DE112017002859T5 - Double mixer for exhaust aftertreatment systems - Google Patents

Abstract

A double mixer (36) for mixing a reducing agent (28) with exhaust gas (16) in a mixing section (34) of a selective catalytic reduction (SCR) aftertreatment system (24) is disclosed. The twin mixer (36) may comprise a first mixer (37) having a grid (40) and a plurality of trapezoidal laminations (48) projecting from the grid (40) in the flow direction of the exhaust gas (16). Further, the double mixer (36) may include a vortex mixer (38) disposed downstream of the first mixer (37) and separated therefrom by a distance. The vortex mixer (38) may include a base (54) and three arrays (56) of swirling vanes (58) projecting from the base (54) in the flow direction of the exhaust gas (16). The swirling vanes (58) in each of the assemblies (56) may be oriented in a common direction (62) that is rotated about 60 ° from the common direction (62) of the swirling vanes (58) in an adjacent assembly (56) is.

Description

Technical area

The present disclosure relates generally to mixers for exhaust aftertreatment systems, and more particularly to a twin mixer for mixing a reductant with exhaust gas in a selective catalytic reduction (SCR) treatment system.

background

Nitric oxide (NO _x ) gases, such as nitric oxide (NO) and nitrogen dioxide (NO 2), are pollutants that can be produced when fuel is burned in internal combustion engines at high temperatures. These gases can have harmful effects and be involved in the formation of smog and acid rain. To comply with regulations requiring ever-decreasing NO _x emissions, engine manufacturers may be forced to employ technologies that substantially reduce NO _x emissions in engine exhaust. One such technology includes selective catalytic reduction (SCR) post-treatment systems that catalyze the reduction of NO _x in the exhaust gas to nitrogen and water before the exhaust gas is released from an exhaust gas outlet, such as a tailpipe. In an SCR aftertreatment system, a reducing agent is injected as a liquid into the exhaust stream of the exhaust pipe, and the mixture of reducing agent and exhaust gas is passed through a downstream SCR catalytic converter, the _x catalyzed using the reducing agent the reduction of NO in the exhaust stream. The reducing agent may be ammonia or it may be urea, which is subsequently hydrolyzed to ammonia in the exhaust gas stream. In connection with diesel engines, a reducing agent consisting of urea and water, as a diesel exhaust fluid (DEF) or AdBlue ^® is referred to.

The reductant should be vaporized prior to introduction into the SCR catalyst and mixed well with the exhaust gas to ensure that the reduction of NO _x in the SCR catalyst is efficient. The evaporation of the reductant not only aids in uniform distribution of the reductant in the exhaust, but also prevents any undesirable accumulation of reductant deposits in the exhaust pipe which could result in reduced conversion efficiencies as well as increased backpressure in the exhaust pipe. In order to promote the evaporation of the reducing agent and the mixing of the reducing agent with the exhaust gas, a mixer can be provided in the exhaust pipe between the injector and the SCR catalyst. However, it may be challenging to provide a mixer that meets the performance requirements of both blending the reductant with the exhaust gas and reducing deposits by promoting reductant evaporation.

An example of a reducing agent mixer is in U.S. Patent Number 8,607,555 described. The patent discloses a mixing element comprising a grid carrying rows of trapezoidal deflector elements oriented in different directions. In addition, the patent discloses a mixing element having four arrays of deflector elements rotated 90 degrees with respect to each other to produce rotational movement of the exhaust gases and reductant flowing through the mixer.

Although the above-mentioned mixing elements are effective, there is still a need for improved mixing systems that promote both the evaporation of the reducing agent and the mixing of the reducing agent with the exhaust gas prior to introduction into the SCR catalyst.

Summary

According to one aspect of the present disclosure, a double mixer is used for Mixing of a reducing agent with exhaust gas in a mixing section of a selective catalytic reduction (SCR) treatment system disclosed. The twin mixer may include a first mixer disposed in the mixing section and having a grid that allows the reducing agent and the exhaust gas to flow therethrough. The first mixer may further comprise a plurality of trapezoidal louvers projecting from the lattice in the flow direction of the exhaust gas. Further, the double mixer may also include a vortex mixer disposed downstream from the first mixer in the mixing section and separated therefrom by a distance. The vortex mixer may have a base that allows the flow of the reducing agent and the exhaust gas, and three rows of vortexing fins projecting from the base in the direction of flow of the exhaust gas. The swirling vanes may be arranged in a triangular configuration about a center of the mixer to cause turbulence in the reductant and the exhaust gas flowing through the vortex mixer. In each of the arrangements, the swirl vanes may be oriented in a common direction that is rotated about 60 ° from the common direction of the swirl vanes in an adjacent arrangement.

