Mixer for mixing exhaust gas

1. A mixer, comprising:

an outer annular portion exterior to an exhaust pipe and an inner annular portion interior to the exhaust pipe, where the outer annular portion comprises a spiral fin extending around the exhaust pipe in a downstream direction with respect to exhaust flow, wherein the inner annular portion is curved and comprises a C-shaped cross-section in the downstream direction, and where the inner annular portion comprises a venturi passage located along its central axis.

2. The mixer of claim 1 , wherein the spiral fin comprises a first end arranged along a first axis and a second end arranged along a second axis, and where the first axis is spaced away from and located upstream of the second axis relative to a direction of exhaust gas flow from an engine.

3. The mixer of claim 2 , wherein the outer annular portion is fluidly coupled to an exhaust passage of the exhaust pipe upstream of the first axis, and where the outer annular portion is fluidly coupled to the interior annular portion downstream of the second axis.

4. The mixer of claim 1 , wherein the outer annular portion and the inner annular portion are hollow and symmetric about a central axis of the exhaust pipe.

5. The mixer of claim 1 , wherein the inner annular portion is fluidly coupled to an exhaust passage at each of a venturi inlet, a venturi throat, and a venturi outlet of the venturi passage.

6. The mixer of claim 1 , wherein the outer annular portion and the inner annular portion are fluidly coupled via one or more perforations.

7. A mixer, comprising:

an outer annular portion exterior to an exhaust pipe and an inner annular portion interior to the exhaust pipe, where the outer annular portion comprises a spiral fin extending around the exhaust pipe in a downstream direction with respect to exhaust flow, wherein the outer annular portion comprises an outer surface angled relative to the exhaust pipe, and where an injector is coupled to the outer surface and positioned to inject into a flow space between the outer annular portion and the exhaust pipe.

8. A system comprising:

an annular mixing passage located outside of an exhaust pipe, wherein the mixing passage is divided into inner and outer passages, the inner passage is fluidly coupled to an exhaust passage at a location upstream of one or more first blades, and the outer passage is fluidly coupled to the exhaust passage at a location downstream of the one or more first blades and upstream of one or more second blades, wherein the inner passage is located between an inner annular surface and the exhaust pipe, and where the inner annular surface is cantilevered to the exhaust pipe.

9. The system of claim 8 , wherein the first blades are twisted in a counterclockwise direction and the second blades are twisted in a clockwise direction.

10. The system of claim 8 , wherein the first and second blades comprise free ends proximal to a central axis of the exhaust passage.

11. The system of claim 8 , wherein the outer passage is located between an outer annular surface and the inner annular surface, and where the outer annular surface and the inner annular surface extend entirely around a circumference of the exhaust pipe.

12. The system of claim 8 , wherein the first and second blades are fixedly coupled to the exhaust pipe and extend in upstream and downstream directions, respectively.

13. A method comprising:

flowing exhaust gas from an exhaust passage to an outer passage of a mixer located exterior to the exhaust passage, where the outer passage surrounds an exhaust pipe of the exhaust passage, wherein the outer passage receives and expels exhaust gas at one or more perforations upstream and downstream of one or more curved fins, a reductant injector positioned to inject into a location between surfaces of the mixer and one or more of the curved fins.

14. The method of claim 13 , wherein flowing exhaust gas further includes flowing exhaust gas through a constriction of the exhaust passage formed by an inner portion of the exhaust passage, wherein the inner portion of the exhaust passage is fluidly coupled to a downstream portion of the outer passage.

15. The method of claim 13 , wherein the mixer is fixed and immovable, and where the mixer does not rotate and slide.

16. The method of claim 13 , wherein there are no additional inlets or other outlets of the mixer other than the one or more perforations fluidly coupling the mixer to the exhaust passage.

17. A method comprising:

flowing exhaust gas from an exhaust passage to an outer passage of a mixer located exterior to the exhaust passage, and where the outer passage surrounds an exhaust pipe of the exhaust passage, wherein the outer passage receives and expels exhaust gas at one or more perforations upstream and downstream of one or more curved fins, and wherein exhaust gas flows in a U-shape through the outer passage.