of slower-moving

bypass air for quieter operation.

Military fighter aircraft use low bypass engines, which are more compact, have high power-to-weight

ratios, plus supersonic and afterburner capabilities, in exchange for things like poor noise control

and high fuel consumption.

Afterburner

High performance engines may have afterburner capability.

Additional fuel is sprayed into a jet pipe section where it mixes with exhaust gas, and

is ignited, producing a second stage of combustion.

Since afterburner is fuel inefficient, it's generally used in short bursts during takeoff,

climb, or combat maneuvers.

The exhaust nozzle is adjustable for maximum exhaust acceleration and to avoid undesirable

back-pressure which can harm forward engine parts.