US20130047583A1 - Aftertreatment system - Google Patents
Aftertreatment system Download PDFInfo
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- US20130047583A1 US20130047583A1 US13/222,723 US201113222723A US2013047583A1 US 20130047583 A1 US20130047583 A1 US 20130047583A1 US 201113222723 A US201113222723 A US 201113222723A US 2013047583 A1 US2013047583 A1 US 2013047583A1
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- catalyst
- exhaust
- aftertreatment system
- scr catalyst
- scr
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Classifications
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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
- F01N3/20—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 specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
- F01N3/2066—Selective catalytic reduction [SCR]
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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
- F01N13/0093—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 of the same type
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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
- 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
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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
- F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
- F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
- F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
- F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
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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
- F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
- F01N3/106—Auxiliary oxidation catalysts
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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
- F01N3/24—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 constructional aspects of converting apparatus
- F01N3/28—Construction of catalytic reactors
- F01N3/2892—Exhaust flow directors or the like, e.g. upstream of catalytic device
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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
- Y02T10/12—Improving ICE efficiencies
Definitions
- the present disclosure is directed to an aftertreatment system and, more particularly, to an aftertreatment system including a selective catalytic reduction catalyst.
- 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 are composed of particulates and gaseous compounds including, among other things, oxides of nitrogen (NO X ).
- NO X oxides of nitrogen Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amounts of particulates and NO X emitted to the atmosphere by an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
- SCR selective catalytic reduction
- a reductant most commonly urea ((NH 2 ) 2 CO) or a water/urea solution
- NH 3 ammonia
- Engine manufacturers implementing the SCR process typically include an oxidation catalyst upstream of the SCR substrate to assist in altering the composition of the exhaust gas stream before it passes to the SCR substrate.
- Such oxidation catalysts typically include a porous substrate made from, coated with, or otherwise including a catalyzing material such as palladium, platinum, vanadium, and/or other precious metals. Such materials facilitate a conversion of NO to NO 2 , thereby increasing the ratio of NO 2 to NO upstream of the SCR substrate.
- the elevated level of NO 2 provided by the oxidation catalyst may assist in both improving NOx conversion over the SCR catalyst and oxidizing soot particles that collect in a particulate filter.
- the substrate used for SCR purposes may need to be very large to help ensure it has enough surface area or effective volume to absorb appropriate amounts of the ammonia required for sufficient catalytic reduction of NO X .
- These large substrates can be expensive and require significant amounts of space within the exhaust system.
- the substrate must be placed far enough downstream of the injection location for the urea solution to have time to decompose into ammonia and to evenly distribute within the exhaust flow for the efficient reduction of NO X . Due to the size of the SCR substrate and the required spacing between the substrate and the injector, packaging an exhaust system utilizing such components can be difficult, and packaging an exhaust system utilizing an oxidation catalyst upstream of the SCR substrate can be even more difficult. In addition, due to the precious metals used to manufacture oxidation catalysts, utilizing an oxidation catalyst can significantly increase the cost of the exhaust system.
- An exemplary SCR-equipped system for use with a combustion engine is disclosed in JP Patent Publication No. 2008/274,851 (the '851 publication) of Makoto published on Nov. 13, 2008.
- This system includes an exhaust gas purification device having a gas accumulation canister, a separate dispersion canister, and a mixing pipe connected between the gas accumulation and gas dispersion canisters.
- a particulate filter and an oxidation catalyst are disposed in the gas accumulation canister, while an SCR catalyst and ammonia reduction catalyst are disposed within the gas dispersion canister.
- a urea injector is located in the mixing pipe, upstream of the SCR catalyst.
- the exhaust system of the '851 patent may be configured to treat exhaust gases, such a system may be problematic in many aftertreatment applications.
- the multiple canisters and catalysts used in the '851 system may increase the cost, packaging complexity, and an overall size of the system.
- the aftertreatment systems of the present disclosure solve one or more of the problems set forth above and/or other problems of the prior art.
- an aftertreatment system for an internal combustion engine includes a treatment device having a combined particulate filter and SCR catalyst.
- the combined particulate filter and SCR catalyst treats uncatalyzed exhaust from the internal combustion engine including between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr.
