METHOD FOR DIAGNOSING AN EXHAUST GAS TREATMENT SYSTEM

Abstract

A method for diagnosing an exhaust treatment system (100), the system (100) comprising an oxidation catalyst device (OC) (10) comprising a catalytic composition (CC) and capable of receiving exhaust gas and oxidizing one or more combustible hydrocarbons (HC) and one or more nitrogen species (NOx species), a selective catalytic reduction (SCR) device (20) disposed downstream of and in fluid communication with the OC (10) and configured to store NOx species and reduce NOx species in the presence of a reductant (36), an upstream NOx sensor (60) disposed upstream of the SCR (20), and a downstream NOx sensor (62) disposed downstream of the SCR (20). the method comprising: Providing exhaust gas to the OC (10) and then to the SCR (20); Measuring an upstream exhaust NOx concentration using the upstream NOx sensor (60); Measuring a downstream exhaust NOx concentration using the downstream NOx sensor (62); Determining a NOx difference by subtracting the downstream exhaust NOx concentration from the upstream exhaust NOx concentration; and Comparing the NOx difference with a difference threshold to determine the OC performance; wherein the SCR reductant loading is below about 1% and / or the SCR (20) is below a NOx light-off temperature while exhaust gas is supplied to the OC (10); characterized in that the upstream NOx sensor (60) is provided downstream of the OC (10), and wherein a NOx difference above the difference threshold indicates a suitable OC-NOx oxidation performance; or that a NOx difference above the difference threshold indicates a suitable OC-NOx oxidation performance, and wherein the exhaust gas provided to the OC (10) comprises rich-phase exhaust gas produced by an internal combustion engine (ICE) (1); or that a NOx difference above the difference threshold indicates suitable OC-NOx oxidation performance, and wherein the exhaust gas provided to the OC (10) is produced by the internal combustion engine (1) operating at a lambda ratio of about 0.91 to about 0.98, the lambda ratio being the actual ICE air-fuel ratio divided by the stoichiometric air-fuel ratio of the ICE (1).

Description

[0001] The present invention relates to a method for diagnosing an exhaust gas treatment system according to the preamble of claim 1, as is essentially known from DE 10 2015 007 751 A1.

[0002] Regarding the further state of the art, reference is made to US 2017 / 0 051 693 A1. INTRODUCTION

[0003] During a combustion cycle of an internal combustion engine (ICE), air / fuel mixtures are provided to the ICE's cylinders. The air / fuel mixtures are compressed and / or ignited and combusted to provide output torque. After combustion, the engine's pistons force the exhaust gases in the cylinders through exhaust valve openings into an exhaust system. The exhaust gas emitted by an internal combustion engine, particularly a diesel engine, is a heterogeneous mixture containing gaseous emissions such as carbon monoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NO x ) and sulfur oxides (SO X ) as well as condensed phase materials (liquids and solids) that represent solids. Liquids can include, for example, water and hydrocarbons.

[0004] Exhaust gas treatment systems may employ catalysts in one or more components configured to perform an aftertreatment process, such as the reduction of NO x , to produce more tolerable exhaust gas components of nitrogen (N2) and water (H2O). One type of exhaust gas technology for reducing NO x -emissions is a selective catalytic reduction (SCR) device, which generally includes a substrate or support with a catalyst compound disposed thereon. By passing the exhaust gas over the catalyst, certain or all exhaust constituents are converted into desired compounds, such as unregulated exhaust components. A reductant is typically sprayed into hot exhaust gases upstream of the SCR, decomposed into ammonia, and absorbed by the SCR device. The ammonia then reduces NO xto nitrogen and water in the presence of the SCR catalyst. Another type of exhaust treatment device is an oxidation catalyst (OC) device, which is typically positioned upstream of an SCR to perform multiple catalytic functions, including oxidizing HC and CO species. Furthermore, OCs can convert NO to NO2 to change the NO as follows: NO x -ratio of the exhaust gas to reduce the NO x -reduction efficiency of the downstream SCR. In some applications (e.g., gasoline engines), a three-way catalyst can be used to combine NOx reduction functions and HC and CO oxidation functions in a single exhaust treatment device. Ensure appropriate reduction of NO x species, especially via an SCR over a wide range of operating conditions, remains a challenge. SUMMARY

[0005] According to the invention, a method for diagnosing an exhaust gas treatment system is presented, which is characterized by the features of claim 1.

[0006] Furthermore, according to the invention, a method for diagnosing an exhaust gas treatment system is presented, which is characterized by the features of claim 2.

[0007] Furthermore, the invention provides a method for diagnosing an oxidation catalyst device of a diesel internal combustion engine exhaust treatment system, which is characterized by the features of claim 3.

[0008] A method is provided for diagnosing an exhaust gas treatment system, wherein the system may include an oxidation catalyst device (OC) having a catalytic composition (CC) capable of receiving exhaust gas and oxidizing one or more combustible hydrocarbons (HC) and one or more nitrogen oxide (NOx) species, a selective catalytic reduction device (SCR) disposed downstream of and in fluid communication with the OC and configured to store NOx species and reduce NOx species in the presence of a reductant, an upstream NOx sensor disposed upstream of the SCR, and a downstream NOx sensor disposed downstream of the SCR.The method includes providing exhaust gas to the OC and then the SCR, measuring an upstream NOx concentration using the upstream NOx sensor, measuring a downstream NOx concentration of the exhaust gas using the downstream NOx sensor, determining a NOx difference by subtracting the downstream NOx concentration of the exhaust gas from the upstream NOx concentration of the exhaust gas, and comparing the NOx difference to a difference threshold to determine OC performance. A NOx difference above the difference threshold may indicate appropriate OC-NOx oxidation performance. The SCR reductant loading may be below about 1% and / or the SCR may be below a NOx light-off temperature while exhaust is supplied to the OC. The exhaust gas provided to the OC may be rich exhaust gas produced by an internal combustion engine.The upstream NOx sensor may be located upstream of the OC. The OC may be above an NH3 conversion efficiency threshold. The CC may be one or more platinum group metals. The SCR may be a selective catalytic reduction filter device. The upstream NOx sensor and the downstream NOx sensor may each be cross-sensitive to NOx and NH3.

