WO2016039720A1

WO2016039720A1 - Exhaust gas mixer device

Info

Publication number: WO2016039720A1
Application number: PCT/US2014/054571
Authority: WO
Inventors: Chengke LIU; Linsong Guo; Chad R. FOSTER
Original assignee: Cummins, Inc.
Priority date: 2014-09-08
Filing date: 2014-09-08
Publication date: 2016-03-17

Abstract

A mixer device for facilitating the formation of turbulence in an exhaust gas stream to enhance the distribution of a reductant in exhaust gases upstream of an SCR substrate to improve NOx conversion and reduce ammonia slip. The mixer device has a first side that is adapted to facilitate turbulence in the exhaust gas stream and a body portion having a plurality of baffle holes and outer layer mixing passages that further facilitate turbulence in the exhaust gas stream. A plurality of protrusions extending from the body portion are adapted to alter a flow direction of at least a portion of the exhaust gas stream to further enhance exhaust gas stream turbulence. Such turbulences may assist in generally uniformly distributing the reductant throughout the exhaust gases, thereby allowing for relatively accurate detection of reductant concentration using a point-measurement device rather than via a more complicated steering wheel probe.

Description

EXHAUST GAS MIXER DEVICE

BACKGROUND

[0001] Embodiments of the present invention generally relate to engine after-treatment systems. More particularly, embodiments of the present invention relate to a mixer device for facilitating the distribution of a reductant in an exhaust gas stream.

[0002] Selective catalytic reduction (SCR) systems typically are configured to provide one or more catalyst elements that, with the aid of a reductant, convert nitrogen oxides (NO_x) in exhaust gases into nitrogen (N₂) and water. The reductant may be injected into the exhaust gas upstream of an SCR catalyst. Typically, engine after-treatment systems attempt to inject a sufficient quantity of reductant into the exhaust gas stream necessary for the conversion of a predetermined amount of the NO_x in the exhaust gas stream so as to prevent NO_x slippage without incurring reductant slippage.

[0003] Often reductant is injected into the exhaust gas stream in the form of urea, with droplets of the injected urea travelling along at least a portion of the SCR system toward an SCR catalyst component, such as, for example, a housing that has an SCR catalyst. In at least some instances, the urea droplets in the exhaust gas upstream may only partially evaporate before reaching the SCR catalyst component. Thus, even when a mixer is positioned upstream of the SCR catalyst component, the distribution of urea, or ammonia (NH₃) provided by the urea, in the exhaust gas stream that enters into the SCR catalyst component may be relatively inconsistent. Further, in at least some instances, the SCR catalyst component may have a plurality of channels through which divided portions of the exhaust gas stream, and the urea or ammonia (NH₃) contained therein, flows and is exposed to an SCR catalyst(s). Thus, as the amount of urea or ammonia (NH₃) flowing through each channel of the SCR catalyst component may vary, the concentration of urea or ammonia in the exhaust gas that exits the different channels may be inconsistent. Further, such inconsistences in the exhaust gas streams that flow through the different channels of the SCR catalyst component may adversely impact ammonia (NH₃) storage and temperature distribution within those channels and/or the associated SCR catalyst(s), thereby impacting the consistency of NO_x conversion at each of the channels.

[0004] Even in instances in which there is a relatively uniform distribution of ammonia

(NH₃) in the exhaust gas stream that exits the SCR catalyst component, the spatial distribution of ammonia (NH₃) in the exhaust gas stream may subsequently become non-uniform as the exhaust gas stream flows downstream to a subsequent component of the SCR system, such as, for example, to a second, downstream SCR catalyst component. For example, ammonia (NH₃) is typically lighter than other components of the exhaust gas stream, such as, for example, carbon dioxide (C0₂), nitrogen (N₂), and oxygen (0₂). Thus, in at least certain instances ammonia (NH₃) in the exhaust gas stream that is exhausted from an SCR catalyst component may begin to ascend toward, and/or reach, an upper portion of the exhaust gas stream before entering into a second, downstream SCR catalyst component. Further, even when a swirl mixer is positioned downstream of the SCR catalyst component, the operation of the swirl mixer may result in the lighter ammonia (NH₃) moving toward a center portion of the exhaust gas stream while heaver components are distributed further outwardly in the exhaust gas stream.

