Patent Description:
SCR catalysts may employ reductants for reducing NOx molecules to elemental nitrogen. One reductant is urea, which may be transformed into ammonia (NH3) in an exhaust aftertreatment system. The reductant may be injected into the exhaust gas feedstream upstream of one or multiple SCR catalysts and may be stored on a surface or otherwise captured for use in reducing NOx molecules to elemental nitrogen and water. Performance of known SCR catalysts is dependent upon temperature, with increased performance being related to increased exhaust gas temperatures.

There is a need to provide a hardware architecture implementation for an exhaust aftertreatment system and associated method to monitor performance of elements of the exhaust aftertreatment system, including the DOC, to improve heavy-duty diesel NOx emissions.

Related technologies are disclosed in <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>.

<CIT> discloses a method involves injecting fuel into an exhaust gas flow, which flows upstream of an oxidation catalyst by an exhaust-gas treatment system. Oxygen levels in the exhaust gas flow upstream and downstream of the catalyst are measured. Difference between the upstream oxygen level and the downstream oxygen level is calculated. Improper operation of the catalyst is determined when the computed difference between the upstream oxygen level and the downstream oxygen level is smaller than predefined limit oxygen level. The predefined limit oxygen level ranges from <NUM> to <NUM>%.

<CIT> discloses a method for determining the NO2 concentration behind a catalytic exhaust gas aftertreatment device in an exhaust gas aftertreatment system of an internal combustion engine by means of an NO2 formation model, which takes into account operating parameters of the exhaust gas aftertreatment system and an aging parameter of the catalytic exhaust gas aftertreatment device, the HC / CO conversion behavior of the catalytic to determine the aging parameter.

<CIT> discloses diesel exhaust treatment articles, systems and methods. An oxygen storage component is utilized and degradation of the oxygen storage component is correlated with degradation of the hydrocarbon conversion efficiency of a catalyst in a diesel engine system.

<CIT> discloses a method of determining aging of a diesel oxidation catalyst (DOC) in an engine exhaust system includes receiving a first sensor signal from a first nitrogen oxides (NOx) sensor positioned in exhaust flow upstream of the DOC. The first sensor signal is indicative of an amount of NOx in the exhaust flow upstream of the DOC. The method further includes receiving a second sensor signal from a second NOx sensor positioned in the exhaust flow downstream of the DOC. The second sensor signal is indicative of an amount of NOx downstream of the DOC. A difference between the first sensor signal and the second sensor signal is calculated by a controller. A DOC aging level based on a predetermined correlation between the difference and DOC aging can then be determined by the controller if at least one predetermined operating condition is satisfied.

<CIT> discloses a method for monitoring an oxidation catalysis device or DOC arranged in an exhaust line of an internal combustion engine of a vehicle, in a predetermined range of inlet and outlet temperatures of the DOC, includes injecting predetermined successive quantities of fuel in stages into the inlet of the DOC, recording the outlet temperature of the DOC after each injected quantity of fuel, recording the total quantity injected for a given stage, for which the outlet temperature of the DOC begins to decrease, determining a characterization of the DOC monitored, then comparing this characterization with a test characterization of a similar DOC which has been established beforehand in order to determine a threshold degradation of the DOC monitored that is not to be exceeded.

An exhaust aftertreatment system and associated method for purifying an exhaust gas feedstream of a lean-burn or other compression-ignition internal combustion engine is described. The system and method for purifying the exhaust gas feedstream includes an oxidation catalyst arranged upstream of a selective catalytic reduction (SCR) catalyst. Elements of the aftertreatment system include a first oxygen sensor arranged to monitor an exhaust gas feedstream upstream of the oxidation catalyst, a second oxygen sensor arranged to monitor the exhaust gas feedstream downstream of the oxidation catalyst, and a downstream NOx sensor arranged to monitor an exhaust gas feedstream downstream of the oxidation catalyst.

A controller is in communication with the first and second wide-band oxygen sensors, and the downstream NOx sensor. The controller includes an instruction set that is executable to determine an engine-out NO2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst, and determine, via the first oxygen sensor, a first parameter associated with O2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst. A consumption of oxygen in the oxidation catalyst due to oxidation reactions is determined via the first oxygen sensor and the second oxygen sensor, and a first concentration of NO2 generated by the oxidation catalyst is determined based upon the consumption of oxygen in the oxidation catalyst. A second concentration of NO2 downstream of the oxidation catalyst is determined based upon the engine-out NO2 concentration and the first concentration of NO2 that is generated by the oxidation catalyst. A NO2/NOx ratio in the exhaust gas feedstream downstream of the oxidation catalyst is determined based upon the second concentration of NO2 downstream of the oxidation catalyst and the NOx concentration measured by the downstream NOx sensor. The oxidation catalyst is evaluated by the controller based upon the NO2/NOx ratio.

An aspect of the disclosure includes the first concentration of NO2 generated by the oxidation catalyst being based upon a consumption of oxygen by HC oxidation and by CO oxidation in the oxidation catalyst.

