US20120124983A1

US20120124983A1 - Exhaust system having reductant nozzle flow diverter

Info

Publication number: US20120124983A1
Application number: US12/952,831
Authority: US
Inventors: Haiping Hong
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2010-11-23
Filing date: 2010-11-23
Publication date: 2012-05-24

Abstract

An exhaust system for use with an engine is disclosed. The exhaust system may have an exhaust passage with an indentation having an upstream wall and a downstream wall. The exhaust system may also have a nozzle disposed within the downstream wall, and a flow diverter cantilevered from the upstream wall partway into the exhaust passage.

Description

TECHNICAL FIELD

The present disclosure is directed to an exhaust system and, more particularly, to an exhaust system having a reductant nozzle flow diverter.

BACKGROUND

Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants are composed of gaseous compounds including, among other things, the oxides of nitrogen (NO_X). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NO_Xemitted to the atmosphere by an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
In order to comply with the regulation of NO_X, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR). SCR is a process where a reductant, most commonly urea ((NH₂)₂CO) or a water/urea solution, is selectively injected into the exhaust gas stream of an engine and adsorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH₃), which reacts with NO_Xin the exhaust gas to form water (H₂O) and diatomic nitrogen (N₂).
Although reductant injections can successfully reduce NO_X, the reductant can also be problematic when utilized under certain conditions. For example, solid urea and urea-byproducts such as cyanuric acid, biuret, melamine, etc., can be deposited near an injection site when exhaust temperatures and velocities are too low. Formation of near-injector deposits can be an irreversible process, causing blockage of the injector and/or restriction on exhaust flow, which can lead to degradation of the NO_Xconversion process and engine operation.
An exemplary SCR-equipped system for use with a combustion engine is disclosed in US Patent Publication No. 20100107614 of Levin et al. published on May 6, 2010 (the '614 publication). This system includes an injector boss disposed within an exhaust passage at a pipe bend. The injector boss forms a recess in a wall of the passage for mounting an injector that sprays reductant into exhaust gas upstream of a catalytic converter. A gas deflector is positioned upstream of the injector and configured to create a high-pressure zone upstream of the deflector and a low-pressure zone downstream of the deflector surrounding an outlet of the injector. The system also includes a bypass flow passage configured to divert a portion of an exhaust flow from the high-pressure zone, and a collector having openings for allowing the bypassed portion of exhaust to flow into the exhaust gas stream and form a gas shield for the liquid reductant spray.

SUMMARY

One aspect of the present disclosure is directed to an exhaust system. The exhaust system may include an exhaust passage having an indentation with an upstream wall and a downstream wall. The exhaust system may also include a nozzle disposed within the downstream wall, and a flow diverter cantilevered from the upstream wall partway into the exhaust passage.
A second aspect of the present disclosure is directed to another exhaust system. This exhaust system may include an exhaust passage configured to receive exhaust from an engine and having a bend portion with an indentation. The exhaust system may also include a flow diverter located in the bend portion and configured to generate a vortex in the exhaust at the indentation.
A third aspect of the present disclosure is directed to yet another exhaust system. This exhaust system may include an exhaust passage configured to receive exhaust from an engine, and an aftertreatment device located within the exhaust passage. The exhaust system may also include a reductant nozzle located upstream of the aftertreatment device and having a tip mounted generally flush with an interior wall of the exhaust passage. The exhaust system may additionally include a flow diverter located upstream of the reductant nozzle and configured to increase a speed of exhaust impinging upon the tip of the reductant nozzle.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a pictorial illustration of an exemplary disclosed exhaust system;

FIG. 2 is a pictorial illustration of a nozzle assembly that may be used in conjunction with the exhaust system of FIG. 1;

FIG. 3 is a cross-sectional illustration of the nozzle assembly of FIG. 2;

FIG. 4 is a pictorial illustration of flow diverter that may be used with the nozzle assembly of FIGS. 2 and 3; and

FIG. 5 is a diagrammatic illustration of exhaust flows at a cross-sectional plane near the nozzle assembly of FIG. 2.

