Exhaust aftertreatment system with an oxidation component bypass for low-temperature SCR

Abstract

An exhaust aftertreatment system configured to treat untreated exhaust gas produced by an engine (12), the system comprising: an exhaust passage (14) for transporting the untreated exhaust gas produced by the engine (12); a bypass channel (30) comprising an inlet (32) for receiving a quantity of the untreated exhaust gas from the exhaust channel (14); a first exhaust treatment component (18) positioned in the bypass channel (30); a valve (36) positioned near the bypass channel (30) and configured to control the amount of untreated exhaust gas entering the inlet (32) of the bypass channel (30); and a second exhaust gas treatment component (20) positioned in the outlet channel (14) downstream of the inlet (32) of the bypass channel (30), wherein an outlet of the bypass channel (30) directs an exhaust gas treated by the first exhaust gas treatment component (18) back to the outlet channel (14) at a location downstream of the second exhaust gas treatment component (20), so that the exhaust gas treated by the first exhaust gas treatment component (18) does not affect the second exhaust gas treatment component (20), wherein the system further comprises an injector (42) configured to meter an exhaust treatment fluid into the exhaust passage (14), wherein the injector (42) is positioned only at a single location positioned upstream of the bypass passage 30.

Description

REGIONThe present disclosure relates to an exhaust aftertreatment system having an oxidation component bypass for selective low temperature catalytic reduction.BACKGROUNDThis section provides background information to the present disclosure, which is not necessarily prior art.Diesel engines produce exhaust gas containing nitrogen oxides (NOx), which is a controlled pollutant. NOxcan be removed from the exhaust gas using a method known as selective catalytic reduction (SCR) in which ammonia (NH 3) is used as a chemical reductant for reactions with the NOxand for forming nitrogen (N 2) on the surface of an SCR catalyst. The ammonia used in the SCR is recovered from a diesel exhaust fluid (DEF), which is a mixture of urea and water dosed into the engine exhaust stream. When the engine exhaust gas has sufficient enthalpy (temperature and flow rate), when the DEF is introduced into the engine exhaust gas stream, the water of the DEF easily evaporates and the urea decomposes into ammonia. However, if the engine exhaust gas does not have sufficient enthalpy, the water does not evaporate so easily and the urea does not decompose sufficiently, which may lead to the formation of solid deposits in the exhaust pipe. This usually occurs when the environment is cold or when the engine has not been in operation for a longer period of time. In both cases, the exhaust aftertreatment system has not been heated by the engine exhaust for a sufficient amount of time and has not built up sufficient enthalpy to prevent the water from easily evaporating and the urea from not adding sufficiently. An exhaust gas aftertreatment system having the features of the preamble of claim 1 is described in DE 10 2015 013 864 A1. Further exhaust gas aftertreatment systems are known from US 2009 / 0 260 349 A1 and DE 698 03 827 T2.One solution that has been proposed for the above-mentioned problem is to modify an exhaust aftertreatment system to include a low temperature SCR catalyst at a location upstream of a diesel oxidation catalyst (DOC). A low temperature SCR catalyst is capable of achieving NOx conversion to nitrogen at lower temperatures (i.e., cold start or cold weather) rather than an SCR catalyst component positioned downstream of the DOC due to the low temperature SCR catalyst component receiving nearly all of the exhaust enthalpy exiting the engine. Unfortunately, the use of a low temperature SCR component upstream of the DOC has some potential disadvantages or trade-offs.First, because the low temperature SCR component must also receive ammonia to convert the NOxto nitrogen, the aftertreatment system may require a first DEF dosing module or injector dedicated to dosing DEF for use by the low temperature SCR component and a second DEF dosing module or injector dedicated to dosing DEF for use by the primary SCR component positioned downstream of the DOC. The additional dosing module or injector increases the complexity and cost of the aftertreatment system.Second, an ammonia slip catalyst (ASC) must be positioned between the low temperature SCR component and the DOC to prevent ammonia that slips through the low temperature SCR component from reaching the DOC and oxidizing to NOxor N 2 O.Third, in systems where the low temperature SCR component is designed to receive all of the exhaust flow from the engine, it is likely that the low temperature SCR component must have a dimension that is too large for positioning immediately downstream of the engine (i.e., too large for engine close coupling or positioning in the engine compartment). On the contrary, such a construction would involve positioning the low temperature SCR component further downstream of the engine and immediately upstream of the DOC. This can cause the exhaust gas to lose a significant amount of enthalpy as it travels through the extended area of the exhaust passage, thereby defeating the benefits of the low temperature SCR