US20080098725A1 - Exhaust system having mid-reducer NOx sensor - Google Patents
Exhaust system having mid-reducer NOx sensor Download PDFInfo
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- US20080098725A1 US20080098725A1 US11/589,832 US58983206A US2008098725A1 US 20080098725 A1 US20080098725 A1 US 20080098725A1 US 58983206 A US58983206 A US 58983206A US 2008098725 A1 US2008098725 A1 US 2008098725A1
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- exhaust
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- nox
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9404—Removing only nitrogen compounds
- B01D53/9409—Nitrogen oxides
- B01D53/9431—Processes characterised by a specific device
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9495—Controlling the catalytic process
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
- F01N13/0097—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are arranged in a single housing
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N9/00—Electrical control of exhaust gas treating apparatus
- F01N9/005—Electrical control of exhaust gas treating apparatus using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2258/00—Sources of waste gases
- B01D2258/01—Engine exhaust gases
- B01D2258/012—Diesel engines and lean burn gasoline engines
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
- B01D53/34—Chemical or biological purification of waste gases
- B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
- B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
- B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
- B01D53/9477—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on separate bricks, e.g. exhaust systems
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
Definitions
- the present disclosure is directed to an exhaust system and, more particularly, to an exhaust system having a NOx sensor disposed between two separate NOx reducers.
- Internal combustion engines including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants.
- air pollutants may be composed of gaseous compounds such as, for example, the oxides of nitrogen (NOx).
- NOx oxides of nitrogen
- sensors for measuring the gaseous emissions of engines are currently available in today's market, the sensors may be insufficiently sensitive to measure the low levels of NOx remaining in the engine's exhaust after treatment of the exhaust in compliance with the emission regulations. That is, although current NOx sensors may be capable of detecting low concentrations of NOx, the emission regulation for NOx may be even lower. Therefore, currently available NOx sensors may be of no use in detecting the concentration of NOx emitted to the environment by today's engines.
- One method that may be implemented by engine manufacturers to dynamically determine the amount of NOx emitted to the environment includes measuring the concentration of NOx prior to the regulation required reductions. This measured value may then be used to predict the concentration of NOx in the subsequently treated exhaust.
- One such method is described in U.S. Pat. No. 6,701,707 (the '707 patent) issued to UPADHYAY et al. on Mar. 9, 2004.
- the '707 patent discloses an exhaust emission control system that utilizes an upstream oxidation catalyst and a downstream SCR catalyst to reduce NOx in a lean exhaust gas environment.
- the exhaust emission control system includes a first NOx sensor located upstream of the oxidation catalyst, and a second NOx sensor located downstream of the SCR catalyst.
- NOx at the tailpipe opening may be measured directly by the second sensor.
- the output and sensitivity of the first NOx sensor is used to estimate the NOx concentration downstream of the SCR catalyst. If the estimated NOx concentration is greater than the measured NOx concentration, a routine indicates degradation of the system.
- the exhaust emission control system of the '707 patent may suitably estimate a NOx concentration downstream of the SCR catalyst based on an upstream measurement, the accuracy of the system may be limited. Specifically, without a dynamic indication of the SCR catalyst's effectiveness, there may be no way to determine how much of the upstream NOx is being removed. It may be possible for the SCR catalyst to remove less than or more than an assumed removal amount, thereby negatively affecting the accuracy of the routine.
- the exhaust system of the present disclosure solves one or more of the problems set forth above.
- the exhaust system may include a housing connected to receive a flow of exhaust.
- the exhaust system may also include a first catalyst disposed within the housing to reduce the concentration of an exhaust constituent, and a second catalyst disposed within the housing downstream of the first catalyst to further reduce the concentration of the exhaust constituent.
- the exhaust system may further include a sensor disposed between the first and second catalysts to generate a signal indicative of the concentration of the exhaust constituent at the location between the first and second catalysts.
- the exhaust system may additionally include a controller in communication with the sensor to receive the signal. The controller may determine, based on the received signal, the concentration of the exhaust constituent at a location downstream of the second catalyst.
- Another aspect of the present disclosure is directed to a method of determining the concentration of an exhaust constituent.
- the method may include receiving a flow of exhaust, and reducing the concentration of the exhaust constituent within the flow of exhaust.
- the method may also include measuring the reduced concentration of the exhaust constituent, and further reducing the concentration of the exhaust constituent within the flow of exhaust.
- the method may further include determining the further reduced concentration of the exhaust constituent based on the measured reduced concentration.
- FIG. 1 is a schematic and diagrammatic illustration of an exemplary disclosed power unit and exhaust system.