[0005] Inconsistencies in the spatial distribution of the components of the exhaust gas stream may also impede the control or operation of the SCR system. For example, according to certain SCR systems, the determination of characteristics relating to the injection of urea into the exhaust gas stream, such as, for example, injection timing and/or the quantity of urea to inject, may consider sensed characteristics of the exhaust gas stream that has exited the SCR catalyst component. For example, certain systems may employ one or more sensors to sense concentration levels of various components of the exhaust gas stream. However, as discussed above, even in the presence of swirl mixer, differences in the properties of various components of the exhaust gas stream may cause inconsistencies in the spatial distribution of those components in the exhaust gas stream. Such inconsistencies may prohibit the use of point- measurement devices that sense the concentration of the components of the exhaust gases at a single point of the exhaust gas stream. For example, a localized sensor point positioned at an outer periphery of the exhaust gas stream may detect a concentration level of a component of the exhaust gas stream that is different than if the localized sensor point were positioned at a central location of the exhaust gas stream. To address such inconsistences in the spatial distribution of the components of the exhaust gas stream, certain SCR systems may use a sensor probe that has multiple arms that extend radially outwardly from a central point, with the arms having multiple openings so as to allow the sensor probe to collect samplings of the exhaust gas stream from a variety of different spatial locations. The collected exhaust gases may then collectively provide a sample that is evaluated by the sensor probe in determining characteristics of the exhaust gas stream. However, such sensor probes are relatively expensive and may have an associated higher installation cost than point-measurement devices.

BRIEF SUMMARY

[0006] An aspect of the present invention is a bow mixer device for facilitating the formation of turbulence in an exhaust gas stream. The bow mixer device may include a body portion having a first side, a second side, and an outer portion. The first side may have an outer portion, a central portion, and a transitional surface. At least the transitional surface may have a generally curved shape. Additionally, the body portion may further include a plurality of outer layer mixing passages that are positioned about at least the outer portion of the body portion and are configured for the passage of a first portion of the exhaust gas stream. The body portion may further include a plurality of baffle holes that are positioned about at least the transitional surface and that are adapted for the passage a second portion of the exhaust gas stream through the body portion. Each of the plurality of baffle holes may be sized to receive a volume of the second portion of the exhaust gas stream that is smaller than a volume of the first portion of exhaust gas stream that is received by each of the plurality of outer layer mixing passages.

[0007] Another aspect of the present invention is a bow mixer device for facilitating the formation of turbulence in an exhaust gas stream. The bow mixer device includes a body portion having a first side and a second side, the first side being adapted to facilitate a first turbulence in the exhaust gas stream to generate a first turbulent exhaust gas stream. The body portion may have a plurality of baffle holes that are adapted to facilitate a second turbulence in the first turbulent exhaust gas stream to generate a second turbulent exhaust gas stream. The plurality of baffle holes may be further adapted to provide a passageway for at least a portion of the second turbulent exhaust gas stream through the body portion. The body portion may further include a plurality of protrusions that project from the second side, the plurality of projections being adapted to alter a flow direction of at least a portion of the second turbulent exhaust gas stream to facilitate a third turbulence in the second turbulent exhaust gas stream.

[0008] Additionally, another aspect of the present invention is an SCR system that includes a first mixer device that is adapted to mix a reductant with an exhaust gas stream to provide a first exhaust gas stream. The SCR system also includes a first SCR catalyst component that is adapted to receive the first exhaust gas stream, the first SCR catalyst component having a first SCR catalyst that is adapted to react with at least a portion of the reductant to generate a second exhaust gas stream. The SCR system further includes a second mixer device having a body portion, the body portion having a first side and a second side. The first side has a generally curved surface that is adapted to facilitate generation of a first turbulence in the second exhaust gas stream to mix the distribution of at least a portion of the reductant in the second exhaust gas stream. The body portion further includes a plurality of a baffle holes that each provide a flow passage through the body portion. The plurality of baffle holes are adapted to facilitate generation of a second turbulence in the second exhaust gas to further mix the distribution of the reductant in the second exhaust gas stream, with the second exhaust gas stream that flows from the second mixer device being a third exhaust gas stream. Additionally, the second SCR catalyst component is adapted to receive the third exhaust gas stream, the second SCR catalyst component having a second SCR catalyst adapted to react with at least a portion of the reductant in the third exhaust gas stream.

[0009] Other aspects of the present invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[00010] Figure 1 illustrates a schematic block diagram of an engine system having an exhaust gas after-treatment system having a bow mixer device positioned downstream of a first SCR catalyst component according to an illustrated embodiment of the present invention.

[00011] Figure 2 illustrates a schematic block diagram of an engine system having an exhaust gas after-treatment system having a bow mixer device positioned upstream of a SCR catalyst component according to an illustrated embodiment of the present invention

[00012] Figure 3 illustrates a front view of a bow mixer device positioned within a mixing conduit according to an illustrated embodiment of the present invention.

