Solar powered free-piston Stirling engine

• US 4,642,988 A
• Filed: 07/29/1983
• Issued: 02/17/1987
• Est. Priority Date: 08/14/1981
• Status: Expired due to Term

• Current Assignee: Glendon M. Benson
• Original Assignee: New Process Industries, Inc.
• Inventors: Benson, Glendon M.
• Primary Examiner(s): Husar, Stephen F.
• Application Number:
  US06/518,607
• Time in Patent Office: 1,299 Days
• Field of Search: 60/517, 60/518, 60/520, 60/525, 60/526, 60/641.8, 60/641.14, 60/641.15, 60/659, 60/676, 60/669, 60/690, 62/6
• US Class Current: 60/641.14
• CPC Class Codes: F02G 1/0435 the engine being of the free piston type
• CPC Class Codes: F02G 1/06 Controlling
• CPC Class Codes: F02G 2244/50 Double acting piston machines
• CPC Class Codes: F02G 2254/11 Catalytic burners
• CPC Class Codes: F02G 2254/30 using solar radiation
• CPC Class Codes: F02G 2258/10 ceramic
• CPC Class Codes: F02G 2270/50 Crosshead guiding pistons
• CPC Class Codes: F03G 6/068 having other power cycles, e.g. Stirling or transcritical, supercritical cycles; combined with other power sources, e.g. wind, gas or nuclear
• CPC Class Codes: Y02E 10/46 Conversion of thermal power into mechanical power, e.g. Rankine, Stirling or solar thermal engines

Abstract

A Stirling engine design which is solar powered is disclosed. A solar receiver converts solar radiation to thermal energy, which is stored in a storage chamber. The engine includes a displacer chamber with a displacer piston which divides the chamber into hot and cold subchambers, the hot subchamber being heated by the storage chamber. A mechanism is provided for cooling the cold subchamber. The engine also includes an alternator chamber with an alternator piston which divides the chamber into working and bounce subchambers, the working subchamber being in fluid communication with the cold subchamber of the displacer. The working fluid circulates through the cold subchamber and the working subchamber and obtains heat from the storage chamber. The working fluid is displaced by the displacer piston to drive the alternator piston, and work output is obtained from the alternator piston.

Claims

1. A solar-powered Stirling engine comprising:

a solar receiver which converts solar radiation to thermal energy;

a storage chamber for thermal energy in heat transfer communication with the receiver;

a displacer including a displacer chamber and a differential area displacer piston with variable electromagnetic damping means dividing the displacer chamber into separate hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the storage chamber;

means for cooling the cold subchamber;

an alternator including an alternator chamber and an alternator piston dividing the alternator chamber into working and bounce subchambers respectively, the working subchamber being in fluid communication with the cold subchamber of the displacer;

a working fluid circulating through be cold subchamber and the working subchamber and in heat transfer communication with the storage chamber, said working fluid being displaced by the displacer piston to drive the alternator piston; and

means for obtaining work output from the alternator piston.

2. The engine of claim 1 wherein the displacer piston includes an internal regenerator, and wherein the working fluid circulates between the hot and cold subchambers through the internal regenerator.

3. The engine of claim 1 and additionally comprising a regenerator external to the displacer, and conduit means conducting the work fluid from the cold subchamber through the regenerator to a position in heat transfer communication with the storage chamber.

4. The engine of claim 1 and additionally comprising a combustion heater in heat transfer communication with the storage chamber for supplying heat in the absence of sufficient solar radiation.

5. The engine of claim 1 wherein the work output obtaining means comprises a linear electric alternator stator proximate the alternator piston and the alternator piston has annular permanent magnets of alternating polarity.

6. The engine of claim 1 and additionally comprising a balance piston operating in opposition to the displacer.

7. The engine of claim 1 wherein the alternator includes a pair of mirror-image alternators operating in synchronization.

8. The engine of claim 1 wherein the storage chamber and the displacer piston have mating tapered concentric rings to minimize dead volume in the hot subchamber.

9. The engine of claim 8 wherein the displacer piston includes an internal regenerator, wherein the ends of the displacer piston defining the hot subchamber and the cold subchamber are porous, and wherein the working fluid circulates through the regenerator.

10. The engine of claim 9 wherein the displacer chamber and displacer piston have confronting concentric tapered rings to minimize dead volume in the cold subchamber.

