Patent Publication Number: US-2023143888-A1

Title: Mixers for use in aftertreatment systems

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a U.S. National Phase Application based on PCT Application No. PCT/US2021/017551, filed Feb. 11, 2021, which claims the benefit of U.S. Provisional Application No. 62/982,354, filed Feb. 27, 2020. The contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to aftertreatment systems for use with internal combustion engines. 
     BACKGROUND 
     Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by engines such as internal combustion engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered internal combustion engines includes a selective catalytic reduction (SCR) system including a SCR catalyst formulated to convert NO x  (NO and NO 2  in some fraction) into harmless nitrogen gas (N 2 ) and water vapor (H2O) in the presence of ammonia (NH 3 ). 
     Generally, a reductant such as a diesel exhaust fluid (e.g., an aqueous urea solution) is inserted into the aftertreatment system as a source of ammonia. The reductant facilitates the decomposition of the constituents of the exhaust gas by the SCR catalyst. However, if the reductant is not mixed substantially with the exhaust gas, the inserted reductant may not completely decompose and lead to reductant deposits being formed on walls or various components of the aftertreatment system. Overtime, the reductant deposits can build up and lead to reduction in a SCR catalytic conversion efficiency (CE) of the SCR catalyst. To facilitate mixing, mixers are used or a reductant injector is mounted offset from a flow axis of the exhaust gas. However, reductant deposit formation remains a challenge in aftertreatment systems. 
     SUMMARY 
     Embodiments described herein relate generally to mixers for promoting mixing of reductant with exhaust gas flowing through an aftertreatment system and reduce reductant deposits. In particular, embodiments described herein include a multi-vane mixer that includes a central hub defining a flow channel that is radially offset from a longitudinal axis of an aftertreatment housing, and a reductant injector that inserts reductant at a non-zero angle with respect to the transverse axis of the aftertreatment system and opposite a circumferential direction of rotation of the exhaust gas that is caused by the mixer. 
     In some embodiments, an aftertreatment system for treating constituents of an exhaust gas produced by an engine, comprises: a housing defining a housing central axis; a selective catalytic reduction (SCR) system disposed in the housing; a mixer disposed in the housing upstream of the SCR system, the mixer comprising: a hub, a tubular member disposed circumferentially around the hub and defining a reductant entry port, and a plurality of vanes extending from the hub to the tubular member such that openings are defined between adjacent vanes of the plurality of vanes to allow the exhaust gas to flow therethrough such that the plurality of vanes swirl the exhaust gas in a circumferential direction with respect to an exhaust gas flow path; and a reductant injector disposed on the housing upstream of the SCR system along a transverse axis of the housing and configured to insert a reductant into the exhaust gas flowing through the housing through the reductant entry port, the reductant being inserted at a non-zero angle with respect to the transverse axis opposite the circumferential direction, wherein a mixer central axis of the mixer defined through the hub is radially offset with respect to the housing central axis at a location in the housing that is upstream of the mixer. 
     In some embodiments, the mixer central axis is horizontally offset from the housing central axis. 
     In some embodiments, the mixer central axis is vertically offset from the housing central axis. 
     In some embodiments, the non-zero angle is in a range of 5 degrees to 60 degrees with respect to the transverse axis. 
     In some embodiments, an auxiliary opening is defined in the tubular member proximate to the reductant entry port. 
     In some embodiments, the housing defines a circular, square, rectangular, oval, elliptical, or polygonal cross-section. 
     In some embodiments, the mixer further comprises a flange extending radially outwards from a rim of an upstream end of the tubular member and secured to an inner surface of the housing. 
     In some embodiments, the aftertreatment system further comprises: a blocking member extending from the hub to the tubular member. 
     In some embodiments, the plurality of vanes extend from the hub to the tubular member around a portion between 130 degrees and 230 degrees of a circumference of the tubular member. 
     In some embodiments, a plurality of throughholes are defined through the blocking member. 
     In some embodiments, a slit is defined through at least one vane of the plurality of vanes. 
