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Bob Mackey
wrote:
How to do that?
Thermally
insulate the surface.
That's the idea
behind ceramic coatings for the piston crown, combustion chamber,
and valve faces.
The insulator needs to be able to run hot on one side, and cool
enough on the
other side to
1) not melt or
weaken the metal
2) not burn or
polymerize the oil
3) not transfer so
much heat that the benefits of high compression are
lost
to cooling drag.
If that is worked
out, then engine BSFC improves, and cooling losses
are reduced.
Just as in a gas
turbine, the cooling drag is minimized by allowing the
hot section to
actually run hot. High temperature, high strength alloys,
and
insulating
ceramics are the key to an efficient aircraft diesel engine.
FWIW, Aluminum is
just about the worst material to use in a diesel head:
low strength at
high temperatures, high thermal conductivity, poor fatigue life, etc.
The argument that
"...heat has to be dissipated - - - some way." really
boils
down to "because
we let the heat get into the aluminum, we need to get it
back
out before the piston melts."
Bob, your theory is correct, however the execution is
difficult and expensive. I think the expense is the big problem in
aviation. The volume is not there to justify the cost of
development. I worked at Oldsmobile in the '80's and we made 3600 engines
every day. That volume must be compared to aviation volumes. Some of
the development costs I am talking about follow. I made a set of titanium
rods and found out you must not let titanium rub against anything else. I
made a set of inconel 718 pistons and found out the benefits did not justify the
costs. They were for a diesel engine by the way. I have made titanium
valves. These work pretty well, but the rubbing observation applies.
Personally, I have used ceramic coatings in several areas of my IV-P gasoline
engine. The new coating technology is something I believe can help every
engine. I think I mentioned this here before.....Pro Stock drag cars are
currently using about $40,000 worth of "coatings" in their engines,
transmissions and axels. At work, we are looking into producing pistons
for NASCAR engines. The piston design running successfully today is
light years from what was running just a few years ago. I was told a few
years ago that a commercial jet cost was 1/2 engines and 1/2 everything
else. Assuming what I was told is true, and GA owners were willing to
spend this kind of money, maybe the research could be paid for. For
example, take a IV-P that would sell for $700,000 where $350,000 was for
the engine. This would compare to the current $80,000 engine and
$350,000 everything else for $430,000. I would accept going slower (280
kts) and burning more fuel with the "trailing edge of technology"
stuff.
Craig Berland
Bored
stiff? Loosen up...
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