I was reading something about jet engines and it stated that the exhaust comes out of the exhaust nozzle at about 1,300mph, and it also said that the compressors help reduce the speed of the air flowing into the core, so is this true? Link for the website it is on

  • $\begingroup$ Related $\endgroup$ – Pondlife Sep 3 '15 at 2:15
  • $\begingroup$ "If you removed the compressors in an airlines engine would it have more thrust?": No, it wouldn't work as well. The other part of the sentence explains that the compressor increases the pressure (hence its name). Without this pressure increase, the engine wouldn't work (at least at subsonic speed). $\endgroup$ – mins Sep 3 '15 at 2:25
  • $\begingroup$ @mins So it would be slower. $\endgroup$ – Ethan Sep 3 '15 at 2:27
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    $\begingroup$ If you remove all compressor stages, as your question implies, then the engine should not start or run at all. The compression is needed unless the speed of the engine is large (supersonic) and enough air enters the engine without being assisted. This type of engine is named ramjet. In that case the turbine is not needed either, since it exists to turn the compressor. $\endgroup$ – mins Sep 3 '15 at 2:38
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    $\begingroup$ @Ethan Yes, much slower. Around 0 mph. It might make a nice flame if you tried to start it, though. $\endgroup$ – reirab Sep 3 '15 at 4:59

In case of jet engines, compressor increases the pressure of the incoming air, which carries out two functions:

  • The pressurised air aids in the combustion with increased effeciency. If the air is not compressed, especially at high altitudes, the combustion process will grind to a stop.
  • If there is no compressor, and by by some miracle combustion happens in combustion chamber, the low pressure in front means that the flame will exit in all the directions. This will stop the turbine.
  • If the compressor is not there, the engine cooling will not be there and combustion chamber and possibly the turbine blades will melt.
  • If the compressor doesn't reduce the air velocity, combustion process will become extremely difficult, the problem faced in scramjet.

In short, if there is no compressor, there will not be an engine as we know it.

The closest engine comes to having no compressor is during a compressor stall, when all the above things happen- the engine flames out and loses thrust while flames exit all over the engine.

C-17 engine compressor stall

In some cases, the engine is damaged beyond economical repair.

There is a type of engine without compressor- the Ramjet engine. However, even here, the incoming air is compressed by the inlet. This engine has no turbine.

Ramjet Engine

"Ramjet operation" by Vector image made by Cryonic07. Sourcepng-drawing was made by Emoscopes and later slighlymodified by Wolfkeeper - Based on Image:Ramjet operation.pngThis vector image was created with Inkscape, and then manually edited.. Licensed under CC BY-SA 3.0 via Commons.

However, the ramjet engine cannot start by itself and can operate only at supersonic speeds.


If you remove the compressor stages entirely, you no longer have an engine. You will have a combustion flamefront that expands in both directions and will not provide enough flow to power the turbines. Lack of cooling flow provided by normal airflow will result in the metals in the engine core melting and likely damage the engine beyond repair.

In short, removing the compressor yields an expensive paperweight that turns into scrap metal if you ever turn it on.


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