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Re: [Phys-l] entropy +- heat



At 04:57 PM 7/22/2006, John D., you wrote:
...
I knew that the efficiency of any heat engine was limited by the
ratio of two temperatures: the peak temperature of the working fluid,
and the temperature of the heat sink.
...
I was deeply confused by this. It didn't figure it out until years later.
And not for lack of trying.


Hmmmm...considering the venerable Otto cycle operating in our autos,
we might suppose that the peak temperature of tyhe working fluid
in the cycle occurs when the spark plug ignites the mixture.
And that temperature would not vary much if the compression
ratio were 6:1 or 12:1

But wait: increasing the compression ratio so dramatically is known
to provide a major lift in thermal efficiency.

It turns out that the "Peak Temperature" in question is that
due to compression, not the much higher ignition temperature.



Brian Whatcott Altus OK Eureka!