AFTERTREATMENT SYSTEM HAVING MULTIPLE DOSING CIRCUITS

Abstract

An aftertreatment system is disclosed for use with a combustion engine. The aftertreatment system may have at least one exhaust passage, and a plurality of dosing circuits configured to inject reductant into the at least one exhaust passage. The aftertreatment system may also have a controller in communication with each of the plurality of dosing circuits. The controller may be configured to determine a failure of a first of the plurality of dosing circuits, and to selectively adjust operation of a second of the plurality of dosing circuits based on the failure.

Description

TECHNICAL FIELD

The present disclosure relates generally to an aftertreatment system and, more particularly, to an aftertreatment system having multiple dosing circuits.

BACKGROUND

Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants can include, among other things, gaseous compounds such as the oxides of nitrogen (NO_X). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NO_X emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to ensure compliance with the regulation of these compounds, some engine manufacturers have implemented a process called Selective Catalytic Reduction (SCR).

SCR is a process where a reductant (most commonly a urea/water solution) is injected into the exhaust gas stream of an engine and adsorbed onto a catalyst. The reductant reacts with NO_X in the exhaust gas to form water (H₂O) and elemental nitrogen (N₂), both of which are unregulated. Care should be taken so that the amount of reductant injected into the exhaust gas stream corresponds with the amount of NO_X in the exhaust gas stream. If too much reductant is injected, some of the reductant may pass through the exhaust system and be discharged into the atmosphere. This can be costly and violate regulations in some areas. If too little reductant is injected, the NO_X may not be adequately reduced. In some situations, such as during a dosing circuit abnormality (e.g., during degraded conversion performance, during a failure, or during a low-dosing event), it can be difficult to accurately control the amount of NO_X being injected.

An exemplary aftertreatment system is disclosed in U.S. Patent Publication No. 2012/0204542 of Norris et al, that published on Aug. 16, 2012 (“the '542 publication”). Specifically, the '542 publication describes a system having two exhaust legs configured to receive parallel flows of exhaust from an engine. A particulate filter is disposed within each leg at a location upstream of an SCR catalyst. A hydrocarbon closer is positioned between each particulate filter and the corresponding SCR catalyst, and a sensor (e.g., an ammonia sensor, a NO_X sensor, a temperature sensor, and/or a pressure sensor) is located downstream of each catalyst. A controller is configured to determine clogging of the particulate filters based on signals from the sensor, calculate uneven flow distribution through the legs based on the clogging, and selectively adjust exhaust flow through the legs via a throttle to compensate for the uneven flow distribution. In addition, operation of the hydrocarbon dosers is controlled based on feedback from the sensor.

While the system of the '542 publication may help to maintain dosing accuracy during uneven exhaust flow caused by particulate filter clogging, the system may still be less than optimal. For example, the system may not be capable of detecting or accommodating a dosing circuit abnormality.

The present disclosure is directed at overcoming one or more of the shortcomings set forth above and/or other problems of the prior art.

SUMMARY

In one aspect, the present disclosure is directed to an aftertreatment system. The aftertreatment system may include at least one exhaust passage, and a plurality of dosing circuits configured to inject reductant into the at least one exhaust passage. The aftertreatment system may also include a controller in communication with each of the plurality of dosing circuits. The controller may be configured to determine a failure of a first of the plurality of dosing circuits, and to selectively adjust operation of a second of the plurality of dosing circuits based on the failure.

In another aspect, the present disclosure is directed to a method of dosing reductant. The method may include dosing reductant into an exhaust flow using a plurality of dosing circuits. The method may also include determining a failure of a first of the plurality of dosing circuits, and selectively adjusting operation of a second of the plurality of dosing circuits based on the failure.