     In some embodiments, an assembly for an aftertreatment system comprises: a hub, a tubular member disposed circumferentially around the hub and defining a reductant entry port, and a plurality of vanes extending from the hub to the tubular member such that openings are defined between adjacent vanes of the plurality of vanes to allow an exhaust gas to flow therethrough such that the plurality of vanes swirl the exhaust gas in a circumferential direction with respect to an exhaust gas flow path of the exhaust gas, a mixer central axis of the mixer defined through the hub is configured to be radially offset with respect to a housing central axis of a housing within which the mixer is positionable at a location upstream of the mixer, wherein the reductant entry port is axially aligned with a central portion of the exhaust gas flow path and configured to allow insertion of the reductant at a non-zero angle with respect to the central portion opposite the circumferential direction. 
     In some embodiments, the mixer central axis is horizontally offset from the housing central axis. 
     In some embodiments, the mixer central axis is vertically offset from the housing central axis. 
     In some embodiments, the non-zero angle is in a range of 5 degrees to 60 degrees with respect to the transverse axis. 
     In some embodiments, an auxiliary opening is defined in the tubular member proximate to the reductant entry port. 
     In some embodiments, the assembly further comprises: a blocking member extending from the hub to the tubular member. 
     In some embodiments, the plurality of vanes extend from the hub to the tubular member around a portion between 130 degrees and 230 degrees of a circumference of the tubular member. 
     In some embodiments, a plurality of throughholes are defined through the blocking member. 
     In some embodiments, a slit is defined through at least one vane of the plurality of vanes. 
     It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing in this disclosure are contemplated as being part of the subject matter disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several implementations in accordance with the disclosure and are therefore not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings. 
         FIG.  1    is a schematic illustration of an aftertreatment system, according to an embodiment. 
         FIG.  2    is a front cross-section view of a housing of an aftertreatment system of  FIG.  1    taken along the line A-A in  FIG.  1   , showing a mixer disposed in the housing and a spray cone produced by a reductant injector mounted on the housing. 
         FIG.  3    is a front cross-section view of a housing of an aftertreatment system of  FIG.  1    taken along the line A-A in  FIG.  1   , showing a mixer disposed in the housing and a spray cone produced by a reductant injector mounted on the housing, according to another embodiment. 
         FIG.  4    is a front cross-section view of a housing of an aftertreatment system of  FIG.  1    taken along the line A-A in  FIG.  1   , showing a mixer disposed in the housing and a spray cone produced by a reductant injector mounted on the housing, according to still another embodiment. 
         FIG.  5    is a front cross-section view of a housing of an aftertreatment system of  FIG.  1    taken along the line A-A in  FIG.  1   , showing a mixer disposed in the housing and a spray cone produced by a reductant injector mounted on the housing, according to yet another embodiment. 
         FIG.  6    is a front perspective view of the mixer of  FIG.  5   . 
         FIG.  7    is a Computational Fluid Dynamic (CFD) simulation showing flow streamlines of an exhaust gas through the mixer of  FIG.  6   . 
         FIG.  8    is a front perspective view of a mixer, according to an embodiment. 
         FIG.  9    is a side perspective view of a mixer, according to another embodiment. 
         FIG.  10    is a schematic flow chart of a method for fabricating an aftertreatment system, according to an embodiment. 
     
    
    
     Reference is made to the accompanying drawings throughout the following detailed description. In the drawings, similar symbols typically identify similar components unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure. 
     DETAILED DESCRIPTION 
     Embodiments described herein relate generally to mixers for promoting mixing of reductant with exhaust gas flowing through an aftertreatment system and reduce reductant deposits. In particular, embodiments described herein include a multi-vane mixer that includes a central hub defining a flow channel that is radially offset from a longitudinal axis of an aftertreatment housing, and a reductant injector that inserts reductant at a non-zero angle with respect to the transverse axis of the aftertreatment system and opposite a circumferential direction of rotation of the exhaust gas that is caused by the mixer. 