- FIG. 1 illustrates a power system including a power unit 10 and an exhaust system 12 .
- the power system may be associated with a mobile vehicle such as a passenger vehicle, a vocational vehicle, a farming vehicle or a construction vehicle.
- the power system may be associated with a stationary machine such as an industrial power generator or a furnace.
- power unit 10 is depicted and described as a four-stroke diesel engine.
- power unit 10 may be any other type of internal combustion engine such as, for example, a gasoline engine, a gaseous fuel-powered engine, a 2-stroke engine or a turbine engine.
- Power unit 10 may include an engine block 14 that at least partially defines a plurality of combustion chambers (not shown). In the illustrated embodiment, power unit 10 includes four combustion chambers. However, it is contemplated that power unit 10 may include a greater or lesser number of combustion chambers and that the combustion chambers may be disposed in an “in-line” configuration, a “V” configuration, or any other suitable configuration.
- power unit 10 may include a crankshaft 16 that is rotatably disposed in engine block 14 .
- a connecting rod (not shown) may connect a plurality of pistons (not shown) to crankshaft 16 so that a sliding motion of each piston within each respective combustion chamber results in a rotation of crankshaft 16 .
- a rotation of crankshaft 16 may result in a sliding motion of the pistons.
- Rotation of crankshaft 16 may function as output from power unit 10 for effecting a desired work such as rotation of a generator or rotation of one or more drive axles of an associated vehicle.
- Exhaust system 12 may include an exhaust manifold 18 having exhaust passageways, each passageway being in fluid communication with an associated combustion chamber of power unit 10 .
- Exhaust manifold 18 may expel exhaust flow away from power unit 10 towards a housing 20 located downstream from exhaust manifold 18 .
- Housing 20 of exhaust system 12 may be a cylindrical or tubular conduit for directing exhaust gasses and particulates away from power unit 10 for processing by various emission controlling devices.
- exhaust manifold 18 may be integral with housing 20 of the exhaust system.
- an exhaust manifold and housing may be integrally stamped or forged from metal.
- exhaust manifold 18 may be secured to housing 20 by one or more fasteners (e.g. rivets, nuts and bolts, etc.) or by deformation (e.g. hemming).
- Housing 20 may also constitute structural support for the various emission controlling devices of the system.
- the emission controlling devices of exhaust system 12 may include a first catalyst 22 and a second catalyst 24 located downstream from first catalyst 22 for reducing the concentration of a constituent within the exhaust from power unit 10 .
- Second catalyst 24 may be incorporated so as to further reduce the concentration of the exhaust constituent beyond that achieved by first catalyst 22 .
- Both catalysts may be disposed across the cylindrical width (i.e., cross section) of housing 20 .
- catalysts 22 and 24 may be either removably or fixedly secured at their respective perimeters to housing 20 .
- exhaust system 12 may include other components such as, for example, a turbine, an exhaust gas recirculation system, a particulate filter, or any other exhaust system component known in the art.
- catalysts 22 and 24 may be SCR catalysts.
- catalysts 22 and 24 may be NOx reducers.
- catalytic conversion of exhaust across catalysts 22 and 24 may involve the reduction of nitrogen oxides to nitrogen gas and water so as to reduce the concentration of oxides of nitrogen in the exhaust flow.
- Reductants contemplated for use in this conversion may include urea and ammonia.
- first catalyst 22 may be a first stage of NOx reduction capable of effecting a first reduction in NOx concentration.
- Second catalyst 24 may be a second stage of NOx reduction capable of effecting a second reduction in NOx concentration.
- the concentration of NOx downstream from second catalyst 24 may be too low for detection by known NOx detection devices and methods.
- nitrogen oxides are only sufficiently concentrated for detection in the location downstream from first catalyst 22 and upstream from second catalyst 24 (i.e., between catalysts 22 and 24 ).
- a sensor 26 may be disposed between first catalyst 22 and second catalyst 24 .
- sensor 26 may detect a concentration of an exhaust constituent which, in one example, is an oxide of nitrogen.
- a controller 28 may be disposed in communication with sensor 26 .
- Various circuits may be associated with controller 28 such as, for example, power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other appropriate circuitry.
- controller 28 may be disposed in a location remote from housing 20 , if desired.
- catalysts 22 and 24 may be selected so as to have substantially similar conversion efficiencies.
- catalysts 22 and 24 may be identical components. The accuracy and precision involved in modeling second catalyst behavior based on known first catalyst behavior may be improved because the second catalyst can be expected to have substantially similar specifications and characteristics as the first catalyst. That is, they may be expected to remove equivalent proportions of an exhaust constituent from the gaseous flow. Identical catalytic components may provide further economic advantages in that similar parts may result in higher part volume, lower component cost and lower stocking expenses.