In yet another aspect, the present disclosure is directed to an engine. The engine may include an engine block at least partially defining a plurality of combustion chambers, an exhaust manifold extending from the plurality of combustion chambers, and a turbocharger connected to the exhaust manifold. The engine may also include a first branch passage connected to an outlet of the turbocharger, and a second branch passage connected to the outlet of the turbocharger in parallel with the first branch passage. The engine may further include at least a first dosing circuit associated with the first branch passage, at least a second dosing circuit associated with the second branch passage, and at least one sensor configured to generate a signal indicative of a performance parameter of the at least a first and at least a second dosing circuits. The engine may additionally include a controller in communication with the at least one sensor and each of the at least a first and at least a second dosing circuits. The controller may be configured to make a determination of one of a failure of the at least a first dosing circuit and occurrence of a low-dosing event based on the signal, to selectively inhibit operation of the at least a first dosing circuit based on the determination, and to selectively increase dosing of the at least a second dosing circuit based on the determination.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic illustration of an engine having an exemplary disclosed aftertreatment system.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary engine 10. For the purposes of this disclosure, engine 10 is depicted and described as a diesel-fueled, internal combustion engine. However, it is contemplated that engine 10 may embody any other type of combustion engine such as, for example, a gasoline engine or a gaseous fuel-powered engine burning compressed or liquefied natural gas, propane, or methane. Engine 10 may include an engine block 12 at least partially defining a plurality of cylinders 14, and a plurality of piston assemblies (not shown) disposed within cylinders 14 to form a plurality of combustion chambers (not shown). It is contemplated that engine 10 may include any number of combustion chambers and that the combustion chambers may be disposed in an in-line configuration (shown), in a “V” configuration, in an opposing-piston configuration, or in any other conventional configuration.

Multiple separate sub-systems may be associated within engine 10 and cooperate to facilitate the production of power. For example, engine 10 may include an air induction system 16, an exhaust system 18, and an aftertreatment system 20. Air induction system 16 may be configured to direct air or an air and fuel mixture into engine 10 for subsequent combustion. Exhaust system 18 may exhaust byproducts of combustion to the atmosphere. Aftertreatment system 20 may function to reduce the discharge of regulated constituents produced by engine 10 to the atmosphere.

Air induction system 16 may include multiple components configured to condition and introduce compressed air into cylinders 14. For example, air induction system 16 may include an air cooler 22 located downstream of one or more compressors 24. Compressor(s) 24 may be connected to pressurize inlet air directed through cooler 22. It is contemplated that air induction system 16 may include different or additional components than described above such as, for example, a throttle valve, variable valve actuators associated with each cylinder 14, filtering components, compressor bypass components, and other known components that may be selectively controlled to affect an air-to-fuel ratio of engine 10, if desired. It is further contemplated that compressor(s) 24 and/or cooler 22 may be omitted, if a naturally aspirated engine is desired.

Exhaust system 18 may include multiple components that condition and direct exhaust from cylinders 14 to the atmosphere. For example, exhaust system 18 may include an exhaust manifold 26 and one or more turbines 28 driven by exhaust flowing through manifold 26. Before or after reaching turbine(s) 26, exhaust manifold 26 may split into at least two parallel branch passages 30, 32. Branch passages 30, 32 may be identical or different, and lead from turbine(s) 28 to the atmosphere. It is contemplated that exhaust system 18 may include different or additional components than described above such as, for example, bypass components, an exhaust compression or restriction brake, an attenuation device, and other known components, if desired.

Each of turbine(s) 26 may be located to receive exhaust leaving engine 10, and may be connected to one or more compressors 24 of air induction system 16 by way of a common shaft to form a turbocharger. As the hot exhaust gases exiting engine 10 move through turbine(s) 28 and expand against vanes (not shown) thereof, turbine(s) 28 may rotate and drive the connected compressor(s) 24 to pressurize inlet air.

