Pulse Detonation Engines (PDE's)

[Eric Moore]

There's an article on Pulse Detonation Engines at:

http://www.aerotechnews.com/SpaceAndTechnology.htm#Space005

How much potential do PDE's have? Will they ever be more than a laboratory
curiousity?

[Ed Majden]

"Eric Moore"
> There's an article on Pulse Detonation Engines at:
>
> http://www.aerotechnews.com/SpaceAndTechnology.htm#Space005
>
> How much potential do PDE's have? Will they ever be more than a
laboratory
> curiousity?

Wasn't the German V1 buzz bomb powered by a PDE pulse jet? Perhaps a
crude one but still a pulse detonation engine of sorts.
Ed Majden

[Bernardz]

In article <x6T%b.633685$X%5.440608@pd7tw2no>, says...
>
> "Eric Moore"
> > There's an article on Pulse Detonation Engines at:
> >
> > http://www.aerotechnews.com/SpaceAndTechnology.htm#Space005
> >
> > How much potential do PDE's have? Will they ever be more than a
> laboratory
> > curiousity?
>
> Wasn't the German V1 buzz bomb powered by a PDE pulse jet? Perhaps a
> crude one but still a pulse detonation engine of sorts.
> Ed Majden
>
>
>

Yes.



--
Mankind's future is in space.

Observations of Bernard - No 48

[Grantland]

Bernardz > wrote:

>In article <x6T%b.633685$X%5.440608@pd7tw2no>, says...
>>
>> "Eric Moore"
>> > There's an article on Pulse Detonation Engines at:
>> >
>> > http://www.aerotechnews.com/SpaceAndTechnology.htm#Space005
>> >
>> > How much potential do PDE's have? Will they ever be more than a
>> laboratory
>> > curiousity?
>>
>> Wasn't the German V1 buzz bomb powered by a PDE pulse jet? Perhaps a
>> crude one but still a pulse detonation engine of sorts.
>> Ed Majden
>>
>>
>>
>
>Yes.

Nope. Pulse-burn. Much less efficient.
>
>
>
>--
>Mankind's future is in space.
>
>Observations of Bernard - No 48
>
>

[Jim Yanik]

"Ed Majden" > wrote in
news:x6T%b.633685$X%5.440608@pd7tw2no:

>
> Wasn't the German V1 buzz bomb powered by a PDE pulse jet? Perhaps a
> crude one but still a pulse detonation engine of sorts.
> Ed Majden
>
>

That's where the "buzz" came from! 8-)

--
Jim Yanik
jyanik-at-kua.net

[Ed Majden]

"Grantland" >
> Nope. Pulse-burn. Much less efficient.
> >
Symantics! It was a pulse jet! Bomarc SAM was a Ram jet and operated
on a different principal but was quite effective as a propulsion system
after getting up to speed by solid booster on the B-model.
Ed

[Grantland]

"Ed Majden" > wrote:

>
>"Grantland" >
>> Nope. Pulse-burn. Much less efficient.
>> >
> Symantics! It was a pulse jet!

>Ed
>
Nope. And what's a ramjet got to do with anything?
Another clumsy hoopster.

Grantland

[Ed Majden]

"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.

[Grantland]

"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.
>
Yes? I never disputed pulse jet. Pulse detonation has been a holy
grail for years. Pulse burn is very inefficient.

Grantland

[Eric Moore]

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?

[Bruce Simpson]

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/

[Bruce Simpson]

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.

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

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

[Keith Willshaw]

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

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

Hmmm

The British edition of scrap heap challenge recently had a program
in which teams had to build a jet propelled car.

The winner built a pulse jet and the 'high tech' isolation of engine
from vehicle seemed to consist of welding the bugger to the frame
though there was lots of duct tape in view :)

Fact is almost every motor car on the road runs with a
pulse detonation engine, its just that the pulse drives
a piston rather than being used for jet effect.

Keith

[Felger Carbon]

"Bruce Simpson" > wrote in message
...
>
> 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.
>
> A craft using such a power-plant will need some very special
attention
> paid to the acoustic and physical isolation of the engine.

Sounds like a micro-Orion. Now, there's an engine with _real_
acoustic and vibration problems! ;-)

[B2431]

>From: "Keith Willshaw"

>Fact is almost every motor car on the road runs with a
>pulse detonation engine, its just that the pulse drives
>a piston rather than being used for jet effect.
>
>Keith
>
Hopefully not a detonation. That would be like slamming the piston face with a
sledge hammer. In fact it's a rapid combustion.

Dan, U.S. Air Force, retired

[QDurham]

Dan wrote in part:
>Hopefully not a detonation. That would be like slamming the piston face with a
sledge hammer. In fact it's a rapid combustion.>

Amen. Detonation is exactly what octane is designed to prevent. The higher
the octane rating, the more resistant to detonation the fuel is.

