DE102012215172A1 - Method for monitoring oxidation catalyst of selective catalytic reduction system for vehicle diesel engine, involves determining catalyst improper operation when difference between oxygen levels is smaller than predefined level - Google Patents

Abstract

The method involves injecting fuel into an exhaust gas flow, which flows upstream of an oxidation catalyst (26) by an exhaust-gas treatment system (20). 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 0 to 10%.

Description

TECHNICAL AREA

The invention relates generally to an exhaust treatment system, and more particularly to a method for monitoring an oxidation catalyst of the exhaust treatment system to determine whether the oxidation catalyst is operating improperly.

BACKGROUND

Exhaust gas treatment systems for diesel engines may include a diesel oxidation catalyst for treating exhaust gas flow from the engine. The diesel oxidation catalyst is a flow device consisting of a canister containing a substrate or a honeycomb structure. The substrate has a large surface coated with an active catalyst layer. As the exhaust gases pass through the active catalyst layer, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles, i. H. unburned fuel and / or oil, oxidizes, thereby reducing harmful emissions.

However, in order for the active catalyst layer to oxidize the carbon monoxide, the gaseous hydrocarbons, and the liquid hydrocarbon particles, the active catalyst layer must be at or above a light-off temperature. Often, once the active catalyst layer reaches the light-off temperature, additional hydrocarbons are injected into the exhaust gas flow by either post-fuel post-injection or a hydrocarbon injector. The additional hydrocarbons injected into the exhaust gas stream may be ignited to further heat the exhaust gas flow.

Vehicles may include a diagnostic system to detect a potential failure of the oxidation catalyst. For example, the diagnostic system may measure a temperature of the exhaust gas upstream and downstream of the oxidation catalyst. If the temperature of the exhaust gas downstream of the oxidation catalyst is significantly higher (ie, the approximate temperature rise can be calculated based on the amount of heat released from the injected hydrocarbons) than the temperature of the exhaust gas upstream of the oxidation catalyst, then a control module may assume that the in oxidize the exhaust gas injected hydrocarbons properly with the oxidation catalyst, wherein an exothermic reaction is generated, and may signal that the oxidation catalyst is functioning properly. If the temperature of the exhaust downstream of the oxidation catalyst is equal to or just slightly higher than the temperature of the exhaust upstream of the oxidation catalyst, then the control module may assume that the hydrocarbons injected into the exhaust flow improperly oxidize with the oxidation catalyst, producing no exothermic reaction, and may signal that the oxidation catalyst is operating improperly.

SUMMARY

A method is provided for monitoring an oxidation catalyst of an exhaust treatment system. The method includes injecting fuel into an exhaust flow that flows through the exhaust treatment system upstream of the oxidation catalyst. An oxygen level in the exhaust gas flow is measured upstream of the oxidation catalyst to define an upstream oxygen level. An oxygen level in the exhaust gas flow is measured downstream of the oxidation catalyst to define a downstream oxygen level. A difference between the upstream oxygen level and the downstream oxygen level is calculated. Improper operation of the oxidation catalyst is detected when the calculated difference between the upstream oxygen level and the downstream oxygen level is less than a predefined oxygen level limit.

There is also provided a method of detecting an improperly functioning oxidation catalyst of an exhaust treatment system. The method includes injecting fuel into an exhaust flow that flows through the exhaust treatment system upstream of the oxidation catalyst. An oxygen level in the exhaust gas flow is measured upstream of the oxidation catalyst to define an upstream oxygen level. An oxygen level in the exhaust gas flow is measured downstream of the oxidation catalyst to define a downstream oxygen level. A percentage difference between the upstream oxygen level and the downstream oxygen level is calculated. A temperature of the exhaust gas flow passing through the exhaust treatment system is measured downstream of the oxidation catalyst and upstream of a particulate filter to define an upstream exhaust gas temperature. A temperature of the exhaust gas flow passing through the exhaust treatment system is measured downstream of the particulate filter to define a downstream exhaust gas temperature. A numerical difference between the downstream exhaust gas temperature and the upstream exhaust gas temperature is calculated. Improper operation of the oxidation catalyst will signals when the calculated difference between the upstream oxygen level and the downstream oxygen level is less than a predefined oxygen level limit and the calculated numerical difference between the downstream exhaust temperature and the upstream exhaust temperature is greater than a predefined temperature limit.

