The present invention relates to an exhaust after treatment system. More particularly, the present invention relates to a mixer assembly for an exhaust after treatment system, and an exhaust after treatment system for diesel engines having said mixer assembly.
BACKGROUND OF THE INVENTION
Diesel engines are the preferred means of producing torque for use in a wide range of applications ranging from uses in transportation such as heavy-duty trucks and trains, off-road agricultural and mining equipment to the large scale production of onsite electrical power to name a few. The virtually unmatched power to mass ratios of diesel engines and the relative safety of the diesel fuel makes diesel engines the preferred choice for use in applications such as long-haul trucks, tractors, earth movers, combines, surface mining equipment, non-electric locomotives, high capacity emergency power generators and the like.
Diesel engines operate at high internal temperature. One consequence of the high operating temperatures of diesel engines is that at least some of the nitrogen present in the engine at the moment of combustion combines with oxygen to form oxides of nitrogen (NOx) including species such as nitrogen monoxide (NO) and nitrogen dioxide (NO2) as exhaust gas. Other harmful exhaust gases that are produced include carbon monoxide (CO) and unburned hydrocarbons (HC). Apart from such harmful gases, diesel engine exhausts also contain particulate matter. However, today's stringent regulatory systems, such as Bharat Stage VI (BS VI) require that there is reduction of such harmful substances from the diesel engine exhaust, and that harmless substances such as oxygen and water are released in the environment.

The devices that are typically used in exhaust after treatment system to reduce the aforementioned harmful substances from diesel engine exhausts consists of Diesel Oxidation Catalysts (DOC), particulate matter (PM) filters, for example, Diesel particulate filters (DPF) and Selective Catalytic Reduction (SCR) catalysts. By using a combination of physical mechanisms and chemical reactions, these systems work towards removal of particulates and harmful gases such as CO, HC and NOx. There are many variances between these systems as there is a continuous need to develop more efficient as well as compact systems.
As one of the systems, the Selective Catalytic Reduction (SCR) provides an effective means of reducing NOx emissions from Diesel engines through reaction with NH3 on SCR catalyst. The process normally involves injecting aqueous solution of urea - Urea Water Solution (UWS) as a spray before SCR. This aqueous urea spray strikes on exhaust tube surfaces & causes local cooling of the wall. Deposition of droplets and wall film formation can occur if the surface temperature decreases below a critical temperature. Evaporation from the wall film leads to further cooling and an increase in risk of formation of melamine complexes.
Thus, there is a need in the art for development of exhaust after treatment systems wherein the urea solution injection is performed close to the engine exhaust manifold where high exhaust temperature can help to reduce deposition phenomena.
OBJECTIVES OF THE INVENTION
The main objective of this invention is to provide an exhaust after treatment system wherein high exhaust temperature can help to reduce deposition phenomena.
Another objective of this invention is to increase the mixing length between DOC and SCR as compared to axial distance between them for complete vaporization of sprayed fluid medium droplets.

Another objective of this invention is to generate swirl and turbulence for enhanced mixing between injected fluid medium and exhaust gas resulting in better vaporization of the fluid medium.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.
According to some aspects of the invention, there is provided a mixer assembly for use in an exhaust after treatment system. The mixer assembly includes a helical passage for flow of exhaust gas, and one or more turbulence generating components that generate turbulence in the exhaust gas passing through the mixer assembly.
In some aspects, the mixer assembly includes an injection device in fluid communication with the helical passage, wherein the injection device injects metered quantity of a fluid medium into the exhaust gas stream flow in the helical passage.
In some aspects, the mixer assembly includes a first perforated baffle plate that forms a first portion of the helical passage for flow of exhaust gas, and a second baffle plate that forms a second portion of the helical passage for flow of exhaust gas.
In some aspects, the first and the second baffle plates are formed to create projections towards each other and connected to each other.

