Can a Jet Engine Work Without Air?

AI Thread Summary
A jet engine operates by accelerating air from its intake and expelling it out the back, generating thrust based on Newton's third law of motion. In a hypothetical scenario where one side of the engine has an atmosphere and the other side is in space, the engine could still produce thrust as it relies on the internal acceleration of gases rather than pushing against external air. The reaction forces generated within the engine are what create thrust, not the surrounding atmosphere. Thus, even without air to push against, if combustion is sustained, thrust could still be achieved. Understanding these principles clarifies that jet engines function as reaction engines, relying on internal processes to generate movement.
kevin90
Messages
2
Reaction score
0
OK I have question about the way jet engine works. I am only 16 and haven't got into any of this stuff in hs yet. my buddy and I were having a disscusion about the way a jet and rockets work and got stump by something. I looked up online how they both work and heard of people refferring to a jet engine "pushing against air/atmosphere" and they have to be in a fluid to work. My question is say a jet engine had an atmosphere on one side(intake) and space on the other would it still work? Would there be force to push, since there is no air to push against?

I nkow its a stupid question, but would really like to know.

Thanks

kevin
 
Science news on Phys.org
Well if that situation were at all possible... I believeit would still work because its not really pushing on the atmosphere, its pushing the gases it just got from its intake out the back from the continuous explosion being produced.
 
A jet is essentially a rocket that doesn't carry its own oxidizer. The reaction thrust (equal and opposite reaction, remember) of the exhaust gas pushes forward on the engine the same way. Nothing is required for it to push against outside.
 
thanks guys...I thought that Newtons 3rd law would apply, but wasn't sure since someone said it had to push against air.
 
You're welcome, Kevin. And welcome to PF as well. This is the most reliable science-oriented site there is, so if anybody else feeds you suspicious theories, run them past us to find out what's what. You have world-class experts in all areas on hand. (I'm not one of them, by the way.)
 
Me neither...

So don't take our word for it :P
 
http://powerlabs.org/turbine.htm" an interesting site about a kid building a jet engine.

oh I forgot...

DON'T TRY IT AT HOME!
 
Last edited by a moderator:
Thanks, Mk. I don't have time to read it now, but it looks very interesting. I've thought about doing that for a few years, but never got around to it.
 
Another way of looking at this situation is to imagine yourself sitting on a chair on a frictionless surface. Then you attempt to throw something away from yourself and the chair you're sitting on..lets say, your shoe for instance...you would slightly move in the opposite direction in which you threw the coin. This happens becuase when you threw the coin, your hand is pushing on the coin and the coin is in turn pushing your hand and thus the chair backwards...this basic idea also applies to the jet engine situation you were referring to
 
  • #10
Danger said:
Thanks, Mk. I don't have time to read it now, but it looks very interesting. I've thought about doing that for a few years, but never got around to it.
Well you are very welcome to thank me Danger.
 
  • #11
kevin90 said:
My question is say a jet engine had an atmosphere on one side(intake) and space on the other would it still work? Would there be force to push, since there is no air to push against?
No it wouldn't.
 
  • #12
McQueen said:
No it wouldn't.
Do you care to elaborate on your answer?

The scenario is a tough mental exercise. I will say that if you could overcome the obvious physical hurdles, i.e. combustion would be supported/sustainable, the engine running without an appreciable back pressure on the outlet and others, then I would say that the engine would indeed produce thrust.

A jet is also referred to as a "reaction engine." That means that the thrust produced is due to the reaction forces. Where do those reaction forces come from? They DO NOT come from the jet "pushing" on the outside atmosphere behind it. The reaction comes from what is happening inside the engine. In a nutshell, the engine itself works on the airstream to accelerate the air out the back end of the engine. Simply stated, the engine applies a force in the direction of the back of the engine to accelerate the air out. Newton's 3rd law kicks in. If the engine is "pushing" the air out (remember, it is being accelerated) then there must be a corresponding force in the opposite direction, i.e. thrust.

So again, if the inlet atmosphere makes it's way out the tail and is accelerated, then the engine will produce thrust.
 
  • #13
McQueen said:
No it wouldn't.
I guess we can never manouvre a rocket in space then. :biggrin:
 

Similar threads

Thermodynamics: The Jet Engine
Replies
3
Views
3K
Plane's Coanda's effect and jet engines sucking in air
Replies
3
Views
1K
I Effects on Engine Overheating and Pressure Dynamics
Replies
4
Views
2K
A Work done during adiabatic expansion on piston
Replies
8
Views
3K
A How Does Jet Injection Work in Fluid Dynamics?
Replies
6
Views
1K
Jet Engines: How Do They Move Forward?
Replies
4
Views
2K
Can a Hybrid Lightning Jet Engine Outperform a Traditional Jet Engine?
Replies
2
Views
1K
Pressures in front and behind LP fan on jet engine
Replies
6
Views
4K
B Could a Warp Jet Revolutionize Space Travel by Compressing Space?
Replies
4
Views
2K
Jet engine thermodynamic non sequitur.
Replies
10
Views
4K

Hot Threads

Recent Insights

Back
Top