- first catalyst 22 is known to remove 50% of NOx from the exhaust directly expelled from power unit 10
- second catalyst 24 having similar properties as the first, may be expected to remove 50% of the NOx from the exhaust downstream from first catalyst 22 .
- a net conversion of 75% would result (50% of the original exhaust constituents from the first stage; 25% of the original exhaust constituents from the second stage).
- catalyst 24 can be expected to remove the same proportion of exhaust constituent from the flow as can catalyst 22 (e.g., when catalysts 22 and 24 are identical components), it may be possible to predict the concentration of an exhaust constituent downstream from catalyst 24 based on information from sensor 26 combined with an estimated or calculated conversion efficiency of catalyst 22 . Specifically, the concentration downstream from catalyst 24 may be approximated as the concentration resulting from the effect of catalyst 22 acting on the exhaust flow as measured at sensor 26 . The concentration downstream from catalyst 24 may be determined according to Eq. 1 below.
- DownstreamConcentration SensorConcentration - ⁇ ⁇ ⁇ Concentration
- ⁇ : DownstreamConcentration ⁇ ⁇ is ⁇ ⁇ the ⁇ ⁇ constituent ⁇ ⁇ concentration ⁇ ⁇ predicted to ⁇ ⁇ be ⁇ ⁇ downstream ⁇ ⁇ from ⁇ ⁇ catalyst ⁇ ⁇ 24
- SensorConcentration ⁇ ⁇ is ⁇ ⁇ the ⁇ ⁇ constituent ⁇ ⁇ concentration ⁇ ⁇ measured ⁇ ⁇ at sensor ⁇ ⁇ 26
- ⁇ ⁇ ⁇ ⁇ Concentration ⁇ ⁇ is ⁇ ⁇ the ⁇ ⁇ estimated ⁇ ⁇ change ⁇ ⁇ in ⁇ ⁇ concentration ⁇ ⁇ across catalyst ⁇ ⁇ 22 ⁇ ⁇ and ⁇ ⁇ therefore ⁇ ⁇ the ⁇ ⁇ expected ⁇ ⁇ change ⁇ ⁇ across ⁇ ⁇ catalyst ⁇ ⁇ 24.
- the total system conversion may be predicted based on complex catalyst models incorporating parameters, such as, known temperature gradients, reaction properties and/or intermediate sensor measurements.
- parameters such as, known temperature gradients, reaction properties and/or intermediate sensor measurements.
- the conversion efficiency of catalyst 22 may be calculated by comparing the expected production of exhaust constituent from power unit 10 to the concentration measured by sensor 26 .
- Estimated production of the exhaust constituent from power unit 10 may be accomplished by one or more controllers, including controller 28 , as a function of variables relating to power unit 10 and/or a vehicle associated therewith.
- one or more engine performance maps relating a fueling amount, ignition timing, power output, engine speed, boost pressure, engine temperature, an air/fuel ratio, and/or other known parameters may be stored within the memory of controller 28 .
- Each of these maps may be in the form of tables, graphs, and/or equations and include a compilation of data collected from lab and/or field operation of power unit 10 .
- Controller 28 may reference one or more of these maps in order to estimate production of an exhaust constituent of power unit 10 for a given operating condition of power unit 10 .
- the estimated production of exhaust constituent from power unit 10 in combination with the exhaust constituent concentration measured by sensor 26 may be used to indicate the conversion efficiency across first catalyst 22 .
- the concentration of the exhaust constituent downstream from second catalyst 24 may be predicted as a function of the estimated constituent production of power unit 10 .
- the conversion efficiency of catalyst 22 may be calculated by comparing the exhaust constituent concentration measured upstream from catalyst 22 to the concentration measured downstream from catalyst 22 .
- a second sensor 30 may be disposed at a location upstream from catalyst 22 for providing a dynamic exhaust constituent concentration measurement at the location upstream from catalyst 22 .
- second sensor 30 may generate a second signal indicative of the concentration of an exhaust constituent as expelled directly from power unit 10 .
- Second sensor 30 may be in communication with controller 28 .
- Controller 28 may determine the concentration of the exhaust constituent downstream of second catalyst 24 based on signals from both sensor 26 and sensor 30 . For example, the concentrations of NOx both downstream and upstream from catalyst 22 may be determined as a function of both signals from sensors 26 and 30 , respectively.
- the relative change in concentration across first catalyst 22 may be used to approximate the conversion efficiency of catalyst 22 .