Another aspect of the disclosure includes determining, via the first oxygen sensor and the second oxygen sensor, the consumption of oxygen in the oxidation catalyst due to HC oxidation and by CO oxidation in the oxidation catalyst.

Another aspect of the disclosure includes determining, via the first oxygen sensor and the second oxygen sensor, a consumption of oxygen in a first selective catalytic reduction (SCR) catalyst due to NOx reduction that is arranged upstream of the oxidation catalyst.

Another aspect of the disclosure includes determining, via the first oxygen sensor and the second oxygen sensor, a consumption of oxygen in the oxidation catalyst due to HC oxidation and CO oxidation in the oxidation catalyst and a consumption of oxygen in the first SCR catalyst due to the NOx reduction in the SCR catalyst.

Another aspect of the disclosure includes a first NOx sensor being arranged to monitor the exhaust gas feedstream upstream of the oxidation catalyst, and the engine-out NO2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst being determined based upon an input from the first NOx sensor.

Another aspect of the disclosure includes an executable model being employed to determine the engine-out NO2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst based upon operation of the internal combustion engine.

Another aspect of the disclosure includes a fault associated with the oxidation catalyst being detected when the NO2/NOx ratio downstream of the oxidation catalyst is greater than a maximum threshold, or when the NO2/NOx ratio downstream of the oxidation catalyst is less than a minimum threshold.

Another aspect of the disclosure includes the first and second oxygen sensors being wide-band oxygen sensors.

Another aspect of the disclosure includes a second selective catalytic reduction (SCR) catalyst arranged downstream of the oxidation catalyst, wherein the downstream NOx sensor is arranged to monitor an exhaust gas feedstream downstream of the second SCR catalyst.

Another aspect of the disclosure includes a method for monitoring an oxidation catalyst for a lean-burn internal combustion engine that includes determining an engine-out NO2 concentration in an exhaust gas feedstream upstream of the oxidation catalyst, and determining, via a first oxygen sensor, a first O2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst. A consumption of oxygen in the oxidation catalyst due to oxidation reactions is determined via the first oxygen sensor and a second oxygen sensor. A first concentration of NO2 generated by the oxidation catalyst is determined based upon the consumption of oxygen in the oxidation catalyst, and a second concentration of NO2 downstream of the oxidation catalyst is determined based upon the engine-out NO2 concentration and the first concentration of NO2 that is generated by the oxidation catalyst. A NO2/NOx ratio in the exhaust gas feedstream downstream of the oxidation catalyst is determined based upon the second concentration of NO2 downstream of the oxidation catalyst and the NOx concentration measured by a downstream NOx sensor. The oxidation catalyst is evaluated based upon the NO2/NOx ratio downstream of the oxidation catalyst.

Another aspect of the disclosure includes a method for monitoring an oxidation catalyst for a lean-burn internal combustion engine that includes determining a consumption of oxygen in the oxidation catalyst due to oxidation reactions, determining a first concentration of NO2 that is generated by the oxidation catalyst based upon the consumption of oxygen in the oxidation catalyst, and determining a second concentration of NO2 downstream of the oxidation catalyst based upon an engine-out NO2 concentration and the first concentration of NO2 that is generated by the oxidation catalyst. A NO2/NOx ratio downstream of the oxidation catalyst is determined based upon the second concentration of NO2 downstream of the oxidation catalyst and a NOx concentration measured by a downstream NOx sensor.

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:.

The appended drawings are not necessarily to scale, and may present a somewhat simplified representation of various preferred features of the present disclosure as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes. Details associated with such features will be determined in part by the particular intended application and use environment.

The components of the disclosed embodiments, as described and illustrated herein, may be arranged and designed in a variety of different configurations. Thus, the following detailed description is not intended to limit the scope of the disclosure, as claimed, but is merely representative of possible embodiments thereof. In addition, while numerous specific details are set forth in the following description to provide a thorough understanding of the embodiments disclosed herein, some embodiments can be practiced without some of these details. Moreover, for the purpose of clarity, certain technical material that is understood in the related art has not been described in detail to avoid unnecessarily obscuring the disclosure. Furthermore, the disclosure, as illustrated and described herein, may be practiced in the absence of an element that is not specifically disclosed herein.

Furthermore, there is no intention to be bound by any expressed or implied theory presented herein. Throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the terms "system" and "subsystem" may refer to one of or a combination of mechanical and electrical devices, actuators, sensors, controllers, application-specific integrated circuits (ASIC), combinatorial logic circuits, software, firmware, and/or other components that are arranged to provide the described functionality. As employed herein, the term "upstream" and related terms refer to elements that are towards an origination of a flow stream relative to an indicated location, and the term "downstream" and related terms refer to elements that are away from an origination of a flow stream relative to an indicated location. The term 'model' refers to a processor-based or processor-executable code and associated calibration that simulates a physical existence of a device or a physical process. The use of ordinals such as first, second and third does not necessarily imply a ranked sense of order, but rather may only distinguish between multiple instances of an act or structure.