[00013] Figure 4 illustrates a cross sectional side view of a bow mixer device positioned in a mixing conduit according to an illustrated embodiment of the present invention.

[00014] The foregoing summary, as well as the following detailed description of certain embodiments of the present invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there is shown in the drawings, certain embodiments. It should be understood, however, that the present invention is not limited to the arrangements and instrumentalities shown in the attached drawings.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

[00015] Certain terminology is used in the foregoing description for convenience and is not intended to be limiting. Words such as "upwardly," "downwardly," "inwardly" and "outwardly" designate directions in the drawings to which reference is made. This terminology includes the words specifically noted above, derivatives thereof, and words of similar import. Additionally, the words "a" and "one" are defined as including one or more of the referenced item unless specifically noted.

[00016] Figure 1 illustrates a schematic block diagram of an engine system 100 having an exhaust gas after-treatment system 102. The engine system 100 includes an engine 104, such as, for example, a combustion engine, including, but not limited to, a diesel, gasoline, natural gas, and/or combined fuel engine. Operation of the engine 104 generates an exhaust gas stream 106 that has an amount of NO_x as a constituent therein. Optionally, according to certain embodiments, the engine system 100 includes a turbocharger having a turbine side 101 on an intake side of the engine 104, and a compressor side 103 on an exhaust side of the engine 104.

[00017] According to the illustrated embodiment, at least a portion of the exhaust gas stream 106 generated by the operation of the engine 104 may be delivered to an after-treatment system 102. The after-treatment system 102 may include one or more after-treatment devices. For example, according to certain embodiments, the after-treatment system 102 may include, but is not limited to, an exhaust gas recirculation (EGR) system 108, a oxidation catalyst (DOC) 110, a particulate filter, such as, for example, a diesel particulate filter (DPF) 112, and/or one or more ammonia oxidation catalysts (AMOx) 114. As shown in Figure 1, according to certain embodiments, the EGR system 108 may include an exhaust flow path 1 16, an EGR valve 118, and an EGR cooler 120. According to such an embodiment, the EGR system 108 may be configured to recirculate at least a portion of the exhaust gas stream 106, which may be cooled by the EGR cooler 120, to an intake side of the engine 104.

[00018] The after-treatment system 102 may also include a selective catalyst reduction

(SCR) system 122. According to certain embodiments, the SCR system 122 includes a reductant injector or doser 124 and one or more SCR catalyst components 130a, 130b. The reductant doser 124 is in fluid communication with a reductant source 126, and is controllable by a controller 128. The reductant source 126 may contain a reductant, such as, for example, ammonia (NH₃), urea, and/or a hydrocarbon, that is supplied for injection by the reductant doser 124 into the exhaust gas stream 106 at a position upstream of the SCR catalyst component 130. The controller 128 may be configured to both determine a ratio of reductant to NO_x in the exhaust gas stream 106, such as, for example, an ammonia to NO_x ratio (ANR) during operation of the engine 104, and to adjust the operation of the reductant doser 124 to achieve a target reductant to NO_x ratio.

[00019] The one or more SCR catalyst components 130a, 130b are configured to provide an SCR catalyst that at least assists in the reductant reacting with NO_x in the exhaust gas to reduce the amount of NO_x in the exhaust gas stream 106. According to certain embodiments, the SCR catalyst components 130a, 130b may include a housing having one or more channels for the flow of divided portions of the exhaust gas stream 106. Additionally, one or more SCR catalysts may be positioned within the channels of the SCR catalyst components 130a, 130b. Further, the SCR system 122 may include a plurality of SCR catalyst components, such as, for example, the first and second SCR catalyst components 130a, 130b as shown, for example, in Figure 1, or a single SCR catalyst component 130, as shown, for example, in Figure 2.

[00020] According to the illustrated embodiment, the controller 128 is structured to functionally execute operations to control the after-treatment system 102, and in particular, at least the SCR system 122. Further, the controller 128 may include a number of modules structured to functionally execute the operations of the controller 128. For example, an exemplary controller 128 includes a system conditions module, a NO_x modeling module, a NO_x reference module, a NO_x error determination module, a NO_x control module, and/or a doser control determination module. In certain embodiments, the controller 128 forms a portion of a processing subsystem including one or more computing devices having memory, processing, and communication hardware. The controller 128 may be a single device or a distributed device, and the functions of the controller 128 may be performed by hardware or software.

