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A mixer for a vehicle exhaust system includes a mixer body defining a mixer central axis and having an inlet configured to receive engine exhaust gas and an outlet. The mixer further includes an upstream baffle positioned within the mixer body and a downstream baffle positioned within the mixer body

A mixer for a vehicle exhaust system includes a mixer body defining a mixer central axis and having an inlet configured to receive engine exhaust gas and an outlet. The mixer further includes an upstream baffle positioned within the mixer body and a downstream baffle positioned within the mixer body to be spaced from the upstream baffle in a direction along the mixer central axis. A doser defines a doser axis and is positioned to spray a reducing agent into an area between the upstream baffle and the downstream baffle such that a mixture of reducing agent and exhaust gas exits the outlet. The mixture moves through a rotational flow path that is at least 360 degrees before exiting the outlet.

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1. A mixer for use with a vehicle exhaust system, the mixer comprising an annular side wall that extends circumferentially around and axially along a central axis of the mixer to define an internal region of the mixer,an upstream baffle including a first upstream flat portion perpendicular to the ce

1. A mixer for use with a vehicle exhaust system, the mixer comprising an annular side wall that extends circumferentially around and axially along a central axis of the mixer to define an internal region of the mixer,an upstream baffle including a first upstream flat portion perpendicular to the central axis that extends circumferentially about 180 degrees around the central axis, an upstream helical portion that extends circumferentially about the central axis, and an axially extending inlet wall that extends between and interconnects the first upstream flat portion and the upstream helical portion, the axially extending inlet wall formed to include a primary inlet opening arranged to receive exhaust gases moving into the internal region during use of the mixer in a vehicle exhaust system, wherein the primary inlet opening is radially spaced apart from the central axis to induce swirling motion of the exhaust gases about the central axis during use of the mixer, anda downstream baffle axially spaced apart from the upstream baffle including a first downstream flat portion being generally perpendicular to the central axis, a second downstream flat portion being generally perpendicular to the central axis, and a downstream helical portion that interconnects the first and second downstream flat portions, wherein the second downstream flat portion is spaced apart axially from the first downstream flat portion and a primary outlet opening of the downstream baffle is located therebetween. 2. The mixer of claim 1, further comprising an extension baffle including a flat extension plate that is generally perpendicular to the central axis, a circumferential wall that extends axially away from the flat extension plate toward the upstream baffle and circumferentially partway about the central axis, and an axially extending side wall coupled to the flat extension plate and the circumferential wall and the extension baffle is formed to include a primary extension inlet opening aligned with the primary outlet opening of the downstream baffle and a primary extension outlet opening adapted to discharge the exhaust gases during use of the mixer. 3. The mixer of claim 2, wherein the downstream baffle, the flat extension plate, the circumferential wall, and the axially extending side wall of the extension baffle cooperate to define the primary extension inlet opening and the axially extending side wall is formed to include the primary extension outlet opening. 4. The mixer of claim 2, wherein the flat extension plate defines an apex and includes a first edge that extends radially outward away from the apex toward the annular side wall and a second edge that extends radially outward from the apex toward the annular side wall and the second edge is circumferentially spaced apart from the first edge by between about 90 degrees and about 180 degrees relative to the central axis. 5. The mixer of claim 2, wherein the flat extension plate is formed to define a secondary opening that extends axially through the flat extension plate and a lip that protrudes axially toward the upstream baffle and the lip is arranged around the secondary opening. 6. The mixer of claim 5, wherein the flat extension plate has a plate thickness measured axially relative to the central axis, the lip has a lip height measured axially relative to the central axis, and the lip height is about three times larger than the plate thickness. 7. The mixer of claim 1, wherein the at least one primary inlet opening is circumferentially spaced apart from the primary outlet opening of the downstream baffle by about 300 degrees. 8. The mixer of claim 1, wherein the first downstream flat portion, the second downstream flat portion, and the downstream helical portion cooperate to define a first side of the downstream baffle that extends at least 180 degrees circumferentially about the central axis and a second side of the downstream baffle that extends 180 degrees or less about the central axis, the first side of the downstream baffle is free of openings, and the second side of the downstream baffle is formed to include a secondary outlet opening that extends axially through the downstream baffle. 