Diesel exhaust fluid decomposition assembly and exhaust aftertreatment system

Abstract

diesel exhaust fluid decomposition assembly comprising: an outlet cover (412), an inlet cover (410) coupled to the outlet cover and a support plate (414) arranged between the outlet cover and the inlet cover, wherein the support plate forms an outlet channel (504) with the outlet cover and an inlet channel (502) with the inlet cover, wherein the inlet channel is fluidically coupled to the outlet channel, wherein the inlet channel is located next to the outlet channel, wherein the outlet cover, the inlet cover and the support plate are axially aligned along a longitudinal axis, and wherein the outlet cover further comprises a plurality of openings (406) formed in a grid pattern.

Description

The present application relates generally to exhaust aftertreatment systems for internal combustion engines, and more specifically, to selective catalytic reduction (SCR) systems in an exhaust aftertreatment system.The invention specifically relates to a diesel exhaust fluid decomposition assembly according to claim 1 or according to claim 14 and to an exhaust gas aftertreatment system having a diesel exhaust fluid decomposition chamber according to claim 11.Exhaust treatment systems receive and treat exhaust gas generated by an internal combustion engine. Typical exhaust aftertreatment systems include any of various components configured to reduce the level of harmful exhaust emissions present in the exhaust. For example, some diesel engine exhaust aftertreatment systems include various components such as a diesel oxidation catalyst (DOC), a particulate filter or diesel particulate filter (DPF), and a selective catalytic reduction (SCR) catalyst. In some exhaust aftertreatment systems, exhaust gas flows first through the diesel oxidation catalyst, then through the diesel particulate filter, and then through the SCR catalyst.Each of the DOC, DPF, and SCR catalyst components is configured to perform a particular treatment of exhaust emissions on the exhaust gas passing through the components. Generally, the DOC reduces the content of carbon monoxide and hydrocarbons present in the exhaust gas by oxidation processes. The DPF filters harmful diesel particulates and soot present in the exhaust gas. Finally, the SCR catalyst reduces the amount of nitrogen oxides (NO x). present in the exhaust gas.The SCR catalyst is configured to reduce NO x to less harmful emissions such as N 2 and H 2 O in the presence of ammonia (NH 3). Since ammonia is not a natural by-product of the combustion process, it must be artificially added to the exhaust gas using a diesel exhaust fluid (DEF) that decomposes into ammonia before the exhaust gas enters the SCR catalyst.However, some prior art exhaust aftertreatment systems do not provide sufficient decomposition and mixing of injected DEF. Conventional systems often cause exhaust gas recirculation within the DEF decomposition tube or low temperature ranges within the decomposition tube. Exhaust gas recirculation and low temperature regions within the decomposition tube may result in insufficient mixing or decomposition, which may result in the formation of solid DEF deposits on the inner walls of the decomposition tube and the DEF injector. Solid DEF deposits include the solid byproducts of incomplete decomposition of urea such as biuret, cyanuric acid, ammelide and ammelin. In addition, insufficient mixing and decomposition may result in a low index of even distribution of ammonia vapor, which may result in uneven distribution of ammonia on the surface of the SCR catalyst, lower NO x- conversion efficiency, and other deficiencies.According to one embodiment, the reducing agent decomposition system includes an exhaust gas chamber which contains an inlet and an outlet. The first exhaust gas distribution component brings about vortex exhaust gas flow profiles in the exhaust gas chamber. The system further includes a second exhaust distribution component positioned within the chamber and capable of being brought into exhaust delivery communication with the inlet. The second exhaust distribution component includes features that effect a swirling exhaust flow profile in a space defined by the second exhaust distribution component. The system further includes a reductant injector coupled to the exhaust chamber.DE 11 2009000 650 T5 discloses a system having a feed device arranged in an exhaust gas duct for selectively introducing a reducing agent into an exhaust gas flow, a housing having an exhaust gas inlet in communication with the exhaust gas duct, wherein the housing defines a first flow path which conducts the exhaust gas flow in a first direction, a second flow path which conducts the exhaust gas flow in a second direction, and a third flow path which conducts the exhaust gas flow back in the first direction, and an exhaust gas outlet in communication with the third flow path.DE 11 2010 002 589 T5 discloses a motor vehicle exhaust system having two monoliths, an upstream monolith and a downstream monolith for treating the exhaust gases circulating in the exhaust system, wherein the upstream monolith and the downstream monolith are arranged in series in the exhaust system, an injection section which is arranged between an upstream surface bounded by the upstream monolith and a downstream surface bounded by the downstream monolith and has a duct for the circulation of an exhaust gas stream which extends from the upstream surface to the downstream surface, wherein the duct has a central axis with a predetermined length between the upstream surface and the downstream surface, wherein the injection