According to another aspect of the present disclosure, a twin mixer for mixing a reductant with exhaust gas in an exhaust pipe upstream of a selective catalytic reduction catalyst (SCR catalyst) is disclosed. The twin mixer may include a first mixer having a planar grid and a plurality of parallel rows of trapezoidal louvers projecting from the planar grid in the flow direction of the exhaust gas. The trapezoidal louvers in each of the parallel rows may alternate in the orientation direction and may be inclined at about 20 ° with respect to the planar lattice. Further, the double mixer may include a vortex mixer downstream of and at a distance from the first mixer. The vortex mixer may have a planar base with a plurality of radial legs extending radially from the center of the base and equally spaced circumferentially. Further, the vortex mixer may include a plurality of trapezoidal swirling vanes protruding from each of the radial legs in the flow direction of the exhaust gas. The trapezoidal swirl vanes projecting from each of the radial legs may be oriented in a common direction which is rotated at an angle with respect to the common direction of the trapezoidal swirl vanes protruding from an adjacent radial leg.

According to another aspect of the present disclosure, a selective catalytic reduction (SCR) aftertreatment system is disclosed in exhaust gases of a diesel engine. The SCR aftertreatment system may include an exhaust pipe configured to convey the exhaust from the diesel engine to an exhaust outlet, an injector configured to inject diesel exhaust fluid (DEF) into the exhaust pipe, and an SCR catalyst downstream of the injector designed to catalyze the reduction of NO _x in the exhaust gas. Further, the SCR aftertreatment system may include a dual mixer disposed in the exhaust pipe downstream of the injector and upstream of the SCR catalyst. The twin mixer may include a first mixer configured to promote evaporation of the DEF flowing therethrough. The first mixer may have a planar grid and a plurality of parallel rows of fins projecting downstream from the planar grid. The fins of the first mixer may be inclined by about 20 ° with respect to the plane grid. Further, the double mixer downstream of the first mixer may comprise a vortex mixer adapted to promote the mixing of the DEF and the exhaust gas flowing therethrough. The vortex mixer may include arrays of fluidizing fins projecting downstream from the vortex mixer. Each of the arrangements of the vortex mixer may comprise a plurality of parallel rows of fluidizing fins oriented in a common direction rotated about 60 ° from the common direction of an adjacent arrangement.

These and other aspects and features of the present disclosure will become more apparent upon reading in conjunction with the accompanying drawings.

list of figures

• 1 FIG. 10 is a schematic illustration of an exhaust after-treatment system for an engine constructed in accordance with the present disclosure having a dual mixer for mixing a reductant with an exhaust gas. FIG.
• 2 FIG. 15 is a perspective view of a first mixer of the double mixer of FIG 1 ,
• 3 FIG. 12 is a plan view of one of the trapezoidal fins formed in accordance with the present disclosure, shown alone, of the mixer. FIG.
• 4 FIG. 10 is a plan view of a vortex mixer of the double mixer of FIG 1 ,
• 5 FIG. 12 is a side perspective view of the vortex mixer constructed in accordance with the present disclosure. FIG.
• 6 FIG. 10 is a side view of the vortex mixer constructed in accordance with the present disclosure. FIG.
• 7 FIG. 12 is a perspective view of a support member formed according to the present disclosure, shown alone, of the vortex mixer. FIG.
• 8th FIG. 12 is a perspective view of a radial leg formed by the present disclosure, shown alone, of the vortex mixer. FIG.
• 9 FIG. 12 is a bottom perspective view of a vortex mixer unit formed by assembling a radial leg with support members in accordance with a method of the present disclosure. FIG.
• 10 FIG. 12 is a bottom perspective view of two of the units assembled according to the method of the present disclosure. FIG.
• 11 Figure 3 is a bottom perspective view of three of the units assembled and welded together at nodes to provide the vortex mixer according to the method of the present disclosure.

