Exhaust aftertreatment system having mixer assembly

Abstract

A mixer assembly for mixing an injected reductant with an exhaust gas output from a combustion engine comprises a mixer housing including a wall defining an exhaust passageway having a longitudinal axis. A tubular swirling device housing extends along a first axis substantially transverse to the longitudinal axis. The tubular swirling device includes a plurality of openings through which exhaust gas enters. The exhaust gas within the tubular swirling device swirls about the first axis and exits at an outlet end of the tubular swirling device. A mixing plate is positioned immediately downstream of the tubular swirling device. The mixing plate swirls the exhaust about a second axis extending parallel to the longitudinal axis.

Claims

1. A mixer assembly for mixing an injected reductant with an exhaust gas output from a combustion engine, comprising: a tubular housing including a reductant inlet, an exhaust gas inlet and an exhaust gas outlet, the tubular housing defining a longitudinal axis along which the exhaust enters the housing; a diversion plate positioned within the housing downstream of the exhaust gas inlet and the reductant inlet and being intersected by the longitudinal axis, the diversion plate urging a first portion of the exhaust gas in a first transverse direction and a second portion of the exhaust gas in a second and opposite transverse direction, wherein the first and second portions of the exhaust gas are urged toward the reductant inlet; and a mixing plate positioned within the housing immediately downstream of the diversion plate, the mixing plate including a surface shaped to swirl the exhaust gas and the reductant about an axis extending parallel to the longitudinal axis.

2. The mixer assembly of claim 1, further including a shield fixed to the diversion plate to block the exhaust gas from directly flowing toward the injected reductant.

3. The mixer assembly of claim 2, wherein the shield is fixed to an outer wall of the housing.

4. The mixer assembly of claim 1, wherein the mixing plate includes apertures of different size and shape to allow mixed exhaust gas and injected reductant to pass therethrough.

5. The mixer assembly of claim 1, further including an injector mount fixed to an outer wall of the housing and the reductant inlet.

6. The mixer assembly of claim 1, wherein the reductant inlet is positioned on a side of the tubular housing.

7. A mixer assembly for mixing an injected reductant with an exhaust gas output from a combustion engine, comprising: a tubular housing including a reductant inlet, an exhaust gas inlet and an exhaust gas outlet, the tubular housing defining a longitudinal axis along which the exhaust enters the housing; an upstream mixing element including a convex portion positioned between a first recess and a second recess, the recesses being shaped to direct the exhaust gas through apertures extending through the upstream mixing element at positions closer to the reductant inlet than an opposite side of the tubular housing, wherein a downstream face of upstream mixing element at least partially defines a reductant receiving duct that extends transversely across the tubular housing; and a downstream mixing element positioned immediately downstream from the upstream mixing element, the downstream mixing element including an upstream surface at least partially defining the reductant receiving duct, the downstream mixing element including curved surfaces having spaced apart exit ducts supplying mixed exhaust gas and injected reductant to the housing exhaust gas outlet.

8. The mixer assembly of claim 7, wherein the exit ducts are positioned to impart a swirling motion to the exhaust gas.

9. The mixer assembly of claim 7, wherein the downstream mixing element includes apertures of different size, wherein at least one of the apertures is bounded by a louver to change the direction of exhaust gas flow.

Description

DRAWINGS

(1) The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

(2) FIG. 1 is a schematic representation of an engine and exhaust aftertreatment system having a mixer assembly according to the principles of the present disclosure;

(3) FIG. 2 is a cross-sectional view of a portion of the aftertreatment system including the mixer assembly;

(4) FIG. 3 is an end view of the mixer assembly;

(5) FIG. 4 is a perspective view of a mixing bowl of the mixer assembly;

(6) FIG. 5 is a cross-sectional view of a portion of the aftertreatment system including another mixer assembly according to the principles of the present disclosure;

(7) FIG. 6 is an end view of the mixer assembly of FIG. 5;

(8) FIG. 7 is a perspective view of a mixing bowl of the mixer assembly of FIG. 5;

(9) FIG. 8 is a perspective view of another mixing bowl according to the principles of the present disclosure;

(10) FIG. 9 is an end view of the mixing bowl of FIG. 8;

(11) FIG. 10 is an exploded perspective view of an alternate mixer assembly; and

(12) FIG. 11 is a fragmentary perspective view of the mixer depicted in FIG. 10.

