Air start steam engine

A method and system for an external combustion engine operable using at least two different working fluids to be supplied to an engine to cause it to do mechanical work. The engine is started by providing a compressed gaseous working fluid at a sufficient pressure to the engine. At the same time the compressed gaseous working fluid is provided to the engine, a second working fluid that is liquid at ambient temperatures is provided to a heater to be heated. The second working fluid is heated to its boiling point and converted to pressurized gas form. Once the pressure is increased to a sufficient level, the second working fluid is injected into the engine to generate power, and the supply of the first working fluid may be stopped. After expansion in the engine, the working fluids are is exhausted from the engine, and the second working fluid may be condensed for separation from the first working fluid. The initial compressed fluid is recompressed for later use. Control circuitry controls the admission of the first and second working fluids responsive to monitoring the load on the engine.