[0009] A method for diagnosing an exhaust treatment system is also provided, wherein the system may include an oxidation catalyst device (OC) having a catalytic composition (CC) capable of receiving exhaust gas and oxidizing one or more combustible hydrocarbons (HC) and one or more nitrogen oxide (NOx) species, a selective catalytic reduction device (SCR) disposed downstream of and in fluid communication with the OC and configured to store NOx species and reduce NOx species in the presence of a reductant, an upstream NOx sensor disposed upstream of the SCR, and a downstream NOx sensor disposed downstream of the SCR.The method may include providing exhaust gas to the OC and subsequently to the SCR for a time frame, measuring an upstream NOx concentration using the upstream NOx sensor during the time frame, measuring a downstream exhaust NOx concentration using the downstream NOx sensor during the time frame, subtracting the integral of the downstream exhaust NOx concentration over the time frame from the integral of the upstream exhaust NOx concentration over the time frame to determine an amount of NH3 produced by the OC during the time frame, and comparing the amount of NH3 produced to an NH3 threshold to determine OC performance. An NH3 amount above the NH3 threshold indicates appropriate OC performance.During the timeframe, the SCR reductant loading may be sufficiently low such that no appreciable NOx reduction occurs within the SCR, and the OC may be above a NOx to NH3 conversion efficiency threshold. The system may further include a particulate filter (PF) device in fluid communication with the OC and the SCR, and the method may further include performing a high-temperature PF regeneration prior to the timeframe. The exhaust gas supplied to the OC may be produced by an internal combustion engine operating at a lambda ratio of less than or equal to 0.97, where the lambda ratio is the actual ICE air-to-fuel ratio divided by the stoichiometric ICE air-to-fuel ratio. The OC performance may be a NOx oxidation performance. The NH3 conversion efficiency threshold may be a temperature above which the conversion of NOx to NH3 is above about 90%.

[0010] A method is also provided for diagnosing an oxidation catalyst (OC) device of a diesel internal combustion engine exhaust treatment system, the system comprising a diesel internal combustion engine configured to receive an air-fuel mixture, combust the air-fuel mixture, and expel the combustion products as exhaust gas via an exhaust conduit, an oxidation catalyst (OC) device having a catalytic composition (CC) capable of receiving exhaust gas from the ICE via the exhaust conduit and oxidizing one or more combustible hydrocarbons (HC) and one or more nitrogen oxide (NOx) species within the exhaust gas, a selective catalytic reduction (SCR) device disposed downstream of and in fluid communication with the OC and configured to store NOx species and reduce NOx species in the presence of a reductant,an upstream NOx sensor located downstream of the OC and upstream of the SCR, and a downstream NOx sensor located downstream of the SCR. The method may include providing exhaust gas from the ICE in sequence to the OC and to the SCR for a time frame, wherein the OC is above a NH3 conversion efficiency threshold and the oxygen content of the exhaust gas is at least 3% lower than the oxygen content of the exhaust gas produced by the ICE operating under stoichiometric air-fuel conditions, measuring an upstream NOx concentration of the exhaust gas for the time frame using the upstream NOx sensor, measuring a downstream NOx concentration of the exhaust gas for the time frame using the downstream NOx sensor,Determining a NOx difference for the time frame by subtracting the downstream NOx exhaust concentrations from the upstream NOx concentrations of the exhaust, comparing the NOx difference to a difference threshold to determine the OC NOx reduction performance, and correlating the OC NOx reduction performance to the OC NOx oxidation performance. The difference threshold may be pre-calibrated or determined using a data map. During the time frame, the temperature of the OC may be above a NOx to NH3 conversion efficiency threshold. The SCR reductant loading may be sufficiently low such that no appreciable reduction of NOx occurs within the SCR. The CC may be one or more platinum group metals. The CC may be able to oxidize NOx while the ICE is operating under stoichiometric and / or lean conditions and may be able to reduce NOx to NH3,while the ICE is operating under rich conditions. The exhaust gas supplied to the OC may be produced by an internal combustion engine operating at a lambda ratio of about 0.91 to about 0.98, where the lambda ratio is the actual ICE air-fuel ratio divided by the ICE's stoichiometric air-fuel ratio. The ICE may power a vehicle.

[0011] Further purposes, advantages and novel features of the embodiment examples will become apparent from the following detailed description of the embodiments and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 illustrates a schematic view of an exhaust aftertreatment system according to one or more embodiments; and Fig. 2 illustrates a flowchart of a method for monitoring and / or diagnosing an exhaust treatment system according to one or more embodiments. DETAILED DESCRIPTION

[0012] In general, this disclosure relates to methods for monitoring and catalytic performance of oxidation catalyst (OC) devices that correlate the reductive activity of OCs with an oxidizing ability thereof. Over time, the catalytic activity of an OC may decrease due to catalyst poisoning and other factors. In particular, the methods monitor the ability of an OC to reduce NOx to NH3 under certain conditions and correlate the reductive activity with the ability of the OC to oxidize NOx species under various conditions. As used herein, "NO X “ to one or more nitrogen oxides. NO x -Substances can N y O x-substances, where y>0 and x>0. Non-limiting examples of nitrogen oxides may include NO, NO2, N2O, N2O2, N2O3, N2O4, and N2O5. The methods disclosed herein are particularly suitable for use with internal combustion engine (ICE) exhaust treatment systems, although other applications are also contemplated. The methods described herein relate to ICE systems, which may include, but are not limited to, diesel engine systems, gasoline direct injection systems, and homogeneous charge compression-ignition engine systems. An ICE may include a plurality of reciprocating pistons attached to a crankshaft, which may be operatively attached to a propulsion system, such as a vehicle propulsion system, to propel a vehicle (e.g., to deliver tractive torque to the propulsion system). For example, an ICE may be any engine configuration or application, including various vehicle applications (e.g.,in automobiles, watercraft, and the like), as well as various non-vehicle applications (e.g., pumps, generators, and the like). While the internal combustion engines may be described in a vehicle-related context (e.g., producing torque), this need not be the case. Therefore, when reference is made to a vehicle, this disclosure should be interpreted as applying to any application of an ICE.