[00021] According to certain embodiments, the after-treatment system 102 may include at least one engine-out NO_x sensor 129 that is used in detecting an NO_x level in the exhaust gas stream 106 upstream of the SCR system 122. In the illustrated embodiment, one or more of the engine-out NO_x sensors 129 may be positioned upstream of the DOC 110, the DPF, and/or the reductant doser 124. Further, according to the illustrated embodiment, the engine-out NO_x sensor 129 may provide a signal for the controller 128 that indicates, and/or is used in determining, a level of NO_x in the exhaust gas at a location upstream of the reductant doser 124. Alternatively, the quantity of engine-out NO_x may be modeled, calculated from an engine operation map, and/or measured from a different location than the location of the engine-out NO_x sensors 129 shown in Figure 1.

[00022] The after-treatment system 102 may also include at least one temperature sensor

131 that is in communication with the controller 128. According to certain embodiments, the temperature sensor 131 can be used to determine a temperature within the SCR catalyst component 130, 130a, 130b such as, for example, the temperature of one or more SCR catalysts that are within the SCR catalyst component 130, 130a, 130b. According to certain embodiments, the temperature sensor 131 is positioned within at least one SCR catalyst component 130, 130a, 130b. Alternatively, the temperature sensor 131 may be positioned upstream and/or downstream of one or more SCR catalyst component 130, 130a, 130b. Further, the temperature of the SCR catalyst component 130, 130a, 130b may be determined in a variety of different manners, including, for example, at least by utilizing a weighted average of temperature sensors 131 that are positioned upstream and downstream of the SCR catalyst component 130, 130a, 130b, or modeling and/or estimating the temperature of the SCR catalyst component 130, 130a, 130b based upon other temperature measurements available in the engine system 100, and more specifically within the after-treatment system 102.

[00023] Referencing Figure 1, according to the illustrated embodiment, a splash mixing plate 132 is positioned adjacent to the reductant doser 124 such that reductant injected into the exhaust gas by the reductant doser 124 strikes the splash mixing plate 132 at a particular angle that facilitates distribution of droplets of the injected reductant in the exhaust gas stream 106. The droplets of reductant may then travel in the exhaust gas stream along a decomposition tube 134 to facilitate at least partial evaporation of the droplets of reductant in the exhaust gas stream 106 before the droplets of reductant reach an SCR catalyst component 130a. Additionally, according to certain embodiments, an upstream mixer 136, such as, for example, a swirl mixer, including, but not limited to a cyclone mixer, may be positioned at an outlet 138 of the decomposition tube 134, and moreover, at a position upstream of a first SCR catalyst component 130a. The upstream mixer 136 may be configured to increase the distribution of at least the reductant droplets and/or evaporated reductant in the exhaust gas. For example, after passing through the decomposition tube 134 and the upstream mixer 136, the urea mixing uniformity index may be around 0.9.

[00024] According to at least embodiments in which the reductant is not completely evaporated in the exhaust gas stream 106 before entering the first SCR catalyst component 130a, the SCR system 122 may include a first SCR catalyst component 130a and a second SCR catalyst component 130b. According to certain embodiments, after flowing through the decomposition tube 134 and the upstream mixer 136, the exhaust gas stream 106 may be divided such that different portions of the exhaust gas stream 106 flow through different channels of the first SCR catalyst component 130a, with the exhaust gas stream 106 flowing in the different channels and being exposed to an SCR catalyst. Generally, as the exhaust gas stream 106 flows through channels in the first SCR catalyst component 130a, at least a portion of the reductant in the exhaust gas stream 106, such as ammonia (NH₃), undergoes a reaction with an SCR catalyst such that a reduction occurs in which nitrogen oxides (NO_x) are converted to nitrogen and water. However, due to at least inconsistent distribution of reductant in the exhaust gas stream 106 as the exhaust gas stream 106 enters into the first SCR catalyst component 130a, as well as temperature distribution and ammonia storage differences for the SCR catalyst(s), the reductant concentration in the exhaust gas stream 106 exiting each of the channels of the first SCR catalyst component 130a is often inconsistent.

