Abstract:
An exhaust gas mixer configured to turn exhaust gas including a reluctant into a backward flow is provided. The mixer is further configured to turn the backward flow into a forward flow and direct the exhaust gas into an SCR.

Description:
TECHNICAL FIELD  
       [0001]    The present disclosure relates to exhaust mixing systems, and more particularly to mixing systems for selective catalytic reduction systems. 
       BACKGROUND  
       [0002]    Selective Catalytic Reduction (SCR) systems may be included in an aftertreatment system for a power system to remove or reduce nitrous oxide (NOx or NO) emissions coming from an engine. The SCR systems include the introduction of a reductant to the exhaust stream. Mixers are added to help mix the reductant in the exhaust stream. Thorough mixing may help the performance of the SCR system by improving the reactions and reducing slip or release of the reductant through the SCR system. 
         [0003]    U.S. Patent Publication No. 2006/0191254 (the &#39;254 publn) shows a system for mixing exhaust gas. The &#39;254 publn discloses vanes added downstream of the introduction of ammonia in the exhaust stream and before the SCR. 
       SUMMARY  
       [0004]    In one aspect, the present disclosure provides an exhaust gas mixer including a structure configured to receive an entering flow of exhaust gas and turn it into a backward flow at an angle greater than 90 degrees to the entering flow. In another aspect, the mixer is further configured to turn the backward flow into a forward flow an angle greater than 90 degrees to the backward flow. A reductant may be sprayed into the exhaust gas before entering the mixer and the mixer may direct the exhaust gas to an SCR. 
         [0005]    In yet another aspect, the present disclosure provides a mixer including a housing and internal baffle. The internal baffle may include a front wall located in the path of the exhaust stream to turn the exhaust stream into the backward direction. 
         [0006]    In still another aspect, the present disclosure provides a method of mixing exhaust gas components. The method includes receiving the exhaust stream and turning it in a backward direction that is at an angle greater than 90 degrees to the entering direction. 
         [0007]    Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]      FIG. 1  is a diagrammatic view of a power system including an engine and an aftertreatment system; 
           [0009]      FIG. 2  is a cross-sectional view of an SCR system and a mixer included in the aftertreatment system shown in  FIG. 1 ; 
           [0010]      FIG. 3  is a frontal cross-sectional view of a mixer included in the SCR system shown in  FIG. 2 ; and 
           [0011]      FIG. 4  is an alternative embodiment of a mixer included in the SCR system. 
       
    
    
     DETAILED DESCRIPTION  
       [0012]    As seen in  FIG. 1 , a power system  10  includes an engine  12  and an aftertreatment system  14  to treat an exhaust stream  13  produced by the engine  12 . The engine  12  may include other features not shown, such as fuel systems, air systems, cooling systems, peripheries, drivetrain components, turbochargers, etc. The engine  12  may be any type of engine (internal combustion, gas, diesel, gaseous fuel, natural gas, propane, etc.), may be of any size, with any number of cylinders, and in any configuration (“V,” in-line, radial, etc.). The engine  12  may be used to power any machine or other device, including on-highway trucks or vehicles, off-highway trucks or machines, earth moving equipment, generators, aerospace applications, locomotive applications, marine applications, pumps, stationary equipment, or other engine powered applications. 
         [0013]    The aftertreatment system  14  includes pre-SCR components  16 , an SCR system  18 , post-SCR components  20 , and an exhaust pipe  22 . The exhaust stream  13  exits the engine  12 , passes through the pre-SCR components  16 , then passes through the SCR system  18 , and then passes through the post-SCR components  20  via the exhaust pipe  22 . The pre-SCR and post-SCR components  16  and  20  may include devices such as regeneration devices, heat sources, oxidation catalysts, diesel oxidation catalysts (DOCs), diesel particulate filters (DPFs), additional SCR systems, lean NOx traps (LNTs), mufflers, or other devices needed to treat the exhaust stream  13  before and after the SCR system  18  and before exiting the power system  10 . 