There is also provided an exhaust treatment system for treating an exhaust flow from an engine of a vehicle. The exhaust treatment system includes an oxidation catalyst and a particulate filter disposed downstream of the oxidation catalyst. A first oxygen sensor is disposed upstream of the oxidation catalyst, and a second oxygen sensor is disposed downstream of the oxidation catalyst and upstream of the particulate filter. A first temperature sensor is disposed downstream of the oxidation catalyst and upstream of the particulate filter, and a second temperature sensor is disposed downstream of the particulate filter. A control module is coupled to the first oxygen sensor, the second oxygen sensor, the first temperature sensor, and the second temperature sensor. The control module serves to receive data from the first oxygen sensor associated with a measured oxygen level upstream of the oxidation catalyst and to define an upstream oxygen level. Data from the second oxygen sensor associated with a measured oxygen level downstream of the oxidation catalyst is also received by the control module and used to define a downstream oxygen level. The control module calculates a percentage difference between the upstream oxygen level and the downstream oxygen level and determines whether the calculated percentage difference between the upstream oxygen level and the downstream oxygen level is less than a predefined oxygen level limit equal to the predefined oxygen level limit or greater than the predefined oxygen level limit. The control module further receives data from the first temperature sensor associated with a measured exhaust gas temperature upstream of the particulate filter and defines an upstream exhaust temperature. Data from the second temperature sensor associated with a measured exhaust gas temperature downstream of the particulate filter is also received by the control module and used to define a downstream exhaust gas temperature. The control module calculates a numerical difference between the downstream exhaust temperature and the upstream exhaust temperature and determines whether the calculated numerical difference between the downstream exhaust temperature and the upstream exhaust temperature is less than a predefined temperature limit equal to the predefined temperature limit or greater than the predefined temperature limit. The control module signals that the oxidation catalyst is improperly functioning when the calculated percentage difference between the upstream oxygen level and the downstream oxygen level is less than the predefined oxygen level limit and the calculated numerical difference between the downstream exhaust temperature and the upstream exhaust temperature is greater than the predefined temperature limit.

Accordingly, the oxygen levels of the exhaust gas upstream and downstream of the oxidation catalyst are used to determine whether the oxidation catalyst is functioning properly or improperly. If the oxidation catalyst is functioning properly, the combustion of hydrocarbons injected into the exhaust gas upstream of the oxidation catalyst reduces the oxygen level in the exhaust gas downstream of the oxidation catalyst. Accordingly, significantly reduced oxygen levels downstream of the oxidation catalyst indicate proper function of the oxidation catalyst, while similar oxygen levels upstream and downstream of the oxidation catalyst indicate that the oxidation catalyst is not functioning properly.

The above features and advantages as well as other features and advantages of the present invention will be readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

1 FIG. 12 is a schematic diagram of an exhaust treatment system for an engine of a vehicle. FIG.

2 FIG. 10 is a flowchart illustrating a method of monitoring an oxidation catalyst of the exhaust treatment system to detect whether the oxidation catalyst is operating improperly.

DETAILED DESCRIPTION

It will be appreciated by those skilled in the art that terms such as "above," "below," "upward," "downward," "above," "below," etc. are used descriptively throughout the figures and are not limitations on the scope of the invention. as defined by the appended claims.

Referring to the figures, in which like reference numerals indicate like parts throughout the several views, there is shown in FIG 20 generally shown an exhaust treatment system. Referring to 1 treats the exhaust treatment system 20 an exhaust gas flow, generally indicated by arrows 22 is specified by a motor 24 of a vehicle. While the exhaust treatment system 20 is described here for the treatment of exhaust gas from a diesel engine, it should be noted that the exhaust treatment system 20 This can be used to exhaust from another type of engine 24 to treat, such as, but not limited to, a gasoline engine.

