WO2016018886A1

WO2016018886A1 - System and method for diagnosing an in-use scr and ammonia oxidation catalyst

Info

Publication number: WO2016018886A1
Application number: PCT/US2015/042413
Authority: WO
Inventors: Michael A. Smith; Jinyong LUO; Saurabh Yashwant JOSHI; Ashok Kumar; Krishna KAMASAMUDRAM; Neal W. Currier; Aleksey Yezerets
Original assignee: Cummins, Inc.
Priority date: 2014-07-29
Filing date: 2015-07-28
Publication date: 2016-02-04

Abstract

A method includes providing a dosing command to adjust a dosing amount for an exhaust aftertreatment system; receiving selective catalytic reduction (SCR) inlet nitrous oxide (NOx) data and ammonia oxidation (AMOx) outlet NOx data; determining an ammonia-to-NOx ratio (ANR) value based on the SCR inlet NOx data and the dosing command; determining a NOx conversion fraction value based on the SCR inlet NOx data and the AMOx outlet NOx data; and determining a state of an in-use SCR and AMOx system of the exhaust aftertreatment system based on the ANR values and the NOx conversion fraction values for a plurality of dosing commands. Each dosing command corresponds with a distinct ANR value.

Description

SYSTEM AND METHOD FOR DIAGNOSING AN IN-USE SCR AND AMMONIA OXIDATION CATALYST

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] The present claims the benefit of priority to U.S. Provisional Patent Application No. 62/030,280, filed July 29, 2014, titled "SYSTEM AND METHOD FOR

DIAGNOSING AN IN-USE SCR AND AMMONIA OXIDATION CATALYST" which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present disclosure relates to exhaust aftertreatment systems. More particularly, the present disclosure relates to diagnosing an in-use selective catalytic reduction and ammonia oxidation system of an exhaust aftertreatment system.

BACKGROUND

[0003] Emissions regulations for internal combustion engines have become more stringent over recent years. Environmental concerns have motivated the implementation of stricter emission requirements for internal combustion engines throughout much of the world. Governmental agencies, such as the Environmental Protection Agency (EPA) in the United States, carefully monitor the emission quality of engines and set acceptable emission standards, to which all engines must comply. Consequently, the use of exhaust aftertreatment systems on engines to reduce emissions is increasing.

[0004] Exhaust aftertreatment system components can be susceptible to failure and degradation. Because the failure or degradation of components may have adverse consequences on the performance and emission-reduction capability of the exhaust aftertreatment system, the detection and, if possible, correction of failed or degraded components is desirable. In fact, some regulations require on-board diagnostic (OBD) monitoring or testing of many of the various components and performance of an exhaust aftertreatment system. SUMMARY

[0005] One embodiment relates to a method of diagnosing a selective catalytic reduction (SCR) and ammonia oxidation (AMOx) system. The method includes providing a dosing command to adjust a dosing amount for an exhaust aftertreatment system; receiving selective catalytic reduction (SCR) inlet nitrous oxide (NOx) data and ammonia oxidation (AMOx) outlet NOx data; determining an ammonia-to-NOx ratio (ANR) value based on the SCR inlet NOx data and the dosing command; determining a NOx conversion fraction value based on the SCR inlet NOx data and the AMOx outlet NOx data; and determining a state of an in-use SCR and AMOx system of the exhaust aftertreatment system based on the ANR values and the NOx conversion fraction values for a plurality of dosing commands. Each dosing command corresponds with a distinct ANR value. In this situation, the controller is able to acquire data regarding performance of the SCR and AMOx system, as indicated by the NOx conversion fraction at various ANR values, to diagnose the health of the system. In one embodiment, this method is performed via a controller on a vehicle such that the diagnosis is performed on an in-use SCR and AMOx system.

[0006] Another embodiment relates to an apparatus. The apparatus includes a dosing module, a nitrous oxide (NOx) conversion fraction module, an ammonia-to-NOx ratio (ANR) module, and a selective catalytic reduction (SCR) and ammonia oxidation (AMOx) module. The dosing module is structured to provide a dosing command to adjust a dosing amount for exhaust gas in an exhaust aftertreatment system. The NOx conversion fraction module is structured to determine a NOx conversion fraction value for the exhaust gas for each dosing command. The ANR module is structured to determine an ANR value based on a selective catalytic reduction (SCR) inlet NOx amount and the dosing command. The SCR and AMOx module is structured to determine a state of an SCR and AMOx system in the exhaust aftertreatment system based on a plurality of determined ANR values and NOx conversion fraction values.

[0007] Still another embodiment relates to a system. The system includes an engine, an exhaust aftertreatment system in exhaust gas-receiving communication with the engine, and a controller communicably coupled to the exhaust aftertreatment system. The exhaust aftertreatment system includes an in-use selective catalytic reduction (SCR) and an ammonia oxidation (AMOx) system having at least one of a SCR catalyst and an AMOx catalyst. The controller structured to provide a dosing command to a delivery mechanism to adjust a dosing amount for the exhaust aftertreatment system; determine an ammonia- to-Nitrous Oxide (NOx) ratio (ANR) value based on SCR inlet NOx data and the dosing command; determine a NOx conversion fraction based on the SCR inlet NOx data and AMOx outlet NOx data; and determine a state of the in-use SCR and AMOx system of the exhaust aftertreatment system based on ANR and NOx conversion fraction values for a plurality of dosing commands. Each dosing command corresponds with a distinct ANR value.

[0008] These and other features, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

[0009] FIG. 1 is schematic diagram of an exhaust aftertreatment system with a controller, according to an example embodiment.

[0010] FIG. 2 is a schematic of a selective catalytic reduction (SCR) and ammonia oxidation (AMOx) system of an exhaust aftertreatment system, according to an example embodiment

[0011] FIG. 3 is a schematic of the controller used with the system of FIG. 1, according to an example embodiment.