[0013] Fig. 1 illustrates an exhaust treatment system 100 utilizing one or more OCs to treat and / or monitor gaseous species, such as exhaust species 8 generated by an ICE 1. The system 100 generally includes one or more exhaust conduits 9 and one or more downstream exhaust treatment devices. Upstream and downstream are defined with respect to the direction of exhaust flow 8 from the ICE 1. As used herein, a plurality of elements described as upstream and / or downstream of each other are necessarily in fluid communication with each other. The exhaust conduit 9, which may include multiple segments, conveys exhaust gas 8 from the ICE 1 to various exhaust aftertreatment devices of the exhaust aftertreatment system 100. The ICE 1 is included in the system 100 for illustrative purposes only, and the disclosure herein is not to be limited to the gaseous sources provided by ICEs.It should be further understood that the embodiments disclosed herein may be applicable to the treatment of exhaust streams including NOx, carbon monoxide (CO), HC, or other chemical species that are desirably combusted or otherwise oxidized by OCs.

[0014] ICE 1 may include one or more cylinders (not shown), each capable of housing a piston (not shown) that can reciprocate therein. Air and fuel are combusted in one or more cylinders, causing the associated pistons to reciprocate therein. The pistons may be attached to a crankshaft (not shown), which is operatively attached to a vehicle powertrain (not shown) to provide, for example, propulsive torque. Exhaust gas 8 may generally include: CO, HC, water, and nitrogen oxides (NO x). The components of the exhaust gas as used herein are not limited to gaseous species. HC refers to combustible chemical species including hydrogen and carbon, and generally includes one or more chemical species of gasoline, diesel fuel, or the like. The exhaust gas 8 is exhausted from the ICE 1 and sequentially communicated with the OC 10 and the selective catalytic reduction (SCR) device 20. A reductant injector 30 is configured to inject the reductant 36 into the exhaust conduit 9 downstream of the OC 10 and upstream of the SCR 20. The system 100 may optionally include a particulate filter (PF) device 40, located, for example, downstream of the SCR 20 as shown. The exhaust gas 8 may be exhausted from the system 100, for example, via a vehicle exhaust pipe.

[0015] The system 100 may further include a control module 50 operatively connected via a number of sensors to monitor the ICE 1 and / or the exhaust treatment system 100. As used herein, the term "module" refers to an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group processor), and memory executing one or more software or firmware programs, combinational logic circuitry, and / or other suitable components that provide the described functionality. The control module 50 may be operatively connected to the ICE 1, the OC 10, SRC 20, PF 40, and / or one or more sensors. As shown, the control module 50 is connected to an upstream NO x sensor 60, which is arranged upstream of SCR 20, and a downstream NO x-Sensor 62, which is arranged downstream of SCR 20. The upstream NOx sensor 60 and the downstream NOx sensor 62 can be in fluid communication with the exhaust line 9, for example, to take samples of exhaust gas 8. The upstream NOx sensor 60 can optionally be arranged upstream of OC. The upstream NO x Sensor 60 and the downstream NO x 62 are configured to provide a NO x-content near their position within the exhaust line 9 and to generate a NOx signal corresponding to the NOx content. A NOx content may, in some embodiments, include a concentration, a mass flow rate, or a volumetric flow rate. A NOx signal generated by a NOx sensor may, for example, be interpreted by the control module 50. A disadvantage of the NOx sensors 60 and 62 is a cross-sensitivity to NOx and NH3, wherein a sensor signal generated by a NOx species is indistinguishable from a signal generated by an NH3 species.

[0016] Generally, SCR 20 includes any device that stores a reductant 36 and utilizes a catalyst to reduce NOx species to the desired chemical species, including, for example, diatomic nitrogen, nitrogen-containing inert species, or species considered acceptable emissions. The reductant 36 may be ammonia (NH3), such as anhydrous ammonia or aqueous ammonia, or generated from a nitrogen and hydrogen-rich substance, such as urea (CO(NH2)2), which can be decomposed to NH3. Additionally or alternatively, the reductant 36 may be any composition capable of decomposing or reacting to form ammonia in the presence of exhaust gas 8 and / or heat. The reductant 36 may be diluted with water in various implementations. In implementations where the reductant 36 is diluted with water, the heat (e.g.,from the exhaust gas), the water, and ammonia is fed to the SCR 20. Non-ammonia reductants may be used as a full or partial alternative to ammonia, as desired. In implementations where the reductant 36 contains urea, the urea reacts with the exhaust gas to produce ammonia, and ammonia is fed to the SCR 20. Equation (1) below provides an exemplary chemical reaction of ammonia production by urea decomposition. CO(NH2)2+H2O→2NH3+CO2 (1)

[0017] It should be understood that equation (1) is merely illustrative and is not intended to limit the decomposition of urea or other reductant 36 to a particular single mechanism and preclude the operation of other mechanisms. Efficient decomposition of urea to NH3 typically requires temperatures above approximately 200°C, and, depending on the amount of urea injected, for example, relative to a flow rate of the exhaust gas 8, urea may crystallize at temperatures below approximately 200°C. Accordingly, reductant injection events 36 and / or dosing amounts are typically set based on, among other things, the system temperature and the exhaust gas 8 flow rate, such that the yield of urea decomposition is maximized and urea crystallization is minimized.