section has an injection device for a reactive agent which is attached to the injection section and is suitable for injecting a reactive agent into the injection section. The injection portion includes at least a first shell disposed in the circulation passage in the path of the exhaust gas flow such that the average path of the exhaust jets is longer by at least 20% with respect to the predetermined length. the injection portion includes a second shell disposed in the circulation passage between the upstream surface and the first shell, and the injection of the reactive agent is performed between the first shell and the second shell.The subject matter of the present application has been developed in response to the current state of the art, and more particularly, in response to the problems and requirements in the art that are not fully solved by currently available exhaust aftertreatment systems using an SCR system. Accordingly, the subject matter of the present application has been developed to provide various embodiments of an apparatus and system for reducing adverse conditions due to formation of DEF deposits that overcome at least some of the above or other shortcomings of the prior art.A diesel exhaust fluid decomposition assembly according to the present invention is set out in claim 1 and in the subordinate claim 14. An exhaust aftertreatment system according to the present invention is set out in claim 11. Further preferred embodiments are set out in the dependent claims.The above problem is solved in a first variant by a diesel exhaust fluid decomposition assembly according to claim 1, comprising an outlet cover, an inlet cover coupled to the outlet cover, and a support plate disposed between the outlet cover and the inlet cover. The carrier plate forms an outlet channel with the outlet cover and an inlet channel with the inlet cover. The inlet channel is fluidly coupled to the outlet channel, and the inlet channel is adjacent to the outlet channel.Preferred embodiments and developments of this diesel exhaust fluid decomposition assembly are the subject matter of claims 2 to 10.A diesel exhaust fluid injector may be coupled to the inlet cover to inject a diesel exhaust fluid into the inlet passage.In certain implementations, the inlet channel has a converging cross-sectional profile, thereby increasing the velocity of a fluid as it passes through the inlet channel.The outlet channel may have a converging cross-sectional profile, thereby increasing the velocity of a fluid as it passes through the outlet channel.At least one first end of the inlet cover or a first end of the outlet cover may form a fluid guide to change the flow direction of a fluid between the inlet channel and the outlet channel.The inlet channel and the outlet channel may each have a non-circular cross-sectional profile.According to some implementations, the support plate is formed from at least two coupled non-planar portions, the at least two non-planar portions each having a first surface that is part of the inlet channel and a second surface that is part of the outlet channel. The at least two coupled non-planar portions may be arranged to form a first region in the outlet channel that includes a converging cross-sectional profile and a second region in the outlet channel that includes a diverging cross-sectional profile.In some implementations, the outlet cover includes a plurality of openings formed in a grid pattern. The plurality of openings may each have a diameter in the range of about 0.2 to 0.3 inches, and the grid pattern may have a grid pitch in the range of about 0.5 to 0.75 inches.According to some implementations, the inlet cover includes an inlet port fluidly coupled to a chamber formed by an outer cover and the inlet cover.The outer cover may be configured to envelop the inner cover and direct a fluid around at least a portion of an outer surface of the inlet cover. At least a portion of the inlet cover may thus be maintained at a temperature substantially corresponding to the temperature of fluid within the chamber.In some implementations, the inlet cover further includes a plurality of openings forming a grid pattern in the inlet cover. All openings each have substantially the same cross-sectional area.The inlet cover may further include a non-circular opening having a cross-sectional area larger than that of an opening of the plurality of openings.The outlet cover may also include a plurality of openings forming a grid pattern extending from a first end of the outlet cover to a second end of the outlet cover. The cross-sectional area of each of the plurality of openings may be selected according to the proximity to the first end.According to a further teaching of the invention, claim 11 relates to an exhaust gas aftertreatment system in which the problem indicated above is solved. This exhaust aftertreatment system includes a housing having an exhaust inlet and an exhaust outlet. The housing is configured to enclose a diesel particulate filter (DPF) and at least one selective catalytic reduction (SCR) catalyst and direct a flow of exhaust gas through the DPF and the SCR. The system also includes a diesel exhaust fluid (DEF) decomposition chamber removably attached to the housing and fluidly coupled to the DPF. The decomposition chamber includes an inlet cover coupled to an outlet cover and a support plate disposed between the outlet cover and the inlet cover. The carrier plate forms an outlet channel with the outlet cover and an inlet channel with the inlet cover. The inlet channel is fluidly coupled to the outlet channel, and the inlet channel is adjacent to the outlet channel.According to some