Inspired by question about engine lubrication in space.
Piston engines are not used for propelling spacecraft, but there are some possible uses for especially Stirling engines and compressors:
- Stirling radioisotope generator
- Gas compressors, for cooling or otherwise
- Power generation from low temperature or pressure differences
But I didn't find a reference of any such being actually used in space, even as a demonstration. It appears that even air conditioning heat pumps used in space applications are not using the piston compressors that are common on Earth.
I guess the answer is no, but I'll ask anyway:
Has any reciprocating piston machine (either engine or compressor) been operated in space?