- an aftertreatment system for an internal combustion engine includes a treatment device having a first SCR catalyst disposed on a particulate filter substrate, and a second SCR catalyst downstream of the first SCR catalyst.
- the first SCR catalyst treats uncatalyzed exhaust from the internal combustion engine.
- the treatment device is characterized by a NOx conversion efficiency greater than approximately 95 percent.
- an exhaust treatment method includes generating exhaust with an internal combustion engine, the exhaust including between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr.
- the method also includes directing the exhaust uncatalyzed from the internal combustion engine to a combined particulate filter and SCR catalyst.
- the method further includes catalytically reducing NOx in the exhaust with the combined particulate filter and SCR catalyst, the combined particulate filter and SCR catalyst forming a first treated exhaust.
- FIG. 1 is a partial schematic view of an aftertreatment system according to an exemplary embodiment of the present disclosure.
- the aftertreatment system 10 may include one or more treatment devices 28 connected to an internal combustion engine 22 , such as, for example, a diesel engine.
- the engine 22 may include an exhaust line 23 directing exhaust generated by the engine 22 to the treatment device 28 .
- the engine 22 may also include a turbocharger 18 connected to the exhaust line 23 , and a compressor 20 driven by the turbocharger 18 via one or more rotating shafts 19 .
- the treatment device 28 may be fluidly connected to an outlet of the turbocharger 18 .
- the treatment device 28 may include one or more canisters 12 fabricated from a one or more corrosion-resistant materials. Such materials may include, for example, stainless steel or other like metals. In further exemplary embodiments, such materials may be treated, coated, and/or other wise provided with corrosion protection.
- the canister 12 includes a single inlet 14 and a single outlet 16 . It is contemplated, however, that the treatment device 28 may include any number of inlets and outlets, as desired.
- the treatment device 28 may include one or more filters, catalysts, and/or combinations thereof to assist in treating components of the flow of exhaust gas 44 .
- the treatment device 28 may include a combined diesel particulate filter and SCR catalyst 30 (hereinafter referred to as “CDS catalyst 30 ”) disposed within the canister 12 .
- the CDS catalyst 30 may include a single filtration media that is configured to form both particulate trapping and SCR functions.
- the CDS catalyst 30 may alternatively be replaced with a separate and dedicated particulate filter and SCR catalyst, if desired.
- the separate filter and SCR catalyst may be disposed within the canister 12 or, alternatively, may be disposed within separate canisters.
- the treatment device 28 may include an additional catalyst 32 disposed within the canister 12 downstream of the CDS catalyst 30 .
- the additional catalyst 32 may be, for example, an SCR catalyst.
- the additional catalyst 32 may include an upstream region 32 A that functions as an SCR catalyst, and a downstream region 32 B that functions as a cleanup catalyst such as, for example, a diesel oxidation catalyst or an ammonia oxidation catalyst.
- the additional catalyst 32 may be a dedicated cleanup catalyst (e.g., catalyst 32 may not provide SCR functionality).
- the CDS catalyst 30 may be configured to perform particulate trapping functions.
- CDS catalyst 30 may include filtration media configured to remove particulate matter from an exhaust flow.
- the filtration media of the CDS catalyst 30 may embody a generally cylindrical deep-bed type of filtration media configured to accumulate particulate matter throughout a thickness thereof in a substantially homogenous manner.
- the filtration media may include a low density material having a flow entrance side and a flow exit side, and may be formed through a sintering process from metallic or ceramic particles. It is contemplated that the filtration media may alternatively embody a surface type of filtration media fabricated from metallic or ceramic foam, a wire mesh, or any other suitable material.
- the CDS catalyst 30 may also be configured to perform SCR functions.
- the filtration media of CDS catalyst 30 may be fabricated from or otherwise coated with a ceramic material such as titanium oxide, a base metal oxide such as vanadium and tungsten, zeolites, and/or a precious metal.
- a ceramic material such as titanium oxide, a base metal oxide such as vanadium and tungsten, zeolites, and/or a precious metal.