In some aspects, a mandrel structure joins the first baffle plate and the second baffle plate to create a boundary of helical passage.
In some aspects, the one or more turbulence generating components include a static mixer device, the static mixer device comprising one or more vanes supported in a support frame.
In some aspects, the vanes of the static mixer device are oriented such that the vanes are obliquely oriented to the exhaust gas flow direction creating a local angle of attack.
In some aspects, the vanes of the static mixer device are imparted with a twist along the exhaust gas flow direction from leading edge of vane to trailing edge.
In some aspects, the one or more turbulence generating components include one or more deflector walls that divides the helical pathway downstream of the static mixer into two or more sub-passages, and wherein the one or more deflector walls has multiple protruding guide vanes that deflect the flow of exhaust gas.
According to some other aspects of the invention, there is provided an exhaust gas after treatment system for a diesel engine, the system comprising an exhaust gas pipe, through which the exhaust gases from engine enters the after treatment system, a DOC assembly in fluid communication with the exhaust gas pipe, a mixer assembly as described above, in fluid communication with and located downstream of the DOC assembly, and an injection device housed in the mixer assembly, where the injection device injects metered quantity of a fluid medium into the exhaust gas stream flow in the helical passage of the mixer assembly. The exhaust gas after treatment system also includes a SCR/SDPF assembly in fluid communication with and located downstream of the mixer assembly.
Other aspects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS
Some of the objects of the invention have been set forth above. These and other objects, features, aspects and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where:
FIGS. 1A and IB illustrate an exhaust after treatment (EAT) system comprising the mixer assembly, where FIG. 1A is a schematic view of the EAT system, and FIG. IB is an exploded schematic view of the EAT system
FIGS. 2A and 2B illustrate a first embodiment of the mixer assembly in detail. FIG. 2A is a schematic view of the mixer assembly, and FIG. 2B is an exploded schematic view of the mixer assembly.
FIG. 3 A and 3B illustrate a first embodiment of the static mixer device as shown in the first embodiment of the mixer assembly.
FIGS. 4A and 4B illustrate a second embodiment of the mixer assembly in detail. FIG. 4A is a schematic view of the mixer assembly, and FIG. 4B is an exploded schematic view of the mixer assembly.
FIG. 5A and 5B illustrate a second embodiment of the static mixer device as shown in the second embodiment of the mixer assembly.
FIG. 6A and 6B illustrate the deflector wall 250 as shown in the second embodiment of the mixer assembly 200.
DETAILED DESCRIPTION
The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials are illustrated for various elements, those

skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized.
Definitions & Abbreviations
The following section includes definitions and full-forms of acronyms used in this specification. If any acronym or word is not elaborated or defined in this section, then said acronym or word will have a meaning commonly defined and acceptable in the art at the time of the filing of this application.
Abbreviations:
DOC: Diesel Oxidation catalyst
SCR: Selective Catalyst reduction
DPF: Diesel Particulate Filter
SDPF: SCR coated DPF
SCR/SPDF: SCR or SPDF
CO: Carbon Monoxide
HC: Hydrocarbon
NOx: Nitrogen Oxides
UI: Uniformity Index
EAT: Exhaust after treatment system
UWS: Urea Water Solution
Definitions:
DOC: Diesel Oxidation Catalyst is catalyst used to oxidise harmful gases CO (Carbon Monoxide) and HC (Unburned Hydrocarbon) coming from engine exhaust.

DPF: Diesel particulate Filter is used to trap fine particulate material e.g soot coming out of engine exhaust.
SCR: Selective catalyst reactor is a catalyst used to convert harmful NOx (Nitrogen oxides) gases present in the engine exhaust into harmless gases.
SDPF: (SCR Coated DPF): It is single unit performing the function of DPF and SCR. Walls of DPF is provided with coating so that both particle trapping and NOx reduction take place in DPF itself.
Uniformity Index (UI): It shows how uniformly the gas flow is distributed at the surface area across the direction of flow in substrate (DOC, DPF, SCR). Higher value of UI confirms more uniform flow which further results in better conversion in catalyst as maximum area is utilized for chemical reactions.
EAT: Exhaust After Treatment system is total system to convert harmful gases and filter particulate matter from engine exhaust that includes DOC, SCR or SDPF with inlet and outlet pipes.
Fluid Communication: The term fluid communication or the phrase "in fluid communication with" herein refers to two or more entities are so connected to allow a fluid (such as, exhaust gas) to flow between them. For example, the sentence "the DOC and the mixer assembly are in fluid communication with each other" means that a fluid (such as, exhaust gas) can flow between the DOC and the mixer assembly.
Overview
The present invention suggests an optimized way of installing an exhaust after treatment system (hereinafter referred to as the EAT system) with a diesel engine, where high exhaust temperature can help to reduce deposition phenomena. This includes close coupled DOC, SCR or SCR coated DPF (SDPF) with a mixer assembly between DOC and SCR or SDPF.