DETAILED DESCRIPTION

An exemplary exhaust system 10 is shown in FIG. 1. Exhaust system 10 may be associated with an engine (not shown), for example an internal combustion engine, and include components that cooperate to control the emission of pollutants by the engine to the atmosphere. Exhaust system 10 may include, among other things, a first treatment canister 12, a second treatment canister 14, and an exhaust passage 16 connecting first and second treatment canisters 12, 14. First treatment canister 12 may be configured to receive exhaust from the engine and implement a first treatment procedure. Second treatment canister 14 may be configured to receive exhaust from first treatment canister 12 via exhaust passage 16 and implement a second treatment procedure.
Each of first and second treatment canisters 12, 14 may include an inlet 18, an outlet 20, and at least one treatment device 22 located between inlet 18 and outlet 20. In the embodiment shown in FIG. 1, first and second treatment canisters 12 and 14 may be about the same length and each include a single inlet 18 and a single outlet 20. It is contemplated, however, that first and second treatment canisters 12, 14 may have different lengths and include any number of inlets 18 and outlets 20, as desired. The treatment devices 22 included within first and second treatment canisters 12, 14 may include, for example, oxidation catalysts, particulate filters, selective catalytic reduction (SCR) substrates, ammonia reduction catalysts, and other devices known in the art.
In one embodiment, exhaust passage 16 may be generally axially-parallel with first and second treatment canisters 12, 14 and connected at opposing ends to an outer cylindrical surface 24, for example to an end cap, of each canister 12, 14 by way of first and second bend portions 26, 28, respectively. First and second bend portions 26, 28, in this embodiment, may be cobra-head type couplings that are capable of bending through an angle of about 90 degrees. First and second bend portions 26, 28 may have generally elliptical openings at cylindrical surfaces 24 and generally circular openings at a central straight portion 30 that extends between first and second bend portions 26, 28. It is contemplated that first and second bend portions 26, 28 may be integral with straight portion 30 or separate components that are joined to straight portion 30, as desired. It is also contemplated that first and second bend portions 26, 28 may embody couplings other than cobra-head types, if desired.
In the disclosed embodiment, first bend portion 26 may be located upstream of second bend portion 28 and configured to receive a nozzle 32. Nozzle 32 may be located at or near an upstream end of straight portion 30 and configured to inject a reductant into the exhaust flowing through exhaust passage 16 and into second treatment canister 14 via second bend portion 28. A gaseous or liquid reductant, most commonly a water/urea solution, ammonia gas, liquefied anhydrous ammonia, ammonium carbonate, an ammine salt solution, or a hydrocarbon such as diesel fuel, may be sprayed or otherwise advanced by nozzle 32 into the exhaust passing through straight portion 30. Straight portion 30 may have a length sufficient to allow the injected reductant time to mix with exhaust and to decompose before entering second treatment canister 14. The length of exhaust passage 16 (i.e., of straight and second bend portions 30, 28) may be based on a flow rate of exhaust passing through exhaust system 10 and/or on a cross-sectional area of straight portion 30. In the example depicted in FIG. 1, the length of straight portion 30 may be about 450 mm, and extend a majority of a length of treatment canisters 12. This length, as will be described in more detail below, may facilitate mixing of exhaust and reductant.
As shown in FIG. 1, nozzle 32 may be located within an indentation 34 of first bend portion 26. Nozzle 32, when located within indentation 34, may have a central axis 36 in general alignment with straight portion 30 such that injections of reductant may flow directly into straight portion 30 in a central flow direction of passing exhaust. Indentation 34 may be a generally cylindrical intrusion into exhaust passage 16 and thereby form an external recess or pocket within the normal confines of first bend portion 26 to receive nozzle 32. Indentation 34 may have an upstream wall 38 that generally faces first treatment canister 12, and a downstream wall 40 oriented about 90° from upstream wall 38 to face straight portion 30. As shown in FIG. 2, upstream and downstream walls 38, 40 may be connected on sides thereof by side walls 42. A tip 44 of nozzle 32 may be open to exhaust passing through first bend portion 26 and generally flush with downstream wall 40.
As shown in FIG. 3, the intrusion of indentation 34 into first bend portion 26 may result in a narrowed flow area 46 at first bend portion 26. Narrowed flow area 46 created by indentation 34 at first bend portion 26 may cause a restriction and corresponding pressure and velocity increase in exhaust passing through first bend portion 26 near an intersection of upstream and downstream walls 38, 40. A flow diverter 48 may be placed at this location to further increase pressures and flow velocities in critical areas of first bend portion 26 near nozzle tip 44 (e.g., in areas above upstream wall 38 and flow diverter 48). In the disclosed embodiment, flow diverter 48 may be generally aligned in a length direction with a plane of symmetry 50 of indentation 34 and cantilevered from upstream wall 38 a distance (i.e., only partway) into narrowed flow area 46 of first bend portion 26.
