Re: Inert Gas in Fuel Tanks

From:         Malcolm Weir <>
Organization: Adaptive Information Systems -- A Hitachi Company
Date:         Thu, 7 Nov 1996 05:42:47 GMT
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Followups:    1
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Woodhams wrote:
> "P. Wezeman" <> writes:
> >this purpose. The newer of these two aircraft, the C-17, has a device
> >that separates ambient air into its two main constituents, oxygen and
> >nitrogen, and sends the nitrogen produced to the fuel tanks. As I
> Can anyone tell me how this device works? I would guess some chemical
> absorbs oxygen from the air flow (leaving nitrogen for the tanks) and
> is periodically heated to expel the oxygen.
> [Moderator's note: Regarding the C-17, one of the test team members
> told me that they used a compressor and, since it acts like a
> centrifuge, they tapped off the compressed gases, being of different
> densities, at different radiuses, or so he thought.  I seem to recall
> that the unit is cylindrical, but I may have been looking at a tank
> and not a compressor.  It sounded good to me, but that doesn't mean
> it's true.  MFS]

The centifuge idea is unlikely to be real: separating gasses this way
is non-trivial.

The three basic options are liquification and subsequent fractional
distillation (most effective), chemical O2 absorbtion (OK, but what if
the O2 scrubber wears out, letting un-scrubbed air into the system?),
or molecular sieves (which are slow, but used on the F16 to collect

My bet would be distillation, particularly if you can grab air from
outside at a low ambient temperature.