Can a Jet Engine Work Without Air?

  • Context: High School 
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    Engine Jet Jet engine
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Discussion Overview

The discussion revolves around the functioning of jet engines in environments with varying atmospheric conditions, specifically whether a jet engine can operate effectively when one side has an atmosphere and the other side is in space. Participants explore the principles of thrust generation, Newton's laws, and the mechanics of jet propulsion.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions if a jet engine can work with an atmosphere on one side and space on the other, expressing uncertainty about the necessity of air for thrust generation.
  • Another participant suggests that the engine would still function because it is not merely pushing against the atmosphere but rather expelling gases produced from combustion.
  • A different viewpoint posits that a jet engine operates similarly to a rocket, relying on reaction thrust rather than needing an external medium to push against.
  • Some participants reference Newton's third law, indicating that thrust is generated by the reaction forces within the engine rather than the external atmosphere.
  • One participant challenges the feasibility of the scenario, stating that the engine would not work under those conditions, while another elaborates on the mechanics of thrust generation, emphasizing the role of internal forces.
  • A humorous remark is made about the implications of maneuvering rockets in space, suggesting a playful acknowledgment of the complexities involved in the discussion.

Areas of Agreement / Disagreement

Participants express differing views on whether a jet engine can function in the described scenario, with some arguing it can and others asserting it cannot. The discussion remains unresolved, with multiple competing perspectives presented.

Contextual Notes

The discussion includes assumptions about the physical conditions necessary for combustion and thrust generation, which are not fully explored or agreed upon by participants.

kevin90
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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
 
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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 because 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:
 

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