[AR] Re: Stopping/restarting solids
- From: Henry Spencer <hspencer@xxxxxxxxxxxxx>
- To: Arocket List <arocket@xxxxxxxxxxxxx>
- Date: Fri, 27 Mar 2020 18:43:41 -0400 (EDT)
On Fri, 27 Mar 2020, ken mason wrote:
Not the same mechanism, Keeping F&Ox apart is different than solid
propellant which already has F&Ox intimately mixed.
But combustion still takes place largely in the gas phase, so things
introduced into the gas could still have an effect. Halon does *not*
separate fuel from oxidizer, it chemically clogs up the combustion
reactions themselves. Even simple fuels burn by complicated multi-step
reaction chains, not in a single step, and partially-burned products of
one fuel molecule's combustion catalyze combustion of the next one. The
details are quite complicated, and not too hard to interrupt if something
grabs hold of an intermediate product and won't let go. As Terry says,
this is why it takes only a little bit of Halon to extinguish fires. In
particular, you can extinguish a fire with a Halon concentration that's
low enough that the air remains breathable. This is why aircraft
in-flight firefighting continues to use Halon, even though it's now hard
to get because it's a banned CFC.
(Technicality: there are actually a bunch of related compounds named
"Halon", in the same way that there are a bunch of different Freons.)
What probably *would* be a problem with Terry's idea: while combustion
takes place largely in the gas phase, the key part of it takes place not
far above the surface, and the wind is blowing *outward* from the surface
as the solid decomposes. So even though you don't need much Halon to
interrupt combustion, getting even a low concentration of it into the
right place might be difficult.
Henry
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