9. The mixer of claim 8, wherein the first upstream flat portion of the upstream baffle is formed to include a plurality of secondary inlet openings that extend axially through the first upstream flat portion of the upstream baffle and the plurality of secondary inlet openings are spaced apart circumferentially and radially from one another. 10. The mixer of claim 1, wherein the first upstream flat portion is formed to include a plurality of secondary inlet openings that are spaced apart circumferentially from one another and aligned circumferentially relative to one another. 11. The mixer of claim 1, wherein the annular side wall is formed to include a doser aperture, the mixer further includes a manifold aligned with the doser aperture, the manifold is arranged to direct fluid into the internal region along a doser axis during use of the mixer, and the doser axis is spaced apart circumferentially from the primary outlet opening of the downstream baffle by about 60 degrees. 12. A mixer comprising a side wall that extends circumferentially around and axially along a central axis of the mixer to define an internal region of the mixer,an upstream baffle including an upstream helical portion that extends circumferentially about and axially along the central axis and an axially extending inlet wall formed to include at least one primary inlet opening,a downstream baffle axially spaced apart from the upstream baffle and including a first downstream flat portion, a second downstream flat portion, and a downstream helical portion that extends circumferentially about the central axis and interconnects the first and second downstream flat portions and the downstream baffle formed to define a primary outlet opening of the downstream baffle located axially between the first downstream flat portion and the second downstream flat portion, andan extension baffle including a flat extension plate, a circumferential wall that extends axially away from the flat extension plate toward the upstream baffle and circumferentially partway about the central axis, and an axially extending side wall coupled to the flat extension plate and the circumferential wall, wherein the downstream baffle, the flat extension plate, the circumferential wall, and the axially extending side wall of the extension baffle cooperate to define a primary extension inlet opening aligned with the primary outlet opening of the downstream baffle, and the axially extending side wall of the extension baffle is formed to include a primary extension outlet opening. 13. The mixer of claim 12, wherein the upstream baffle further includes a first upstream flat portion that is generally perpendicular to the central axis and a second upstream flat portion that is generally perpendicular to the central axis, the second upstream flat portion is spaced apart axially from the first upstream flat portion, and the first upstream flat portion extends circumferentially about 180 degrees around the central axis. 14. The mixer of claim 13, wherein the first upstream flat portion is formed to include a plurality of secondary inlet openings that are spaced apart circumferentially from one another and aligned circumferentially relative to one another. 15. The mixer of claim 12, wherein the at least one primary inlet opening is radially spaced apart from the central axis. 16. The mixer of claim 15, wherein the first upstream flat portion of the upstream baffle is formed to include a plurality of secondary inlet openings that extend axially through the first upstream flat portion of the upstream baffle and the upstream helical portion is formed without openings. 17. The mixer of claim 16, wherein the at least one primary inlet opening includes a first primary inlet opening and a second primary inlet opening radially spaced apart from the first primary inlet opening. 18. The mixer of claim 12, wherein the flat extension plate defines an apex and includes a first edge that extends radially outward away from the apex and a second edge that extends radially outward from the apex and the second edge is circumferentially spaced apart from the first edge by between about 90 degrees and about 180 degrees relative to the central axis. 19. The mixer of claim 12, wherein the first downstream flat portion, the second downstream flat portion, and the downstream helical portion cooperate to define a first side of the downstream baffle that extends at least 180 degrees circumferentially about the central axis and a second side of the downstream baffle that extends 180 degrees or less about the central axis, the first side of the downstream baffle is free of openings, and the second side of the downstream baffle is formed to include a secondary outlet opening that extends axially through the downstream baffle. 20. The mixer of claim 12, wherein the downstream baffle is formed to include at least one secondary outlet opening that extends axially through the downstream baffle and the flat extension plate is formed to include at least one secondary extension opening that extends axially through the flat extension plate. 21. The mixer of claim 12, wherein the side wall is formed to include a doser aperture, the mixer further includes a manifold aligned with the doser aperture, the manifold is arranged to direct fluid into the internal region along a doser axis during use of the mixer, and the doser axis is spaced apart circumferentially from the primary outlet opening of the downstream baffle by about 60 degrees.