Referring to the drawings, wherein like reference numerals correspond to like or similar components throughout the several Figures, <FIG>, consistent with embodiments disclosed herein, schematically illustrates elements of an embodiment of an exhaust aftertreatment system <NUM> for purifying the exhaust gas feedstream <NUM> of an internal combustion engine <NUM>, wherein the internal combustion engine <NUM> is controlled to operate primarily in a lean-burn air/fuel ratio combustion environment. The exhaust aftertreatment system <NUM> is configured to purify the exhaust gas feedstream <NUM> to achieve target tailpipe emissions in-use.

One example of the internal combustion engine <NUM> is a multi-cylinder compression-ignition internal combustion engine that is classified as a heavy-duty (HD) engine. In one embodiment, the internal combustion engine <NUM> is disposed on a vehicle. The vehicle may include, but not be limited to a mobile platform in the form of a heavy-duty commercial vehicle, an industrial vehicle, an agricultural vehicle, a watercraft, or a train. Alternatively, the internal combustion engine <NUM> may be arranged as a stationary device, such as for powering an electric power generator.

The exhaust gas feedstream <NUM> generated by the internal combustion engine <NUM> may contain various byproducts of combustion, including unburned hydrocarbons, carbon monoxide, nitrides of oxide (NOx), particulate matter, etc. The exhaust gas feedstream <NUM> is monitored by a first oxygen sensor <NUM>, and in some embodiments, a second engine-out exhaust gas sensor that is referred to hereinafter as a first NOx sensor <NUM>. In one embodiment, the first oxygen sensor <NUM> is a wide-band oxygen sensor that is capable of monitoring the exhaust gas feedstream <NUM> over a range of air/fuel ratios from less than <NUM>:<NUM> to greater than <NUM>:<NUM>. The first NOx sensor <NUM> is an engine-out exhaust gas sensor that is capable of monitoring NOx constituents in the exhaust gas feedstream <NUM> for purposes of monitoring and/or controlling operation of the engine <NUM> and monitoring one or more elements of the exhaust aftertreatment system <NUM>. In one embodiment, the first NOx sensor <NUM> may be supplemented by or supplanted with a controller-executed algorithmic model that is capable of estimating NOx constituents in the exhaust gas feedstream <NUM> based upon engine operating parameters. In addition, there may be one or more other engine-out exhaust gas sensors (not shown) that are capable of monitoring one or multiple constituents of the exhaust gas feedstream <NUM>, including, e.g., another NOx sensor, a temperature sensor, etc..

Engine control includes controlling various engine operating parameters, including controlling engine control states to minimize various exhaust gas constituents through chemical reaction processes that include, by way of non-limiting examples, oxidation, reduction, filtering, and selective reduction. Other engine control states include controlling operating parameters to warm up the engine <NUM> and control heat transfer to various elements of the exhaust aftertreatment system <NUM> to effect efficacious operation thereof. Heat transfer to the elements of the exhaust aftertreatment system <NUM> may be employed for warmup and catalyst light-off, regeneration of a particulate filter, etc..

The exhaust aftertreatment system <NUM> includes, in one embodiment, a first selective catalytic reduction (SCR) catalyst <NUM> that is arranged upstream of an exhaust subsystem <NUM>. In some embodiments, the exhaust aftertreatment system <NUM> includes only the exhaust subsystem <NUM>.

When the exhaust aftertreatment system <NUM> includes only the exhaust subsystem <NUM>, it is configured to purify the exhaust gas feedstream <NUM> of the internal combustion engine <NUM> to achieve a first tailpipe emissions target in-use. When the exhaust aftertreatment system <NUM> includes the first SCR catalyst <NUM> upstream of the exhaust subsystem <NUM>, it is configured to purify the exhaust gas feedstream <NUM> to achieve a second tailpipe emissions target in-use, wherein the second tailpipe emissions target is less than the first tailpipe emissions target that is achievable with the exhaust subsystem <NUM> alone. The tailpipe emissions targets may be in the form of regulatory emissions targets that are imposed by the US Environmental Protection Agency, the California Air Resources Board, the European Union, or other regulatory bodies. The tailpipe emissions targets may instead be in the form of in-house or user emissions targets, such as may be imposed by a private fleet owner.

The first SCR catalyst <NUM> may be placed in an engine compartment in an underhood location, and thus may be closely coupled to the engine <NUM>. The first SCR catalyst <NUM> may be fluidly coupled to an exhaust manifold <NUM> of the engine <NUM>, or to a fluid outlet of a turbocharger or supercharger of the engine <NUM>. Alternatively, the first SCR catalyst <NUM> may be located underbody.