- decomposed reductant entrained within an exhaust flow passing through the CDS catalyst 30 may be absorbed onto the surface of and/or within the filtration media, where the reductant may react with NOx (NO and NO 2 ) in the exhaust gas to form water (H 2 O) and diatomic nitrogen (N 2 ).
- NOx NO and NO 2
- CDS catalyst 30 may perform both particulate trapping and SCR functions throughout the media of CDS catalyst 30 or, alternatively, in serial stages, as desired. If NO 2 levels within the exhaust are sufficiently high, the exothermic reaction between the reductant and the
- the additional catalyst 32 may comprise an upstream region 32 A and a downstream region 32 B.
- a single substrate brick of catalyst 32 may include an upstream region ( 32 A) located proximate and/or adjacent the CDS catalyst 30 .
- the upstream region 32 A may be fabricated from or otherwise coated with a material that absorbs reductant onto its surface or otherwise internalizes reductant for reaction with NOx (NO and NO 2 ) in the exhaust gas passing therethrough. Such a reaction may form water (H 2 O) and diatomic nitrogen (N 2 ).
- the substrate brick of catalyst 32 may include a downstream region ( 32 B) located proximate and/or adjacent the outlet 16 .
- the downstream region 32 B may be disposed adjacent to and downstream of the upstream region 32 A, and may be coated with or otherwise contain a different catalyst than the upstream region 32 A.
- Such catalysts may include an oxidation catalyst configured to oxidize residual reductant in the exhaust.
- an exemplary oxidation catalyst may be, for example, a diesel oxidation catalyst (DOC) or an ammonia oxidation (AMOx) catalyst.
- DOC diesel oxidation catalyst
- AMOx ammonia oxidation
- Such oxidation catalysts may comprise any suitable substrate coated with or otherwise containing a catalyzing material, for example a precious metal, that catalyzes a chemical reaction to alter a composition of exhaust passing through the oxidation catalyst.
- a catalyzing material for example a precious metal
- such an oxidation catalyst may include palladium, platinum, vanadium, or a mixture thereof that facilitates oxidation of residual ammonia gas and/or entrained reductant.
- Such catalysts may also facilitate the oxidation of NO in the exhaust to NO 2 .
- the additional catalyst 32 may alternatively or additionally perform particulate trapping functions (e.g., the additional catalyst 32 may include a particulate trap such as a continuously regenerating technology particulate filter or a catalyzed continuously regenerating technology particulate filter), hydrocarbon oxidation functions, carbon monoxide oxidation functions, and/or other functions known in the art.
- a particulate trap such as a continuously regenerating technology particulate filter or a catalyzed continuously regenerating technology particulate filter
- hydrocarbon oxidation functions e.g., carbon dioxide oxidation functions, and/or other functions known in the art.
- a gap 34 may be maintained at the opposing ends of canister 12 , proximate the inlet 14 and outlet 16 , respectively.
- a gap 34 may also be maintained between the CDS catalyst 30 and the additional catalyst 32 .
- the gaps 34 may act as manifolds that facilitate substantially equal distribution of exhaust across faces of the respective catalysts 30 , 32 disposed within the canister 12 .
- end portions 46 , 48 of the canister 12 enclosing the gaps 34 at the inlet 14 and outlet 16 , respectively may be removably connected to a center portion of canister 12 that encloses the CDS catalyst 30 and the additional catalyst 32 .
- the end portions 46 , 48 may be bolted or latched to the center portion, if desired. With this configuration, the end portions 46 , 48 may be selectively removed for inspection and/or replacement of the various catalysts 30 , 32 .
- One or more removable couplings 26 may be connected to the end portions 46 , 48 to facilitate the selective removal of the treatment device 28 from the aftertreatment system 10 .
- Such couplings 26 may comprise any removable air-tight coupling device known in the art.
- such couplings 26 may comprise one or more clamps, brackets, pieces of flexible tubing, and/or other like devices configured to facilitate a removable connection between the canister 12 and other components of the aftertreatment system 10 .
- the couplings 26 may embody cobra-head type couplings that are capable of bending through an angle of about 90 degrees.
- Such couplings 26 may have an elliptical opening at the canister 12 and a circular opening at an opposite end of the coupling 26 .
- other types of couplings may be utilized, if desired.