     Reductant deposits are a significant concern in operation of aftertreatment systems. Reductant deposits can build up in the SCR system or other components of the aftertreatment system and lead to reduction in a SCR catalytic conversion efficiency (CE) of the SCR system and increase backpressure. Various mixers have been used to facilitate mixing of the reductant with the exhaust gas to reduce reductant deposits. Other solutions have used asymmetrically mounted reductant injectors. Such reductant injectors, however can increase the risk of reductant deposit formation at the reductant injector tip due to the presence of flow recirculation in a cavity which the reductant injector is mounted. Moreover, asymmetrically mounted reductant injection typically cannot avoid impingement on the walls of the reductant port (in which the reductant injector is mounted) without increasing the size of this port, when a spray with large cone angle is used. Increasing the size of the reductant port may increase the amount of exhaust assist flow, i.e., flow of exhaust gas through the reductant port in a direction transverse to the main gas flow. This in turn may reduce the impact of interception of spray droplets with exhaust gas streams from the main flow that promotes reductant mixing and reduces reductant deposits, because the larger amount of exhaust gas entering the larger reductant port reduces the amount of main flow and weakens it. 
     In contrast, various embodiments of the mixers for mixing a reductant with an exhaust gas may provide one or more benefits including, for example: (1) delivering highly uniform flow and reductant profile at an inlet of a downstream reductant injector; (2) reducing pressure drop; (3) allowing for dynamic control of spatial distribution of reductant droplets under varying operating conditions; (4) allowing integration of wide reductant spray cone angles; and (5) reduce flow recirculation near a tip of a reductant injector, thereby reducing risk of reductant deposits near a tip of a reductant injector that is symmetrically mounted as well as in the mixer and in a downstream SCR system. 
       FIG.  1    is a schematic illustration of an aftertreatment system  100 , according to an embodiment. The aftertreatment system  100  is configured to receive exhaust gas (e.g., diesel exhaust gas from an engine  10 ) and treat constituents (e.g., particulate matter, NO x , CO, CO 2 ) of the exhaust gas. The aftertreatment system  100  includes a reductant storage tank  110 , a reductant insertion assembly  112 , a mixer  120 , and a SCR system  150 , and may also include an oxidation catalyst  142 , and a filter  144 . 
     The engine  10  may include, for example, a diesel engine, a gasoline engine, a natural gas engine, a dual fuel engine, a biodiesel engine, an E-85 engine, or any other suitable engine. In some embodiments, the engine  10  includes a diesel engine. The engine  10  combusts fuel and generates an exhaust gas that includes NO x , CO, CO 2 , and other constituents. 
     The aftertreatment system  100  includes a housing  101  in which components of the aftertreatment system  100  are disposed. The housing  101  may be formed from a rigid, heat-resistant and corrosion-resistant material, for example, stainless steel, iron, aluminum, metals, ceramics, or any other suitable material. The housing  101  may have any suitable cross-section, for example, circular, square, rectangular, oval, elliptical, polygonal, or any other suitable shape. The housing  101  defines a housing central axis A L . In some embodiments, the housing  101  may have a circular cross-section and the housing central axis A L  is an axis extending longitudinally through a center point of the housing  101  (i.e., a point equidistant from the periphery of the housing  101 ). In other embodiments, in which the housing  101  has a non-circular cross section (e.g., square, rectangular, oval, elliptical, polygonal, or any other suitable cross-section), the housing central axis A L  is an axis extending longitudinally through a geometric center or centroid of the cross-sectional shape defined by the housing  101  (i.e., the arithmetic mean position of all the points in the cross-sectional shape defined by the housing  101 ). 
     An inlet conduit  102  is fluidly coupled to an inlet of the housing  101  and structured to receive exhaust gas from the engine  10  and communicate the exhaust gas to an internal volume defined by the housing  101 . Furthermore, an outlet conduit  104  may be coupled to an outlet of the housing  101  and structured to expel treated exhaust gas into the environment (e.g., treated to remove particulate matter and/or reduce constituents of the exhaust gas such as NO x  gases, CO, unburnt hydrocarbons, etc. included in the exhaust gas produced by the SCR system  150 ). 