component.SUMMARYIn this section, a general summary of the disclosure is provided, which is not a comprehensive disclosure of its full scope or all of its features.Accordingly, the present disclosure provides an exhaust aftertreatment system configured to treat exhaust gas generated by an engine. The system includes an exhaust passage for transporting exhaust gas produced by the engine; a bypass passage including an inlet for receiving an amount of the exhaust gas from the exhaust passage; a first exhaust treatment component positioned in the bypass passage; a valve positioned proximate the bypass passage and configured to control the amount of exhaust gas entering the inlet of the bypass passage; and a second exhaust treatment component positioned in the exhaust passage downstream of the inlet of the bypass passage, wherein an outlet of the bypass passage directs the exhaust gas treated by the first exhaust treatment component back to the exhaust passage at a location downstream of the second exhaust treatment component such that the exhaust gas treated by the first exhaust treatment component does not act on the second exhaust treatment component.According to the invention, it is provided that the system further comprises an injection valve configured to meter an exhaust gas treatment fluid into the outlet channel, wherein the injection valve is positioned only at a single location positioned upstream of the bypass channel.The system according to the first aspect may further include a third exhaust treatment component and a fourth exhaust treatment component positioned downstream of the second exhaust treatment component.In the system according to the first aspect, the valve can be either passively controlled or actively controlled. When the valve is actively controlled, the system according to the first aspect may further include a controller configured to actively control the valve.In the system according to the first aspect, the outlet of the bypass passage may extend through the center of the second exhaust treatment component.Alternatively, the outlet may extend parallel to the exhaust passage and may include a branch that directs the exhaust gas treated by the first exhaust treatment component back to the exhaust passage at the location downstream of the second exhaust treatment component such that the exhaust gas treated by the first exhaust treatment component does not act on the second exhaust treatment component.The system according to the first aspect may further comprise a third exhaust treatment component downstream of the second exhaust treatment component, wherein the branch directs the exhaust gas treated by the first exhaust treatment component back to the exhaust passage at a location downstream of the third exhaust treatment component such that the exhaust gas treated by the first exhaust treatment component does not act on either the second exhaust treatment component or the third exhaust treatment component.The system according to the first aspect may further include a canister communicating with the exhaust passage, wherein the canister houses the entire bypass passage, the first exhaust treatment component positioned in the bypass passage, the valve positioned in the vicinity of the bypass passage, and the second exhaust treatment component positioned downstream of the inlet of the bypass passage. In such a configuration, the outlet may extend through a center of the second exhaust treatment component.According to a second aspect of the present disclosure, there is provided an exhaust aftertreatment system configured to treat exhaust gas generated by an engine, comprising an exhaust passage for carrying the exhaust gas generated by the engine; a bypass passage including an inlet for receiving an amount of exhaust gas from the exhaust passage; a first SCR component positioned in the bypass passage; a valve positioned proximate the bypass passage and configured to control the amount of exhaust gas entering the inlet of the bypass passage and always allowing an amount of exhaust gas to pass through the valve downstream of the inlet of the bypass passage; an injector configured to meter an exhaust treatment fluid into the exhaust passage, wherein the injector is positioned only at a single location positioned upstream of the bypass passage; an oxidation exhaust treatment component positioned in the exhaust passage downstream of the inlet of the bypass passage; and a second SCR component positioned downstream of the oxidation exhaust treatment component, wherein an outlet of the bypass passage directs the exhaust treated by the first SCR component back to the exhaust passage at a location downstream of the oxidation exhaust treatment component and upstream of the second SCR component such that the exhaust treated by the first SCR component does not affect the oxidation exhaust treatment component.The system of the second aspect may further include a particulate filter positioned downstream of the oxidation exhaust treatment component and upstream of the second SCR component, and a slip catalyst positioned downstream of the second SCR component.In the system according to the second aspect, a controller is provided which is configured to actively control the valve.In the system according to the second aspect, the outlet of the bypass passage may extend through the center of the oxidation exhaust treatment