- the aftertreatment system 10 may include a mixing tube 24 connected to the inlet 14 via one or more of the couplings 26 described above.
- the aftertreatment system 10 may also include a reductant injector 36 fluidly connected to the mixing tube 24 .
- the reductant injector 36 may be disposed upstream of the treatment device 28 (e.g., within an upstream end of the mixing tube 24 or within one of the coupling 26 ) and configured to inject a reductant into the exhaust flowing through the mixing tube 24 .
- a gaseous or liquid reductant most commonly a water/urea solution, ammonia gas, liquefied anhydrous ammonia, ammonium carbonate, an amine salt, or a hydrocarbon such as diesel fuel, may be sprayed or otherwise advanced by the reductant injector 36 into the exhaust passing through the mixing tube 24 .
- the reductant injector 36 may be disposed at any desired distance upstream of the CDS catalyst 30 to allow the injected reductant sufficient time to mix with exhaust and to sufficiently decompose before entering the CDS catalyst 30 .
- an even distribution of sufficiently decomposed reductant within the exhaust passing through the CDS catalyst 30 may enhance NO X reduction therein.
- the distance between the reductant injector 36 and the inlet 14 of the canister 12 may be based on a flow rate of exhaust passing through aftertreatment system 10 and/or on a cross-sectional area of the mixing tube 24 .
- the distance between the reductant injector 36 and the inlet 14 of the canister 12 may be 2 feet or more.
- a mixer 38 may be disposed within the mixing tube 24 .
- the mixer 38 may include vanes or blades inclined to generate a swirling motion of the exhaust as it flows through the mixing tube 24 .
- the mixer 38 may include a ring extending from internal walls of the mixing tube 24 radially inward a distance toward a longitudinal axis of the mixing tube 24 . Such a ring may be configured to promote exhaust flow turbulence within the mixing tube 24 , thereby assisting in incorporating the reductant into the exhaust.
- the mixer 38 may be disposed upstream or downstream (shown in FIG. 1 ) of the reductant injector 36 .
- the aftertreatment system 10 may also include one or more probes situated to monitor operating characteristics and/or other parameters of the aftertreatment system 10 .
- a first probe 40 may be situated within the gap 34 proximate the inlet 14 upstream of the CDS catalyst 30 .
- a second probe 42 may be situated within the gap 34 proximate the outlet 16 downstream of the additional catalyst 32 .
- first probe 40 may be a temperature probe configured to generate a first signal indicative of a temperature of the exhaust entering CDS catalyst 30 .
- the first signal may be utilized by a controller (not shown) to determine, among other things, an operating temperature and predicted efficiency of the CDS catalyst 30 .
- the second probe 42 may be utilized to detect a constituent of the exhaust exiting catalyst 32 , for example a concentration of NOx or an amount of residual reductant.
- the second probe 42 may generate a second signal indicative of this constituent, and the second signal may be utilized to determine, among other things, an actual effectiveness of the CDS catalyst 30 and/or the additional catalyst 32 . It is contemplated that at least one of the probes 40 , 42 may be configured to monitor other parameters of the aftertreatment system 10 , and may be utilized for other purposes, if desired.
- the aftertreatment system 10 of the present disclosure may be applicable to any engine configuration requiring the treatment of exhaust where component packaging is an important issue. While known aftertreatment systems utilize a DOC catalyst upstream of an SCR catalyst for converting NO to NO 2 , such DOC catalysts are typically disposed in large canisters, and due to the precious metals utilized in DOC catalysts, such catalysts are costly.
- the aftertreatment system 10 of the present disclosure operates without using a DOC catalyst upstream of the treatment device 28 . As a result, the disclosed system 10 takes up less space downstream of the engine 22 , and is less expensive, less complicated, and easier to package on vehicles utilizing the engine 22 than known systems.
- the engine 22 of the present disclosure may be calibrated to generate exhaust having increased NOx levels (thereby increasing the amount of NO 2 in the exhaust) and decreased soot levels.
- the timing of in-cylinder fuel injections may be advanced, the pressure of such injections may be increased, the flow of recirculated exhaust gas into the engine 22 may be reduced or eliminated, and/or the throughput of the compressor 20 and/or the turbocharger 18 may be increased in order to facilitate generating such exhaust.