[00025] After exiting the channels of the first SCR catalyst component 130a, the exhaust gas stream 106 encounters a bow mixer device 140. Figures 3 and 4 illustrate front and cross sectional side views, respectively, of an embodiment of a bow mixer device 140. The bow mixer device 140 includes a body portion 142 having a first surface 144 and an opposing second surface 146. According to the illustrated embodiment, the body portion 142 is generally cup- shaped. For example, in the illustrated embodiment, at least a portion of the first surface 144 has a generally concave cross-sectional profile, as shown in Figure 4. Moreover, according to the illustrated embodiment, the first surface 144 may have a central point or portion 148a that is axially recessed inwardly from an outer portion 150a of the first surface 144 along a central axis 152 of the bow mixer device 140. One or more transition surfaces 154a between the outer portion 150a and the central portion 148a may provide a transition from the outer portion 150a to the central portion 148a. According to the illustrated embodiment, the second surface 146 may have a shape and configuration that is similar to that of the first surface 144. For example, according to the illustrated embodiment, the second surface 146 include a transition surface 154b that extends from an outer portion 150b to a central portion 148b of the second surface 146 in a similar direction and distance as the first surface 144. However, according to other embodiments, the shape of the second surface 146 may be different than the shape of the first surface 144.

[00026] The transition surfaces 154a, 154b may take a variety of shapes and configurations. For example, according to the illustrated embodiment, transition surfaces 154a, 154b may each form at least a portion of a circular shaped segment that extends along the majority, if not all, of the first and second surfaces 144, 146, respectively. Further, for example, according to certain embodiments, the profile of the first and second surfaces 144, 146 may each be similar to a segment of a circle having a radius of around 5 to 10 inches, and more specifically, around 7.5 inches. However, such sizes are exemplary, and may vary based on a number of different factors, including, for example, engine system 100 and after-treatment system 102 architectures, including size constraints of the location at which the bow mixer device 140 is positioned and pressures within the after-treatment system 102, among other considerations.

[00027] The body portion 142 includes an outer portion 147 having an outer edge 151 at the periphery of the body portion 142 may be arranged in a variety of different configurations. For example, in the illustrated embodiment, the outer edge 151 may generally have a circular shape, such as, for example, a diameter of about 5 to 10 inches, and more specifically around 7.5 inches. However, again, such sizes are exemplary, and may vary based on a number of different factors, including, for example, engine system 100 and after-treatment system 102 architectures, among other considerations. Further, according to certain embodiments, portions of the outer edge 151 may be segmented, such as, for example, separated from other portions of the outer edge 151 by one or more outer layer mixing passages 158. For example, according to the illustrated embodiment, six outer layer mixing passages 158 may inwardly extend from the outer edge 151 and through the body portion 142 so that at least a portion of the body portion 142 is partitioned to provide six outer layer segments 153a-f along at least a portion of the outer periphery of the body portion 142. Further, according to the illustrated embodiment, the outer layer mixing passages 158 may extend from the outer portions 150a, 150b and to at least a portion of the transition surfaces 154a, 154b on the first and second sides 144, 146, respectively, of the body portion 142. However, according to other embodiments, rather than extending to/from the outer edge 151 , the outer layer mixing passages 158 may be positioned near, but do not extend into or across, the outer edge 151. The outer layer mixing passages 158 may have a variety of different shapes or configurations, such as, for example, a semi-circular shape, as shown, for example, in Figure 3.

[00028] The body portion 142 may also include a plurality of baffle holes 158 that at least extend through the body portion 142 from the first surface 144 to the second surface 146 of the bow mixer device 140. The plurality of baffle holes 158 may be positioned at various locations about at least the transition surfaces 154a, 154b and in a variety of different arrangements or configurations. Additionally, the baffle holes 158 may have a variety of shapes and sizes. For example, in the illustrated embodiment, the baffle holes 158 have a generally semi-circular shape that are similar to, but smaller than, the outer layer mixing passages 156. However, according to other embodiments, the outer layer mixing passages 158 may have a generally smaller or equal size than the baffle holes 158, including, for example, a smaller, similar, or larger area, length, height, and/or width. Further, for example, in the illustrated embodiment, a plurality of baffle holes 158 may be radially arranged in one sets of baffle holes 158. For example, in the illustrated embodiment, the bow mixer device 140 includes a first set 160a, second set 160b, and a third set 160c of baffle holes 158, with each set 160a-c having at least six baffle holes 158. According to such an embodiment, the first set 160a of baffle holes 158 may be generally equally spaced about the body portion 142 along a first baffle hole diameter (Di), the second set 160b of baffle holes 158 being generally equally space about a second baffle hole diameter (D₂) that is smaller than the first baffle hole diameter (Di), and the third set 160c of baffle holes 158 being generally equally spaced about a third baffle hole diameter (D₃) that is smaller than the second baffle hole diameter (D₂).

