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I've never been clear on what, exactly, is the problem of ethanol in gas. I
know manufacturers want us to avoid it, but I was never clear just why. I
figured alcohol can't damage any metal parts of the engine, so gaskets and
diaphragms would seem to be the only things vulnerable. I've been told that
"Marvin Dribbler" carbs have gaskets and seals and varnish coatings that
alcohol attacks (1930s technology again :o) and wonder if engine driven fuel
pumps might also be vulnerable. I also figured fuel injection systems
wouldn't vapor lock. This is an area where it is pretty difficult to cull
the "urban legend" from the actual situation. I went to the EAA and got
their paper on the subject and discovered some interesting tidbits:
* Embry Riddle found it saved $10 /hr using mogas instead of 100LL OVER AND
ABOVE the price differences between mogas and avgas. 230 hp engines save as
much as $35/hr on maintenance by switching to mogas. Several other
revelations on how damaging lead is.
Then, I contacted Earl Lawrence at EAA and he gave me some details that
amazed me.
* Mogas with alcohol ( in concentrations of 8%-10% it turns out) WILL vapor
lock in aircraft fuel injection systems (like my IO-360). SUBMERGED pumps
at pressures > 23 psi or so will make that go away. Neither submerged or
high pressure by itself will solve the problem. Need both. Automotive
injection systems with hi pressure rail AND RETURN will not vapor lock.
Concentrations below about 3% are very much less apt to vapor lock, so my
practice of putting 10 gal of mogas in my Velocity and topping off the 28
gal tank with 100LL is not a significant vapor lock risk.
* Alcohol by itself is not all that corrosive, nor is mogas. Problems
occur with normal concentrations (8% - 10% or greater of alcohol in the
gas). What happens is "phase separation" where temperature changes and what
not cause water to contaminate the gas, and the water/alcohol mixture
separates from the gas and settles to the bottom of the system. This stuff
is VERY corrosive. It attacks aluminum, steel and, basically, "every epoxy
known to man". It will not dissolve your airplane instantly - it is a long
term corrosive effect. You can work around it, but you have to design for
phase separation from the git-go. The guy said "Jeffcoat" or some such
stuff will protect your tank, but if there's pinholes in the Jeffcoat, this
stuff WILL attack your composite tank.
The guy was very straight with me, and gave me specifics (like where all the
STC folks say adamantly NO mogas in injected engines PERIOD, he said mogas
with under 3% alcohol was OK. The part about phase separated alcohol/water
was scary. I tried for half an hour to get him to tell me some way to work
around that and came up empty. MTBE is OK, as is ETBE, but they're both
going away. The only thing left to oxygenate auto fuel is alcohol, and
there's no way to keep it from damaging your tanks. He pointed out that
alcohol is not added to mogas until the tank wagon is filled at the
terminal. Then the alcohol is added to the tank wagon (it's never allowed
to touch gas in the refinery or terminal storage tanks), and dumped
immediately into the ground.
Y'all be careful with this stuff .... Jim S.
marc wrote:
> I found this interesting; I suppose too much alcohol might make the fuel
> more susceptible to high altitude or vapor lock maladies.......so cool
> that fuel.
>
> Subject: Checking autogas for alcohol
>
> Since I have the Peterson autogas STC for my O320, I thought I should
> have the proper tools for testing autogas for alcohol. Peterson wants us
> to avoid gasoline with alcohol. In fact they warn us against it. They
> recommend a graded beaker with which to mix a little water and a lot of
> gasoline. So I bought a beaker that is about as tall as your fist with a
> thumb sticking up. The diameter is about the same as a fat fountain pen.
> It is a 10 ml beaker with gradations on it. I put 1 ml of water in the
> beaker followed by about 9 ml of autogas. Then I put my thumb over the
> top and shook the heck out of it. There was alcohol in the autogas,
> because the line where the water had been just moved up almost 1 ml to
> just under the 2 ml mark. Or about 10% alcohol. Duh.
>
> The test works very quickly. There is little need to allow it to rest
> very long. 15 or 20 seconds maximum. I bought the beaker from the
> pharmaceutical chain store "Medicine Shoppe". But you can probably get
> one from almost any normal drug store. They will likely have to order
> it.
>
> The people selling gasoline usually have no idea about the product they
> are selling, so it is up to us to make the test. Be careful of where you
> dispose of the mixture! If you are observed by the environmental Nazis,
> you may face a fine and stern lecture. I guess we could pour it on a rag
> and pretend to clean the tar off the side of your car.
>
> A user
>
> Comment:With the phaseout of MTBE by Federal regulation, the areas of
> the country that require oxygenate only have ethanol readily available
> to use, so more and more mogas is going to be ethanol contaminated. If
> you have your own 10,000 gallon tank, you will be able to buy RBOB,
> reformulated blendstock for oxygenate blending, IOW mogas before the
> ethanol is added. This will be generally available since ethanol is
> being blended at the truck terminal, NOT at the refinery, due to
> pipeline problems in dealing with ethanol (it favors water, as you've
> noted, and God never made a dry pipeline).
>
> Marc Wiese
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T
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