- the elevated NOx levels resulting from such engine calibration may ensure passive regeneration of the CDS catalyst 30 due to the exothermic reduction reaction at the SCR catalyst contained therein, and may also increase the fuel efficiency of the engine 22 .
- Such NOx levels may be, for example, between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr. In further exemplary embodiments, such NOx levels may be greater than approximately 10 g NOx/kW-hr. Due to such calibration, the engine 22 may generate exhaust having a NO 2 to NO ratio of approximately 1 to 2. In addition, such engine calibration may result in an improvement in fuel efficiency and a reduction in soot production by the engine 22 . The exhaust flow through the aftertreatment system 10 will now be described.
- the engine 22 may generate uncatalyzed exhaust 44 containing a complex mixture of air pollutants including, among other things, NO X and soot.
- the exhaust 44 may pass from the engine 22 , through the turbocharger 18 , via the exhaust line 23 .
- the uncatalyzed exhaust 44 may then enter the mixing tube 24 , where reductant may be injected into the exhaust 44 by the reductant injector 36 upstream of mixer 38 .
- the swirl and/or turbulence of the exhaust 44 promoted by mixer 38 may be utilized to entrain and distribute reductant within the exhaust 44 .
- the reductant may continue to homogenize within the uncatalyzed exhaust 44 , and the reductant may begin to decompose into ammonia.
- the length and location of the mixing tube 24 together with the mixer 38 , may promote decomposition of the injected reductant.
- the uncatalyzed exhaust 44 may be directed from the mixing tube 24 into the canister 12 via the inlet 14 .
- the exhaust 44 may flow from inlet 14 into the gap 34 upstream of CDS catalyst 30 , and due to the change in cross-sectional area and/or volume between the mixing tube 24 and the end portion 46 , the uncatalyzed exhaust 44 may expand upstream of the CDS catalyst 30 .
- Such expansion may facilitate a substantially equal distribution of the exhaust 44 across a face of the CDS catalyst 30 .
- the bulk of the reductant may be decomposed, thereby facilitating NOx reduction within the CDS catalyst 30 and the additional catalyst 32 .
- the CDS catalyst 30 may treat the uncatalyzed exhaust 44 as the exhaust 44 passes through the CDS catalyst 30 .
- particulate matter may be removed from the exhaust 44 , and NOx within the exhaust 44 may react with the reductant at the SCR catalyst.
- the exhaust 44 may be catalytically reduced by the SCR catalyst to form water and diatomic nitrogen.
- the CDS catalyst 30 may form a first treated exhaust from the uncatalyzed exhaust 44 .
- Such a first treated exhaust may be, for example, exhaust that has undergone a catalytic reduction process in which NO has been formed from NO 2 .
- the first treated exhaust may exit the CDS catalyst 30 and enter the additional catalyst 32 , where catalytic reduction of NOx contained in the first treated exhaust may occur and residual reductant carried by the first treated exhaust may be absorbed.
- the additional catalyst 32 comprises an SCR catalyst
- the SCR catalyst may catalytically reduce the first treated exhaust.
- the SCR catalyst of the additional catalyst 32 may form a second treated exhaust from the first treated exhaust.
- Such a second treated exhaust may be, for example, treated exhaust that has undergone an additional catalytic reduction process in which NO has been formed from NO 2 .
- the treatment device 28 may be characterized by a NOx conversion efficiency greater than approximately 95 percent.
- NOx conversion efficiency means the percentage of NOx contained by the exhaust that is catalytically reduced to N 2 upon passing through the SCR catalysts or the treatment device 28 .
- the NOx conversion efficiency values discussed herein are associated with treatment devices at or near the beginning of their useful life.
- the CDS catalyst 30 may be characterized by a NOx conversion efficiency of approximately 90 percent or less.
- the CDS catalyst 30 may provide such a NOx conversion efficiency while producing advantageous levels of backpressure upstream of the treatment device 28 and while having a size suitable for packaging in the aftertreatment system 10 of the engine 22 .
