GB2550173A

GB2550173A - Mixer for after-treatment system

Info

Publication number: GB2550173A
Application number: GB1608275.2A
Authority: GB
Inventors: Tummala Srikanth; Dimopoulos Athanasios
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2016-05-11
Filing date: 2016-05-11
Publication date: 2017-11-15
Also published as: GB201608275D0

Abstract

A mixer 128, eg a swirl mixer, for an engine after-treatment system 102 includes a cylindrical enclosure 130. A number of blades 142 are arranged at regular intervals around the inner periphery 144 of the cylindrical enclosure 130. The blades 142 extend radially towards a central axis 146 of the cylindrical enclosure 130. Each blade 142 is twisted or bent about its longitudinal axis 150. The mixer 128 may be a unitary component formed from sheet metal. The mixer may be provided between a diesel particulate filter (DPF, 106, fig.1) and a selective catalytic reduction (SCR) unit (108).

Description

Mixer for After-treatment Systems

Technical Field [0001] The present disclosure relates to the field of after-treatment systems in machines. More particularly, the present disclosure relates to a swirl mixer in after-treatment systems that facilitates mixing of exhaust gases with a reductant.

Background [0002] Exhaust after-treatment systems in engines are known to use selective catalytic reduction (SCR) modules to convert nitrogen oxides (NOx) of exhaust gas into a less harmful constituent. Exhaust after-treatment systems typically include a conduit with a mixing chamber that receives a flow of exhaust gas. A reductant, such as urea aqueous solution, is injected into the mixing chamber to mix with the inflowing exhaust gas. A heat of the exhaust gas may thermally decompose the reductant to produce ammonia. This ammonia is used as a reductant for NOx in the SCR modules.

[0003] A thorough mixing of ammonia and exhaust gas is desirable to improve a reaction between ammonia and NOx, and thereby reduce NOx emissions and prevent a release of reactive ammonia into the atmosphere. If the reductant is insufficiently mixed with the exhaust gas, a portion of the reductant may be lost, such as by adherence to an inner wall of the conduit, in turn causing a possible shortage of ammonia in the SCR modules. As a result, the associated reductant injection process may be unable to achieve NOx conversion targets.

[0004] Mixing devices such as swirl mixers are known to facilitate mixing of the reductant with the exhaust gases in the mixing chamber. Such mixing devices include surfaces that interact with an incoming flow, such as of a reductant-exhaust gas mixture, so that said mixture may further mix with each other. However, surfaces of such mixers are shaped in a manner that may cause the inflowing reductant-exhaust gas mixture to impact against said surfaces, generating a backflow pressure against the exhaust gas’ regular flow. Such a phenomenon may affect a mixing efficiency and an overall treatment of the exhaust gas. Therefore, room remains to further improve upon mixer designs.

[0005] US Patent No. 8,511,076 discloses a mixing system for an exhaust system that facilitates reduced deflection and flow resistance to a flow of exhaust gas through a set of blades of the mixing system.

Summary of the Invention [0006] Various aspects of the present disclosure disclose a mixer for an engine after-treatment system. The mixer includes a substantially cylindrical enclosure. Further, a number of blades are arranged at regular intervals along an inner periphery of the substantially cylindrical enclosure. The blades radially extend towards a central axis of the substantially cylindrical enclosure. In addition, each blade defines a longitudinal axis and is twisted about the longitudinal axis.

[0007] Certain aspects of the present disclosure disclose an after-treatment system for an engine. The after-treatment system includes a conduit configured to receive a flow of exhaust gas from the engine. A reductant injector is configured to inject a reductant into the conduit. Further, a mixer is positioned within the conduit, downstream of the injector. The mixer includes a substantially cylindrical enclosure with a number of blades arranged at regular intervals along an inner periphery of the substantially cylindrical enclosure. The blades radially extend towards a central axis of the substantially cylindrical enclosure. In addition, each blade also defines a longitudinal axis, and is twisted about the longitudinal axis.

Brief Description of the Drawings [0008] FIG. 1 is a schematic view of an exemplary after-treatment system with a sectioned cutout that depicts a first reductant mixing section and a second reductant mixing section of the after-treatment system, in accordance with the concepts of the present disclosure; [0009] FIG. 2 is an enlarged perspective view of a mixer applied within the second reductant mixing section of FIG. 1, in accordance with the concepts of the present disclosure; [0010] FIG. 3 is an end view of the mixer of FIG. 2, in accordance with the concepts of the present disclosure; [0011] FIG. 4 is a profile of a blade of the mixer of FIG. 2, in accordance with the concepts of the present disclosure; [0012] FIG. 5 is a side view of the mixer of FIG. 2, in accordance with the concepts of the present disclosure; [0013] FIG. 6 is an embodiment of the mixer of FIG. 2, in accordance with an embodiment of the present disclosure; [0014] FIG. 7 is an end view of the embodiment of the mixer of FIG. 6, in accordance with the concepts of the present disclosure; [0015] FIG. 8 is another embodiment of the mixer of FIG. 2, in accordance with the concepts of the present disclosure; and [0016] FIG. 9 is an end view of the embodiment of the mixer of FIG. 8, in accordance with the concepts of the present disclosure.

