Pulse detonation?

http://www.popsci.com/popsci/aviatio...3272-1,00.html

Is pulse detonation applicable for rocket technology? Considering
"loud" isn't really that big an issue for a rocket. And considering
rockets carry their own fuel and oxidizer, it would seem that pulse
detonation technology would be something that would be easier to use
and develop instead of trying to make into an advance jet engine
first.

Arthur Hansen

P.S. Thanks, Slashdot.org for noticing this neat article!

Arthur Hansen wrote:

http://www.popsci.com/popsci/aviatio...3272-1,00.html

Is pulse detonation applicable for rocket technology? Considering
"loud" isn't really that big an issue for a rocket. And considering
rockets carry their own fuel and oxidizer, it would seem that pulse
detonation technology would be something that would be easier to use
and develop instead of trying to make into an advance jet engine
first.

Arthur Hansen

P.S. Thanks, Slashdot.org for noticing this neat article!

One goes to the trouble of trying to develop pulse detonation engines
precisely *because* they're airbreathers.

If your application doesn't require airbreathing over a wide Mach
nuber range, you use rockets.

(Iain McClatchie) wrote in message
The article is enthusiastic but not informative. Here's a basic

question: why would a pulse detonation engine be any more efficient

than a fanjet?


PDE are more efficient because they use a constant volume process
rather than a constant pressure process like a rocket or gas
turbine. The reason that constant pressure processes are more efficient
requires a bit of analysis. But rest assured if you run the numbers
you get better efficiency. Most of that has to do with the fact that
the highest temperature reached is higher for a constant volume
process.

Why is it constant volume?.The shock wave travels from the closed end of
the tube to the open end. After the shock-wave the pressure rises a
lot, this higher pressure is pushing on the closed face of the
tube producing thrust. Now the detonation wave travels faster than the
local speed of sound in the unburnt(un-shocked) fuel/air. So the shock
wave gets to travel the full length of the tube without any fuel air
exiting. Note that after the shock-wave passes the burnt fuel air
mixture is *not* stationary, its moving toward the exit plane.
Once the shock-wave reaches the open end of the tube a
expansion wave then travels back down the tube. And when it reached
the closed end the "thrust" pressure is removed. So the total thrust
of a single pulse last for the duration of the travel time of the
shock-wave and expansion wave.

I have left out a lot of details and i'm not the best at explaining
things. There is a lot of papers on this stuff in all the usual
journals.


With all the problems they have I can't see them being used for a
while. One problem is how to design a nozzle that is efficient without
constant mass flow conditions?

(Arthur Hansen) wrote in message
om...
http://www.popsci.com/popsci/aviatio...3272-1,00.html

Is pulse detonation applicable for rocket technology? Considering
"loud" isn't really that big an issue for a rocket. And considering
rockets carry their own fuel and oxidizer, it would seem that pulse
detonation technology would be something that would be easier to use
and develop instead of trying to make into an advance jet engine
first

Arthur Hansen

P.S. Thanks, Slashdot.org for noticing this neat article!

It has been proposed. But the big gain with PDE is not that big a gain
when compared to a rockets. The driving force on PDE research is for
air-breathers were fuel economy makes you lots of money. Rocket
engines however are in fact very close the theoretical thermodynamic
limits of efficiency. The gains, in any, are outweighed by the
unsteady nature of PDE.

(Iain McClatchie) wrote in message . com...
(Arthur Hansen) wrote in message om...
http://www.popsci.com/popsci/aviatio...3272-1,00.html

Is pulse detonation applicable for rocket technology? Considering
"loud" isn't really that big an issue for a rocket. And considering
rockets carry their own fuel and oxidizer, it would seem that pulse
detonation technology would be something that would be easier to use
and develop instead of trying to make into an advance jet engine
first.

Arthur Hansen

P.S. Thanks, Slashdot.org for noticing this neat article!

The article is enthusiastic but not informative. Here's a basic
question: why would a pulse detonation engine be any more efficient
than a fanjet?

The basic premise is that "exploding" fuel is more energetic and
efficient than just burning it, isn't it?

I can imagine that the detonation wave compresses the unburned fuel-
air to much higher pressures before burning than the compressor in a
turbojet core would. And I know that burning at higher compression
is good because when you expand the gas back down to ambient pressure
you recover more of the heat added as work and less ends up as
residual exhaust temperature.

It seems that PD technology seems to hold higher fuel efficiencies by
more perfectly combusting fuel and oxidizer because of very highly
defined pulsed explosions. Ergo, more efficient thrusters. IIRC,
aren't they hoping for a 500% increase in fuel efficiency?

But how do you get the detonation wave to accelerate lots of unburned
air out the back of the tube? Puffs of fuel detonated between long
stretches of unburned air? [This would have the advantage of a
variable "bypass" ratio -- just change the ratio of puff to unburned
air.]

I'm not sure there is "un-burned" air at that point, but I could be
very wrong. I'm just an enthusiast, after all.

Arthur Hansen

In article ,
Arthur Hansen wrote:
Is pulse detonation applicable for rocket technology?

In principle, yes. It offers very high combustion pressures without
needing high-pressure pumps.

In practices, maybe someday. The fact that it's been coming "real soon
now" for going on fifty years is not encouraging.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

In article , (Henry Spencer) wrote:
In article ,
Arthur Hansen wrote:
Is pulse detonation applicable for rocket technology?

In principle, yes. It offers very high combustion pressures without
needing high-pressure pumps.

In practices, maybe someday. The fact that it's been coming "real soon
now" for going on fifty years is not encouraging.

Sounds like 1940's German V1 engine.

Maybe strap a V1 intake to a ramjet. Use pulse jet for low speeds
& lock the shutters open for high speed ramjet operations?

____
Fox2

"When caught between two evils, I generally pick
the one I've never tried before." - Mae West

(Greg) writes:
good explanation snipped

Why is it constant volume?.The shock wave travels from the closed end of
the tube to the open end. After the shock-wave the pressure rises a
lot, this higher pressure is pushing on the closed face of the
tube producing thrust. Now the detonation wave travels faster than
the

One small thing -- of course, pushing on the closed face of the tube
isn't what causes thrust.
--
Joseph J. Pfeiffer, Jr., Ph.D. Phone -- (505) 646-1605
Department of Computer Science FAX -- (505) 646-1002
New Mexico State University http://www.cs.nmsu.edu/~pfeiffer
Southwestern NM Regional Science and Engr Fair: http://www.nmsu.edu/~scifair

In article GIv0b.8326$cj1.7746@fed1read06, Fox2 wrote:
Sounds like 1940's German V1 engine.

There are similarities but it's not really that close. The *detonation*
part is new, and is a major source of difficulties. Combustion in the
V-1's pulsejet was ordinary burning, not detonation.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

Joe Pfeiffer wrote in message
One small thing -- of course, pushing on the closed face of the tube
isn't what causes thrust.

Indeed this is exactly what produces the thrust. In normal rockets
also. If you sum (integrate) all the pressure forces on a thrust
chamber walls and nozzle walls, you will find a net force in the
excepted direction. This is how thrust of a engine is often
calculated (checked) with CFD codes (including viscus losses i think).

Of course this is the same as working out the average exhaust velocity
and using conservation of momentum. But this dose not tell us where the
thrust is transmitted to the engine structure. ie all the trust is not
on the nozzle, so there is no need to make the nozzle that strong. In
fact a very large portion of the net thrust comes from the injector
plate.