The exhaust treatment system 20 has an oxidation catalyst 26 and a particle filter 28 on, the downstream of the oxidation catalyst 26 is arranged. When used with a diesel engine 24 may be the oxidation catalyst 26 and the particulate filter 28 as a diesel oxidation catalyst 26 or a diesel particulate filter 28 be designated. The exhaust treatment system 20 also has a first oxygen sensor 30 , which is upstream of the oxidation catalyst 26 is arranged, and a second oxygen sensor 32 on, the downstream of the oxidation catalyst 26 and upstream of the particulate filter 28 is arranged. The first oxygen sensor 30 and the second oxygen sensor 32 may include any type and / or type of sensor capable of detecting an oxygen level in the exhaust gas flow passing through the exhaust treatment system 20 flows, to capture. For example, the first oxygen sensor 30 and the second oxygen sensor 32 each comprise a nitrogen oxide (NOx) sensor, a pure oxygen (O2) sensor or a lambda sensor. The exhaust treatment system 20 further includes a first temperature sensor 34 , downstream of the oxidation catalyst 26 and upstream of the particulate filter 28 is arranged, and a second temperature sensor 36 , the downstream of the particulate filter 28 is arranged. The first temperature sensor 34 and the second temperature sensor 36 may be of any type and / or type of sensor capable of determining the temperature of the exhaust gas passing through the exhaust treatment system 20 flows, to capture.

The oxidation catalyst 26 is a flow-through device that consists of a canister with a substrate 40 or a honeycomb structure. The substrate 40 has a large surface coated with an active catalyst layer. The diesel oxidation catalyst 26 handles the exhaust gas flow from the diesel engine 24 to reduce the toxicity of the exhaust gas, ie to reduce toxic emissions of the exhaust gas including, but not limited to, nitrogen oxides (NO), carbon monoxide (CO) and / or hydrocarbons (HC). As the exhaust gases pass through the active catalyst layer, carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles, ie unburned fuel and / or oil, are oxidized, thereby reducing harmful emissions. The oxidation of carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles with the active catalyst layer is an exothermic reaction that generates heat. The active catalyst material may include platinum group metals (PGM) and convert a percentage of the nitrogen oxides in the exhaust into nitrogen and carbon dioxide or water and also oxidizes a percentage of the carbon monoxide to carbon dioxide and oxidizes a percentage of the unburned hydrocarbons to carbon dioxide and water.

The active catalyst layer of the oxidation catalyst 26 must be heated to a light-off temperature of the catalyst before the active catalyst layer becomes operable and oxidizes the nitrogen oxides, the carbon monoxide and the unburned hydrocarbons. Accordingly, the exhaust gas must heat the active catalyst layer to the light-off temperature before the reaction between the active catalyst layer and the exhaust gas begins. To the diesel oxidation catalyst 26 and / or other components of the exhaust treatment system 20 to heat up quickly, including, but not limited to, the particulate filter 28 and / or a selective catalytic reduction unit, hydrocarbons may be injected into the exhaust gas flow. The hydrocarbons are ignited to generate heat in the exhaust gas that is added to the oxidation catalyst 26 and / or other components of the exhaust treatment system 20 is transmitted. The hydrocarbons may pass through a late post-injection process or through a hydrocarbon injector 42 be injected.

The particle filter 28 filters particulate material, ie soot, from the exhaust of the engine 24 , The particle filter 28 can be one or more substrates 44 exhibit. The particulate matter collects on the substrates 44 when the exhaust gas passes through the particulate filter 28 flows. The particle filter 28 is occasionally regenerated to remove the accumulated particulate matter. The regeneration of the particle filter 28 includes heating the particulate filter 28 to a temperature sufficient to burn the collected particulate matter to carbon dioxide.

The exhaust treatment system 20 may also include a selective catalytic reduction (SCR) system, commonly known as 48 is designated. The SCR system 48 has an exhaust fluid injector 50 containing an exhaust fluid such as, but not limited to, a mixture Urea and water, injected into the flow of exhaust gas. A mixer 52 mixes the exhaust fluid with the exhaust gas. When heated by the exhaust gas, the exhaust fluid forms ammonia. The SCR system 48 also has a converter 54 on. The converter 54 has a catalyst that causes or accelerates a chemical reaction between the ammonia generated by the exhaust fluid and the NOx (nitrogen oxides) in the exhaust gas to form nitrogen and water vapor.

