Re: THERMODYNAMICS [Re: Technology: Inverted energy source..]

From: Robert J. Bradbury (
Date: Sat Mar 18 2000 - 06:01:20 MST

On Fri, 17 Mar 2000, Spike Jones wrote:

> I wrote:
> > so your efficiency is (368-294)/368 = ~20%. Going to LN2 bricks
> > as the sink @ 63K gives you (368-63)/368 = 82%. So your engine
> > efficiency goes way up. Maybe you get 3-4x the MPG?
> Nyet.

Ti ne nravitsa moy calculatsi? Ti svolach.

(I think I can get away with saying this because Eugene isn't on
the list currently and won't trash my grammar or spelling).

> > Actually, there might be some problems with doing the calculation
> > this way since the operating temperature that should be used
> > might need to be closer to the fuel-air temperature in the cylinder.
> Ja. The temperature you need for calculating Carnot efficiency
> is the temperature of the exhaust when the exhaust valve opens.

This makes more sense. The question *is* what is that temperature
in a gas engine and/or a diesel engine?

> It wouldnt buy much to dump the waste heat into a really cold
> source other than you can get by with a smaller cooling system.

Its the difference that counts. When you can't up the operating
temperature any more due to the material limits, the only way to
go is to lower the heat sink temperature. What isn't clear (to me)
is how close to the high temperature limits current internal combustion
engines operate? And is the limit due more to thermal expansion
creating greater friction *or* being near the strength limits of
the materials at high temperatures?

Ceramic engines really sounded like the way to go when I read
about them.


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