[00029] As shown in at least Figure 4, one or more protrusions 162 that are adjacent to one or more of the baffle holes 158 may extend from the second surface 146 of the body portion 142. For example, according to the illustrated embodiment, each protrusion 162 may be extend from the second surface 146 at a location at or adjacent to a baffle hole 158, with the protrusion 162 oriented to alter the flow path of the exhaust gas stream 106 that is exiting the baffle hole 158 so as to facilitate mixing of that exhaust gas stream with other exhaust gas streams that are or have flown through the one or more other baffle holes 158. According to the illustrated embodiment, each protrusion 162 may extend in or more directions, such as, for example, extending at least partially upwardly, downwardly, and/or outwardly from the second surface 146 of the body portion 142.

[00030] Referencing Figure 4, the exhaust gas stream 106a that exits the first SCR catalyst component 130a, and which may have a non-uniform mixing of reductant, such as, for example, ammonia (NH₃), flows toward the first surface 144 of the bow mixer device 140. At least portions of the exhaust gas stream 106a flows into the first surface 144, which may cause a change in the direction of flow for at least those exhaust gases. Further, in the illustrated embodiment, the curved shape of the first surface 144 of the bow mixer device 140 may at least assist in facilitating dispersing the flow of exhaust gas stream 106a that flows into or near the first surface 144 of the bow mixing plate 140 in a number of different directions. The resulting disbursement of at least portions of the exhaust gas stream 106a in a variety of different directions at least assists in the formation of turbulence in the exhaust gases 106b that are adjacent to and/or approaching the first surface 144 of the bow mixer device 140. Moreover, non-uniform turbulence in the exhaust gases that are encountering or adjacent to the first side 144 of the bow mixer device 140, may facilitate mixing of the components in the exhaust gas stream 106a, such as, for example, mixing of reductant, including ammonia (NH₃), in those exhaust gases.

[00031] Additionally, the exhaust gases in the exhaust gas stream 106a may then be subjected to further turbulence as those exhaust gases 106b pass through the baffle holes 158 and/or the outer layer mixing passages 158. Such additional turbulence provides an additional opportunity to mix, or disburse the components of the exhaust gas stream 106b. Further the direction the exhaust gases 106c pass through the baffle holes 158 and/or through the outer layer mixing passages 158 may be further altered by the protrusions 162 that extend from the second surface 146 of the body portion 142 of the bow mixer device 140. Such additional turbulence may again provide yet another opportunity to further mix or disburse the components of the exhaust gas stream 106c.

[00032] Thus, when the flow of the exhaust gas stream 106d resumes downstream of the bow mixer device 140, the exhaust gases may have been subjected to turbulence both as the exhaust gases approached, passed through, and exited the bow mixer device 140. Moreover, by subjecting the exhaust gases repeatedly to such enhanced turbulence, reductant, such as ammonia (NH₃), in the exhaust gases that are flowing from the bow mixer device 140 may generally be relatively uniformly disbursed or distributed within the exhaust gas 106d. Such relatively homogenous distribution of the reductant, such as ammonia (NH₃), in the exhaust gas stream 106d may improve the ability of downstream SCR catalyst component 130b to convert nitrogen oxides (NO_x) in the exhaust gas stream 106d, while also reducing the potential for reductant slippage.

[00033] Additionally, such relatively uniform distribution of the components of the exhaust gas stream 106d, including the reductant, downstream of the bow mixer device 140 may allow for the use of one or more point-measurement devices 164 to sense the concentration of the components of the exhaust gas stream 106, including, for example, the concentration of reductant in the exhaust gas stream 106d. For example, referencing Figures 1 and 4, according to certain embodiments, the point-measurement device 164 may be an ammonia (NH₃) sensor that is positioned adjacent to the inlet 166 of the second SCR catalyst component 130b. Such positioning of the point-measurement device 164 downstream of the bow mixer device 140 may allow the point-measurement device 164 to relatively accurately detect the concentration of ammonia (NH₃) in the exhaust gas stream 106d. Moreover, the accuracy of such detection may be facilitated by the exhaust gas stream 106 having been subjected to the enhanced turbulence that was facilitated by the upstream bow mixer device 140.

