Re: Inert Gas In Fuel Tanks

From:         bmackey@ucsd.edu (bob mackey)
Organization: San Diego SuperComputer Center at UCSD
Date:         21 Oct 96 02:29:17 
References:   1 2 3
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On 03 Sep 96 01:16:54 , Bob Falkiner <falkiner@interlog.com> wrote:


>Mikeit takes only a small percentage of an inert gas to render an explosive atmosphere
>"safe" regardless of what the gas is. It comes down to energy of explosion
>and energy to heat up inert gases to the point where the combustion is
>self containing.  If you blow up the main fuel tank, inert gas protection
>is not going to mean much, and if you just want to protect the air space in the
>thank. then a little bit of exhaust gas is going to be hard to beat.

The explosive limits of a fuel-air mixture vary widely depending on
the fuel, the pressure, and the temperature. As Bob F. suggests, the
key is whether there is enough heat output from combustion, to sustain
a temperature rise that can continue the combustion. But it is not
generally true that a few percent of exhaust gas will suspress
combustion. I'm sure that will be obvious if you consider how that
exhaust gas came into being...A fuel air mixture burned without
choking itself on its own exhaust. Of course the pressures and
temperatures in the cylinder were different than in the fuel tank, but
we wish to make the tank truly non-explosive.

Two extreme fuel examples are hydrogen and acetylene. With either of
these gases, adding 90% exhaust to a fuel-air mixture will leave the
mixture explosive.

-bob mackey
 bmackey@ucsd.edu