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From: "Gary Casey" <glcasey@adelphia.net>
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Subject: V8's, liquid cooling
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<<Which of course, is the reason why the TCM liquid cooled engines weigh so
much less and occupy so much less bulk than do the air-cooled engines.
Right?>>

The TCM liquid-cooled engines shared the same design with their air-cooled
ancestors, with lots of space between cylinders.  Each cylinder was still a
separate entity with a full coolant jacket, all connected by external
plumbing and consequently the engine is heavy compared to the air-cooled
version.  A liquid-cooled engine designed from scratch would have little or
no clearance between cylinders and have a much shorter, lighter crank.  And
hence be competitive with the air-cooled equivalent.

<<Why aren't we looking more into oil cooling like the
http://www.thielert.com/ ?  I believe that is the way to go.>>

It certainly can be done.  However, oil cooling has a number of
disadvantages to overcome.  First, oil is about 80% as dense as water, so it
requires 25% more volumetric flow to have the same mass flow rate.  Second,
the specific heat of oil is only about 0.5, half that of water, so it
requires twice the mass flow if the temperature rise is to be the same.
Finally, oil is more viscous, reducing the turbulence at the boundary layer.
This turbulence is what pulls the heat from the metal.  The advantage of oil
cooling is that it can be run at higher temperatures, reducing the required
air flow through the radiator (except that you have to pump a lot more oil
than water through, which again increases the overall size.

Increasing the percentage of cooling done by the oil can have some
advantages.  Spraying oil on the underside of the pistons removes heat from
the source, reducing piston temperatures and reducing the amount of heat
that has to be transferred through the rings and piston skirt.

Finally, I think George mentioned that air cooled engines typically can
achieve a lower BSFC than liquid-cooled (automotive) engines.  Existing
aircraft engines are certainly close to the optimum configuration.  They
have large cylinders, open combustion chambers, dual plugs and high surface
temperatures.  The only problem with this is that the compression ratio that
can be run is limited.  The automotive engine can attempt to overcome its
disadvantages with a higher compression ratio.  The nod probably goes to the
aircraft-type air-cooled engine when it comes to BSFC.  I believe a
purpose-designed liquid cooled engine would be equivalent, maybe better.

Gary Casey