Detailed description

In the drawing, to which reference is now made, and in particular in 1 , is an exhaust aftertreatment system 10 for an internal combustion engine 12 like a diesel engine 14 , shown. The exhaust aftertreatment system 10 may include components that contain at least a portion of the pollutants in one of the engine 12 through an exhaust pipe 18 expelled exhaust 16 Remove before the exhaust gas from an exhaust outlet 20 , such as a tailpipe, is released. In particular, the aftertreatment system 10 one in the exhaust pipe 18 arranged particulate filter 22 include, the particles from the exhaust gas 16 filters out. Downstream of the particulate filter 22 in the exhaust pipe 18 can a system 24 for post-treatment by means of selective catalytic reduction (SCR) to the reduction of NO _x in the exhaust gas 16 to catalyze nitrogen and water. In alternative embodiments of the aftertreatment system 10 may be missing a particulate filter.

The SCR aftertreatment system 24 can an injector 26 for injecting a reducing agent 28 from a supply source 30 in the exhaust pipe 18 flowing exhaust gas 16 include. The reducing agent 28 can be a mixture of urea and water (also called diesel exhaust fluid (DEF) when the engine 12 a diesel engine is, or AdBlue ^® designates), and the urea can in the exhaust pipe 18 be hydrolyzed to ammonia. Alternatively, the reducing agent 28 Be ammonia. The reducing agent 28 Can first as a liquid in the exhaust pipe 18 injected and later in the exhaust pipe 18 be vaporized (see more details below). Downstream of the injector 26 can be a catalyst 32 which is the reducing agent 28 used to reduce NO _x in the exhaust 16 to catalyze nitrogen and water before releasing the exhaust gas through the outlet 20 he follows.

The SCR aftertreatment system 24 can also be a mixed route 34 include, such as a mixing tube 35 , the part of the exhaust pipe 18 is and is between the injector 26 and the SCR catalyst 32 extends. In the mixing section 34 can the reducing agent 28 vaporized and / or decomposed into smaller droplets and mixed with the exhaust gas before entering the catalyst 32 is initiated. For this purpose, the mixing section 34 a double mixer 36 included, from a first mixer 37 and a vortex mixer 38 downstream from the first mixer 37 consists. In particular, the first mixer 37 Liquid droplets of the reducing agent 28 evaporate and / or decompose the reducing agent liquid into smaller droplets while the vortex mixer 38 Further improve the evaporation of the reducing agent and cause a swirling motion in the reducing agent and in the exhaust gas to promote a thorough mixing.

The first mixer 37 and the vortex mixer 38 can be separated by a distance that can be optimized based on performance. In a non-limiting example, the first mixer 37 and the vortex mixer 38 by about 51 mm (2 inches) to about 178 mm (7 inches) apart, although depending on various design considerations, such as the volumetric flow rate of the reducing agent and the diameter of the exhaust pipe, the separation distance may vary from this range.

In addition, because of the corrosive action of the reducing agent 28 and the vibrations in the exhaust pipe 18 both the first mixer 37 as well as the vortex mixer 38 Made of a material that is resistant to corrosion and robust enough to withstand vibration. For example, the first mixer 37 and the vortex mixer 38 both made of stainless steel.

now to 2 : The first mixer 37 is shown alone. The first mixer 37 can a flat grid 40 comprising, consisting of a plurality of first support elements 42 is formed, which is perpendicular to a plurality of second support elements 44 are arranged and these intersect to holes 46 to delimit the passage of the reducing agent 28 and the exhaust gas 16 through the mixer 37 enable. From the grid 40 can in the flow direction of the exhaust gas 16 (ie downstream in the exhaust pipe 18 ) several fins 48 stick out what the evaporation of the reducing agent 28 promotes. All slats 48 of the first mixer 37 may have a common shape and the same dimensions. In particular, all slats 48 a trapezoidal shape with a broader base 49 and a narrower upper end 51 have (see 3 ). In one embodiment, the first mixer 37 have a diameter (d) of about 127 mm (5 inches), and each of the fins 48 may have a thickness (t) of from about 1 to about 2 mm or from about 1 to about 1.6 mm (see 2 ) and a length (l) extending from the base 49 to the top 51 extending, of about 15 (± 2) mm have (see 3 ). In addition, in this embodiment, the width (w) of the base 49 about 10.5 (± 1) mm, and the width (w) of the upper end 51 may be about 6 (± 1) mm (see 3 ). The dimensions of the mixer 37 and the slats 48 However, with the Diameter of the exhaust pipe 18 be scalable, with larger exhaust pipes 18 larger mixer 37 / fins 48 are used. Moreover, the slats 48 in alternative embodiments, other shapes such as, but not limited to, square, rectangular, triangular, spherical, oval, or other polygonal and informal configurations.