(13) Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

(14) Example embodiments will now be described more fully with reference to the accompanying drawings.

(15) Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

(16) The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms a, an, and the may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms comprises, comprising, including, and having, are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

(17) When an element or layer is referred to as being on, engaged to, connected to, or coupled to another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being directly on, directly engaged to, directly connected to, or directly coupled to another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., between versus directly between, adjacent versus directly adjacent, etc.). As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

(18) Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as first, second, and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

(19) Spatially relative terms, such as inner, outer, beneath, below, lower, above, upper, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as below or beneath other elements or features would then be oriented above the other elements or features. Thus, the example term below can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

(20) With reference to FIG. 1, an exhaust aftertreatment system 10 is provided that may treat exhaust gas output by a combustion engine 12. The exhaust aftertreatment system 10 may include an exhaust gas passageway 14, an oxidation catalyst (e.g., a diesel oxidation catalyst or DOC) 16, a filter (e.g., a diesel particulate filter (DPF)) 18, a mixer assembly 20 and a selective catalytic reduction (SCR) catalyst 22. The DOC 16, filter 18, mixer assembly 20 and SCR catalyst 22 are disposed within the exhaust gas passageway 14 such that some or all of the that exhaust gas output from engine 12 flows therethrough.

(21) A hydrocarbon (HC) injector 24 may be disposed at least partially within the exhaust gas passageway 14 upstream of the DOC 16. The HC injector 24 may receive hydrocarbon fuel from a fuel source 26 and may inject into the fuel into the stream of exhaust gas upstream of the DOC 16. A burner (not shown) may be disposed at least partially within the exhaust gas passageway 14 upstream of the DOC 16 at or adjacent the HC injector 24. The burner may ignite the fuel injected by the HC injector 24 to regenerate the DOC 16 and/or the filter 18.

(22) A reductant injector 28 may be disposed adjacent to or partially within the mixer assembly 20 upstream of the SCR catalyst 22. The reductant injector 28 may receive a reductant (e.g., urea) from a reductant tank 30 and inject the reductant into an exhaust stream in the mixer assembly 20. As will be described in more detail below, reductant may mix with exhaust gas within the mixer assembly 20 prior to flowing through the SCR catalyst 22.

(23) Referring now to FIGS. 2-4, the mixer assembly 20 may include a mixer housing or pipe 32, an injector housing 34, a mixing bowl 36, a first mixing plate 38 and a second mixing plate 40. The mixer housing 32 can be generally cylindrical and may be directly or indirectly connected to a housing 42 of the SCR catalyst 22. The mixer housing 32 may include an injector opening 44 through which the injector housing 34 and/or the reductant injector 28 may extend.

(24) The injector housing 34 may be an annular member including a flange 46, a generally cylindrical portion 48, and a generally frustoconical portion 50. As shown in FIG. 2, a cap 52 may engage a first end 54 of the cylindrical portion 48. While not specifically shown in FIG. 2, the reductant injector 28 may extend through an aperture 56 in the cap 52 and spray reductant into the cylindrical and frustoconical portions 48, 50. The cylindrical portion 48 may include a plurality of apertures 58 extending therethrough. The frustoconical portion 50 may include a plurality of louvers 60 defining openings into the injector housing 34. A distal end 62 of the frustoconical portion 50 may engage the mixing bowl 36 and may extend through an aperture 64 in the mixing bowl 36. In some configurations, the distal end 62 may include a static mixer having louvers and apertures, for example, to provide additional turbulence.

(25) The mixing bowl 36 may be a generally bowl-shaped structure that may be stamped and/or otherwise formed from sheet metal, for example. It will be appreciated that the mixing bowl could be formed by any suitable process and from any suitable material. The mixing bowl 36 may include an upstream end portion 66, a collar portion 68, a step or flange portion 70 and a downstream rim 72 that cooperate to define a mixing chamber 74. The flange portion 70 may be disposed between the upstream end portion 66 and the collar portion 68 and may include the aperture 64 through which the injector housing 34 extends. An outer diametrical surface of the rim 72 can be welded, fastener or pressed into engagement with the inner diametrical surface of the mixer housing 32, for example.