     A first sensor  103  may be positioned in the inlet conduit  102 . The first sensor  103  may comprise a NO x  sensor configured to measure an amount of NO x  gases included in the exhaust gas flowing into the SCR system  150  and may include a physical sensor or a virtual sensor. In various embodiments, a temperature sensor, a pressure sensor, an oxygen sensor, or any other sensor may also be positioned in the inlet conduit  102  so as to determine one or more operational parameters of the exhaust gas flowing through the aftertreatment system  100 . 
     A second sensor  105  may be positioned in the outlet conduit  104 . The second sensor  105  may comprise a second NO x  sensor configured to determine an amount of NOx gases expelled into the environment after passing through the SCR system  150 . In other embodiments, the second sensor  105  may comprise a particulate matter sensor configured to determine an amount of particulate matter in the exhaust gas being expelled into the environment. In still other embodiments, the second sensor  105  may comprise an ammonia sensor configured to measure an amount of ammonia in the exhaust gas flowing out of the SCR system  150 , i.e., determine the ammonia slip. This may be used as a measure of a catalytic conversion efficiency of the SCR system  150  for adjusting an amount of reductant to be inserted into the SCR system  150 , and/or adjusting a temperature of the SCR system  150  so as to allow the SCR system  150  to effectively use the ammonia for catalytic decomposition of the NO x  gases included in the exhaust gas flowing therethrough. In some embodiments, an ammonia oxidation (AMOX) catalyst may be positioned downstream of the SCR system  150  so as to decompose any unreacted ammonia in the exhaust gas downstream of the SCR system  150 . 
     The aftertreatment system  100  may include various other components such as an oxidation catalyst  142  (e.g., a diesel oxidation catalyst) positioned upstream of the SCR system  150  and configured to decompose unburnt hydrocarbons and/or CO included in the exhaust gas. In some embodiments, a filter  144  may be disposed downstream of the oxidation catalyst and upstream of the SCR system  150  and configured to remove particulate matter (e.g., soot, debris, inorganic particles, etc.) from the exhaust gas. 
     The SCR system  150  is formulated to decompose constituents of an exhaust gas flowing therethrough in the presence of a reductant, as described herein. In some embodiments, the SCR system  150  may include a selective catalytic reduction filter (SCRF). The SCR system  150  includes a catalyst formulated to catalyze the decomposition of NO x  gases. Any suitable catalyst may be used such as, for example, platinum, palladium, rhodium, cerium, iron, manganese, copper, vanadium based catalyst, any other suitable catalyst, or a combination thereof. The catalyst may be disposed on a suitable substrate such as, for example, a ceramic (e.g., cordierite) or metallic (e.g., kanthal) monolith core which can, for example, define a honeycomb structure. A washcoat can also be used as a carrier material for the SCR system  150 . Such washcoat materials may comprise, for example, aluminum oxide, titanium dioxide, silicon dioxide, any other suitable washcoat material, or a combination thereof. 
     A reductant injector  156  is disposed on the housing  101  upstream of the SCR system  150  and configured to insert a reductant into the exhaust gas flowing through the housing  101 . The reductant injector  156  is mounted symmetrically on a sidewall of the housing  101  such that the reductant injector  156  is mounted in axial alignment with a transverse axis A T  of the housing  101 , for example, in a reductant port defined in the housing  101 , i.e., aligned with a central portion of an exhaust gas flow path of the exhaust gas flowing through the housing  101 . As described herein, the term “transverse axis” implies an axis of the housing  101  that is perpendicular to the housing central axis A L  of the housing  101 . In various embodiments, the reductant injector  156  may comprise a nozzle having predetermined diameter, and configured to insert a spray cone SC of the reductant into the exhaust gas. 