Still referring to 2 : The slats 48 of the first mixer 37 can be at a fixed angle (α) with respect to the plane of the grid 40 be oriented, depending on the execution of the mixer 37 can vary between about 10 ° and about 80 °. In one arrangement, the fixed angle (α) of the slats 48 about 20 ° (± 0.05 °), since this angle, as the Applicants have found, compared to other angles a favorable reduction of deposits in the exhaust pipe 18 causes. In addition, the slats can 48 integral with the first carrier elements 42 be formed (or otherwise attached thereto) and extend from it to several rows 50 To form lamellae. The slats 48 in each of the rows 50 can alternate in the orientation direction, with a lamella 48 pointing in one direction and an immediately adjacent lamella 48 pointing in the opposite direction as shown. In addition, the slats 48 of the mixer 37 in several columns 53 be aligned parallel to the second support elements 44 are, and all slats 48 in each of the columns 53 may be pointing in the same direction, so that the direction of orientation of the slats 48 between adjacent columns 53 replaced. Although shows 2 seven rows 50 and seven columns 53 Slats, with three to seven slats 48 in each of the rows / columns, it is understood, however, that the number of rows 50 , the number of columns 53 and the number of slats 48 in each row / column depending on the diameter of the exhaust pipe 18 can vary, with larger pipe diameters using more rows / columns and more fins in each row / column. Also, the first mixer 37 curved tabs 52 to attach (eg by welding) the mixer 37 on the inner walls of the exhaust pipe 18 to allow the first mixer 37 in the exhaust pipe 18 is held stationary.

In 4 to 5 is the vortex mixer 38 shown alone. The vortex mixer 38 can be a base 54 comprising a passage of the reducing agent 28 and the exhaust gas 16 allows. Also, the vortex mixer 38 several orders 56 of swirling fins 58 include that in the exhaust pipe 18 from the base 54 in the flow direction of the exhaust gas 16 (ie downstream in the exhaust pipe 18 ) protrude. As used herein, an "array" is a group of swirling lamellae 58 in parallel rows 60 are arranged, with all swirling fins 58 in the arrangement in a common direction 62 are oriented and the ends 59 the slats all in the common direction 62 showing (see 4 ). In addition, in each of the arrangements 56 the rows 60 be at regular intervals from each other, and the swirling lamellae 58 in each of the rows 60 can be evenly spaced, creating a regular, repeating pattern of swirling lamellae 58 provided. The arrangements 56 may be the same and may be arranged with respect to each other such that one is a center 64 of the vortex mixer 38 orbiting configuration is provided, which may be either clockwise or counterclockwise, in the reducing agent and in the exhaust gas passing through the mixer 38 flow, causing a whirling movement. For example, the illustrated vortex mixer 38 three orders 56 on, taking the common direction 62 each of the orders 56 about 60 ° opposite the common direction 62 an immediately adjacent arrangement 56 is rotated to a triangular configuration around the center 64 although other numbers of arrangements with different angles of rotation with respect to each other are possible. Accordingly, the vortex mixer 38 in the illustrated embodiment, a triple rotational symmetry.

It should be noted that the vortex mixer 38 in the exhaust pipe 18 is held stationary and does not rotate, and the swirling motion by the orbiting configuration of the assemblies 56 is caused. In alternative embodiments of the mixer 38 need the arrangements 56 not completely the same. Even though 4 to 5 four rows 60 swirling lamellae 58 in each of the arrangements 56 and three to four swirling blades 58 in each of the rows 60 It should be understood that alternative embodiments of the vortex mixer 38 may have more or less rows and / or fins in each row. For example, the number of rows 60 and the number of swirling blades 58 in each of the rows 60 with the diameter of the exhaust pipe 18 be scalable.