[0012] FIG. 4 is a flow diagram of a method of diagnosing a SCR and AMOx system of an exhaust aftertreatment system, according to an example embodiment.

[0013] FIG. 5 is a graph of a fresh (i.e., healthy) and a thermally aged SCR and AMOx system, according to an example embodiment DETAILED DESCRIPTION

[0014] Referring the Figures generally, the various embodiments disclosed herein relate to a system and a method of diagnosing an in-use selective catalytic reduction (SCR) and ammonia oxidation (AMOx) system of an exhaust gas aftertreatment system. As a brief overview (described more fully herein), some diesel engine exhaust aftertreatment systems include an SCR and AMOx system. The SCR includes an SCR catalyst that is designed to reduce the nitrous oxides in exhaust gas to nitrogen and other less pollutant compounds. To accomplish this reduction, a reductant is sprayed into the exhaust gas stream prior to the exhaust gas reaching the SCR system. Over the SCR catalyst, the nitrous oxides (NOx) react with the reductant, in the form of ammonia, to form nitrogen, which decreases the nitrous oxides (NOx) in the exhaust gas. The AMOx catalyst decreases the ammonia that is not used in the SCR system to also nitrogen and other less harmful compounds. Therefore, the SCR uses ammonia to reduce the NOx amount in the exhaust gas while the AMOx catalyst reduces any unused ammonia from the SCR, such that large quantities of both NOx and ammonia are not expelled via the tailpipe of the aftertreatment system to the environment.

[0015] According to the present disclosure, a controller provides one or more dosing commands to adjust the reductant dosing amount in the aftertreatment system. The controller adjusts the dosing amount to effect a less than and greater than stoichiometric condition of the ammonia-to-nitrous oxide ratio (ANR). At stoichiometric ANR, there is substantially no ammonia leaving the tailpipe (i.e., mostly all of the ammonia is used to reduce mostly all of the NOx in the exhaust gas). During an ammonia slip condition (typically, for ANR greater than stoichiometric), there is an amount of unconverted ammonia in the SCR. The AMOx catalyst acts as a backup to convert the unconverted ammonia in the SCR to nitrogen and other compounds. As the controller commands various dosing amounts, the controller receives data to determine a NOx conversion fraction (i.e., percentage of NOx converted by the SCR and AMOx system to nitrogen and other compounds relative to the NOx initially in the exhaust gas (i.e., entering the SCR) and the ANR. Based on one or more correlations (see FIG. 5), the controller determines whether the SCR and AMOx system is healthy or degraded (e.g., thermally aged).

Accordingly, the correlation may also provide an indication of substantially what the NOx conversion fraction should be at various ANR values. As such, the controller is able to determine a state of the SCR and AMOx system based on the determined ANR and NOx conversion fraction. This is explained more fully herein. Based on the state determined (e.g., healthy, degraded, dosing amount commanded is inaccurate), the controller may provide one or more notifications (e.g., a fault code). Accordingly, the system and method described herein enable the diagnosis of an in-use SCR and AMOx system. As such, service appointments may be avoided, which may increase the convenience of such system and method for the vehicle operator.

[0016] As used herein, the term "data point" (unless otherwise specified) refers to an ANR value and a corresponding NOx conversion fraction. In one embodiment, these values are plotted on a graph such that the ANR value is the x-value and the NOx conversion fraction is the y-value. As described herein, when the controller adjusts the dosing amount to adjust the ANR value, the NOx conversion fraction is also adjusted. This interdependency is the basis for the "data point" reference.

[0017] Referring now to FIG. 1, an engine-exhaust aftertreatment system with a controller is shown, according to an example embodiment. For clarity, FIG. 2 depicts a close-up of the SCR and AMOx system for the exhaust aftertreatment system. FIGS. 1-2 are collectively described below.

[0018] As shown in FIG. 1, the engine system 10 includes an internal combustion engine 20 and an exhaust aftertreatment system 22 in exhaust gas-receiving communication with the engine 20. According to one embodiment, the engine 20 is structured as a

compression-ignition internal combustion engine that utilizes diesel fuel. However, in various alternate embodiments, the engine 20 may be structured as any other type of engine (e.g., spark-ignition) that utilizes any type of fuel (e.g., gasoline). Within the internal combustion engine 20, air from the atmosphere is combined with fuel, and combusted, to power the engine. Combustion of the fuel and air in the compression chambers of the engine 20 produces exhaust gas that is operatively vented to an exhaust manifold (not shown) and to the aftertreatment system 22.

[0019] The exhaust aftertreatment system 10 includes a diesel particular filter (DPF) 40, a diesel oxidation catalyst (DOC) 30, a selective catalytic reduction (SCR) system 52 with an SCR catalyst 50, and an ammonia oxidation (AMOx) catalyst 60. The SCR system 52 further includes a reductant delivery system that has a diesel exhaust fluid (DEF) source 54 that supplies DEF to a DEF doser 56 via a DEF line 58.

[0020] In an exhaust flow direction, as indicated by directional arrow 29, exhaust gas flows from the engine 20 into inlet piping 24 of the exhaust aftertreatment system 22. From the inlet piping 24, the exhaust gas flows into the DOC 30 and exits the DOC into a first section of exhaust piping 28A. From the first section of exhaust piping 28A, the exhaust gas flows into the DPF 40 and exits the DPF into a second section of exhaust piping 28B. From the second section of exhaust piping 28B, the exhaust gas flows into the SCR catalyst 50 and exits the SCR catalyst into the third section of exhaust piping 28C. As the exhaust gas flows through the second section of exhaust piping 28B, it is periodically dosed with DEF by the DEF doser 56. Accordingly, the second section of exhaust piping 28B acts as a decomposition chamber or tube to facilitate the

decomposition of the DEF to ammonia. From the third section of exhaust piping 28C, the exhaust gas flows into the AMOx catalyst 50 and exits the AMOx catalyst into outlet piping 26 before the exhaust gas is expelled from the system 22. Based on the foregoing, in the illustrated embodiment, the DOC 30 is positioned upstream of the DPF 40 and the SCR catalyst 50, and the SCR catalyst 50 is positioned downstream of the DPF 40 and upstream of the AMOX catalyst 60. However, in alternative embodiments, other arrangements of the components of the exhaust aftertreatment system 22 are also possible.