     The reductant storage tank  110  is structured to store a reductant. The reductant is formulated to facilitate decomposition of the constituents of the exhaust gas (e.g., NO x  gases included in the exhaust gas). Any suitable reductant may be used. In some embodiments, the exhaust gas comprises a diesel exhaust gas and the reductant comprises a diesel exhaust fluid. For example, the diesel exhaust fluid may comprise urea, an aqueous solution of urea, or any other fluid that comprises ammonia, by-products, or any other diesel exhaust fluid as is known in the arts (e.g., the diesel exhaust fluid marketed under the name ADBLUE®). For example, the reductant may comprise an aqueous urea solution having a particular ratio of urea to water. In some embodiments, the reductant can comprise an aqueous urea solution including 32.5% by mass of urea and 67.5% by mass of deionized water, including 40% by mass of urea and 60% by mass of deionized water, or any other suitable ratio of urea to deionized water. 
     A reductant insertion assembly  112  is fluidly coupled to the reductant storage tank  110 . The reductant insertion assembly  112  is configured to selectively insert the reductant into the exhaust gas. The reductant insertion assembly  112  may comprise various structures to facilitate receipt of the reductant from the reductant storage tank  110  and delivery to the SCR system  150 , for example, pumps, valves, screens, filters, etc. 
     A mixer  120  is disposed in the housing  101  upstream of the SCR system  150  proximate to the reductant injector  156  and configured to facilitate mixing of the reductant inserted by the reductant injector  156  with the exhaust gas. Referring also now to  FIG.  2   , the mixer  120  includes a hub  122 . In some embodiments, the hub  122  may be solid. In other embodiments, the hub  122  may define a channel to allow a portion of the exhaust gas to flow therethrough. 
     A tubular member  124  is disposed circumferentially around the hub  122 . The tubular member  124  may be cylindrical in shape. The outer tubular member  124  may have a diameter that is smaller than a diameter of the housing  101 . The outer tubular member  124  may have a generally circular cross section and defines a generally linear exhaust flow path. In other embodiments the outer tubular member  124  can have other cross-sectional shapes and the gas flow path through the outer tubular member may be linear or non-linear. For example, the tubular member  124  can have conical, frustoconical, aerodynamic or other shapes. In some embodiment, the tubular member  124  is configured as a venturi body. In such embodiments, the tubular member  124  may have a diameter at an inlet thereof that is larger than an outlet of the tubular member  124 . 
     A plurality of vanes  126  extend from an outer surface of the hub  122  to the tubular member  124  such that openings  127  are defined between adjacent vanes  126  to allow primary streamlines of the exhaust gas to flow therethrough. In some embodiments, the plurality of vanes  126  may include a set of upstream vanes and a set of downstream vanes. The vanes  126  may be inclined at an angle (e.g., in range of 10 degrees to 80 degrees) from the hub to the tubular member  124  so as to cause swirling in the exhaust gas as the exhaust gas flows through the openings  127  in a circumferential direction A with respect to the exhaust gas flow path (e.g., a clock-wise direction). A flange  128  extends radially outwards from a rim of an upstream end of the tubular member  124 . The flange  128  may be secured (e.g., welded, or coupled via screws, nuts, bolts, rivets, etc.) to an inner surface of the housing  101  to mount the mixer  120  in the housing  101 . 
     In some embodiments, the blocking member  125  that blocks or otherwise resists the flow of the exhaust gas extend around a portion of the gas flow path not covered by the portion around which the plurality of vanes  126  extend. In some embodiments in which the mixer  120  includes a set of upstream vanes, the blocking member  125  may be located upstream from the reductant entry port  131  on a side of the mixer  120  where the reductant entry port  131  is located. As shown in  FIG.  2   , the blocking member  125  may include a wall that extends from the hub  122 . In other embodiments, the blocking member  125  may be a component separate from the plurality of vanes  126 . In some embodiments, the vanes  126  of may extend around a portion between 130° and 230° of a circumference of the tubular member  124 . In other embodiments the vanes  126  may extend around a portion between 170° and 190° of the circumference of tubular member  124 . In still other embodiments, the vanes  126  may extend around a portion of about 180° of the circumference of the tubular member  124 . 
