US20120204541A1

US20120204541A1 - Exhaust mixer element and method for mixing

Info

Publication number: US20120204541A1
Application number: US13/026,654
Authority: US
Inventors: Jianwen Li; Rahul Mital; Kimberly O'Kane; Shouxian Ren
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2011-02-14
Filing date: 2011-02-14
Publication date: 2012-08-16
Also published as: DE102012002776A1; CN102678233A

Abstract

According to one aspect of the invention, a mixer element to be placed between an internal combustion engine exhaust manifold and catalytic converter is provided. The mixer element includes a tubular conduit that receives an exhaust gas flow from the internal combustion engine, a first mixer configured to induce a first vortex of the exhaust gas flow in a first rotational direction and an injector disposed in the tubular conduit downstream of the first mixer, the injector being configured to inject a diesel emission fluid flow into the exhaust gas flow. The mixer element also includes a second mixer positioned downstream of the injector and a third mixer positioned downstream of the second mixer, the third mixer being configured to induce a second vortex of the exhaust gas flow and the diesel emission fluid mixture in a second rotational direction, opposite of the first rotational direction.

Description

FIELD OF THE INVENTION

Exemplary embodiments of the invention are related to internal combustion engines, and more particularly, to exhaust after treatment systems of internal combustion engines.

BACKGROUND

Manufacturers of internal combustion engines, more particularly diesel engines, are presented with the challenging task of complying with current and future emission standards for the release of nitrogen oxides, particularly nitrogen monoxide, as well as unburned and partially oxidized hydrocarbons, carbon monoxide, particulate matter, and other pollutants. In order to reduce the pollutant emissions of a diesel engine, an exhaust gas after treatment system is used to reduce pollutants within the exhaust gas flowing from the engine.
Exhaust gas after treatment systems typically include one or more after treatment devices, such as oxidation catalysts, catalytic converters, mixer elements and emissions fluid injectors. Emissions fluid injectors for diesel engines (also called diesel emissions fluid injectors or DEF injectors) may inject a urea or other suitable ammonia based fluid into the exhaust flow to improve the performance of catalytic converters. Further, mixer elements are sometimes used to facilitate urea and exhaust gas mixing to improve catalytic converter operation. As emissions standards increase, improving the mixture of urea and exhaust gas prior to entering the catalytic converter is desired. Exhaust after treatment apparatus designed to improve urea and exhaust gas mixing may have an increased overall length of system, thereby causing packaging issues for today's increasingly complex vehicles.

SUMMARY OF THE INVENTION

In one exemplary embodiment, a mixer element to be placed between an internal combustion engine exhaust manifold and catalytic converter is provided. The mixer element includes a tubular conduit that receives an exhaust gas flow from the internal combustion engine, a first mixer configured to induce a first vortex of the exhaust gas flow in a first rotational direction and an injector disposed in the tubular conduit downstream of the first mixer, the injector being configured to inject a diesel emission fluid flow into the exhaust gas flow. The mixer element also includes a second mixer positioned downstream of the injector and a third mixer positioned downstream of the second mixer, the third mixer being configured to induce a second vortex of the exhaust gas flow and the diesel emission fluid mixture in a second rotational direction, opposite of the first rotational direction.
In another exemplary embodiment, a method for distributing a urea flow within a mixer element is provided, where the method includes receiving an exhaust gas flow from an internal combustion engine into the mixer element, inducing a first vortex of the exhaust gas flow in a first rotational direction in a first region of the mixer element and injecting a urea fluid into the exhaust gas flow downstream of the first region. The method further includes causing a radial component to the urea fluid and exhaust flow in a second region of the mixer element, wherein the second region is downstream of the first region, and inducing a second vortex of a mixture of the fluid and exhaust gas flow in a second rotational direction opposite of the first rotational direction, wherein the second vortex is formed downstream of the second region.
The above features and advantages, and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of an embodiment of an internal combustion engine;

FIGS. 2A and 2B are schematic views of embodiments of exhaust after treatment systems;

FIG. 3 is a schematic view of an embodiment of a mixer element;

FIG. 4 is a schematic view of another embodiment of a mixer element;

FIG. 5 is a perspective view of an embodiment of a mixer;

FIG. 6 is a perspective view of another embodiment of a mixer; and

FIG. 7 is a perspective view of yet another embodiment of a mixer.

DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
FIG. 1 is a schematic diagram of an embodiment of an engine system 100. The engine system 100 includes an internal combustion engine 102, an exhaust system 104 and an engine controller 106. The exhaust system 104 includes an exhaust manifold 108, an exhaust after treatment apparatus 110 and an exhaust conduit 112. Cylinders 116 are located in internal combustion engine 102, wherein the cylinders receive a combination of combustion air and fuel. The combustion air/fuel mixture is combusted resulting in reciprocation of pistons (not shown) located in the cylinders 116. The reciprocation of the pistons rotates a crankshaft (not shown) to deliver motive power to a vehicle powertrain (not shown) or to a generator or other stationary recipient of such power (not shown) in the case of a stationary application of the internal combustion engine 102. The combustion of the air/fuel mixture causes a flow of exhaust gas 118 through the exhaust manifold 108 and into the exhaust gas after treatment apparatus 110, wherein the exhaust after treatment apparatus 110 includes an exhaust gas conduit 119, an oxidation catalyst 120, a mixer element 122 and a catalytic converter 124. The exhaust after treatment apparatus 110 reduces or treats various regulated constituents of the exhaust gas 118 prior to its release to the atmosphere. In an exemplary embodiment, the mixer element 122 receives a fluid supply 125 used to treat diesel exhaust gas 118 flow to conform with emissions regulations. In addition, an exemplary fluid supply 125 that includes a fluid to be mixed with exhaust gas 118, may be a urea solution that may be referred to as a diesel emission fluid or emission fluid. In exemplary embodiments, the process of reducing exhaust pollutants within the catalytic converter 124 is improved by mixing urea and exhaust gas, wherein the treated exhaust 126 is released through exhaust conduit 112 to the atmosphere.
The exhaust after treatment apparatus 110 and fluid supply 125 are operationally coupled to and controlled by engine controller 106. The engine controller 106 collects information regarding the operation of the internal combustion engine 102 from sensors 128 a-128 n, such as temperature (intake system, exhaust system, engine coolant, ambient, etc.), pressure, exhaust flow rates, NOx concentrations and, as a result, may adjust the amount of fluid injected into mixer element 122. As used herein the term controller refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. As depicted, fluid supply 125 is used in catalytic reduction reactions to reduce pollutants in exhaust gases. Fluid supply 125 may include any suitable fluid that can be mixed with exhaust gas from internal combustion engines for the purpose of emission reduction, such as a urea solution for NOx emission reduction and/or hydrocarbons for diesel particulate filter regeneration. In an exemplary exhaust after treatment apparatus 110, the fluid supply 125 includes a water-based urea solution injected into the exhaust gas 118. The ammonia produced by hydrolysis of the urea reacts with the nitrogen oxide emissions and is converted into nitrogen and water within the catalytic converter 124, thereby reducing exhaust gas emissions of the internal combustion engine 102.
FIG. 2A is a side view of an exemplary exhaust after treatment apparatus 200. The exhaust after treatment apparatus 200 receives exhaust gas flow 118 from internal combustion engine 102 (FIG. 1). The exhaust after treatment apparatus 200 includes conduit 202, oxidation catalyst 120, fluid injector 214, mixer element 122, catalytic converter 124 and exhaust gas conduit 112. An exemplary fluid injector 214 injects a supply of emission fluid into a flow of the exhaust gas 118 to be mixed within mixer element 122 prior to its entry into the catalytic converter 124. The mixer element 122 is configured to evenly distribute the injected emission fluid with the exhaust gas flow. Accordingly, the improved distribution of the emission fluid, such as urea, in the form of droplets, within the exhaust gas flow 118 enhances the performance of catalytic converter 124.