implementations of the system, the inlet channel has a converging cross-sectional profile, which increases the velocity of a fluid as it passes through the inlet channel.The outlet channel may have a converging cross-sectional profile, thereby increasing the velocity of a fluid as it passes through the outlet channel.The support plate may be formed from at least two coupled non-planar portions, each of the two non-planar portions having a first surface that is part of the inlet channel and an opposing second surface that is part of the outlet channel.The system may also include a plurality of SCR catalysts each having an inlet surface, the DEF decomposition chamber configured to provide a substantially uniform distribution of DEF and exhaust gas at the inlet surfaces of the plurality of SCR catalysts.In yet another embodiment according to claim 14, a diesel exhaust fluid decomposition assembly includes an outlet cover, an inlet cover coupled to the outlet cover, and a support plate disposed between the outlet cover and the inlet cover. The carrier plate forms an outlet channel with the outlet cover for guiding an exhaust gas flow in a first direction and an inlet channel with the inlet cover for guiding the exhaust gas flow in a second direction, which is parallel but opposite to the first direction.Reference throughout this specification to features, advantages, or similar formulations does not mean that all features and advantages that may be realized with the subject matter of the present disclosure may be found or should be found in a single embodiment or implementation form of the subject matter. Rather, language referring to the features and advantages should be understood to mean that a particular feature, advantage, or characteristic described in connection with an embodiment may be found in at least one embodiment. A discussion of the features and advantages and similar formulations herein may, but need not necessarily, relate to the same embodiment or embodiment.The described features, advantages, and characteristics of the subject matter of the present disclosure may be combined in any suitable manner in one or more embodiments and / or implementations. One skilled in the art will understand that the subject matter of the present disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment or implementation. In other instances, additional features and advantages may be seen in certain embodiments and / or implementations that may not be present in all embodiments or implementations of the subject matter of the present disclosure. These features and advantages of the present subject matter will become more apparent from the following description and the appended claims, or may be realized by the application of the subject matter as set forth below.In order that the advantages of the subject matter may be more readily understood, a more detailed description of the subject matter briefly described above will follow with reference to specific embodiments illustrated in the accompanying drawings. Since it is understood that these drawings represent only typical embodiments of the subject matter and are therefore not to be considered as limiting the scope thereof, the subject matter will be described and explained in more detail and detail by means of the drawings, in which: FIG. 1 illustrates an embodiment of an internal combustion engine system according to embodiments of the present disclosure, FIG. 2 shows an embodiment of the system for treating exhaust gases, FIG. 3 illustrates another embodiment of the system according to embodiments of the present disclosure, FIG. 4 illustrates an embodiment of the decomposition chamber according to embodiments of the present disclosure, FIG. 5 shows a further embodiment of the decomposition chamber, and FIG. 6 is a top view of a cross section of the system according to embodiments of the present disclosure.Reference herein to "one embodiment" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the subject matter of the present disclosure. The appearances of the phrase "in one embodiment" and similar language herein may or may not necessarily be referring to one and the same embodiment. Likewise, the use of the term "implementation" means an implementation having a particular feature, structure, or characteristic described in connection with one or more embodiments of the subject matter of the present disclosure, but if explicit different association is absent, then an implementation may be associated with one or more embodiments.The described features, structures, or characteristics of the subject matter of the present disclosure may be combined as appropriate in one or more embodiments. In the following description, numerous specific details are set forth in order to provide a more detailed understanding of embodiments of the subject matter. However, one skilled in the art will recognize that the subject matter may be practiced without one or more specific details or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of the subject matter.FIG. 1 shows an embodiment of an engine system 10 according to an embodiment of the present disclosure. The system 10 includes an internal combustion engine 100 and an exhaust aftertreatment system 200 coupled to the exhaust outlet 110 of the engine. The internal combustion engine 100 may be a compression-ignited internal combustion engine, for example a diesel engine, or a spark-ignited internal combustion engine, for example a gasoline engine. The engine 100 may include various although not shown sensors such as temperature sensors and mass flow sensors.The exhaust aftertreatment system 200 is coupled to an