- the concentration of the exhaust constituent downstream from second catalyst 24 may be accurately predicted as a function of the concentration measured by sensor 30 .
- the estimated change in exhaust constituent concentration across second catalyst 24 may be used to reliably predict the exhaust constituent concentration downstream from second catalyst 24 .
- the disclosed exhaust system may be applicable to any combustion-type device such as, for example, an engine, a furnace, or any other device known in the art wherein it is desirable to measure the concentration of pollutant exhaust constituents.
- the disclosed exhaust system may be a simple, inexpensive and compact solution for accurately estimating the concentration of NOx within an engine's exhaust flow, even when the concentration of NOx is lower than that detectable by known NOx sensors.
- fuel may be injected into the combustion chambers of power unit 10 , mixed with the air therein, and combusted by power unit 10 to produce a mechanical work output and an exhaust flow of hot gases.
- the exhaust flow may contain a complex mixture of air pollutants composed of gaseous material such as oxides of nitrogen (NOx), as well as solid particulates.
- NOx oxides of nitrogen
- This NOx laden exhaust flow may be directed from the combustion chambers of power unit 10 to housing 20 by exhaust manifold 18 .
- NOx may be removed from the exhaust flow by first catalyst 22 and second catalyst 24 .
- the reduction in exhaust constituent concentration downstream from catalyst 22 may be measured by sensor 26 and communicated to controller 28 . Further reduction in the concentration of the exhaust constituent may occur at second catalyst 24 , downstream from first catalyst 22 .
- Controller 28 may determine the further reduction in exhaust constituent concentration downstream from sensor 26 based on the previously measured reduction in concentration.
- the first stage of concentration reduction at first catalyst 22 may be measured to involve removal of about 50% of the constituent from the exhaust flow. If second catalyst 24 is identical to first catalyst 22 , the second stage of concentration reduction may be approximated to involve removal of about 50% of the remaining constituent from the already reduced exhaust flow. According to such an exemplary embodiment, a concentration of the exhaust constituent may be reduced from, for example, 120 parts per million (ppm) to 60 ppm by first catalyst 22 (assuming 50% conversion efficiency). If second catalyst 24 is substantially identical to first catalyst 22 , an additional 50% reduction in exhaust constituent concentration may be used to estimate an exhaust constituent concentration of 30 ppm downstream from second catalyst 24 .
- ppm parts per million
- the concentration of NOx downstream from second catalyst 24 may be estimated as a function of the measured NOx concentration between first catalyst 22 and second catalyst 24 , as well as the assumed conversion efficiency of second catalyst 24 based on its similarity to first catalyst 22 .
- the conversion efficiency of catalyst 22 may be calculated or predicted by one of several methods.
- the conversion efficiency across catalyst 22 may be calculated by comparing the estimated production of the constituent by power unit 10 to the constituent concentration measured between catalysts 22 and 24 .
- the constituent production of power unit 10 may be estimated as a function of variables relating to power unit 10 and/or a vehicle associated therewith.
- the conversion efficiency of catalyst 22 may be calculated by comparing the exhaust constituent concentration measured upstream from catalyst 22 to the concentration measured downstream from catalyst 22 .
- a second sensor 30 may be disposed at a location upstream from catalyst 22 for providing a dynamic exhaust constituent concentration measurement at the location upstream from catalyst 22 .
- the net reduction in constituent concentration may be calculated as a function of both the constituent concentration measured between catalysts 22 and 24 , as well as the amount of further constituent concentration reduction as approximated by dynamic calculation of catalyst 22 conversion efficiency.
- the constituent concentration downstream from second catalyst 24 may be estimated as a function of a conversion efficiency prediction and a measurement of the constituent concentration before it reaches undetectable levels, that is, before the second stage reduction. Accordingly, the disclosed power system and exhaust system may obviate the need for developing highly sophisticated and expensive NOx or other exhaust constituent detectors. Moreover, because each stage of exhaust constituent reduction is performed by an identical catalyst component, the characteristics of the second catalyst and its associated effects may be accurately and reliably modeled from the characteristics and associated effects of the first catalyst. Finally, because the two catalysts are identical, there are lower associated component costs, storage costs and specification uncertainties.
- the total system conversion may be predicted based on complex catalyst models incorporating parameters, such as, known temperature gradients, reaction properties and/or intermediate sensor measurements.
Abstract
Description
- The present disclosure is directed to an exhaust system and, more particularly, to an exhaust system having a NOx sensor disposed between two separate NOx reducers.
- Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants may be composed of gaseous compounds such as, for example, the oxides of nitrogen (NOx). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of gaseous compounds emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to demonstrate compliance with the regulation of these compounds, manufacturers have incorporated the use of sensors located at the tail pipe opening of the engine.
- Although sensors for measuring the gaseous emissions of engines are currently available in today's market, the sensors may be insufficiently sensitive to measure the low levels of NOx remaining in the engine's exhaust after treatment of the exhaust in compliance with the emission regulations. That is, although current NOx sensors may be capable of detecting low concentrations of NOx, the emission regulation for NOx may be even lower. Therefore, currently available NOx sensors may be of no use in detecting the concentration of NOx emitted to the environment by today's engines.
- One method that may be implemented by engine manufacturers to dynamically determine the amount of NOx emitted to the environment includes measuring the concentration of NOx prior to the regulation required reductions. This measured value may then be used to predict the concentration of NOx in the subsequently treated exhaust. One such method is described in U.S. Pat. No. 6,701,707 (the '707 patent) issued to UPADHYAY et al. on Mar. 9, 2004. Specifically, the '707 patent discloses an exhaust emission control system that utilizes an upstream oxidation catalyst and a downstream SCR catalyst to reduce NOx in a lean exhaust gas environment. The exhaust emission control system includes a first NOx sensor located upstream of the oxidation catalyst, and a second NOx sensor located downstream of the SCR catalyst. During operation of an associated engine, NOx at the tailpipe opening may be measured directly by the second sensor. In order to detect degradation of the system, the output and sensitivity of the first NOx sensor is used to estimate the NOx concentration downstream of the SCR catalyst. If the estimated NOx concentration is greater than the measured NOx concentration, a routine indicates degradation of the system.
- Although the exhaust emission control system of the '707 patent may suitably estimate a NOx concentration downstream of the SCR catalyst based on an upstream measurement, the accuracy of the system may be limited. Specifically, without a dynamic indication of the SCR catalyst's effectiveness, there may be no way to determine how much of the upstream NOx is being removed. It may be possible for the SCR catalyst to remove less than or more than an assumed removal amount, thereby negatively affecting the accuracy of the routine.
- The exhaust system of the present disclosure solves one or more of the problems set forth above.
- One aspect of the present disclosure is directed to an exhaust system. The exhaust system may include a housing connected to receive a flow of exhaust. The exhaust system may also include a first catalyst disposed within the housing to reduce the concentration of an exhaust constituent, and a second catalyst disposed within the housing downstream of the first catalyst to further reduce the concentration of the exhaust constituent. The exhaust system may further include a sensor disposed between the first and second catalysts to generate a signal indicative of the concentration of the exhaust constituent at the location between the first and second catalysts. The exhaust system may additionally include a controller in communication with the sensor to receive the signal. The controller may determine, based on the received signal, the concentration of the exhaust constituent at a location downstream of the second catalyst.
- Another aspect of the present disclosure is directed to a method of determining the concentration of an exhaust constituent. The method may include receiving a flow of exhaust, and reducing the concentration of the exhaust constituent within the flow of exhaust. The method may also include measuring the reduced concentration of the exhaust constituent, and further reducing the concentration of the exhaust constituent within the flow of exhaust. The method may further include determining the further reduced concentration of the exhaust constituent based on the measured reduced concentration.
