[Stoves] venturi system -ratios of air and gas?

[David Young]

On Sat, Jan 09, 2016 at 12:52:36AM +0100, Boll, Martin Dr. wrote:
> After reading Crispin's  Sentences:
> " It is likely that a propane flame is not premixed. A natural gas flame
> probably is. Being pre-mixed doesn't mean it is 100% supplied, only that it is an aid-enriched gas mix that is depending on available air near the flame
> to complete combustion."
> 
> The switch in my brain clicked !! :
> 
> If the mixture is complete, we will not have a usable flame, but an explosion, could be a slow-migrating one, but far of a flame we can use.

I wonder if an oxyacetylene torch provides a counter-example to the
explosion hypothesis?  Acetylene and O2 at 10 psi combine in a mixing
chamber before exiting the torch in a jet.  The velocity of the flame
is, I suppose, close to the velocity of the oxyfuel jet?  In this way
the flame is "held" at the torch tip---and it is a very useful flame!
If the oxyfuel jet is too fast, then the flame is quite diffuse, and I
suppose that it could just blow out.  If the oxyfuel jet is too slow,
then the flame burns inside of the torch instead of outside of it (the
dangerous condition called "flashback").

Now, if you mix oxyacetylene and O2 under a trash can or in a balloon,
and ignite the mixture, you do get an explosion.  (The explosion could
end very badly for you and bystanders, so please don't do it.)  I think
the important difference is that instead of a measured rate of gas
burning, you have a large, stagnant volume that, for all practical
purposes, ignites all at once.

Dave

-- 
David Young
dyoung at pobox.com    Urbana, IL    (217) 721-9981