The EAT system and associated methods as described herein can significantly improve ammonia uniformity at SCR/SDPF face by breaking and evaporating fluid medium droplets (for example, aqueous solution of urea, introduced as a spray in the EAT system after DOC) using the mixer assembly. The mixer assembly increases particle residence time by significantly enhancing flow path length between DOC and SCR/SPDF and by causing secondary turbulence using double cross swirl exhaust flow.
To elaborate, hot exhaust gas from engine enters the EAT system through an inlet pipe. It then enters DOC wherein oxidation of CO and HC takes place. Downstream of DOC, exhaust gas enters the mixer assembly. In the mixer assembly, distance between DOC and SCR or SDPF is increased by guiding major part of the flow of exhaust gases through a helical/elliptical passage which is oriented substantially transverse to the axial direction of the flow. This passage is created with the help of two baffles; one perforated baffle located immediately downstream of the DOC and one baffle upstream of the SCR/SPDF. The helical passage greatly increases the mixing length as compared to axial distance between DOC and SCR/SPDF, thus ensuring maximum residence time for vaporization of droplets of a fluid medium (for example, aqueous solution of urea, UWS, introduced in the EAT system as a spray after DOC). The perforated baffle located downstream of the DOC has a significantly large opening to direct major part of the flow into the helical passage. The remaining part of the flow follows an axial route passing through the perforations of the perforated baffle to mix with the flow passing through the helical passage. Turbulence is generated due to mixing of the two flows. The turbulence enhances the vaporization rate of the fluid medium. In some embodiments, provision is also made to inject the fluid medium into the helical passage, more particularly, at the location where the major part of exhaust gas flow is entering into the helical passage. An injection device is oriented such that it will inject metered quantity of fluid and the injected fluid impacts a static mixer device approximately in a perpendicular direction to plane of entry into the static mixer device. This ensures

that the injected fluid does not impinge on the walls of the helical passage and thus promote efficient mixing. The static mixer device located in the helical passage consists of a number of vanes distributed along the perimeter of a section of the helical passage in different configurations, which may include, but not limited to, radial placement of vanes or parallel placement of vanes or oblique placement of vanes. Radial vanes are supported by one or more number of concentrically placed support rings, thus dividing the static mixer device into small channels for gas to flow through. The construction of the vanes is such that the leading edge of the vanes is along the flow, thus preventing separation of the flow from the vane, and the trailing edge is at an angle to the flow direction, thus creating a local angle of attack with respect to the flow direction and creating a swirl at the exit from the vane. This swirl further enhances the turbulence in the flow, optimizing the mixing of injected fluid with the exhaust gas. Also, the larger droplet of injected fluid medium upon impacting with hot surface of the vanes of the static mixer device breaks up into smaller droplet and as a consequence, vaporization rate of the fluid medium droplet increases and thus better mixing of the fluid medium with exhaust gas is achieved.
The helical passage downstream of the static mixer device is divided further into two or more channels by placement of one or more walls in the passage and along the flow direction. These wall/walls have perforations and protruding guide vanes such that the flow is diverted through the perforations. The guiding vanes are oriented such that the alternate vanes divert flow in opposite direction so as to promote cross flow through the wall. Furthermore, the protruding vanes can be imparted twists to divert flow towards the perforated baffle downstream of DOC, or the baffle upstream of the SCR/SPDF. A number of configurations comprising of different protruding vane lengths, angle of orientation with respect to wall, and twist imparted to the vanes can be optimized. These possible configurations of the wall aforementioned promote enhanced turbulence and serve as way for secondary particle breakup further enhancing vaporization of fluid medium