         [0014]    The SCR system  18  includes a reductant system  24 , mixer  26 , and SCR  28 . The reductant system  24  introduces or supplies a reductant  30  into the exhaust stream  13 . The mixer  26  mixes the reductant  30  with the exhaust stream  13  and introduces the mixture to the SCR  28 . The reductant  30  may be urea, ammonia, diesel fuel, or other hydrocarbon used by the SCR  28  to reduce or otherwise remove NOx or NO emissions from the exhaust stream  13 . 
         [0015]      FIG. 2  illustrates a cross-sectional view of the SCR system  18 . The reductant system  24  is shown to include a reductant source  32 , pump  34 , valve  36 , and injector  38 . The reductant source  32  may be a tank, vessel, absorbing material, or other device capable of storing and releasing the reductant  30 . If the reductant  30  used is the same as the fuel used to power the engine  12 , then the reductant  30  may be the engine&#39;s  12  fuel tank. 
         [0016]    The pump  34  is an extraction device capable of pulling the reductant  30  from the reductant source  32 . The valve  36  may be included to help regulate or control the delivery of the reductant  30 . The injector  38  is a device capable of creating a reductant spray  40  or otherwise introducing the reductant  30  in the exhaust stream  13 . 
         [0017]    The reductant system  24  may also include a preliminary mixer or diffuser  42  as needed to aid in mixing of the reductant  30  with the exhaust stream  13 . The diffuser  42  may be any structure to disrupt the flow of the exhaust stream  13  and facilitate dispersion of the reductant  30  into the exhaust stream  13 . The diffuser  42  may include orifices, deflectors, swirlers, baffles, or other structures that disrupt flow of the exhaust stream  13 . 
         [0018]      FIG. 2  also illustrates the mixer  26 . The exhaust pipe  22  is connected to the mixer entrance pipe  44 , extending into an interior  46  of the mixer  26 . A structure  47  of the mixer  26  includes a housing  48  and baffle  50 . Defining the interior  46  is the housing  48 . The baffle  50  is located in the interior  46  of the mixer  26 . 
         [0019]    The housing  48  may include a back wall  52  and outer wall  54 . The mixer entrance pipe  44  enters through a pipe opening  55  in the back wall  52  of the housing  48 . The outer wall  54  extends forward from the periphery of the back wall  52  to meet the SCR  28 . 
         [0020]    The internal baffle  50  may include a front wall  56 , side wall  58 , and openings  59 . The front wall  56  is directly in the path of or in front of the exhaust stream  13  as it enters the mixer  26  through the mixer entrance pipe  44 . The side wall  58  extends rearward from the periphery of the front wall  56 . The openings  59  may be formed as cutouts in the side wall  58  and may be located in a portion of side wall  58  closer to the back wall  52  of the housing  48  than to the front wall  56  of the baffle  50 . The openings  59  may also be a singular opening  59 . The openings  49  may also be formed by the side wall  58  stopping short of the back wall  52 . 
         [0021]    Support structures (not shown) may also be added to support the baffle  50 . The support structures may extend from the end of the side wall  58 , the mixer entrance pipe  44 , or the housing to support the baffle  50 . 
         [0022]    The SCR  28  includes an SCR entrance  60 , SCR body  62 , SCR exit  64 , and SCR housing  66 . The SCR entrance  60  is in fluid communication with the mixer  26  and the SCR body  62 . The SCR housing  66  contains the SCR body  62  and may be coupled to, proximate, or be an extension from the mixer housing outer wall  54 . In alternative embodiments, the SCR  28  may be separated or further downstream from the mixer  26  and not proximate each other. The mixer housing  48 , SCR housing  66 , and other aftertreatment system  14  components may be double walled or include insulation as needed to reduce skin temperatures. 