exhaust pipe of an exhaust manifold. The exhaust gas flowing through the exhaust pipe is represented by the exhaust gas outlet 110. At least a portion of the exhaust outlet 110 flows through the exhaust aftertreatment system 200. Generally, the exhaust aftertreatment system 200 is configured to remove various chemical compounds and particulate emissions present in the exhaust outlet 110 received from the exhaust pipe. After treatment by the exhaust aftertreatment system 200, the exhaust gas is exhausted to the atmosphere via an exhaust pipe (not shown). In some implementations, the exhaust aftertreatment system 200 is mounted on a vehicle that houses the engine.In the depicted embodiment, the exhaust aftertreatment system 200 includes an oxidation catalyst 210, a particulate filter or diesel particulate filter (DPF) 220, a selective catalytic reduction (SCR) system 230 with a diesel exhaust fluid (DEF) supply system 232, a DEF decomposition chamber 234, and an SCR catalyst 235. In an exhaust flow direction indicated by a directional arrow 244, the exhaust outlet 110 passes through the oxidation catalyst 210, the DPF 220, the decomposition chamber 234, and the SCR catalyst 235, and is then exhausted to the atmosphere via the exhaust pipe. In other words, the DPF 220 is disposed downstream of the oxidation catalyst 210, and the SCR catalyst 235 is disposed downstream of the DPF 220.The oxidation catalyst 210, the DPF 220, the decomposition chamber 234, and the SCR catalyst 235 may be coupled to each other through an exhaust pipe. Generally, the exhaust gas treated in the exhaust aftertreatment system 200 and released to the atmosphere will thus contain fewer pollutants, for example diesel particulates, NO x and hydrocarbons such as carbon monoxide and carbon dioxide, than untreated exhaust gas.The oxidation catalyst 210 may be any of the Diesel Oxidation Catalyst (DOC) known in the art. Generally, the oxidation catalyst 210 is configured to oxidize at least a portion of the particulates, e.g., the soluble organic fraction of soot, in the exhaust gas and to reduce unburned hydrocarbons and CO in the exhaust gas to less environmentally harmful compounds. For example, the oxidation catalyst 210 may reduce the hydrocarbon and CO concentrations in the exhaust gas to meet the prescribed emissions standards.The DPF 220 may be one of the particulate filters known in the art configured to reduce particulate concentrations, e.g., soot and ash, in the exhaust gas to meet prescribed emissions standards. The DPF 220 may be electrically coupled to a controller that controls various characteristics of the DPF 220, such as the timing and duration of filter regeneration phases.The SCR system 230 includes a DEF delivery system 232 that includes a DEF source 233, a pump 236, and a DEF delivery mechanism 238 (e.g., an injector). The DEF source 233 may be a container or tank that can hold DEF, such as ammonia (NH 3) or urea. The DEF source 233 is in a DEF delivery connection with the pump 236, which is configured to pump DEF from the DEF source to the DEF delivery mechanism 238. The DEF supply mechanism 238 is coupled to the exhaust pipe at a location upstream of the decomposition chamber 234 and downstream of the DPF 220. The delivery mechanism 238 includes an injector that is selectively controllable to inject DEF 250 directly into the exhaust stream through an introduction port or tube of the injector into the DEF decomposition chamber 234.In some embodiments, the diesel exhaust liquid is urea that decomposes as it flows through the decomposition chamber 234, thereby producing ammonia. The ammonia reacts with NO x, in the presence of the SCR catalyst 235 to reduce NO x to less harmful emissions such as N 2 and H 2 O. The ability of the SCR catalyst 235 to reduce NO x to less harmful emission is largely dependent on the ability of the diesel exhaust liquid to decompose to ammonia.For safety reasons in connection with the storage of gaseous ammonia, ammonia is typically not injected directly into the exhaust gas. Accordingly, the exhaust aftertreatment system 200 is configured to inject the diesel exhaust liquid or reductant into the exhaust gas that is capable of decomposing into gaseous ammonia in the presence of exhaust gas under certain conditions. The DEF commonly used by conventional exhaust aftertreatment systems is a urea-water solution.The decomposition of DEF into gaseous ammonia generally proceeds in three stages. First, the DEF mixes with exhaust gas, and water is removed from the DEF by an evaporation process. Second, the temperature of the exhaust gas causes a thermolysis induced phase change in the DEF and decomposition of the DEF into isocyanic acid (HNCO) and NH 3. Third, the isocyanic acid reacts with water in a hydrolysis process under certain pressure and temperature conditions, thereby decomposing into ammonia and carbon dioxide (CO 2). The gaseous ammonia is then introduced at the inlet surface of the SCR catalyst 235, flows through the catalyst, and is consumed in the NO x- reduction process. Unused ammonia exiting the SCR system may be reduced to N 2 and other less harmful or less toxic constituents using an ammonia oxidation catalyst.The feed mechanism 238 injects DEF into the decomposition chamber 234. Upon injection into the exhaust stream, the injected DEF is heated by the exhaust stream, thereby inducing decomposition of DEF into ammonia. As the DEF and exhaust mixture flows through the decomposition chamber, the DEF continues to mix with the exhaust before entering the SCR catalyst 235. As described below, the configuration of the decomposition chamber 234 allows the DEF to sufficiently