droplets. The baffle upstream of the SCR/SPDF includes a large opening directing the flow of exhaust gases towards the SCR/SPDF.
The enhanced vaporization and mixing performed in the mixer assembly significantly reduces the problem of deposition of droplets and wall film formation and thus results in enhanced performance of the SCR/SPDF.
Description of Drawings
FIGS. 1A and IB illustrate an exhaust after treatment (EAT) system 10 comprising a mixer assembly 100, where FIG. 1A is a schematic view of the EAT system 10, and FIG. IB is an exploded schematic view of the EAT system 10. The EAT system 10 also includes a DOC 12, a SCR/SDPF 14, and a fluid injector 16 in fluid communication with each other as illustrated. In FIG. IB, the arrows 18, 20, 22, 24 show the general direction of flow of exhaust gas in the EAT system 10, where the arrow 18 represents flow of exhaust gas coming from an engine into the DOC 12, the arrow 20 represents flow of exhaust gas from the DOC to the mixer assembly 100, the arrow 22 represents flow of exhaust gas from the mixer assembly 100 to the SCR/SDPF 14, and the arrow 24 represents the flow of exhaust gas out of the SCR/SPDF 14. In operation, exhaust gas flow from a diesel engine to the DOC 12 via an exhaust pipe. The exhaust gas after passing through the DOC 12 moves to the mixer assembly 100 and subsequently to the SCR/SPDF 14. Then, the exhaust gas is either passed through other pollution control devices or is emitted out to the atmosphere.
The DOC 12, the Diesel Oxidation Catalyst, is a catalyst used to oxidise harmful gases CO (Carbon Monoxide) and HC (Unburned Hydrocarbon) coming from engine exhaust. It is well known to a person skilled in the art and hence, it is not elaborated in detail here.
Similarly, the SCR/SPDF 14, can be a Selective catalyst reactor (SCR), which is a catalyst used to convert harmful NOx (Nitrogen oxides) gases present in the engine exhaust into harmless gases, or a SDPF (SCR coated DPF) where the

function of SCR can be integrated in DPF by providing suitable coating at walls of DPF. The SCR and SPDF are well known to a person skilled in the art and hence, are not elaborated in detail here.
The fluid injector 16 is an injection device used for injecting metered quantities of aqueous solution of urea as a spray. The fluid injector 16 is a well-known component to a person skilled in the art and hence, it is not elaborated in detail here.
FIGS. 2A and 2B illustrate a first embodiment of the mixer assembly 100 in detail. FIG. 2A is a schematic view of the mixer assembly 100, and FIG. 2B is an exploded schematic view of the mixer assembly 100. As illustrated, in this embodiment, the mixer assembly 100 includes an outer casing 102, a first perforated baffle 104, a second baffle 106, a mandrel 108, and a static mixer device 110. The outer casing 102 also includes a port 103 for attaching the fluid injector 16 to the mixing assembly 100.
The mixer assembly 100 can be made in any suitable shape, such as an elliptical, cylindrical, racetrack, or any polyhedral or rounded shape. In some embodiments, as shown in the Figures 2A-2B, the mixer assembly 100 has an elliptical shape.
The mixer assembly 100 can be sized in accordance with the size of the diesel engine and the EAT system 10 in which it is employed. In some embodiments, for example, for use with a small to medium size diesel engine, the mixer assembly 100 may have a length ranging between 50 mm and 350 mm, a width ranging between 50 mm and 350 mm, and depth ranging between 50 mm and 200 mm. The outer casing 102 may have a thickness ranging between 1.5 mm and 2.0 mm.
The first perforated baffle 104, the second baffle 106, and the mandrel 108 may be shaped and dimensioned to form a helical passage to allow for the exhaust gas to flow helically through the mixer assembly 100. The baffles 104, 106 may be connected to each other by the mandrel 108. The helical passage formed by the baffles 104, 106 is oriented substantially traverse to the axial direction of flow of the exhaust gas coming from the DOC 12. The helical passage increases the

mixing length of the injected fluid and the exhaust gas as compared to the axial distance between the DOC 12 and the SCR/SDPF 14. This ensures an increased residence time for vaporization of droplets of the injected fluid medium in the exhaust gas.
In addition, the perforations in the baffle 104 allows for a portion of the exhaust gas to flow in an axial route through the perforations. This axial flow of a portion of the exhaust gas collides with the helical flow from the helical passage and mixes with the helical flow. The mixing of the two flows results in turbulence, which further enhances the vaporization rate of the injected fluid in the exhaust gas. In some embodiments, the baffles 104, 106 are formed to include projections towards each other to form the helical passage.
In some embodiments, the helical passage has a width ranging between 50 mm and 345 mm, and a height ranging between 20 mm and 75 mm.
In some embodiments, the mandrel 108 may have a base diameter ranging between 30 mm and 70 mm, and a top diameter ranging between 15 mm and 30 mm, and a height ranging between 40 mm and 90 mm.
In some embodiments, the first perforated baffle 104 may have a length ranging between 45 mm and 345 mm, a width ranging between 45 mm and 345 mm, a pitch ranging between 20 mm and 75 mm, and thickness ranging between 1 mm and 2 mm. Perforation on perforated baffle can be round, oval, elliptical, cubical or any other polygonal shape. The diameter of each perforation on the perforated baffle ranges 104 between 2 mm and 10 mm. The perforations may have a density ranging between 2 to 10 per 10 centimetres square.
In some embodiments, the second baffle 106 may have a length ranging between 45 mm and 345 mm, a width ranging between 45 mm and 345 mm, a pitch ranging between 20 mm and 75 mm, and thickness ranging between 1 mm and 2 mm.
The port 103 may have a diameter ranging between 10 mm and 50 mm and may be positioned at a height ranging between 20mm and 100 mm from the base of the