11. The engine of claim 10 wherein the rings in the displacer chamber confronting the displacer piston have apertures at the bases of the tapered rings to allow the working fluid to pass through the apertures from the cold subchamber to the working subchamber.

12. The engine of claim 11 wherein the concentric rings on the displacer chamber are hollow, and additionally comprising means for flowing a cooling fluid through said hollow ring to cool the cold subchamber.

13. The engine of claim 12 wherein the cooling means comprises a conduit for a cooling fluid external to the Stirling engine, and additionally comprising a fan for drawing ambient cooling air over the Stirling engine and the conduit.

14. The engine of claim 13 wherein the cooling fluid is a phase-change fluid.

15. The engine of claim 1 wherein the displacer piston includes concentric tapered rings projecting into the cold subchamber, and wherein the cooling means comprises a plurality of hollow concentric tapered projections extending into the cold subchamber, said projections being complementary to and meshing with the tapered rings of the displacer piston, said projections including apertures between adjacent projections so that the working fluid circulates between the cold chamber and the working subchamber through the projections.

16. The engine of claim 1 wherein the alternator piston and portions of the alternator chamber defining the working subchamber include confronting complementary tapered concentric rings which nest together to minimize dead volume.

17. The engine of claim 1 wherein the alternator piston is annular and comprises a plurality of magnets, and wherein the work output obtaining means comprises a stator core within the annular alternator piston with coils in which electrical voltage is generated by the moving magnets of the alternator piston.

18. The engine of claim 1 and additionally comprising a displacer gas spring on the cold side of the displacer to bias the displacer piston back toward the hot side of the displacer.

19. The engine of claim 18 wherein the volume of the displacer gas spring is variable to alter the stroke of the displacer piston.

20. The engine of claim 1 wherein the alternator includes an alternator gas spring in the bounce subchamber, and means for varying the volume of the alternator gas spring to vary the stroke of the alternator piston.

21. The engine of claim 1 wherein the storage chamber contains an alkaline metal as the phase-change heat transfer fluid.

22. The engine of claim 1 wherein the storage chamber includes containers encapsulating a phase change material for storing thermal energy.

23. The engine of claim 1 wherein the alternator includes two co-linear alternators having armature pistons that stroke in phase opposition, and additionally comprising a balance piston co-linear with the displacer piston that strokes in phase opposition relative to the displacer piston.

24. The engine of claim 1 wherein the solar receiver, the storage chamber and the displacer comprise an integral unit.

25. The engine of claim 24 wherein the solar receiver, storage chamber and displacer are of equal diameter.

26. The engine of claim 24 wherein the solar receiver, storage chamber and displacer are constructed of materials having substantially equal thermal expansion properties.

27. The engine of claim 1 wherein the cold subchamber cooling means comprises an air-cooled radiator.

28. The engine of claim 27 wherein the radiator is integral with the engine.

29. The engine of claim 1 wherein the alternator piston is solid and includes a plurality of annular magnets, and wherein the work output means includes a stator circumscribing the alternator piston with coils in which an electric voltage is generated by the moving magnets of the alternator piston.

30. The engine of claim 1 wherein the displacer piston is impervious to the working fluid, and additionally comprising an annular regenerator circumscribing the displacer piston, the working fluid circulating through said regenerator.

31. The engine of claim 1 wherein the work output obtaining means comprises a crank for obtaining mechanical work output.

32. The engine of claim 1 wherein said storage chamber includes extended surface area for enhancing said heat transfer.

33. The engine of claim 7 wherein the bounce subchambers of each alternator are interconnected to center the alternators.

34. The engine of claim 8 wherein the rings are hollow and include an internal reinforcing structure to prevent deformation.

35. The engine of claim 10 wherein the rings are hollow and include an internal reinforcing structure to prevent deformation.

36. The engine of claim 20 wherein the varying means includes means for maintaining a constant reciprocation frequency by varying stroke and phase to provide a constant voltage output.

37. A solar powered electrical generator comprising:

a solar receiver which converts solar radiation to thermal energy;

a storage chamber for thermal energy in heat transfer communication with the receiver;

a Stirling engine including a displacer piston thermally coupled to the storage chamber and driven by heat from the storage chamber, and an alternator piston driven by the displacer piston, the alternator piston being annular and including a plurality of magnets of alternating polarity; and

a stator within the alternator piston and including coils in which electricity is generated by the magnets in the alternator piston.