         [0023]    The SCR body  62  includes a catalyst facilitating the reaction, reduction, or removal of NOx emissions from the exhaust stream  13  as it passes through the SCR  28  in a SCR flow direction  68 . The SCR body  62  may be a honeycomb or other structure made from or coated with an appropriate material. The material may be an oxide, such as vanadium oxide or tungsten oxide, coated on an appropriate substrate, such as titanium dioxide. 
         [0024]    The mixer  26  provides a torturous mixer flow path  70  to the exhaust stream  13  passing through it. The mixer flow path  70  may include multiple flow passages and flow directions, as described below. The exhaust stream  13  enters the mixer  26  in an entering flow direction  72  through the entrance pipe  44  within a entering flow passage  74 . Exiting the entering flow passage  74 , the exhaust stream  13  is directed into the front wall  56  of the baffle  50 , causing the exhaust stream  13  to turn in the first turn flow direction  76  within a first turn passage  78 . The first turn flow direction  76  redirects the exhaust stream  13  backward relative to the entering flow direction  72 . The first turn flow direction  76  may be substantially a 180 degree backward turn. 
         [0025]    Exiting the first turn passage  78 , the exhaust stream  13  follows a backward flow direction  80  in a backward flow passage  82  defined by the mixer entrance pipe  44  and the side wall  58  of the baffle  50 . The backward flow direction  80  may be substantially parallel, but in the reverse direction as the entering flow direction  72 . In alternative embodiments, the backward flow direction  80  may diverge away from or toward the entering flow direction  72 . In the shown embodiment, the first turn flow direction  76  is substantially a 180 degree forward turn. As a result, the backward flow direction  80  travels in a reverse, 180 degree, direction relative to the forward flow direction  90 . 
         [0026]    In alternative embodiments, the first turn flow direction  76  may be more or less than  180  degrees. The first turn flow direction  76  may be any turn greater than 90 degrees to provide the forward flow direction  90  that is opposed to the entering flow direction  72 . As a result, the backward flow direction  80  travels at an angle greater than 90 degrees to the entering flow direction  72 . The backward flow direction  80  may also vary along the backward flow passage&#39;s  82  length. 
         [0027]    Exiting the backward flow passage  82 , the exhaust stream  13  is directed into the back wall  52  of the housing  48  and through the openings  59 , causing the exhaust stream  13  to move in the second turn flow direction  84  within a second turn flow passage  86 . The second turn flow direction  84  redirects the exhaust stream  13  forward relative to the backward flow direction  80  and in the same general direction as the entering flow direction  72 . 
         [0028]    Exiting the second turn flow passage  86 , the exhaust stream  13  follows a forward flow direction  90  in a forward flow passage  92  defined by the side wall  58  of the baffle  50  and the housing  48 . A shown, the forward flow direction  90  may be substantially parallel, but in the reverse direction as the backward flow direction  80 . In alternative embodiments, the forward flow direction  90  may diverge away from or toward the backward flow direction  80 . In the illustrated embodiment, the forward flow direction  90  is in substantially the same direction as the entering flow direction  72 . In alternative embodiments, the forward flow direction  90  may be different from the entering flow direction  72 . In the shown embodiment, the second turn flow direction  84  is substantially a 180 degree forward turn. As a result, the forward flow direction  90  travels in a reverse, 180 degree, direction relative to the backward flow direction  80 . 
         [0029]    In alternative embodiments, the second turn flow direction  84  may be more or less than 180 degrees. The second turn flow direction  84  may be any turn greater than 90 degrees to provide the forward flow direction  90  that is opposed to the backward flow direction  80 . As a result, the forward flow direction  90  travels at an angle greater than 90 degrees to the backward flow direction  80 . The forward flow direction  90  may also vary along the forward flow passage&#39;s  92  length. 
         [0030]    The mixer  26  accordingly creates overlapping flows that may be substantially parallel or may be at angles to one another. For example, the entering flow direction  72  may overlap to at least some extent the backward flow direction  80 . Similarly, the forward flow direction  90  may overlap to at least some extent the backward flow direction  80 . 