Flow diverter 48 may embody a generally curved protrusion fixedly connected to upstream wall 38 by, for example, welding. Alternatively, flow diverter 48 may be an integral portion of upstream wall 38, if desired. As shown in FIG. 3, flow diverter 48 may be tilted up away from or down toward upstream wall 38 by an angle (δ) in the range of about 0-30°. By adjusting δ, an exhaust flow proximity relative to downstream wall 40 may be varied and it has been found that, by keeping angle δ within the disclosed range, an exhaust flow having desired pressures and velocities may be directed within a desired distance of nozzle tip 44. A thickness (t) of flow diverter 48 may be in the range of about 1-2 mm. By maintaining the thickness of flow diverter 48 within its disclosed range, it may be ensured that flow diverter 48 may be sufficiently rigid to withstand a maximum force of exhaust flows possible through exhaust system 10. As shown in FIG. 4, flow diverter 48 may have a width (W_D) and a length (L) that are functions of a width (W_I) of indentation 34. For example, W_Dmay be in the range of about 0.2 to 0.8 times W_I(W_D=(0.2 to 0.8)×W_I), and L may be in the range of about 0.2 to 1.5 times W_I(L=(0.2 to 1.5)×W_I). These dimensional relationships may provide a desired swirling flow pattern at downstream wall 40, as will be described in more detail below. Flow diverter 48 may taper from a wider base end 52 to a narrower tip end 54 by an angle (ω) in the range of about 0-20°. The taper of flow diverter 48 may provide for enhanced rigidity (i.e., reduced drag at tip end 54) while still providing the desired flow pattern at downstream wall 40. Flow diverter 48 may be curved along its length (i.e., have an axis of curvature generally parallel with a length direction) and have a contour at base end 52 that generally matches a contour of upstream wall 38. This contour of flow diverter 48 may provide for enhanced adhesion to upstream wall 38 and rigidity along its length. The rigidity of flow diverter 48 may extend the life of flow diverter 48 and improve exhaust flow consistency through narrowed flow area 46. In addition, matching the contours of flow diverter 48 with upstream wall 38 may be desirable for a smooth transition of exhaust flow along upstream wall 38 and an upper surface of flow diverter 48.
As shown in FIG. 5, the location and geometry of flow diverter 48 may generate a strong double vortex 56 in the exhaust flow at or near downstream wall 40 causing exhaust to impinge upon nozzle tip 44. Specifically, as exhaust from first treatment canister 12 enters first bend portion 26 and nears narrowed flow area 46, a velocity of the exhaust may increase. When the exhaust at narrowed flow area 46 nears and is obstructed by flow diverter 48, an area of high pressure may be generated at an upstream concave side of flow diverter 48 while an area of low pressure may be generated at a downstream convex side of flow diverter 48. The high pressure area may function to push or shed the exhaust off the sides of flow diverter 48 and downward toward a base of downstream wall 40. Another area of high pressure may then be generated at the base of downstream wall 40 that, together with the low pressure area at the downstream side of flow diverter 48, may cause the exhaust to reverse direction and flow upward directly past tip 44 of nozzle 32. Accordingly, double vortex 56 (or a vortex pair) may be generated and visible, with multiple areas 58 of high exhaust velocity at downstream wall 40 near the outer walls of first bend portion 26 and toward a center of first bend portion 26 along symmetry plane 50. In one embodiment, the exhaust flows near tip 44 may increase by about 100% as a result of placing flow diverter 48 as disclosed. Simultaneously, two substantially identical pockets 60 of low pressure and velocity exhaust may be observed between areas 58. Areas 58 and pockets 60 may be located within a common plane that is generally parallel with downstream wall 40 (i.e., in a plane generally perpendicular to exhaust flow through straight portion 30 of exhaust passage 16). It has been shown that the increased near-nozzle velocity due to double vortex 56 can reduce deposits at tip 44 by about 50% to 95%
Double vortex 56 may continue in the length direction of straight portion 30. Specifically, as can be seen in FIG. 3, circulating flows of high velocity exhaust may be observed at locations along straight portion 30 and downstream of first bend portion 26. The distance that the circulating flows extend along straight portion 30 may vary and depend at least partially on a flow rate of exhaust within exhaust system 10 and geometry of flow diverter 48 and indentation 34. In the disclosed embodiment, double vortex 56 may be observed at a distance from nozzle tip 44 of about 200 mm, or about one-half the total length of straight portion 30.
In addition to the increased velocities at nozzle tip 44 helping to reduce or even eliminate deposit buildup of liquid reductant near nozzle tip 44, the extension of double vortex 56 along the length of straight portion 30 may also enhance mixing of exhaust and reductant within exhaust passage 16. In addition, transient vortex shedding created by double vortex 56 (i.e., the swirling motion along passage 16) may cause reductant injections at nozzle tip 44 to oscillate vertically (up and down) along plane 50 (referring to FIG. 5), thereby generating a mixing action of reductant within the swirling exhaust. In the disclosed embodiment when an exhaust flow through straight portion 30 varies from about 220-2200 kg/hr, the spray of reductant from nozzle tip 44 may oscillate through a range of about 20-90° and at a frequency of about 50-500 Hz. Based on an injection distance along straight portion 30, the oscillating spray, when it exceeds about 50° relative to plane 50, may swing across an entire diameter of straight portion 30.