Still referring to 4 to 5 In the illustrated embodiment with three arrangements 56 can the base 54 of the vortex mixer 38 three radial legs 66 have, extending radially from the center 64 of the mixer 38 extend, and the three radial legs 66 can be in the circumferential direction 68 be at regular intervals of about 120 ° from each other (see 4 ). Also, with each of the radial legs 66 several swirling lamellae 58 may be integrally formed (or otherwise attached thereto) and may protrude from one of the rows of lamellae 60 in one of the arrangements 56 to build. Each of the radial legs 66 can namely the last row of lamellae 60 in an arrangement 56 wear before the orientation direction of the swirling lamellae 58 in an adjacent arrangement 56 rotated by 60 °. Also, each of the radial legs 66 a curved flap 70 have, extending from the vortex mixer 38 extends to a mounting of the mixer 38 on the inner walls of the exhaust pipe 18 to allow for example by welding. In other embodiments, more or less radial legs may be used.

now to 5 In the illustrated embodiment with three radial legs 66 can the base 54 furthermore, three grids 72 between the radial legs 66 have the arrangements 56 wear and connect with each other. The grids 72 can consist of several carrier elements 74 be formed, each spanning two adjacent grid to the mixer 38 Bondability and structural robustness. In particular, each of the support elements 74 a first carrier element 76 in one of the grids 72 comprising, integral with a second support member 78 in an adjacent grid 72 formed (or otherwise attached to) is. In each of the grids 72 can have several first carrier elements 76 perpendicular to a plurality of second carrier elements 78 be arranged and these intersect to holes 80 to delimit the passage of the reducing agent 28 and the exhaust gas 16 through the mixer 38 enable. Moreover, the first carrier elements 76 integral with the swirling blades 58 formed (or otherwise attached) to one of the rows 60 in an arrangement 56 define. In addition, the first carrier elements 76 in every grid 72 parallel to the radial leg 66 run, the swirling lamellae 58 in the same arrangement 56 carries while the second carrier elements 78 perpendicular to the first carrier elements 76 and the radial leg 66 in the arrangement 56 can run and connect them together. Moreover, in other embodiments, where a different number of radial legs 66 is used, a corresponding number of grids 72 between the radial legs 66 be formed.

The base 54 of the vortex mixer 38 can be plan and in a plane 81 extend, and the swirling fins 58 can be from a downstream area 83 the base at a fixed angle (α) with respect to the plane 81 the base 54 , as in 6 shown, project. The angle (α) may be about 45 °, although under certain circumstances other angles between about 5 ° and about 80 ° may be used. Besides, as in 4 to 5 shown, all swirling slats 58 of the vortex mixer 38 have completely identical shapes and dimensions. In particular, the swirling lamellae 58 be trapezoidal (see 4 to 5 ), with lengths (l) from the lower end 82 to the top 59 every slat 58 about 30 mm (see 6 ). For alternative versions of the mixer 38 can the swirling fins 58 however, may well have other shapes (eg, square, rectangular, triangular, spherical, oval, other polygonal shapes, etc.) and dimensions. The diameter of the vortex mixer 38 can be scalable with the exhaust pipe dimensions, such that larger mixers are used with larger exhaust pipes. In a non-limiting arrangement, the vortex mixer can 38 have a diameter (d) of about 127 mm (5 inches) (see 4 ).

As in 7 shown, can be any of the support elements 74 slots 86 exhibit to when installing the vortex mixer 38 a connection with other support elements 74 to enable. For example, the first carrier elements 76 each slots 86 have on the upstream side 88 are arranged while the second support elements 78 each slots 86 may have, on the downstream side 90 are arranged. Accordingly, the grids 72 of the vortex mixer 38 by connecting the slots 86 the first carrier elements 76 with the slots 86 the second carrier elements 78 to be assembled. Likewise, as in 8th shown, each of the radial legs 66 slots 86 have on the upstream side 92 are arranged so that during assembly of the vortex mixer 38 the slots 86 the radial leg 66 with the slots 86 the second carrier elements 78 can be connected (see further details below).