[0021] The DOC 30 may have any of various flow-through designs. Generally, the DOC 30 is structured to oxidize at least some particulate matter, e.g., the soluble organic fraction of soot, in the exhaust and reduce unburned hydrocarbons and CO in the exhaust to less environmentally harmful compounds. For example, the DOC 30 may be structured to reduce the hydrocarbon and CO concentrations in the exhaust to meet the requisite emissions standards for those components of the exhaust gas. An indirect consequence of the oxidation capabilities of the DOC 30 is the ability of the DOC 30 to oxidize NO into N0₂. In this manner, the level of N0₂ exiting the DOC 30 is equal to the N0₂ in the exhaust gas generated by the engine 20 plus the N0₂ converted from NO by the DOC 30. [0022] In addition to treating the hydrocarbon and CO concentrations in the exhaust gas, the DOC 30 may also be used in the controlled regeneration of the DPF 40, SCR catalyst 50, and AMOx catalyst 60. This can be accomplished through the injection, or dosing, of unburned HC into the exhaust gas upstream of the DOC 30. Upon contact with the DOC 30, the unburned HC undergoes an exothermic oxidation reaction which leads to an increase in the temperature of the exhaust gas exiting the DOC 30 and subsequently entering the DPF 40, SCR catalyst 50, and/or the AMOx catalyst 60. The amount of unburned HC added to the exhaust gas is selected to achieve the desired temperature increase or target controlled regeneration temperature.

[0023] The DPF 40 may be any of various flow-through designs, and is structured to reduce particulate matter concentrations, e.g., soot and ash, in the exhaust gas to meet requisite emission standards. The DPF 40 captures particulate matter and other constituents, and thus needs to be periodically regenerated to burn off the captures constituents. Additionally, the DPF 40 may be configured to oxidize NO to form N0₂ independent of the DOC 30.

[0024] As discussed above, the SCR system 52 includes a reductant delivery system with a reductant (e.g., DEF) source 54, pump (not shown) and delivery mechanism or doser 56. The reductant source 54 can be a container or tank capable of retaining a reductant, such as, for example, ammonia (NH₃), DEF (e.g., urea), or diesel oil. The reductant source 54 is in reductant supplying communication with the pump, which is configured to pump reductant from the reductant source to the delivery mechanism 56 via a reductant delivery line 58. The delivery mechanism 56 is positioned upstream of the SCR catalyst 50. The delivery mechanism 56 is selectively controllable to inject reductant directly into the exhaust gas stream prior to entering the SCR catalyst 50. As described herein, the controller 100 is structured to control the timing and amount of the reductant delivered to the exhaust gas. In some embodiments, the reductant may either be ammonia or DEF, which decomposes to produce ammonia. As briefly described above, the ammonia reacts with NOx in the presence of the SCR catalyst 50 to reduce the NOx to less harmful emissions, such as N₂ and H₂0. The NOx in the exhaust gas stream includes N0₂ and NO. Generally, both N0₂ and NO are reduced to N₂ and H₂0 through various chemical reactions driven by the catalytic elements of the SCR catalyst 50 in the presence of NH₃. [0025] The SCR catalyst 50 may be any of various catalysts known in the art. For example, in some implementations, the SCR catalyst 50 is a vanadium-based catalyst, and in other implementations, the SCR catalyst is a zeolite-based catalyst, such as a Cu-Zeolite or a Fe-Zeolite catalyst. In one representative embodiment, the reductant is aqueous urea and the SCR catalyst 50 is a zeolite-based catalyst.

[0026] The AMOx catalyst 60 may be any of various flow-through catalysts configured to react with ammonia to produce mainly nitrogen. As briefly described above, the AMOx catalyst 60 is structured to remove ammonia that has slipped through or exited the SCR catalyst 50 without reacting with NOx in the exhaust. In certain instances, the

aftertreatment system 22 can be operable with or without an AMOx catalyst. Further, although the AMOx catalyst 60 is shown as a separate unit from the SCR catalyst 50 in FIGS. 1-2, in some implementations, the AMOx catalyst 60 may be integrated with the SCR catalyst 50, e.g., the AMOx catalyst 60 and the SCR catalyst 50 can be located within the same housing. According to the present disclosure, the SCR catalyst 50 and AMOx catalyst 60 are positioned serially, with the SCR catalyst 50 preceding the AMOx catalyst 60 (see, e.g., FIG. 2).

[0027] As referred to herein, the SCR catalyst 50 and AMOx catalyst 60 form the SCR and AMOx system. Accordingly, health or degradations determined are in regard to those catalysts.

[0028] Various sensors, such as NOx sensors 12, 14, 55, 57 and temperature sensors 16, 18, may be strategically disposed throughout the exhaust aftertreatment system 22 and may be in communication with the controller 100 to monitor operating conditions of the engine system 10. As shown, more than one NOx sensor may be positioned upstream and downstream of the SCR catalyst 50. In this configuration, the NOx sensor 12 measures the engine out NOx while NOx sensor 55 measures the SCR catalyst 50 inlet NOx amount. This is due to DOC 30/DPF 40 potentially oxidizing some portion of the engine out NOx whereby the engine out NOx amount would not be equal to the SCR catalyst 50 inlet NOx amount. Accordingly, this configuration accounts for this potential

discrepancy. The NOx amount leaving the SCR catalyst 50 may be measured by NOx sensor 57 and/or NOx sensor 14. In some embodiments, there may be only NOx sensor 57 or NOx sensor 14. The NOx sensor 57 (in some embodiments, NOx sensor 14) is positioned downstream of the SCR catalyst 50 and structured to detect the concentration of NOx in the exhaust gas downstream of the SCR catalyst (e.g., exiting the SCR catalyst).

