Engine

A method of operating an externally heated thermodynamic engine having a closed working-fluid circuit, the engine comprising:

• a thermodynamic expander for extracting work from vaporised working fluid fed to a feed for it,
• a condenser downstream of the expander for condensing expanded vaporised working fluid exhausting from the expander,
• a liquid tank downstream from the condenser,
• pump means downstream from the liquid tank for pumping out condensed working fluid from it, and
• means for heating and at least partially vaporising working fluid pumped to it from the pump and feeding the heated working fluid to the expander,
• the heating means having at least one inlet for working fluid pumped to it and at least one output from which the working fluid is fed to the expander;
• the engine being adapted and arranged for operation with a working fluid including at least two different boiling point constituent fluids and
• the pump means being adapted to pump from the liquid tank to the heating means both the different boiling point constituent fluids in a determined ratio as liquids;
• wherein the method includes the operating steps of:
• the working fluid is fed to the expander in at least partially vaporised state,
• vapour and/or liquid of the higher boiling point liquid is caused to release heat energy in the expander to vapour of the lower boiling point constituent fluid for production of work in the expander and
• the higher boiling point liquid is caused to be liquid on exit from exhaust of the thermodynamic expander.