A first reductant delivery system <NUM> is arranged to inject a reductant into the exhaust gas feedstream upstream of the first SCR catalyst <NUM>. Operation of the first reductant delivery system <NUM> may be controlled by a first controller <NUM>. The first reductant delivery system <NUM> includes, in one embodiment, a single reductant injector <NUM> having an injection nozzle that is positioned to inject reductant into the exhaust gas feedstream upstream of the first SCR catalyst <NUM>. The first reductant delivery system <NUM> is configured to controllably supply a metered flow of reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM> to facilitate NOx reduction therethrough. The first controller <NUM> is operatively connected to the first reductant delivery system <NUM> and in communication with the first NOx sensor <NUM> and the first temperature sensor <NUM>. The first controller <NUM> includes a first instruction set <NUM> that is executable to control the first reductant delivery system <NUM> to inject reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM> based upon inputs from the first NOx sensor <NUM>, and a second, downstream NOx sensor <NUM> that is arranged to monitor the exhaust gas feedstream at the tailpipe downstream of the exhaust subsystem <NUM>, and other sensors.

In one embodiment, a first heating device <NUM> is arranged to transfer heat to the exhaust gas feedstream upstream of the first SCR catalyst <NUM>. In one embodiment, the first heating device <NUM> is a controllable heating element that is arranged in the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM>. The first heating device <NUM> may be an electrically-powered resistive heater or heating element, a burner, or another heater, to inject heat energy into the exhaust gas flow and the injected reductant. In one embodiment, a first temperature sensor <NUM> is arranged to monitor temperature of the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM>. In one embodiment, an additional exhaust gas sensor <NUM> is arranged to monitor the exhaust gas feedstream <NUM> downstream of the first SCR catalyst <NUM>. In one embodiment, the additional exhaust gas sensor <NUM> monitors constituents in the exhaust gas feedstream <NUM> for purposes of monitoring and/or controlling operation of the engine <NUM> and/or the first reductant delivery system <NUM>. The additional exhaust gas sensor <NUM> may be configured to monitor one or constituents of the exhaust gas feedstream <NUM>, including, e.g., a NOx sensor, etc. In one embodiment, a second oxidation catalyst (not shown) is arranged upstream of the first SCR catalyst <NUM>. The first controller <NUM> interfaces and communicates with other controllers e.g., second controller <NUM> and an engine controller, via a communication bus <NUM>.

The term "controller" and related terms such as microcontroller, control, control unit, processor, etc. refer to one or various combinations of Application Specific Integrated Circuit(s) (ASIC), Field-Programmable Gate Array(s) (FPGA), electronic circuit(s), central processing unit(s), e.g., microprocessor(s) and associated non-transitory memory component(s) in the form of memory and storage devices (read only, programmable read only, random access, hard drive, etc.). The non-transitory memory component is capable of storing machine readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuit(s), input/output circuit(s) and devices, signal conditioning, buffer circuitry and other components, which can be accessed by and executed by one or more processors to provide a described functionality. Input/output circuit(s) and devices include analog/digital converters and related devices that monitor inputs from sensors, with such inputs monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms mean controller-executable instruction sets including calibrations and look-up tables. Each controller executes control routine(s) to provide desired functions. Routines may be executed at regular intervals, for example every <NUM> microseconds during ongoing operation. Alternatively, routines may be executed in response to occurrence of a triggering event. Communication between controllers, actuators and/or sensors may be accomplished using a direct wired point-to-point link, a networked communication bus link, e.g., communication bus <NUM>, a wireless link, or another communication link. Communication includes exchanging data signals, including, for example, electrical signals via a conductive medium; electromagnetic signals via air; optical signals via optical waveguides; etc. The data signals may include discrete, analog and/or digitized analog signals representing inputs from sensors, actuator commands, and communication between controllers.

In one embodiment, the first SCR catalyst <NUM> is a catalytic element that employs a reductant to reduce NOx molecules to form elemental nitrogen (N2) and other inert gases. In one embodiment, the reductant is urea, which can be converted to ammonia (NH3) that is stored on the substrate of the first SCR catalyst <NUM>. Alternatively, the reductant may be gaseous ammonia. The first SCR catalyst <NUM> includes a ceramic or metallic substrate having flow channels that have been coated with suitable materials that include by way of non-limiting examples: metals, such as vanadium, copper, cerium, and/or other materials. The coated materials effect chemical reactions to reduce, in the presence of ammonia, NOx molecules in the exhaust gas feedstream to form elemental nitrogen (N2) and other inert gases, under certain conditions of the exhaust gas feedstream related to temperature, flowrate, air/fuel ratio and others.

The exhaust subsystem <NUM> includes a plurality of fluidly connected exhaust purifying elements for purifying engine exhaust gas prior to expulsion out the tailpipe to ambient air. An exhaust purifying element is a device that is configured to oxidize, reduce, filter and/or otherwise treat constituents of the exhaust gas feedstream <NUM>, including but not limited to hydrocarbons, carbon monoxide, nitrides of oxygen (NOx), particulate matter, and ammonia. In the non-limiting embodiment shown, first, second, third, and fourth exhaust purifying elements <NUM>, <NUM>, <NUM>, and <NUM>, respectively, are arranged in series.