Aftertreatment system 20 may include components configured to trap, catalyze, reduce, or otherwise remove regulated constituents from the exhaust flow of branch passages 30 and 32 prior to discharge to the atmosphere. For example, aftertreatment system 20 may include, among other things, a plurality of dosing circuits 34 each having one or more catalyst substrates 36 located downstream from one or more reductant injectors 38. In one embodiment, a single dosing circuit 34 may be associated with each of branch passages 30, 32, in another embodiment (shown in FIG. 1), multiple dosing circuits 34 may be associated with each of branch passages 30, 32 and disposed in series. In either embodiment, a gaseous or liquid reductant, most commonly urea ((NH₂)₂CO), a water/urea mixture, a hydrocarbon such as diesel fuel, or ammonia gas (NH₃), may be sprayed or otherwise advanced into the exhaust flow of passages 30, 32 at a location upstream of catalyst substrate(s) 36 by reductant injector(s) 38. This process of injecting reductant upstream of catalyst substrate(s) 36 is known as dosing.

Catalyst substrates 38 may be arranged into bricks or packs, which are placed in parallel and/or series relative to the flow of exhaust in branch passages 30, 32. For example, an arrangement of multiple individual substrates 36 may be placed to receive exhaust flow from a particular one of branch passages 30 or 32 in parallel with each other. In this configuration, a primary exhaust flow may be divided between the different substrates 36, pass through the substrates 36, and then rejoin into a single flow again at a location downstream of the substrates 36. In other configurations, the exhaust from a single branch passage 30 or 32 may pass through multiple layers of substrates 36 as a single flow or through multiple layers of substrates 36 wherein the substrates of each layer are arranged in parallel with each other. Many different configurations may be possible.

To facilitate dosing of catalyst substrate(s) 36 by reductant injectors 38, an onboard supply 40 of reductant and a pressurizing device (e.g., a pump) 42 may be associated with reductant injectors 38. In some embodiments, a single supply 40 and/or a single pump 42 may be associated with multiple or all of injectors 38. In the disclosed embodiment, however, each injector 38 is provided with a dedicated supply 40 and a dedicated pump 42. Other configurations may also be possible. The reductant sprayed into branch passages 30, 32 may flow downstream with the exhaust from engine 10 and be adsorbed onto an upstream surface of catalyst substrate(s) 36, where the reductant may react with NO_X (NO and NO₂) in the exhaust gas to form water (H₂O) and elemental nitrogen (N₂), both of which may be unregulated. This process performed by substrate(s) 36 may be most effective when a concentration of NO_X to NO₂ supplied to substrate(s) 36 is about 1:1.

To help provide the correct ratio of NO to NO₂, an oxidation catalyst 44 may be located upstream of substrates 36 and injectors 38, in some embodiments. Oxidation catalyst 44 may be, for example, a diesel oxidation catalyst (DOC). As a DOC, oxidation catalyst 44 may include a porous ceramic honeycomb structure or a metal mesh substrate coated with a material, for example a precious metal, which catalyzes a chemical reaction to alter the composition of the exhaust. For instance, oxidation catalyst 44 may include a washcoat of palladium, platinum, vanadium, or a mixture thereof that facilitates the conversion of NO to NO₂.

In one embodiment, oxidation catalyst 44 may also perform particulate trapping functions. That is, oxidation catalyst 44 may be a catalyzed particulate trap such as a continuously regenerating particulate trap or a catalyzed continuously regenerating particulate trap. As a particulate trap, oxidation catalyst 44 may function to trap or collect particulate matter.

Aftertreatment system 20 may also include components configured to help regulate the treatment of exhaust by dosing circuits 34 prior to discharge to the atmosphere. Specifically, exhaust control system 20 may include a controller 46 in communication with one or more sensors 48 and with the components of each dosing circuit 34. And based on input from each of sensors 48, controller 46 may determine an amount of NO_X being produced by engine 10, a performance parameter of catalyst substrates 36 (e.g., a reduction efficiency), a history of the performance parameter (e.g., the reduction efficiency tracked over a period of time), an amount of reductant passing through catalyst substrates 36, a failure of any one or more of dosing circuits 34, and/or an amount of reductant that should be sprayed by reductant injectors 38 into the exhaust flow of branch passages 30, 32 to sufficiently reduce the NO_X present within the exhaust in light of current conditions (e.g., in light of any known abnormalities such as component failures, inefficiencies, low-dosing events, etc.). Controller 46 may then regulate operation of each dosing circuit 34 to inject (or stop injecting) an appropriate amount of urea into the exhaust flows of branch passages 30, 32 such that an overall level of exhaust constituents being discharged to the atmosphere by both branch passages 30, 32 is less than a desired and/or regulated level.