         [0031]    Exiting the forward flow passage  92 , the exhaust stream  13  follows an exit flow direction  94  in a exit flow passage  96  defined by the front wall  56  of the baffle  50 , SCR entrance  60 , and the outer wall  54  of the housing  48 . The exit flow passage  96  opens and delivers the exhaust stream  13  to the SCR  28 . The exhaust stream  13  then passes through the SCR  28  in the SCR flow direction  68 . In the illustrated embodiment, the SCR flow direction  68  is in substantially the same direction as the entering flow direction  72 . 
         [0032]    In alternative embodiments, additional structures may be added to make the SCR flow direction  68  different from the entering flow direction  72 , as needed for the application. In yet other embodiments, no forward flow direction  90  or forward flow passage  92  may be included. The backward flow passage  82  or second turn flow passage  86  may open into and deliver the exhaust stream  13  to the SCR  28 . 
         [0033]      FIG. 3  shows the mixer  26  to have a circular cross-section and a cylindrical shape. In alternative embodiments the mixer  26  may have a square, triangular, oval, oblong, rectangular, or other shape. In alternative embodiments the mixer  26  may have a conical, box, or other three-dimensional shape. The shape and size of the mixer  26  may vary depending on size constraints and flow considerations of a given application. The mixer  26  may symmetrically extend around or encompass the entrance pipe  44 , as shown. In alternative embodiments the mixer  26  may extend around only a portion of the entrance pipe  44 , be non-symmetrical, or be skewed to one side or another. 
         [0034]      FIG. 4  shows an alternative embodiment of the baffle  50  that may include a deflector  98  and may also include a rear wall  100 . The deflector  98  may extend at an angle from the periphery of the front wall  56  and extend to the side wall  58 . The deflector  98  may also extend further forward and eliminate the front wall  56  or extend further backward and eliminate the side wall  58 . The rear wall  100  is an extension from the side wall  58 , providing the openings  59  at a distance from the back wall  52  of the housing  48 . 
       INDUSTRIAL APPLICABILITY  
       [0035]    The overlapping forward, backward, and entering flow directions  90 ,  80 , and  72  provide a back and forth tortuous flow path  70  the exhaust stream  13  must follow. The forward, backward, and entering flow directions  90 ,  80 , and  72  may follow substantially opposite directions compared to one another. This flow path  70  may cause mixing of the reductant  30  into the exhaust stream  13 . The first and second turn flow directions  76  and  84  may make the flow path  70  tortuous to cause the mixing of the reductant  30  with the exhaust stream  13 . As a result, the mixer  26  may provide a substantially homogenized dispersion of reductant  30  in the exhaust stream  13  being introduced into the SCR  28 . 
         [0036]    The mixer  26  provides this tortuous flow path  70  over a given mixer length  102 . The mixer length  102  may be defined or determined by the packaging and size constraints of the application. Because of the overlapping flow path  70 , the mixer length  102  may be substantially less than the length of the flow path  70 . The length of the flow path  70  is the straight line length of the flow path  70  through the mixer  26 . In some embodiments, the flow path  70  length may be more than twice as long as the mixer length  102 . It is understood that the ratio of flow path  70  length to mixer length  102  will vary widely depending on the specific design implemented. 
         [0037]    The elongated flow path  70  may provide a longer flow path than would otherwise be possible in a given application. The longer flow path  70  may provide increased mixing time and travel distance for a given mixer length  102 . The increased mixing time and travel distance may provide for the creation of a homogenized dispersion of reductant  30  in the exhaust stream  13 . 
         [0038]    While the above description is directed to the mixing of the reductant  30  used for the SCR  28  into the exhaust stream  13 , it is understood that other applications of the mixer  26  exist. The mixer  26  may be used to mix any exhaust gas components or any liquid flows. 
         [0039]    Although the embodiments of this disclosure as described herein may be incorporated without departing from the scope of the following claims, it will be apparent to those skilled in the art that various modifications and variations can be made. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.