Steam engines with reciprocating pistons were once used for various transportation systems including railway locomotives, ships and automobiles. Later versions of steam engines used for automobiles are equipped with multiple cylinders with reciprocating pistons, a steam generator that includes a boiler and a burner, a condenser, and a water tank. In these engines, engine activities involve the following four stages: first stage—water is pumped into the steam generator; second stage—steam is generated by the stream generator; third stage—the steam is taken into a valve-controlled working chamber of the engine at minimum cylinder volume, and the steam pushes the piston and gives rotational force to the driveshaft; fourth stage—the steam is exhausted by the piston, and the exhaust steam is cooled by the condenser, and goes back to the water tank.
The steam piston engine used for automobiles is well known for its ability to produce large torque. It is reported that Stanley 20 HP two-cylinder engine develops 640 ft-lbs of maximum torque, and the legendary Doble car engine develops 2200 ft-lbs of maximum torque. (James D. Crank, “A Fresh View of the Steam Car for Today,” Doble Steam Motors Corporation, Stanleysteamers.com). It is said that the Doble cars produced between 1923 and 1939 weighing over 4000 lbs could accelerate from 0 to 70 mph in under 5 seconds, and could maintain a top speed of 95 mph. Most steam-powered cars, however, could not start the engine instantaneously. The is commonly believed to be the main reason that the steam engine car lost the battle against the internal combustion engine cars. The problem of inability to start instantaneously was solved by providing a carburetor and spark plugs according to a paper entitled “Steam Motor-Vehicles” presented by Abner Doble, Vice President of General Engineering Company, presented on Oct. 20, 1916 in Cleveland.
Other improvements include the non-condensing cylinder, in which the cylinder head is covered with a steam jacket to prevent cylinder condensation, and the uniflow cylinder, in which the working fluid is let out of the main exhaust ports located in the middle of the cylinder wall enabling the superheated water vapor to get out of the cylinder when the piston is at around the end of the compression phase. Another improvement is multiple expansion engines, in which the exhaust vapor is reused to power the engine. A steam engine that does not use a separate boiler was invented by H. S. White of England (Provisional Patent No. 282580) as described in Steam Car Developments and Steam Aviation, Vol. IV. June 1935, No 40) though no reports on production of the engine is found. In this engine, a steam-generating chamber is affixed to the cylinder head of a piston cylinder and communications between the steam-generating chamber and the piston cylinder is controlled by a valve, and the water is pressure-fed into the steam-generating chamber by a pump.
The accepted thermodynamic standard with which the performance of the steam engine is compared is called Rankine cycle that is a special case (in the sense that the working fluid is water instead of hot air) of the Stirling cycle that consists of isothermal compression, isovolumetric pressure rise (or heating), isothermal expansion, and isovolumetric outlet (cooling). In the steam piston engine, like in the Stirling engine, the working fluid does not leave the engine's working chamber. The uniqueness of the water substance (similarly to any other condensable substance) is that if the saturated water vapor is compressed at constant temperature, the saturated water vapor will become a mixture of water and water vapor, and if the compression is continued further at the same temperature, the pressure will remain constant, and the mixture will finally become saturated water (see, for example, page 4–14 of Mark's Standard Handbook for Mechanical Engineering, 9th Edition by Eugine A. Avallone and Theodore Baumeister III, McGraw Hill Company. Some Stirling cycle engine patents are relevant to the present invention. A Stirling engine that uses a compression mechanism and an expansion mechanism, as the engine of this invention does, is shown in U.S. Pat. No. 6,109,040.
The steam piston engine, if properly built and operated, may be as efficient as the Stirling engine, which has a reputation of being highly efficient. Regardless, the steam engine that uses an alternative fuel such as liquefied natural gas that costs a fraction of gasoline (to produce the same amount of energy) should be welcome by the users in general. The water that may be considered a curse (because it increases the weight) in non-stationary applications may be considered a blessing in stationary applications. In distributed electricity generation for households, the engine may be used for generating electricity, and the reject water may be used for general use in the house or heating the house in winter. In such an application, the electricity generated by the steam engine may be used not only for daily household use but also for producing hydrogen for hydrogen-powered automobiles. The steam engine that uses sunlight for a source of energy, as described in this specification, may also be a possibility.