FIG. 2B is a side view of another exemplary exhaust after treatment apparatus 220. The exhaust after treatment apparatus 220 receives exhaust gas flow 232 from internal combustion engine 102 (FIG. 1). The exhaust after treatment apparatus 220 includes mixer element 222, oxidation catalyst 224, particulate filter 226, exhaust conduit 228 and injector 230. In an exemplary embodiment, injector 230 injects a fluid supply of hydrocarbons into the exhaust gas flow 232 to be mixed within or by mixer element 222 prior to its entry into oxidation catalyst 224. The mixer element 222 is configured to evenly distribute the injected fluid with the exhaust gas flow 232. Accordingly, the improved distribution of hydrocarbons within the exhaust gas flow 232 enhances the performance of the oxidation catalyst 224 and particulate filter 226, thereby providing a treated exhaust gas 234 to be released to the atmosphere. FIGS. 3-7 discuss detailed exemplary embodiments of mixer elements 122, 222 that may be used in either embodiment of exhaust after treatment device 200, 220 shown in FIGS. 2A and 2B.
FIG. 3 is a side schematic view of exemplary mixer element 122. In the embodiment, mixer element 122 includes a tubular conduit 302 a mixer 304, a mixer 306, a mixer 308, a fluid injector 214 and an inlet cone 216 (to be coupled to the converter). The mixer element 122 receives the exhaust gas flow 118 from conduit 202 (FIG. 2) and directs the exhaust gas flow 118 through mixer 304 to create a vortex 312, which has a swirling or rotational flow in direction 314. An exemplary fluid injector 214 injects a fluid 318, such as urea, into the vortex 312 as the fluid 318 and exhaust gas flow 118 are directed downstream 340 towards mixer 306. An exemplary mixer 306 has a geometry or structure that causes the injected fluid 318 to break up into small droplets to enhance mixing with the exhaust gas flow 118, thereby forming mixture 322. In an exemplary embodiment, the mixture 322 acquires a vortex flow in direction 314 as it flows downstream 340. The vortex flow of the mixture 322 includes a radial flow component 320 of injected fluid induced by mixer 306. In addition, the mixture 322 flows into mixer 308, where a vortex 324 is formed by the geometry of the mixer 308. The vortex 324 of the injected fluid and exhaust mixture 322 acquires a rotation or swirl in a direction 326, which is the opposite of direction 314. In one embodiment, the vortex 324 includes a radial flow component 328 and axial flow component 330. Further, the vortexes 312 and 324 include tangential components, wherein the tangential components cause the rotational swirl in directions 314 and 326, respectively. In an exemplary embodiment of mixer element 122, the tangential flows of the vortex 312, 324 include tangential flow components that are larger than flow components in the radial direction. In addition, the formation of vortexes 312 and 324 cause an increase break-up and entrainment of fluid 318 in the exhaust gas 118 while increasing the flow length or path for mixing injected fluid with exhaust gas 118; without adding to an overall length 339 of mixer element 122. In addition, the exemplary mixer element 122 includes inlet cone 216 that causes expansion of mixture flow 332, further enhancing distribution of the injected fluid, such as urea, within the exhaust gas. As depicted, the vortex 312 is formed in a first region 342 of the mixer element 122. Fluid 318 is injected into vortex 312 and broken up by mixer 306, causing radial flow 320 of the injected fluid in a second downstream region 344. In some embodiments, injector 214 may be used to inject hydrocarbons, such as diesel fuel, to be mixed with vortex 312 to mix hydrocarbon fluid with the exhaust gas 118. Accordingly, fluid 318, emission fluid and injected fluid refer to any suitable exhaust treatment fluid, including, but not limited to, urea, diesel fuel or other suitable fluids.
The configuration of fluid injector 214 along with mixers 304, 306 and 308 provide a mixed flow 332 of distributed injected fluid and exhaust gas flowing to catalytic converter 124. The exemplary tubular structure 302 of mixer element 122 has a diameter 336, axis 338 and length 339. The illustrated arrangement of mixer element 122 provides a desired distribution and mixture of injected fluid 318 with exhaust gas flow 118 to enhance operation of catalytic converter 124 while limiting length 339 to address packaging needs. Vortexes 312 and 324 improve mixing by having a twisting effect caused by opposing flow directions 314 and 326, respectively. The twisting effect is obtained by utilizing one mixer that has an opposite orientation relative to a downstream mixer, where the opposing orientations cause opposite swirling vortex flows. The mixers 304, 306 and 308 are placed within the