[00034] Referencing Figure 3, according to the illustrated embodiment, a mixing assembly

170 may be provided that includes the bow mixer device 140 positioned within an interior region 172 of a mixing conduit 174. With respect to the engine system 100 illustrated in Figure 1 , according to certain embodiments, a first end 176 of the mixing conduit 174 may be configured for operable connection to the outlet 178 of the first SCR catalyst component 130, such as, for example, by the use of female clamp lips 180. Similarly, the mixing conduit 174 may include a second end 184 that is configured for operable connection to the inlet 166 of the second SCR catalyst component 130, such as, for example, by the use of male clamp lips 184. According to certain embodiments, the outer edge 151 of the body portion 142 may be configured to be adjacent to, and/or abut against, an inner surface 186 in the interior region 172 of the mixing conduit 174. Additionally, the bow mixer device 140 may be operably connected to the mixing conduit 174 in a number of manners, including, for example, by one or more welds, press fit, or a mechanical fastener, such as, for example, a pin, bolt, clamp, and/or screw, among other mechanical fasteners. Additionally, as illustrated by at least Figure 3, according to the illustrated embodiment, the outer edge 151 of the body portion 142 may have, a generally circular configuration that generally conforms to inner diameter of the interior region 172 of the mixing conduit 174.

[00035] Given the relatively narrow thickness of the bow mixer device 140 (as indicated by "W" in Figure 4) along the central axis 152 of the bow mixer device 140, the bow mixer device 140 may be sized to allow for the outlet 178 of the first SCR catalyst component 130a to be positioned in relative close proximity to the inlet 166 of the second SCR catalyst component 130b. For example, according to certain embodiments, the bow mixer device 140 may have a thickness of approximately 1 to 2 inches, and more specifically 1.1 inches, which may allow the outlet 178 of the first SCR catalyst component 130a to be positioned in relatively close proximity to the inlet 166 of the second SCR catalyst component 130b. However, again, such sizes are exemplary, and may vary based on a number of different factors, including, for example, engine system 100 and after-treatment system 102 architectures, among other considerations. The ability to position the outlet 178 of the first SCR catalyst component 130a in relatively close proximity to the inlet 166 of the second SCR catalyst component 130b through use of the bow mixer device 140 may assist in minimizing temperature losses in the exhaust gas stream 106 as the exhaust gas stream 106 travels from the first SCR catalyst component 130a and to the second SCR catalyst component 130b. Alternatively, according to other embodiments, the bow mixer device 140 may be welded to a portion of the outlet 178 of the first SCR catalyst component 130.

[00036] Additionally, referencing Figure 2, for at least certain SCR systems 122', the bow mixer device 140 may also be positioned upstream of a first SCR catalyst component 130. For example, according to embodiments in which at least a relatively large portion an injected reductant, such as urea, is generally converted to ammonia (NH₃) before reaching an SCR catalyst component 130 and/or the SCR catalyst(s) contained therein, the bow mixer device 140 may be positioned upstream of, or at, the inlet 168 of the first, and possibly only, SCR catalyst component 130.

[00037] Various features and advantages of the present invention are set forth in the following claims. Additionally, changes and modifications to the described embodiments described herein will be apparent to those skilled in the art, and such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its intended advantages. While the present invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered illustrative and not restrictive in character, it being understood that only selected embodiments have been shown and described and that all changes, equivalents, and modifications that come within the scope of the inventions described herein or defined by the following claims are desired to be protected.

[00038] While the invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. A bow mixer device for facilitating the formation of turbulence in an exhaust gas stream, the bow mixer device comprising:

a body portion having a first side, a second side, and an outer portion, the first side having an outer portion, a central portion, and a transitional surface, at least the transitional surface having a generally curved shape, the body portion further including a plurality of outer layer mixing passages positioned about at least the outer portion of the body portion and configured for the passage of a first portion of the exhaust gas stream, the body portion further including a plurality of baffle holes positioned about at least the transitional surface and adapted for the passage a second portion of the exhaust gas stream through the body portion, each of the plurality of baffle holes being sized to receive a volume of the second portion of the exhaust gas stream that is smaller than a volume of the first portion of exhaust gas stream that is received by each of the plurality of outer layer mixing passages.

2. The bow mixer device of claim 1, further including a plurality of protrusions that project from the second side of the body portion, at least a portion of the plurality of protrusions positioned adjacent to one or more of the plurality of baffle holes, the plurality of protrusions adapted to facilitate turbulence in at least a portion of the second portion of the exhaust gas stream that passes through the plurality of baffle holes.

3. The bow mixer device of claim 2, wherein one or more of the plurality of protrusions project from the second side of the body portion in a direction that is different than a direction that at least another protrusion of the plurality of protrusions projects from the second surface.

4. The bow mixer device of claim 3, wherein the plurality of outer layer mixing passages are adapted to provide a plurality of outer layer segments along at least a portion of the outer portion of the first surface, at least one of the plurality of outer layer segments being separated from another one of the plurality of outer layer segments by an adjacent outer layer mixing passage of the plurality of outer layer mixing passages.