The exhaust treatment system 20 further comprises a control module 56 , such as, but not limited to, an engine control unit 24 to the operation of the exhaust treatment system 20 to control and / or monitor. The control module 56 is with the first oxygen sensor 30 , the second oxygen sensor 32 , the first temperature sensor 34 and the second temperature sensor 36 coupled to receive data therefrom. The control module 56 may include a computer and / or processor and includes all the software, hardware, memory, algorithms, connections, sensors, etc. that are necessary to operate the exhaust treatment system 20 to monitor, regulate and / or control. Thus, a method that is described below and in 2 generally with 60 is shown as being executed by a program attached to the control module 56 is operable. It should be noted that the control module 56 may comprise any device capable of analyzing data from various sensors, comparing data, making the necessary decisions required to operate the exhaust treatment system 20 to monitor and / or control, and carry out the required tasks that are necessary to the operation of the exhaust treatment system 20 to monitor and / or control. The control module 56 serves the various tasks of the procedure 60 as described below.

Referring to 2 instructs the procedure 60 injecting fuel, as generally by box 62 is indicated in the exhaust gas flow passing through the exhaust treatment system 20 flows. The fuel may include, but is not limited to, diesel fuel. The fuel becomes in the exhaust gas flow upstream of the oxidation catalyst 26 injected. The fuel is passed through the hydrocarbon injector 42 for combustion and increasing the temperature of the exhaust gas injected. The elevated temperature of the exhaust gas is used to oxidize the catalyst 26 and / or the particulate filter 28 to heat up faster. If the fuel in the exhaust gas flow ignites and burns, the oxygen in the exhaust gas flow is consumed and the level of oxygen in the exhaust gas flow is reduced.

An oxygen level in the exhaust gas flow is through the first oxygen sensor 30 upstream of the oxidation catalyst 26 measured, as generally by box 64 is specified. The control module 56 receives the data from the first oxygen sensor 30 , the measured oxygen level upstream of the oxidation catalyst 26 and use the data to define an upstream oxygen level. An oxygen level in the exhaust gas flow is through the second oxygen sensor 32 downstream of the oxidation catalyst 26 measured, as generally by box 66 is specified. The control module 56 receives the data from the second oxygen sensor 32 , the measured oxygen level downstream of the oxidation catalyst 26 and use the data to define a downstream oxygen level.

The control module 56 then calculates a percentage difference between the upstream oxygen level and the downstream oxygen level, as generally by box 68 is specified. The percent difference between the upstream oxygen level and the downstream oxygen level is calculated by dividing the upstream oxygen level by the downstream oxygen level to define an oxygen level quotient, and multiplying the oxygen level quotient by one hundred. The percent difference represents the relative amount of change between the upstream oxygen level and the downstream oxygen level. Alternatively, it should be noted that the first oxygen sensor 30 and the second oxygen sensor 32 their measured values each to the control module 56 as a percentage, in which case the control module can calculate the percentage difference by taking the numerical difference between the upstream and downstream readings.

The control module 56 then determines whether the calculated percent difference between the upstream oxygen level and the downstream oxygen level is less than a predefined oxygen level limit, equal to the predefined oxygen level limit or greater than the predefined oxygen level limit, as generally boxed 70 is specified. The predefined oxygen level limit is a defined value stored in the memory of the control module 56 is stored, and represents a minimal change in the oxygen levels between the upstream oxygen level and the downstream oxygen level, which is a properly functioning oxidation catalyst 26 indicates. Accordingly, if the percentage difference is less than the predefined oxygen level limit, as generally with 72 is indicated, then the oxidation catalyst 26 may not work properly, while if the percentage difference is equal to or greater than the predefined oxygen limit, as is generally the case with 74 is indicated, then the oxidation catalyst 26 can work properly.

The predefined oxygen level limit is preferably between the range of zero percent (0%) and ten percent (10%) and is more preferably about equal to or greater than three percent (3%) due to sensor accuracy. However, it should be appreciated that the predefined oxygen level limit may be defined to any value, including values that are not within the preferred range described above, and the specific configuration and operation of the exhaust treatment system 20 is dependent.

If the control module 56 determines that the calculated percent difference is equal to or greater than the predefined oxygen level limit, as generally with 74 is specified, then the control module 56 find that the oxidation catalyst 26 works properly, and may further signal that the oxidation catalyst 26 working properly, as generally by box 75 is specified. A proper function of the oxidation catalyst 26 may be signaled in any manner, such as, but not limited to, recording a pass value in the memory of the control module 56 and providing some form of guidance to an operator, such as, but not limited to, a visual signal. Alternatively, the proper function of the oxidation catalyst 36 signaled by the absence of a signal, ie the control module 56 only provides clues to the operator when the oxidation catalyst 26 not working properly.