Detailed Description [0017] Referring to FIG. 1, there is shown a representation of an engine system 100 in conjunction with an engine after-treatment system 102 (referred to as after-treatment system 102 for ease of reference). The engine system includes an internal combustion engine, referred to as an engine 104. The engine 104 may have a multi-cylinder engine configuration. The engine 104 may be applicable in machines, such as including general heavy machineries and conventional mobile equipment. General heavy machineries and conventional mobile equipment may include, but not limited to, off-highway trucks, mining trucks, skid steer loaders, wheel loaders, track type tractors, excavators, dozers, wheel loaders, etc. The present disclosure also envisions an extended application of the engine 104 to stationary machines, such as power generation systems and other electric power generating machines. Although the present disclosure contemplates employment of a multi-cylinder diesel engine, an equivalent application of the aspects of the present disclosure may be directed to other engine types as well.

[0018] The after-treatment system 102 is applied for treating exhaust gases of the engine 104. The after-treatment system 102 includes a Diesel Particulate Filter (DPF) 106 and a Selective Catalyst Reduction Module (referred to as SCR module 108) that facilitate treatment of exhaust gases of the engine 104, prior to an emission of the exhaust gases into an environment 110. An exhaust conduit, or simply a conduit 112, is fluidly connected between the DPF 106 and the SCR module 108. The conduit 112 facilitates accommodation of a number of reductant injectors 116 that facilitate injection of a reductant into a mixing chamber 118 defined within the conduit 112. Reductant injectors 116 may be referred to as injectors 116, for ease in reference, hereinafter.

[0019] The DPF 106 may be selected from one of widely available DPFs in the art. The DPF 106 is fluidly connected to an exhaust port 120 of the engine 104 to receive exhaust gas from the engine 104 in a raw, untreated state. Upon reception of the exhaust gas, the DPF 106 is configured to filter or separate soot or diesel particulate matter from the inflowing exhaust gas.

[0020] The SCR module 108 is fluidly connected downstream to the DPF 106 to receive exhaust gases from the DPF 106. The SCR module 108 includes a catalyst, such as titanium oxide, and other active catalytic components of oxides of base metals to convert nitrogen oxides in the exhaust gases into diatomic nitrogen and water. Base metals may include, but are not limited to, vanadium, molybdenum, and/or tungsten. As with the DPF 106, the SCR module 108 may also be chosen from among the widely known SCR modules in the art.

[0021] The conduit 112 is fluidly connected between the DPF 106 and the SCR module 108, as aforementioned. The conduit 112 is positioned downstream to the DPF 106, along an exhaust gas flow direction, A. The conduit 112 includes the mixing chamber 118 that receives the exhaust gas from the DPF 106 and an amount of the reductant from the injectors 116. The mixing chamber 118 facilitates mixing of the exhaust gas with the reductant, and a delivery of a subsequently formed reductant-exhaust gas mixture to the SCR module 108, for further treatment. The mixing chamber 118 generally embodies an enclosed space or a mixing space, and may be shaped and structured as conventionally known. The mixing chamber 118 includes a first reductant mixing section 122 and a second reductant mixing section 124 (discussed later).

[0022] The injectors 116 are arranged on the conduit 112, such as along a length of the conduit 112, as shown. The injectors 116 are configured to inject a predetermined quantity of the reductant into the mixing chamber 118. To this end, the injectors 116 are adapted to receive the reductant, such as a Diesel Emission Fluid (DEF), which is inclusive of anhydrous ammonia, aqueous ammonia, urea aqueous solution, or urea, from a fluid reductant tank (not shown). In general, the injectors 116 may receive a continuous supply of the reductant from the fluid reductant tank. However, each injector 116 among the injectors 116 may alternatively include a dedicated DEF supply line to receive DEF, although a common rail may be provided to equalize a pressure of DEF injection into the mixing chamber 118. A DEF supply may be facilitated by a DEF pump.