[0018] Equations (2) - (6) provide exemplary chemical reactions for NO x-Reduction with ammonia. 6NO+4NH3→5N2+6H2O (2) 4NO+4NH3+O2→N2+6H2O (3) 6NO2+8NH3→7N2+12H2O (4) 2NO2+4NH3+O2→3N2+6H2O (5) NO+NO2+2NH3→2N2+3H2O (6)

[0019] It is understood that equations (2) - (6) are merely illustrative and are not intended to limit the SCR 20 to a specific NO x reduction mechanism or NOx reduction mechanisms, nor to exclude the operation of other mechanisms. The SCR 20 may be configured to control one of the above-mentioned NO x -Reduction reactions, combinations of the above NO x -Reduction reactions and other NO x -reduction reactions.

[0020] As in Fig. 1, SCR 20 includes a catalytic composition (CC) 22 packaged in a shell or canister generally defining an upstream side 20' (i.e., inlet) and a downstream side 20" (i.e., outlet) and in fluid communication with exhaust conduit 9 and optionally other exhaust treatment devices (e.g., OC 10). The shell or canister may ideally be made of a material that is largely inert to the exhaust constituents, such as stainless steel. SCR 20 is configured to receive exhaust gas 8 and reductant 36 at the upstream side 20'. A reductant 36 may be supplied from a reductant supply source (not shown) and injected into exhaust conduit 9 at a location upstream of SCR 20 using an injector 30 or other suitable method of supplying the reductant.The reducing agent 36 may be in the form of a gas, a liquid, or an aqueous solution, such as an aqueous urea solution. The reducing agent 36 may be mixed with air in the injector 30 to assist in the dispersion of the injected spray. A turbulator 38 (i.e., a mixer) may also be disposed within the exhaust conduit 9 in close proximity to the injector 30 and / or the SCR 20 to further assist in the thorough mixing of the reducing agent 36 with the exhaust gas 8 and / or the uniform distribution throughout the SCR 20 and in particular throughout the CC 22. The turbulator 38 may consist of a fixed or movable housing configured to mix, vaporize, and / or otherwise communicate with the reducing agent 36 within the conduit 9. For example, the turbulator 38 may comprise a rotating body having one or a plurality of guide vanes.The turbulator 38 may be made of metal or electrically conductive material.

[0021] The CC 22 can be a porous material with a large surface area that can work efficiently to reduce NO in the presence of a reducing agent 36, such as ammonia. x-components in the exhaust gas 8. For example, the catalyst composition may contain a zeolite and one or more base metal components, such as iron (Fe), cobalt (Co), copper (Cu) or vanadium (V), sodium (Na), barium (Ba), titanium (Ti), tungsten (W), and combinations thereof. In a particular embodiment, the catalyst composition may contain a zeolite impregnated with one or more of copper, iron, or vanadium. In some embodiments, the zeolite may be a β-zeolite, a Y-zeolite, a ZM5 zeolite, or any other crystalline zeolite structure, such as a chabazite or a USY (ultrastable Y-type) zeolite. In a particular embodiment, the zeolite comprises chabazite. In a particular embodiment, the zeolite comprises SSZ.Suitable CCs 22 can exhibit high thermal structural stability, particularly when used in tandem with PFs or when incorporated into selective catalytic reduction filter (SCRF) devices regenerated using high-temperature soot combustion processes. CC 22 can also optionally comprise one or more basic metal oxides as promoters to further reduce SO3 formation and extend catalyst life. The one or more basic metal oxides can, in some embodiments, include WO3, Al2O3, and MoO3. In one embodiment, WO3, Al2O3, and MoO3 can be used in combination with V2O5.

[0022] SCR 20 may have a light-off temperature above which CC 22 exhibits the desired or appropriate catalytic activity or yield (e.g., reduction of NOx species). The light-off temperature may depend, among other things, on the type of catalytic materials comprising CC 22 and the amount of catalytic materials in SCR 20. For example, a CC 22 comprising V2O5 may have a light-off temperature of approximately 300°C. In another example, a CC 22 comprising finely impregnated zeolite may have a light-off temperature of approximately 350°C. In another example, a CC 22 comprising Cu-impregnated zeolite may have a light-off temperature of approximately 150°C. When SCR 20 operates at a temperature below its light-off temperature, undesirable NO x breakthrough and NH3 slip may occur, with NO xand / or NH3 are not converted or stored by the SCR 20. NO x Breakthrough and NH3 slip can be particularly problematic immediately after engine start-up and in cold conditions. NO x Breakthrough can also be enhanced, for example, by lean-burn combustion strategies commonly implemented in diesel engines. Lean-burn strategies coordinate combustion at higher than stoichiometric air-to-fuel mass ratios to improve fuel economy and produce hot exhaust gas with a relatively high content of O2 and NO. x -Species.

[0023] The high O2 content can reduce NO x species in some scenarios.

[0024] CC 22 may be disposed on a substrate body, such as a metal or ceramic brick, a plate, or a monolithic honeycomb structure. For example, CC 22 may be deposited onto the substrate body as a washcoat. A monolithic honeycomb structure may contain several hundred to several thousand parallel flow cells per square inch, although other configurations are also suitable. Each of the flow cells may be defined by a wall surface onto which the CC 22 may be washcoated. The substrate body may be formed of a material capable of withstanding the temperatures and chemical environment associated with the exhaust gas 8.Some specific examples of materials that may be used include ceramics such as extruded cordierite, α-alumina, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica-magnesia, zirconium silicate, sillimanite, petalite, or a heat- and corrosion-resistant metal such as titanium or stainless steel. The substrate may, for example, comprise a non-sulfating TiO2 material. The substrate body may include, be integral with, or be proximate to the heater 40, as described below. One example of an exhaust treatment device is an SCRF, which provides the catalytic aspects of the SCR in addition to the particulate matter filtration properties. Generally, an SCRF comprises a CC 22 applied to a filter substrate, such as a ceramic or SiC wall-flow monolith filter, wound or packed fiber filters, open-cell foams, sintered metal fibers, etc.In some embodiments, the SCRF filter substrate may include, be integral with, or be proximate to the heater 40, as described below.