[0029] The temperature sensors 16 are associated with the DOC 30 and DPF 40, and thus can be defined as DOC/DPF temperature sensors 16. The DOC/DPF temperature sensors 16 are strategically positioned to detect the temperature of exhaust gas flowing into the DOC 30, out of the DOC and into the DPF 40, and out of the DPF 40 before being dosed with reductant (e.g., DEF, etc.) by the doser 56. The temperature sensors 18 are associated with the SCR catalyst 50 and thus can be defined as SCR temperature sensors 18. The SCR temperature sensors 18 are strategically positioned to detect the temperature of exhaust gas flowing into and out of the SCR catalyst 50.

[0030] Although the exhaust aftertreatment system 22 shown includes one of an DOC 30, DPF 40, SCR catalyst 50, and AMOx catalyst 60 positioned in specific locations relative to each other along the exhaust flow path, in other embodiments, the exhaust

aftertreatment system 22 may include more than one of any of the various catalysts positioned in any of various positions relative to each other along the exhaust flow path as desired. Further, although the DOC 30 and AMOX catalyst 60 are non-selective catalysts, in some embodiments, the DOC 30 and AMOX catalyst 60 can be selective catalysts.

[0031] FIG. 1 is also shown to include an operator input/output (I/O) device 120. The operator I/O device 120 is communicably coupled to the controller 100, such that information may be exchanged between the controller 100 and the I/O device 120, wherein the information may relate to one or more components of FIG. 1 or

determinations (described below) of the controller 100. The operator I/O device 120 enables an operator of the vehicle (or another passenger) to communicate with the controller 100 and one more components of the vehicle and components of FIG. 1. For example, the operator input/output device 120 may include, but is not limited, an interactive display, a touchscreen device, one or more buttons and switches, voice command receivers, etc. Via the I/O device 120, the controller 100 may provide a fault notification based on the determined state of the SCR and AMOx system. [0032] The controller 100 is structured to control the operation of the engine system 10 and associated sub-systems, such as the internal combustion engine 20 and the exhaust gas aftertreatment system 22. According to one embodiment, the components of FIGS. 1-2 are embodied in a vehicle. The vehicle may include an on-road or an off-road vehicle including, but not limited to, line -haul trucks, mid-range trucks (e.g., pick-up trucks), tanks, airplanes, and any other type of vehicle that utilizes an SCR system.

Communication between and among the components may be via any number of wired or wireless connections. For example, a wired connection may include a serial cable, a fiber optic cable, a CAT5 cable, or any other form of wired connection. In comparison, a wireless connection may include the Internet, Wi-Fi, cellular, radio, etc. In one embodiment, a controller area network ("CAN") bus provides the exchange of signals, information, and/or data. The CAN bus includes any number of wired and wireless connections. Because the controller 100 is communicably coupled to the systems and components of FIG. 1, the controller 100 is structured to receive data from one or more of the components shown in FIG. 1. For example, the data may include NOx data (e.g., an incoming NOx amount from NOx sensor 55 and an outgoing NOx amount from NOx sensor 57), dosing data (e.g., timing and amount of dosing delivered from doser 56), and a vehicle operating data (e.g., engine speed, vehicle speed, engine temperature, etc.) received via one or more sensors. As another example, the data may include an input from operator input/output device 120. As described more fully herein, with this data, the controller 100 diagnoses in-use SCR and AMOx systems. The structure and function of the controller 100 is further described in regard to FIG. 3.

[0033] As such, referring now to FIG. 3, an example structure for the controller 100 is shown according to one embodiment. As shown, the controller 100 includes a processing circuit 101 including a processor 102 and a memory 103. The processor 102 may be implemented as a general-purpose processor, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a digital signal processor (DSP), a group of processing components, or other suitable electronic processing components. The one or more memory devices 103 (e.g., RAM, ROM, Flash Memory, hard disk storage, etc.) may store data and/or computer code for facilitating the various processes described herein. Thus, the one or more memory devices 103 may be communicably connected to the processor 102 and provide computer code or instructions to the processor 102 for executing the processes described in regard to the controller 100 herein. Moreover, the one or more memory devices 103 may be or include tangible, non- transient volatile memory or non-volatile memory. Accordingly, the one or more memory devices 103 may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described herein.

[0034] The memory 103 is shown to include various modules for completing the activities described herein. More particularly, the memory 103 includes modules structured to diagnose an in-use SCR and AMOx system. While various modules with particular functionality are shown in FIG. 2, it should be understood that the controller 100 and memory 103 may include any number of modules for completing the functions described herein. For example, the activities of multiple modules may be combined as a single module, additional modules with additional functionality may be included, etc. Further, it should be understood that the controller 100 may further control other vehicle activity beyond the scope of the present disclosure.

[0035] As shown, the controller 100 includes a dosing module 104, a NOx conversion fraction module 105, an ammonia-to-NOx ratio (ANR) module 106, a correlation module 107, an SCR and AMOx state determination module 108, and a notification module 109. The dosing module 104 is structured to provide a dosing command to adjust a reductant dosing amount and a timing of dosing injection. Accordingly, the dosing command may be provided to a doser, such as doser 56 (FIG. 1). The dosing module 104 may also accumulate dosing data regarding the amount and timing of reductant to determine an approximate amount of ammonia being created to determine an ANR.