-
FIG. 1 is a schematic and diagrammatic illustration of an exemplary disclosed power unit and exhaust system. -
FIG. 1 illustrates a power system including apower unit 10 and anexhaust system 12. In one embodiment, the power system may be associated with a mobile vehicle such as a passenger vehicle, a vocational vehicle, a farming vehicle or a construction vehicle. Alternatively, the power system may be associated with a stationary machine such as an industrial power generator or a furnace. - For the purposes of this disclosure,
power unit 10 is depicted and described as a four-stroke diesel engine. One skilled in the art will recognize, however, thatpower unit 10 may be any other type of internal combustion engine such as, for example, a gasoline engine, a gaseous fuel-powered engine, a 2-stroke engine or a turbine engine.Power unit 10 may include anengine block 14 that at least partially defines a plurality of combustion chambers (not shown). In the illustrated embodiment,power unit 10 includes four combustion chambers. However, it is contemplated thatpower unit 10 may include a greater or lesser number of combustion chambers and that the combustion chambers may be disposed in an “in-line” configuration, a “V” configuration, or any other suitable configuration. - As also shown in
FIG. 1 ,power unit 10 may include acrankshaft 16 that is rotatably disposed inengine block 14. A connecting rod (not shown) may connect a plurality of pistons (not shown) tocrankshaft 16 so that a sliding motion of each piston within each respective combustion chamber results in a rotation ofcrankshaft 16. Similarly, a rotation ofcrankshaft 16 may result in a sliding motion of the pistons. Rotation ofcrankshaft 16 may function as output frompower unit 10 for effecting a desired work such as rotation of a generator or rotation of one or more drive axles of an associated vehicle. -
Exhaust system 12 may include anexhaust manifold 18 having exhaust passageways, each passageway being in fluid communication with an associated combustion chamber ofpower unit 10.Exhaust manifold 18 may expel exhaust flow away frompower unit 10 towards ahousing 20 located downstream fromexhaust manifold 18. -
Housing 20 ofexhaust system 12 may be a cylindrical or tubular conduit for directing exhaust gasses and particulates away frompower unit 10 for processing by various emission controlling devices. In one embodiment,exhaust manifold 18 may be integral withhousing 20 of the exhaust system. For example, an exhaust manifold and housing may be integrally stamped or forged from metal. Alternatively,exhaust manifold 18 may be secured to housing 20 by one or more fasteners (e.g. rivets, nuts and bolts, etc.) or by deformation (e.g. hemming).Housing 20 may also constitute structural support for the various emission controlling devices of the system. - The emission controlling devices of
exhaust system 12 may include afirst catalyst 22 and asecond catalyst 24 located downstream fromfirst catalyst 22 for reducing the concentration of a constituent within the exhaust frompower unit 10.Second catalyst 24 may be incorporated so as to further reduce the concentration of the exhaust constituent beyond that achieved byfirst catalyst 22. Both catalysts may be disposed across the cylindrical width (i.e., cross section) ofhousing 20. Furthermore,catalysts exhaust system 12 may include other components such as, for example, a turbine, an exhaust gas recirculation system, a particulate filter, or any other exhaust system component known in the art. - In one exemplary embodiment of the present disclosure,
catalysts catalysts catalysts first catalyst 22 may be a first stage of NOx reduction capable of effecting a first reduction in NOx concentration.Second catalyst 24 may be a second stage of NOx reduction capable of effecting a second reduction in NOx concentration. In one embodiment, the concentration of NOx downstream fromsecond catalyst 24 may be too low for detection by known NOx detection devices and methods. Thus, it may be possible that nitrogen oxides are only sufficiently concentrated for detection in the location downstream fromfirst catalyst 22 and upstream from second catalyst 24 (i.e., betweencatalysts 22 and 24). - As illustrated in
FIG. 1 , asensor 26 may be disposed betweenfirst catalyst 22 andsecond catalyst 24. In particular,sensor 26 may detect a concentration of an exhaust constituent which, in one example, is an oxide of nitrogen. Acontroller 28 may be disposed in communication withsensor 26. Various circuits may be associated withcontroller 28 such as, for example, power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other appropriate circuitry. Moreover, becausesensor 26 may be in communication withcontroller 28 by either wired or wireless transmission,controller 28 may be disposed in a location remote fromhousing 20, if desired. - In the event that it may be desirable to accurately predict the concentration of an exhaust constituent downstream from
catalyst 24 based on the conversion efficiency ofcatalyst 22, several embodiments of the present disclosure may provide a reliable model. For example,catalysts catalysts - In a simplified example, if
first catalyst 22 is known to remove 50% of NOx from the exhaust directly expelled frompower unit 10,second catalyst 24, having similar properties as the first, may be expected to remove 50% of the NOx from the exhaust downstream fromfirst catalyst 22. In this implementation, a net conversion of 75% would result (50% of the original exhaust constituents from the first stage; 25% of the original exhaust constituents from the second stage). - Assuming that
catalyst 24 can be expected to remove the same proportion of exhaust constituent from the flow as can catalyst 22 (e.g., whencatalysts catalyst 24 based on information fromsensor 26 combined with an estimated or calculated conversion efficiency ofcatalyst 22. Specifically, the concentration downstream fromcatalyst 24 may be approximated as the concentration resulting from the effect ofcatalyst 22 acting on the exhaust flow as measured atsensor 26. The concentration downstream fromcatalyst 24 may be determined according to Eq. 1 below. -
- Alternatively, even in situations where the conversion efficiency of the
