Ideal expansion in heat engine?

[altalab]

I am considering using an a/c rotary vane compressor as an expander in a solar generating project. The working fluid is R134a refrigerant. From volume measurements I've determined it takes a 12cc space to a 36cc space before dumping, or 1:3. From what I've heard it should be more like 1:9. I've considered using a smaller and larger unit in a compound configuration or installing a cutoff device at the inlet. My questions are:
1) What is the ideal expansion ratio for efficiency regardless of resulting power/speed output?

2) What is the correct sizing steps for double and triple compound expansion?

3) Does throttling behave in any way like the results from a admission percentage cutoff device?

Thanks

 

[radomir]

Expansion is limited by thermodynamic characteristics of the working media (gas making work)and ambient conditions where it is exhausted to. In other words the exhaust total pressure (dynamic + static) has to be larger than surrounding ambient pressure.

Thus it would be nice to have expansion 1:9 but you have to provide sufficient compression first.