INDUSTRIAL APPLICABILITY

The exhaust system of the present disclosure may be applicable to any engine configuration requiring injections of fluid as part of an exhaust treatment process, where depositing and/or mixing of the fluid is an important issue. The disclosed exhaust system may help to reduce or eliminate buildup of the deposits and enhance mixing by generating a double vortex within an exhaust flow at a location of the fluid injection. Operation of exhaust system 10 will now be described.
Referring to FIG. 1, exhaust containing a complex mixture of air pollutants may be directed from an engine (not shown) into first treatment canister 12 via inlet 18. The exhaust may flow from inlet 18 through treatment device 22, where the exhaust may undergo one or more treatment processes. The treatment processes performed within first treatment canister 12 may include, among other things, a conversion process of NO to NO₂and/or a particulate removal process. After undergoing the treatment processes within first treatment canister 12, the exhaust may exit first treatment canister 12 via outlet 20, and enter first bend portion 26 of exhaust passage 16.
As the exhaust flows into first bend portion 26, the exhaust may approach narrowed flow area 46 and, because of the associated restriction, increase in pressure and velocity. A center portion of this flow may then be obstructed by flow diverter 48 and caused to divert from its original flow path toward the sides of flow diverter 48. This diversion may initiate the swirling motion of double vortex 56 at downstream wall 40. The motion of double vortex 56 may cause high-velocity exhaust to flow past and impinge upon tip 44 of nozzle 32, thereby removing existing and inhibiting future deposits of injected fluid. The swirling exhaust may then continue through first bend portion 26 and into straight portion 30, wherein the swirling motion may generate oscillations in a spray pattern of nozzle 32 and facilitate blending of reductant sprayed by nozzle 32 with exhaust.
The exhaust flow from straight portion 30, now entrained with fluid from nozzle 32, may enter second treatment canister 14 via second bend portion 28 and inlet 18. Within treatment device 22 of second treatment canister 14, the exhaust, in the presence of the injected fluid, may undergo additional treatment processes. In one example the additional treatment processes may include, among other things, a reduction process where NO_xin the exhaust flow is reduced to innocuous substances. The exhaust may exit second treatment canister 14 via outlet 20.
It will be apparent to those skilled in the art that various modifications and variations can be made to the exhaust system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the exhaust system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalent.

