Carnot and Stirling cycles

Discussion on Stirling or "hot air" engines (all types)
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Carnot and Stirling cycles

Postby Barthooca » Sat Apr 01, 2017 12:42 am


I am I am trying to understand and model the Carnot Cycle.

I used Excel for simple modeling and plotting (

Now I get how to draw hot and cold isotherms, but I don't know how to get the shape (curvature) of adiabats. Is there any equation that I could use?

I assume hot and cold temperatures as well as two volumes (compressed and decompressed), how do I get adiabats for my specific values?

Moreover, I get the whole idea behind Carnot Cycle, but I don't get why the cycles are sometimes shown with curved adiabats and sometimes adiabats are simply straight lines (V = const.). Like in pictures below.


With curved adiabats, volume compresses further after isothermal compression and later decompresses even further after isothermal decompression. Why? If you think of an engine, how is it possible that after isothermal compression cylinder can go even further reducing the volume? Is there some empty/dead space? Same question for decompression.

Why doesn't the second image have this adiabatic volume change?

Can someone direct me to any good example or literature on modeling Stirling cycles/engines?


Ian S C
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Re: Carnot and Stirling cycles

Postby Ian S C » Sat Apr 01, 2017 1:24 am

I'm not a mathematician or physicist, my opinion is the pure Carnot cycle engine won't work. I suggest that you put Carnot Cycle in the search box at the top right corner of this page, you will be surprised, by a stack of threads on the subject.
Ian S C

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Re: Carnot and Stirling cycles

Postby Alexandr » Fri Apr 14, 2017 11:09 pm

>>>Why doesn't the second image have this adiabatic volume change?<<<
The ideal Stirling cycle has two isotherms and two vertical lines that show the isochoric process.

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Re: Carnot and Stirling cycles

Postby MikeB » Tue Apr 25, 2017 4:50 am

Even in an ideal Stirling Engine the piston has to move to draw power, which will result in a small change in volume.

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