(26) As shown in FIG. 4, an exterior surface 75 of the collar portion 68 (e.g., the surface of the collar portion 68 that generally faces an inlet 77 of the mixer housing 32) may be generally concave such that a central portion 71 of the exterior surface 75 is disposed further downstream than lateral portions 73 of an exterior surface 76. As shown in FIG. 2, the exterior surface 76 of the upstream end portion 66 (e.g., the surface of the upstream end portion 66 that generally faces an inlet 77 of the mixer housing 32) may be generally convex such that an upper end 78 of the exterior surface 76 is disposed further upstream than a lower end 80 of the exterior surface 76.

(27) As shown in FIGS. 3 and 4, a pair of recesses 82 may be formed in lateral side portions of the upstream end portion 66. The recesses 82 extend along the perimeter of the upstream end portion 66 and generally diverge from each other as they extend from a lower portion of the upstream end portion 66 toward the flange portion 70. In this manner, the recesses 82 are shaped to funnel or direct exhaust gas flowing into the mixer housing 32 toward the injector housing 34 and the collar portion 68 (as indicated by arrows A in FIG. 3) so that exhaust gas will flow into the injector housing 34 (i.e., between the louvers 60 and/or through the apertures 58) and flow into the mixing chamber 74 through the aperture 64 in the flange portion 70. In the particular embodiment depicted in FIGS. 2-4, all of the exhaust gas that enters the mixer housing 32 through the inlet 77 will be directed into the injector housing 34 and through the aperture 64 as indicated by the arrows A in FIG. 2. In this manner, the exhaust gas will be thoroughly mixed with the reductant from reductant injector 28 into the injector housing 34 and in the mixing chamber 74. Mixing bowl 36 includes a curved interior or downstream surface 83 shaped in such a manner that exhaust passing through aperture 64 is redirected substantially ninety degrees to flow toward SCR 22.

(28) The first mixing plate 38 may include a plurality of louvers 84 and apertures 86 through which the mixture of reductant and exhaust gas may flow. The second mixing plate 40 may include a plurality of apertures 88 through which the mixture of reductant and exhaust gas may flow. The first and second mixing plates 38, 40 may increase the turbulence of the flow upstream of the SCR catalyst 22 to facilitate further mixing of the exhaust gas and the reductant prior to entering the SR catalyst 22. The mixing plates 38, 40 may also spread the mixture of reductant and exhaust gas over a larger cross-sectional area so that the mixture will flow into the SCR catalyst 22 over a larger cross-sectional area. It will be appreciated that the mixer assembly 20 could include any number of mixing plates and/or static mixers configured in any desired manner. In some embodiments, the contours of the mixing bowl and/or the shape and position of one or more mixing plates 38, 40 may direct the mixture of exhaust gas and reductant away from a lower portion (from the frame of reference of FIG. 2) of the SCR catalyst 22 and toward a central region of the SCR catalyst 22.

(29) While the mixer assembly 20 is described above as mixing exhaust gas with reductant from the reductant injector 28 and providing the mixture to the SCR catalyst 22, it will be appreciated that the mixer assembly 20 could be used in conjunction with the HC injector 24 rather than the reductant injector 28. That is, the mixer assembly 20 could be provided upstream of the DOC 16, and the HC injector 24 could inject fuel into the injector housing 34 and mixing chamber 74 to be mixed with the exhaust gas prior to being ignited.

(30) FIGS. 5-7 depict another configuration of the mixing bowl 36 in which apertures 90 and louvers 92 are formed in the recesses 82 to allow a relatively small portion of the exhaust gas to flow therethrough rather than flowing into the injector housing 34 and the aperture 64. Louvers 92 redirect the exhaust flowing through apertures 90 to flow along curved interior surface 83. This flow pattern minimizes the number of large urea droplets contacting surface 83. If liquid urea droplets do impinge upon surface 83, the modified flow pattern quickly causes the liquid to evaporate.