decompose and mix with the exhaust gas before entering the SCR catalyst 235 to provide a sufficiently uniform distribution of ammonia on the inlet surface of the SCR catalyst 235.FIG. 2 shows an embodiment of the exhaust treatment system 200. The system 200 is configured such that the smallest possible longitudinal space is occupied in a vehicle. Referring to FIG. 2, the longitudinal axis is represented by directional arrow 262. The system 200 keeps longitudinal space consumption in a vehicle low by supporting the SCR catalyst 235 on the DPF 220. Exhaust enters the DPF 220 and continues to flow in a direction indicated by directional arrows 268. By passing the gas through the DPF 220 in a first longitudinal direction and then through the SCR catalyst 235 in a second parallel but opposite direction, the system 200 maintains a sufficiently large distance for treatment of the exhaust gas while reducing the overall longitudinal space occupied by the system 200.A cover 270 is attached to the system 200 and encloses an outlet opening 272 and an inlet opening 274 of the decomposition chamber 234. The cover 270 forms a chamber that fluidly couples the DPF 220 and the decomposition chamber 234. In other words, exhaust gas flowing through the DPF 220 flows through the chamber provided by the cover 270 to the inlet port 274 of the decomposition chamber 234. A housing (not shown) directs the exhaust gas from the decomposition chamber 234 into at least one SCR catalyst 235. In the illustrated embodiment, the system 200 includes a plurality of SCR catalysts 235. The SCR catalysts 235 have similar dimensions as a traditional passenger car SCR catalyst in one embodiment. For example, each SCR catalyst 235 may have a diameter in the range of 5 to 6 inches and a length in the range of 9 to 12 inches.In one embodiment, the sum of the cross-sectional areas of the SCR catalysts 235 is substantially equal to the cross-sectional area of the DPF 220. In another embodiment, the sum of the mass flow rates of the SCR catalysts 235 is substantially equal to the mass flow rate of the DPF 220. In other words, the system 200 includes a quantity of SCR catalysts 235 capable of maintaining an exhaust gas flow rate and pressure equal to the DPF 220. In some embodiments, this is accomplished with a single SCR catalyst 235 having a diameter sufficient to maintain the indicated exhaust flow rate. In another embodiment, the exhaust flow rate and pressure are maintained with an array of SCR catalysts 235 that may together maintain the exhaust flow rate and pressure of the DPF 220.Decomposition chamber 234 is shaped to include an inlet channel fluidly coupled to inlet port 274 and an outlet channel fluidly coupled to the inlet channel. The inlet channel and the outlet channel will be described in more detail with reference to FIGS. 4, 5 to 6.FIG. 3 illustrates another embodiment of the system 200 according to the present disclosure. As described above, the system 200 includes a housing 302 enclosing the DPF and the SCR catalysts 235. The DPF 220 is formed with an outlet 304 that passes through the housing 302 as shown. The cover 270 is removably coupled to the housing 302 and provides a seal that prevents exhaust gases from escaping. Exhaust gases flow into a chamber formed by the cover from the outlet 304 of the DPF to the inlet 274 of the decomposition chamber 234. The chamber is formed by inner surfaces of the cover 270 and the housing 302. The exhaust gas passes through the chamber and into the opening 274 of the decomposition chamber 234.In one embodiment, decomposition chamber 234 is removably coupled to housing 302. Decomposition chamber 234 is coupled to housing 302 by a fastener (not shown). For example, the decomposition chamber 234 may be fixed by screws, bolts, etc.In another embodiment, decomposition chamber 234 is fixedly coupled to housing 302. For example, decomposition chamber 234 may be welded to housing 302.In another embodiment, the decomposition chamber 234 is integrally formed with the housing.An opening 306 in the housing 302 may have a profile that matches an outer profile of the decomposition chamber 234. The opening 306 in the housing 302 is configured to receive an outlet surface of the decomposition chamber, which will be described in more detail with reference to FIG. 5. The opening 306 is arranged and configured to allow the exhaust gas to flow from the decomposition chamber 234 to the SCR catalysts 235. The SCR catalysts 235 may have a circular cross-sectional profile as shown. In one embodiment, the SCR catalysts 235 are arranged radially, with a first layer (SCR catalyst 235 a) over and adjacent to the DPF 220. A second layer of SCR catalysts 235 bmay be disposed in a compact arrangement over the first layer of SCR catalysts 235. Together, the clusters of SCR catalysts 235 a, 235 bare configured to maintain the flow rate of the exhaust gas from the DPF 220.FIG. 4 shows an embodiment of decomposition chamber 234, in accordance with embodiments of the present disclosure. Decomposition chamber 234, in one embodiment, is a substantially rectangular device having a plurality of openings 402 on an inlet side 404 for receiving exhaust gas and a plurality of openings 406 on an opposite outlet side 408 for the outlet of the exhaust gas. For clarity and simplicity, only one representative opening of the plurality of openings 402, 406 is numbered in FIG. 4.The decomposition chamber 234 is formed of an inlet cover 410, an outlet cover 412, and a support plate 414 disposed between the inlet cover 410 and the outlet cover 412. The support plate 414 may include mounting apertures 416 for receiving a fastener and coupling