component. Alternatively, the outlet may extend parallel to the exhaust passage and may include a branch that directs the exhaust gas treated by the first SCR component back to the exhaust passage at the location downstream of the oxidation exhaust treatment component such that the exhaust gas treated by the first SCR component does not act on the oxidation exhaust treatment component.When the system according to the second aspect further comprises a particulate filter downstream of the oxidation exhaust treatment component, the branch may direct the exhaust gas treated by the first SCR component back to the exhaust passage at a location downstream of the particulate filter, such that the exhaust gas treated by the first SCR component does not act on either the oxidation exhaust treatment component or the particulate filter.According to the second aspect, the system may comprise a container communicating with the exhaust passage, wherein the container houses the entire bypass passage, the first SCR component positioned in the bypass passage, the valve positioned in the vicinity of the bypass passage, and the oxidation exhaust treatment component positioned downstream of the inlet of the bypass passage. In this configuration, the outlet may extend through a center of the oxidation exhaust treatment component.According to a third aspect of the present disclosure, there is provided an exhaust after-treatment system configured to treat exhaust gas generated by an engine, comprising an exhaust passage for transporting the exhaust gas generated by the engine; a canister communicated with the exhaust passage; a bypass passage provided entirely in the canister, the bypass passage including an inlet for receiving an amount of the exhaust gas entering the canister from the exhaust passage; a first SCR component positioned in the bypass passage; a valve positioned in the canister near the bypass passage configured to control the amount of the exhaust gas entering the inlet of the bypass passage and always allowing an amount of the exhaust gas to pass through the valve downstream of the inlet of the bypass passage; an injector configured to meter an exhaust treatment fluid into the exhaust passage at a single location positioned upstream of the canister; an oxidation exhaust treatment component positioned in the canister downstream of the inlet of the bypass passage; and a second SCR component positioned in the canister downstream of the oxidation exhaust treatment component, wherein an outlet of the bypass passage directs the exhaust treated by the first SCR component back to a location in the canister downstream of the oxidation exhaust treatment component and upstream of the second SCR component such that the exhaust treated by the first SCR component does not affect the oxidation exhaust treatment component.Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are for illustration purposes only and are not intended to limit the scope of the present disclosure.DRAWINGSThe drawings described herein are for illustrating selected embodiments only and not all possible implementations, and are not intended to limit the scope of the present disclosure. FIG. 1 is a schematic illustration of an exhaust system according to a principle of the present disclosure; FIG. 2 is a schematic illustration of an exhaust system according to a principle of the present disclosure; and FIG. 3 is a schematic illustration of an exhaust system according to a principle of the present disclosure.In the several views of the drawings, corresponding reference numerals indicate corresponding parts throughout.DETAILED DESCRIPTIONExemplary embodiments will now be described in more detail with reference to the accompanying drawings.Example embodiments are provided so that this disclosure will be thorough and will fully convey the scope to those skilled in the art. Numerous specific details are set forth, such as examples of specific components, devices, and methods, for providing a thorough understanding of the embodiments of the present disclosure. It will be apparent to those skilled in the art that the specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed as limiting the scope of the disclosure. In some example embodiments, well-known methods, well-known device structures, and well-known technologies are not described in detail.The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. As used herein, the singular forms "a", "an", and "the / s" are intended to include the plural forms as well, unless the context expressly indicates otherwise. The terms "comprises," "comprises(d)," "contains(d)," and "has(d)" are meant to be inclusive and therefore indicate the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The method steps, methods, and operations described herein are not to be understood as requiring their performance in the particular order discussed or illustrated, unless specifically indicated as the order of performance. It will be further understood that further or alternative steps may be employed.When an element or layer is described as being "on," "engaged to," "connected to," or "coupled to" another element or layer, it may be directly on, engaged to, connected to, or coupled to the other element or layer, or intervening elements or layers may be present. On the other hand, when an element is described as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another