5. The bow mixer device of claim 4, wherein the plurality of baffle holes are arranged in two or more sets of baffles holes, a first set of the two or more sets of baffle holes being generally equally spaced about a first baffle hole diameter, a second set of the two or more sets of baffle holes being generally equally spaced along a second baffle hole diameter, the second baffle hole diameter being smaller than the first baffle hole diameter.

6. The mixing device of claim 5, wherein the body portion has a width of approximately 1 inches to 2 inches.

7. The mixing device of claim 6, wherein the transitional surface has a radius of approximately 5 to 10 inches.

8. A bow mixer device for facilitating the formation of turbulence in an exhaust gas stream, the bow mixer device comprising:

a body portion having a first side and a second side, the first side adapted to facilitate a first turbulence in the exhaust gas stream to generate a first turbulent exhaust gas stream, the body portion having a plurality of baffle holes adapted to facilitate a second turbulence in the first turbulent exhaust gas stream to generate a second turbulent exhaust gas stream, the plurality of baffle holes further adapted to provide a passageway for at least a portion of the second turbulent exhaust gas stream through the body portion, the body portion further including a plurality of protrusions that project from the second side, the plurality of projections adapted to alter a flow direction of at least a portion of the second turbulent exhaust gas stream to facilitate a third turbulence in the second turbulent exhaust gas stream.

9. The bow mixer device of claim 8, wherein the first surface has a generally curved shape.

10. The bow mixer device of claim 9, wherein the outer portion of the body portion includes an outer edge, the outer edge having a generally circular shape, and wherein the outer layer mixing passages are positioned along at least the outer edge.

11. The bow mixer device of claim 8, wherein the body portion further includes a plurality of outer layer mixing passages positioned along at least an outer edge of the body portion and adapted for the passage of at least a portion of the a first portion of the second turbulent exhaust gas stream through the body portion, each of the plurality of outer layer mixing passages having a size that is larger than a size of each of the plurality of baffle holes.

13. The bow mixer device of claim 11, wherein the bow mixer device is operably secured to an SCR catalyst component.

14. The bow mixer device of claim 13, wherein the bow mixer device is welded to an outlet of the SCR catalyst component.

15. The bow mixer device of claim 11, wherein the bow mixer device is operably secured to an interior region of a mixing conduit, the mixing conduit adapted to be operably connected to a first SCR catalyst component and a second SCR catalyst component.

16. An SCR system comprising :

a first mixer device adapted to mix a reductant with an exhaust gas stream to provide a first exhaust gas stream;

a first SCR catalyst component adapted to receive the first exhaust gas stream, the first SCR catalyst component having a first SCR catalyst adapted to react with at least a portion of the reductant to generate a second exhaust gas stream;

a second mixer device having a body portion, the body portion having a first side and a second side, the first side having a generally curved surface adapted to facilitate generation of a first turbulence in the second exhaust gas stream to mix the distribution of at least a portion of the reductant in the second exhaust gas stream, the body portion further including a plurality of a baffle holes that each provide a flow passage through the body portion, the plurality of baffle holes adapted to facilitate generation of a second turbulence in the second exhaust gas to further mix the distribution of the reductant in the second exhaust gas stream, the second exhaust gas stream flowing from the second mixer device as a third exhaust gas stream; and

a second SCR catalyst component adapted to receive the third exhaust gas stream, the second SCR catalyst component having a second SCR catalyst adapted to react with at least a portion of the reductant in the third exhaust gas stream.

17. The SCR system of claim 16, further including a point-measurement device positioned between the second mixer device and the second SCR catalyst component, the point- measurement device configured to sense a concentration of reductant in the third exhaust gas stream.

18. The SCR system of claim 17, wherein the second mixer device includes a plurality of outer layer mixing passages positioned at least along an outer periphery of the body portion and configured to provide a passage for at least a portion of the second exhaust gas stream.

19. The SCR system of claim 18, further including a plurality of protrusions that project from the second side of the body portion, at least a portion of the plurality of protrusions positioned adjacent to one or more of the plurality of baffle holes, the plurality of protrusions adapted to facilitate generation of a third turbulence in at least a portion of the second exhaust gas stream that passes through the plurality of baffle holes.

20. The SCR system of claim 19, further including a diesel oxidation catalyst, a diesel particulate filter, a reductant doser, and an ammonia oxidation catalyst, and wherein the first mixer device is a swirl mixer.