(31) Additionally or alternatively, apertures and louvers could be formed in the exterior surface 76 between the recesses 82. Additionally or alternatively, one or more bypass apertures or passages could be formed in the mixing bowl 36 at or near the aperture 64 and/or at or near the rim 72 so that relatively small amounts of exhaust gas can bypass the injector housing 34. Additionally or alternatively, one or more bypass apertures or passages could be formed in the inner diametrical surface of the mixer housing 32 so that relatively small amounts of exhaust gas can bypass the injector housing 34 and the mixing chamber 74.

(32) While the mixer assemblies 20 shown in FIGS. 2 and 5 are oriented horizontally, it will be appreciated that these assemblies could be oriented vertically. As shown in FIG. 2, the injector housing 34 may have an axis of rotation (i.e., a longitudinal axis) that is disposed at a non-perpendicular angle relative to the longitudinal axis of the mixer housing 32. In the vertical orientation, this configuration may be particularly advantageous in that liquid droplets can fall away from the injector 28 rather than forming deposits on the injector 28.

(33) FIGS. 8 and 9 depict yet another configuration of a mixing bowl 136 that includes one continuous recess 182 in upstream end portion 166 instead of the pair of recesses 82 described above. Like the recesses 82 of the mixing bowl 36 described above, the recess 182 is shaped to funnel or direct exhaust gas outward and upward so that the exhaust gas will flow around collar portion 168 and into the injector housing 34 and through aperture 164 in flange portion 170 in a similar manner as described above and shown in FIGS. 2 and 3.

(34) FIGS. 10 and 11 depict an alternate mixer assembly 220 including a mixer housing or pipe 232, an injector housing 234, a mixing bowl 236, a first mixing plate 238, and a second mixing plate 240. Mixer housing 232 is substantially similar to previously described mixing housing 32. Similarly, injector housing 234 is substantially similar to the previously described injector housing 34. In particular, injector housing 234 includes a flange 246 coupled to a swirling device 247. Swirling device 247 includes a cylindrical portion 248 and a frustoconical portion 250. A cap 252 is fixed to flange 246 and cylindrical portion 248. Please refer to the earlier sections of the specification for greater detail.

(35) Mixing bowl 236 is substantially similar to previously described mixing bowl 236 and the alternate configurations depicted in FIGS. 4-9. Mixing bowl 236, however, includes an aperture 290 associated with a louver 292 extending across pipe 232 a distance approximately half of the inner diameter of the pipe. Aperture 290 and louver 292 are positioned centrally within the circular cross-section of pipe 232. Exhaust gas flows through aperture 290 and is re-directed by louver 292. As described in detail with relation to the other embodiments, exhaust gas also flows through apertures extending through cylindrical portion 248, frustoconical portion 250 to pass through aperture 264 of mixing bowl 236.

(36) First mixing plate 238 includes a stepped shape when viewed from the side such that a first portion 243 is positioned axially closer to injector housing 234 than a second portion 245. An intermediate portion 251 interconnects first portion 243 and second portion 245. Intermediate portion 251 is spaced apart from a collar portion 268 of mixing bowl 236 to define a pinch point or orifice therebetween. The orifice generates a region of increased gas velocity to entrain the smaller droplets of reductant and urge these droplets toward second portion 245 positioned on the same side of pipe as the injector. First portion 243 includes a plurality of louvers 284 and apertures 286 through which the mixture of reductant and exhaust gas may flow. Second portion 245 includes a plurality of substantially cylindrically-shaped apertures 249 provided to allow reductant and exhaust gas to flow therethrough. Louvers 284 are substantially crescent shaped and arranged in an arc to create a swirling exhaust gas motion. As larger droplets of reductant attempt to increase their distance from the injector, the swirling exhaust gas pattern generated by louvers 284 urges the droplets toward the injector such that they evaporate near the center of the pipe 232.

(37) Second mixing plate 240 may include a plurality of apertures 288 through which the mixture of reductant and exhaust gas may flow. The shape, size, and position of various apertures 288 are defined to further mix the exhaust gas and reductant prior to entering a downstream catalyst. Mixing plates 238, 240 may distribute the mixture of reductant and exhaust gas over a desired inlet area of the downstream catalyst to optimize efficiency of catalyst operation.

(38) The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.