Controller 46 may embody a single or multiple microprocessors, field programmable gate arrays (FPGAs), digital signal processors (DSPs), etc, that include a means for controlling an operation of aftertreatment system 20 in response to signals received from the various sensors. If multiple microprocessors are utilized, the different microprocessors may communicate with each other and/or with a master controller, if desired, to accomplish the disclosed functions. For example, a dedicated microprocessor may be associated with each dosing circuit 34 and configured to control dosing of only that circuit (based on commands from a common master controller), to detect abnormalities of that circuit, and to communicate the abnormalities to the master controller. Numerous commercially available microprocessors can be configured to perform the functions of controller 46. It should be appreciated that controller 46 could readily embody a microprocessor separate from that controlling other non-exhaust related engine functions, or that controller 46 could be integral with a general engine microprocessor and be capable of controlling numerous engine functions and modes of operation. If separate from a general engine microprocessor, controller 46 may communicate with the general engine microprocessor via data links or other methods. Various other known circuits may be associated with controller 46, including power supply circuitry, signal-conditioning circuitry, actuator driver circuitry (i.e., circuitry powering solenoids, motors, or piezo actuators), communication circuitry, and other appropriate circuitry.

Sensors 48 may be any type of sensors known in the art that provide an indication as to functionality and/or performance of individual dosing circuits 34. For example, a first sensor 48a may embody a constituent sensor configured to generate a constituent signal indicative of a presence and/or concentration of a particular constituent within the exhaust flow of one or both of branch passages 30, 32 at a location upstream and/or downstream of catalyst substrates 36. For instance, first sensor 48a may be a NO_X sensor configured to determine an amount (i.e., a quantity, a relative percent, a ratio, etc.) of NO and/or NO₂ present within the exhaust of engine 10. First sensor 48a may generate the constituent signal and send it to controller 46 for further processing.

A second sensor 48b of aftertreatment system 20 may embody a reductant sensor configured to generate a slip signal indicative of a presence of reductant within the exhaust flow of branch passages 30, 32 downstream of catalyst substrates 36. Second sensor 48b may generate the slip signal and send it to controller 46 for further processing.

A third sensor 48c of aftertreatment system 20 may be associated with supply 40, pump 42, and/or injector 38. For example, sensor 48c may be a fluid level sensor, a temperature sensor, and/or a pressure sensor configured to generate a reductant signal indicative of an amount of reductant available (e.g., an amount of reductant remaining and/or thawed) for injection. Alternatively, third sensor 48c could be configured to generate a signal indicative of a displacement position of pump 42, a pressure of injector 38, and/or a functional status of pump 42 and injector 38. This signal may be directed from sensor 48c to controller 46 for further processing.

It is contemplated that sensors 48 could be fewer or greater in number, have different functionality, and/or be associated with different components of aftertreatment system 20, if desired. It is also contemplated that any one or more of sensors 48 may alternatively embody a virtual sensor. A virtual sensor may produce a model-driven estimate based on one or more known or sensed operational parameters of engine 10 and/or aftertreatment system 20. For example, based on a known operating speed, load, temperature, boost pressure, ambient conditions (humidity, pressure, temperature, etc.), and/or other parameters of engine 10, a model may be referenced to determine an amount of NO and/or NO₂ produced by engine 10. Similarly, based on a known or estimated NO_X production of engine 10, a flow rate of exhaust exiting engine 10, and/or a temperature of the exhaust, the model may be referenced to determine an amount of NO and/or NO₂ leaving catalyst 44 and entering catalyst substrate 36. As a result, any signal (e.g., the constituent production signal) directed from sensor 48 to controller 46 may be based on calculated and/or estimated values rather than direct measurements, if desired. It is contemplated that rather than a separate element, these virtual sensing functions may alternatively be accomplished by controller 46, if desired.

