Pulse Jets

On Mon, 08 Dec 2003 22:10:32 -0800, Erik Max Francis
wrote:

Lloyd Lee-Lim wrote:

One rather trivial thing I wondered about was why the experts were
driving the vehicles. I would think it would've been much more fun
if the team members got to drive. And since the contest was about
going faster and one of the guys on the pulse jet team looked a
little skinnier, why didn't he drive?

When they're doing something extra dangerous, they only let the experts
drive.

That's right -- and I bet you thought we were strapped in for our own
safety -- wrong, it's the only way they could stop us from running
away :-)

--
you can contact me via http://aardvark.co.nz/contact/

On 08 Dec 2003 23:06:25 GMT, (MattWriter) wrote:

The combustion is rapid, but not very fast.
A PDE is similar, but may not use air but oxidiser and the combustion
is designed to happen at supersonic speeds.

It still sounds extremely inefficient, not to mention the problem with stress
on all parts of the engine. Why are pulsejets/PDE's sometimes mentioned in
connection with extremely high-performance vehicle concepts (hypersonic
reconnaissance planes, RLVs)?

The PDE has the potential to be extermely efficient and you can see
that by considering the compression ratios achieved.

A pulsejet uas a compression ratio of about 1.2:1 and is
extraordinarily inefficient.

A regular auto engine has a compression ratio closer to 11:1 and is
far more efficient.

A diesel engine can have a compression ratio as high as 20:1 or
greater and is even more efficient.

The compression ratio of a PDE could, in theory be very much higher
thanks to the effects of the very narrow shockwave generated as part
of the combustion rpocess.

--
you can contact me via http://aardvark.co.nz/contact/

On 08 Dec 2003 23:06:25 GMT, (MattWriter) wrote:

The combustion is rapid, but not very fast.
A PDE is similar, but may not use air but oxidiser and the combustion
is designed to happen at supersonic speeds.

It still sounds extremely inefficient, not to mention the problem with stress
on all parts of the engine. Why are pulsejets/PDE's sometimes mentioned in
connection with extremely high-performance vehicle concepts (hypersonic
reconnaissance planes, RLVs)?

The PDE has the potential to be extermely efficient and you can see
that by considering the compression ratios achieved.

A pulsejet uas a compression ratio of about 1.2:1 and is
extraordinarily inefficient.

A regular auto engine has a compression ratio closer to 11:1 and is
far more efficient.

A diesel engine can have a compression ratio as high as 20:1 or
greater and is even more efficient.

The compression ratio of a PDE could, in theory be very much higher
thanks to the effects of the very narrow shockwave generated as part
of the combustion rpocess.

--
you can contact me via http://aardvark.co.nz/contact/

In article ,
MattWriter wrote:
What's the difference between a pulsejet and a PDE?

In a pulsejet, the fuel-air mixture burns. Perhaps intermittently, but
it's still more or less normal combustion, a relatively gentle process
taking place at modest speed.

In a PDE, the fuel-air (or fuel-oxidizer) mixture explodes: a blast wave
propagates through it at supersonic speed. Much faster, much more violent.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

In article ,
MattWriter wrote:
What's the difference between a pulsejet and a PDE?

In a pulsejet, the fuel-air mixture burns. Perhaps intermittently, but
it's still more or less normal combustion, a relatively gentle process
taking place at modest speed.

In a PDE, the fuel-air (or fuel-oxidizer) mixture explodes: a blast wave
propagates through it at supersonic speed. Much faster, much more violent.
--
MOST launched 30 June; first light, 29 July; 5arcsec | Henry Spencer
pointing, 10 Sept; first science, early Oct; all well. |

MattWriter wrote:
The combustion is rapid, but not very fast.
A PDE is similar, but may not use air but oxidiser and the combustion
is designed to happen at supersonic speeds.

It still sounds extremely inefficient, not to mention the problem with stress
on all parts of the engine. Why are pulsejets/PDE's sometimes mentioned in
connection with extremely high-performance vehicle concepts (hypersonic
reconnaissance planes, RLVs)?

Both share the limited number of parts.

They have limited lifespans, can explode and shake themselves apart, and
can be designed to explode just after their projected life.

All ideal for space technology.

I don't think anyone has actually seriously proposed pulsejets for
launch-assist.

They tend to have even poorer performance than most jet engines with
regards to performance at high airspeeds.
Their very poor fuel consumption may not be that much of an issue if they
are only run for a few dozen seconds.

PDEs are somewhat different, and I'll leave it to someone who knows a
bit more to comment.

MattWriter wrote:
The combustion is rapid, but not very fast.
A PDE is similar, but may not use air but oxidiser and the combustion
is designed to happen at supersonic speeds.

It still sounds extremely inefficient, not to mention the problem with stress
on all parts of the engine. Why are pulsejets/PDE's sometimes mentioned in
connection with extremely high-performance vehicle concepts (hypersonic
reconnaissance planes, RLVs)?

Both share the limited number of parts.

They have limited lifespans, can explode and shake themselves apart, and
can be designed to explode just after their projected life.

All ideal for space technology.

I don't think anyone has actually seriously proposed pulsejets for
launch-assist.

They tend to have even poorer performance than most jet engines with
regards to performance at high airspeeds.
Their very poor fuel consumption may not be that much of an issue if they
are only run for a few dozen seconds.

PDEs are somewhat different, and I'll leave it to someone who knows a
bit more to comment.

Bruce Simpson wrote:

By comparison,a pulsejet, even a very large one, is more like someone
beating you rapidly about the head and body with a pillow.

Fun for the first minute or so, starts to suck shortly after that.

D.
--
The STS-107 Columbia Loss FAQ can be found
at the following URLs:

Text-Only Version:
http://www.io.com/~o_m/columbia_loss_faq.html

Enhanced HTML Version:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Corrections, comments, and additions should be
e-mailed to , as well as posted to
sci.space.history and sci.space.shuttle for
discussion.

Bruce Simpson wrote:

By comparison,a pulsejet, even a very large one, is more like someone
beating you rapidly about the head and body with a pillow.

Fun for the first minute or so, starts to suck shortly after that.

D.
--
The STS-107 Columbia Loss FAQ can be found
at the following URLs:

Text-Only Version:
http://www.io.com/~o_m/columbia_loss_faq.html

Enhanced HTML Version:
http://www.io.com/~o_m/columbia_loss_faq_x.html

Corrections, comments, and additions should be
e-mailed to , as well as posted to
sci.space.history and sci.space.shuttle for
discussion.

What's the difference between a pulsejet and a PDE? A pulsejet is just the
old V-1 Buzzbomb engine; a pipe with a kerosene burner and a one way flapper on
the front. Simplicity itself. Which is why it's still interesting while
inefficient. short-lived flappers are the hangup.
The PDE is a potential thing of beauty; a rocket engine which uses discrete
supersonic explosions rather than continuous combustion whith subsonic exhaust.

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