mixer assembly 100, where the base of the mixer assembly 100 is referred to as the portion of the mixer assembly 100 closest to the SCR/SPDF 14.
FIG. 3 A and 3B illustrate a first embodiment of the static mixer device 110 as shown in the first embodiment of the mixer assembly 100. The static mixer device 110 includes a rectangular support frame 112 and vanes 114 fitted within the frame 112. The support frame 112 is divided into two halves with a plate 116 at the center of the frame 112. The vanes 114 are fitted in two slots with their parallel trailing edge 120 and leading edge 118 twisted in different directions.
In some embodiment, the vanes 114 of the static mixer device 110 are oriented such that the vanes 114 are obliquely oriented to the exhaust gas flow direction creating a local angle of attack. In some embodiments, the vanes 114 are shaped such that the leading edge 118 of the vanes 114 is along the direction of flow of the exhaust gas. This prevents separation of the exhaust gas flow from the vanes 114. The trailing edge 120 of the vanes 114 is at an angle to the flow direction. The angled trailing edge 120 creates a swirl in the exhaust gas flowing though the vanes 114. The swirl enhances turbulence in the exhaust gas flow. The resulting turbulence aids in mixing of the injected fluid with the exhaust gas.
The static mixer device 110 is positioned downstream of the injection port 16, and the static mixer device 110 and the injection port 16 are oriented such that the injected fluid impacts the static mixer device 110 approximately in a perpendicular direction to the plane of entry into the static mixer device 110. Since the exhaust gas passing through the vanes 114 is hot, the surface of the vanes 114 gets heated, this results in large droplets of the injected fluid impacting the hot surface of the vanes 114 and breaking up into smaller droplets, which increases the vaporization rate of the fluid medium droplets and further improves mixing of the fluid medium with the exhaust gas.
The static mixer device 110 is sized to fit within the helical passage. In some embodiments, the static mixer device 110 has a length ranging between 30 mm and 60 mm, a width ranging between 20 mm and 50 mm, a depth ranging between

5 mm and 20 mm. The support frame 112 has a thickness ranging between 1.5 mm and 2 mm, and the plate 116 has a thickness ranging between 1 mm and 1.5 mm. In some embodiments, vanes 114 are 6 to 16 in number, positioned equally spaced apart on the support frame 112. In some embodiments, each vane 114 has a length ranging between 30 mm and 70 mm, a width ranging between 10 mm and 30 mm, a thickness ranging between 1 mm and 1.5 mm. The angle between the leading edge 118 and the trailing edge 120 of the vanes 114 ranges between 30° and 60°.
The mixer assembly 100 and its subcomponents are made of stainless steel alloy which has good corrosion resistance and good oxidation resistance up to temperature of about 870 C. In some embodiments, the outer casing 102, the baffles 104 and 106, the mandrel 108, and the static mixer device 110 and its subcomponents, i.e., the support frame 112, the vanes 114, and the plate 116 are made of AISI 304. AISI 304 is an austenitic stainless steel which has Carbon C (<0.07), Chromium Cr (17%-19.5%), Nickel Ni (8-10.5%). Material of other component of the EAT system 10, like inlet pipe, outlet pipe can be AISI 439 or AISI 441 (alloy of stainless steel) or AISI 409(alloy of stainless steel).
In some embodiments, the components of the mixer device 100 may be manufactured by known manufacturing processes for sheet metals, such as die punching, blanking, and trimming.
In some embodiments, the outer casing 102, the baffles 104 and 106, the mandrel 108, and the static mixer device 110 are welded together to form the mixer assembly 100.
FIGS. 4A and 4B illustrate a second embodiment of the mixer assembly 200 in detail. FIG. 4A is a schematic view of the mixer assembly 200, and FIG. 4B is an exploded schematic view of the mixer assembly 200. As illustrated, in this embodiment, the mixer assembly 200 includes an outer casing 202, a first perforated baffle 204, a second baffle 206, and a static mixer device 210. The outer casing 202 and the baffles 204 and 206 of the second embodiment (mixer

