From: Doug Jones (djones@xcor.com)
Date: Wed Mar 06 2002 - 09:26:46 MST
James Rogers wrote:
>
> On 3/5/02 10:24 PM, "Adrian Tymes" <wingcat@pacbell.net> wrote:
> > (You know, I wonder if a simple high-pressure carbon dioxide grenade
> > might make a viable anti-combustion-engine weapon, if it could remove or
> > at least heavily dilute oxygen in the area for long enough to stall the
> > engine.)
>
> Carbon dioxide probably isn't the best choice. It becomes a liquid at
> relatively low pressures and behaves in an extremely non-ideal manner
> (gas-wise that is) when it is de-pressurized. In systems that use
> pressurized CO2 as propellant, you have to carefully limit your bleed rate
> from the pressure resevoir or it quickly drops off to anemic levels as the
> propellant rapidly becomes extremely cold.
This turns out not to be the case. If you tap off _liquid_ from a CO2
bottle, the pressure will only drop about 20% from full to liquid
exhaustion[1], and the cold gas + ice that results is very effective at
suppressing combustion. Hint: it is used in fire extinguishers for a
reason.
> Of course, there are plenty of other inert gases that you could use to
> quench combustion that exhibit better behavior e.g. the heavy noble gases.
> Plain old nitrogen makes a great cheap gas propellant that is also mostly
> inert.
Sure, nitrogen would work, but one can carry a much larger quantity of
CO2 much more conveniently, precisely because it *is* a liquid under
pressure, and thus is much more dense. Halon is better than either N2
or CO2, of course, but CO2 is cheap.
-- Doug Jones, Rocket Plumber [1] I have verified this experimentally for several liquids "vapacked" as saturated liquids in equilibrium with their own vapor. The general result applies for any subcritical vapacked liquid, from CO2, N2O, or C2H6 at room temperature, to water at 400-500 K, or LOX at 120-150 K. It is a simple and robust method for storing and delivering large volumes of gas (+ liquid or ice) quickly.
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