38. The generator of claim 37 wherein the Stirling engine comprises a displacer including a displacer chamber, the displacer piston dividing the chamber into separate hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the storage chamber;

means for cooling the cold subchamber;

an alternator including an alternator chamber, the alternator piston dividing the alternator chamber into working and bounce subchambers respectively, the working subchamber being in fluid communication with the cold subchamber of the displacer; and

a working fluid circulating through the cold subchamber and the working subchamber and in heat transfer communication with the storage subchamber, said working fluid being displaced by the displacer piston to drive the alternator piston.

39. The generator of claim 38 wherein the cooling means comprises a conduit for a cooling fluid external to the Stirling engine, and additionally comprising a fan for drawing ambient cooling air over the Stirling engine and the conduit.

40. The generator of claim 37 and additionally comprising a combustion heater in heat transfer communication with the storage chamber for supplying heat in the absence of solar radiation.

41. The generator of claim 37 wherein the Stirling engine includes a pair of mirror-image alternator pistons, and a pair of mirror-image stators within the respective alternator pistons.

42. The generator of claim 37 wherein the storage chamber contains an alkaline metal as the phase-change heat transfer fluid.

43. The generator of claim 37 wherein the storage chamber includes containers encapsulating a phase change material for storing thermal energy.

44. The generator of claim 37 wherein the displacer piston has an annular portion comprising a plurality of magnets of alternating polarity, and additionally comprising a displacer stator within the annular portion of the displacer piston, said displacer stator including coils in which electricity is generated by the magnets in the moving displacer piston.

45. The generator of claim 37 wherein the solar receiver includes a shutter to prevent loss of heat energy when solar radiation is unavailable.

46. The generator of claim 37 wherein the displacer piston is located within a displacer cylinder, and wherein the solar receiver, the storage chamber and the displacer cylinder are integral.

47. The generator of claim 46 wherein the displacer cylinder, the solar receiver and the storage chamber are of equal diameter.

48. The generator of claim 47 wherein the displacer cylinder, the solar receiver and the storage chamber are constructed of materials having substantially equal thermal expansion properties.

49. A Stirling engine comprising:

a heat source;

a displacer including a displacer cylinder and a displacer piston reciprocal in the displacer cylinder and dividing the displacer cylinder into hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the heat source, the displacer piston including an internal regenerator, concentric tapered fins projecting into the cold subchamber, and apertures on the sides of the displacer piston confronting the hot and cold subchambers;

a plurality of hollow concentric tapered projections extending into the cold subchamber, said projections being complementary to and meshing with the tapered fins of the displacer piston, said projections including apertures between adjacent projections;

a cooling fluid circulated through the hollow projections to cool the cold subchamber;

an alternator including an alternator chamber and an alternator piston dividing the alternator chamber into working and bounce subchambers respectively, the working subchamber being in fluid communication with the cold subchamber of the displacer through the apertures in the projections;

a working fluid circulating between the hot and cold subchambers through the displacer piston, and the working subchamber through the projections, said working fluid being displaced by a displacer piston to drive the alternator piston; and

means for obtaining work output from the alternator.

50. The engine of claim 49 wherein the heat source includes a solar receiver which converts solar radiation to thermal energy, and a storage chamber for thermal energy in heat transfer communication with the receiver.

51. The engine of claim 49 in which the area of the displacer piston confronting the hot subchamber is larger than the area of the displacer piston confronting the cold subchamber.

52. The engine of claim 49 wherein the displacer piston has concentric tapered rings projecting into the hot subchamber, and in which the heat source includes concentric tapered projections extending into the hot subchamber, said projections being complementary to and meshing with the tapered rings of the displacer piston in the hot subchamber.

53. The engine of claim 49 and additionally comprising a balancer piston operating in opposition to the displacer piston.

54. The engine of claim 49 wherein the displacer includes a linear driver, and additionally comprising means for varying the status of the linear drive.

55. The engine of claim 54 and additionally comprising means for sensing the work output of the alternator and wherein the varying means is responsive to the sensing means.

56. The engine of claim 49 wherein the work output obtaining means from the alternator piston is a linear electric alternator.

57. The engine of claim 49 wherein the alternator includes a pair of mirror-image alternators operating in synchronization.