[0023] The injectors 116 may be applicable for installation into generic multicylinder engine configurations, and may be one or more in number. However, the number of injectors 116 may vary depending upon an engine size as emissions from larger engines may require additional quantities of DEF to neutralize constituents of the filtered exhaust gas. As the depicted embodiment pertains to a relatively large-scale engine, four injectors 116 are exemplarily included. Nevertheless, a variation in the number of injectors 116 may be contemplated. Correspondingly, the conduit 112 includes provisions for accommodating the injectors 116. In an embodiment, the injectors 116 are threadably engaged with the conduit 112, although other engagement measures, such as those attained by a luer-lock fastening, clipped fastening, etc., are possible.

[0024] The injectors 116 are configured to inject the reductant into the mixing chamber 118 periodically or according to preset injection pattern. A reductant injection may be such that a fine atomized spray of DEF is introduced into the mixing chamber 118 to facilitate an effective mix of the DEF with an incoming exhaust gas. In an embodiment, the injectors 116 may be positioned at an incline to the mixing chamber 118 so as to inject the DEF at an angle to the flow of exhaust gas. An angled injection of reductant may facilitate an appropriate mixing of the reductant with the exhaust gas. An ensuing thorough mix of the atomized DEF spray with the exhaust gas facilitates lowering of the concentration of nitrogen oxides of the exhaust gas. An area where the reductant is first introduced within the mixing chamber 118, and perhaps an immediate vicinity into which a diffusion of the reductant naturally propagates after injection, represents the first reductant mixing section 122 of the mixing chamber 118.

[0025] The second reductant mixing section 124 is defined downstream to the first reductant mixing section 122. The second reductant mixing section 124 includes a swirl mixer 128 (interchangeably referred to as a mixer 128, for ease in reference, hereinafter). The mixer 128 is positioned within the conduit 112 and is configured to receive the reductant-exhaust gas mixture from the first reductant mixing section 122. The mixer 128 facilitates the inflowing reductant-exhaust gas mixture to be swirled and turned, so as to further mix the reductant with the exhaust gas and attain an improved level of a mixture uniformity index between the reductant and the exhaust gas.

[0026] The mixer 128 is generally circular in construction and includes a substantially cylindrical enclosure (termed simply as an enclosure 130 for ease of reference). It is however possible that the mixer 128 embodies an alternate construction, such as having an elliptical construction or a rectangular construction. The enclosure 130 is shaped as a shell with a first axial end 132 and a second axial end 134 (best shown in FIG. 2). The enclosure 130 may resemble a metallic casing having a hollow passage defined across the first axial end 132 and the second axial end 134. The hollow passage facilitates the inflowing reductant-exhaust gas mixture to flow past the mixer 128 and enter the SCR module 108 positioned further downstream to the mixer 128. The mixer 128 may be positioned such that the second axial end 134 receives the exhaust gas from the first reductant mixing section 122, while the first axial end 132 sustains an exhaust gas release into the SCR module 108. Further, an outer periphery 138 of the mixer 128 may comply with inner confines of the conduit 112 so as to adhere to an inner wall 140 of the conduit 112. In that way, the mixer 128 is properly assembled within the conduit 112. In an embodiment, the conduit 112, or at least a portion of the conduit 112 that surrounds the second reductant mixing section 124, embodies a cylindrical shape to comply with a shape of the mixer’s enclosure 130. The mixer 128 may be assembled to the inner wall 140 of the conduit 112 by conventional fastening means, such as those involving threaded fasteners, etc.

[0027] Referring to FIG. 2 and 3, the mixer 128 is shown in detail, with a surrounding assembly around the mixer 128 removed to better depict the structural configurations, features, and contours of the mixer 128. The mixer 128 includes a number of blades 142a, 142b, 142c, 142d, 142e, 142f, 142g, and 142h, that are arranged at the first axial end 132 of the mixer 128. Since the blades 142a, 142b, 142c, 142d, 142e, 142f, 142g, and 142h, have a common profile and design, the blades 142a, 142b, 142c, 142d, 142e, 142f, 142g, and 142h, will be collectively referred to as blades 142. Therefore, details pertaining to the blades 142a, 142b, 142c, 142d, 142e, 142f, 142g, and 142h, may be discussed further by referencing a singular blade (blade 142) alone. It will be understood that details discussed by referencing the blade 142 is applicable for each of the blades 142a, 142b, 142c, 142d, 142e, 142f, 142g, and 142h. The blades 142 are positioned at regular intervals along an inner periphery 144 of the enclosure 130. More particularly, the blades 142 are bent from the inner periphery 144 and radially extend towards a central axis 146 of the enclosure 130, as shown. Further, blades 142 define respective longitudinal axes 150a, 150b, 150c, 150d, 150e, 150f, 150g, and 150h. As with referencing the blades as blades 142, the longitudinal axes 150a, 150b, 150c, 150d, 150e, 150f, 150g, and 150h may also be collectively referenced as longitudinal axes 150, or a singular axis may be referenced as longitudinal axis 150, for ease in reference.