Claims

1. An exhaust system, comprising:

an exhaust passage having an indentation with an upstream wall and a downstream wall;

a nozzle disposed within the downstream wall; and

a flow diverter cantilevered from the upstream wall partway into the exhaust passage.

2. The exhaust system of claim 1, wherein the flow diverter is tilted relative to the upstream wall by an angle less than about 30 degrees.

3. The exhaust system of claim 1, wherein the flow diverter tapers in width from a base end to a tip end at an angle less than about 20 degrees.

4. The exhaust system of claim 1, wherein a cantilevered length of the flow diverter is about 0.2 to 1.5 times a width of the flow diverter.

5. The exhaust system of claim 1, wherein a width of the flow diverter is about 0.2 to 0.8 times a width of the indentation.

6. The exhaust system of claim 1, wherein a thickness of the flow diverter is about 1 to 2 mM.

7. The exhaust system of claim 1, wherein the flow diverter is curved and has an axis of curvature parallel with a length direction.

8. The exhaust system of claim 1, wherein the indentation is located within a bend portion of the exhaust passage.

9. The exhaust system of claim 8, wherein the indentation restricts exhaust flow through the bend portion.

10. The exhaust system of claim 1, wherein the flow diverter increases near-nozzle exhaust velocities and swirling in a plane generally parallel with the downstream wall.

11. The exhaust system of claim 10, wherein the flow diverter increases near-nozzle exhaust velocities by about 100%.

12. The exhaust system of claim 10, wherein the increased velocities continue in a length direction of the exhaust passage.

13. The exhaust system of claim 12, wherein the increased velocities continue for about ½ of a length of the exhaust passage.

14. The exhaust system of claim 1, wherein the flow diverter causes injections from the nozzle to oscillate relative to a plane of symmetry through the flow diverter.

15. The exhaust system of claim 14, wherein the flow diverter causes the injections to oscillate through a range of about 20-90°.

16. The exhaust system of claim 14, wherein the flow diverter causes the injections to oscillate across an entire diameter of the exhaust passage.

17. The exhaust system of claim 1, wherein the flow diverter reduces reductant deposits at the nozzle by about 50-95%.

18. An exhaust system, comprising:

an exhaust passage configured to receive exhaust from an engine and having a bend portion with an indentation; and

a flow diverter located in the bend portion and configured to generate a vortex in the exhaust at the indentation.

19. The exhaust system of claim 18, wherein the flow diverter tapers in width from a base end to a tip end at an angle less than about 20 degrees.

20. The exhaust system of claim 18, wherein a length of the flow diverter is about 0.2 to 1.5 times a width of the flow diverter.

21. The exhaust system of claim 18, wherein the flow diverter is curved and has an axis of curvature parallel with a length direction.

22. The exhaust system of claim 18, wherein the flow diverter extends from the indentation partway through the exhaust passage.

23. The exhaust system of claim 18, wherein the vortex is located within a plane generally perpendicular to a flow direction through the bend portion.

24. The exhaust system of claim 23, wherein the vortex increases near-nozzle exhaust velocities by about 100%.

25. The exhaust system of claim 23, wherein the vortex continues in a length direction of the exhaust passage.

26. The exhaust system of claim 25, wherein the vortex continues for about ½ of a length of the exhaust passage.

27. An exhaust system, comprising:

an exhaust passage configured to receive exhaust from an engine;

a treatment device located within the exhaust passage;

a reductant nozzle located upstream of the aftertreatment device and having a tip mounted generally flush with an interior wall of the exhaust passage; and

a flow diverter located upstream of the reductant nozzle and configured to increase a speed of exhaust impinging upon the tip of the reductant nozzle.