The first exhaust purifying element <NUM> is an oxidation catalyst for oxidizing NO and other constituents in the exhaust gas feedstream <NUM>, in certain embodiments, and is referred to hereafter as an oxidation catalyst <NUM>.

The second exhaust purifying element <NUM> is a particulate filter for filtering particulate matter from the exhaust gas feedstream, in one embodiment.

The third exhaust purifying element <NUM> is a selective catalyst reduction (SCR) catalyst, i.e., a second SCR catalyst <NUM> in one embodiment. In one embodiment, the second SCR catalyst <NUM> is a urea-based device that employs gaseous ammonia to react with and reduce NOx molecules to form elemental nitrogen (N2) and other inert gases. The injected reductant may be urea, which can be converted to ammonia (NH3), and stored on the substrate of the second SCR catalyst <NUM> to react with and reduce NOx molecules. A second reductant delivery system <NUM> is arranged to inject reductant into the exhaust gas feedstream <NUM>' upstream of the second SCR catalyst <NUM>.

In one embodiment, a second heating element <NUM> may be interposed in the exhaust gas feedstream downstream of the second exhaust purifying element <NUM> and upstream of the third exhaust purifying element <NUM>, and may be, in one embodiment, an electrically-powered resistive heater or heating element, a burner, or another heater, to inject heat energy into the exhaust gas flow and the injected reductant.

The fourth exhaust purifying element <NUM> may be an ammonia oxidation catalyst that is arranged downstream of the second SCR catalyst <NUM> and operates to oxidize unused ammonia from the second SCR catalyst <NUM> to eliminate or minimize ammonia slip in one embodiment.

The second reductant delivery system <NUM> includes, in one embodiment, a second reductant injector <NUM> having an injection nozzle that is positioned to inject reductant into the exhaust gas feedstream downstream of the second exhaust purifying element <NUM>, i.e., the particulate filter, and upstream of the second SCR catalyst <NUM>. The second reductant delivery system <NUM> is configured to controllably supply a metered flow of reductant into the exhaust gas feedstream <NUM>' upstream of the second SCR catalyst <NUM> to facilitate NOx reduction through the second SCR catalyst <NUM>.

Operation of the second reductant delivery system <NUM> may be controlled by a second controller <NUM>. The second reductant delivery system <NUM> is configured to controllably supply a metered flow of reductant into the exhaust gas feedstream upstream of the second SCR catalyst <NUM> to facilitate NOx reduction therethrough. The second controller <NUM> is operatively connected to the second reductant delivery system <NUM> and in communication with the second NOx sensor <NUM>, a second temperature sensor <NUM>, and a third temperature sensor <NUM>. The second controller <NUM> includes a second instruction set <NUM> that is executable to control the second reductant delivery system <NUM> to inject reductant into the exhaust gas feedstream <NUM>' upstream of the second SCR catalyst <NUM> based upon inputs from the various sensors.

Each of the first, second, third, and fourth exhaust purifying elements <NUM>, <NUM>, <NUM>, and <NUM>, respectively, includes a ceramic or metallic substrate having flow channels that have been coated with suitable materials that include by way of non-limiting examples: platinum-group metals such as platinum, palladium and/or rhodium; other metals, such as vanadium, copper, cerium, and/or other materials. The coated materials effect chemical reactions to oxidize, reduce, filter, or otherwise treat constituents of the exhaust gas feedstream under certain conditions related to temperature, flowrate, air/fuel ratio and others. The embodiment shown includes the elements of the exhaust aftertreatment system <NUM> in one arrangement, which is illustrative. Other arrangements of the elements of the exhaust aftertreatment system <NUM> may be employed within the scope of this disclosure, with such arrangements including the addition of other exhaust purifying elements and/or omission of one or more of the exhaust purifying elements, depending upon requirements of the specific application.

The sensors for monitoring the various exhaust purifying elements of the exhaust subsystem <NUM> include a second oxygen sensor <NUM> that is arranged in the exhaust gas feedstream downstream of the oxidation catalyst <NUM>, the second (downstream) NOx sensor <NUM>, and, in one embodiment, temperature sensors <NUM>, <NUM>. Other sensors (not shown) may include, for example, a particulate matter sensor, a delta pressure sensor for monitoring pressure drop across the SCR catalyst <NUM>, additional temperature sensors, and/or other sensing devices and models for monitoring the exhaust gas feedstream. The second NOx sensor <NUM> may have wide-band air/fuel ratio sensing capability. Such sensors and models may be arranged to monitor or otherwise determine parameters relegated to the exhaust gas feedstream at specific locations. As such, the aforementioned sensors and/or models may be advantageously employed to monitor performance of individual ones of the exhaust purifying elements, monitor parameters associated with performance of a subset of the exhaust purifying elements, or monitor parameters associated with performance of the exhaust aftertreatment system <NUM>.