[0036] The NOx conversion fraction module 105 is structured to determine a NOx conversion fraction for the exhaust gas for each ANR value, wherein the ANR value is affected by the dosing command. Accordingly, the NOx conversion fraction module 105 may receive NOx data regarding the exhaust gas stream from the engine 20. For example, the NOx data may include an SCR inlet NOx amount from NOx sensor 55 (represented as NOx,inlet in equation (1) below). The NOx data may also include an SCR outlet NOx amount, which may be provided by NOx sensor 57 (represented as NOx,outlet in equation (1) below). Based on these two amounts, a NOx conversion amount may be determined by the NOx conversion fraction module 105. According to one embodiment, the conversion fraction amount may be determined as follows:

[(NOx, inlet - NOx, outlet)/NOx,inlet] x 100 = NOx conversion fraction percent

(1)

The NOx conversion fraction provides an indication of the efficacy of the SCR and AMOx system. For example, a relatively higher conversion fraction indicates that a substantial amount of the NOx present in the exhaust stream is being reduced to nitrogen and other less pollutant compounds. However, a relatively lower conversion fraction indicates that the NOx in the exhaust gas stream is substantially not being converted to nitrogen and other less pollutant compounds. The use of this data point (i.e., the NOx conversion fraction for each determined ANR value) is described below. In various alternate embodiments, the NOx conversion fraction may be determined using other methods, such as model based with more or less data inputs.

[0037] The ANR module 106 is structured to determine an ANR value for each dosing command based on a selective catalytic reduction (SCR) inlet NOx amount and the dosing command. The SCR inlet NOx amount corresponds with the denominator in the ANR. This value may be based on that acquired from sensor 55 or determined using one or more formulas and processes. The ammonia value may be based on the chemical relationship of reductant plus SCR catalyst to ammonia, which is therefore based on the amount supplied. In one embodiment, each dosing command corresponds with a distinct ANR value. As mentioned above, the dosing module 104 is structured to vary the timing and amount of dosing provided to the exhaust gas stream. According to the present disclosure, the controller 100 - when diagnosing the SCR and AMOx system - selectively varies and monitors the dosing amount. For certain ANR values, the stoichiometric relationship of NOx to ammonia is approximately 1 : 1. Accordingly, the difference of the outgoing NOx with the inlet NOx corresponds with the amount of ammonia. As such, this ammonia amount and the NOx inlet amount may serve as the determined ANR. It should be noted that various other methods, formulas, models, and processes may be used to determine the ANR, such that the aforementioned example is not meant to be limiting. All such variations are intended to be within the spirit and scope of this disclosure.

[0038] With the aforementioned in mind, ANR values over one correspond with relatively more ammonia than needed to convert the NOx present in the exhaust gas. In comparison, ANR values less than one correspond with relatively less ammonia than needed to convert substantially all of the NOx present in the exhaust. In certain embodiments, the dosing module 104 is structured to provide at least one dosing command to vary the ANR.

[0039] The correlation module 107 is structured to track each dosing command with each determined ANR and NOx conversion fraction. Accordingly, each dosing command may represent a data point for each determined ANR and NOx conversion fraction. In one embodiment, with the data points, the correlation module 107 is able to determine a correlation (i.e., generate one or more statistics) regarding the ANR versus NOx conversion fraction over a range of ANR values (below, at, and above a stoichiometric ANR value). In one embodiment, the correlation module 107 tracks the data points (e.g., each dosing command corresponds with a distinct ANR value and a corresponding distinct NOx conversion fraction) and generates a line of best fit, as in FIG. 5. In other embodiments, various other statistics, formulas, and the like may be used to determine a state of the SCR and AMOx system (described below). In certain alternate embodiments, a single data point (determined ANR and NOx conversion fraction) may be used and compared against the healthy and degraded data correlations shown in FIG. 5. The correlation module 107 function is described further in regard to the SCR and AMOx state determination module 108.

[0040] The SCR and AMOx state determination module 108 is structured to determine a state of the SCR and AMOx system based on a plurality of ANR and NOx conversion fraction values based on a plurality of dosing commands, wherein each dosing command corresponds with a distinct ANR value. One example implementation is as follows. The dosing module 104 provides a plurality of dosing commands (e.g., a sweeping function) to correspond with a plurality of ANR values. The NOx conversion fraction module 105 determines a corresponding NOx conversion fraction for each ANR value. With this plurality of data points, a plurality of ANR versus NOx conversion fraction data points may be tracked. In some embodiments, they are plotted on a graph. The resulting data points may be compared against the data points for healthy and degraded SCR and AMOx systems, as depicted in FIG. 5.

[0041] As such, referring now to FIG. 5, FIG. 5 depicts a graph of experimental data for healthy and degraded SCR and AMOx systems as a function of ANR and NOx conversion fraction, according to one example embodiment. For the portion of the graph where the ANR value is less than one (i.e., below stoichiometric), for a healthy SCR and AMOx system, the NOx conversion fraction is substantially equal to the ANR value. As mentioned above, this is due to not all the NOx being converted when insufficient ammonia is present where the NOx converted amount is approximately equal to the amount of ammonia. Accordingly, for this portion of the graph, the line of best fit corresponds with an approximate slope of one - a linear portion. At a stoichiometric ANR (e.g., ANR substantially equal to one), the slope is substantially not equal to one and the oxidation of ammonia is decreased (i.e., ammonia slip is increased). Lines 502 and 504 show that the NOx conversion fraction (line 502) and ammonia slip (504) increase for a healthy SCR and AMOx system as a function of increasing ANR value. In comparison, for a degraded SCR and AMOx system, the NOx conversion fraction decreases with increase ANR (line 506) and the ammonia slip amount (line 508) increases at a faster rate relative to the ammonia slip for a healthy SCR and AMOx system.

