Abstract:
An exhaust system comprises a conical shell having an indentation helically traversing the exhaust passage so as to impart mixing on an engine exhaust gas flowing through an inner passage defined by the conical shell. The indentation may be formed into the conical shell via a stamping process.

Description:
TECHNICAL FIELD 
       [0001]    The present application relates to an exhaust system. 
       BACKGROUND AND SUMMARY 
       [0002]    A technology such as Selective Catalyst Reduction (SCR) may be utilized for NOx reduction and to achieve diesel emissions requirements. In one approach, aqueous urea is sprayed into the exhaust gas stream which subsequently reacts with NOx on the surface of an SCR catalyst, resulting in reduction of engine-out NOx emissions. For improved NOx reduction under some conditions, the liquid urea sprayed into the diesel exhaust is typically atomized and mixed before it reaches the catalyst substrate. 
         [0003]    In one mixing approach, a two-mixer system may be utilized to provide such mixing, where a first element (e.g., an atomizer) of the system redirects the exhaust flow and catches the urea spray for atomization, and a second element (e.g., a twist mixer) aids in mixing the exhaust flow. As an example, the atomizer may include several (e.g., nine) louvers, and the twist mixer may include a helical mixing element which is welded onto a center rod. 
         [0004]    The inventors of the present application have recognized a problem in such previous solutions. First, the atomizer is typically stamped and processed as a round element to fit into the exhaust system, and the numerous louvers add to the weight and cost of the two-mixer system. Second, the mixing element of the twist mixer typically requires separate fabrication. Further, traditional twist mixers may be welding-intensive, in that the center rod and a stiffener bar are welded at the outlet, and the whole assembly is then welded to a conical shell. 
         [0005]    Accordingly, in one example, some of the above issues may be addressed by an exhaust passage comprising an exterior wall having an inwardly-protruding indentation traversing at least once around the exhaust passage in a helical path. The exterior wall then defines an interior passage configured to receive engine exhaust gas and direct the engine exhaust gas via the inwardly-protruding indentation. In this way, by having the indentation structure configured within the wall of the passage, separate elements traditionally welded into mixing devices may be eliminated, such as a mixing element, center rod, and stiffener bar, if desired. The exhaust passage may further include an atomizer of a partial disc shape positioned in the exhaust passage upstream of the portion comprising the inwardly-protruding indentation, which is configured to redirect exhaust flow and catch a fluid spray for atomization. The partial disc shape eliminates the overall circular design (e.g., with a circular perimeter) of traditional atomizers, and may utilize fewer louvers than traditional atomizers, thus reducing the weight and cost of the system. As such, the exhaust passage can achieve good atomization and mixing, at a lower manufacturing cost. 
         [0006]    It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  illustrates an exhaust system for receiving engine exhaust gas. 
           [0008]      FIG. 2  illustrates an isometric view of a portion of the exhaust system of  FIG. 1  in greater detail and drawn approximately to scale. 
           [0009]      FIG. 3  illustrates a side view of the portion of the exhaust system of  FIG. 2  drawn approximately to scale. 
           [0010]      FIG. 4  illustrates an isometric view of another portion of the exhaust system of  FIG. 1  in greater detail and drawn approximately to scale. 
           [0011]      FIG. 5  illustrates a front view of the portion of the exhaust system of  FIG. 4  drawn approximately to scale. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Embodiments of an exhaust passage are disclosed herein. Such an exhaust passage may be utilized for NOx reduction in an exhaust stream, as described in more detail hereafter. Various of the figures are drawn approximately to scale, including  FIGS. 2-5 . 
         [0013]      FIG. 1  illustrates an exhaust system  100  for transporting exhaust gases produced by internal combustion engine  110 . As one non-limiting example, engine  110  includes a diesel engine that produces a mechanical output by combusting a mixture of air and diesel fuel. Alternatively, engine  110  may include other types of engines such as gasoline burning engines, among others. 