the decomposition chamber 234 to the housing as described above with reference to FIG. 3. The support plate 414 also forms a boundary between the inlet side 404 and the outlet side 408.In an embodiment, the plurality of holes 406 of the outlet cover 412 are arranged in a grid pattern. The grid pattern may look as shown, or the plurality of grid openings 406 may alternatively be arranged vertically and horizontally. In another embodiment, the plurality of apertures 406 may be arranged in a pattern based on the cross-sectional profile of a single aperture. In other words, if the cross-sectional profile of the single opening 406 is a hexagon, the corresponding grid pattern may resemble a honeycomb structure. In one embodiment, the pitch 418 in the grid pattern is in the range of about 0.5 to 0.75 inches. The term pitch refers to the distance between successive corresponding points in the grid pattern. In other words, the term pitch refers to how many times the pattern repeats. Each opening in the outlet cover 412 may have a diameter in the range of about 0.2 to 0.3 inches.In another embodiment, each opening 406 has a non-circular cross-sectional profile. In this embodiment, each opening 406 of the outlet cover 412 may have a cross-sectional area similar to the cross-sectional area of a circular opening having a diameter in the range of about 0.2 to 0.3 inches.The openings 406 of the outlet cover 412 may each have a uniform cross-sectional area.In an alternative embodiment, the cross-sectional area of the openings 406 varies according to the location of the opening in the outlet cover 412. For example, apertures 406 closer to a first end 430 of the outlet cover 412 may have a cross-sectional area that is less than apertures 406 closer to a second end 432 of the outlet cover 412, or vice versa.The configuration (e.g., amount, size, pattern, etc.) of the openings 406 may depend on the configuration (e.g., amount, size, pattern, etc.) of the SCR catalysts to provide a relatively uniform distribution of DEF and exhaust gas at the inlets of the SCR catalysts.In one embodiment, the inlet cover 410 is formed with an inlet opening 420. The inlet port 420 is formed at an end of the inlet cover 410 and allows entry of a DEF spray from a DEF injector. A DEF spray tube, not shown, may be attached to the inlet cover 410 over the inlet port 420 to restrict the flow of exhaust gas through the inlet port 420, but to allow the flow of injected DEF through the inlet port 420 into the inlet channel of the decomposition chamber 234.In another embodiment, the inlet cover 410 is formed with the inlet opening 420 and a plurality of smaller openings 402 disposed around the inlet opening 420. In one example, the smaller openings 402 are similar in size to the openings 406 of the outlet cover 412. Through the plurality of smaller openings 402, exhaust gas enters the inlet channel of the decomposition chamber 234.FIG. 5 shows another embodiment of the decomposition chamber 234. In the illustrated embodiment, decomposition chamber 234 is comprised of three separate parts, inlet cover 410, support plate 414 and outlet cover 412. The inlet cover 410, the support plate 414 and the outlet cover 412 may each be made of stamped metal such as steel or aluminum. The material for decomposition chamber 234 is chosen to be chemically resistant to the toxic environment of the exhaust gas.In another embodiment, decomposition chamber 234 is made of a chemically resistant polymer or other composite material.The inlet cover 410 and the outlet cover 412 may be attached to the support plate 414 to form the decomposition chamber 234. In one embodiment, the inlet cover 410 is removable to facilitate repairs or replacement of the inlet cover 410. Likewise, the outlet cover 412 may be removable. In an alternative embodiment, the inlet cover 410 and the outlet cover 412 are formed as a unitary device with the support plate 414.The support plate 414 defines an inlet channel 502 with the inlet cover 410 and an outlet channel 504 with the outlet cover 412, both of which will be described in more detail below with reference to FIG. 6. The support plate 414 is formed with a curved portion 506 and an opening 508. The curved portion 506 directs the exhaust flow into the inlet duct 502 towards the opening 508. The opening 508 forms a passage between the inlet channel 502 and the outlet channel 504.A corresponding curved portion 510 may be formed in the inlet cover 410 to urge the exhaust flow toward the exhaust passage 504. In an alternative embodiment, those skilled in the art will appreciate that a similar curved region may be formed in the outlet cover 412 to direct the flow of exhaust gas.In another embodiment, the support plate 414 includes an exhaust flow diverter 512. In the illustrated embodiment, the diverter 512 is comprised of a rolled sheet of material resembling a line. In alternative embodiments, the diverter 512 may be formed in any shape that directs the exhaust flow into the curved portion 510 of the inlet cover 410. Together, the diverter 512 and the curved portion 510 direct the exhaust flow from the inlet duct 502 through the opening 508 and into the outlet duct 504.FIG. 6 shows a top view of a cross-section of the system 200 according to embodiments of the present disclosure. Usually, the injected diesel exhaust liquid may not completely decompose into ammonia due to locally limited exhaust gas recirculation, low temperature ranges of exhaust gas, poor mixing of diesel exhaust liquid and exhaust gas, or unfavorable droplet size of the injected diesel exhaust liquid. Sometimes, injected diesel exhaust liquid forms solid deposits on