The first controller <NUM> includes the first instruction set <NUM> that is executable to control the first reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM>, on systems that employ the first reductant delivery system <NUM>. This includes the first instruction set <NUM> being executed to control the first reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM> to achieve a target reductant/NOx ratio that is input to the first SCR catalyst <NUM> to achieve a first target NOx reduction level, on systems that employ the first reductant delivery system <NUM>. Alternatively, or in addition, the first controller <NUM> controls, via the first instruction set <NUM>, the first reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM> upstream of the first SCR catalyst <NUM> to achieve a target ammonia storage level on the first SCR catalyst <NUM> in anticipation of a projected need for NOx reduction, and as part of controlling the exhaust gas feedstream that is input to the exhaust aftertreatment system <NUM>.

The second controller <NUM> includes the second instruction set <NUM> that is executable to control the second reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM>' upstream of the second SCR catalyst <NUM>, on systems that employ the second reductant delivery system <NUM>. The second instruction set <NUM> is executed to control the second reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM>' upstream of the second SCR catalyst <NUM> to achieve a target reductant/NOx ratio that is input to the second SCR catalyst <NUM> to achieve a second target NOx reduction level. Alternatively, or in addition, the second controller <NUM> controls, via the second instruction set <NUM>, the second reductant delivery system <NUM> to inject the reductant into the exhaust gas feedstream <NUM>' upstream of the second SCR catalyst <NUM> to achieve a target ammonia storage level on the second SCR catalyst <NUM> in anticipation of a projected need for NOx reduction, and as part of controlling the exhaust gas feedstream that is input to the exhaust aftertreatment system <NUM>.

Referring now to <FIG> with continued reference to an embodiment of the exhaust aftertreatment system <NUM> that is described with reference to <FIG>, a method, routine, and/or monitoring algorithm <NUM> are described for monitoring the oxidation catalyst <NUM> employing information that is provided by the first oxygen sensor <NUM> arranged upstream of the oxidation catalyst <NUM>, and the second oxygen sensor <NUM> arranged downstream of the oxidation catalyst <NUM>. Information from the first and second oxygen sensors is employed by the monitoring algorithm <NUM> to evaluate the capability of the oxidation catalyst <NUM> to oxidize NO to form NO2.

The oxidation catalyst <NUM> oxidizes NO in the exhaust gas feedstream to form NO2, thus increasing an NO2/NOx ratio when compared to the engine-out NO2/NOx ratio. The increased NO2/NOx ratio improves SCR conversion efficiency in a downstream SCR catalyst in the presence of a reductant, up to an optimum point. However, when the NO2/NOx ratio is greater than the optimum point, there is a negative effect on NOx conversion efficiency in the downstream SCR catalyst. Evaluating the capability of the oxidation catalyst <NUM> to oxidize NO facilitates determining the capability of the exhaust aftertreatment system <NUM> to convert NOx emissions to N2 and oxygen, including implementation of an oxidation catalyst efficiency diagnostic.

Referring again to <FIG>, the monitoring algorithm <NUM> is illustrated as a collection of blocks in a logical flow graph, which represents a sequence of operations that can be implemented in hardware, software, and/or firmware components that have been configured to perform the specified functions. In the context of software, the blocks represent computer instructions that, when executed by one or more processors, perform the recited operations. Furthermore, although the various steps shown in the flowchart diagram appear to occur in a chronological sequence, at least some of the steps may occur in a different order, and some steps may be performed concurrently or not at all. For convenience and clarity of illustration, the monitoring algorithm <NUM> is described with reference to the internal combustion engine <NUM> and exhaust aftertreatment system <NUM> shown in <FIG>.

Execution of the monitoring algorithm <NUM> may proceed as follows. As employed herein, the term "<NUM>" indicates an answer in the affirmative, or "YES", and the term "<NUM>" indicates an answer in the negative, or "NO".

The initial step of the monitoring algorithm <NUM> is to determine whether entry criteria to enable further execution of the monitoring algorithm <NUM> are met (Step <NUM>). The entry criteria include, by way of non-limiting examples, determining that the internal combustion engine <NUM> is in a warmed-up state and is operating at or near a steady-state speed/load operating condition, determining that the airflow, and thus engine load, is greater than a minimum threshold, and determining that the first reductant delivery system <NUM> of the first SCR catalyst <NUM> is deactivated, i.e., determining that the first SCR catalyst <NUM> is not being used to actively reducing NOx emissions.

Inputs from the first oxygen sensor <NUM>, the first NOx sensor <NUM> (when used), the second oxygen sensor <NUM>, and the second NOx sensor <NUM> are monitored to determine an engine-out NO2 concentration, an engine-out O2 concentration, a downstream NOx concentration, and a downstream O2 concentration (Step <NUM>).

The measurements from the first oxygen sensor <NUM> and the second oxygen sensor <NUM> are used to determine conversion of NO to NO2 in the oxidation catalyst <NUM> with the arrangement as shown in the exhaust aftertreatment system <NUM> described with reference to <FIG>. This technique is based on the following chemical reaction equations.