         [0014]    Exhaust system  100  may include one or more of the following: an exhaust manifold  120  for receiving exhaust gases produced by one or more cylinders of engine  110 , a mixing region  130  arranged downstream of exhaust manifold  120  for receiving a liquid reductant, a selective catalytic reductant (SCR) catalyst  140  arranged downstream of the mixing region  130 , and a noise suppression device  150  arranged downstream of catalyst  140 . Additionally, exhaust system  100  may include a plurality of exhaust pipes or passages for fluidically coupling the various exhaust system components. For example, as illustrated by  FIG. 1 , exhaust manifold  120  may be fluidically coupled to mixing region  130  by one or more of exhaust passages  162  and  164 . Catalyst  140  may be fluidically coupled to noise suppression device  150  by exhaust passage  166 . Finally, exhaust gases may be permitted to flow from noise suppression device  150  to the surrounding environment via exhaust passage  168 . Note that while not illustrated by  FIG. 1 , exhaust system  100  may include a particulate filter and/or diesel oxidation catalyst arranged upstream or downstream of catalyst  140 . Furthermore, it should be appreciated that exhaust system  100  may include two or more catalysts. 
         [0015]    In some embodiments, mixing region  130  can include a greater cross-sectional area or flow area than upstream exhaust passage  164 . Mixing region  130  may include a first portion  132  and a second portion  134 . The first portion  132  of mixing region  130  may include an injector  136  for selectively injecting a liquid into the exhaust system. As one non-limiting example, the liquid injected by injector  136  may include a liquid reductant  178  such as ammonia or urea. The liquid reductant  178  may be supplied to injector  136  through conduit  174  from a storage tank  176  via an intermediate pump  172 . The second portion  134  of mixing region  130  may be configured to accommodate a change in cross-sectional area or flow area between the first portion  132  and the catalyst  140 . Note that catalyst  140  can include any suitable catalyst for reducing NOx or other products of combustion resulting from the combustion of fuel by engine  110 . 
         [0016]    Note that with regards to vehicle applications, exhaust system  100  may be arranged on the underside of the vehicle chassis. Additionally, it should be appreciated that the exhaust passage may include one or more bends or curves to accommodate a particular vehicle arrangement. Further still, it should be appreciated that in some embodiments, exhaust system  100  may include additional components not illustrated in  FIG. 1  and/or may omit components described herein. 
         [0017]      FIGS. 2 and 3  illustrate a portion of the exhaust passage for receiving engine exhaust gas, namely the second portion  134  of mixing region  130 . At least a portion of second portion  134  comprises an exterior wall  200  having an inwardly-protruding indentation  202 . As described above, the exhaust gas leaving the engine may first pass through a first portion such as first portion  132 , wherein a fluid such as a liquid reductant (e.g., ammonia, urea, etc.) is injected into the exhaust system. As such, inwardly-protruding indentation  202  of second portion  134  then aids in further mixing of the engine exhaust gas before the engine exhaust gas reaches SCR catalyst  140 . In this way, by better mixing the engine exhaust gas, performance of SCR catalyst  140  may be further enhanced, and thus, NOx may be further reduced. 
         [0018]    Exterior wall  200  defines an interior passage  204  configured to receive the engine exhaust gas. As introduced above, inwardly-protruding indentation  202  is configured to redirect the engine exhaust gas, so as to promote mixing. Inwardly-protruding indentation  202  may be configured in a variety of ways. For example, inwardly-protruding indentation  202  may traverse at least once around the exhaust passage in a path  206 . As an example, path  206  may be a coiled path angled with respect to a cross-section  208  of second portion  134 , as indicated at  210 . For example, path  206  may be a helical path around the perimeter of the exhaust passage pipe. Further, in some embodiments, such a helical path may be substantially left-handed so as to promote mixing of the engine exhaust gas in a downstream direction toward SCR catalyst  140 . It should be appreciated that inwardly-protruding indentation  202  which traverses the exhaust passage at least once may in some embodiments traverse the exhaust passage more than once. As an example, in some embodiments, inwardly-protruding indentation  202  may traverse the exhaust passage at least twice. As another example, inwardly-protruding indentation  202  may traverse the exhaust passage several times (e.g., five times). Further, inwardly-protruding indentation  202  may be substantially continuous in some embodiments. However, in some embodiments, inwardly-protruding indentation  202  may be a combination of a plurality of separate indentations that together form the path (e.g., the helical path). 
