Pulse Jets

On 08 Dec 2003 05:00:54 GMT, (MattWriter) wrote:

What's the difference between a pulsejet and a PDE?

A pulsejet burns its fuel by way of a mechanism called deflagration.

Deflagration is also the way fuel burns inside your car's engine.
It's a relatively gentle process and happens at quite a leisurely
pace.

The PDE burns its fuel by way of detonation (hence the name).

Detonation is a far more violent process and happens extremely
quickly.

I like to use the following as a demostration of the difference.

A gallon of gasoline has more energy than a stick of dynamite but a
gasoline burns (in normal circumstances) by way of deflagration and
dynamite detonates.

If you take your gallon of gasolone and lay a trail on the ground,
then light one end -- you'll notice that the flame travels along that
trail at a few yards a second. That's the speed of a flame front
during the deflagration process -- it's really very, very slow
compared to a detonation.

If you laid a trail of high-explosive (something that detonates) along
the same distance and set off one end -- the exposive (detonation)
proces would race along that trail at many thousands of feet per
second -- significantly faster than with the gasoline.

Another comparison would be to take the gallon of gasoline and pour it
out on the ground in a big round patch. Then stand well back and
ignite that gasoline. The result will be a very impressive "woof!" --
but it's unlikely to hurt you or even knock you over.

Now take your stick of dynamite and place it the same distance away
before setting it off. It is at this point you will notice the rather
significant difference between deflagration and detonation -- if
you're still alive that is :-)

----
I can be contacted via http://aardvark.co.nz/contact/

In article ,
Bruce Simpson wrote:

If anyone has any specific questions then fire away and I'll do my
best to answer them.

Cool! I'm not a regular watcher of Junkyard Wars, but I happened
to see that episode.

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?

Also, I've always suspected that they seed the junkyard with parts
that the teams are going to need. (I stopped watching the show when
they told a team to look in the trunk of a demolished car and they
found a brand new roll of plastic sheeting that they desperately
needed.) Do they seed the junkyard?

It's still an entertaining and educational show.

+++
Lloyd Lee-Lim

In article ,
Bruce Simpson wrote:

If anyone has any specific questions then fire away and I'll do my
best to answer them.

Cool! I'm not a regular watcher of Junkyard Wars, but I happened
to see that episode.

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?

Also, I've always suspected that they seed the junkyard with parts
that the teams are going to need. (I stopped watching the show when
they told a team to look in the trunk of a demolished car and they
found a brand new roll of plastic sheeting that they desperately
needed.) Do they seed the junkyard?

It's still an entertaining and educational show.

+++
Lloyd Lee-Lim

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)?


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

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)?


Matt Bille
)
OPINIONS IN ALL POSTS ARE SOLELY THOSE OF THE AUTHOR

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.

Also, I've always suspected that they seed the junkyard with parts
that the teams are going to need. (I stopped watching the show when
they told a team to look in the trunk of a demolished car and they
found a brand new roll of plastic sheeting that they desperately
needed.) Do they seed the junkyard?

Yes, of course. They'd have to ensure that both teams have adequate,
functioning parts to build their machines.

--
__ Erik Max Francis && && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
\__/ The tremor of awe is the best in man.
-- Goethe

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.

Also, I've always suspected that they seed the junkyard with parts
that the teams are going to need. (I stopped watching the show when
they told a team to look in the trunk of a demolished car and they
found a brand new roll of plastic sheeting that they desperately
needed.) Do they seed the junkyard?

Yes, of course. They'd have to ensure that both teams have adequate,
functioning parts to build their machines.

--
__ Erik Max Francis && && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
\__/ The tremor of awe is the best in man.
-- Goethe

On Mon, 8 Dec 2003 22:15:02 +0000 (UTC), Lloyd Lee-Lim
wrote:

Cool! I'm not a regular watcher of Junkyard Wars, but I happened
to see that episode.

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?

It was pretty important that the person driving the turbojet-powered
kart be the expert. There are a number of things that the driver of
that vehicle had to keep his eye on; oil pressure, compressor
pressure, exhaust temperature and RPMs. If any one of these were to
shift out of the safe operating range the result could have been a
very nasty and rapid "deconstruction" of that engine - with possibly
serious injury caused to the driver and/or bystanders.

By comparison, the pulsejet-powered vehicle was much safer to drive -
but in order to be fair and equitable, it was decided that both
vehicles should be driven by the respective experts.

And thanks for the compliment -- that's the first time anyone has
called me "skinnier" for an awfully long time ;-)

Also, I've always suspected that they seed the junkyard with parts
that the teams are going to need. (I stopped watching the show when
they told a team to look in the trunk of a demolished car and they
found a brand new roll of plastic sheeting that they desperately
needed.) Do they seed the junkyard?

Yes, it's no secret that in some challenges (not all) specific "key"
pieces are seeded. If they didn't do that then a great deal of the
time they'd end up with no working machine at the end of 10 hours.

For example, in the case of the Jet Racers episode, if there didn't
happen to be a suitably sized turbocharger on the heap, or if no
suitable U-bend were found then one or both of the vehicles could not
have been completed. You have to remember that the show would be
pretty damned boring if the competition day consisted of the teams
flipping a coin to see who'd go on to the next round :-)

It's still an entertaining and educational show.

It certainly is. In these days of "reality TV" shows like Survivor
and endless soap operas, it's about the only show I'll actually make a
point of not missing.

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

On Mon, 8 Dec 2003 22:15:02 +0000 (UTC), Lloyd Lee-Lim
wrote:

Cool! I'm not a regular watcher of Junkyard Wars, but I happened
to see that episode.

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?

It was pretty important that the person driving the turbojet-powered
kart be the expert. There are a number of things that the driver of
that vehicle had to keep his eye on; oil pressure, compressor
pressure, exhaust temperature and RPMs. If any one of these were to
shift out of the safe operating range the result could have been a
very nasty and rapid "deconstruction" of that engine - with possibly
serious injury caused to the driver and/or bystanders.

By comparison, the pulsejet-powered vehicle was much safer to drive -
but in order to be fair and equitable, it was decided that both
vehicles should be driven by the respective experts.

And thanks for the compliment -- that's the first time anyone has
called me "skinnier" for an awfully long time ;-)

Also, I've always suspected that they seed the junkyard with parts
that the teams are going to need. (I stopped watching the show when
they told a team to look in the trunk of a demolished car and they
found a brand new roll of plastic sheeting that they desperately
needed.) Do they seed the junkyard?

Yes, it's no secret that in some challenges (not all) specific "key"
pieces are seeded. If they didn't do that then a great deal of the
time they'd end up with no working machine at the end of 10 hours.

For example, in the case of the Jet Racers episode, if there didn't
happen to be a suitably sized turbocharger on the heap, or if no
suitable U-bend were found then one or both of the vehicles could not
have been completed. You have to remember that the show would be
pretty damned boring if the competition day consisted of the teams
flipping a coin to see who'd go on to the next round :-)

It's still an entertaining and educational show.

It certainly is. In these days of "reality TV" shows like Survivor
and endless soap operas, it's about the only show I'll actually make a
point of not missing.

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

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/