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#### 喷气式发动机如何工作

Jet Engine, How it works ?

Jet engines have been the successful drivers of aircrafts for nearly a century now

In this video

We will explain the technology behind the jet engine in a logical step-by-step manner

A jet engine keeps an aircraft moving forward using a very simple principle

The same that makes an air-filled balloon move

Yes, Newton’s third law of motion

Just like the reaction force produced by the air moves the balloon

The reaction force produced by the high speed jet at the tail of the jet engine makes it move forward

So the working of jet engine is all about producing a

high-speed jet at the exit

The higher the speed of the jet,the greater the thrust force

The thrust force makes an aircraft move forward

Such high-speed exhaust is achieved by a combination of techniques

If you can heat the incoming air to a high temperature，

it will expend tremendously and will create the high velocity jet

For this purpose,a combustion chamber is used

An atomized form of the fuel is burnt in the combustion chamber

Effective combustion requires air to be at moderately high temperature and pressure

To bring the air to this condition

A set of compressor stages are used

and its temperature and pressure rise to a level suitable to sustain combustion

The compressor receives the energy for the rotation from a turbine

which is placed right after the combustion chamber

The compressor and turbine are attached to the same shaft

The High-energy fluid that leaves the chamber makes the turbine blades turn

You can see that

the turbine blades have a special airfoil shape

which creates lift force and make them turn

As the turbine absorbs energy from the fluid

its pressure drops

Through these steps

we have achieved our objective

A really hot and high-speed air emitted from the exit of the engine

The engine case becomes narrower towards the outlet

which results in even greater jet velocity

In short

the synchronized operation of the compressor combustion chamber and turbine makes the aircraft move forward

Modern aircrafts use a slightly [improved] compressor turbine arrangement called a two spool

Here two independent turbine compressor stages are used

The shaft of the outer compressor turbine passes concentric through the inner one

The outer turbine is subjected to a low energy fluid and will run at a lower speed than the inner turbine

This [low-speed] helps to reduce centrifugal stress induced at the root

Some modern aircrafts even use a three spool engine

The engine we have discussed so far is more specifically called as turbo jet engine

Turbo jet engines tend to Produce high levels of noise

Revolutionary Improvement was made to this engine by fitting a large fan with the low pressure spool

Such engines are called Turbofan engines

and almost every commercial aircraft run on them

A Turbofan engine bypass is a huge amount of air

The ever narrowing bypass duct provides a good jet velocity to the bypassed air

In a turbofan engine,

the majority of the thrust force comes from the fans reaction force

Further the fan greatly improves Airflow in the system by sucking in more air

Thus it helps to improve the thrust

This means high thrust creation with an expense of slightly more fuel

This is the reason why Turbofan engines are highly fuel economical

The noise produced by a jet engine is highly dependent on the exit jet velocity

Since in a turbofan the bypassed cold air gets mixed with the hot air

it is possible to keep the outlet velocity within a limit

Thus it overcomes the noise problem

With quieter exhaust and better fuel economy,

the turbofan engines continued to dominate aircraft propulsion systems

We hope this provided a nice introduction to the working of jet engines.

Thank you for watching this video