[0025] The SCR 20 may store (i.e., absorb and / or adsorb) the reductant for interaction with the exhaust gas 8. The reductant may be stored, for example, within the SCR catalyst as ammonia. During operation of SCR 20, injected reductant 36 may be stored within SCR 20 and subsequently consumed during reduction reactions with NOx species. A given SCR device has a reductant capacity, or an amount of reductant or reductant derivative that can be stored. The amount of reductant stored within an SCR device relative to the capacity of the SCR device may be referred to as the "reductant loading" of the SCR device, and in some instances may be expressed as a % loading (e.g., 90% reductant loading).

[0026] The system 100 includes PF 40 located downstream of SCR 20. For example only, the PF device 40 may include a diesel particulate filter (DPF). The PF device 40 filters the carbon, soot, and other particulates from the exhaust gas 8. The PF device 40 generally includes a filter, such as a ceramic or SiC wall-flow monolith filter packaged in a canister or enclosure. The canister may be made of stainless steel, for example, and have an inlet and an outlet in fluid communication with exhaust conduits 9. In some embodiments, the exhaust treatment system 100 may further include a selective catalytic reduction (SCRF) filter device. In some embodiments, the exhaust treatment system 100 may include an SCRF device as an alternative to an SCR 20 and a PF 40.SCRF devices generally provide catalytic aspects of SCR devices in addition to the particulate filtering capabilities of PF devices. For example, an SCRF device may include a filter carrier or filter substrate immersed in a washcoat containing an SCR catalyst component. Over time, PFs and SCRFs can build up particulate matter and require regeneration through high-temperature combustion. PFs, for example, can be regenerated through post-injection strategies. A post-injection strategy is a modification of a normal internal combustion engine injection strategy by adding or replacing a fuel injection event. During operation of an ICE, such as ICE 1, fuel and air are injected into a cylinder and combusted, reciprocating a piston within the cylinder, which subsequently transfers mechanical work to an associated crankshaft.During or following the piston movement via the combustion event, combustion products are expelled from the cylinder as exhaust gases. A post-injection strategy involves injecting or otherwise delivering fuel into an engine cylinder after the initial air / fuel mixture has been delivered to or generated within the cylinder, but such that the post-injected fuel is substantially or completely combusted within the cylinder. Alternatively, in some cases, the post-injected fuel is only partially combusted, and the exhaust gas contains a higher amount of unburned fuel (e.g., HC). By introducing additional fuel into the cylinder, post-injection accordingly transfers additional heat to the exhaust gas expelled from the cylinder, which can subsequently assist in the regeneration of a PF.A post-injection strategy may be referred to as a "rich mode," in which the ICE 1 receives air / fuel mixtures that are richer than the stoichiometric combustion ratio. While operating in a rich mode, the ICE 1 may emit exhaust streams with increased HC content and reduced oxygen content relative to the stoichiometric air-fuel ICE operating modes. A post-injection strategy may further involve reducing the amount of air supplied to one or more ICE cylinders to increase the magnitude of the rich mode. A rich mode may often require both a post-injection strategy in combination with a reduced air supply to one or more ICE cylinders.

[0027] OC 10 is a flow-through device comprising a catalytic composition (CC) 12 and configured to receive exhaust gas 8. OC 10 is generally used to oxidize various exhaust gas species 8, including HC, CO, and NO xSpecies. CC 12 may be housed in a housing, such as a metal casing having an inlet (i.e., upstream) and an outlet (i.e., downstream) port, or otherwise configured to provide structural support and facilitate the flow of fluid (e.g., exhaust) through OC 10. The housing may ideally be made of a material that is largely inert to the exhaust constituents, such as stainless steel, and may have any suitable shape or size, including a cylindrically shaped compartment. The compartment may further include attachment features, such as a cylindrical inlet tube near an inlet port and a cylindrical outlet tube near an outlet port of the compartment, for fluidly coupling OC 10 to exhaust conduit 9 and / or another component of exhaust treatment system 100.It should be noted that OC 10, including the housing, may include one or more additional components to facilitate operation of the OC 10 or the exhaust treatment system 100, including, but not limited to, various sensors.

[0028] CC 12 can comprise many different catalytically active materials and their physical configurations and optionally comprise a substrate, such as a porous ceramic matrix or the like. Catalytically active materials can include platinum group metal catalysts, metal oxide catalysts, and combinations thereof. Suitable platinum group metals can include Pt, Pd, Rh, Ru, Os, or Ir, or combinations thereof, including alloys thereof. In one embodiment, suitable metals include Pt, Pd, Rh, and combinations thereof, including alloys thereof. A suitable metal oxide catalyst can include, for example, iron oxides, zinc oxides, aluminum oxides, perovskites, and combinations thereof. In one embodiment, CC 12 can consist of Pt and Al2O3. In many embodiments, CC 12 comprises zeolite impregnated with one or more catalytically active base metal components.The zeolite may comprise a β-zeolite, a Y-zeolite, a ZM5 zeolite, or any other crystalline zeolite structure, such as a chabazite or a USY (ultrastable Y-type) zeolite. In a particular embodiment, the zeolite comprises chabazite. In a particular embodiment, the zeolite comprises SSZ. It should be understood that the CC 12 is not limited to the examples provided and may include any catalytically active device capable of oxidizing HC and CO species, reducing NOx species, and optionally oxidizing NOx species. In particular, a CC used in a diesel oxidation catalyst may oxidize HC, CO, and NOx species under certain conditions and reduce NOx under other conditions. In another example, a three-way catalyst, such as one used in combination with a gasoline ICE, can oxidize HC and CO and reduce NOx under certain conditions.