[0042] Accordingly, the SCR and AMOx state determination module 108 makes a determination of the accumulated data points relative to the behavior for healthy and degraded SCR and AMOx system. According to one example embodiment, the state determinations may be as follows. For ANR values below stoichiometric, the SCR and AMOx state determination module 108 determines that the SCR and AMOx system is degraded if the NOx conversion fraction is below or substantially below the correlation (i.e., the linear best fit line). Because the slope is approximately equal to one, the correlation expected is the ANR value is approximately equal to the NOx conversion fraction (e.g., ANR of 0.8 would correspond with an 80 % NOx conversion rate). In one example embodiment, this determination corresponds with ANR values between 0.4 and 0.9. This condition indicates that not all of the ammonia being supplied (via the reaction of the reductant and the SCR catalyst) is being used in the NOx conversion reaction despite there being less ammonia than needed to convert the NOx in the exhaust gas stream. Accordingly, the SCR and AMOx system may be thermally aged, degraded, and otherwise not meeting a performance criterion. In another example, still referring to ANR values below stoichiometric, the SCR and AMOx state determination module 108 determines that the commanded dosing amount is inaccurate based on a NOx conversion fraction falling above or substantially above the correlation. In one example, this determination is based on a line of best fit (based on the plurality of data points) not being linear. This situation indicates that NOx is being reduced by a greater amount than the provided ammonia. As such, the controller 100 determines that the dosing amount commanded is substantially not the dosing amount provided. Similarly, still for ANR values below stoichiometric, the SCR and AMOx state determination module 108 determines the commanded dosing amount is accurate based on a NOx conversion fraction substantially matching the correlation (e.g., ANR of 0.8 and NOx conversion fraction of 80%). In other words, the plurality of data points yield a linear relationship for a predetermined range of ANR values (e.g., 0.4 to 0.9) for the ANR versus NOx conversion fraction graph. In some embodiments, the determination that the state of the SCR and AMOx system is degraded is based on an ANR value between 0.85 and 1.0 and the corresponding NOx conversion fraction being below the line of best fit.

[0043] Finally, for ANR values above the ANR stoichiometric condition (e.g., greater than one as shown in FIG. 5), the SCR and AMOx state determination module 108 determines that the state of the SCR and AMOx system is degraded based on the NOx conversion fraction decreasing and an ammonia slip amount increasing for increasing ANR values above the ANR stoichiometric condition. For a healthy SCR and AMOx system, for ANR values between 1 and 1.4, the line of best fit, line 502, is nonlinear but increasing in NOx conversion fraction for increasing ANR values. After ANR of approximately 1.4, the ANR versus NOx conversion fraction is substantially horizontal. This indicates that increasing the NOx conversion fraction levels out despite the increasing ANR value. However, for degraded or unhealthy SCR and AMOx systems, the NOx conversion fraction line of best fit is substantially parabolic with the vertex occurring near the stoichiometric condition (see line 506). For ANR values above the stoichiometric condition (greater than one), the NOx conversion fraction decreases with increasing ANR value. However, the increasing ANR value corresponds with an increasing ammonia slip amount (see line 508). With the aforementioned behavior defined for healthy versus degraded SCR and AMOx systems, the SCR and AMOx state determination module 108 may make a state determination based on ANR values above the stoichiometric condition. For example, for ANR values greater than 1.4, if the NOx conversion fraction is not substantially horizontal (i.e., a horizontal line of best fit with an r-squared value of approximately 0.1 and lower), the SCR and AMOx state determination module 108 may determine the SCR and AMOx system to be degraded. In another example, if the NOx conversion fraction increases for ANR values between 1.0 and 1.4, the SCR and AMOx state determination module 108 may determine the SCR and AMOx system to be healthy.

[0044] Thus, the controller 100 is capable of diagnosing the system for ANR values less than, equal to, or greater than one (i.e., the stoichiometric condition) as described above. Accordingly, the dosing module 104 may provide a sweeping range of dosing commands to cause a variety of ANR values and the SCR and AMOx state determination module 108 may make a SCR and AMOx system state determination based on the corresponding NOx conversion fraction value for a plurality of ANR values.

[0045] Based on these determined states, the notification module 109 is structured to provide one or more notifications. The notifications may correspond with a fault code, a notification (e.g., on the operator I/O device 120), and the like. The notification indicates the state (e.g., healthy or degraded) for the SCR and AMOx system. In this situation, the operator of the vehicle may receive a notification as to how the SCR and AMOx system is functioning and whether it needs to be serviced. The modules described above are structured to perform inside or outside of a service environment. As such, the diagnosis may be performed with an in-use SCR and AMOx system. This may avoid potentially costly diagnostic procedures performed in service bay environments.

[0046] Referring now to FIG. 4, a method 400 of diagnosing a SCR and AMOx system of an exhaust aftertreatment system is shown according to an example embodiment. In one example embodiment, method 400 may be implemented with the controller 100 of FIG. 1. Accordingly, method 400 may be described in regard to FIGS. 1-3. [0047] At process 402, the controller 100 provides a dosing command to adjust a dosing amount of reductant in the exhaust aftertreatment system (e.g., via the dosing module 104). At process 404, the controller 100 receives SCR inlet NOx data and AMOx outlet NOx data. In some embodiments, when an AMOx system is not included, the controller 100 receives SCR inlet NOx data and SCR outlet NOx data. Based on the SCR inlet and AMOx outlet NOx data, the controller 100 determines a NOx conversion fraction (process 408). At process 406, the controller 100 determines an ANR value based on the SCR inlet NOx data and the dosing command. As mentioned above, the dosing command may provide an indication of the amount of reductant supplied while the SCR inlet NOx data provides an indication of the NOx amount entering the SCR. The SCR inlet NOx data may be determined by a sensor, such as NOx sensor 55, or may be calculated using a model, formula, or the like. The SCR inlet NOx amount serves as the denominator in the ammonia-to-NOx ratio. At process 410, the controller 100 correlates ANR versus NOx conversion fraction for each ANR value, where the ANR value is adjusted by the dosing amount. The correlation may include, but is not limited, placing each data point (ANR with corresponding NOx conversion fraction determined - x and y coordinates) on a graph, such as the graph in FIG. 5, and comparing those data points to data points for healthy and degraded SCR and AMOx systems. Thus, a plurality of data points may be acquired such that various parts of the graph corresponding with different ANR values may be analyzed. Accordingly, based on at least one of the correlation and the determined ANR values and NOx conversion fractions, the controller 100 determines a state of the in- use SCR and AMOx system (process 412).

