<HTML>The condensor to change it back to a liquid after it has been used is easy to build. It is similar to the radiator/condensor for a steam engine. At 88F you would need 1071 PSI to convert CO2 into a liquid. However using liquid nitrogen which can drop the temperature down to -56.6C, the pressure can be 5.2 Atm. Portable CO2 recondensors are available. They're just hard to find.
The system would run like this:
Liquid CO2 tank-heat expander-storage tank-motor-exhaust-condensor-liquid co2 pump-liquid CO2 tank.
The reason I asked, I'm about 3 months away from having a steam engine running on liquid CO2. I have a liquid co2 20lb tank, heat expander, storage tank (10lb@250PSI). I am working on the portable recondensor currently. I take it no one else is working on this type of idea? If not CO2 then how about ammonia or other state change gases?
Good chart for CO2 info: [
scifun.chem.wisc.edu];