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A flow-through muffler includes a plurality of heat conducting walls, baffles, or partitions that together define a plurality of passages arranged to form acoustic waveguides, attenuators, and/or cancellation chambers, the walls, baffles, or partitions increasing a surface area exposed to the exhaus

A flow-through muffler includes a plurality of heat conducting walls, baffles, or partitions that together define a plurality of passages arranged to form acoustic waveguides, attenuators, and/or cancellation chambers, the walls, baffles, or partitions increasing a surface area exposed to the exhaust gases to facilitate extraction of heat while attenuating or canceling the resulting sound pressure waves. The muffler may have a cooling arrangement mounted thereon, and thermoelectric generator elements or other heat-powered device, such as a reformer, connected across the heat differential between the cooling arrangement and an exterior surface of the muffler housing that is in thermal contact with the heat conducting walls, bafflers, or partitions. In addition, the muffler may be made tuneable by providing a device for varying a length of one of the passages relative to another passage, and by including a sound cancellation chamber at an intersection of the passages. In addition, the internal surfaces of the muffler may be coated with a catalyst to provide a combination muffler and catalytic converter.

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I claim: 1. A flow-through muffler, comprising: a housing including a lower section and a lid, and a plurality of internal baffles arranged to form unobstructed flow-through passages extending from an inlet to an outlet of said housing, said baffles being constructed of a heat conducting material,

I claim: 1. A flow-through muffler, comprising: a housing including a lower section and a lid, and a plurality of internal baffles arranged to form unobstructed flow-through passages extending from an inlet to an outlet of said housing, said baffles being constructed of a heat conducting material, wherein said baffles form a plurality of passages in communication with an inlet chamber and a convergence chamber, said passages having different lengths, and sound carried by said passages being canceled in said convergence chamber; and at least one mechanism for diverting acoustic waves into passages of different predetermined lengths to adjust a wavelength canceled by acoustic waves exiting said passages in said convergence chamber. 2. A flow-through muffler as claimed in claim 1, wherein an exterior surface of one of said lower section and said lid is made of a heat conductive material, wherein said baffles extract heat from an exhaust stream passing through said passages and conduct said heat to an exterior surface of said muffler, and further comprising at least one thermo-electric generator in contact with said exterior surface, a heat exchanger for creating a heat differential across said thermo-electric generator. 3. A flow-through muffler as claimed in claim 2, further comprising an insulator surrounding said thermo-electric generator and situated between said heat exchanger and said exterior surface. 4. A flow-through muffler as claimed in claim 2, wherein said heat exchanger comprises a plurality of heat dissipating fins. 5. A flow-through muffler as claimed in claim 2, wherein said heat exchanger comprises a plurality of pipes for circulating coolant through said heat exchanger. 6. A flow-through muffler as claimed in claim 1, wherein at least said lower housing and at least a portion of said baffles form a one-piece casting. 7. A flow-through muffler as claimed in claim 6, wherein said lid include a portion of said baffles depending therefrom. 8. A flow-through muffler as claimed in claim 1, wherein said lower housing and at least a portion of said baffles are formed of sheet metal. 9. A flow-through muffler as claimed in claim 8, wherein said lid includes a portion of said baffles depending therefrom. 10. A flow-through muffler as claimed in claim 1, wherein said passages have an s-shape, including straight inlet passages, first intermediate passages extending transversely to said straight inlet passages, straight intermediate passages extending transversely from said first intermediate passages, second intermediate passages extending transversely from said second intermediate passages, and straight outlet passages extending transversely from said inlet passages and straight intermediate passages. 11. A flow-through muffler as claimed in claim 10, comprising two sets of said s-shaped passages, and further comprising additional outlet passages extending transversely for said straight outlet passages of each of said two sets of s-shaped passages, said additional outlet passages opening into a convergence chamber for cancelling sound waves that have passed through said s-shaped passages. 12. A flow-through muffler as claimed in claim 11, further comprising a straight central passage between said s-shaped passages for permitting direct passage of exhaust gases with minimal back-pressure. 