US Patent 7762055 Externally heated engine

An externally heated engine is provided which has at least two pistons. The first piston has a first side (working side) and a second side opposite the first side. The first side of the first piston and the first cylinder define a first working chamber containing working fluid. The second side of the first piston and the first cylinder define a first opposite chamber containing an opposing fluid. A heater heats the working fluid in the first cylinder. Preferably, the cylinder is heated by a heat source so that the working fluid has a temperature of no more than 500° Fahrenheit with a temperature difference between the heat source and the working fluid of less than 5° Fahrenheit. The second piston reciprocates within a second cylinder, and has a first side (working side) and a second side opposite the first side. The first side and the cylinder define a working chamber containing working fluid. The second side of the piston and the cylinder define a second opposite chamber containing an opposing fluid. The working fluid in the second cylinder is cooled to a temperature of below 35° Fahrenheit.