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

On Mar 8, 9:26 am, Robert Clark wrote:
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

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.

On Mar 8, 10:21 am, wrote:

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.

forgot to add, that makes for a darn big engine

On Mar 8, 10:21 am, wrote:
On Mar 8, 9:26 am, Robert Clark wrote:



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

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.

?????

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

On Mar 8, 11:19 am, 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.

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.\

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.

wrong, There is internal friction from turning the air

This frictional heating could also be reduced
by using molecularly smooth surfaces

no such thing for practical use. That is unatainimum

and/or by injecting low viscosity
gas along the sides at a matching speed to the entering air speed

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

On Mar 8, 12:11 pm, wrote:
On Mar 8, 11:19 am, 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.

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.\

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.

wrong, There is internal friction from turning the air

This frictional heating could also be reduced
by using molecularly smooth surfaces

no such thing for practical use. That is unatainimum

and/or by injecting low viscosity

gas along the sides at a matching speed to the entering air speed

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

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.
http://pubs.acs.org/cgi-bin/abstract...la063738o.html

Bob Clark

On Mar 8, 1:49 pm, Robert Clark wrote:

Are you saying it is impossible to have a high velocity air stream go
around and around many times in a torus shaped chamber?

yes. if it only has an inlet and outlet.

Molecularly smooth surfaces have been a well-known phenomenon in
materials science for several years now:


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

Dear Robert Clark:

"Robert Clark" wrote in message
...
....
Are you saying it is impossible to have a high
velocity air stream go around and around many
times in a torus shaped chamber?

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

David A. Smith

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
roportion 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?

--
"The reasonable man adapts himself to the world; the unreasonable
man persists in trying to adapt the world to himself. Therefore,
all progress depends on the unreasonable man."
--George Bernard Shaw

Robert Clark wrote:

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?
[snip awful crap]

"Barbarella," the ice car.
"You can teach them to type but you can't teach them to grow tits."

Hey stooopid - propulsion is about momentum transfer not energy. If
you had any brains - ha ha ha - you'd converge shock waves at the
distal end of the scramjet, thereby elongating the combustion chamber
and eliminating material considerations for afterburner containment
temperature. But, you don't.

--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/lajos.htm#a2