element or layer, there may be no intervening elements or layers present. Other wording used to describe the relationship between elements should be interpreted in a similar manner (for example, "between" versus "directly between", "next" versus "directly next", etc.). As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or sections, these elements, components, regions, layers, and / or sections should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or portion from another region, layer, or portion. Terms such as "first," "second," and other numerical terms used herein do not imply a sequence or order unless clearly indicated by context. Thus, a first element, component, region, layer, or portion discussed below could be referred to as a second element, component, region, layer, or portion without departing from the teachings of the example embodiments.Spatial terms such as "inner / inner / inner", "outer / outer / outer", "below", "under", "lower / lower / lower", "over", "upper / upper / upper", and the like may be used herein to simplify the description to more easily describe the relationship of an element or feature to one or more other elements or features as depicted in the figures. Space-related terms may be intended to include, in addition to the orientation depicted in the figures, various orientations of the device in use or operation. For example, if the device in the figures is turned over, elements described as "below" or "below" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary term "below" may encompass both an orientation of above and below. The device may also be otherwise (rotated 90 degrees or in other orientations) oriented, and the spatially relative descriptive terms used herein are interpreted accordingly.FIG. 1 schematically illustrates an exhaust system 10 according to a first aspect of the present disclosure. Exhaust system 10 may include at least one engine 12 communicating with a fuel source (not shown) that, once exhausted, generates exhaust gases that are discharged into an exhaust passage 14 having an exhaust aftertreatment system 16. The exhaust aftertreatment system 16 is positioned downstream of the engine 12 and may include a plurality of exhaust treatment components 18, 20, 22, 24, and 26 that may include catalyst coated substrates or filters. In the illustrated embodiment, component 18 may be a first or low temperature SCR component, component 20 may be a DOC component, component 22 may be a diesel particulate filter (DPF) that may be catalyst coated, component 24 is a second SCR component, and component 26 may be an optional second ASC component. Other known exhaust treatment components (e.g., three-way catalysts, NOx trap catalysts, etc.) may be used without limitation. Each of the exhaust treatment components 20, 22, 24, and 26 may be enclosed in a single housing or container 28, if desired. Alternatively, all components 20, 22, 24 and 26 may be separately housed in a respective container and separated from each other by short portions of the outlet channel 14.In the illustrated embodiment, the outlet channel 14 includes a bypass channel 30 that includes the low temperature SCR component 18. The bypass passage 30 includes an inlet 32 branched from the exhaust passage 14 and receiving at least a portion of the engine exhaust gas therein, and an outlet 34 supplying the engine exhaust gas treated by the low temperature SCR component 18 back to the exhaust passage 14. To ensure that at least a portion of the engine exhaust gas is forced to enter the bypass passage 30, if desired, a valve 36 may be positioned in the exhaust passage 14 immediately downstream of the inlet 32. The valve 36 may be passively controlled, for example, by a spring (not shown) that allows the valve to open when the exhaust flow rate in the exhaust passage 14 reaches a predetermined threshold, or the valve 36 may be actively controlled by an exhaust aftertreatment controller 38. Alternatively, the valve 36 may be controlled by an electronic control unit (ECU) 40 of the engine 12. When the valve 36 is actively controlled, the valve 36 may be any type of electrically controlled valve known to those skilled in the art. Regardless, it should be appreciated that the valve 36 is designed to always allow a portion of the engine exhaust to flow through the valve 36 to the exhaust treatment components 20, 22, 24, and 26. This reduces the amount of engine exhaust gas allowed to enter the bypass passage 30.In particular, by controlling the amount of engine exhaust gas allowed to enter the bypass passage 30, a smaller size (e.g., diameter and length) of the low temperature SCR 18 as compared to the remaining exhaust treatment components 20, 22, 24, and 26 may be provided, thereby allowing packaging of the low temperature exhaust treatment component 18 in a configuration that is parallel to the exhaust passage 14. Moreover, the smaller size of the low temperature SCR 18 allows the bypass passage 30 to be coupled close to the engine 12. Thus, because the low temperature SCR catalyst component 18 receives nearly all of the exhaust enthalpy exiting the engine 12, the low temperature SCR 18 is able to achieve the SCR at lower temperatures (i.e., cold start or cold weather) rather than the downstream positioned SCR catalyst component 24. Further, by always allowing a portion of the engine exhaust to