Stirling cycle engine

An engine, comprising:

• a first positive displacement machine, connected to an inlet duct, including at least one orbiting piston;
• a second positive displacement machine, connected to an outlet duct, including at least one orbiting piston;
• an intermediate duct connected to the first and second positive displacement machines;
• a kinematic connection linking the first and second positive displacement machines;
• a heater for raising the temperature and pressure of a gaseous working fluid in the intermediate duct which causes the working fluid pressure to rise equally in the first and second positive displacement machines, such that substantially no energy is required in the transfer of working fluid from the first positive displacement machine to the second positive displacement machine;
• and
• a device that shuts off the supply of working fluid from the first positive displacement machine and diverts a proportion of the supply of working fluid away from the second positive displacement machine,
• wherein, in operation of the engine, the first positive displacement machine causes a volume of the working fluid to flow through the intermediate duct to the second positive displacement machine, the heated and pressurized volume of working fluid drives the second positive displacement machine, and the second positive displacement machine drives the first positive displacement machine via the kinematic connection.