Pulse Detonation Engines (PDE's)

Aviation Week has had articles on PD engines every so often for at
least the past six years.
Walt BJ

"Gord Beaman" wrote in message
...
Bruce Simpson wrote:


To give you an idea of the difference (in terms of shock, vibration
and noise) -- in a deflagration, the flame travels at just a few
meters per second, in a detonation the flame front effectively travels
at several times the speed of sound.

Yes, the operative word here is 'effectively' because there's
actually no defined flame-front at all. As the normal flame front
progresses across the firing chambre a certain area of the
remaining fuel/air charge starts getting squeezed (and heated by
it) till it's internal temperature arrives at it's ignition point
then the whole remaining area detonates almost instaneously
producing an extremely high spike of pressure which is
practically useless against the inertia of the piston/crank etc.
This spike quickly punches and burns holes in the piston etc.

The big problem with regards to power from a detonation is
that it all most always occurs during the compression stroke.
During the normal operating cycle the spark is fired to ignite
the mixture substantially before the piston reaches the top of
the compression stroke, with the normal "slow" burn the flame
front hasn't burned far before the piston reaches top dead center
and started back down during the power stroke. Maximum
pressure is achieved during the power stroke.
The ignition for the detonation likely comes from a normal
spark event (there are other causes) but the environment in the
combustion chamber has put mixture to close to the ignition
point and it all -or portions of it- tip over the edge and start
burning before the normal flame front gets there.

"John Keeney" wrote:


"Gord Beaman" wrote in message
.. .
Bruce Simpson wrote:


To give you an idea of the difference (in terms of shock, vibration
and noise) -- in a deflagration, the flame travels at just a few
meters per second, in a detonation the flame front effectively travels
at several times the speed of sound.

Yes, the operative word here is 'effectively' because there's
actually no defined flame-front at all. As the normal flame front
progresses across the firing chambre a certain area of the
remaining fuel/air charge starts getting squeezed (and heated by
it) till it's internal temperature arrives at it's ignition point
then the whole remaining area detonates almost instaneously
producing an extremely high spike of pressure which is
practically useless against the inertia of the piston/crank etc.
This spike quickly punches and burns holes in the piston etc.

The big problem with regards to power from a detonation is
that it all most always occurs during the compression stroke.

I don't think so John, the added pressure from the squeezing of
the fuel/air charge by the advancing flame front wouldn't have
risen nearly high enough 'before' TDC.

During the normal operating cycle the spark is fired to ignite
the mixture substantially before the piston reaches the top of
the compression stroke, with the normal "slow" burn the flame
front hasn't burned far before the piston reaches top dead center
and started back down during the power stroke. Maximum
pressure is achieved during the power stroke.
The ignition for the detonation likely comes from a normal
spark event (there are other causes)

I doubt this too because there'd be a second flame front from
that therefore you wouldn't get the 'instantaneous ignition' of
heating an area up to it's ignition point and having it all
detonate at once.

but the environment in the
combustion chamber has put mixture to close to the ignition
point and it all -or portions of it- tip over the edge and start
burning before the normal flame front gets there.


It's true that it ignites before the normal flame front gets
there but IMO it has nothing to do with mixture and everything to
do with temperature derived from increasing pressure.
--

-Gord.

Hi Bruce, Nice to see you in this group. Did your neighbour successfully
sell the property?
regards
AL
"Bruce Simpson" wrote in message
...
On Sat, 28 Feb 2004 17:22:40 GMT, "Ed Majden"
wrote:


"Grantland" "Grantland"
Nope. Pulse-burn. Much less efficient.

Symantics! It was a pulse jet!



Fiesler Fi-103 (V1) Specifications

Engine: Argus pulse-jet
600 pounds of thrust
Length: 25' 4"
Wingspan: 17' 6"
Weight: 4800 lbs. Fully fueled
Fuel: 150 gallons of Acetylene gas
1 mile per gallon
Range: Approximately 160 miles from launch site
Performance: Speed between 360-400 mph
Flew at altitude of 2000-3000 ft
Average flight time of 22 minutes
Armament: 2337 pound war head

Not as efficient, but still an early prototype PULSE JET!!! Different
principal perhaps! Time marches on and so do design techniques.

Sorry but the V1 was not powered by acetylene -- they used very
low-grade gasoline. There would be no way to (safely) store sufficient
acetylene onboard even if they wanted to use it as a fuel.

Acetylene was used for starting in very cold weather but most
certainly never as a fuel.

