How a Jet Engine Works: From Intake to Thrust
Modern airliners are powered by turbofan engines that are quieter, more efficient and more reliable than almost any other machine humans have built. Their working cycle is often summarised in four words: suck, squeeze, bang, blow. Here is what that actually means.
1. Suck — the intake and fan
At the front, a huge fan draws in enormous quantities of air. In a modern turbofan, most of this air bypasses the core and is accelerated straight out the back — this “bypass air” provides the majority of the thrust and is why big engines are so efficient and relatively quiet.
2. Squeeze — the compressor
The air destined for the core passes through a series of compressor stages, each with spinning and stationary blades, squeezing it to many times atmospheric pressure. Compressing the air raises its temperature and packs in the oxygen needed for efficient combustion.
3. Bang — the combustor
In the combustion chamber, fuel is sprayed into the high-pressure air and ignited. The mixture burns continuously (not in pulses), producing a stream of very hot, high-energy gas that expands rapidly.
4. Blow — the turbine and exhaust
The hot gas rushes through the turbine, spinning it like a windmill. The turbine is connected by shafts to the compressor and fan at the front, so it powers the whole cycle. The gas then exits through the exhaust nozzle, and the reaction to that rearward-moving jet — plus the bypass air — pushes the aircraft forward.
Why turbofans, not turbojets?
Early jets were pure turbojets: all the air went through the core. Turbofans move a large mass of air relatively slowly via the bypass, which is far more fuel-efficient at airliner speeds and much quieter. The ratio of bypass air to core air is the engine’s bypass ratio, and it has grown steadily over the decades.
Frequently asked questions
How much thrust does a jet engine produce?
A large widebody engine can produce well over 100,000 pounds of thrust — enough that a single one exceeds the total power of many early jet airliners combined.
Can a jet engine restart in flight?
Yes. Engines can be relit in flight within a defined envelope, using the airflow (windmilling) or an auxiliary power unit to get them spinning.
Want the aerodynamics side too? See the four forces of flight, or browse How Aircraft Work.