assembly 200) are similar in construction and features as the outer casing 102, and baffles 104 and 106 of the first embodiment (mixer assembly 100) as described above. In the second embodiment (mixer assembly 200), a mandrel is not used to join the baffles 204, 206. Instead, the mixer assembly 200 includes a deflector wall 250 between the baffles 204 and 206 that connects the baffles 204 and 206 to each other. The deflector wall 250 includes protruding vanes 252. The outer casing 202 also includes a port 203 for attaching the fluid injector 16 to the mixing assembly 200.
FIG. 5 A and 5B illustrate a second embodiment of the static mixer device 210 as shown in the second embodiment of the mixer assembly 200. The static mixer device 210 includes a circular ring-shaped support frame 212. The support frame 212 has slots in which radial vanes 214 are fitted.
In some aspects, the vanes 214 of the static mixer device 210 are oriented such that the vanes 214 are obliquely oriented to the exhaust gas flow direction creating a local angle of attack. In some embodiments, the leading edge 218 of each vane is along the flow, and the trailing edge 220 of each vane is bend at angle to form a crisscross flow structure. The crisscross flow structure causes a swirl in the exhaust gas flowing though the vanes 214. The swirl enhances turbulence in the exhaust gas flow. The resulting turbulence aids in mixing of the injected fluid with the exhaust gas.
Similar to the static mixer device 110 illustrated in the first embodiment, the static mixer device 210 is positioned downstream of the injection port 16, and the static mixer device 210 and the injection port 16 are oriented such that the injected fluid impacts the static mixer device 210 approximately in a perpendicular direction to the plane of entry of the static mixer device 210. Since the exhaust gas passing through the vanes 214 is hot, the surface of the vanes 214 gets heated, this results in large droplets of the injected fluid impacting the hot surface of the vanes 214 and breaking up into smaller droplets, which increases the vaporization rate of the fluid medium droplets and further improves mixing of the fluid medium with the exhaust gas. Further, in some embodiments, the radial vanes 214 are extruding

radially outwards of support frame 212 and welded to the baffles 204, 206 and outer casing 202. An air gap is maintained between the vanes 214 of the static mixer device 210 and surrounding baffles 204, 206 and the outer casing 202. The vanes 214 are continuously heated by exhaust gas and the heat is not directly dissipated to the baffles 204, 206 or the outer casing 202. This further enhances the break up and vaporization of fluid medium droplet.
The static mixer device 210 is sized to fit within the helical passage. In some embodiments, the static mixer device 210 has a diameter ranging between 30 mm and 50 mm, a depth ranging between 10 mm and 20 mm. The support frame 212 has a thickness ranging between 1 mm and 2 mm. In some embodiments, vanes 214 are 4 to 10 in number, positioned equally spaced apart on the support frame 212. In some embodiments, each vane 214 has a length ranging between 10 mm and 50 mm, a width ranging between 10 mm and 30 mm, a thickness ranging between 1 mm and 2 mm. The angle between the leading edge 218 and the trailing edge 220 of the vanes 214 ranges between 30° and 60°.
FIG. 6A and 6B illustrate the deflector wall 250 as shown in the second embodiment of the mixer assembly 200. As shown, the deflector wall 250 and the protruding vanes 252 divide the flow into two channels within the helical passage. In some embodiments, as shown, the protruding vanes 252 made in the deflector wall 250 by cutting out portions of the deflector wall 250 and then bending those portions. This results in perforations in the deflector wall 250 next to the vanes 252. The flow of the exhaust gas crisscrosses through these perforations and guiding vanes between the two channels formed by the wall 250, and further increases turbulence and vaporization of the fluid medium droplets. In some embodiments, the vanes 252 are oriented such that the alternate vanes divert flow in the opposite direction to promote cross flow through the wall 250. Further, in some embodiments, the vanes are bent upwards or downwards to direct the flow towards the perforated baffle 204 or the second baffle 206, to further increase turbulence.