Oxidation of NO to NO2, which can be completed in the oxidation catalyst at the warmed-up operating temperature is expressed as follows.

The NOx reduction reaction, as completed in the SCR catalyst, is expressed as follows.

4NO + 4NH<NUM> + O<NUM> => 4N<NUM> + <NUM><NUM>O     [<NUM>].

The fast NOx reduction reaction, as completed in the SCR catalyst, is expressed as follows.

NO + NO<NUM> + 2NH<NUM> => 2N<NUM> + <NUM><NUM>O     [<NUM>].

The NOx reduction reaction, completed in the SCR catalyst, is expressed as follows.

6NO<NUM> + 8NH<NUM> => 2N<NUM> + <NUM><NUM>O     [<NUM>].

The oxidation of CO to CO2, completed in the oxidation catalyst at operating temperature, is expressed as follows.

The oxidation of HC completed in the oxidation catalyst at operating temperature; where a and b are # of atoms (H and C respectively), is expressed as follows.

CbHa + (b+a/<NUM>)O<NUM> = bCO<NUM> + a/<NUM><NUM>O     [<NUM>].

To determine the amount of NO oxidized by the oxidation catalyst <NUM>, the engine-out concentrations for NO2, HC and CO can be measured via the aforementioned sensors and/or modeled based upon engine operating parameters.

All engine-out NO2 is consumed by the first SCR catalyst <NUM> during NOx reduction.

The O2 consumption for oxidation of CO, HC and reduction of NOx in the first SCR catalyst <NUM> is performed by monitoring the O<NUM> concentrations in the exhaust gas both prior to the first SCR catalyst <NUM> and after the oxidation catalyst <NUM>. With the NO2 production measured (or modeled) and a delta in NOx concentration in the exhaust over the first SCR catalyst <NUM>, the O2 consumption can be determined as follows:.

Calculating the engine-out NO concentration (eoNO) is determined as follows:.

Calculating the NO concentration consumed by a fast NOx reaction (EQ. <NUM>) is determined as follows:.

Subtracting the unreduced NOx yields as follows:.

wherein:
NOxS2 is the NOx concentration from the second NOx sensor <NUM>.

The O2 consumption in the first SCR catalyst <NUM> due to NOx reduction is determined as follows (Step <NUM>):.

O2NOx = eoO2s1 - (NOreduced/<NUM>)     [<NUM>].

The O2 consumption in the oxidation catalyst <NUM> caused by oxidation reactions including HC and CO oxidation is determined as follows (Step <NUM>) using the following relationship:.

O2HC&CO = O2S1 - O2S2 - O2NOx     [<NUM>].

With O<NUM> consumption known for HC and CO oxidation, then the first SCR catalyst <NUM> does not reduce NOx and instead allows NOx to pass through to the oxidation catalyst <NUM>. Monitoring the change in O2 concentrations will allow for the NO2 make-up of the oxidation catalyst <NUM> to be determined.

The NO2 concentration generated by the oxidation catalyst <NUM> is determined based upon the O2 consumption in the oxidation catalyst <NUM>, as follows (Step <NUM>):.

NO2DOC = (O2S1 - O2S2 - O2HC&CO)*<NUM>     [<NUM>].

The second NO2 concentration downstream of the oxidation catalyst <NUM> is determined based upon the engine-out NO2 concentration and the first NO2 concentration generated by the oxidation catalyst <NUM> (Step <NUM>), as follows. The total NO2 levels in the exhaust gas can be determined by the relation:.

NO<NUM> = eoNO<NUM> + NO2DOC     [<NUM>].

A NO2/NOx ratio downstream of the oxidation catalyst <NUM> is determined based upon the second NO2 concentration downstream of the oxidation catalyst <NUM>, the engine-out NO2 concentration and the downstream NOx concentration (step <NUM>). The NO2/NOx ratio into the underbody SCR catalyst <NUM> can be determined as follows:.

The NO2/NOx ratio downstream of the oxidation catalyst <NUM> is evaluated to determine whether it is within an allowable range (Step <NUM>). The allowable range for the NO2/NOx ratio is an application-specific calibrated value, and may be determined and clarified during engine system development at another time.

When the NO2/NOx ratio downstream of the oxidation catalyst <NUM> is within the allowable range (Step <NUM>)(<NUM>), no fault is indicated (Step <NUM>), and a report is generated that is communicated to another on-board or off-board controller indicating that the oxidation catalyst <NUM> is operating in compliance with its specification.

When the NO2/NOx ratio downstream of the oxidation catalyst <NUM> is greater than a maximum threshold of the allowable range, or less than a minimum threshold of the allowable range (Step <NUM>)(<NUM>), a fault is indicated, and a report is generated that is communicated to another on-board or off-board controller indicating a potential fault with the oxidation catalyst <NUM> that may require further action (Step <NUM>).