[0028] Referring to FIGS. 2, 3, and 4, a profile and structural details of the blade 142 is shown. The blade 142 includes a first edge 152 and a second edge 154 (FIG. 4). The first edge 152 is coupled to the enclosure 130 at the inner periphery 144. The second edge 154 is an end of the blade 142 defined towards the central axis 146 (FIG. 2) of the enclosure 130. The blade 142 is twisted by having the second edge 154 twisted or rotated relative to the first edge 152 about the longitudinal axis 150 (best shown in FIG. 4). Moreover, the second edge 154 of the blade 142 is positioned at a distance from the central axis 146 (best visualized in FIGS. 2 and 3). In that manner, blades 142 of the enclosure 130 cumulatively define a gap 156 (FIG. 3) around the central axis 146 of the enclosure 130. Although not limited, this gap 156 is circular in shape. In an embodiment, second edges 154 of the blades 142 may cumulatively define other shapes around the central axis 146 as well, such as a rectangular shape, a polygonal shape, an irregular shape, or any other shape that depends on the way in which the blades 142 are formed, such as during a manufacturing process.

[0029] Referring to FIG. 4, the blade 142 may include a number of additional features that are characteristic to attain a turned and swirled motion of the reductant-exhaust gas mixture, across the mixer 128 (i.e. from the second axial end 134 to the first axial end 132). More particularly, the blade 142 may be broadly categorized into having a first segment 158 and a second segment 160 (FIG. 4). The first segment 158 may correspond to a blade portion disposed in closer proximity to the inner periphery 144 of the enclosure 130, while the second segment 160 may be identified as being a blade portion disposed distally to the inner periphery 144, adjacent to the gap 156 (FIG. 3) around the central axis 146 of the enclosure 130. More particularly, the second segment 160 is of a predetermined length that terminates at an end (or the second edge 154) that is distanced from the central axis 146 of the enclosure 130 to define the gap 156. Moreover, the end (or the second edge 154) terminates at a fixed radius with respect to the central axis 146 of the enclosure 130. The first segment 158 is integrally and contiguously joined to the second segment 160 via a joining portion 162. The joining portion 162 is defined such that the first segment 158 is seamlessly merged with the second segment 160, imparting curvature continuity between a surface of the first segment 158 and a surface of the second segment 160. Both the first segment 158 and the second segment 160 are substantially planar, defining a first plane 166 and a second plane 168, respectively. Further, the first segment 158 and the second segment 160 are defined such that the first plane 166 is offset from the second plane 168.

[0030] Referring to FIG. 5, owing to the twisted configuration between the first segment 158 and the second segment 160 about the longitudinal axis 150, the offset may be envisioned to be an angular variation (Θ) between the first edge 152 and the second edge 154 that attunes to an exemplary prescribed limit of 45 degrees. Variations to this prescribed limit are possible, and which may depend upon an extent of mixing required between the exhaust gas and the reductant. As an example, a higher degree of mixing requirement between the reductant and the exhaust gas, such as in large-scale engine applications, may correspond to an increase in the angular offset from the prescribed angular limit. Conversely, a reduced mixing requirement may correspond to a lessened angle of twist than the prescribed angular limit. In an exemplary embodiment, an angular range between the first edge 152 and the second edge 154 may take a value in a range between 40 degrees to 50 degrees. In an embodiment, the angle between the first edge 152 and the second edge 154 may be based on a size of the conduit 112. For example, a conduit with an increased diameter may require the blades 142 to include an angle which is higher than 45 degrees. Conversely, smaller diameter conduits may require the blades 142 to define an angle lower than 45 degrees. Further, radial extensions of the blade 142 towards the central axis 146 is such that the plane of the first segment 158 (i.e. the first plane 166) is perpendicular to a tangent 170 formed relative to a radius of the inner periphery 144 of the enclosure 130 at a point 172 where the blade 142 meets the inner periphery 144. Therefore, the longitudinal axis 150 (and a general extension of the blade 142) may be defined at right angles with said tangent 170.