As will be described in the following section, the signals from sensors 48 may be utilized by controller 46 to determine an abnormality of aftertreatment system 20 (e.g., of a particular dosing circuit 34 of aftertreatment system 20). And based on the abnormality, controller 46 may be configured to adjust operation of aftertreatment system 20 (e.g., to adjust operation of a different dosing circuit 34) to accommodate the abnormality and maintain engine 10 compliant with emission regulations.

INDUSTRIAL APPLICABILITY

The aftertreatment system of the present disclosure may be applicable to any engine where consistent emission control is desired. The disclosed aftertreatment system may be particularly applicable to diesel engine applications for use in maintaining NO_X produced by the engine below regulated levels, even when experiencing system abnormalities. Operation of aftertreatment system 20 will now be described in detail.

During operation of engine 10, aftertreatment system 20 may experience any number of different abnormalities that have the potential to negatively affect exhaust emissions. If not otherwise accounted for, these abnormalities could result in the forced shutdown of engine 10, causing a loss of productivity and stranding the associated machine away from service. Examples of the different abnormalities can include system degradation, system failure, and low-dosing events. Each of these examples will be explored below to further illustrate the disclosed concepts.

System degradation may be a normally occurring phenomenon that is exhibited by a slow reduction in NO_X conversion efficiency over time. In particular, over time, catalyst substrates 36 may age and lose their ability to convert NO_X to H₂O and N₂. This reduction in efficiency can be exhibited by an increase in an amount of NO_X detected downstream of catalyst substrates 36 and/or an increase in an amount of reductant injected into the exhaust at an upstream location in order to sufficiently reduce the amount of NO_X normally present in the exhaust. In some instances, the reduction in efficiency may be caused by only one catalyst substrate 36 and/or one brick, of substrates 36. That is, the different catalyst substrates 36 of a particular aftertreatment system 20 (i.e. of each dosing circuit 34) may not age at the same rate.

Many different actions may be taken in response to detecting a reduction in NO_X conversion efficiency of a particular catalyst substrate 36. For example, additional reductant may be injected by the dosing circuits 34 associated with the underperforming catalyst substrates 36. While this may be effective in some situations, in other situations an increase in reductant injections may only serve to waste reductant without significantly improving NO_X conversion. That is, the substrate 36 may already be saturated and injecting additional reduction may not be helpful. Instead, it may be more beneficial to increase reductant injections by dosing circuits 34 not associated with the underperforming catalyst substrate 36 in an effort to offset the reduced efficiency. For example, if the catalyst substrates 36 of branch passage 30 are determined to be underperforming, it may be beneficial to increasing dosing of the catalyst substrates 36 of branch passage 32. In this example, although the NO_X conversion of branch passage 30 may not improve, the conversion of NO_X in branch passage 32 may improve enough to offset the higher levels of NO_X being discharged from branch passage 30. In particular, for a given engine 10, the sum of emissions produced by all branch passages 30, 32 is what is regulated and not the emissions of each individual branch passage 30, 32. Accordingly, if branch passage 32 is controlled to have extremely low NO_X emissions, the overall NO_X emissions of the associated engine 10 may still be less than a regulated amount, even though branch passage 30 may be discharging a majority of the emissions. Accordingly, when the abnormality of degraded performance is detected with respect to one particular dosing circuit 34 (e.g., of a dosing circuit 34 associated with branch passage 30), controller 46 may adjust operation of another dosing circuit 34 (e.g., of a dosing circuit 34 associated with another branch passage 32) to account for the degradation.

