Mixing device for mixing a spray from an injector into a gas and system comprising same

1. A mixing device for mixing a spray from an injector into a gas flowing through a substantially tubular chamber from an upstream side to a downstream side, said mixing device comprising:

a partially open wall on a side upstream of said spray; and

a closed wall on a side downstream of said spray;

said closed wall and said partially open wall together forming a surface closed onto itself defining a mixing cavity, wherein the closed wall is an integral part of a larger piece that also presents a baffle portion on either side of the mixing cavity, said mixing cavity comprising:

a spray inlet opening for receiving a conical spray from said injector; and

an outlet opening in a plane intersecting an axis of said injector,

and a skirt portion arranged directly upstream of a space below the outlet opening; and a downstream side of said mixing device being shaped so as to define a helicoidal groove for circumferentially guiding said gas from said outlet opening in a downstream direction.

2. The mixing device according to claim 1 , wherein said partially open wall is permeable to gas.

3. The mixing device according to claim 1 , wherein said partially open wall comprises a wall with perforations.

4. The mixing device according to claim 3 , wherein at least some of said perforations are provided with louvers.

5. The mixing device according to claim 1 , wherein said partially open wall at least partially follows a conical surface parallel with the outer boundary of said spray.

6. The mixing device according to claim 1 , wherein said outlet opening is perpendicular to an injection axis of said injector.

7. The mixing device according to claim 1 , further comprising a spray disperser arranged at said outlet opening.

8. The mixing device according to claim 7 , wherein said spray disperser is a mesh.

9. The mixing device according to claim 1 , wherein said closed wall bends or tapers towards the upstream side in a direction approaching said spray inlet opening.

10. The mixing device according to claim 1 , wherein said mixing cavity is shaped as a cylindrical or frustoconical pipe with perforations in at least the partially open wall or as a cylindrically or frustoconically shaped mesh surface.

11. The mixing device according to claim 1 , wherein the partially open wall and the closed wall are two separately formed pieces, distinct from any wall of the substantially tubular chamber and joined together so as to form the surface closed onto itself defining the mixing cavity.

12. A system for treating exhaust gas, the system comprising:

a substantially tubular chamber receiving a flow of exhaust gas to be treated;

a mixing device for mixing a spray from an injector into a gas flowing through a substantially tubular chamber from an upstream side to a downstream side, the mixing device including a partially open wall on a side upstream of said spray and a closed wall on a side downstream of said spray, the partially open wall and the closed wall being two separately formed pieces, distinct from any wall of the substantially tubular chamber and joined together so as to form a surface closed onto itself to define a mixing cavity, the mixing cavity including a spray inlet opening for receiving a conical spray from said injector and an outlet opening intersecting an axis of said injector;

an injector mounting location aligned with the spray inlet opening; and

a swirl plate downstream of the mixing device, the swirl plate having an annular inlet zone;

the mixing device being shaped so as to open up a helicoidal space between the mixing device and the swirl plate, the helicoidal space serving as a flow channel from the outlet opening to the annular inlet zone.

13. The system according to claim 12 , wherein an axis of the injector mounting location does not intersect with a longitudinal axis of the substantially tubular chamber.

14. The system according to claim 12 , wherein the mixing device is arranged so as to substantially block any flows of gas from the upstream side to the downstream side other than flows entering said mixing device through the partially open wall and leaving the mixing device through the outlet opening.

15. The system according to claim 12 , further comprising a swirl baffle downstream of said mixing device, wherein a part of said closed wall that is further removed from a longitudinal axis of said substantially tubular chamber is at a greater distance from the swirl baffle than a part of the closed wall that is closer to the longitudinal axis of the substantially tubular chamber.

16. A system for treating exhaust gas, the system comprising:

a substantially tubular chamber receiving a flow of exhaust gas to be treated;

a mixing device for mixing a spray from an injector into a gas flowing through the substantially tubular chamber from an upstream side to a downstream side, the mixing device including a partially open wall on a side upstream of said spray and a closed wall on a side downstream of said spray, the partially open wall and the closed wall being two separately formed pieces, distinct from any wall of the substantially tubular chamber and joined together so as to form a surface closed onto itself to define a mixing cavity, the mixing cavity including a spray inlet opening for receiving a conical spray from said injector and an outlet opening intersecting an axis of said injector;

a swirl plate downstream of the mixing device, the swirl plate having an annular inlet zone, wherein the mixing device is shaped so as to open up a helicoidal space between said mixing device and the swirl plate, the helicoidal space serving as a flow channel from said outlet opening to the annular inlet zone; and

an injector mounting location aligned with the spray inlet opening.