[0031] Referring to FIG. 5, a side view of the mixer is shown. The mixer is shown to include a peripheral wall 174 that forms the enclosure 130. The peripheral wall 174 imparts the mixer 128 with a width, W. The blades 142 are arranged on the enclosure 130 such that the first plane 166 of the first segment 158 extends across the width, W, of the mixer 128, from the first axial end 132 towards the second axial end 134. In the depicted embodiment, the first plane 166 also extends generally angularly to the width, W. Therefore, it may be envisioned that the first edge 152, from where the blade 142 is bent to the peripheral wall 174 (or the outer periphery 138), is also at least partially extended (such as up to a midway) across the width, W, while also being angularly defined in relation to the width, W.

[0032] In an embodiment, the enclosure 130 and the blades 142 are integrally formed, and thus the mixer 128 may be construed as being a unitary component. To this end, the mixer 128 may be manufactured from a single piece of sheet metal. An exemplary manufacturing process may include cutting the sheet metal into an elongated strip. Thereafter, a number of spaced cuts may be formed on the elongated strip, such as by conventional shearing or stamping operation. In an embodiment, the number of spaced cuts depend upon the number of blades 142 required. Next, the elongated strip may be bent and rolled into a shell, such as having a circular cross-section, and be fastened by welding at a weld line 178 (see example in FIG. 6), to form the enclosure 130. Subsequently, each of the blades 142 may be bent from the enclosure 130 at the first edge 152 of the inner periphery 144 so as to be radially directed towards the central axis 146 of the enclosure 130. Finally, the blades 142 may be twisted along the longitudinal axis 150 of the blades 142, such as by twisting the second edge 154 relative to the first edge 152, to form the mixer 128. A specialized function of twisting the blades 142 may be possible by way of special purpose machines (SPMs) that are customized for the development of such mixer designs.

[0033] Referring to FIG. 6, 7, 8, and 9, embodiments of the mixer 128 is shown. The embodiments are marked as mixer 628 (FIGS. 6 and 7) and mixer 828 (FIGS. 8 and 9). The mixers 628, 828 are generally similar in overall form and function to the mixer 128. However, the mixers 628, 828 differ from the mixer 128 in terms of mixer arrangement, blade architecture, and enclosure configuration, as will be elaborated further below.

[0034] Referring to FIGS. 6 and 7, aspects of the mixer 628 will be discussed. As with the mixer 128, the mixer 628 includes a substantially cylindrical enclosure (or simply an enclosure 630) that includes blades 642a, 642b, 642c, 642d, 642e, and 642f, defined at regular intervals from an inner periphery 644 of the enclosure 630. Similar to the discussion of the blade 142, a forthcoming description of the blades 642a, 642b, 642c, 642d, 642e, and 642f, of the mixer 628 will be restricted to a representative blade (blade 642) alone, for ease in understanding and reference. Nonetheless, aspects discussed for the blade 642 will be equivalently applicable for each of the blades 642a, 642b, 642c, 642d, 642e, and 642f, of the mixer 628.

[0035] Similar to the mixer 128, the mixer 628 includes a first axial end 632 and a second axial end 634. Blades 642 are formed at the first axial end 632. However, an arrangement of the mixer 628 within the conduit 112 may be visualized such that the first axial end 632 receives the reductant-exhaust gas mixture from the first reductant mixing section 122, while the second axial end 634 allows a release of said mixture to the SCR module 108 for further treatment.

[0036] The blade 642 possesses a first bend defined at a first edge 652 relative to the inner periphery 644 of the enclosure 630. In contrast to the structure of the mixer 128, the first edge 652 of the blade 642 is defined at an angle varied from the angular deployment of the first edge 152 relative to the enclosure 130 (FIG. 5). More particularly, the first edge 652 is defined parallel to a central axis 646 (or a width, Wi) of the enclosure 630 of the mixer 128. In that way, the blade 642 refrains from interfering with an overall curvature of the enclosure 630, which may otherwise weaken or depart from an intended cylindrical structure of the enclosure 630. As with the blade 142, the blade 642 also includes a first segment 658, a second segment 660, and defines a longitudinal axis 650 (only a single longitudinal axis is shown for clarity). Although the first segment 658 and the second segment 660 is shown for a single blade 642f alone, blade 642f will be referred to as blade 642 so as to represent each of blades 642a, 642b, 642c, 642d, 642e, and 642f. The blade 642 is formed by having the first segment 658 bent radially inwards from the inner periphery 644 towards the central axis 646 of the enclosure 630 and the second segment 660 bent from the first segment 658. More particularly, the blade 642 is twisted along the longitudinal axis 650, such that the longitudinal axis 650 forms a bend line between the first segment 658 and the second segment 660. As with the blade 142, the blade 642 also includes a joining portion 662 to seamlessly integrate the first segment 658 and the second segment 660. The joining portion 662 may be defined as a radial or a second bend of the blade 642 extended towards the central axis 646 of the enclosure 630.