The wall 250 is positioned within the helical passage downstream of the static mixer device 210 and follows the helical passage towards the SCR/SPDF 14. In some embodiments, the wall 250 may have a length ranging between 60 mm and 120 mm, a thickness ranging between 1 mm and 2 mm.
The vanes 252 may have a length ranging between 5 mm and 20 mm, and may be angled at an angle ranging between 20° and 60° away from the wall 250. In some embodiments, the vanes 252 may further be imparted an upward or downward twist at an angle ranging between 15° and 30°.
In some embodiments, the static mixer device 210 may include a plurality of walls similar to wall 250 arranged within the helical passage to further enhance vaporization of the injected fluid in the mixer assembly 200.
In some embodiments, the components of the mixer assembly 200 may be manufactured by known manufacturing processes for sheet metals, such as, die punching, blanking, and trimming.
In some embodiments, the outer casing 202, the baffles 204 and 206, the static mixer device 210, and the deflector wall 250 are welded together to form the mixer assembly 200.
Various other modifications, adaptations, and alternative designs are of course possible in light of the above teachings. Therefore, it should be understood at this time that within the scope of the appended claims the invention might be practiced otherwise than as specifically described herein.
ADVANTAGES
1. The present invention presents an advantage that it increases length of flow path between DOC and SCR/SDPF.
2. Another advantage of the present invention is that it allows breakup of large size droplets of injected fluid medium into smaller size droplets for high evaporation rate with suitable stator mixer.

3. Another advantage of the present invention is that it provide way of turbulence in double closed elliptical or helical swirl chamber which enhances mixing of fluid medium with exhaust gas.
4. Another advantage of the present invention is that it provides high ammonia and Velocity UI on SCR/SDPF.
5. Another advantage of the present invention is that it provides minimum fluid medium deposition on the walls of the structure.

We Claim

1.A mixer assembly (100, 200) for use in an exhaust after treatment system
(10), the mixer assembly (100, 200) comprising:
a helical passage for flow of exhaust gas; and
one or more turbulence generating components that generate turbulence in the exhaust gas passing through the mixer assembly (100, 200).
2. The mixer assembly (100, 200) as claimed in claim 1, wherein the mixer assembly (100, 200) includes an injection device (16) in fluid communication with the helical passage, wherein the injection device (16) injects metered quantity of a fluid medium into the exhaust gas stream flow in the helical passage.
3. The mixer assembly (100, 200) as claimed in claim 1, wherein the mixer assembly (100, 200) includes:
a first perforated baffle (104, 204) that forms a first portion of the helical passage for flow of exhaust gas; and
a second baffle (106, 206) that forms a second portion of the helical passage for flow of exhaust gas.
4. The mixer assembly (100) as claimed in claim 3, wherein the first and the
second baffles (104, 106) are formed to create projections towards each other and
connected to each other.

5. The mixer assembly (100) as claimed in claim 3, wherein a mandrel (108) structure joins the first baffle (104) and the second baffle (106) to create a boundary of helical passage.
6. The mixer assembly (100, 200) as claimed in claim 1, wherein the one or more turbulence generating components include a static mixer device, the static mixer device comprising one or more vanes (114, 214) supported in a support frame (112, 212).
7. The mixer assembly (100, 200) as claimed in claim 6, wherein the vanes (114, 214) of the static mixer device (110, 210) are oriented such that the vanes (114, 214) are obliquely oriented to the exhaust gas flow direction creating a local angle of attack.
8. The mixer assembly (100, 200) as claimed in claim 6, wherein the vanes (114, 214) of the static mixer device (110, 210) are imparted with a twist along the exhaust gas flow direction from leading edge (118, 218) of vane (114, 214) to trailing edge (120, 220).
9. The mixer assembly (200) as claimed in claim 6, wherein the one or more turbulence generating components include one or more deflector walls (250) that divides the helical pathway downstream of the static mixer (210) into two or more sub-passages, and wherein the one or more deflector walls (250) has multiple protruding guide vanes (252) that deflect the flow of exhaust gas.
10. An exhaust gas after treatment system (10) for a diesel engine, the system (10) comprising:

an exhaust gas pipe, through which the exhaust gases from engine enters the after treatment system (10);
a DOC assembly (12) in fluid communication with the exhaust gas pipe;
the mixer assembly (100, 200) as claimed in claim 1, in fluid communication with and located downstream of the DOC assembly (12);
an injection device (16) housed in the mixer assembly (100, 200), wherein the injection device (16) injects metered quantity of a fluid medium into the exhaust gas stream flow in the helical passage of the mixer assembly (100, 200).
a SCR/SDPF assembly (14) in fluid communication with and located downstream of the mixer assembly (100, 200).