US20110099974A1

US20110099974A1 - Reductant spray injector boss

Info

Publication number: US20110099974A1
Application number: US12/611,214
Authority: US
Inventors: Gregory A. Griffin
Original assignee: International Engine Intellectual Property Co LLC
Current assignee: International Engine Intellectual Property Co LLC
Priority date: 2009-11-03
Filing date: 2009-11-03
Publication date: 2011-05-05

Abstract

A mounting boss (36) for mounting a spray injector (16) on an exhaust pipe (32) of a vehicle exhaust system (12) includes a first wall (38) and a second wall (44). The first wall (38) extends at an obtuse angle to an outer surface (40) of the exhaust pipe (32) and defines a first interior surface (42). The second wall (44) extends at an obtuse angle with the outer surface (40) of the exhaust pipe (32) and defines a second interior surface (46). The first interior surface (42) and the second interior surface (46) define a recirculation area (48) that is in fluid communication with the exhaust pipe (32). The recirculation area (48) has a decreasing cross-sectional area in the direction of the flow of exhaust gas in the exhaust pipe (12). An aperture (50) is disposes in the first wall (38) for receiving the spray injector (16).

Description

BACKGROUND

Embodiments described herein relate generally to exhaust after treatment systems. More particularly, embodiments described herein relate to a reductant spray injector mount for an exhaust after treatment system.
Typically, exhaust after treatment systems are used to reduce oxides of Nitrogen (NOx) from engines. SCR systems are a type of exhaust after treatment system that relies on injection of a reductant solution into the exhaust line of a vehicle upstream of an SCR catalyst. In the SCR catalyst, the reductant is decomposed, and the catalyst emits various gases and liquids depending on the reductant, however NOx is not emitted.
The reductant is introduced into the SCR system at a spray injector. Formation of solid reductant deposits can occur downstream of the spray injector due to the accumulation of liquid wall film at particular regions in the SCR system, particularly at the location where the spray impinges on the exhaust pipe wall. As the wall film is in contact with the exhaust pipe walls, which are colder than the exhaust gases and typically below 130-degrees C., the water evaporates out of the wall film and forms solid reductant deposits.
At higher exhaust gas flow rates, liquid wall film and solid deposits can build-up in and around the mounting device for the spray injector. The primary location of deposit formation is at the injector mounting region, including the injector tip. The spray droplets are captured in these regions because there is exhaust flow separation and recirculation at these regions. The exhaust flow separation and recirculation occurs due to the geometrical change in the exhaust flow pipe to mount the injector and to introduce the reductant spray.
Since the solid reductant deposits can result in failure of the after treatment system, the deposits need to be removed. The deposits are typically manually cleaned out of the after treatment system.

SUMMARY OF THE INVENTION

A mounting boss for mounting a spray injector on an exhaust pipe of a vehicle exhaust system includes a first wall and a second wall. The first wall extends at an obtuse angle to an outer surface of the exhaust pipe and defines a first interior surface. The second wall extends at an obtuse angle with the outer surface of the exhaust pipe and defines a second interior surface. The first interior surface and the second interior surface define a recirculation area that is in fluid communication with the exhaust pipe. The recirculation area has a decreasing cross-sectional area in the direction of the flow of exhaust gas in the exhaust pipe. An aperture is disposed in the first wall for receiving the spray injector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an engine having an exhaust after treatment system with a reductant spray injector.

FIG. 2 is a perspective view of an exhaust pipe having a spray injector boss.

FIG. 3 is a section view of the exhaust pipe having the spray injector boss.