[0037] The first segment 658 and the second segment 660 are substantially planar portions of the blade 642, defining a first plane 666 and a second plane 668, respectively. Alike the configuration of the mixer 128, the first plane 666 of the first segment 658 is substantially perpendicular to a tangent 670 (FIG. 7) of a radius of the inner periphery 644 of the enclosure 630 at a point 672 where the blade 642 meets the inner periphery 644. The second segment 660 may be bent from the first segment 658 such that the first plane 666 is angularly offset (θ’, see FIG. 6) from the second plane 668 at a prescribed limit of 45 degrees, for example. Variations of this angular offset may be contemplated based on mixing requirements between the exhaust gas and the reductant, as aforementioned. As an example, a generally larger angle between the first plane 666 and the second plane 668 may be contemplated for improved mixing such as for large-scale engine applications, while a lesser angular offset between the first plane 666 and the second plane 668 may be contemplated for reduced mixing requirements. As with the structural aspects of the blades 142 of the mixer 128, in an exemplary embodiment, an angular range between the first segment 658 and the second segment 660 may also take a value in a range between 40 degrees to 50 degrees.

[0038] Referring to FIG. 7, an end view of the mixer 628 is depicted. From the end view (such as from the first axial end 632) of the enclosure 630, the first segment 658 is hidden behind the second segment 660 and is hardly construable. This is because the first edge 652 along with the first segment 658 assumes a parallel deployment in relation to the width, Wi, of the mixer 628. Therefore, the first segment 658 may have substantially negligible impact on a reductant-exhaust gas mixture flowing axially across the mixer 628. However, since the second segment 660 is twisted (or bent) from the first segment 658, a surface of the second segment 660 forms a characteristic profile that shapes or determines a flow of the reductant-exhaust gas mixture flowing across the mixer 628. The second segment 660 is generally triangular shaped with a base 690 of the triangle being positioned adjacent to the inner periphery 644, and a vertex portion 692 of the triangle being positioned closer to the central axis 646 of the enclosure 630. The vertex portion 692 defines an end 694 of the blade 642 towards the central axis 646 and terminates at a fixed radius from the central axis 646 (see FIG. 7). Therefore, the end 694 of the blade 642 is distanced from the central axis 646 of the enclosure 630. With each of the blades 642 assuming a similar configuration as the blade 642, a gap 656 is defined at the central axis 646 of the enclosure 630, which is similar to the gap 156 of the mixer 128.

[0039] The enclosure 630 and the blades 642 may be integrally formed and a manufacturing of the mixer 628 may remain similar to the manufacturing process as has been described for the mixer 128. Therefore, it may be contemplated that the enclosure 630 and the blades 642 are formed, such as from a singular piece of sheet metal that undergoes a series of shearing and bending operations, as noted above.

[0040] Referring to FIGS. 8 and 9, the mixer 828 is shown. In principle, the aspect presented for the mixer 828 remains similar to the aspects divulged for the mixer 628, involving structural features that abstain from interfering with the overall structure of the mixer body. In particular, an enclosure 830 of the mixer 828 is inclusive of a polygonal cross-section. Therefore, the enclosure 830 may define a number of sides 896. Although not limited, the enclosure 830 is octagonal shaped inclusive of eight sides 896. A number of blades 842a, 842b, 842c, 842d, 842e, 842f, 842g, and 842h (collectively, blades 842) is incorporated into the mixer 828. The number of blades 842 incorporated to the mixer 828 may be proportional to said number of sides 896. For example, if eight sides 896 are provided on the enclosure 830, eight number of blades 842 may be provided, with each blade 842 accommodated per side 896. In so doing, each blade 842 may be bent from its respective side 896 at first edge 858 without interfering with the overall polygonal shape of the enclosure 830. As a result, a shape of the enclosure 830 may be retained in spite of the bend defined at the first edge 858. Additionally, the embodiments of the mixers 128 and 628 discussed in connection with FIGS. 1 to 7 may suitably incorporate the aspects of the mixer 828. Therefore, it may be envisioned that the mixers 128 and 628 incorporate a polygonal (or an octagonal) cross-section as has been disclosed for the mixer 828 in FIG. 8 and 9. Although a shape of the blades 842 in FIGS. 8 and 9 are shown to be generally planar, it needs to be understood that the depiction of the blades 842 is for representational purposes alone and need to be viewed as being purely exemplary in nature.