A temperature of the exhaust gas flow is determined by the first temperature sensor 34 upstream of the particulate filter 28 and downstream of the oxidation catalyst 26 measured, as generally by box 76 is specified. The control module 56 receives the data from the first temperature sensor 34 , the measured temperature of the exhaust gas upstream of the particulate filter 28 and use the data to define an upstream exhaust gas temperature. A temperature of the exhaust gas flow is determined by the second temperature sensor 36 downstream of the particulate filter 28 measured, as generally by box 78 is specified. The control module 56 receives the data from the second temperature sensor 36 , the measured temperature of the exhaust gas downstream of the particulate filter 28 and use the data to define a downstream exhaust gas temperature.

The control module 56 then calculates a numerical difference between the downstream exhaust gas temperature and the upstream exhaust gas temperature, as generally by box 80 is specified. The numerical difference is calculated by subtracting the upstream exhaust gas temperature from the downstream exhaust gas temperature. The numerical difference represents the absolute amount of change between the upstream exhaust temperature and the downstream exhaust temperature.

The control module 56 then determines whether the calculated numerical difference between the downstream exhaust temperature and the upstream exhaust temperature is less than a predefined temperature limit equal to the predefined temperature limit or greater than the predefined temperature limit, as generally represented by box 82 is specified. When the exhaust gas contains excess hydrocarbons present in the oxidation catalyst 26 due to an improperly functioning oxidation catalyst 26 were not oxidized, then the hydrocarbons with the catalyst on the transducer 54 be oxidized, which is an exothermic reaction that generates heat. Accordingly, if the numerical difference does not indicate an increase in temperature or a moderate increase in temperature, as generally associated with 84 is specified, then the control module 56 assume that there are no excess hydrocarbons in the exhaust gas flow, and that the oxidation catalyst 26 working properly, as generally by box 86 is specified. In contrast, if the numerical difference is significantly greater than the predefined temperature limit, as generally with 88 is specified, the control module 56 assume that excess hydrocarbons in the exhaust gas flow due to an improperly functioning oxidation catalyst 26 were present.

The predefined temperature limit is the maximum amount of temperature change between the upstream exhaust temperature and the downstream exhaust temperature for a properly functioning oxidation catalyst 26 , Accordingly, if the numerical difference is less than the predefined temperature limit, then the control module 56 assume that the oxidation catalyst 26 Properly works as the temperature of the exhaust gas over the particulate filter 28 has not increased significantly. However, if the numerical difference is equal to or greater than the predefined temperature limit, then the control module may 56 assume that the oxidation catalyst 26 does not work properly because the temperature of the exhaust gas is above the particulate filter 28 has increased significantly.

Preferably, the predefined temperature limit is between the range of seventy-five degrees Celsius (75 ° C) and one hundred and twenty-five degrees Celsius (125 ° C), and more preferably about one hundred degrees Celsius (100 ° C). However, it should be appreciated that the predefined temperature limit may be defined to any value, including values that are not within the preferred range described above, and the specific configuration and operation of the exhaust treatment system 20 is dependent.

If the control module 56 determines that the calculated percent difference between the upstream oxygen level and the downstream oxygen level is less than the predefined oxygen level limit, as generally with 72 is specified, and the calculated numerical difference between the downstream exhaust gas temperature and the upstream exhaust gas temperature is greater than the predefined temperature limit, as generally with 88 is specified, then the control module 56 determine and / or signal that the oxidation catalyst 26 working improperly, ie not working properly, as generally by box 90 is specified. An improper function of the oxidation catalyst 26 may be signaled in any manner such as, but not limited to, recording a failed value in the memory of the control module 56 or providing any form of cues to the operator, such as, but not limited to, a visual alert or the like.