13. A flow-through muffler as claimed in claim 1, wherein said baffles are zig-zag shaped structures extending between said inlet and said outlet and generally parallel to each other. 14. A flow-through muffler as claimed in claim 1, wherein said baffles comprise a plurality of walls extending from said lower housing transversely to a longitudinal axis of said housing extending from said inlet to said outlet, and a plurality of walls extending from said lid also in direction transverse to said longitudinal direction, said walls extending from said lid being staggered with respect to said walls extending from said lower housing so as to form at least one labyrinthine passage between said inlet and said outlet. 15. A flow-through muffler as claimed in claim 1, wherein said baffles form a central flow-through passage between said inlet and said outlet, and a plurality for side passages in communication with an inlet side of said central passage, said side passages being closed at one end and arranged to reflect acoustic energy so as to cancel or dissipate the acoustic energy in the passages. 16. A flow-through muffler as claimed in claim 1, wherein said baffles from a plurality of wavy walls extending parallel to a longitudinal axis extending from said inlet to said outlet. 17. A flow-through muffler as claimed in claim 16, further comprising flow-diverting walls at least at an inlet side of said baffles. 18. A flow-through muffler as claimed in claim 1, further comprising flow-diverting walls at least at an inlet side of said baffles. 19. A flow-through muffler as claimed in claim 1, wherein said baffles are formed by a plurality of tubes extending transversely from one of said lower housing and said lid. 20. A flow-through muffler as claimed in claim 19, wherein said plurality of tubes further form a flow diverting on at least an inlet side of a main section of said tubes. 21. A flow-through muffler as claimed in claim 1, wherein said baffles extend from said lid. 22. A flow-through muffler as claimed in claim 1, further comprising a mechanism for adjusting a length of at least one of said passages relative to a length of another one of said passages to adjust a wavelength canceled by acoustic waves exiting said passages in said convergence chamber. 23. A flow-through muffler as claimed in claim 22, wherein said mechanism adjusts lengths of at least first set of said passages relative to lengths of a second set of said passages. 24. A flow-through muffler as claimed in claim 23, wherein said passages in said first set comprise fixed sections and telescoping sections that fit within and are moveable relative to said fixed sections to adjust lengths of passages formed by said fixed and telescoping sections. 25. A flow-through muffler as claimed in claim 24, wherein said telescoping sections are manually movable. 26. A flow-through muffler as claimed in claim 24, wherein said telescoping sections are movable by a motor. 27. A flow-through muffler as claimed in claim 26, further comprising a motor controller for controlling said motor in response to signals output by a MAPS sensor and a motor speed or RPM detector. 28. A flow-through muffler as claimed in claim 22, further comprising at least two passages and said mechanism comprises an adjustable wall section forming a movable wall of one of said passages to adjust a length of said one of the passages and thereby adjust a frequency of sound canceled in said convergence chamber. 29. A flow-through muffler as claimed in claim 28, wherein said adjustable wall section is a u-shaped member slidable in one of said passages. 30. A flow-through muffler as claimed in claim 29, wherein said u-shaped member is manually adjustable. 31. A flow-through muffler as claimed in claim 29, wherein said u-shaped member is adjustable by a motor. 32. A flow-through muffler as claimed in claim 31, wherein said u-shaped member is connected to said motor by a screw drive. 33. A flow-through muffler as claimed in claim 31, further comprising a motor controller for controlling said motor in response to signals output by a MAPS sensor and a motor speed or RPM detector. 34. A flow-through muffler as claimed in claim 28, further comprising a second said adjustable wall section. 35. A flow-through muffler as claimed in claim 28, further comprising at least three said adjustable wall sections. 36. A flow-through muffler as claimed in claim 1, further comprising at least one mechanism for diverting acoustic waves into passages of different predetermined lengths to adjust a wavelength canceled by acoustic waves exiting said passages in said convergence chamber. 37. A flow-through muffler as claimed in claim 36, wherein said mechanism comprises a pivotal flow diverter member. 38. A flow-through muffler as claimed in claim 36, wherein said mechanism comprises a rotary valve. 39. A flow-through muffler as claimed in claim 1, wherein a path length difference between said passages in feet is 1875 multiplied by a number of cylinders in an engine connected to said muffler, divided by a speed of the engine (RPM) and the number of revolutions per firing of each cylinder. 