Exhaust system

1. An exhaust system configured for converting thermal energy to mechanical energy, the exhaust system comprising:

a source of thermal energy provided by a temperature difference between an exhaust gas having a first temperature and a heat sink having a second temperature that is lower than said first temperature;

a conduit configured for conveying said exhaust gas;

a heat engine disposed in thermal relationship with said conduit and configured for converting thermal energy to mechanical energy, wherein said heat engine includes a first element formed from a first shape memory alloy having a crystallographic phase changeable between austenite and martensite at a first transformation temperature in response to said temperature difference between said exhaust gas and said heat sink; and

a member formed from a conductive material and disposed in contact with said conduit so that said member abuts said conduit and transfers thermal energy from said conduit to said first element via conduction;

wherein said member includes a plurality of bristles each extending from and flexible with respect to said member and disposed in contact with said first element.

2. The exhaust system of claim 1 , wherein said first shape memory alloy changes crystallographic phase from martensite to austenite to thereby dimensionally contract at a localized region in response to said exhaust gas.

3. The exhaust system of claim 2 , wherein said first shape memory alloy changes crystallographic phase from austenite to martensite to thereby dimensionally expand at said localized region in response to said heat sink.

4. The exhaust system of claim 3 , wherein said first shape memory alloy alternately dimensionally expands at said localized region in response to said second temperature and dimensionally contracts at said localized region in response to said first temperature to thereby convert thermal energy to mechanical energy.

5. The exhaust system of claim 1 , further including an insulator disposed in contact with said conduit and configured for thermally insulating said conduit and said member.

6. The exhaust system of claim 5 , wherein said insulator is disposed in contact with said member.

7. The exhaust system of claim 1 , further including a plurality of heat engines.

8. The exhaust system of claim 1 , further including at least a second element formed from a second shape memory alloy having a crystallographic phase changeable between austenite and martensite at a second transformation temperature in response to said temperature difference between said exhaust gas and said heat sink.

9. The exhaust system of claim 1 , wherein said first element further has at least a second transformation temperature along a thickness of said first element at which said crystallographic phase changes between austenite and martensite.

10. The exhaust system of claim 1 , further including an apparatus configured for adjusting said temperature difference between said exhaust gas and said heat sink.

11. The exhaust system of claim 1 , further including a generator configured for converting mechanical energy to electricity, wherein said generator is driven by said heat engine.

12. The exhaust system of claim 11 , wherein said first shape memory alloy alternately dimensionally expands at a localized region in response to said second temperature and dimensionally contracts at another localized region in response to said first temperature to thereby convert thermal energy to mechanical energy and drive said generator.

13. An exhaust system configured for converting thermal energy to mechanical energy, the exhaust system comprising:

a source of thermal energy provided by a temperature difference between an exhaust gas having a first temperature and a heat sink having a second temperature that is lower than said first temperature;

a conduit configured for conveying said exhaust gas;

a heat engine disposed in thermal relationship with said conduit and configured for converting thermal energy to mechanical energy, wherein said heat engine includes a first element formed from a first shape memory alloy having a crystallographic phase changeable between austenite and martensite at a first transformation temperature in response to said temperature difference between said exhaust gas and said heat sink;

a member formed from a conductive material and disposed in contact with said conduit so that said member abuts said conduit and transfers thermal energy from said conduit to said first element via conduction, wherein said member includes a plurality of bristles each extending from and flexible with respect to said member and disposed in contact with said first element to thereby change said crystallographic phase between austenite and martensite;

an insulator disposed in contact with said conduit and said member and configured for thermally insulating said conduit and said member; and

a generator configured for converting mechanical energy to electricity, wherein said first shape memory alloy alternately dimensionally expands at a localized region in response to said second temperature and dimensionally contracts at another localized region in response to said first temperature to thereby convert thermal energy to mechanical energy and drive said generator.

14. An exhaust system configured for converting thermal energy to mechanical energy, the exhaust system comprising:

a source of thermal energy provided by a temperature difference between an exhaust gas having a first temperature and a heat sink having a second temperature that is lower than the first temperature;

a plurality of conduits each configured for conveying said exhaust gas along an axis, wherein each of said plurality of conduits has an interior surface and is radially disposed about and spaced apart from said axis;

a housing centered on and rotatable with respect to said axis, wherein each of said plurality of conduits is disposed within said housing and in fluid communication with said exhaust gas and said heat sink;

a torque ring;

a plurality of first elements each connected to said torque ring and formed from a first shape memory alloy having a crystallographic phase changeable between austenite and martensite at a first transformation temperature in response to said temperature difference between said exhaust gas and said heat sink;

a plurality of heat engines;

wherein each of said plurality of heat engines includes a respective one of said plurality of first elements disposed within a respective one of said plurality of conduits; and

a plurality of members each formed from a conductive material;

wherein each of said plurality of members is disposed in contact with said interior surface of a respective one of said plurality of conduits so that each of said plurality of members abuts said respective one of said plurality of conduits and transfers thermal energy from said respective one of said plurality of conduits to said respective one of said plurality of first elements via conduction;

wherein said first shape memory alloy alternately dimensionally expands at a localized region in response to said second temperature and dimensionally contracts at said localized region in response to said first temperature so that said torque ring rotates said housing and thereby converts thermal energy to mechanical energy.