Industrial Applicability [0041] Referring to FIGS. 1 to 5, an operation of the mixer 128 will be discussed. After each combustion cycle, the engine 104 releases exhaust gas as a by-product of combustion. The exhaust gas passes into the DPF 106 for filtration of an exhaust gas soot and the diesel particulate matter present in the flow. Once filtered by the DPF 106, the exhaust gas passes into the conduit 112 to reach to the first reductant mixing section 122. At this stage, the injectors 116 inject an amount of reductant (DEF) into the mixing chamber 118 that propagates and diffuses into a voluminous flow of exhaust gas. As a result, the injected reductant mixes with the exhaust gas at the first reductant mixing section 122, forming a homogeneous reductant-exhaust gas mixture. At this stage, a certain level of uniformity between the exhaust gas and the reductant is attained. However, as a further degree of uniformity between the reductant and the exhaust gas is required, the reductant-exhaust gas mixture flows further downstream into the second reductant mixing section 124.

[0042] As the reductant-exhaust gas mixture enters the second reductant mixing section 124, the reductant-exhaust gas mixture advances to interact with the mixer 128 and strikes against the blades 142 of the mixer 128. In so doing, the reductant-exhaust gas mixture splits into multiple flow portions creating a turbulent vortex flow downstream. More particularly, a portion of the reductant-exhaust gas mixture interacting with the first segment 158 diverts the reductant-exhaust gas mixture into a first direction, denoted by arrow, B (FIG. 4). Similarly, another portion of the reductant-exhaust gas mixture interacting with the second segment 160 diverts into an alternate direction denoted by arrow, C (FIG. 4, also see arrows in FIG. 5). The directions denoted by arrows B and C may depend upon the angular offset between the first segment 158 and the second segment 160. In effect, given a multi-blade configuration (blades 142) of the mixer 128, an inflowing reductant-exhaust gas mixture may spilt into multiple flow streams with varying angular directions, creating turbulence downstream and ensuring a thorough mix between the reductant and the exhaust gas. More particularly, the angular offset (Θ) between the first segment 158 and the second segment 160 allows the reductant-exhaust gas mixture to be swirled and turned so that the reductant-exhaust gas mixture may further mix with each other and attain a uniformity index of at least 0.96. Thereafter, a thoroughly mixed reductant-exhaust gas mixture formed may be delivered to the SCR module 108 for further treatment.

[0043] Given the integral structure of the mixer 128, a flow of the reductant-exhaust gas mixture is relatively easily attained, as integrated components are conceptually characterized as having seamless bends, turns, and comers, in contrast to a fabricated component that otherwise may be inclusive of fasteners, flange portions, etc., and which may serve as an obstruction to a flow. Moreover, the twisted configuration of the blades 142 impart minimal impaction to the reductant on a surface of the first segment 158 and the second segment 160, and yet is configured to achieve a swirl of the reductant-exhaust gas mixture to attain a uniformity index of 0.96.

[0044] Referring to FIGS. 6 and 7, an operation of the mixer 628 will be discussed. The operation will be discussed in conjunction with FIG. 1. As a reductant-exhaust gas mixture flows with a certain level of uniformity index from the first reductant mixing section 122, the reductant-exhaust gas mixture flows into the second reductant mixing section 124 and strikes the blades 642 of the mixer 628. Given the angular offset of the first segment 658 relative to the second segment 660, the reductant-exhaust gas mixture splits into a twin stream flow, one guided by the first segment 658, and the other diverted by the second segment 660. Owing to the multi-blade design (blades 642), such a phenomenon is sustained across each of the blades 642. In consequence, a turbulent vortex flow is created as the reductant-exhaust gas mixture flows further downstream, towards the SCR module 108. The ensuing exhaust streams interact and mix with each other, ensuring a furtherance in mixing between the reductant and the exhaust gas mixture, and thereby helping the reductant-exhaust gas mixture attain a higher uniformity index. As the SCR module 108 receives the reductant-exhaust gas mixture with the enhanced uniformity index, the SCR module 108 is able to better a conversion rate of NOx present in the exhaust gas.

[0045] Moreover, the angular offset between the first segment 658 and the second segment 660 helps in reinforcing the blade 642’s structure as the two segments 658,660 act as stiffeners or support ribs relative to each other. Therefore, one segment supports the other, strengthening an overall structure of the blade 642 and of the mixer 628. Additionally, as the first edge 652 (first bend) of the mixer 628 is defined parallel to the width, Wi, the blades 642 abstain from interfering with an overall structure and rigidity of the mixer 628. Additionally, it may also become relatively easy for the enclosure 630 to be assembled (or disassembled) within the mixing chamber 118 of the conduit 112 as deformations arising out of structural interferences are absent since the first bend (first edge 652) is parallel to the width, Wi or central axis 646. Further, the second bend formed at the joining portion 662 allows more area of a sheet metal (such as when integrally manufacturing the mixer 628) to be made available to shape and support the blades 642.