[0048] As mentioned above, the determined state may correspond with the

determinations described above in regard to the SCR and AMOx state determination module 108 (e.g., a NOx conversion fraction relative to an ANR value). For example, the controller 100 may determine that the commanded dosing amount is accurate based on a linearity of ANR versus NOx conversion fraction for ANR values between 0.4 and 0.9. The determination may be based on a line of best fit having an r-squared value greater than or equal to 0.8. In other embodiments, other r-squared values may be chosen to signify linearity. Similarity, as mentioned above, an r-squared value of less than or equal to 0.1 may indicate a horizontal line. However, other r-squared values or indicators may be used to signify horizontal lines. In another example, the controller 100 may determine that the commanded dosing amount is inaccurate based on a nonlinearity (e.g., r-squared values less than 0.8) of ANR versus NOx conversion fraction for ANR values between 0.4 and 0.9. In yet another example, the controller 100 may determine that the state of the SCR and AMOx system is degraded based on a NOx conversion fraction falling below the correlation. This determination may be based on the data point with the ANR value closest to, but not exceeding, the ANR value stoichiometric condition (e.g., of ANR values 0.8, 0.9, 0.7, and 0.95, the controller looks at the NOx conversion fraction determined for the ANR of 0.95 and if it is below the expected linear line (based on a line of best for the other data points) - or not equal to ninety- five percent - the controller determines that the system is degraded). Based on the determined state, the controller generates and provides a notification (process 412), where the notification provides an operator of the state of the SCR and AMOx system (e.g., healthy).

[0049] The schematic flow chart diagrams and method schematic diagrams described above are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of representative embodiments. Other steps, orderings and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the methods illustrated in the schematic diagrams.

[0050] Additionally, the format and symbols employed are provided to explain the logical steps of the schematic diagrams and are understood not to limit the scope of the methods illustrated by the diagrams. Although various arrow types and line types may be employed in the schematic diagrams, they are understood not to limit the scope of the corresponding methods. Indeed, some arrows or other connectors may be used to indicate only the logical flow of a method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of a depicted method. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown. It will also be noted that each block of the block diagrams and/or flowchart diagrams, and combinations of blocks in the block diagrams and/or flowchart diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and program code. [0051] Many of the functional units described in this specification have been labeled as modules, in order to more particularly emphasize their implementation independence. For example, a module may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. A module may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

[0052] Modules may also be implemented in machine-readable medium for execution by various types of processors. An identified module of executable code may, for instance, comprise one or more physical or logical blocks of computer instructions, which may, for instance, be organized as an object, procedure, or function. Nevertheless, the executables of an identified module need not be physically located together, but may comprise disparate instructions stored in different locations which, when joined logically together, comprise the module and achieve the stated purpose for the module.

[0053] Indeed, a module of computer readable program code may be a single instruction, or many instructions, and may even be distributed over several different code segments, among different programs, and across several memory devices. Similarly, operational data may be identified and illustrated herein within modules, and may be embodied in any suitable form and organized within any suitable type of data structure. The operational data may be collected as a single data set, or may be distributed over different locations including over different storage devices, and may exist, at least partially, merely as electronic signals on a system or network. Where a module or portions of a module are implemented in machine-readable medium (or computer-readable medium), the computer readable program code may be stored and/or propagated on in one or more computer readable medium(s).

[0054] The computer readable medium may be a tangible computer readable storage medium storing the computer readable program code. The computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, holographic, micromechanical, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. [0055] More specific examples of the computer readable medium may include but are not limited to a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), an optical storage device, a magnetic storage device, a holographic storage medium, a micromechanical storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, and/or store computer readable program code for use by and/or in connection with an instruction execution system, apparatus, or device.

[0056] The computer readable medium may also be a computer readable signal medium. A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electrical, electro-magnetic, magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport computer readable program code for use by or in connection with an instruction execution system, apparatus, or device. Computer readable program code embodied on a computer readable signal medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, Radio Frequency (RF), or the like, or any suitable combination of the foregoing

[0057] In one embodiment, the computer readable medium may comprise a combination of one or more computer readable storage mediums and one or more computer readable signal mediums. For example, computer readable program code may be both propagated as an electro-magnetic signal through a fiber optic cable for execution by a processor and stored on RAM storage device for execution by the processor.

[0058] Computer readable program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the "C" programming language or similar programming languages. The computer readable program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone computer-readable package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

[0059] The program code may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the schematic flowchart diagrams and/or schematic block diagrams block or blocks.

[0060] Example and non-limiting module implementation elements include sensors (e.g., sensor 12) providing any value determined herein, sensors providing any value that is a precursor to a value determined herein, datalink and/or network hardware including communication chips, oscillating crystals, communication links, cables, twisted pair wiring, coaxial wiring, shielded wiring, transmitters, receivers, and/or transceivers, logic circuits, hard-wired logic circuits, reconfigurable logic circuits in a particular non-transient state configured according to the module specification, any actuator including at least an electrical, hydraulic, or pneumatic actuator, a solenoid, an op-amp, analog control elements (springs, filters, integrators, adders, dividers, gain elements), and/or digital control elements.