It should be noted that a Delta temperature difference across the oxidation catalyst 26 measured and from the control module 56 in determining the proper function of the oxidation catalyst 26 can be used. For example, a significant increase in the temperature downstream of the oxidation catalyst indicates that an exothermic reaction is occurring across the oxidation catalyst and that the oxidation catalyst is functioning properly. However, if there is no significant increase in the temperature of the exhaust gas over the oxidation catalyst, then the oxidation catalyst may not function properly, or alternatively, the hydrocarbon injector may malfunction. If an exothermic reaction over the particulate filter 28 occurs as described above, then this is an indication that hydrocarbons have been successfully injected into the exhaust flow, indicating that the hydrocarbon injector 42 works properly and that the oxidation catalyst is not working properly.

The above description describes an exemplary embodiment of the exhaust treatment system 20 , this in 1 is shown. It should be noted that the exhaust treatment system 20 may differ from the exemplary embodiment shown and described herein. For example, the exhaust treatment system does not need a particulate filter 28 or no system 48 for selective catalytic reduction.

The detailed description and drawings or figures support and describe the invention, but the scope of the invention is defined solely by the claims. While some of the best modes and other embodiments for carrying out the claimed invention have been described in detail, various alternative constructions and embodiments for carrying out the invention as defined in the appended claims are provided.

Claims (10)

A method of monitoring an oxidation catalyst of an exhaust treatment system, the method comprising: Injecting fuel into an exhaust gas flow passing through the exhaust treatment system upstream of the oxidation catalyst; Measuring an oxygen level in the exhaust gas flow upstream of the oxidation catalyst to define an upstream oxygen level; Measuring an oxygen level in the exhaust gas flow downstream of the oxidation catalyst to define a downstream oxygen level; Calculating a difference between the upstream oxygen level and the downstream oxygen level; and Determining improper operation of the oxidation catalyst when the calculated difference between the upstream oxygen level and the downstream oxygen level is less than a predefined oxygen level limit. The method of claim 1, further comprising signaling a proper operation of the oxidation catalyst when the calculated difference is equal to or greater than the predefined limit. The method of claim 1, wherein calculating the difference between the upstream oxygen level and the downstream oxygen level is further defined as calculating a percentage difference between the upstream oxygen level and the downstream oxygen level. The method of claim 3, wherein calculating the percentage difference between the upstream oxygen level and the downstream oxygen level comprises dividing the upstream oxygen level by the downstream oxygen level to define an oxygen level quotient, and multiplying the oxygen level quotient by one hundred. The method of claim 3, wherein the predefined oxygen level limit is in the range of zero percent (0%) to ten percent (10%). The method of claim 1, further comprising measuring a temperature of the exhaust flow passing through the exhaust treatment system downstream of the oxidation catalyst and upstream of a particulate filter to define an upstream exhaust temperature and measuring a temperature of the exhaust flow flowing through the exhaust treatment system downstream of the particulate filter. to define a downstream exhaust gas temperature. The method of claim 6, further comprising calculating a numerical difference between the downstream exhaust temperature and the upstream exhaust temperature. The method of claim 7, wherein signaling the improper operation of the oxidation catalyst when the calculated difference between the upstream oxygen level and the downstream oxygen level is less than the predefined oxygen level limit is further defined as signaling improper operation of the oxidation catalyst when the calculated difference between the oxidation catalyst upstream oxygen level and the downstream oxygen level is less than a predefined oxygen level limit and the calculated numerical difference between the downstream exhaust temperature and the upstream exhaust temperature is greater than a predefined temperature limit. The method of claim 8, wherein the predefined temperature limit is in the range of seventy-five degrees Celsius (75 ° C) and one hundred and twenty-five degrees Celsius (125 ° C). Method according to claim 1, further comprising providing a control module for monitoring the oxidation catalyst, the control module comprising all the hardware and software necessary to: Receive data from a first oxygen sensor that measures the oxygen level upstream of the oxidation catalyst to define the upstream oxygen level; Receive data from a second oxygen sensor that measures the oxygen level downstream of the oxidation catalyst to define the downstream oxygen level; calculate the difference between the upstream oxygen level and the downstream oxygen level; determine whether the calculated difference between the upstream oxygen level and the downstream oxygen level is less than the predefined oxygen level limit, equal to the predefined oxygen level limit or greater than the predefined oxygen level limit; and signal that the oxidation catalyst is operating improperly when the calculated difference between the upstream oxygen level and the downstream oxygen level is determined to be less than the predefined oxygen level limit.

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