I spent some time next to 3350 cubic inch engines which could be destroyed in
seconds by detonation -- even when using 130-145 octane fuel (purple and very
expensive.) Boost the manifold pressure, haul back on the RPM -- and the
engine might actually depart from the wing in a few seconds. Not recommended.

Quent

[[email protected]]

(B2431) wrote:

>
>>From: "Keith Willshaw"
>
>>Fact is almost every motor car on the road runs with a
>>pulse detonation engine, its just that the pulse drives
>>a piston rather than being used for jet effect.
>>
>>Keith
>>
>Hopefully not a detonation. That would be like slamming the piston face with a
>sledge hammer. In fact it's a rapid combustion.
>
>Dan, U.S. Air Force, retired

Most damned absolutely correct. It seems that damned near
everyone thinks otherwise.

I've heard supposedly experienced and knowledgeable mechanics say
"You'll see a power rise during detonation", when in fact the
powerful blasts of detonation are so shortlived that they produce
almost no useful energy. (lots of destructive energy though)
--

-Gord.

[[email protected]]

(QDurham) wrote:

>Dan wrote in part:
>>Hopefully not a detonation. That would be like slamming the piston face with a
>sledge hammer. In fact it's a rapid combustion.>
>
>Amen. Detonation is exactly what octane is designed to prevent. The higher
>the octane rating, the more resistant to detonation the fuel is.
>
>I spent some time next to 3350 cubic inch engines which could be destroyed in
>seconds by detonation -- even when using 130-145 octane fuel (purple and very
>expensive.) Boost the manifold pressure, haul back on the RPM -- and the
>engine might actually depart from the wing in a few seconds. Not recommended.
>
>Quent
>
Very true Quent...I've got about 16 years experience operating
3350's and I agree. Our Dash One for the Argus has a warning
under the heading of 'Detonation' which states "Detonation will
be evidenced by a rapid rise in Cyl Head temp, closely followed
by a rapid drop in torque, closely follower by structural parts
of the engine emitting from the exhaust stacks" :)

Sure kept us young buck engineers on our toes!...

ps: It's 115-145 octane actually, everything else is correct!.
--

-Gord.

[Bruce Simpson]

On Mon, 1 Mar 2004 23:18:55 -0000, "Keith Willshaw"
> wrote:

>
>"Bruce Simpson" > wrote in message
...
>> On 29 Feb 2004 18:57:36 -0800, (Eric Moore)
>
>> 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.
>>
>> A craft using such a power-plant will need some very special attention
>> paid to the acoustic and physical isolation of the engine.
>>
>
>Hmmm
>
>The British edition of scrap heap challenge recently had a program
>in which teams had to build a jet propelled car.
>
>The winner built a pulse jet and the 'high tech' isolation of engine
>from vehicle seemed to consist of welding the bugger to the frame
>though there was lots of duct tape in view :)

That was me -- I was the "expert" on that episode.

>Fact is almost every motor car on the road runs with a
>pulse detonation engine, its just that the pulse drives
>a piston rather than being used for jet effect.

No, that's incorrect.

A conventional piston-engine does not detonate its fuel -- it uses a
process called deflagration which is a *far* gentler combustion
process.

It's also worth noting that a pulsejet (such as the one we used on
Scrapheap) also uses deflagration rather than detonation.

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.

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

[[email protected]]

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.
--

-Gord.

[WaltBJ]

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

[John Keeney]

"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.

[[email protected]]

"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.

[Alfred Loo]

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/

[Bruce Simpson]

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/

[Eric Moore]

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.

[Bruce Simpson]

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/

[Thomas Schoene]

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/prt/pde/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

[Bruce Simpson]

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/prt/pde/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/

[rnf2]

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...

[rnf2]

On Tue, 09 Mar 2004 20:14:12 +1300, Bruce Simpson
> wrote:

>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.


given time and the technology... what would you asy is the chances of
a pulse jet space shuttle?

pulse jet in the atmosphere using air... and when reaching high enough
altitudes... closing a valve in the engine so the rear combustion
chamber is isolated and then injecting oxidiser with the fuel...
converting the airbreathing Pulse jet to a rocket...

[David Lesher]

(Eric Moore) writes:


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


Scaring away potential neighbors.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[WaltBJ]

The PDE technique offers one solution to the problem of hypersonic
thrust - burning the fuel-air mix in the millisecond or so of time
available. Consider the fact that the fuel-air mix has to combust and
go through the engine faster than the vehicle is moving or the
incoming air just piles up and you don't get any thrust. A rocket
doesn't have this problem. Detonation occurs much faster than
combustion - and if the duct is acoustically resonant (there's a nice
problem with changing velocities!) the engine will be maximally
efficient. Even if it never flies it'd be a good addition to a rock
concert.
Walt BJ