"Jay Honeck" wrote:

The adding of ethanol to gasoline has made the auto-gas STC unusable
for many aircraft owners, nationwide. So far, we're okay (in Iowa,
which is pretty funny) and are able to purchase untainted mogas -- but
the long-range situation seems untenable. We, as a nation, are
inexorably being forced toward the addition of alcohol into ALL
gasoline, so it seems...

On the Cherokee 235 user's group, there is a guy who's been
successfully using ethanol-gas in his aircraft. It's ruined his
fiberglass tip tanks, but he apparently expected this to happen.
Otherwise, the engine is running fine, or so he reports. (Personally,
I think he's crazy, ruining tip tanks that run close to $4K *apiece*,
but that's just me...)

Longer term, he is also risking corrosion damage to main tanks and pumps,
since ethanol, being hygroscopic, tends to join with any water, including
that from humidity in the air, and settle to the bottom of tanks. This
is a particular problem where humidity is high, and the fuel is left in
the tank for any period of time before being used.

The water content can also add to the risk of vapor lock or ice crystals
forming in the fuel where those things are already a problem, such as
where winter grade fuel is not used until the heat of the summer.

His experience has led to a more interesting (to me) discussion about
the possibility of REMOVING ethanol from gasoline. Several ideas have
been postulated (evaporation; heating; adding water), but none of them
sound particularly safe or easy.

Any chemists out there? Anyone know a way to remove the ethanol from
mogas, so that we may safely use it in our aircraft?

Without directly answering the question, also keep in mind that ethanol
is an octane booster. If it is removed from E10 fuel, as an example,
there is a loss of 2 or 3 points of octane. (This is also a problem
where the ethanol has combined with water and dropped out of the gasoline
mix.)

An engine like a Rotax turbo approved for use of Mogas requires a minimum
of 91 or 92 octane, and that is the rating for premium fuel. Thus, if
the ethanol is removed, even from premium fuel, the octane wouldn't be
high enough to use in the engine. The only possibility would be to start
with Sunoco Ultra, which is a 94 octane fuel, which I understand is 93
octane without the ethanol. Perhaps Sunoco will offer it as mogas
without the ethanol.

One way of removing ethanol would be to mix water with the fuel, and let
it sit for a while. The ethanol would combine with water, then you could
drain both off, (along with any other soluble compounds in the fuel).