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Could we just circulate the air in scramjet propulsion?

This is an obvious idea so there must be some reason why it won't work. In scramjet propulsion a big problem is that the airstream is moving so fast it is difficult to achieve complete combustion in the short time the air is in the engine, even with the great amount of slowing used in scramjets. So why not just have the air circulate around and around to allow sufficient time for combustion? The space shuttle takes about 500 seconds to reach orbit. Let's say 200 seconds of this is during the altitude and velocity conditions when a scramjet might operate. Prior to that we could use the known airbreathing turbojet and ramjet methods. So if the air during the scramjet phase is made to circulate only for one second before being ejected we still only need to be carrying on board at any one time (1/200th)*(5 times more air mass than pure O2) = 1/40th oxidizer mass needed to be carried during this phase than a rocket. Keep in mind also during the earlier turbojet and ramjet phases we don't need to carry any oxidizer. Since the air is being circulated in a circle, ideally it is not being slowed down so should not create extreme heating. You now have one second to complete combustion compared to the times measured in milliseconds for usual scramjets. Am I missing something here?

Bob Clark

Reply to
Robert Clark
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Yes, big time

First the errors in thinking

Turning is "slowing down" the air. A change (turning) in velocity (which is speed and direction) requires an acceleration, which requires a force. The force is friction which is removing energy from the air. There is your heating

Assuming there is no friction and there is a "one second" loop for "circulation". Speed of the air? let's say 1000 mph for a scamjet,. So 1000 mph x 5280 feet/mile x 1 hr/3600 seconds times 1 second = a loop of 1467 feet.

Reply to
charliexmurphy

forgot to add, that makes for a darn big engine

Reply to
charliexmurphy

?????

The air being circulated around and around means it would go around many times in one second. It would not have to go around a circumference of 1467 feet. The circumference hence the diameter could be much smaller than this. The frictional slowing for high Mach speeds would only be a small proportion of the entering speeds and would mostly be for the boundary layer against the sides. This frictional heating could also be reduced by using molecularly smooth surfaces and/or by injecting low viscosity gas along the sides at a matching speed to the entering air speed.

Bob Clark

Reply to
Robert Clark

Physics. do those who work in the field a favor and stop trying to help.

Reply to
me

Wrong, It can't be. It is a closed system, the flowrate in has to match the flow rate out. For the same entrance and exit area and same entrance and exit velocity, the air can't go in it and spend some time (1 sec) without one of 2 things 1. The system has to have the volume to hold on one sec of flow rate or 2. you are compressing the air.\

wrong, There is internal friction from turning the air

no such thing for practical use. That is unatainimum

and/or by injecting low viscosity

Why make it more complicated. You are adding bandaids to bandaids

Reply to
charliexmurphy

That still wouldn't help with the short time the supersonic air stays inside the combustion chamber to add useful thrust to the craft. It won't be very useful if combustion finally occurs when the air and the fuel are outside the craft 100 meters away.

Bob Clark

Reply to
Robert Clark

You again.

You show up here with your clueless ideas.

You aren't a mathematician, you lack the basic knowledge of physics. What is your background? Your posts clearly show a lack of any formal technical education or a failure of obtaining one.

It isn't an obvious idea and it won't work

Take an inner tube and put a small in it anywhere. Blow air into valve stem, there is no way to make it go around. it is going directly from the stem to the hole. Don't respond with fancy inputs or other devices. They add complexity and friction and require additional energy. And don't propose a vortex like in a vacuum, it had high losses

When someone provides reason for your idea not to work, accept it, you don't have the knowledge to know otherwise

Reply to
behlingjo

Are you saying it is impossible to have a high velocity air stream go around and around many times in a torus shaped chamber? Molecularly smooth surfaces have been a well-known phenomenon in materials science for several years now:

Large Area, Molecularly Smooth (0.2 nm rms) Gold Films for Surface Forces and Other Studies. Langmuir, 23 (14), 7777 -7783, 2007. 10.1021/la063738o.

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Bob Clark

Reply to
Robert Clark

Are you saying it is impossible to inject a fluid in a torus shaped chamber and have it circulate many times around and around?

Bob Clark

Reply to
Robert Clark

yes. if it only has an inlet and outlet.

So what. They aren't commercially viable. Especially for large surfaces and consumer use.

Reply to
charliexmurphy

Dear Robert Clark:

No, what he is saying is that it is impossible to do that *and* get any net thrust out of it.

David A. Smith

Reply to
N:dlzc D:aol T:com (dlzc)

Robert Clark wrote: : : The air being circulated around and around means it would go around :many times in one second. It would not have to go around a :circumference of 1467 feet. The circumference hence the diameter could :be much smaller than this. :

So you are changing the direction of that air mass many, many times in one second.

: : The frictional slowing for high Mach speeds would only be a small :proportion of the entering speeds and would mostly be for the boundary :layer against the sides. This frictional heating could also be reduced :by using molecularly smooth surfaces and/or by injecting low viscosity :gas along the sides at a matching speed to the entering air speed. :

Why not just build a magic perpetual motion machine and use it to spin a propellor?

Reply to
Fred J. McCall

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