flow through the valve 36 to the remaining exhaust treatment components 20, 22, 24, and 26, at least a portion of the exhaust enthalpy may reach those components to aid those components in reaching a light-off temperature during cold start or cold weather conditions.Although not required in the present disclosure, the exhaust aftertreatment system 16 may further include components, such as a heat boosting device or a burner (not shown), for increasing a temperature of the exhaust gases flowing through the exhaust passage 14. Increasing the temperature of the exhaust gas is advantageous for achieving catalyst light-off in the first SCR component 18 during cold weather conditions and starting the engine 12 and initiating regeneration of the DPF component 22.To aid in reducing emissions produced by the engine 12, the exhaust aftertreatment system 16 may include a dosing module or injector 42 for periodically dosing an exhaust treatment fluid (e.g., DEF) into the exhaust stream. As shown in FIG. 1, the dosing module 42 may be positioned upstream of the low temperature SCR component 18 and attached to the exhaust passage 14 at the inlet 32 of the bypass passage 30, and is operable to inject an exhaust treatment fluid into the exhaust flow. To do so, the dosing module 42 is in flow communication with a reactant tank 44 and a pump 46 via an inlet line 48 to dose an exhaust treatment fluid, such as diesel fuel or DEF, into the outlet channel 14 upstream of the low temperature exhaust treatment component 18. The dosing module 42 may also be in communication with the reactant tank 44 via a return line 50. The return line 50 allows any exhaust treatment fluid that is not dosed into the exhaust stream to be returned to the reactant tank 44. The flow of exhaust treatment fluid through the inlet line 48, the dosing module 42, and the return line 50 further aids in cooling the dosing module 42 so that the dosing module 42 does not overheat. Although not shown in the drawings, the dosing module 42 may also be configured to include a cooling jacket that directs a coolant around the dosing module 42 for cooling thereof.The amount of exhaust treatment fluid required to effectively treat the exhaust flow may vary with load, engine speed, exhaust temperature, exhaust flow, engine fuel injection control, desired NOx reduction, barometric pressure, relative humidity, EGR rate, and engine coolant temperature. A NOx sensor or meter 52 may be positioned downstream of the exhaust treatment components 22, 24, 26, and 28. The NOx sensor 52 is operable to output a signal indicative of the exhaust NOx content to the controller 38 or the ECU 40. All or some of the engine operating parameters may be transmitted from the engine controller 40 to the controller 38 via the engine / vehicle data bus. The controller 38 could also be included as part of the ECU 40. The exhaust temperature, exhaust flow, and exhaust backpressure, and other vehicle operating parameters may be measured by respective sensors, as indicated in FIG. 1.The amount of exhaust treatment fluid required to effectively treat the exhaust flow may also be dependent on the size of the engine 12. In this regard, large diesel engines used in locomotives, marine applications, and stationary applications may have exhaust flow rates that exceed the capacity of a single dosing module 42. Accordingly, although only a single dosing module 42 is shown for dosing exhaust treatment fluid into the exhaust passage 14, it should be appreciated that multiple dosing modules 42 for injecting reactant are contemplated by the present disclosure as long as the multiple dosing modules 42 are positioned upstream of the low temperature SCR component 18 at the inlet 32 of the bypass passage 30. As mentioned above, no second injector 42 is required for the second SCR component 24 attached to the canister 28, thereby reducing the complexity and cost of the system 16.According to the present disclosure, the engine exhaust gas entering the bypass passage 30 and treated by the low temperature SCR component 18 is not allowed to remix with the engine exhaust gas in the exhaust passage 14 downstream of the valve 36 and upstream of the DOC component 20. On the contrary, the outlet 34 of the bypass passage 30 enters the canister 28 and includes a length 35 that extends coaxially with the outlet passage 14 and the canister 28, and bypasses the DOC component 20 by passing through the center of the DOC component 20. As shown, the length 35 is more than a length of the DOC component 20 such that the outlet 34 extends throughout the DOC component 20 and extends outward from the DOC component 20. Alternatively, although not shown, it should be appreciated that the outlet 34 may be constructed to bypass both the DOC component 20 and the DPF component 22 by passing through a center of each of these components. Regardless, it should be appreciated that the engine exhaust entering the bypass passage 30 and being treated by the low temperature SCR component 18 is not allowed to remix with the engine exhaust until it reaches a location downstream of at least the DOC component 20. Because the DOC component 20 is bypassed, the exhaust aftertreatment system 16 requires only one injector(s) 42 at a single location (i.e., upstream of the low temperature SCR component 18) and does not require injectors 42 downstream of the DOC component 20 and