mixer element 122 at selected axial positions along length 339 and may be any suitable mixer geometry or orientation to achieve the desired mixing of injected fluid 318 and exhaust gas flow 118. In an exemplary embodiment, a distance 341 between mixer 304 and fluid injector 214 is about the same as diameter 336. Distance 342 between fluid injector 214 and mixer 306 is determined to optimize break up of injected fluid 318. In addition, distance 344 between mixer 306 and 308 may be up to three times diameter 336. Exemplary distances 344 may include half, one, two and three times diameter 336. Non limiting examples of mixers 304, 306 and 308 include helical mixers, swirl mixers and impingement mixers.
FIG. 4 is a side schematic view of an exemplary mixer element 400. The mixer element 400 includes a tubular conduit 402, a mixer 404, a mixer 406, fluid injector 414 and an inlet cone 428. The mixer element 400 receives exhaust gas flow 118 from conduit 202 (FIG. 2) and directs the flow through mixer 404 to create a vortex 410 having a rotational flow in direction 412. The fluid injector 414 injects a fluid 416 into the vortex 410 as the exhaust gas flows downstream 440, thereby forming mixture 417. The mixture 417 of injected fluid and exhaust enters mixer 406 which forms a vortex 418 that flows in rotational direction 420. The vortex 418 of the injected fluid 416 and exhaust gas 118 swirls in direction 420, which is the opposite of direction 412, thereby creating a twisting effect to improve mixing. In one embodiment, the vortex 418 includes a radial component 422 and an axial component 424 of flow. Further, the vortexes 410 and 418 include tangential components, wherein the tangential components cause the rotational swirl in directions 412 and 420, respectively. The configuration of fluid injector 414, along with mixers 404 and 406, provide a uniform flow 426 of distributed injected fluid 416 and exhaust gas 118 to catalytic converter 124. Thus, the illustrated arrangement of mixer element 400 provides improved injected fluid distribution across a length 430 that enables the mixer element 400 to meet design and packaging constraints while improving emissions control. The mixers 404 and 406 are placed within the mixer element 400 at selected axial positions along length 430 and may be of any suitable mixer geometry or orientation to produce the desired flow control and mixing of fluid 416 and exhaust gas 118. Non limiting examples of mixers 404 and 406 include helical mixers, swirl mixers and impingement mixers. Therefore, it should be noted that the schematic diagrams of FIGS. 3 and 4 show mixers (304, 306, 308, 404, 406) placed within mixer elements 122 and 400, where the mixers may be any suitable mixer structure and geometry that provides the desired mixing and flow control properties at the selected locations within the mixer elements 122 and 400. Exemplary mixers to be placed in mixer elements 122 and 400 are discussed in further detail below with reference to FIGS. 5-7.
Referring to FIGS. 3 and 4, the exemplary mixer elements 122 and 400 are configured to improve distribution of injected fluid 318 and 416 within exhaust gas flow 118. The embodiments include mixers configured to form vortexes (312, 324, 410, 418), wherein the downstream vortexes (324, 418) have a rotational or swirling flow in an opposite direction than that of upstream vortexes (312, 410). Thus, the twisting or counter-rotation of the upstream and downstream flows cause improved mixing of the injected fluid 318 and 416 within the exhaust gas 118. For example, improved mixing and distribution of urea improves vaporization of the urea droplets as the mixture flows into catalytic converter 124. Further, the configuration of the mixer elements 122 and 400 enable improved mixing over a reduced length of the tubular conduits 302, 402, thereby providing reduced emissions in a smaller package to meet packaging constraints. In some embodiments where the length of the tubular conduit 339 and exhaust after treatment apparatus 110 (FIG. 1) are favorable to urea mixing, a mixer element 122 without mixer 304 may achieve a desired emissions reduction.