- the SCR catalyst of the additional catalyst 32 may be characterized by a NOx conversion efficiency of at least approximately 50 percent.
- the SCR catalyst of the additional catalyst 32 may be characterized by a NOx conversion efficiency of between approximately 50 percent and approximately 80 percent.
- the respective NOx conversion efficiencies of the SCR catalysts may combine to result in a NOx conversion efficiency of the treatment device 28 greater than approximately 95 percent.
- Such NOx conversion efficiency levels may be required to comply with exhaust emission standards.
- exemplary treatment device embodiments including a CDS catalyst 30 having a NOx conversion efficiency of approximately 90 percent or less, and an additional catalyst 32 having an SCR catalyst with a NOx conversion efficiency of between approximately 50 percent and approximately 80 percent, may be capable of oxidizing a greater amount of soot per unit volume of exhaust than, for example, a treatment device including a single CDS catalyst having a NOx conversion efficiency of approximately 95 percent. It is understood that, for example, passive soot regeneration may improve inversely with NOx conversion to N 2 . This relationship is a result of NO 2 being consumed by the passive soot oxidation reaction and the NOx reduction reactions taking place at the one or more SCR catalysts of the treatment device 28 .
- lower levels of NOx reduction at the CDS catalyst 30 may allow for higher levels of soot reduction on the substrate of the CDS catalyst 30 .
- Such NOx reduction may be furthered and/or completed at the additional catalyst 32 in order to achieve a NOx conversion efficiency of the treatment device greater than approximately 95 percent.
- the second treated exhaust may pass from the SCR catalyst of the additional catalyst 32 to the downstream oxidation catalyst of the additional catalyst 32 .
- the oxidation catalyst may catalytically oxidize the second treated exhaust.
- residual reductant entrained within the second treated exhaust may be oxidized.
- the exhaust may pass through the gap 34 proximate the end portion 48 , and may be discharged to the atmosphere or other downstream exhaust system components via the outlet 16 .
- the aftertreatment system 10 may be simple, compact, and relatively inexpensive.
- the aftertreatment system 10 may be simple and compact because it may utilize only a single canister having catalysts that provide multiple functions.
- the CDS catalyst 30 may provide both particulate trapping and NOx reduction functionality, while the additional catalyst 32 may provide NOx reduction and oxidation functionality.
- the simplicity of the aftertreatment system 10 may result in a lower cost solution to exhaust aftertreatment and may require less packaging space than known systems.
Abstract
An aftertreatment system for an internal combustion engine includes a treatment device having a combined particulate filter and SCR catalyst. The combined particulate filter and SCR catalyst treats uncatalyzed exhaust from the internal combustion engine including between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr.
Description
- The present disclosure is directed to an aftertreatment system and, more particularly, to an aftertreatment system including a selective catalytic reduction catalyst.
- 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 are composed of particulates and gaseous compounds including, among other things, oxides of nitrogen (NOX). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amounts of particulates and NOX emitted to the atmosphere by an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
- In order to comply with the regulation of particulates and NOX, some engine manufacturers have implemented a strategy called selective catalytic reduction (SCR). SCR is a process where a reductant, most commonly urea ((NH2)2CO) or a water/urea solution, is selectively injected into the exhaust gas stream of an engine and absorbed onto a downstream substrate. The injected urea solution decomposes into ammonia (NH3), which reacts with NOX in the exhaust gas to form water (H2O) and diatomic nitrogen (N2). Engine manufacturers implementing the SCR process typically include an oxidation catalyst upstream of the SCR substrate to assist in altering the composition of the exhaust gas stream before it passes to the SCR substrate. Such oxidation catalysts typically include a porous substrate made from, coated with, or otherwise including a catalyzing material such as palladium, platinum, vanadium, and/or other precious metals. Such materials facilitate a conversion of NO to NO2, thereby increasing the ratio of NO2 to NO upstream of the SCR substrate. The elevated level of NO2 provided by the oxidation catalyst may assist in both improving NOx conversion over the SCR catalyst and oxidizing soot particles that collect in a particulate filter.