     A reductant entry port  131  is defined in the tubular member  124  and configured to allow insertion of the reductant into the exhaust gas flow path of the exhaust gas flowing through the mixer  120 . In some embodiments, the reductant entry port  131  may be defined upstream of the plurality of vanes. In some embodiments in which the mixer  120  includes a set of upstream vanes and a set of downstream vanes, the reductant entry port  131  may be defined between the set of upstream and downstream vanes. The reductant entry port  131  is axially aligned with a central portion of the exhaust gas flow path (e.g., aligned with the transverse axis A T ) and configured to allow insertion of the reductant at a non-zero angle with respect to the central portion opposite the circumferential direction. For example, the reductant injector  156  that is mounted along the transverse axis A T  of the housing  101  is configured to insert a reductant into the exhaust gas through the reductant entry port  131  at a non-zero angle with respect to the transverse axis A T  opposite the circumferential direction in which the exhaust gas swirls. In some embodiments, the tubular member  124  also defines an auxiliary opening  133  proximate to the reductant entry port  131  and is configured to allow an auxiliary stream of exhaust to flow therethrough between the housing  101  and tubular member  124 . The auxiliary stream may further facilitate mixing of the reductant with the exhaust gas and reduce reductant deposits, for example, in the reductant entry port. 
     Reductant spray cones produced by reductant injectors are polydisperse and have a finite width. While spray cone angle (i.e., the angle of spread of the spray cone) is a useful measure of the extent of the spray footprint, another useful metric to assess the degree of dispersion in drop size distribution is the relative span factor (RSF). The RSF is defined as a ratio of a difference between maximum droplet size to minimum droplet size of the reductant to the mean droplet size, and is an indicator of the range of reductant droplet size in the reductant spray relative to mean drop size. A larger RSF indicates a more polydisperse spray. Variations in RSF can impact mixing of the reductant with the exhaust gas. 
     To facilitate mixing of the sprayed reductant inserted by the symmetrically mounted reductant injector  156  that may have a wide range of RSFs, a mixer central axis A M  of the mixer  120  defined through the hub  122  is radially offset with respect to the housing central axis A L  of the housing  101  such that a flow axis of the exhaust gas at a location in the housing  101  that is upstream of the mixer  120  is also offset from the mixer central axis A M . The plurality of openings  127  defined between the plurality of vanes  126 , in addition to causing swirling in the exhaust gas, alter the flow axis of the exhaust gas because of the mixer central axis A M  being offset from the housing central axis A L . The openings  127  direct several primary intercepting exhaust gas streams to selectively alter the trajectory of the reductant spray droplets and to redistribute them. Sprays with various RSF’s can be optimally redistributed by varying the vane angle of the plurality of vanes  126  and/or orientations based on the application. The symmetrically mounted reductant injector  156  reduces flow recirculation proximate to the tip of the reductant injector  156  thereby reducing the risk of reductant deposits and allowing large spray cone angles. 
     In this manner, the mixer  120  provides multistage oblique virtual interception of the reductant droplets by altering the flow axis of the exhaust gas, increasing mixing, and reducing reductant deposits. Virtual interception refers to the ability of the mixer  120  to generate exhaust gas streams that intercept a reductant spray without the use of splash plates or solid devices. Virtual interception selectively alters the trajectory of the reductant droplets and redistributes the reductant droplets. Particularly, the mixer  120  is configured to provide oblique virtual interception because the reductant spray is introduced at a non-zero or oblique angle relative to one or more primary exhaust gas streams produced by the plurality of vanes  126  (as shown in  FIG.  3   ). 
     In some embodiments, as shown in  FIG.  2   , the mixer central axis A M  is horizontally offset from the housing central axis A L  of the housing  101  by a distance x (e.g., in a range of 0 to 20 millimeters). The reductant injector  156  is mounted symmetrically with respect to the transverse axis A T  of the housing  101  and configured to insert reductant at an angle of about 0 degrees with respect to a transverse axis A T  of the housing  101  such that a central axis of the spray cone SC generated by the reductant injector  156  is aligned with the transverse axis A T . 
