In article aAtzf.740928$xm3.441347@attbi_s21,
"Dave Lyon" wrote:

"jw" wrote in message
ups.com...

Dave Lyon wrote:
See my other post for more detail. In summary: Pure acetylene at
15-ish
pounds doesn't "burn", a process which does indeed require oxygen.
Instead, it "deflagrates", a process of chemical breakdown that has no
need whatsoever for oxygen to be present in order to happen. (presence
of oxygen may in fact inhibit deflagration in some cases) The only
commonality between the two processes is that they both generate a lot
of heat.


I read your other post. Thanks, very informative. But, I have a
question.
If acetylene "defagrates" at around 15 psi, how do they get it into my
tank
at 250 psi or more?

I am sure someone will correct me if I'm wrong, but I think that is the
reason for the acetone and matrix in acetylene tanks. It helps to
stabilize the acetylene and prevent(or at least limit) this problem.

JW


OK, I've done a little research (very little)

This is what I've found from http://en.wikipedia.org/wiki/Deflagration

Deflagration is a process of subsonic combustion that usually propagates
through thermal conductivity (hot burning material heats the next layer of
cold material and ignites it). Deflagration is different from detonation
which is supersonic and propagates through shock compression

The best I can tell, deflagration IS combustion. Combustion REQUIRES an
oxidizer of some sort.

If I'm still wrong, please point me to a site where I can learn more.

Whoever wrote that piece is wrong to use the word "burning" or
"combustion", as well as in what they state deflagration to be. In fact,
the only thing I can see there that matches with what I was taught in
chemistry class is the "subsonic" part. Deflagration IS NOT combustion,
DOES NOT require oxygen, and CAN happen in materials not normally
thought of as "flammable" or "explosive". Combustion, or even
detonation, MAY come as an "after-effect" of deflagration, depending on
the presence of oxygen and what the breakdown products are, but they
aren't the same thing.

Deflagration is the *BREAKING* of a molecule's bonds (such as the
double-bond in the acetylene molecule - see "Note 1/ASCII art" below)
resulting in some other compound(s), each of which may or may not be
"deflagratable", flammable, or explosive in its own right, plus
bond-energy released in the form of heat.

Combustion/detonation (AKA "Oxidization", whether at high or low speeds)
is the combining of oxygen atoms with atoms/molecules of some other
compound, *FORMING NEW BONDS*, resulting in heat, various oxides, and
water, depending on what the fuel is.

To an observer, the "macro-result" - the overall effect at the scale we
humans are equipped to observe directly - of deflagration is quite
similar to, possibly indistinguishable from, combustion, but lacking a
need for any oxygen to sustain the reaction. At the molecular, "micro"
level, which we humans aren't equipped to observe directly, the two
processes are completely different, and might even qualify to be called
"complete opposites".

Deflagration requires no oxygen, and unless the material deflagrating is
known, might produce any number of unpredictable "other stuff" molecules
that don't necessarily include any "-oxide"s or water, and may be
flammable/explosive materials in and of themselves.

Combustion, on the other hand, whether "just a regular speed burn", or
the high-speed shockwave of detonation, absolutely requires oxygen,
which combines with the fuel in the classic "oxidization" reaction to
release energy in the form of heat, and for a "perfect mix" of
hydrocarbon fuel and oxygen, results in a nicely stable, slightly warm
mixture of CO2 and H2O.



(Note 1/ASCII art)
An acetylene (C2H2) molecule - Each "/", and "\" is a molecular bond,
the "=" is the double-bond. C is a carbon atom, H is a hydrogen atom:


H H
\ /
C=C
/ \
H H

When C2H2 deflagrates, it splits the double-bond, resulting in two CH2
molecules - each about as stable as a manic-depressive on LSD, and about
as "freindly" and "choosy" as a pre-paid whore - plus energy in the form
of heat. Since there are two bonds on each of the carbon atoms going
begging, each of the resulting CH2 molecules is desperately looking for
something to bond with. Add 4 atoms of hydrogen, and the CH2 molecules
will snatch 2 atoms each, transforming into two molecules of methane -
CH4 - which *IS* flammable/explosive in the presence of oxygen and
igition source. Add 6 atoms of oxygen (in the form of 3 molecules of O2)
instead, and you end up with a nice stable CO2 and H2O molecule for each
half of the "broken" acetylene molecule, plus more heat (from breaking
the three O2 bonds to allow each atom of O to go its own way) to
"tickle" the parent reaction.

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