[0029] OC 10 may store and / or oxidize NOx species in the exhaust gas 8 that are formed, for example, during fuel combustion. In some embodiments, for example, OC 10 may be used to convert NO to NO2 to optimize the exhaust NO:NO2 ratio for downstream SCRs and / or SCRFs, which generally operate more efficiently with exhaust streams having a NO:NO2 ratio of about 1:1. Accordingly, in many embodiments, OC 10 is located upstream of optional SCRs and SCRF devices. OC 10 may have a light-off temperature above which CC 12 exhibits the desired or appropriate catalytic activity relative to the oxidation of NOx species. An OC 10 NOx oxidation light-off temperature may also correspond to the temperature at which NOx species are released by CC 12.The light-off temperature may depend, among other things, on the type of catalytic materials composing CC 12 and the amount of catalytic materials in OC 10. In general, CC 12 may have a NOx oxidation light-off temperature of about 150°C to about 200°C. For example, some CCs 12 achieve 50% conversion of NO species at about 230°C. When OC 10 operates at a temperature below its NOx oxidation light-off temperature, the NO2:NOx fuel ratio of exhaust gas 8 transferred from OC 10 to a downstream SCR 20 is not optimized.

[0030] OC 10 may additionally or alternatively store HC and / or catalyze the oxidation (e.g., combustion) of HC and CO species in the exhaust gas. Combustion generally involves the oxidation of HC and / or CO species in the presence of oxygen to generate heat, water, and CO2. In some cases, HC and / or CO may be present in exhaust gas 8 as a result of undesirable incomplete combustion of, for example, fuel. In other cases, HC may be present in exhaust gas 8 to implement various control strategies by ICE 1 and / or system 100. For example, OC 10 may be used to exothermically oxidize HC to assist one or more exhaust treatment devices of system 100 in reaching light-off temperatures. OC 10 may additionally or alternatively be used to oxidize HC for post-injection and auxiliary injection regeneration strategies.Post-injection strategies, such as those used for regeneration of PFs and / or catalysts, manipulate engine calibrations so that fuel injected into the engine cylinders is expelled into the exhaust system 100 at least partially unburned. When the post-injected fuel comes into contact with OC 10, heat released during fuel oxidation is supplied to the exhaust treatment system and can aid in the regeneration of various treatment devices, such as particulate filters (PFs) and SCRFs. Likewise, auxiliary injection strategies, such as those used for regeneration of PFs and / or catalysts, inject fuel into the system 100 downstream of ICE 1 to contact the fuel with OC 10, after which heat is released from the exothermic combustion of fuel.

[0031] OC 10 may have a light-off temperature above which CC 12 exhibits the desired or appropriate catalytic activity relative to the oxidation of CO and / or HC species. An OC 10 CO and / or HC light-off temperature may also correspond to the temperature at which CO and / or HC species are released by CC 12. The light-off temperature may depend, among other things, on the type of catalytic materials comprising CC 12 and the amount of catalytic materials in OC 10. For example, some CCs 12 may have a CO oxidation light-off temperature of about 150°C to about 175°C. For example, some CCs 12 may have an HC oxidation light-off temperature of about 175°C to about 250°C. If OC 10 operates at a temperature below its CO and / or HC oxidation light-off temperature, undesirable CO and / or HC breakthrough may occur.

[0032] Methods for diagnosing the catalytic performance of OCs are limited in both their opportunistic availability and their accuracy. Methods for monitoring the catalytic performance of an OC are provided herein, utilizing the cross-sensitivity of NOx sensors and the phenomenon under certain conditions where OC 10 catalytically converts NOx to NH3. Specifically, oxidation catalyst materials (e.g., CC 12) can reduce NOx species to NH3 under rich conditions and at high temperatures (e.g., greater than about 350°C). The reduction of NOx species to NH3 by OC 10 can be correlated with OC 10 NOx oxidation capabilities, which can be used, for example, to monitor OC 10 performance. The reduction of NOx species to NH3 and the oxidation of NOx species may be catalyzed by the same catalytic elements (i.e., CC 12), which in some embodiments may include PGM.

[0033] Fig.2 illustrates a method 200 for diagnosing an exhaust treatment system. The method 200 is described with reference to system 100, but, as previously described, is not to be construed as limited by the particular configuration of system 100. The method 200 includes providing 210 exhaust gas 8 to OC 10 and subsequently to SCR 20, measuring 220 a NOx concentration upstream of SCR 20 (e.g., via upstream NOx sensor 60), measuring 230 a NOx concentration downstream of SCR 20 (e.g., via downstream NOx sensor 62), determining 240 an upstream-downstream NOx difference, and determining 250 an OC 20 performance using the NOx difference. For example, the upstream NOx concentration and the downstream NOx concentration may comprise an average concentration over a time frame.The upstream NOx sensor 60 and the downstream NOx sensor 62 are cross-sensitive to NOx and NH3. Exhaust gas 8 may be provided 210 by ICE 1 to OC 10 and subsequently to SCR 20, and ICE 1 may optionally power a vehicle. Providing 210, measuring 220, and measuring 230 may, for example, occur during a time frame. OC 10 includes CC 12 capable of oxidizing NOx while OC 10 is below a NOx to NH3 conversion yield threshold (e.g., ICE 1 is operating at stoichiometric and / or lean conditions), as described below, and is capable of reducing NOx to NH3 while OC 10 is above a NOx to NH3 yield threshold (e.g., ICE 1 is operating at rich conditions).