       FIG.  3    shows a mixer  220  disposed in the housing  101  according to another embodiment. The mixer  220  includes a hub  222 , a tubular member  224 , a plurality of vanes  226 , a blocking member  225 , and a flange  228 , as described with respect to the mixer  120 . However, different from the mixer  120 , a mixer central axis of the mixer  220  is aligned with the housing central axis A L  of the housing  101 , and the reductant injector  156  is configured to insert the reductant at a non-zero angle α, for example, in a range of 5 degrees to 60 degrees with respect to the transverse axis A T  of the housing  101 . 
       FIG.  4    shows the mixer  120  mounted in the housing  101  as described with respect to  FIG.  2   . Different from  FIG.  2   , the reductant injector  156  is configured to insert the reductant at an angle α in a range of 5 degrees to 60 degrees with respect to the transverse axis A T  of the housing  101 . 
       FIG.  5    shows the mixer  120  mounted in the housing  101  such that the mixer central axis A M  of the mixer  120  is also vertically offset from the housing central axis A L  of the housing  101 . For example, the mixer central axis of the mixer  120  may be radially offset from the housing central axis A L  by a distance R (e.g., in a range of 0 to 15 millimeters), and located at an angle β from the transverse axis A T  in a range of 30 degrees to 60 degrees. 
     As previously described herein, in addition to primary intercepting exhaust gas streams due to the portion of the exhaust gas flowing through the openings  127  defined between adjacent vanes  126 , one or more auxiliary exhaust gas streams are obtained because of the portion of the exhaust gas flowing through the auxiliary opening  133  in the tubular member  124 . The momentum from the auxiliary gas stream or streams helps to dynamically assist or oppose momentum of the primary intercepting exhaust gas streams at various spray cone angles and reductant spray cones with different RSFs. For example,  FIG.  6    shows a side perspective view of the mixer  120  mounted in the housing  101  as shown in  FIG.  5   . The reductant entry port  131  is defined in the tubular member  124  to allow reductant to be inserted into the flow path of the exhaust gas flowing through the mixer  120 , and the auxiliary opening  133  is defined proximate to the reductant entry port  131 . 
       FIG.  7    shows flow streamlines of the primary and auxiliary streamlines of the exhaust gas flowing through the mixer  120 . The momentum of the auxiliary streams affects the reductant spray cone and alters the reductant spray trajectory at different degrees under different flow conditions, which allows ability for dynamic control of the reductant spray trajectory and uniformity. Therefore, the one or more auxiliary gas streams can be introduced through auxiliary openings to allow closer dynamic control of the spatial distribution of the reductant spray droplets under different operating conditions. 
     Thus, various combinations of oblique virtual interception of the reductant spray and radial offset of the mixer central axis A M  are possible so as to achieve a desired ratio of exhaust gas to reductant spray momentum. In this manner, optimal spatial distribution of droplets in the exhaust gas can be achieved. All such configurations are contemplated and should be understood as being encompassed by the various embodiments described in this application. 
     In various embodiments, a mixer may be configured to provide a plurality of auxiliary exhaust gas streams. For example,  FIG.  8    shows a front perspective view of a mixer  320 , according to another embodiment. The mixer  320  includes a tubular member  324 , a plurality of vanes  326  including a set of upstream vanes and a set of downstream vanes extending from a hub  322  to the tubular member  324 , a flange  328  extending radially outwards from a rim of an upstream end of the tubular member  324 , and a blocking member  325  coupled to the hub  322  associated with the downstream vanes  326 . A reductant injector is disposed to insert a reductant spray cone SC between the upstream vanes and the downstream vanes  326  of the plurality of vanes  326 . The blocking member  325 , which is located proximate to a location where the spray cone SC is inserted, defines a plurality of throughholes  329  therethrough. A plurality of auxiliary exhaust gas streams is produced by the exhaust gas flowing through the throughholes  329  further facilitating mixing of the reductant with the exhaust gas and reducing reductant deposits. 
