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Asked by anon-74191 on 29 Apr 2020.
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Paul Pitcher answered on 29 Apr 2020:
Jet engines take in air and most of the thrust is produced by a large fan. The fan is what you can see when you look at the front of the jet. It shifts a large amount of air to produce the trust, a lot like a fan for a desk in an office. That main fan is driven by the engine core, which is a complex system including an intake, a compressor, a combustion chamber, a turbine, then finally an outlet or nozzle. The main purpose of the core is to drive the large fan, although it does produce some thrust itself. This is how the jet engine on a passenger aircraft works – this is a “turbofan”. There are other types of jet engine, for example, turbojet on a fighter, turboshaft on a helicopter. There are also more exotic type such as scramjets and ramjets – look at the SR-71 blackbird aircraft for examples of those.
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Charles Sparey answered on 29 Apr 2020:
Jet engines are generally made up of three parts.
At the front, there is the compressor that sucks in the air and compresses it – that is it forces the air into an ever reducing space, increasing its temperature and pressure.
Next, there is the combustion chamber – or burner. The fuel, generally a medium to heavier oil type like kerosene is then continuously injected into the compressed air in the combustion chamber. This immediately ignites and causes the temperature (and the pressure) of the air to rapidly increase.
This rapid increase of air temperature and pressure then drives the waste gases out of the combustion chamber through the turbine. As the gas flows over the turbine blades, it causes them to spin and it is this rotary motion that drives the compressor before being expelled into the outside atmosphere.
How this then drives the aircraft forward depends on the type of engine.
A pure turbojet relies on the thrust generated by the high speed gasses being expelled from the engine and, through conservation of momentum, provides the forward thrust on the aircraft engine.
A turbo fan (probably the most common type) has an additional power turbine that drives a giant fan that is situated in front of the compressor. It is this fan, that as it spins, provides most of the forward thrust of the engine as it pulls itself forward through the air, although this air flow is combined with the exhaust gas flow from the engine as well which does provide additional thrust, the ratio of the two being known as the amount of engine bypass. For commercial airliners it is the fan that you see when you look into the engine.
The final type would be a turboshaft or turboprop type engine where all of the useful work in driving the aircraft comes from the power turbine that then drives a shaft connected to a propeller or similar. These types of engines are also used to power helicopters.
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Tom Gunter answered on 29 Apr 2020:
A helpful way to remember how a jet engine works is ‘Suck –> squash –> bang –> blow’
Suck: the fan (or first compressor blades) at the front of the engine suck the air in.
Squash: the compressor squashes (compresses) the air so that the pressure increases
Bang: inside the combustion chamber the fuel is added and ignited, leading to a hugh increase in temperature and pressure.
Blow: the hot gases rush out of the back of the jet engine. This action causes an equal and opposite reaction (Newton’s third law) that pushes the jet engine forwards.The turbine at the back of the engine uses some of the energy to turn the compressor and the fan at the front, meaning that the jet engine will keep running – so long as you keep giving it fuel!
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Nicola Grahamslaw answered on 29 Apr 2020:
Most engines work by burning fuel mixed with air which makes it expand! This expanding air is then under pressure and can be used to do work. Imagine if you had a balloon which is blown up but not knotted – you could let that air out and point it at a windmill, and you’d make the windmill go round. Burning fuel in the air has the same effect as blowing up that balloon, it gives the air energy and makes the air want to expand.
The exact method of the air doing the work is slightly different for different types of engines:
Some modern engines have what’s called a bypass, where there’s a big fan around the outside of the engine and a smaller one in the middle. The expanding hot air coming out of the back of the engine is used to make a turbine (like a windmill) spin, and this is attached to both of the front fans so it makes them both turn too. The outer fan pushes lots of air from in front of the plane through to behind the plane, which pushes the plane forward. And at the same time the smaller fan in the middle delivers some air into the middle of the engine, ready for more burning to keep that turbine spinning and keep the process going and going.
Other engines don’t have bypass, most of the hot expanded air just shoots out of the back really fast and that produces thrust. In this case, it would be like taping your balloon to a toy car and then letting the air out backwards which would make the car move forwards. Just a little bit of this air is used for fan-turning, just enough to get more air into the engine for the next round of expanding.
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Graeme Ralph answered on 29 Apr 2020:
Yes, to put it simply air goes into the fan blades and is compressed next kerosene is added and lit with the compressed air, this gas goes much faster and turns turbine blades (that power the compressor) and finally this gas ejects out the back of the engine propelling the engine forward.
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Juan Carlos Fallas-Chinchilla answered on 29 Apr 2020:
Adding to the great answers: there are very special materials inside the jet engines (nickel alloys and super-alloys) making all of this possible. Some components inside these engines operate at high temperatures. Other components work at lower temperatures and need to be strong but light (i.e titanium alloys in the fan).
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Jean-Luc Bulber answered on 30 Apr 2020:
Safran is an international high-technology group and tier-1 supplier of systems and equipment in the Aerospace and Defense markets. They have a very good video on YouTube that explains how jet engines work, by compressing the air and then forcing it into combustion chambers where kerosene (fuel) is sprayed into it. The mixture of air and fuel is then ignited, and the gases that form expand rapidly and are exhausted through the rear of the combustion chambers.
You can find the YouTube video here: https://youtu.be/kz5kv0RfeUc
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Simon Porter answered on 30 Apr 2020:
Yes. They are awesome but quite noisy (depending on the configuration of their exhaust nozzles of course…!) and come in a massive range of different sizes.
Basically, they work exactly the same as a car engine: Suck, Squeeze, Bang, Blow.
The difference is that in a car engine the processes happen in set repetitive cycles, whereas in a jet engine they happen continuously.
The big fan at the front of a typical passenger jet engine draws air in (Suck),
Then it passes through a multi-stage compressor (Squeeze),
Enters a combustion chamber where fuel is continuously sprayed through very fine nozzles to mix it with the air, ingnited – initially by a spark but subsequently by the combustion already happening in the chamber (Bang),
Finally it exits the engine down the exhaust (Blow).
There are fan blades in the exhaust (they are called turbine blades) and they use the heat and expanding gases from the Combustion Chamber to drive the compressor and fan at the front of the engine.
Thus the engine can keep going as long as there is combustion happening in the combustion chamber. -
Martin McKie answered on 21 May 2020:
Hi There Alfie,
Check out the video below:
Best Regards
Martin
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