[0046] In general, the blades 142, 642 of the mixers 128, 628 also provide a minimum impact area for the reductant-exhaust gas mixture (or reductant alone) to be deposited over the surfaces of the segments 158,160 and 658,660, respectively. As a result, effects of condensation of the reductant over the blades 142, 642 may be mitigated, as otherwise portions of the reductant may adhere to the blades 142, 642 and crystallize over a period and may potentially affect a flow of the reductant-exhaust gas mixture across the mixers 128, 628.

[0047] It should be understood that the above description is intended for illustrative purposes only and is not intended to limit the scope of the present disclosure in any way. Thus, one skilled in the art will appreciate that other aspects of the disclosure may be obtained from a study of the drawings, the disclosure, and the appended claim.

Claims

Claims What is claimed is:

1. A mixer for an engine after-treatment system, the mixer comprising: a substantially cylindrical enclosure; and a plurality of blades arranged at regular intervals along an inner periphery of the substantially cylindrical enclosure and radially extending towards a central axis of the substantially cylindrical enclosure, each blade defining a longitudinal axis and being twisted about the longitudinal axis.

2. The mixer of claim 1, wherein each blade comprises a first segment joined to a second segment via a joining portion, the first segment and the second segment being substantially planar, wherein each blade is twisted about the joining portion.

3. The mixer of claim 2, wherein a plane of the first segment is substantially perpendicular to a tangent of a radius of the inner periphery of the substantially cylindrical enclosure at a point where each blade meets the inner periphery.

4. The mixer of claim 3, wherein the substantially cylindrical enclosure defines a peripheral wall having a width and each blade is arranged such that the plane of the first segment extends across the width.

5. The mixer of claim 3, wherein the plane of the first segment is offset from a plane of the second segment.

6. The mixer of claim 5, wherein the offset is an angular offset of 45 degrees.

7. The mixer of claim 2, wherein the second segment is of a predetermined length that terminates at an end that is distanced from the central axis of the substantially cylindrical enclosure.

8. The mixer of claim 7, wherein the end of each of the plurality of blades define a gap at the central axis of the substantially cylindrical enclosure.

9. The mixer of claim 7, wherein the end of each of the plurality of blades terminate at a fixed radius defined with respect to the central axis of the substantially cylindrical enclosure.

10. The mixer of any preceding claim, wherein the mixer is a swirl mixer.

11. The mixer of any preceding claim, wherein the substantially cylindrical enclosure and the plurality of blades are integrally formed.

12. An after-treatment system for an engine, comprising: a conduit configured to receive a flow of exhaust gas from the engine; a reductant injector configured to inject reductant into the conduit; a mixer positioned within the conduit, downstream of the reductant injector, the mixer comprising: a substantially cylindrical enclosure; and a plurality of blades arranged at regular intervals along an inner periphery of the substantially cylindrical enclosure and radially extending towards a central axis of the substantially cylindrical enclosure, each blade defining a longitudinal axis and being twisted about the longitudinal axis.

13. The after-treatment system of claim 12, wherein each blade comprises a first segment joined to a second segment via a joining portion, the first segment and the second segment being substantially planar, wherein each blade is twisted about the joining portion.

14. The after-treatment system of claim 13, wherein a plane of the first segment is substantially perpendicular to a tangent of a radius of the inner periphery of the substantially cylindrical enclosure at a point where each blade meets the inner periphery.

15. The after-treatment system of claim 14, wherein the substantially cylindrical enclosure defines a peripheral wall having a width and each blade is arranged such that the plane of the first segment extends across the width.

16. The after-treatment system of claim 14, wherein the plane of the first segment is offset from a plane of the second segment.

17. The after-treatment system of claim 16, wherein the offset is an angular offset of 45 degrees.

18. The after-treatment system of claim 13, wherein the second segment is of a predetermined length that terminates at an end that is distanced from the central axis of the substantially cylindrical enclosure.

19. The after-treatment system of claim 18, wherein the end of each of the plurality of blades define a gap around the central axis of the substantially cylindrical enclosure.

20. The after-treatment system of claim 18, wherein the end of each of the plurality of blades terminate at a fixed radius defined with respect to the central axis of the substantially cylindrical enclosure.