Russell Kent wrote:

Paul wrote:

There is some experimental evidense in the home built community such
that wrapping the exhaust pipes with asbestos and silcon rubber slows the
oxidation process on the outside of the pipes (corrosion). That's
1400 F. I don't know if that will work at 1700 F.

Hmm.  Any oxygen barrier will help with corrosion; that is probably a worthy goal for
the ceramic coating.

I always assumed that most of the heat transfer took place by radiation.

Well, I am certainly no expert.  I can see where radiation might be the primary
transfer method from the exhaust gases to the manifold, and from the manifold to the
cowl air, but for the coatings, and possibly wrappings, I would think that conduction
would be the primary transfer method.

Perhaps the best all-around solution is a low thermal conductivity material coating the
interior of the exhaust manifold, and a higher thermal conductivity material coating
the exterior.  Both would need to be oxygen impermeable at 1000+ deg F.  I may be
*completely* off my rocker here (remember I'm a software engineer :-), but could one
use the ceramic coatings on the inside and paint/anodize the outside of an otherwise
normal mild steel manifold?

Russell

They do have some high temp paints that work more or less on 
piston engine exhaust pipes. Working on a rotary exhaust would 
be a real test.

Anodise is a process they use on aluminum. Chrome plating perhaps.
Stainless is just a lot easier but it too corrodes judging by
looking a Tracy Crook's exhaust pipes. Inconel is best if you can afford
it. 0.040 thick Inconel holds up quite well with minimal corrosion.

Paul Lamar
 
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