DETAILED DESCRIPTION

Referring FIG. 1, a schematic diagram of an engine 10 having an exhaust system, generally shown at 12, includes an exhaust gas passageway 14 for emitting the exhaust gases from the engine 10. A spray injector 16 is in fluid communication with the exhaust gas passageway 14 for spraying reductant into the exhaust system 12.
The exhaust gas passageway 14 is formed with an exhaust inlet pipe 18, having an inlet 20 connected to an exhaust outlet 22 of the engine 10, and an exhaust outlet pipe 24, having an outlet 26 for venting the exhaust gases to the atmosphere. In the direction of flow of the exhaust gases on the exhaust gas passageway 14, the exhaust system 12 has an after treatment system 28, including a diesel oxidation catalyst/diesel particulate filter (DOC/DPF) 30 upstream of an SCR catalyst 31. The spray injector 16 is located downstream of the DOC/DPF 30 and upstream of the SCR catalyst 31 on an exhaust pipe 32 of the exhaust gas passageway 14.
The exhaust pipe 32 has an inside pipe wall 34 and typically has a diameter of about 75 to 100 mm, although other diameters are possible. The exhaust gas flows through the injector portion 32 at varying flow rates, typically ranging from about 0.02 kg/s to 0.5 kg/s, however other flow rates are possible.
Referring now to FIG. 2 and FIG. 3, the spray injector 16 is designed in accordance with the following considerations from prior art spray injectors. At lower exhaust gas flow rates, much of the reductant sprayed from prior art spray injectors impinge on the pipe wall 34 opposite the injection location. Since the spray velocity is higher than the low exhaust gas flow velocity, the spray penetrates further into the exhaust flow and impinges on the pipe wall 34 opposite of the spray injector. At lower exhaust gas rates, the wall temperatures are generally below 300-degrees C. in the spray impingement area, which results in wall film growth and solid deposit formation after long durations of operation. However, at lower exhaust gas flow rates, there is little to no droplet capture in the recirculation area, i.e. the enlarged portion of the pipe where the spray injector is mounted and the spray is introduced into the pipe.
At higher exhaust gas flow rates, there is little to no spray impingement on the pipe wall 34 due to the higher exhaust gas velocity because the exhaust gas carries the spray downstream with the exhaust gas. The high flow rate and the high exhaust gas temperature maintains the wall temperatures at greater than 300-degrees C., which reduces the likelihood of any spray impingement on the pipe wall 34 forming solid deposits. However, one area that the exhaust gas does not maintain a high wall temperature is at the recirculation area, where there are low local flow velocities. Due to the relatively lower wall temperature and the low local flow velocities, formation of solid deposits is likely at the recirculation area. Thus, at the higher exhaust gas flow rates, there is significant capture of droplets in the recirculation area, resulting in wall film formation at the recirculation area that could potentially plug up the injector and prevent the introduction of spray into the exhaust pipe.
To address these issues, the spray injector 16 is mounted at a mounting boss 36 in sealed fluid communication with the exhaust gas passageway 14. The mounting boss 36 has a first wall 38 that is at an obtuse angle to an outer surface 40 of the exhaust pipe 32. The obtuse angle is generally about 120 to 140-degrees, and advantageously about 130-degrees from the surface of the exhaust pipe 32, however other angles are possible. The first wall 38 defines a first interior surface 42.
A second wall 44 of the mounting boss 36 is generally convex and elongate, also forming an obtuse angle with the outer surface 40 of the exhaust pipe 32, the angle generally being about 155 to 175-degrees, and advantageously about 165-degrees, however other angles are possible. The second wall 44 defines a second interior surface 46 having a generally concave shape. Together, the first interior surface 42 and the second interior surface 46 of the mounting boss 36 define a recirculation area 48 of decreasing cross-sectional internal area in the direction from the first wall 38 to the opposite end, or in the direction of the flow of exhaust gas in the exhaust pipe 32. The recirculation area 48 is in fluid communication with the exhaust pipe 32 and permits the introduction of reductant spray into the exhaust gas without mounting the injector directly into the exhaust pipe.
The spray injector 16 introduces the reductant spray into the recirculation area 48 through an aperture 50 disposed generally centrally in the first wall 38. A lip 52 of the mounting boss 36 may extend from the first wall and provide a flat surface 54 for mounting of the spray injector 16. The spray injector 16 is mounted at the first wall 38 and configured to direct the spray through the aperture 50, which has an axis A that is generally 30 to 50-degrees, and advantageously at about a 40-degree angle with respect to an axis B of the exhaust pipe 32, however other angles are possible.
The nozzle of the spray injector is either introduced through the aperture 50 or is in sealed engagement with the aperture. Although other configurations are possible, the mounting boss 36 length to height ratio is about 7:1, where the length L is measured from the center of the aperture 50 to the junction of the second wall 44 with the outer surface 40 of the pipe, and where the height H is measured from the outer surface of the pipe to the aperture 50. The mounting boss 36 also has an injection angle of about 40-degrees with respect to the axis B of the exhaust pipe 32. Further, length to height mounting boss 36 ratios of about 4.4:1 and less generally result in reductant solids accumulation.
Since the temperature of the first interior surface 42 and the second interior surface 46 of the mounting boss 36 is lower than the pipe wall temperature due to the separation and recirculation of exhaust gas that occurs at the recirculation area 48, the mounting boss is more likely to develop wall film. At high exhaust gas flow rates, the elongate mounting boss 36 shape, and in particular the length of the second wall 44, in combination with the angle of the injector 16, enough clearance is provided for the reductant spray such that less wall film is accumulated on the first interior 42 surface, the second interior surface 46 and at the injector tip. Additionally, at low flow rates, the injector 16 is mounted at the first wall 38 at an angle such that the spray has a longer path and a longer residence time through the exhaust gas flow before it impinges on the pipe wall 34, and the exhaust gas has more time to react with the spray before it impinges on the pipe wall.
With the mounting boss 36, the location of the injector 16 and the geometry of the after treatment system 28 upstream of the injector is not changed. Maintaining the current location and geometry allows the easy incorporation of the mounting boss 36 into existing after treatment systems 28 and does not require changing the chassis packaging space. It is possible that the mounting boss 36 can be attached to the exhaust pipe 32 with a weld or with bolts or other fasteners, among other methods of attachment. In the case of a welded or fastened connection, the mounting boss 36 is generally cast or machined. In another embodiment, the mounting boss 36 and the exhaust pipe 32 have an integral construction, for example two stamped sheet metal halves that are joined at a seam.
The mounting boss 36 is made of any metallic material that is resistant to the corrosive nature of the reductant and the after treatment system 28. The mounting boss 36 is made of 300 or 400-series stainless steels that are resistant to the corrosive after treatment system 28, however other materials are possible.