FIG. 5 is an exemplary helical mixer 500 that may be placed in a mixer element, such as mixer elements 122 or 400 (FIGS. 3 and 4). The helical mixer 500 includes blade 502, blade 504 and blade 506 positioned within a tubular sleeve 508. The helical mixer 500 is configured to receive a fluid flow as it flows downstream 340, thereby forming a swirling or vortex pattern 512. In embodiments, the vortex pattern 512 may be referred to as a flow tunnel, where the vortex 512 forms a tunnel of swirling or rotational flow surrounding a substantially axial flow 514. Axial flow 516 also flows downstream 340 radially outwardly of the vortex 512. Accordingly, the magnitude of axial flow 514 may be greater than axial flow 516, wherein axial flow 514 is closer to the axis of the tubular sleeve 508 and axial flow 516 is closer to an outer circumference of the tubular sleeve 508. The depicted flow behavior is caused by the geometry of exemplary helical mixer 400. Thus, exemplary helical mixers 400 are configured to create a vortex pattern 512 with an axial flow component 514 that is greater than an axial flow component 516.
FIG. 6 is an exemplary swirl mixer 600 that may be placed in mixer elements 122 or 400 (FIGS. 3 and 4). The swirl mixer 600 includes blade 602, blade 604, blade 606, blade 608 and support members 610 to be positioned within a tubular sleeve (not shown). The surface area of blades 602, 604, 606 and 608 further enhance vaporization of injected fluid, such as urea flow 318 and 416 (FIGS. 3 and 4) as it flows through the swirl mixer 600. Embodiments of swirl mixer 600 may include thru holes 612 in blades 602, 604, 606 and 608 to enhance break-up of fluid droplets. The illustrated swirl mixer 600 is configured to form a vortex pattern 614 of fluid flow, such as a flow of exhaust gas 118 (FIGS. 3 and 4) or a mixture of injected fluid and exhaust (324, 418, FIGS. 3 and 4) flowing downstream 340.
FIG. 7 is an exemplary impingement mixer 700 that may be placed within mixer elements 122 or 400 (FIGS. 3 and 4). The impingement mixer 700 includes blades 702 and support members 704 to be positioned within a tubular sleeve (not shown). The impingement mixer 700 is configured to be impinged upon by a fluid flowing within mixer element 122 or 400 (FIGS. 3 and 4). The impingement mixer 700 includes suitable structures or geometry that cause a flow of fluid to break up into smaller components and flow in a desired direction. Specifically, impingement mixer 700 includes blades 702 (also referred to as fins), wherein droplets of injected emission fluid impact the blades 702 to form small droplets or vapor that are directed by the blades 702 to mix with exhaust gas flow. An exemplary impingement mixer 700 enhances vaporization of fluid to improve distribution and mixing with exhaust gas. For example, the mixer 306 (FIG. 3) may be an impingement mixer 700 with blades 702 that cause the injected fluid 318 (FIG. 3) to break up into droplets and flow in radial direction 320 (FIG. 3), thereby improving the distribution of the injected fluid within the exhaust gas as the mixture flows downstream 340.
Referring to FIGS. 3-7, in an exemplary embodiment of mixer element 122, mixers 304 and 308 are each helical mixers 500 and mixer 306 is an impingement mixer 700. The helical mixer 304, 500 forms a vortex 312 and turbulence causing a Venturi effect to occur for axially flowing fluid 318 droplets. The Venturi effect can lead to an atomization or break-up of the fluid 318 droplets to improve distribution within the exhaust gas flow 118. The arrangement and geometry of the mixers 304, 306 and 308 within the mixer element 122 provides improved distribution of fluid flow 318 for improved catalytic reduction within catalytic converter 124. Moreover, the arrangement allows use of the improved mixer element 122 in engine systems 100 (FIG. 1) having exhaust system packaging constraints. In another exemplary embodiment of mixer element 122, mixer 308 is a swirl mixer 600 and mixer 306 is an impingement mixer 700. In addition, mixer 304 is a helical mixer 500. In the example, the arrangement causes a twisting and turbulence of the vortexes 312 and 324 flowing in opposing directions 314 and 326, respectively, to result in improved mixing of injected fluid 318 with exhaust gas flow 118.
In an exemplary embodiment of mixer element 400, mixer 404 is a swirl mixer 600 and mixer 406 is an impingement mixer 700. The swirl mixer 404, 600 generates a vortex that enhances fluid 416 droplet break-up in exhaust gas flow 118, entrainment and increases mixing length, thereby improving the mixture with exhaust 118. The impingement mixer 406, 700 generates additional turbulence downstream 340 to enhance distribution of injected fluid 416.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the present application.

