On Thu, 11 Sep 2003 03:20:59 -0400, Gary Coffman
wrote:

On Wed, 10 Sep 2003 14:12:24 GMT, "Karl Townsend" wrote:
I'm curious, they claim a thermal efficiency of 50%, nearly double that of
an automotive diesel. How do they do it? and why can't it be done in the
automotive size engine?

Cube square relation. The larger the engine, the more volume it has
with respect to surface area. Heat losses are through the surface area.
So the larger the engine, the smaller the percentage of total heat is
lost through the engine surfaces. Thus more heat is retained in the
combustion gases, where it can do useful work expanding against
the piston. So it can be more efficient.

Gary

Same thing for an engine with fewer cylinders and same displacement.

The relativley long stroke (vs bore) also has no bearing on the
compression ratio (and peak cylinder pressure) - that's determined by
the ratio of cylinder volume at TDC vs BDC (which would be the same
for any given bore size).


Laurie Forbes