Re: AvGas Screaming

[Mitch Loescher <Loescher@tamu.edu>]

>what exactly is synthetic oil made of?  what is different in its
>production that gives it the name "synthetic"?

Oil is made of a basestock and additives.  The additives come as a carrier
fluid and the magic molecules themselves.  

Normal dino juice is made by distilling crude oil and taking a fraction at
about 500-800 Deg F on the tower.  Distillation is a manufacturing process
which _separates_ a mixture of liquids by their differing volatilities.
Light molecules go up the tower and heavy ones go down the tower.  You can
"draw-off" liquids at any point in the process.  The stuff the makes it all
the way down after all the goodies have been separated out is then sold as
asphalt.  The point is that this is only a separation process.  You wind up
with a mixture of some of whatever oil you started out with, that happens to
be the particular molecules that lubricate best.  That becomes the basestock
for regular oils.

Synthetics are made entirely differently.  They start out as small molecules
that are put through many steps that chemically react them into other
molecules.  The advantage here is that you get a very controlled molecule
and only that molecule.  You can then design the system to make whatever you
find is a good lubricant.  You won't have any heavies that precipitate out
at high temperature.  You won't have any long chain paraffins that turn to
wax in the cold and prevent flow.  You won't have any lights that volatilize
and burn off at high temperatures.  You can make tough molecules that don't
physically break under the high stresses.  Basically you can make whatever
you want because you're synthesizing the molecules, not just separating out
whatever happens to be in that boiling range in the crude they happen to be
running that day.

Most synthoils are C20+ esters.  They start out as ethylene or propylene (C2
and C3 respectively) and are oligomerized (reacted) into C8, C10, C12, C14,
C9, C15, etc. monoolefins.  These are partially oxidized to the
corresponding long chain alcohol and to the 1-aldehyde in what are called
the POx and OXO processes.  They are then reacted into the ester to form the
very long chain ester.  Why these esters?...well they happen to have all the
best properties of lubeoils and can be made inexpensively using existing
feedstocks and technologies.  All along the process, each step is controlled
to make the desired product so you get a very consistent and only the
desired product.  It's just more expensive than straight distillation of
crude oil.

The additives consist of soluble organic bases to neutralize the acids that
are produced by combustion and get into the oil, polyisobutylene to improve
viscosity index and cut mist formation, antioxidants to help the oil resist
oxidation, and surfactants to keep solids suspended as colloids so they
don't settle out until the filter has a chance to get them.  That's the
majority of the additives.  The base oil that the additives are shipped in
should be a synthetic base if the additive is going into a synthetic
basestock.  I think this is the reason for "100% synthetic" marketing and
little disclaimers like "exclusive of additive carrier oil"...which means
that the additives are shipped in dino juice which is added to the synthetic
base stock.

Synthetics still get all the crap that blows by the rings so they still get
dirty just like dinojuice.  They will still burn if they get into the
combustion chamber and foul the plugs.  They will still leak out openings
through which dinojuice did.  They will still refuse to flow through plugged
oil galleries if regular oil refused too.  They still need to be filtered
well.  They are not miracle fluids, but they will coke less in turbo
bearings because of the greater stability of the base molecules.  They will
form more stable films in the high shear hydrodynamic bearings, and they
will break less leading to retention of properties for a longer time.

To anyone who's interested in more about oils, I have the oil FAQ on my
motorcycle web page under the articles section...
http://www-chen.tamu.edu/homepage/mel1523/hawkgt.htm.

 - Mitch