upstream of the second SCR component 24. Furthermore, the NOx treated by the low-temperature SCR component 18 to form N 2 cannot be reoxidized by the DOC component 20.Given the dosing of the exhaust treatment fluid into the exhaust stream at a location upstream of the low temperature SCR component 18, a mixing device 54 may be provided in the container 28 at a location downstream of the length 35 and upstream of the second SCR component 24. The mixing device 54 aids in redistributing the ammonia before it enters and is treated by the second SCR component 24. Any mixing device 54 known to those skilled in the art may be used.Referring now to FIG. 2, an exhaust aftertreatment system 16 according to a second aspect of the present disclosure is illustrated. The configuration shown in FIG. 2 is similar to the configuration shown in FIG. 1, but differs in that the bypass outlet 34 does not pass through the center of the DOC component 20, but runs parallel to the outlet passage 14 to a location downstream of the DOC component 20 or to a location downstream of both the DOC component 20 and the DPF component 22. In this regard, the bypass outlet 34 has a length selected to pass through the DOC component 20 and then extend to and into the canister 28 at a branch 34 athat directs the exhaust gas to the canister 28 at a location downstream of the DOC component 20, or to and into the canister 28 at a branch 34 bthat directs the exhaust gas to the canister 28 at a location downstream of both the DOC component 20 and the DPF component 22. Moreover, it should be appreciated that although the mixing device 54 is positioned between the DPF component 22 and the second SCR component 24, the mixing device 54 may be positioned between the DOC component 20 and the DPF component 22 without departing from the scope of the present disclosure.Regardless of whether the system 16 includes the branch 34 aor the branch 34 b, it should be appreciated that the engine exhaust entering the bypass passage 30 and treated by the low temperature SCR component 18 is not permitted to remix with the engine exhaust until it reaches a location downstream of at least the DOC component 20. Because the DOC component 20 is bypassed, the exhaust aftertreatment system 16 requires only one injector(s) 42 at a single location (i.e., upstream of the low temperature SCR component 18) and does not require injectors 42 downstream of the DOC component 20 and upstream of the second SCR component 24. Furthermore, the NOx treated by the low-temperature SCR component 18 to form N 2 cannot be reoxidized by the DOC component 20. Moreover, it should be appreciated that although the injector 42 is mounted to inject the exhaust treatment fluid into the exhaust passage 14 as shown in FIG. 2, the injector(s) 42 may be coupled to the inlet 32 of the bypass passage 30 as desired.Referring now to FIG. 3, an exhaust aftertreatment system 16 according to a third aspect of the present disclosure is illustrated. The exhaust aftertreatment system 16 is similar to those shown in FIGS. 1 and 2, but the exhaust aftertreatment system 16 is entirely contained within a single canister 28. With such a configuration, the reservoir 28 may be coupled close to the engine 12 so that nearly all of the exhaust enthalpy exiting the engine 12 may be used to create conditions that may ensure that the exhaust treatment fluid water easily evaporates and the urea sufficiently decomposes properly.In the illustrated configuration, the engine exhaust flows through the exhaust passage 14 and enters the canister 28. Upon entering the canister 28, at least a portion of the engine exhaust may be diverted through the valve 36 into the bypass passage 30 that is fully positioned in the canister 28. However, as mentioned above, it should be appreciated that at least a portion of the engine exhaust is always allowed to flow through the valve 36 to the DOC component 20 through the outlet 15. As the engine exhaust diverted by the valve 36 enters the inlet 32 of the bypass passage 30, the engine exhaust is treated by the low temperature SCR component 18 and enters the outlet 34 of the bypass passage 30. However, the outlet 34 does not allow the engine exhaust treated by the low temperature SCR component 18 to remix with the engine exhaust that has flowed through the valve 36 at a location upstream of the DOC component 20. In contrast, the outlet 34 includes a length 35 designed to pass through the center of the DOC component 20 and remix with the engine exhaust at a location downstream of the DOC component 20. As shown, the length 35 is more than a length of the DOC component 20 such that the outlet 34 extends throughout the DOC component 20 and extends outward from the DOC component 20. Alternatively, the length 35 may be constructed to pass through the center of both the DOC component 20 and the DPF component 22.Because the DOC component 20 is bypassed, the exhaust aftertreatment system 16 requires only one injector(s) 42 at a single location (i.e., upstream of the low temperature SCR component 18) and does not require injectors 42 downstream of the DOC component 20 and upstream of the second SCR component 24. Furthermore, the NOx treated by the low-temperature SCR component 18 to form N 2 cannot be reoxidized by the DOC component 20. Moreover, it should be appreciated that although the injector(s) 42 are mounted on the exhaust passage 