On Wed, 09 Aug 2006 22:01:21 -0500, James Robinson
wrote:

"Jim Carter" wrote:

Some have been posting about using 92 or 93 octane mogas and removing
the Ethanol to get to the 90 or so octane for the old 80/87 engines. If
the testing and rating is different between mogas and avgas, is there a
conversion chart or algorithm somewhere so that we at least start with
the right stuff before we try to remove the ethanol?

They are close. Here's a link to an article that seems to sum up the
octane business in layman's terms:

http://www.prime-mover.org/Engines/G...es/octane.html

Well, it says the lower number (aviation lean) for aviation fuel will
be within one or two digits of the "motor octane" (MOR) on the gas
station pump. But US pumps don't tell you the MOR, they tell you the
anti-knock index (AKI), or (MON + RON)/2. As a rule of thumb the MOR
is 5 less than the AKI. (And the research octane number RON is 5 more
than the AKI.)

Thus the MON of autogas rated 87 octane is about 82, which makes it
about the equivalent of 80-octane aviation fuel.. Autogas with a pump
rating of 91 (premium) would be like 86-octane aviation fuel, if there
were such a beast.

(According to the site, aviation rich, the higher value in 80/87 is
only important in supercharged engines.)

This site: http://www.cheresources.com/greengas.shtml

says refineries *can* use catalytic naptha reforming and/or fluidized
catalytic cracking to produce a bunch of stuff, but mustly MTBE and
tertiary amyl methyl ether (TAME). The other refinery products
available for blending have various problems including causing cancer
(benzine), releasing sulphur, and gunking up your tailpipe.

So I haven't found anything on-line (yet) that absolutely persuades me
that high-test isn't just regular with more alcohol in it. (Which is
the part of my screed that actually relates to this thread.

Now for a slight change of direction. If you're writing your
legislators, one thing to remind them of is that we got the TEL out of
gasoline, NOT because it was making us sick (although I was never keen
on eating the blackberries that grow right alongside the highways
everywhere in Oregon), but because it destroyes catalytic converters.
And whatever anybody's opinion about catalytic converters is, nobody
is proposing CCs for the tiny piston-powered general aviation fleet.
Therefore efforts to remove the TEL from aviation fuel for
"environmental" reasons are quixotic and contrary to good sense.

In fact, a good case could be made for a mandate that TEL in avfuel be
REDUCED from the current ridiculous levels to something that wouldn'f
foul sparkplugs without drastic leaning.

THAT would make everybody happy.

Don