second catalyst 24 is different than the conversion efficiency of thefirst catalyst 22, the total system conversion may be predicted based on complex catalyst models incorporating parameters, such as, known temperature gradients, reaction properties and/or intermediate sensor measurements. Various embodiments for estimating or measuring the conversion efficiency ofcatalyst 22, and therefore ofcatalyst 24, are contemplated by the present disclosure; however, several exemplary embodiments are recited below for the purpose of aiding the reader in understanding the concepts herein. - According to one embodiment of the present disclosure, the conversion efficiency of
catalyst 22 may be calculated by comparing the expected production of exhaust constituent frompower unit 10 to the concentration measured bysensor 26. Estimated production of the exhaust constituent frompower unit 10 may be accomplished by one or more controllers, includingcontroller 28, as a function of variables relating topower unit 10 and/or a vehicle associated therewith. - For example, one or more engine performance maps relating a fueling amount, ignition timing, power output, engine speed, boost pressure, engine temperature, an air/fuel ratio, and/or other known parameters may be stored within the memory of
controller 28. Each of these maps may be in the form of tables, graphs, and/or equations and include a compilation of data collected from lab and/or field operation ofpower unit 10.Controller 28 may reference one or more of these maps in order to estimate production of an exhaust constituent ofpower unit 10 for a given operating condition ofpower unit 10. - Therefore, the estimated production of exhaust constituent from
power unit 10 in combination with the exhaust constituent concentration measured bysensor 26 may be used to indicate the conversion efficiency acrossfirst catalyst 22. To the extent that the conversion efficiency ofcatalyst 24 may be assumed to be substantially equivalent to the above calculated conversion efficiency ofcatalyst 22, the concentration of the exhaust constituent downstream fromsecond catalyst 24 may be predicted as a function of the estimated constituent production ofpower unit 10. - In another exemplary embodiment of the present disclosure, the conversion efficiency of
catalyst 22 may be calculated by comparing the exhaust constituent concentration measured upstream fromcatalyst 22 to the concentration measured downstream fromcatalyst 22. In this implementation, asecond sensor 30 may be disposed at a location upstream fromcatalyst 22 for providing a dynamic exhaust constituent concentration measurement at the location upstream fromcatalyst 22. - According to this embodiment,
second sensor 30 may generate a second signal indicative of the concentration of an exhaust constituent as expelled directly frompower unit 10.Second sensor 30 may be in communication withcontroller 28.Controller 28 may determine the concentration of the exhaust constituent downstream ofsecond catalyst 24 based on signals from bothsensor 26 andsensor 30. For example, the concentrations of NOx both downstream and upstream fromcatalyst 22 may be determined as a function of both signals fromsensors - Therefore, the relative change in concentration across
first catalyst 22, as measured bysensors catalyst 22. To the extent that the conversion efficiency ofcatalyst 24 may be assumed to be substantially equivalent to the above calculated conversion efficiency ofcatalyst 22, the concentration of the exhaust constituent downstream fromsecond catalyst 24 may be accurately predicted as a function of the concentration measured bysensor 30. - Accordingly, the estimated change in exhaust constituent concentration across
second catalyst 24, as applied to the concentration measurement generated bysensor 26, may be used to reliably predict the exhaust constituent concentration downstream fromsecond catalyst 24. - The disclosed exhaust system may be applicable to any combustion-type device such as, for example, an engine, a furnace, or any other device known in the art wherein it is desirable to measure the concentration of pollutant exhaust constituents. In fact, the disclosed exhaust system may be a simple, inexpensive and compact solution for accurately estimating the concentration of NOx within an engine's exhaust flow, even when the concentration of NOx is lower than that detectable by known NOx sensors. The operation of
power unit 10 andexhaust system 12 will now be explained. - Referring to
FIG. 1 , fuel may be injected into the combustion chambers ofpower unit 10, mixed with the air therein, and combusted bypower unit 10 to produce a mechanical work output and an exhaust flow of hot gases. The exhaust flow may contain a complex mixture of air pollutants composed of gaseous material such as oxides of nitrogen (NOx), as well as solid particulates. This NOx laden exhaust flow may be directed from the combustion chambers ofpower unit 10 tohousing 20 byexhaust manifold 18. NOx may be removed from the exhaust flow byfirst catalyst 22 andsecond catalyst 24. The reduction in exhaust constituent concentration downstream fromcatalyst 22 may be measured bysensor 26 and communicated tocontroller 28. Further reduction in the concentration of the exhaust constituent may occur atsecond catalyst 24, downstream fromfirst catalyst 22.Controller 28 may determine the further reduction in exhaust constituent concentration downstream fromsensor 26 based on the previously measured reduction in concentration. - In the event that a statutorily regulated NOx exhaust concentration is lower than that which is detectable by existing NOx sensors, use of substantially identical NOx reducers along with predictions of estimated NOx production and NOx reduction may be leveraged to obviate the need for sufficiently sensitive NOx sensors. Alternatively, it may be desirable to incorporate this implementation of NOx measurement, even if the regulated level of NOx concentration is high enough for detection by either presently known or future NOx sensors. For example, this implementation may be advantageous in reducing the cost of monitoring NOx concentration, for increasing measurement accuracy, and for incorporation as an after-market NOx measuring system. Moreover, because the NOx sensor is shielded from heat, particulates and other foreign materials by the upstream catalyst, the reliability and/or lifetime of the NOx sensor is increased.