         [0019]    Inwardly-protruding indentation  202  may have a variety of shapes and structure. As an example, inwardly-protruding indentation  202  may be a trough depressed into exterior wall  200  and wrapping around second portion  134 . Such a trough may have, for example, a semi-circle cross-section, as indicated at  212 . However, it should be appreciated that a semicircular cross-section is just one example shape of many suitable shapes for inwardly-protruding indentation  202 . For example, in some embodiments, inwardly-protruding indentation  202  may have a shape corresponding to a different arc. As yet another example, in some embodiments, inwardly-protruding indentation  202  may have a geometric shape, such that the cross-section is substantially inverted-trapezoidal, for example. 
         [0020]    Due to the inwardly-protruding indentation  202 , interior passage  204  may be referred to as having internally protruding screw-like threads, where the “threads” created by inwardly-protruding indentation  202  redirect incoming engine exhaust gas by imparting rotational motion about the axis of the exhaust passage, thus promoting mixing. As an example, engine exhaust gas may enter the second portion  134  with a first amount of rotational motion, which may be relatively little or none; however, upon impacting inwardly-protruding indentation  202 , additional rotational motion may be imparted into the flow. In this way, second portion  134  may be configured as a twist mixing device. As described above, the cross-sectional shape of inwardly-protruding indentation  202  may be a variety of shapes. For example, the “threadform” of the “thread” may be a variety of shapes, such as an arc, square, triangle, trapezoid, etc. 
         [0021]    Inwardly-protruding indentation  202  may be further parameterized as follows. The depth of the protrusion into the interior of the exhaust passage (e.g., thread depth  214 ) may be selected to be less than approximately 20% of the diameter of the exhaust passage at which the thread is located. In this way, reduced backpressure may be provided. Also, the relative width of the thread to the depth of the thread may be selected to be substantially a ratio of within about 10% of 3:1. Further, the distance from the trough of one thread to the next (e.g., thread pitch  216 ) may be approximately 40% (+−10%) of the diameter of the exhaust passage at which the thread is located. The diameter in between the largest diameter of a thread and the smallest diameter of the thread (pitch diameter) may be approximately 85% (+−10%) of the largest diameter of the thread. Further still, in some embodiments, an integer number of threads may be provided, such that the beginning portion  218  and the ending portion  220  of inwardly-protruding indentation  202  occur at substantially a same location on second portion  134  with respect to an axis of second portion  134 . 
         [0022]    Moreover, in addition to the shape of inwardly-protruding indentation  202  as indicated at  212 , rounded transitions such as indicated at  222  and  224  may be utilized to smoothly transition the surface of the exterior wall  200  to inwardly-protruding indentation  202 . Further, the beginning portion  218  and the ending portion  220  of inwardly-protruding indentation  202  may be tapered so as to smoothly transition the surface of the exterior wall  200  to inwardly-protruding indentation  202 . Accordingly, such smooth transitions allow for an interior surface of interior passage  204  to likewise smoothly transition into inwardly-protruding indentation  202 . 
         [0023]    Further, second portion  134  may be substantially tapered inward in an upstream direction. This may include the exterior walls  200  of the second portion  134  tapering inward so that the cross-sectional area of the passage becomes larger in the direction of exhaust flow. Said another way, second portion  134  may be tapered such that the diameter of the passage becomes larger in the direction of exhaust flow. As an example, in some embodiments, second portion  134  may be a conical shell. In such a case, exterior wall  200  has a given thickness so as to form the shell. As such, inwardly-protruding indentation  202  protruding into exterior wall  200  protrudes into the shell, and thus redirects air of the interior passage  204 . As an example, inwardly-protruding indentation  202  may be stamped into the conical shell (e.g., by stamping flutes into the conical shell). Further, the conical shell can be broken up into a first portion and a second portion (e.g., a lower piece and an upper piece) to ease the manufacturing and assembly process. 
         [0024]    Unlike traditional twist mixers which require fabrication of a separate mixing element which is then welded on to a center rod and a stiffener bar at the outlet, wherein the whole assembly is then welded to the conical shell, second portion  134  comprises a conical shell with inwardly-protruding indentation  202 . In this way, second portion  134  as described herein allows for the separate mixing element of traditional twist mixers to be eliminated, as well as the center rod, stiffener bar and associated welding, if desired. 