the inner walls of an exhaust system. Solid DEF deposits may adversely affect the performance of the engine and exhaust treatment system. Advantageously, as will be discussed with reference to FIG. 6, decomposition chamber 234 overcomes these deficiencies. Directional arrows are drawn throughout the system 200 to indicate the direction of exhaust flow.As described above, the system 200 includes the cover 270 attached to the housing 302. Provided within the cover 270 and coupled to the housing 302 is the decomposition chamber 234. Provided within the housing are the DPF 220 (not visible here) and the SCR catalysts 235 a, 235 b(wherein the SCR catalysts 235 aare arranged next to the DPF 220 and the SCR catalysts 235 bare arranged above the catalysts 235 a). The SCR catalyst 235 may be any of various catalysts known in the art. For example, in some embodiments, the SCR catalyst 235 is a vanadium-based catalyst, and in other implementations, the SCR catalyst is a zeolite-based catalyst, such as a Cu zeolite or an Fe zeolite catalyst. In one embodiment, the SCR catalysts 235 a, 235 bare coaxially disposed and include coplanar inlets (see, for example, FIG. 3 ).The cover 270 directs the exhaust flow from the DPF 220 to the decomposition chamber 234. The cover 270 envelopes the decomposition chamber 234, and as a result, exhaust gas circulates around the outside of the decomposition chamber 234 before reaching the inlet port 420. Accordingly, the decomposition chamber 234 is maintained at the same temperature as the exhaust gas, and low temperature regions do not occur. Thus, the decomposition chamber 234 advantageously prevents the formation of solid DEF deposits.In one embodiment, a DEF injector 602 is coupled to the decomposition chamber 234 proximate the inlet port 420. As described above with reference to FIG. 1, the DEF injector 602 injects diesel exhaust liquid (DEF) into the exhaust stream. Decomposition chamber 234 provides non-circular inlet and outlet passages 502, 504 for the decomposition of DEF to ammonia. The support plate 414 acts as a manifold plate to provide both the high back pressure (by increasing the cross-sectional area of the exhaust flow path) and the uniform distribution of the exhaust flow to multiple SCR catalysts 235 a, 235 b.In one embodiment, the inlet channel 502 is formed by an inner surface of the inlet cover 410 and a surface of the support plate 414. The inlet channel 502 may be formed with a converging cross-sectional area. Stated differently, the cross-sectional area of the inlet channel 502 is greater at the inlet opening 420 than at the passage 508. The reduction in cross-sectional area causes the exhaust flow rate to increase slightly and the exhaust pressure to decrease locally limitedly, and both increase the mixing of DEF from the injector 602 with exhaust gas. The volume of the inlet chamber 502 is selected so that ample space for DEF is available to the system 200 under all conditions.The outlet chamber 504 is disposed adjacent the inlet chamber 502 and directs the exhaust gas to flow generally parallel but opposite the direction of exhaust flow of the inlet chamber. The outlet chamber 504 is formed of a surface of the support plate 414 and the outlet cover 412. As described above with reference to the inlet channel 502, the cross-sectional area of the outlet chamber 504 also converges. By the converging cross-sectional area, the exhaust flow is evenly distributed across the perforated outlet cover 412. As a result, the exhaust gas flows smoothly into the individual SCR catalysts 235 a, 235 band ultimately into the exhaust pipe 610 of the vehicle.In the above description, certain terms such as "upward", "downward", "upper", "lower", "horizontal", "vertical", "left", "right", and the like may be used. These terms are used as appropriate to make the description somewhat more comprehensible when relative relationships are involved. However, these terms do not state anything about absolute relationships, positions and / or orientations. For example, an "upper" surface of an object may become a "lower" surface simply by turning the object around. However, the object is still the same. Furthermore, the terms "include," "comprise," "have," and variations thereof mean "including, but not limited to," unless expressly stated otherwise. A list of items listed does not mean that some or all of the items listed are mutually exclusive and / or include, unless expressly stated otherwise. The terms "a" and "the" also mean "one or more" unless expressly stated otherwise. Further, the term "plurality" may be defined as "at least two".Moreover, examples herein where an element is "coupled" to another element may include direct and indirect coupling. A direct coupling may be defined such that one element is coupled to and in some contact with another element. Indirect coupling may be defined as coupling between two elements that do not have direct contact with each other, but in which one or more additional elements are located between the coupled elements. Further, the term of securing an element to another element as used herein may include direct attachment and indirect attachment. Moreover, the term "minor" as used herein does not necessarily include a contact. For example, one element may be adjacent to another element without contacting that element.The subject matter of the present disclosure may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the subject matter is thus indicated not by the above descriptions but by the appended claims. All changes which come within the meaning and range of equivalence of the claims are intended to be included within their scope.

