The invention relates to the field of expanders, devices that extract work from pressurized gas while expanding the gas. Specifically, the invention relates to the field of positive displacement rotary expanders, more commonly known as rotary engines. More specifically this invention relates to a rotary steam engine. The invention also relates to the fields of gas compressors and pumps because positive displacement expanders generally can operate in reverse, and to the field of combustion engines having separate compressor, combustor, and expander sections as the expander of the present invention are also applicable to such engines.
Most engines for conversion of heat energy to mechanical energy involve expanding a heated, pressurized, gas by means of a device--an expander--that extracts work from the expansion of the gas. Examples include the traditional high pressure steam engine, wherein hot pressurized steam is expanded through an expander that extracts work, where that expander typically comprises a piston in a chamber or a turbine. Internal combustion engines also require an expansion of heated gas, as they involve a three stage process involving first compressing air, heating the air, and expanding the heated air while extracting work. A typical gas turbine engine (Brayton Cycle) involves separate areas for the compression, heating, and expansion of the gas, while a typical automobile engine (Otto Cycle) utilizes the same piston and cylinder for all three functions.
Expanders may be of the positive displacement type, where gas is admitted to a chamber, one or more walls of the chamber are then allowed to move under the influence of the gas pressure, thereby expanding the volume of the chamber. The moving wall can be called a piston, regardless of the actual shape or configuration of the parts that form the chamber. A positive displacement expander is often more efficient than a turbine at low speeds, while requiring less complex machining and cheaper materials than impulse and reaction turbines. Because of their slow rotation, positive displacement expanders may be less subject to metallurgical creep at high temperatures than are high speed turbines. Positive displacement expanders may also be less subject to erosion from impact of wet steam than are turbines because of the lower impact velocity.
Expanders of the positive displacement type repeatedly expand gas through the same components. Re-using the chamber in this manner requires valves whereby pressurized gas may be admitted to the chamber and expanded gas may be released from the chamber. Typically, a plurality of valves are required, at least one of which admits gas to the chamber and at least one of which releases gas from the chamber. Cylindrical rotary positive displacement expanders are those in which the chamber is formed by a central rotating element that rotates in a cavity. The rotating element is equipped with one or more protrusions or vanes that form the moving wall or piston of the chamber.
The prior art includes an extremely wide variety of rotary positive displacement engines which are testaments to human ingenuity. These devices utilize rotors, valves or other means to deliver the powering charge, such as pressurized steam, to a rotary expansion chamber, to extract work from the charge and to exhaust the spent charge. While such functions are common to all rotary positive displacement engines, the means for carrying out these functions, as embodied in the configuration of the moving parts are limited only by the imagination of the inventors. However many prior rotary positive displacement engine designs are victims of their own ingenuity in that the designs, while apparently functional on paper, are difficult if not impossible, to carry out in metal, as the machining and tolerances required to limit leakage are simply too complex to provide a practical rotary positive displacement engine at a competitive cost. Furthermore, many of the prior engine designs require clearances which are only achievable at ambient temperature, but not in operation at elevated temperatures.
The present invention is directed to a rotary positive displacement engine that overcomes the shortcomings of the prior art which render the previous designs impractical. The first obstacle to practicality that the present invention overcomes is that of complexity. The present invention is based on a design that is simple to manufacture and reproduce in that all of the significant rotating components of the engine are cylindrical. Furthermore, the bores that these components rotate in are also cylindrical. This assures ease of manufacture as a cylinder is the easiest shape to machine.
The second obstacle to practicality that the present design overcomes is the necessity for compromising on the tolerances for the rotating parts. The present design provides that the clearances of the major rotating parts are adjustable at operating temperature, so that very tight clearances can be achieved. This assures the most energy efficient operation. The present invention is applicable to rotary positive displacement engine designs having single or multiple power rotors and barrier rotors, as well as to single or compound operation. The present design is also applicable to low or high pressure operation.
A rotary positive displacement engine in accordance with the present invention includes one or more power rotors, which are acted upon by a pressurized charge of gas, such as steam, and an annular barrier rotor geared for synchronous rotation with the power rotors. The rotors rotate within intersecting cylindrical bores in the engine housing. The power rotors have cylindrical outer surfaces from which vanes extend which are acted upon by the powering charge. The barrier rotor has an outer cylindrical surface, located in close proximity to the cylindrical surface of the power rotors, and ports for delivering the powering charge to the power rotors. The barrier rotor thus forms both a charge delivery mechanism and a barrier between the exhaust ports and the expanding gas powering the engine. Located within the barrier rotor is a stator which has ports in fluid communication with the ports in the barrier rotor when the respective ports are aligned. The location of the barrier rotor is adjustable with respect to the power rotors to permit the clearances between the confronting surfaces of the barrier rotor and the power rotors to be adjusted to extremely tight tolerances under operating conditions which provides highly efficient operation.