Claims

1. A mixer element to be placed between an internal combustion engine exhaust manifold and a catalytic converter, the mixer element comprising:

a tubular conduit that receives an exhaust gas flow from the internal combustion engine;

a first mixer configured to induce a first vortex of the exhaust gas flow in a first rotational direction;

an injector disposed in the tubular conduit downstream of the first mixer, the injector being configured to inject a diesel emission fluid into the exhaust gas flow;

a second mixer positioned downstream of the injector; and

a third mixer positioned downstream of the second mixer, the third mixer being configured to induce a second vortex of the exhaust gas flow and the diesel emission fluid mixture in a second rotational direction, opposite of the first rotational direction.

2. The mixer element of claim 1, wherein the second mixer is configured to induce a radial flow of diesel emission fluid.

3. The mixer element of claim 1, wherein the exhaust gas flow and the diesel fluid mixture flow from the third mixer comprises axial and tangential flow components.

4. The mixer element of claim 1, wherein the first mixer comprises a helical mixer and the third mixer comprises a helical mixer.

5. The mixer element of claim 4, wherein the third mixer has a substantially opposite orientation relative to the first mixer.

6. The mixer element of claim 1, wherein the first mixer comprises a helical mixer and the third mixer comprises a swirl mixer.

7. The mixer element of claim 1, wherein the third mixer comprises swirl blades with thru holes to improve a break up of diesel emission fluid droplets.

8. The mixer element of claim 1, wherein the second mixer comprises an impingement mixer.

9. The mixer element of claim 1, wherein the first vortex comprises a first axial flow component that is less than a second axial flow component, wherein the second axial flow component is closer an axis of the tubular than the first axial conduit flow component.

10. The mixer element of claim 1, wherein the diesel emission fluid comprises urea.

11. A method for distributing a urea flow within a mixer element, the method comprising:

receiving an exhaust gas flow from an internal combustion engine into the mixer element;

inducing a first vortex of the exhaust gas flow in a first rotational direction in a first region of the mixer element;

injecting a urea fluid into the exhaust gas flow downstream of the first region;

causing a radial component to the urea fluid and exhaust gas flow in a second region of the mixer element, wherein the second region is downstream of the first region; and

inducing a second vortex of the fluid and exhaust gas flow in a second rotational direction opposite of the first rotational direction, wherein the second vortex is formed downstream of the second region.

12. The method of claim 11, wherein inducing the second vortex of the fluid and exhaust gas flow comprises forming axial and tangential flow components.

13. The method of claim 11, wherein inducing the first vortex through a helical mixer.

14. The method of claim 13, wherein forming the second vortex comprises forming the second vortex by one of a helical mixer and a swirl mixer.

15. The method of claim 11, comprising forming a flow tunnel within the first vortex, wherein a magnitude of a first axial component of the first vortex is less than a magnitude of a second axial component of the exhaust gas flow, wherein the second axial component is closer to an axis of the mixer element than the first axial component.

16. The method of claim 11, wherein forming the second vortex comprises breaking up droplets of the mixture by swirl blades.

17. The method of claim 11, wherein causing the radial component to the urea flow comprises flowing the urea flow through an impingement mixer.

18. A mixer element to be placed between an exhaust manifold and catalytic converter, the mixer element comprising:

a tubular that receives an exhaust gas flow;

a first mixer configured to form a first vortex of the exhaust gas flow in a first rotational direction;

an injector disposed on the tubular downstream of the first mixer, the injector being configured to inject a fluid flow into the exhaust gas flow; and

a second mixer positioned downstream of the injector, the second mixer comprising blades, wherein droplets of the fluid flow impact the blades to form small droplets that are directed by the blades to mix with the exhaust gas flow.

19. The mixer element of claim 18, wherein the first mixer comprises a swirl mixer and the second mixer comprises an impingement mixer.

20. The mixer element of claim 18, wherein the fluid flow comprises diesel emission fluid or hydrocarbons.