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

On Thu, 4 Mar 2004 16:49:57 +0800, "Alfred Loo"
wrote:

Hi Bruce, Nice to see you in this group. Did your neighbour successfully
sell the property?

Yes, but then I shifted anyway -- too many other neighbours. Now I
have a *much* better place to make noise -- and it even has an 800m
sealed runway :-)

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

Bruce Simpson wrote in message . ..
On 29 Feb 2004 18:57:36 -0800, (Eric Moore)
wrote:

If this PDE research pans out, what would such an engine be used on?

A high-speed, high-altitude cruise missile (Something like FastHawk or
ARRMD)?

An SR-71 replacement (possibly manned, but probably not)?

The first stage of a two stage reusuable space launch system?

Something else?

There are significant problems to using PDEs as a propulsive source.
The magnitude of the shockwaves produced is extremely high as are the
levels of vibration.


If it can't be used as a propulsive source, then what CAN it be used for?


A craft using such a power-plant will need some very special attention
paid to the acoustic and physical isolation of the engine.

On 6 Mar 2004 18:07:31 -0800, (Eric Moore)
wrote:

Bruce Simpson wrote in message . ..
On 29 Feb 2004 18:57:36 -0800, (Eric Moore)
wrote:

If this PDE research pans out, what would such an engine be used on?

A high-speed, high-altitude cruise missile (Something like FastHawk or
ARRMD)?

An SR-71 replacement (possibly manned, but probably not)?

The first stage of a two stage reusuable space launch system?

Something else?

There are significant problems to using PDEs as a propulsive source.
The magnitude of the shockwaves produced is extremely high as are the
levels of vibration.


If it can't be used as a propulsive source, then what CAN it be used for?

Right now -- not very much, if the published results are anything to
go by :-)

However, once they get the technology sorted I suspect the most common
application will be for hypersonic pilotless vehicles such as missiles
or as an air-breathing first-stage for low-cost re-usable low-earth
orbit or sub-orbital vehicles.

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

Bruce Simpson wrote:
On 6 Mar 2004 18:07:31 -0800, (Eric Moore)
wrote:

If it can't be used as a propulsive source, then what CAN it be used
for?

Right now -- not very much, if the published results are anything to
go by :-)

Aviation Week has an article this issue about the Air Force Research
Laboratory's Combustion Science Branch, which plans to test-fly a Scaled
Composites LongEZ sportplane with a four-cylinder PDE in lieu of a
conventional engine. Sounds like they think it will work, though it's going
to be a loud SOB. And they basically admit that they don't see this as a
practical operation: the plane will only make a few flights and nothing
cross-country. But it's a start.

I think these are the same people:

http://www.pr.afrl.af.mil/divisions/...News/news.html


--
Tom Schoene Replace "invalid" with "net" to e-mail
"Our country, right or wrong. When right, to be kept right, when
wrong to be put right." - Senator Carl Schurz, 1872

On Wed, 10 Mar 2004 01:31:20 GMT, "Thomas Schoene"
wrote:

Bruce Simpson wrote:
On 6 Mar 2004 18:07:31 -0800, (Eric Moore)
wrote:

If it can't be used as a propulsive source, then what CAN it be used
for?

Right now -- not very much, if the published results are anything to
go by :-)

Aviation Week has an article this issue about the Air Force Research
Laboratory's Combustion Science Branch, which plans to test-fly a Scaled
Composites LongEZ sportplane with a four-cylinder PDE in lieu of a
conventional engine. Sounds like they think it will work, though it's going
to be a loud SOB. And they basically admit that they don't see this as a
practical operation: the plane will only make a few flights and nothing
cross-country. But it's a start.

I think these are the same people:

http://www.pr.afrl.af.mil/divisions/...News/news.html

I think this is a "proof of concept" configuration rather than a
practical demonstration of the technology.

Have you seen the ancilliary equipment required to make that engine
work -- and despite all the weight and complexity, it's actually
*less* powerful than a traditional pulsejet of the same volume/weight.

Still, a journey of a thousand miles starts with a single step and I
suspect those doing the R&D on PDEs are under some pressure to
demonstrate progress so as to justify their budgets.

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

On Wed, 03 Mar 2004 09:26:37 +1300, Bruce Simpson
wrote:


To give you an idea of the difference (in terms of shock, vibration
and noise) -- in a deflagration, the flame travels at just a few
meters per second, in a detonation the flame front effectively travels
at several times the speed of sound.


Basicly it's the difference between low-order explosives like black
powder, and high order explosives like RDX...