Industrial Applicability

In general, the teachings of the present disclosure may be applicable in many industries, including, but not limited to, automotive, construction, agricultural, mining, power generation, and rail transportation applications, and the like. a. In particular, the technology disclosed herein may find application in many types of engines and machines having SCR aftertreatment systems. It can also find application in other types of exhaust aftertreatment systems in which a reagent is mixed with exhaust gas.

now to 9 to 11 : The steps are shown figuratively when mounting the vortex mixer 38 may be required. And show it 9 to 11 Steps involved in assembling the vortex mixer 38 with three arrangements 56 However, it should be understood that the concepts disclosed herein are similar Can be applied to a vortex mixer with a larger or smaller number of arrangements. First, each of the three radial legs 66 separately with several carrier elements 74 be merged to three units 102 to build. 9 shows, for example, one of the units 102 by plugging in the slots 86 of the radial leg 66 in slots 86 of three of the second support elements 78 is formed. Subsequently, the three units 102 be joined together by the slots 86 the support elements 74 as in 10 to 11 be shown connected to each other. This can be done in particular by first having two of the units 102 be joined together by the slots 86 the first carrier elements 76 one of the units 102 in the slots 86 the second carrier elements 78 another unit 102 plugged in to one of the grids 72 provide that the two radial legs 66 connects (see 10 ). The exposed first and second support members 76 and 78 the two assembled units 102 can then by connecting the slots 86 the first carrier elements 76 and the second carrier elements 78 with the third unit 102 be joined together (see 11 ).

Once they are put together, the units can 102 at the nodes 106 (or crossing points of the radial legs 66 and the first carrier elements 76 with the second carrier elements 78 ) to the ready assembled vortex mixer 38 be welded (see 11 ). As in 11 shown, the units can 102 on an upstream surface 109 the base 54 welded together (see also 6 ). It is noted here that 9 to 11 a possible method for mounting the vortex mixer 38 but there are many alternative ways to mount the mixer 38 gives. For example, the radial legs 66 first in the middle 64 welded together, and the grid 72 can between the radial thighs 66 by connecting the carrier elements 74 and welding the carrier elements 74 at the nodes 106 to be assembled. Variants such as these also fall within the scope of the present disclosure.

As disclosed herein, a dual mixer is used to address the problem of balancing the requirements for reducing reductant deposits and improving the mixing quality of the reductant with the exhaust gas in an SCR aftertreatment system. By separating the function of the mixers of the double mixer disclosed herein, improved performance is achieved both in terms of reduction of deposits and on mixing quality over single mixers of the prior art. The dual mixer of the present disclosure includes a first mixer located downstream of the reductant injector to reduce the formation of deposits by trapping the reductant liquid from the injector and dispersing it into smaller droplets. The first mixer comprises a grid structure and a plurality of trapezoidal louvers protruding from the lattice at an angle of 20 ° to promote evaporation of the reducing agent and reduce the formation of deposits. Further, the double mixer comprises downstream of the first mixer comprises a vortex mixer which improves the evaporation of the left by the first mixer droplets and the gas phase mixture of the reducing agent to the exhaust gas promotes, in order to improve the NO _x -Umwandlungswirkungsgrade on the downstream SCR catalytic converter. Namely, the vortex mixer has an orbiting configuration of three arrays of trapezoidal fins which exert a moderate swirling force on the mixture of reducing agent and exhaust gas which is strong enough to provide sufficient mixing but weak enough to prevent undesired driving Reducing agent droplets to avoid the walls of the exhaust pipe. In addition, the vortex mixer has a cross-linked lattice framework with triple rotational symmetry, which provides a more stable and structurally more robust structure than prior art mixers having fewer interconnections. The technology disclosed herein may find widespread commercial applicability in a wide range of fields including, but not limited to, construction, mining, agricultural, automotive, and rail applications.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 8607555 [0004]

Claims (10)