[0061] Accordingly, 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 disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

WHAT IS CLAIMED IS:

1. A method, comprising:

providing a dosing command to adjust a dosing amount for an exhaust aftertreatment system;

receiving selective catalytic reduction (SCR) inlet nitrous oxide (NOx) data and ammonia oxidation (AMOx) outlet NOx data;

determining an ammonia-to-NOx ratio (ANR) value based on the SCR inlet NOx data and the dosing command;

determining a NOx conversion fraction value based on the SCR inlet NOx data and the AMOx outlet NOx data; and

determining a state of an in-use SCR and AMOx system of the exhaust aftertreatment system based on the ANR values and the NOx conversion fraction values for a plurality of dosing commands, wherein each dosing command corresponds with a distinct ANR value.

2. The method of claim 1, wherein the dosing command is structured to increase the dosing amount such that the determined ANR value is above an ANR stoichiometric condition value with each dosing command.

3. The method of claim 2, further comprising determining that the state of the SCR and AMOx system is degraded based on the NOx conversion fraction value decreasing and an ammonia slip amount increasing for increasing ANR values above the ANR stoichiometric condition value.

4. The method of claim 1, further comprising providing a dosing command to adjust the dosing amount such that the determined ANR value is at least one of less than and equal to an ANR stoichiometric condition value.

5. The method of claim 4, further comprising correlating the ANR values versus the NOx conversion fraction values for each ANR value, wherein the correlation includes a line of best fit for the ANR values versus the NOx conversion fraction values.

6. The method of claim 5, further comprising determining that the

commanded dosing amount is inaccurate based on the line of best fit being nonlinear for the ANR values between 0.4 and 0.9.

7. The method of claim 5, further comprising determining that the state of the SCR and AMOx system is degraded based on the NOx conversion fraction value falling below the line of best fit.

8. The method of claim 7, wherein the determination is based on the corresponding ANR value closest to the ANR stoichiometric condition value, wherein the corresponding ANR value does not exceed the ANR stoichiometric condition value.

9. The method of claim 5, wherein the determination that the state of the SCR and AMOx system is degraded is based on an ANR value between 0.85 and 1.0, wherein the corresponding NOx conversion fraction value is below the line of best fit.

10. An apparatus, comprising:

a dosing module structured to provide a dosing command to adjust a dosing amount for exhaust gas in an exhaust aftertreatment system;

a nitrous oxide (NOx) conversion fraction module structured to determine a NOx conversion fraction value;

an ammonia-to-NOx ratio (ANR) module structured to determine an ANR value based on a selective catalytic reduction (SCR) inlet NOx amount and the dosing command; and

a selective catalytic reduction (SCR) and ammonia oxidation (AMOx) module structured to determine a state of an SCR and AMOx system in the exhaust aftertreatment system based on a plurality of determined ANR values and NOx conversion fraction values.

11. The apparatus of claim 10, wherein the dosing module is structured provide the dosing command to adjust the dosing amount such that the ANR value is above an ANR stoichiometric condition value.

12. The apparatus of claim 11 , wherein the SCR and AMOx module is structured to determine that the state of the SCR and AMOx system is healthy based on at least one of (i) a line of best fit for the ANR values versus the NOx conversion fraction values being substantially horizontal for the ANR values greater than 1.4 and (ii) the line of best fit being nonlinear but increasing in NOx conversion fraction value for the ANR values between 1.0 and 1.4.

13. The apparatus of claim 10, wherein the dosing module is structured to provide the dosing command to adjust the dosing amount such that the ANR value is at least one of less than and equal to an ANR stoichiometric condition value.

14. The apparatus of claim 13, further comprising a correlation module structured to correlate the ANR values versus the NOx conversion fraction values for each ANR value, wherein the correlation includes a line of best fit for the ANR values versus the NOx conversion fraction values.

15. The apparatus of claim 14, wherein the SCR and AMOx module is structured to determine that the dosing amount is accurate based on the line of best fit being substantially linear for the ANR values between 0.4 and 0.9.

16. The apparatus of claim 14, wherein the SCR and AMOx module is structured to determine that the state of the SCR and AMOx system is degraded based on the NOx conversion fraction falling below the line of best fit.

17. A system, comprising :

an engine;

an exhaust aftertreatment system in exhaust gas-receiving communication with the engine, the exhaust aftertreatment system including an in-use selective catalytic reduction (SCR) and an ammonia oxidation (AMOx) system having at least one of a SCR catalyst and an AMOx catalyst; and

a controller communicably coupled to the exhaust aftertreatment system, the controller structured to:

provide a dosing command to a delivery mechanism to adjust a dosing amount for the exhaust aftertreatment system;

determine an ammonia-to-Nitrous Oxide (NOx) ratio (ANR) value based on SCR inlet NOx data and the dosing command; determine a NOx conversion fraction value based on the SCR inlet NOx data and AMOx outlet NOx data; and

determine a state of the in-use SCR and AMOx system of the exhaust aftertreatment system based on ANR values and NOx conversion fraction values for a plurality of dosing commands, wherein each dosing command corresponds with a distinct ANR value.

18. The system of claim 17, further comprising a NOx sensor, wherein the controller is communicably coupled to and structured to receive SCR inlet NOx data and AMOx outlet NOx data from the NOx sensor.

19. The system of claim 17, wherein the controller is further structured to determine that the state of the SCR and AMOx system is degraded based on the NOx conversion fraction values decreasing and an ammonia slip amount increasing for increasing ANR values above an ANR stoichiometric condition value.

20. The system of claim 17, wherein the controller is further structured to determine that the state of the SCR and AMOx system is degraded based on the NOx conversion fraction values falling below a line of best fit for the ANR values versus the NOx conversion fraction values for the ANR values at or below an ANR stoichiometric condition value.