Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml
Date: Tue, 19 Aug 2003 08:31:55 -0400
Message-ID: <redirect-2532950@logan.com>
From: "Gary Casey" <glcasey@adelphia.net>
Subject: autogas
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<<1)  The engine had a slightly greater tendency to collect carburetor ice.

2)  When leaning the mixture, the "peak" was "softer".  Since I had no EGT
gauge I just went by leaning to peak RPM and then enrichening slightly.  On
Avgas the peak was "sharper", i.e., little extra leaning caused the rapid
dropoff
in RPM.  On Autogas it was "softer" and the actual peak was slightly harder
to
discern.

3)  I used to run ARCO-brand gas, until one of my friends chastized me about
"that cheap crappy gas that he wouldn't even put in his car".  I then
switched
to Exxon.  With sufficient effort I could almost imagine that the Exxon gas
ran slightly smoother.
- Rob Wolf>>

These characteristics are likely all a result of the higher vapor pressure
of autogas.  The increased tendency for icing would be because more of the
fuel evaporates sooner, reducing the temperature of the mixture in the
carburetor throat.  A "softer peak" could be a result of improved mixture
preparation, again because more of the fuel is vapor in the intake manifold.
This would improve the ability to run lean and delay the onset of roughness.
If the actual peak EGT was rounded off, that would contradict this.

I would think that the 320/360 with its header tank would be appropriate for
autogas.  As I understand it, the real issue the FAA had with the fuel is
not in the engine at all, but related to the fuel delivery system and its
resistance to vapor lock.  The Cessna 150, with its high wing and gravity
feed, is almost impossible to vapor lock.  Low wings planes would be most
susceptible, but the header tank takes most of the problem away - at least
that's what I would think.  A low-wing plane without a header would be a
completely different thing.

This may be just folklore, but many years ago I was told that of the major
brands only Mobil owned their own refineries and pipelines.  All the other
companies shared both and just added their proprietary additives at
distribution.  Supposedly Mobil fuel was more consistent.  At Mercury Marine
we also found that engines run on Mobil would last longer at high power
settings because there would be less carbon and varnish buildup in the
engine.  Since then I have favored Mobil when given a choice.  For what its
worth.

Gary Casey