Many different types of system failures may be possible. For example, a particular supply 40 of reductant could freeze (e.g., a heater and/or temperature sensor associated with the supply 40 may fail), supply 40 may have been drained of reductant (e.g., supply 40 may leak), pump 42 may be damaged or leaking, injector 38 may stop functioning or inject an amount of reductant different from what is desired, etc. When a system failure occurs, reductant may not be injected at all or injected in an amount different that required to adequately reduce NO_X without wasting reductant. These failures can be detected in any number of different ways (e.g., based on NO_X detection, reductant detection, temperature detection, pressure detection, etc.). In addition, controller 46 may determine system failure based on signals generated by the failed components themselves and/or based on signals generated by other engine systems. That is, it may be possible for controller 46 to not detect the failure directly, but instead simply receive notification of a failure.

When a component of a particular dosing circuit 34 is determined to have failed, controller 46 may accommodate the failure using the remaining operational dosing circuits 34. For example, if one dosing circuit 34 associated with branch passage 30 is determined to have failed, the remaining dosing circuit 34 also associated with branch passage 30 may be caused to increase its dosing to a level previously provided by both dosing circuits 34. In this way, branch passage 30 may continue to discharge about the same amount of NO_X. Additionally or alternatively, one or more of the dosing circuits 34 associated with branch passage 32 may be caused by controller 46 to increase their injection amounts to accommodate the passage 30-failure by lowering the amount of NO_X discharged from branch passage 32 to an extremely low level in the manner described above. In this way, while the amount of NO_X discharged to the atmosphere by branch passage 30 may be higher due to the failure, the overall discharge amount of engine 10 may remain substantially unchanged (i.e., aftertreatment system may continue to maintain an overall consistent discharge of exhaust emissions). Accordingly, when the abnormality of failure is detected with respect to one particular dosing circuit 34, controller 46 may adjust operation of another dosing circuit 34 (e.g., of a dosing circuit 34 associated with the same or another branch passage 30, 32) to accommodate the failure.

In some operations and/or applications (e.g., during idling and/or operation at low load and speed), the amount of reductant that each dosing circuit 34 is commanded to inject may be so low that injection accuracy is negatively affected. In particular, there may be a low-dosing limit for each dosing circuit 34, below which injectors 38 cannot reliably inject reductant with a desired degree of accuracy. If unaccounted for, engine 10 could potentially violate regulations and discharge more NO_X than desired at these times, even though injectors 38 are being commanded to inject the correct amounts of reductant. The low-dosing event may be determined based on the amount of NO_X detected within branch passages 30, 32, based on the amount of reductant detected downstream of catalyst substrates 36, and or based on a monitored speed and/or load of engine 10.

In these situations, instead of causing all dosing circuits 34 to inject the same low levels of reductant, controller 46 may instead cause one or more of dosing circuits 34 to stop injecting completely. In addition, controller 46 may then distribute the required amount of dosing between the remaining operational dosing circuits 34. This may result in an increased amount of reductant injected by each operational dosing circuit 34, such that the amount of injected reductant for each circuit 24 is above the low injection limit. Accordingly, when the abnormality of low-dosing is detected, controller 46 may completely shut down or otherwise inhibit dosing of particular dosing circuits 34 and simultaneously adjust operation of the remaining dosing circuits 34 to accommodate the low-dosing event.

It will be apparent to those skilled in the art that various modifications and variations can be made to the aftertreatment system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the aftertreatment system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.

Claims

1. An aftertreatment system, comprising:

at least one exhaust passage;

a plurality of dosing circuits configured to inject reductant into the at least one exhaust passage; and

a controller in communication with each of the plurality of dosing circuits, the controller being configured to: determine a failure of a first of the plurality of dosing circuits; and selectively adjust operation of a second of the plurality of dosing circuits based on the failure.

2. The aftertreatment system of claim 1, wherein:

the at least one exhaust passage includes a first passage and a second passage in parallel with the first passage;

the first of the plurality of dosing circuits is associated with the first passage; and

the second of the plurality of dosing circuits is associated with the second passage.