Double mixer (36) for mixing a reducing agent (28) with exhaust gas (16) in a mixing section (34) of a selective catalytic reduction (SCR) treatment system (24), comprising: a first mixer (37) disposed in the mixing section (34) and having a grid (40) for allowing the reductant (28) and the exhaust gas (16) to flow therethrough, the first mixer (37) further comprising a plurality of trapezoidal Louvers (48) projecting from the grid (40) in the flow direction of the exhaust gas (16); and a vortex mixer (38) disposed downstream of the first mixer (37) in the mixing section (34) and separated by a distance from the first mixer (37), the vortex mixer (38) having a base (54) for passage therethrough the reducer (28) and the exhaust gas (16), the vortex mixer (38) further comprising three arrays (56) of swirl vanes (58) projecting from the base (54) in the flow direction of the exhaust gas (16) a triangular configuration about a center (64) of the vortex mixer (38) are arranged to cause a swirling motion in the reducing agent (28) and the exhaust gas (16) flowing through the vortex mixer (38), the fluidizing vanes (58 ) in each of the assemblies (56) are oriented in a common direction (62) that is rotated about 60 ° from the common direction (62) of the swirling vanes (58) in an adjacent assembly (56). Double mixer (36) after Claim 1 wherein the first mixer (37) is adapted to promote the evaporation of the reducing agent (28) passing therethrough, and wherein the vortex mixer (38) is adapted to promote the mixing of the reducing agent (28) with the exhaust gas (16). Double mixer (36) after Claim 2 wherein the grid (40) of the first mixer (37) is planar and wherein the trapezoidal laminations (48) are inclined by about 20 ° with respect to the grid (40). Double mixer (36) after Claim 3 wherein the grid (40) of the first mixer (37) is formed of a plurality of first support members (42) arranged perpendicular to and crossing a plurality of second support members (44), and wherein the trapezoidal slats (48) are integral with the first one Carrier elements (42) are formed and projecting therefrom. Double mixer (36) after Claim 4 wherein the first mixer (37) has a plurality of parallel rows (50) of trapezoidal laminations (48) and wherein the trapezoidal laminations (48) in each of the parallel rows (50) alternate in the orientation direction. Double mixer (36) after Claim 5 wherein the first mixer (37) has seven parallel rows (50) of trapezoidal louvers (48) and wherein each of the parallel rows (50) has three to seven of the trapezoidal louvers (48). Double mixer (36) after Claim 5 wherein each of the trapezoidal louvers (48) of the first mixer (37) has a length of about 15 mm and a thickness of between about 1 mm and about 2 mm. Double mixer (36) after Claim 5 wherein each of the assemblies (56) of the vortex mixer (38) has parallel rows (60) of swirling vanes (58) oriented in the common direction (62). Double mixer (36) after Claim 8 wherein the base (54) of the vortex mixer (38) has three radial legs (66) each extending radially from the center (64) of the vortex mixer (38) and spaced approximately 120 ° apart in the circumferential direction (68), wherein the base (54) further comprises three grids (72) between the three radial legs (66) and wherein each of the grids (72) is formed of intersecting support members (74). A dual mixer (36) for mixing a reductant (28) with exhaust gas (16) in an exhaust pipe (18) upstream of a selective catalytic reduction catalyst (SCR catalyst), comprising: a first mixer (37) a planar grid (40) and a plurality of parallel rows (50) of trapezoidal laminations (48) projecting from the planar grid (40) in the flow direction of the exhaust gas (16), the trapezoidal laminations (48) in each of the parallel rows (50) alternate in the direction of orientation and are inclined at about 20 ° with respect to the planar grid (40); and a vortex mixer (38) downstream of the first mixer (37) and spaced from the first mixer (37), the vortex mixer (38) having a planar base (54) with a plurality of radial legs (66) extending radially from the first mixer (37) Center (64) of the base (54) and in the circumferential direction (68) are equally spaced from each other, and the vortex mixer (38) further comprises a plurality of trapezoidal swirling fins (58) extending from each of the radial legs (66) in the flow direction of the exhaust gas (16), wherein the trapezoidal swirl vanes (58) projecting from each of the radial legs (66) are oriented in a common direction (62) which is at an angle with respect to the common direction (62) of the trapezoidal swirling fins (58) by a adjacent radial leg (66) protrude, is rotated.

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