       FIG.  9    shows a front perspective view of a mixer  420 , according to another embodiment. The mixer includes a hub  422 , a tubular member  424 , a plurality of vanes  426  extending from the hub  422  to the tubular member  424 , a blocking member  425  also extending from the hub  422  to the tubular member  424 , and a flange  428  extending radially outwards from a rim of an upstream end of the tubular member  424 . A mixer central axis of the mixer  420  may be radially offset from a longitudinal axis of housing in which the mixer  420  is disposed. A reductant entry port  431  is defined in the tubular member  424  upstream of the plurality of vanes  426  through which a spray cone of the reductant is inserted into the flow path of the exhaust gas flowing through the mixer  420 . A slit  429  is defined through a vane  426   a  of the plurality of vanes  426 , which is located distal from the reductant entry port  431 . The slit  429  generates an auxiliary exhaust gas stream in addition to an auxiliary exhaust gas stream produced through the hub  422  so as to facilitate mixing and reduce reductant deposits. While  FIG.  9    shows only one vane  426   a  defining the slit  429 , in other embodiments, more than one vane, for example, 2, 3, 4, or all of the vanes of the plurality of vanes  426 , may define one or more slits therethrough. 
     While the present disclosure describes various mixers, systems and methods described herein may include any of the mixers described in U.S. Pat. Application No. 16/442,014, filed Jun. 14, 2019, the entire disclosure of which is incorporated herein by reference. 
       FIG.  10    is a schematic flow chart of a method  500  for fabricating an aftertreatment system (e.g., the aftertreatment system  100 ), according to an embodiment. The method  500  includes a providing a housing (e.g., the housing  101 ) for the aftertreatment system, at  502 . At  504 , a SCR system (e.g., the SCR system  150 ) is disposed in the housing. At  506 , a mixer (e.g., the mixer  120 ,  220 ,  320 ,  420 ) is disposed in the housing  101  upstream of the SCR system  150 . The mixer includes a hub (e.g., the hub  122 ,  222 ,  322 ,  422 ) and a tubular member (e.g., the tubular member  124 ,  224 ,  324 ,  424 ) disposed circumferentially around the hub and defining a reductant entry port. A plurality of vanes (e.g., the plurality of vanes  126 ,  226 ,  326 ,  426 ) extend from the hub to the tubular member such that openings are defined between adjacent vanes of the plurality of vanes to allow exhaust gas to flow therethrough. The plurality of vanes are configured to swirl the exhaust gas in a circumferential direction with respect to an exhaust gas flow path. The mixer is disposed such that a mixer central axis of the mixer defined through the hub is radially offset with respect to a housing central axis of the housing such that a flow axis of the exhaust gas at a location in the housing that is upstream of the mixer is also offset from the mixer central axis. A reductant injector (e.g., reductant injector  156 ) is disposed on the housing upstream of the SCR system along a transverse axis of the housing, at  508 . The reductant injector is configured to insert a reductant into the exhaust gas flowing through the housing through the reductant entry port at a non-zero angle with respect to the transverse axis opposite the circumferential direction of rotation of the exhaust gas. 
     It should be noted that the term “example” as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples). 
     As used herein, the terms “about” and “approximately” generally mean plus or minus 10% of the stated value. For example, about 0.5 would include 0.45 to 0.55, about 10 would include 9 to 11, about 1000 would include 900 to 1100. 
     The term “coupled” and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. 
     It is important to note that the construction and arrangement of the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements; values of parameters, mounting arrangements; use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Additionally, it should be understood that features from one embodiment disclosed herein may be combined with features of other embodiments disclosed herein as one of ordinary skill in the art would understand. Other substitutions, modifications, changes, and omissions may also be made in the design, operating conditions, and arrangement of the various exemplary embodiments without departing from the scope of the present embodiments. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any embodiments or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular embodiments. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.