3. The aftertreatment system of claim 1, wherein:

the at least one exhaust passage includes a single passage; and

the first of the plurality of dosing circuits is disposed in series with the second of the plurality of dosing circuits.

4. The aftertreatment system of claim 1, wherein the controller is configured to increase dosing of the second of the plurality of dosing circuits based on the failure to maintain an overall consistent discharge of exhaust emissions.

5. The aftertreatment system of claim 4, wherein the controller is further configured to shut down the first of the plurality of dosing circuits based on the failure.

6. The aftertreatment system of claim 1, wherein the failure includes one of a failure of a supply of reductant, a failure of a pump, or a failure of an injector.

7. The aftertreatment system of claim 1, wherein the failure includes a reduction in conversion efficiency of the first of the plurality of dosing circuits.

8. The aftertreatment system of claim 1, wherein the controller is further configured to:

determine a demand for dosing from each of the plurality of dosing circuits that is below a threshold amount; and

selectively inhibit operation of the first of the plurality of dosing circuits to cause an amount of reductant injected by the second of the plurality of dosing circuits to increase above the threshold amount.

9. The aftertreatment system of claim 1, further including at least one sensor configured to detect a performance parameter of the plurality of dosing circuits, wherein the controller is configured to determine the failure based on signals from the at least one sensor.

10. The aftertreatment system of claim 9, wherein the at least one sensor is an exhaust constituent sensor.

11. The aftertreatment system of claim 9, wherein the at least one sensor is slip Sensor.

12. The aftertreatment system of claim 9, wherein the at least one sensor is a reductant supply sensor.

13. A method of dosing reductant, comprising:

dosing reductant into an exhaust flow using a plurality of dosing circuits;

determining a failure of a first of the plurality of dosing circuits; and

selectively adjusting operation of a second of the plurality of dosing circuits based on the failure.

14. The method of claim 13, wherein:

dosing reductant into an exhaust flow includes dosing reductant into parallel legs of the exhaust flow;

the first of the plurality of dosing circuits is associated with a first of the parallel legs; and

the second of the plurality of dosing circuits is associated with a second of the parallel Legs.

15. The method of claim 13, wherein dosing reductant into an exhaust flow includes dosing reductant into of the exhaust flow at multiple locations in series with each other.

16. The method of claim 13, wherein selectively adjusting operation of the second of the plurality of dosing circuits includes selectively increasing dosing of the second of the plurality of dosing circuits based on the failure to maintain an overall consistent discharge of exhaust emissions.

17. The method of claim 16, further including selectively shutting down the first of the plurality of dosing circuits based on the failure.

18. The method of claim 16, wherein determining the failure includes determining the failure of one of a supply or reductant, a pump, or an injector.

19. The method of claim 18, further including:

determining a demand for dosing from each of the plurality of dosing circuits that is below a threshold amount; and

selectively inhibiting operation of the first of the plurality of dosing circuits so as to cause an amount of reductant injected by the second of the plurality of dosing circuits to increase above the threshold amount.

20. An engine, comprising:

an engine block at least partially defining a plurality of combustion chambers;

an exhaust manifold extending from the plurality of combustion chambers;

a turbocharger connected to the exhaust manifold;

a first branch passage connected to an outlet of the turbocharger;

a second branch passage connected to the outlet of the turbocharger in parallel with the first branch passage;

at least a first dosing circuit associated with the first branch passage;

at least a second dosing circuit associated with the second branch passage;

at least one sensor configured to generate a signal indicative of a performance parameter of the at least a first and at least a second dosing circuits; and

a controller in communication with the at least one sensor and each of the at least a first and at least a second dosing circuits, the controller being configured to: make a determination of one of a failure of the at least a first dosing circuit and occurrence of a low-dosing event based on the signal; selectively inhibit operation of the at least a first dosing circuit based on the determination; and selectively increase dosing of the at least a second dosing circuit based on the determination so as to maintain an overall consistent discharge of exhaust emissions from both of the first and second branch passages.