58. The engine of claim 49 and additionally comprising a conduit for the cooling fluid external to the Stirling engine, and additionally comprising a fan for drawing ambient air over the Stirling engine and the conduit.

59. The engine of claim 49 and additionally comprising a displacer gas spring on the cold side of the displacer to bias the displacer piston back toward the hot side of the displacer.

60. The engine of claim 49 wherein the volume of the displacer gas spring is variable to alter the stroke of the displacer piston.

61. The engine of claim 49 wherein the alternator includes an alternator gas spring in the bounce subchamber, and means for varying the volume of the alternator gas spring to vary the stroke of the alternator piston.

62. The engine of claim 49 wherein the heat source includes a combustor which converts fuel energy to thermal energy and a heat transport means for transferring the thermal energy to the hot subchamber.

63. The engine of claim 62 wherein the combustor and hot subchamber are ceramic and the heat transport means is a heat pipe with zinc heat transport fluid.

64. The engine of claim 63 wherein the ceramic is silicon carbide.

65. The engine of claim 63 wherein the ceramic is silicon nitride.

66. The engine of claim 62 wherein the combustor and hot subchamber are metal and the heat transport means is a heat pipe with an alkaline metal heat transport fluid.

67. The engine of claim 49 wherein the displacer is fabricated from ceramic compounds.

68. The engine of claim 67 wherein the ceramic compounds are silicon based compounds.

69. The engine of claim 49 wherein the displacer includes a gas spring of cross-sectional area A_hs in the hot subchamber and a gas spring of cross-sectional area A_cs in the cold subchamber, where A_cs is greater than A_hs and where A_cs -A_hs yields a differential drive area that provides a drive force in opposition to the drag force of the displacer and where A_cs +A_hs yields the effective area of the gas spring that provides a spring force in opposition to the inertial force of the displacer.

70. The engine of claim 69 wherein at least one gas spring has a variable volume that is adjusted in response to engine requirements.

71. The engine of claim 69 wherein, in addition, an electric drive means provides displacer control in response to engine requirements.

72. The engine of claim 69 wherein the gas spring in the hot subchamber comprises a self-centering sealing means.

73. The engine of claim 72 wherein the sealing means is a radially floating ring with gas bearing support.

74. The engine of claim 49 wherein the displacer piston and alternator piston are supported by gas bearing means.

75. The engine of claim 74 wherein the gas bearing means comprises hydrodynamic gas bearings provided by piston rotation.

76. The engine of claim 74 wherein the gas bearings means comprises hydrostatic gas bearings provided by the engine-contained gas that is pressurized by the amplitude of the gas pressure wave produced by the engine and stored in a valved reservoir supplying gas feed to the hydrostatic gas bearing orifices.

77. The engine of claim 74 wherein gas bearing support means during startup and shutdown is provided by a separate hydrostatic gas bearing supply comprising:

an actuator;

a positive displacement element driven by actuator;

a fluid conduit that connects positive displacement element to hydrostatic gas bearing orifices located circumferentially to displacer piston and alternator piston;

a bleed line that connects cold subchamber to positive displacement element; and

an actuator energy source.

78. The engine of claim 49 wherein the alternator piston comprises:

a plunger of cylindrical geometry with axial slots, formed of highly permeable material, and overlaid and with radially-poled permanent magnet tubular rings axially arrayed with adjacent rings of opposite polarity;

a stator, external to plunger, formed of highly permeable laminations that are radially stacked and contain therein electric coils in which electrical voltage is generated by the moving magnets of the alternator piston.

79. The engine of claim 75 wherein the stator includes torque windings to produce piston rotation.

80. A solar-powered Stirling engine comprising:

a solar receiver which converts solar radiation to thermal energy;

a storage chamber for thermal energy in heat transfer communication with the receiver;

a displacer including a displacer chamber and a displacer piston dividing the displacer chamber into separate hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the storage chamber, the storage chamber and the displacer piston having mating tapered concentric rings to minimize dead volume in the hot subchamber, the displacer chamber and the displacer piston having confronting concentric tapered rings to minimize dead volume in the cold subchamber, the concentric rings on the displacer chamber being hollow, the displacer piston including an internal regenerator and the ends of the displacer piston being porous;

means for flowing a cooling fluid through the hollow rings in the displacer chamber to cool the cold subchamber;

an alternator including an alternator chamber and an alternator piston dividing the alternator chamber into working and bounce subchambers respectively, the working subchamber being in fluid communication with the cold subchamber of the displacer;

a working fluid circulating through the cold subchamber and the working subchamber through the regenerator and in heat transfer communication with the storage chamber, said working fluid being displaced by the displacer piston to drive the alternator piston; and

means for obtaining work output from the alternator piston.