When the NO2 production of the oxidation catalyst <NUM> is greater than the upper threshold, or less than the lower threshold (Step <NUM>), it indicates a potential occurrence of a fault associated with the oxidation catalyst <NUM>. Various operating conditions related to the internal combustion engine <NUM> and the exhaust aftertreatment system <NUM> may be captured and stored in the second controller <NUM> for further evaluation and for use in root cause analysis.

The second controller <NUM> can generate an oxidation catalyst fault report indicating either an absence of a fault in the oxidation catalyst <NUM> (No Fault), or a potential occurrence of a fault associated with the oxidation catalyst <NUM> (Fault). The oxidation catalyst fault report may be communicated to another on-board controller, and then to a vehicle operator via a dashboard indicator lamp. The oxidation catalyst fault report may be communicated to a diagnostic scan tool, such as in response to an inquiry. The oxidation catalyst fault report may be communicated, via wireless communication, to a remotely-located controller that may employ the information for purposes of vehicle and fleet management. The vehicle may be scheduled for service for purposes of further diagnostics and repair in response to the potential occurrence of a fault associated with the oxidation catalyst <NUM>. In this manner, an oxidation catalyst for an embodiment of an exhaust aftertreatment system of a lean-burn internal combustion engine may be regularly and periodically monitored employing upstream and downstream NOx sensors to detect occurrence of a fault.

Furthermore, when the NO2 production of the oxidation catalyst is above or below minimum or maximum thresholds during certain operating conditions, it may negatively affect emissions performance of the exhaust aftertreatment system <NUM>.

As used herein, the terms "system" and "subsystem" may refer to one of or a combination of mechanical and electrical devices, actuators, sensors, controllers, application-specific integrated circuits (ASIC), combinatorial logic circuits, software, firmware, and/or other components that are arranged to provide the described functionality. As employed herein, the term "upstream" and related terms refer to elements that are towards an origination of a flow stream relative to an indicated location, and the term "downstream" and related terms refer to elements that are away from an origination of a flow stream relative to an indicated location. As employed herein, the term 'model' refers to a processor-based or processor-executable code and associated calibration that simulates a physical existence of a device or a physical process. As used herein, the terms 'dynamic' and 'dynamically' describe steps or processes that are executed in real-time and are characterized by monitoring or otherwise determining states of parameters and regularly or periodically updating the states of the parameters during execution of a routine or between iterations of execution of the routine. As employed herein, the terms "calibration", "calibrated", and related terms refer to a result or a process that correlates a desired parameter and one or multiple perceived or observed parameters for a device or a system. A calibration as described herein may be reduced to a storable parametric lookup table, a plurality of executable equations or another suitable form that may be employed as part of a measurement or control routine. As employed herein, a parameter is defined as a measurable quantity that represents a physical property of a device or other element that is discernible using one or more sensors and/or a physical model. A parameter can have a discrete value, e.g., either "<NUM>" or "<NUM>", or can be infinitely variable in value. The use of ordinals such as first, second and third does not necessarily imply a ranked sense of order, but rather may only distinguish between multiple instances of an act or structure.

Claim 1:
A system for monitoring an oxidation catalyst (<NUM>) for a lean-burn internal combustion engine (<NUM>), the system comprising:
a first oxygen sensor (<NUM>) arranged to monitor an exhaust gas feedstream upstream of the oxidation catalyst;
a second oxygen sensor (<NUM>) arranged to monitor the exhaust gas feedstream downstream of the oxidation catalyst;
a downstream NOx sensor (<NUM>) arranged to monitor an exhaust gas feedstream downstream of the oxidation catalyst; and
a controller (<NUM>, <NUM>), in communication with the first and second oxygen sensors, and the downstream NOx sensor;
the controller including an instruction set (<NUM>, <NUM>), wherein the instruction set is executable to:
determine, via the first oxygen sensor, a first parameter associated with O2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst; and
determine, via the first oxygen sensor and the second oxygen sensor, a
consumption of oxygen in the oxidation catalyst due to oxidation reactions; characterized in that the instruction set is further executable to:
determine an engine-out NO2 concentration in the exhaust gas feedstream upstream of the oxidation catalyst;
determine a first concentration of NO2 generated by the oxidation catalyst based upon the consumption of oxygen in the oxidation catalyst;
determine a second concentration of NO2 downstream of the oxidation catalyst based upon the engine-out NO2 concentration and the first concentration of NO<NUM> that is generated by the oxidation catalyst;
determine a NO2/NOx ratio in the exhaust gas feedstream downstream of the oxidation catalyst based upon the second concentration of NO2 downstream of the oxidation catalyst and a NOx concentration measured by the downstream NOx sensor;
evaluate the NO2/NOx ratio in the exhaust gas feedstream downstream of the oxidation catalyst; and
detect a fault associated with the oxidation catalyst when the NO2/NOx ratio downstream of the oxidation catalyst is greater than a maximum threshold.