40. A flow-through muffler as claimed in claim 39, wherein said path length difference is 7500/RPM for an eight cylinder engine with two revolutions between firings. 41. A flow-through muffler as claimed in claim 1, further comprising length-defining members situated in said passages for defining lengths of said passages. 42. A flow-through muffler as claimed in claim 41, wherein said length defining members are pivotal members arranged to pivot to a position transverse to axes of respective passages in order to terminate the passages and thereby define their lengths. 43. A flow-through muffler as claimed in claim 1, wherein an exterior surface of one of said lower section and said lid is made of a heat conductive material, wherein said baffles extract heat from an exhaust stream passing through said passages and conduct said heat to an exterior surface of said muffler, and further comprising a heat exchanger and a reformer situated between said exterior surface of said housing and said heat exchanger. 44. A flow-through muffler as claimed in claim 43, wherein said reformer is arranged to convert diesel fuel into hydrogen gas. 45. A flow-through muffler as claimed in claim 1, wherein said baffles are coated with a catalyst selected to reduce pollutants in the exhaust stream. 46. A tuneable muffler, comprising an input, a cancellation chamber, and an output in communication with the cancellation chamber, and a plurality of passages having different lengths and extending between the input and the cancellation chamber, and further comprising an adjustment device for varying a length of at least one of said plurality of passages in order to vary a frequency of acoustic waves canceled in said cancellation chamber. 47. A tuneable muffler as claimed in claim 46, wherein a first set of said plurality of passages comprise fixed sections and telescoping sections that fit within and are moveable relative to said fixed sections to adjust lengths of passages formed by said fixed and telescoping sections. 48. A flow-through muffler as claimed in claim 47, wherein said telescoping sections are manually movable. 49. A flow-through muffler as claimed in claim 47, wherein said telescoping sections are movable by a motor. 50. A flow-through muffler as claimed in claim 49, further comprising a motor controller for controlling said motor in response to signals output by a MAPS sensor and a motor speed or RPM detector. 51. A flow-through muffler as claimed in claim 46, further comprising at least two passages and said mechanism comprises an adjustable wall section forming a movable wall of one of said passages to adjust a length of said one of the passages and thereby adjust a frequency of sound canceled in said convergence chamber. 52. A flow-through muffler as claimed in claim 51, wherein said adjustable wall section is a u-shaped member slidable in one of said passages. 53. A flow-through muffler as claimed in claim 52, wherein said u-shaped member is manually adjustable. 54. A flow-through muffler as claimed in claim 52, wherein said u-shaped member is adjustable by a motor. 55. A flow-through muffler as claimed in claim 54, wherein said u-shaped member is connected to said motor by a screw drive. 56. A flow-through muffler as claimed in claim 54, further comprising a motor controller for controlling said motor in response to signals output by a MAPS sensor and a motor speed or RPM detector. 57. A flow-through muffler as claimed in claim 51, further comprising a second said adjustable wall section. 58. A flow-through muffler as claimed in claim 51, further comprising at least three said adjustable wall sections. 59. A flow-through muffler as claimed in claim 46, further comprising at least one mechanism for diverting acoustic waves into passages of different predetermined lengths to adjust a wavelength canceled by acoustic waves exiting said passages in said convergence chamber. 60. A flow-through muffler as claimed in claim 59, wherein said mechanism comprises a pivotal flow diverter member. 61. A flow-through muffler as claimed in claim 59, wherein said mechanism comprises a rotary valve. 62. A flow-through muffler as claimed in claim 46, wherein a path length difference between said passages in feet is 1875 multiplied by a number of cylinders in an engine connected to said muffler, divided by a speed of the engine (RPM) and the number of revolutions per firing of each cylinder. 63. A flow-through muffler as claimed in claim 62, wherein said path length difference is 7500/RPM for an eight cylinder engine with two revolutions between firings. 64. A flow-through muffler as claimed in claim 46, further comprising length-defining members situated in said passages for defining lengths of said passages. 65. A flow-through muffler as claimed in claim 64, wherein said length defining members are pivotal members arranged to pivot to a position transverse to axes of respective passages in order to terminate the passages and thereby define their lengths.