Claims

A diesel exhaust fluid decomposition assembly comprising: an outlet cover (412); an inlet cover (410) coupled to the outlet cover; and a support plate (414) disposed between the outlet cover and the inlet cover, wherein the support plate forms an outlet channel (504) with the outlet cover and an inlet channel (502) with the inlet cover, wherein the inlet channel is fluidly coupled to the outlet channel, wherein the inlet channel is adjacent to the outlet channel, wherein the outlet cover, the inlet cover, and the support plate are axially aligned along a longitudinal axis, and wherein the outlet cover further comprises a plurality of openings (406) formed in a grid pattern.The diesel exhaust fluid decomposition assembly of claim 1, characterized in that the inlet channel (502) has a converging cross-sectional profile whereby the velocity of a fluid increases as it passes through the inlet channel and / or that the outlet channel (504) has a converging cross-sectional profile whereby the velocity of a fluid increases as it passes through the outlet channelThe diesel exhaust fluid decomposition assembly of any preceding claim, characterized in that a first end of the inlet cover (410) or a first end of the outlet cover (412) forms a fluid directing device (510) for changing the direction of fluid flow of a fluid between the inlet duct (502) and the outlet duct (504).The diesel exhaust fluid decomposition assembly of any preceding claim, characterized in that the support plate (414) is formed from at least two coupled non-planar portions, each of the at least two non-planar portions having a first surface that is part of the inlet duct (502) and an opposing second surface that is part of the outlet duct (504), wherein, preferably, the at least two coupled non-planar portions are arranged to form, in the outlet duct (504), a first region having a converging cross-sectional profile and a second region having a diverging cross-sectional profile.The diesel exhaust fluid decomposition assembly of any preceding claim, wherein the plurality of apertures (406) each have a diameter in the range of about 0.51 to 0.76 cm (0.2 to 0.3 inches) and the grid pattern has a grid spacing in the range of about 1.27 to 1.91 cm (0.5 to 0.75 inches).The diesel exhaust fluid decomposition assembly of any preceding claim, characterized in that the inlet cover (410) comprises an inlet opening (420) fluidly coupled to a chamber (234) formed by an outer cover (270) and the inlet cover (410), the chamber (234) fluidly coupling the inlet opening to a diesel particulate filter (220), wherein, preferably, the outer cover (270) is configured to envelop the inlet cover (410) and direct a fluid around at least a portion of an outer surface of the inlet cover (410) such that at least a portion of the inlet cover is maintained at a temperature substantially corresponding to the temperature of fluid within the chamber (234).The diesel exhaust fluid decomposition assembly of any preceding claim, characterized in that the inlet channel (502) and the outlet channel (504) each have a non-circular cross-sectional profile.The diesel exhaust fluid decomposition assembly of any preceding claim, characterized in that it comprises a diesel exhaust fluid injector (602) coupled to the inlet cover (410) for injecting a diesel exhaust fluid into the inlet duct (502).The diesel exhaust fluid decomposition assembly of any preceding claim, characterized in that the inlet cover (410) has a plurality of apertures (402) forming a grid pattern in the inlet cover, each aperture having substantially the same cross-sectional area, wherein, preferably, the inlet cover (410) further comprises a non-circular aperture having a cross-sectional area greater than that of an aperture of the plurality of apertures.The diesel exhaust fluid decomposition assembly of any preceding claim, characterized in that the outlet cover (412) comprises the plurality of openings (406) forming a grid pattern extending from a first end of the outlet cover to a second end of the outlet cover, and a cross-sectional area of each individual opening of the plurality of openings (406) is selected subsequent to proximity to the first end in the grid pattern.An exhaust aftertreatment system (200) comprising: a housing (302) having an exhaust inlet and an exhaust outlet, the housing configured to surround a diesel particulate filter (DPF) (220) and at least one selective catalytic reduction (SCR) catalyst (235) and to direct a flow of exhaust gas through the DPF and the SCR, the DPF (220) fluidly coupled to the exhaust inlet and configured to direct the flow of exhaust gas in a first direction, a diesel exhaust fluid (DEF) decomposition chamber (234) removably attached to the housing (302) and in fluid communication with the DPF, wherein the decomposition chamber (234) is disposed between the DPF and the SCR, the decomposition chamber (234) comprising: an inlet cover (410) coupled to an outlet cover (412); and a support plate (414) disposed between the outlet cover and the inlet cover, the support plate forming an outlet channel (504) with the outlet cover and an inlet channel (502) with the inlet cover, the inlet channel being fluidly coupled to the outlet channel, the inlet channel being adjacent to the outlet channel, wherein the outlet cover, the inlet cover, and the support plate are axially aligned along a longitudinal axis, and wherein the support plate is formed from at least two coupled non-planar portions, wherein each of the at least two non-planar portions forms a first surface that is part of the inlet channel and an opposing second surface, which is part of the outlet channel.The exhaust aftertreatment system of claim 11, characterized in that the inlet passage (502) has a converging cross-sectional profile whereby the velocity of a fluid increases as it flows through the inlet passage and / or that the outlet passage (504) has a converging cross-sectional profile whereby the velocity of a fluid increases as it flows through the outlet passage.The exhaust aftertreatment system of claim 11 or 12, characterized in that a plurality of SCR catalysts (235) are provided, each comprising an inlet surface, the DEF decomposition chamber (234) configured to provide a substantially uniform distribution of DEF and exhaust gas at the inlet surfaces of the plurality of SCR catalysts.A diesel exhaust fluid decomposition assembly comprising: an outlet cover (412); an inlet cover (410) coupled to the outlet cover; and a support plate (414) disposed between the outlet cover and the inlet cover, wherein the support plate forms with the outlet cover an outlet channel (504) for directing an exhaust flow in a first direction and with the inlet cover an inlet channel (502) for directing the exhaust flow in a second direction parallel to but opposite the first direction, wherein the outlet cover, the inlet cover, and the support plate are aligned axially along a longitudinal axis; and wherein the support plate is formed from at least two coupled non-planar portions, wherein each of the at least two non-planar portions has a first surface that is part of the inlet channel and an opposing second surface that is part of the outlet channel.

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