81. The engine of claim 80 wherein the cooling means comprises a conduit for a cooling fluid external to the Stirling engine, and additionally comprising a fan for drawing ambient cooling air over the Stirling engine and the conduit.

82. The engine of claim 81 wherein the cooling fluid is a phase-change fluid.

83. A solar-powered Stirling engine comprising:

a solar receiver which converts solar radiation to thermal energy;

a storage chamber for thermal energy in heat transfer communication with the receiver;

a displacer including a displacer chamber and a displacer piston dividing the displacer chamber into separate hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the storage chamber, the displacer piston having concentric tapered rings projecting into the cold subchamber;

a plurality of hollow concentric tapered projections extending into the cold subchamber, said projections being complementary to and meshing with the tapered rings of the displacer piston, said projections including apertures between adjacent projections;

an alternator including an alternator chamber and an alternator piston dividing the alternator chamber into working and bounce subchambers respectively, the working subchamber being in fluid communication with the cold subchamber of the displacer;

a working fluid circulating through the cold subchamber and the working subchamber through the apertures between adjacent projections and in heat transfer communication with the storage chamber, said working fluid being displaced by the displacer pistons to drive the alternator pistons; and

means for obtaining work output from the alternator piston.

84. A solar-powered Stirling engine comprising:

a solar receiver which converts solar radiation to thermal energy;

a storage chamber for thermal energy in heat transfer communication with the receiver;

a displacer including a displacer chamber and a displacer piston dividing the displacer chamber into separate hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the storage chamber;

means for cooling the cold subchamber;

an alternator including an alternator chamber and an alternator piston dividing the alternator chamber into working and bounce subchambers respectively, the alternator piston and portions of the alternator chamber defining the working subchamber including confronting complementary tapered concentric rings which nest together to minimize dead volume, the working subchamber being in fluid communication with the cold subchamber of the displacer;

a working fluid circulating through the cold subchamber and the working subchamber and in heat transfer communication with the storage chamber, said working fluid being displaced by the displacer piston to drive the alternator piston; and

means for obtaining work output from the alternator piston.

85. A solar-powered Stirling engine comprising:

a solar receiver which converts solar radiation to thermal energy;

a storage chamber for thermal energy in heat transfer communication with the receiver;

a displacer including a displacer chamber and a displacer piston dividing the displacer chamber into separate hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the storage chamber;

means for cooling the cold subchamber;

an alternator including an alternator chamber and an annular alternator piston having a plurality of magnets dividing the alternator chamber into working and bounce subchambers respectively, the working subchamber being in fluid communication with the cold subchamber of the displacer;

a working fluid circulating through the cold subchamber and the working subchamber and in heat transfer communication with the storage chamber, said working fluid being displaced by the displacer piston to drive the alternator piston; and

a stator core within the annular alternator piston with coils in which electrical voltage is generated by the moving magnets of the alternator piston.

86. A solar-powered Stirling engine comprising:

a solar receiver which converts solar radiation to thermal energy;

a storage chamber for thermal energy in heat transfer communication with the receiver;

a displacer including a displacer chamber and a displacer piston dividing the displacer chamber into separate hot and cold subchambers respectively, the hot subchamber being in heat transfer communication with the storage chamber;

a displacer gas spring on the cold side of the displacer to bis the displacer piston back toward the hot side of the displacer;

means for cooling the cold subchamber;

an alternator including an alternator chamber and an alternator piston dividing the alternator chamber into working and bounce subchambers respectively, the working subchamber being in fluid communication with the cold subchamber of the displacer;

a working fluid circulating through the cold subchamber and the working subchamber and in heat transfer communication with the storage chamber, said working fluid being displaced by the displacer piston to drive the alternator piston; and

means for obtaining work output from the alternator piston.

87. The engine of claim 86 wherein the volume of the displacer gas spring is variable to alter the stroke of the displacer piston.