[0034] During performance of method 200 (e.g., during the time frame), the OC may be above a NOx to NH3 conversion yield threshold. The NOx to NH3 conversion yield threshold is generally a function of one or more of the temperature of the OC 10, the oxygen content of exhaust gas 8 supplied to the OC 10, and the amount of CC 12 (e.g., the OC 10 PGM loading), with higher temperatures of the OC 10, lower oxygen content of the exhaust gas 8, and higher catalytic loading of the CC 12 increasing the NOx to NH3 conversion yield thresholds. The temperature of the OC 10 and the oxygen content of the exhaust gas 8 may be determined for a particular OC 10 (e.g., with a particular PGM loading) such that a desired amount of NOx is reduced to NH3 above the CC 12. A suitable NOx reduction efficiency may, for example, be at least about 90%, at least about 95%, or about 99%.In other embodiments, a suitable NOx reduction yield may include any yield that is, for example, measurable or traceable to a model.

[0035] A suitable DOC temperature may, for example, be at least about 350°C. A desired oxygen content of the exhaust gas 8 may be lower than the oxygen content of the exhaust gas 8 produced, for example, by an ICE operating under stoichiometric conditions. During performance of method 200, the exhaust gas 8 may optionally include an elevated level of HC relative to the HC level of the exhaust gas 8 produced by the ICE 1 operating under stoichiometric conditions. During performance of method 200, the ICE 1 may operate in a rich mode and produce a rich-phase exhaust gas 8. Certain stoichiometric air-fuel ratios may vary, for example, depending on the composition of the atmospheric air and / or the composition of the fuel.A rich operating mode of the ICE, or rich exhaust, may be uniformly defined by a lambda ratio (λ) calculated by the actual air-fuel ratio divided by the stoichiometric air-fuel ratio. Accordingly, at stoichiometric conditions, λ = 1, at lean conditions, λ > 1, and at rich conditions, λ < 1. In one embodiment, the exhaust gas 8 provided to the OC 10 is produced by the ICE 1 operating at a lambda ratio less than or equal to 0.97 (i.e., at least 3% lower than the oxygen content of the exhaust gas 8 produced when the ICE 1 operates under stoichiometric air-fuel conditions). In some embodiments, the exhaust gas 8 provided to the OC 10 is produced by the ICE 1 operating at a lambda ratio of about 0.91 to about 0.98.

[0036] In some embodiments, the SCR 20 may have a reductant 36 loaded below about 1%, and / or the SCR 20 may be below its NOx light-off temperature. In other embodiments, the SCR 20 may have a reductant 36 loading sufficiently low that no appreciable NOx reduction occurs within the SCR, and / or the SCR 20 may be below its NOx light-off temperature. In some embodiments, the method 200 optionally includes performing a PF 40 high temperature regeneration prior to providing 210, measuring 220, and measuring 230. Regeneration of the PF 40 may ensure a high temperature of the OC 10 and a low SCR 20 reductant 36 loading.

[0037] Under the conditions described above, the OC 10 reduces at least a portion of the NOx present in the exhaust gas 8 to NH3, and exhaust gas 8 downstream of the OC 10 will comprise NH3 and optionally NOx, where the NOx represents an amount or concentration of NOx in the exhaust gas 8 that has not been reduced to NH3. When the exhaust gas 8 subsequently enters the SCR 20, NH3 is stored in the CC 22. A low SCR 20 reductant 36 loading allows any NOx in the exhaust gas 8 to pass through the SCR 20 unreduced and subsequently detected by the downstream NOx sensor 62. Based on the expected NOx to NH3 yield of OC 10 under the particular conditions of system 100, the amount or concentration of NOx in the exhaust gas 8 exiting the OC 10 may exhibit a deficit in the catalytic (i.e., reducing) capacity of the OC 10.This amount of NOx is equal to the NOx difference, which may be determined 240 by subtracting the downstream NOx concentration from the upstream NOx concentration. Similarly, in one embodiment, the NOx difference may include an amount of NH3 calculated by subtracting the integral of the downstream exhaust NOx concentration over a time frame from the integral of the upstream exhaust NOx concentration over the time frame to determine an amount of NH3 produced by the OC during the time frame.

[0038] A differential threshold (i.e., an acceptable maximum amount of NOx present in exhaust gas 8 downstream of OC 10 or an acceptable minimum amount of NH3 produced by OC 10) may be determined to identify a minimum level of acceptable reduction capability of OC 10 and may be unique for various operating parameters of system 100 (i.e., temperature of OC 10, oxygen concentration of exhaust gas 8, etc.). For example, under certain operating conditions of system 100, a model may determine the NOx to NH3 conversion efficiency (e.g., 5%, 50%, 90%, 99.999%) for CC 12. This conversion efficiency may be used to determine the differential threshold.The difference threshold may be pre-calibrated or determined using a data map comprising a plurality of values ​​corresponding to one or more aspects of the system 100, such as, but not limited to, ICE calibration, NOx concentration of exhaust 8, HC concentration of exhaust 8, and CC 12 temperature. Similarly, the difference threshold may be specific to a particular OC 10. For example, a higher amount of CC 12 (e.g., PGM) will increase NH 3 formation, and accordingly, the threshold should be set higher. Similarly, a CC 12 comprising Pt will form more NH 3 than a CC 3 comprising Pt, Pd, and Rh, and accordingly should have a higher threshold.

[0039] A comparison of the NOx difference with the difference threshold can indicate the suitability of the catalytic (i.e., reducing) performance of OC 10. For example, a NOx difference greater than the difference threshold can indicate unsuitable catalytic reducing performance of OC 10. More importantly, the suitability of the reducing performance of OC 10 can be correlated with the suitability of the oxidizing performance of OC 10. Therefore, by determining the catalytic ability of OC 10 to reduce NOx to NH3, the catalytic ability of OC 10 to oxidize one or more of NOx, HC, and CO, among others, can be determined. More specifically, the catalytic ability of OC 10 to convert NOx to NH3 at or above a NOx to NH3 conversion efficiency threshold (e.g.,under rich conditions) can be correlated with the catalytic ability of OC 10 to oxidize, among others, one or more of NOx, HC and CO below the NOx to NH3 conversion efficiency threshold (e.g., under stoichiometric or lean conditions).