- In one exemplary embodiment, the first stage of concentration reduction at
first catalyst 22 may be measured to involve removal of about 50% of the constituent from the exhaust flow. Ifsecond catalyst 24 is identical tofirst catalyst 22, the second stage of concentration reduction may be approximated to involve removal of about 50% of the remaining constituent from the already reduced exhaust flow. According to such an exemplary embodiment, a concentration of the exhaust constituent may be reduced from, for example, 120 parts per million (ppm) to 60 ppm by first catalyst 22 (assuming 50% conversion efficiency). Ifsecond catalyst 24 is substantially identical tofirst catalyst 22, an additional 50% reduction in exhaust constituent concentration may be used to estimate an exhaust constituent concentration of 30 ppm downstream fromsecond catalyst 24. Thus, the concentration of NOx downstream fromsecond catalyst 24 may be estimated as a function of the measured NOx concentration betweenfirst catalyst 22 andsecond catalyst 24, as well as the assumed conversion efficiency ofsecond catalyst 24 based on its similarity tofirst catalyst 22. The conversion efficiency ofcatalyst 22 may be calculated or predicted by one of several methods. - According to one embodiment of the present disclosure, the conversion efficiency across
catalyst 22 may be calculated by comparing the estimated production of the constituent bypower unit 10 to the constituent concentration measured betweencatalysts power unit 10 may be estimated as a function of variables relating topower unit 10 and/or a vehicle associated therewith. - Alternatively, the conversion efficiency of
catalyst 22 may be calculated by comparing the exhaust constituent concentration measured upstream fromcatalyst 22 to the concentration measured downstream fromcatalyst 22. In this implementation, asecond sensor 30 may be disposed at a location upstream fromcatalyst 22 for providing a dynamic exhaust constituent concentration measurement at the location upstream fromcatalyst 22. - By equating the proportion of the constituent reduced by
catalyst 22 to the proportion of the constituent reduced bycatalyst 24, a reliable estimate of the effect ofcatalyst 24 may be provided. Accordingly, the net reduction in constituent concentration may be calculated as a function of both the constituent concentration measured betweencatalysts catalyst 22 conversion efficiency. - Because the conversion efficiency and therefore the amount of concentration reduction across
second catalyst 24 may be modeled based on that offirst catalyst 22, the constituent concentration downstream fromsecond catalyst 24 may be estimated as a function of a conversion efficiency prediction and a measurement of the constituent concentration before it reaches undetectable levels, that is, before the second stage reduction. Accordingly, the disclosed power system and exhaust system may obviate the need for developing highly sophisticated and expensive NOx or other exhaust constituent detectors. Moreover, because each stage of exhaust constituent reduction is performed by an identical catalyst component, the characteristics of the second catalyst and its associated effects may be accurately and reliably modeled from the characteristics and associated effects of the first catalyst. Finally, because the two catalysts are identical, there are lower associated component costs, storage costs and specification uncertainties. - Alternatively, even in situations where the conversion efficiency of the
second catalyst 24 is different than the conversion efficiency of thefirst catalyst 22, the total system conversion may be predicted based on complex catalyst models incorporating parameters, such as, known temperature gradients, reaction properties and/or intermediate sensor measurements. - It will be apparent to those skilled in the art that various modifications and variations can be made to the exhaust system of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the exhaust system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.
Claims (20)
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
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US11/589,832 US20080098725A1 (en) | 2006-10-31 | 2006-10-31 | Exhaust system having mid-reducer NOx sensor |
PCT/US2007/021909 WO2008054627A1 (en) | 2006-10-31 | 2007-10-12 | Exhaust system having mid-reducer nox sensor |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
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US11/589,832 US20080098725A1 (en) | 2006-10-31 | 2006-10-31 | Exhaust system having mid-reducer NOx sensor |
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US20080098725A1 true US20080098725A1 (en) | 2008-05-01 |
Family
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Family Applications (1)
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US11/589,832 Abandoned US20080098725A1 (en) | 2006-10-31 | 2006-10-31 | Exhaust system having mid-reducer NOx sensor |
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WO (1) | WO2008054627A1 (en) |
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