Claims

1. A mounting boss for mounting a spray injector on an exhaust pipe of a vehicle exhaust system, comprising:

a first wall that extends at an obtuse angle to an outer surface of the exhaust pipe, the first wall defining a first interior surface;

a second wall that extends at an obtuse angle with the outer surface of the exhaust pipe, the second wall defining a second interior surface, wherein the first interior surface and the second interior surface define a recirculation area in fluid communication with the exhaust pipe, the recirculation area having a decreasing cross-sectional area in the direction of the flow of exhaust gas in the exhaust pipe; and

an aperture disposed in the first wall for receiving the spray injector.

2. The mounting boss of claim 1 wherein the obtuse angle of the first wall is about 120 to 140-degrees from the outer surface of the exhaust pipe.

3. The mounting boss of claim 1 wherein the obtuse angle of the second wall is about 155 to 175-degrees from the outer surface of the exhaust pipe.

4. The mounting boss of claim 1 wherein the second interior surface has a generally concave shape.

5. The mounting boss of claim 1 wherein the aperture has an axis that is about 30 to 50-degrees from an axis of the exhaust pipe.

6. The mounting boss of claim 1 further comprising a lip extending from the first wall and having a flat surface.

7. The mounting boss of claim 1 wherein the mounting boss has a length to height ratio of about 7:1, wherein the length is measured from a center of the aperture to a junction of the second wall with a surface of the exhaust pipe, and wherein the height is measured from the surface of the pipe to the center of the aperture.

8. A mounting boss for mounting a spray injector on an exhaust pipe of a vehicle exhaust system, the exhaust pipe having a pipe axis, the mounting boss comprising:

a first wall defining an aperture for receiving a spray injector, the aperture having an axis that is about 30 to 50-degrees from the pipe axis;

a second wall extending from the first wall to an outer surface of the exhaust pipe, the second wall defining a second interior surface having a generally concave shape, and

a recirculation area defined by the first interior surface and the second interior surface and in fluid communication with the exhaust pipe.

9. The mounting boss of claim 8 wherein the axis of the aperture is about 40-degrees from the pipe axis.

10. The mounting boss of claim 8 wherein the first wall is about 130-degrees from the outer surface of the exhaust pipe.

11. The mounting boss of claim 8 further comprising a lip extending from the first wall and having a flat surface.

12. The mounting boss of claim 8 wherein the recirculation area has a decreasing cross-sectional area in the direction of the flow of exhaust gas in the exhaust pipe.

13. The mounting boss of claim 8 wherein the mounting boss has a length to height ratio of about 7:1, wherein the length is measured from a center of the aperture to a junction of the second wall with a surface of the exhaust pipe, and wherein the height is measured from the surface of the pipe to the center of the aperture.

14. A method of spraying reductant into an exhaust gas passageway formed by at least one exhaust pipe for emitting exhaust gases from an engine to the ambient, the method comprising:

positioning a reductant spray injector in fluid communication with the exhaust gas passageway for spraying reductant into the exhaust gas passageway;

locating a mounting boss in fluid communication with the exhaust pipe, the mounting boss comprising a first wall extending at an obtuse angle to an outer surface of the exhaust pipe, a second wall extending at an obtuse angle with the outer surface of the exhaust pipe, and an aperture disposed in the first wall for receiving the reductant spray injector; and

spraying the reductant from the reductant spray injector into the exhaust pipe at an angle of about 30 to 50-degrees with respect to an axis of the exhaust pipe.

15. The method of claim 14 further comprising forming a recirculation area within the mounting boss and in fluid communication with the exhaust pipe.

16. The method of claim 14 further comprising integrally forming the mounting boss with the exhaust pipe.

17. The method of claim 14 wherein the obtuse angle of the first wall is about 120 to 140-degrees from the outer surface of the exhaust pipe.

18. The method of claim 14 wherein the obtuse angle of the second wall is about 155 to 175-degrees from the outer surface of the exhaust pipe.

19. The method of claim 14 further comprising introducing the spray injector into an aperture in the first wall of the mounting boss.

20. The method of claim 19 wherein the mounting boss has a length to height ratio of about 7:1, wherein the length is measured from a center of the aperture to a junction of the second wall with a surface of the exhaust pipe, and wherein the height is measured from the surface of the pipe to the center of the aperture.