         [0025]    In addition to mixing the engine exhaust gas before it reaches the catalyst, it may be further beneficial to atomize the exhaust prior to such mixing. As such, mixing region  130  may further include an atomizer positioned in the exhaust passage upstream of inwardly-protruding indentation  202  and downstream of injector  136 .  FIGS. 4 and 5  illustrate an example of such an atomizer  400  having a non-circular perimeter. Atomizer  400  may comprise louvers configured to redirect the engine exhaust gas and catch a fluid spray, for example from injector  136 , for atomization. In one embodiment, atomizer  400  comprises exactly three louvers, as depicted in  FIGS. 4 and 5 . 
         [0026]    In some embodiments, each of the louvers may be configured substantially differently. For example, each of the three louvers may have a different depth. In the depicted example, a first louver  402  of the three louvers may have a smaller depth  404  than a depth  406  of an adjacent second louver  408 . Likewise, second louver  408  may have a smaller depth  406  than a depth  410  of adjacent third louver  412 . As another example, each of the three louvers may be optionally positioned at a different angle. As yet another example, the three louvers may be nonuniformly spaced apart. 
         [0027]    As further depicted, atomizer  400  may have a partial disc shape. As such, when positioned in the exhaust passage upstream of the inwardly-protruding indentation  202 , (e.g., upstream of the twist mixing device comprising the trough), the partial disc shape defines a free region  414  above the atomizer and a free region  416  below the atomizer, through which the engine exhaust gas can flow unobstructedly. 
         [0028]    Atomizer  400  may be positioned within mixing region  130  upstream of inwardly-protruding indentation  202 , for example, adjacent to a narrower end of the conical shell. As such, a width  418  of atomizer  400  may be substantially the same as a diameter of the narrower end of the conical shell, such that exhaust gas may pass through atomizer  400  into interior passage  204 . In some embodiments, atomizer  400  may be positioned within second portion  134 , such as within region  226  as indicated in  FIG. 2 . However, in some embodiments, atomizer  400  may be positioned within first portion  132  of mixing region  130 , so as to be located directly adjacent to the narrower end of the conical shell, such as within region  228 . 
         [0029]    Thus, whereas traditional atomizers typically have nine louvers, and are stamped and processed as a round element to fit into the exhaust system, atomizer  400  of a partial disc shape uses three louvers. In this way, by eliminating the circular design and additional louvers, the weight of atomizer  400  is reduced in comparison to traditional atomizers, and thus, the cost of the system may also be reduced. 
         [0030]    Thus, the partial disc shape allows for atomization to still be achieved, yet with a reduced impact to weight and cost. This is because the configuration allows for louvers to be positioned in the region where engine exhaust gas typically receives the majority of the fluid spray. In this way, the louvers can then redirect a majority of the engine exhaust gas, whereas a minority of the engine exhaust gas may flow unobstructedly through the free regions  414  and  416  above and below the atomizer respectively. This minority amount of the engine exhaust gas flowing unobstructedly through the free regions  414  and  416  is offset by the cost and weight savings achieved by atomizer  400 . Further, exhaust back pressure effects can be reduced. 
         [0031]    In this way, exhaust system  100  can achieve good atomization and mixing, while allowing for manufacturing costs and time to be significantly reduced. For example, in comparison to traditional exhaust systems, exhaust system  100  comprising atomizer  400  and a second portion  134  with inwardly-protruding indentation  202  (e.g., a twist mixing device) may reduce process time and assembly time (e.g., by approximately 10% and 20%, respectively) in comparison to that of traditional mixing devices. Further, exhaust system  100  may significantly reduce weight, cost and tooling (e.g., by approximately 50%) in comparison to that of traditional mixing devices. 
         [0032]    Note that the example control and estimation routines included herein can be used with various engine and/or vehicle system configurations. The specific routines described herein may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various acts, operations, or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the features and advantages of the example embodiments described herein, but is provided for ease of illustration and description. One or more of the illustrated acts or functions may be repeatedly performed depending on the particular strategy being used. Further, the described acts may graphically represent code to be programmed into the computer readable storage medium in the engine control system. 
         [0033]    It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. For example, the above technology can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine types. The subject matter of the present disclosure includes all novel and nonobvious combinations and subcombinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein. 
         [0034]    The following claims particularly point out certain combinations and subcombinations regarded as novel and nonobvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. 
         [0035]    Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.