Claims

[1] A method for diagnosing an exhaust gas treatment system (100), the system (100) comprising an oxidation catalyst device (OC) (10) comprising a catalytic composition (CC) and capable of receiving exhaust gas and oxidizing one or more combustible hydrocarbons (HC) and one or more nitrogen species (NOx species), a selective catalytic reduction device (SCR) (20) disposed downstream of and in fluid communication with the OC (10) and configured to store NOx species and reduce NOx species in the presence of a reductant (36), an upstream NOx sensor (60) disposed upstream of the SCR (20), and a downstream NOx sensor (62) disposed downstream of the SCR (20). the method comprising: Providing exhaust gas to the OC (10) and then to the SCR (20); Measuring an upstream exhaust NOx concentration using the upstream NOx sensor (60); Measuring a downstream exhaust NOx concentration using the downstream NOx sensor (62); Determining a NOx difference by subtracting the downstream exhaust NOx concentration from the upstream exhaust NOx concentration; and Comparing the NOx difference with a difference threshold to determine the OC performance; wherein the SCR reductant loading is below about 1% and / or the SCR (20) is below a NOx light-off temperature while exhaust gas is supplied to the OC (10); characterized by , that the upstream NOx sensor (60) is provided downstream of the OC (10), and wherein a NOx difference above the difference threshold indicates a suitable OC-NOx oxidation performance; or that a NOx difference above the difference threshold indicates a suitable OC-NOx oxidation performance, and wherein the exhaust gas provided to the OC (10) comprises rich-phase exhaust gas produced by an internal combustion engine (ICE) (1); or that a NOx difference above the difference threshold indicates suitable OC-NOx oxidation performance, and wherein the exhaust gas provided to the OC (10) is produced by the internal combustion engine (1) operating at a lambda ratio of about 0.91 to about 0.98, the lambda ratio being the actual ICE air-fuel ratio divided by the stoichiometric air-fuel ratio of the ICE (1). [2] A method for diagnosing an exhaust gas treatment system (100), the system (100) comprising an oxidation catalyst device (OC) (10) comprising a catalytic composition (CC) and capable of receiving exhaust gas and oxidizing one or more combustible hydrocarbons (HC) and one or more nitrogen species (NOx species), a selective catalytic reduction device (SCR) (20) disposed downstream of and in fluid communication with the OC (10) and configured to store NOx species and reduce NOx species in the presence of a reductant (36), an upstream NOx sensor (60) disposed upstream of the SCR (20), and a downstream NOx sensor (62) disposed downstream of the SCR (20), the method comprising: Providing exhaust gas to the OC (10) and subsequently to the SCR (20) for a time frame; Measuring an upstream NOx concentration of the exhaust gas using the upstream NOx sensor (60) during the time frame; Measuring a downstream exhaust NOx concentration using the downstream NOx sensor (62) during the time frame; Subtracting the integral of the downstream exhaust NOx concentration over the time frame from the integral of the upstream exhaust NOx concentration over the time frame to determine an amount of NH3 produced by the OC (10) during the time frame; and Comparing the amount of NH3 formed with an NH3 threshold to determine the OC performance, wherein an NH3 amount above the NH3 threshold indicates suitable OC performance; wherein during the time frame the SCR reductant loading is sufficiently low such that no appreciable NOx reduction occurs within the SCR (20) and the OC (10) is above a NOx to NH3 conversion efficiency threshold. [3] A method for diagnosing an oxidation catalyst device (OC) (10) of a diesel internal combustion engine (ICE) exhaust treatment system (100), the system (100) comprising a diesel ICE configured to receive an air-fuel mixture, combust the air-fuel mixture, and expel the combustion products as exhaust gas via an exhaust conduit, an oxidation catalyst device (OC) (10) having a catalytic composition (CC) capable of receiving exhaust gas from the ICE (1) via the exhaust conduit and oxidizing one or more combustible hydrocarbons (HC) and one or more nitrogen oxide (NOx) species within the exhaust gas, a selective catalytic reduction (SCR) device (20) disposed downstream of and in fluid communication with the OC (10) and configured to store NOx species and reduce NOx species in the presence of a reducing agent (36),an upstream NOx sensor (60) located downstream of the OC (10) and upstream of the SCR (20), and a downstream NOx sensor (62) located downstream of the SCR (20), the method comprising: Providing exhaust gas from the ICE (1) in sequence to the OC (10) and to the SCR (20) for a time frame, wherein the OC (10) is above an NH3 conversion efficiency threshold and the oxygen content of the exhaust gas is at least 3% lower than the oxygen content of the exhaust gas produced by the ICE (1) operating under stoichiometric air-fuel conditions; Measuring an upstream NOx concentration of the exhaust gas for the time frame using the upstream NOx sensor (60); Measuring a downstream NOx concentration of the exhaust gas for the time frame using the downstream NOx sensor (62); Determining a NOx difference for the time frame by subtracting the downstream NOx exhaust concentrations from the upstream exhaust NOx concentrations; Comparing the NOx difference with a difference threshold to determine the OC-NOx reduction performance; and Correlating OC-NOx reduction performance with OC-NOx oxidation performance. [4] A process according to any one of the preceding claims, wherein the CC comprises one or more platinum group metals. [5] A method according to any preceding claim, wherein the SCR comprises a selective reduction filter device. [6] A method according to any one of the above claims, wherein the upstream NOx sensor (60) and the downstream NOx sensor (62) are each cross-sensitive to NOx and NH3. [7] The method of any of the above claims, wherein the system (100) further comprises a particulate filter (PF) device (40) in fluid communication with the OC (10) and the SCR (20), and the method further comprises performing a high temperature PF regeneration prior to the timeframe. [8] A method according to any one of the preceding claims, wherein the CC is capable of oxidising NOx while the ICE (1) is operating under stoichiometric and / or lean conditions and is capable of reducing NOx to NH3 while the ICE (1) is operating under rich conditions.

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