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How Jet Engines Work: An easy to understand explanation

By Captain Les, Publisher of CaptainJetson.com

How jet engines work is a subject most flyers don’t know much about. But, did you ever wonder how jet engines thrust you safely from point A to B every time you fly?

Here’s a basic and easy to understand explanation for you, on how jet engines work:

The next time you are in the airplane between New York and Paris, flying across the vast Atlantic Ocean you will appreciate the safety and reliability of the jet engines.

Article updated July 21, 2020.

Watch how the USAF is testing its jet engines here. YouTube.

Modern jet engines

Today’s jet engines typically provide near-perfect reliability.

You’ll be surprised to find out how easy it is to understand the basics of how this fascinating piece of machinery functions.

The following describes a jet engine continuously running, from start to shut down. The basic principle of a jet engine works the same whether you are on the ground or in the air.

The 4 phases of how a basic Jet Engine works: SUCK, SQUEEZE, BANG, BLOW

To keep things simple and help you visualize the workings of the engine, think of the four words suck, squeeze, bang, and blow.

how a jet engine works
The inside of a jet engine. Photo: GE/Canva.

1. “Suck” is the first phase of how a jet engine works

The air enters (is sucked into) the engine through those metal fan blades (also referred to as “impeller blades”) in the front. 

After the air passes the fan blades in the front of the engine, fuel is also introduced and sucked in, where it is mixed with air.

jet engine inlet fan blades impeller
Air “sucks” into the fan blades in the front. Photo: CaptainJetson.com.

2. “Squeeze” is the second phase

A compressor “squeezes” (compresses) the ingested air/fuel mixture.

The compressed air/fuel mixture is then approaching an electric spark, where it goes into the next phase: 

B757 Rolls Royce jet engine
The squeezed air is mixed with fuel and then ignited inside the engine. Here showing a B757 Rolls Royce engine. Photo: CaptainJetson.com.

3. “Bang” is the third phase

Combustion, the “bang”, occurs when the fuel and air mixture is ignited.

This action happens inside what’s called a combustion chamber, located inside (the core) of the engine. 

jet engine combustion
A jet engine. Source: Emoscopes.

4. “Blow” is the fourth and final phase

The ignition of the air and fuel mixture creates a fast-moving exhaust, “blow”, through the jet nozzle (see picture above).

The “jets of gas” inside the engine shoot backward.

As a result of this action, the airplane is being “pushed” forward.

…this is based on Newton’s Third Law of Motion:

“For every action, there is an equal and opposite reaction”.

You can compare this to an air-filled  balloon: 

if you let the air escape from the balloon the balloon will thrust away.

Exhaust pipe on a B757
The back of the jet engine, where the burning gases cause thrust. Photo; CaptainJetson.com.

Did you know?

  • The basic principle of how a jet engine works is actually similar to that of a car engine.
  • The “gas pedal” on your jet, one for each engine, is called a throttle. Another name for this device is “thrust lever“. The thrust levers are moved by the hand.
  • To go faster, or to apply more power: Move the throttles forward (in your car you press your gas pedal).
  • To go slower, or to apply less power: Move the throttles back (in your car you depress your gas pedal).
B757 airplane throttles
2 Boeing 757 jet airplane throttles (white knobs attached to brown-colored levers). One for each engine. Photo: CaptainJetson.com.
Jet display
A jet engine on display without cover plates. Photo: Aerohow.

Bonus info for those of you who are into a little bit of deeper understanding

The above description of a jet engine is about the bare basics.

The Fanjet

Modern fanjet engines use some of the energy created by the exhaust (“bang”) to drive an added shaft, which turns a fan near the engine’s intake

That fan pushes a proportion of the incoming air, known as the “bypass”, AROUND the engine’s hot core and out of the back (instead of directing the bypassed air INTO the engine), thus providing additional thrust. 

This fan air is creating a “bypass thrust”.

Bypass thrust is more fuel-economical to use than core thrust alone.

Another way to look at bypass thrust is to think about it as fan air made into additional thrust.

how jet engines work
Jet engine with bypass air (fan air ducts) schematic. Source: GE/CANVA.

Comments or questions on how jet engines work? You can contact us here.

Featured Image: Les “Jetson”, Boeing 767 captain. CaptainJetson.com.

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