14 for injecting the exhaust treatment fluid into the exhaust flow as shown in FIG. 3, the injector(s) 42 may be coupled to an exterior of the canister 28 at a location proximate the bypass passage 30.In view of the introduction of the exhaust treatment fluid into the exhaust stream at a location upstream of the low temperature SCR component 18, it may be desirable to provide a mixing device 54 in the container 28 at a location downstream of the outlet 34 and upstream of the second SCR component 24. The mixing device 54 aids in redistributing the ammonia before it enters and is treated by the SCR component 24. Any mixing device 54 known to those skilled in the art may be used.The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and may be used in a selected embodiment, even if not specifically shown or described. This can also be changed in various ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Claims

An exhaust aftertreatment system configured to treat untreated exhaust gas produced by an engine (12), the system comprising: an exhaust passage (14) for carrying untreated exhaust gas produced by the engine (12); a bypass passage (30) comprising an inlet (32) for receiving an amount of untreated exhaust gas from the exhaust passage (14); a first exhaust treatment component (18) positioned in the bypass passage (30); a valve (36) positioned proximate the bypass passage (30) and configured to control the amount of untreated exhaust gas entering the inlet (32) of the bypass passage (30); A second exhaust treatment component (20) positioned in the exhaust passage (14) downstream of the inlet (32) of the bypass passage (30), an outlet of the bypass passage (30) directing an exhaust gas treated by the first exhaust treatment component (18) back to the exhaust passage (14) at a location downstream of the second exhaust treatment component (20) such that the exhaust gas treated by the first exhaust treatment component (18) does not act on the second exhaust treatment component (20), the system further comprising an injector (42) configured to meter an exhaust treatment fluid into the exhaust passage (14), wherein the injector (42) is positioned only at a single location positioned upstream of the bypass passage 30.The system of claim 1, further comprising a third exhaust treatment component (22, 24, 26) and a fourth exhaust treatment component (22, 24, 26) in the exhaust passage (14) positioned downstream of the second exhaust treatment component (20).The system of any preceding claim, wherein the valve (36) is either passively controlled or actively controlled.The system of any preceding claim, further comprising a controller (40) configured to actively control the valve (36).The system of any preceding claim, wherein the outlet (34) comprises a length (35) greater than a length of the second exhaust treatment component (20) and extends coaxial with the outlet channel (14) and through and out of the center of the second exhaust treatment component (20).The system of any of claims 1-4, wherein the outlet (34) extends parallel to the outlet channel (14) and comprises a length (35) that extends past the second exhaust treatment component (20) and communicates with the outlet channel (14) at a branch (34a, 35b) that directs the exhaust gas treated by the first exhaust treatment component (18) back to the outlet channel (14) at the location downstream of the second exhaust treatment component (20), wherein the exhaust gas treated by the first exhaust treatment component (18) does not affect the second exhaust treatment component (20).The system of claim 6, further comprising a third exhaust treatment component (22, 24, 26) downstream of the second exhaust treatment component (20) in the exhaust passage (14), wherein the branch (34b) directs the exhaust treated by the first exhaust treatment component (18) back to the exhaust passage (14) at a location downstream of the third exhaust treatment component (22, 24, 26), wherein the exhaust treated by the first exhaust treatment component (18) does not act on either the second exhaust treatment component (20) or the third exhaust treatment component (22, 24, 26).The system of any of claims 1-4, further comprising a reservoir (28) communicating with the outlet channel (14), wherein the reservoir (28) houses the entire bypass channel (30), the first exhaust treatment component (18) positioned in the bypass channel (30), the valve (36) positioned near the bypass channel (30), and the second exhaust treatment component (20) positioned downstream of the inlet (32) of the bypass channel (30).The system of claim 8, wherein the outlet (34) comprises a length (35) greater than a length of the second exhaust treatment component (20) and extends coaxial with the outlet channel (14) and through and out of a center of the second exhaust treatment component (20).The system of any preceding claim, wherein the first exhaust treatment component (18) is a first SCR exhaust treatment component and the second exhaust treatment component (20) is an oxidation exhaust treatment component.The system of claim 10, further comprising a particulate filter (22) positioned downstream of the oxidation exhaust treatment component (20) and upstream of the second SCR component, and a slip catalyst (26) positioned downstream of the second SCR component (24).

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