- In some applications, the substrate used for SCR purposes may need to be very large to help ensure it has enough surface area or effective volume to absorb appropriate amounts of the ammonia required for sufficient catalytic reduction of NOX. These large substrates can be expensive and require significant amounts of space within the exhaust system. In addition, the substrate must be placed far enough downstream of the injection location for the urea solution to have time to decompose into ammonia and to evenly distribute within the exhaust flow for the efficient reduction of NOX. Due to the size of the SCR substrate and the required spacing between the substrate and the injector, packaging an exhaust system utilizing such components can be difficult, and packaging an exhaust system utilizing an oxidation catalyst upstream of the SCR substrate can be even more difficult. In addition, due to the precious metals used to manufacture oxidation catalysts, utilizing an oxidation catalyst can significantly increase the cost of the exhaust system.
- An exemplary SCR-equipped system for use with a combustion engine is disclosed in JP Patent Publication No. 2008/274,851 (the '851 publication) of Makoto published on Nov. 13, 2008. This system includes an exhaust gas purification device having a gas accumulation canister, a separate dispersion canister, and a mixing pipe connected between the gas accumulation and gas dispersion canisters. A particulate filter and an oxidation catalyst are disposed in the gas accumulation canister, while an SCR catalyst and ammonia reduction catalyst are disposed within the gas dispersion canister. A urea injector is located in the mixing pipe, upstream of the SCR catalyst.
- Although the exhaust system of the '851 patent may be configured to treat exhaust gases, such a system may be problematic in many aftertreatment applications. In particular, the multiple canisters and catalysts used in the '851 system may increase the cost, packaging complexity, and an overall size of the system.
- The aftertreatment systems of the present disclosure solve one or more of the problems set forth above and/or other problems of the prior art.
- In an exemplary embodiment of the present disclosure, an aftertreatment system for an internal combustion engine includes a treatment device having a combined particulate filter and SCR catalyst. The combined particulate filter and SCR catalyst treats uncatalyzed exhaust from the internal combustion engine including between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr.
- In another exemplary embodiment of the present disclosure, an aftertreatment system for an internal combustion engine includes a treatment device having a first SCR catalyst disposed on a particulate filter substrate, and a second SCR catalyst downstream of the first SCR catalyst. The first SCR catalyst treats uncatalyzed exhaust from the internal combustion engine. The treatment device is characterized by a NOx conversion efficiency greater than approximately 95 percent.
- In an additional exemplary embodiment of the present disclosure, an exhaust treatment method includes generating exhaust with an internal combustion engine, the exhaust including between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr. The method also includes directing the exhaust uncatalyzed from the internal combustion engine to a combined particulate filter and SCR catalyst. The method further includes catalytically reducing NOx in the exhaust with the combined particulate filter and SCR catalyst, the combined particulate filter and SCR catalyst forming a first treated exhaust.
-
FIG. 1 is a partial schematic view of an aftertreatment system according to an exemplary embodiment of the present disclosure. - An
exemplary aftertreatment system 10 is shown inFIG. 1 . Theaftertreatment system 10 may include one ormore treatment devices 28 connected to aninternal combustion engine 22, such as, for example, a diesel engine. Theengine 22 may include anexhaust line 23 directing exhaust generated by theengine 22 to thetreatment device 28. Theengine 22 may also include aturbocharger 18 connected to theexhaust line 23, and acompressor 20 driven by theturbocharger 18 via one or morerotating shafts 19. In such an embodiment, thetreatment device 28 may be fluidly connected to an outlet of theturbocharger 18. - The
treatment device 28 may include one ormore canisters 12 fabricated from a one or more corrosion-resistant materials. Such materials may include, for example, stainless steel or other like metals. In further exemplary embodiments, such materials may be treated, coated, and/or other wise provided with corrosion protection. In the embodiment shown inFIG. 1 , thecanister 12 includes asingle inlet 14 and asingle outlet 16. It is contemplated, however, that thetreatment device 28 may include any number of inlets and outlets, as desired. - As shown in
FIG. 1 , thetreatment device 28 may include one or more filters, catalysts, and/or combinations thereof to assist in treating components of the flow ofexhaust gas 44. For example, thetreatment device 28 may include a combined diesel particulate filter and SCR catalyst 30 (hereinafter referred to as “CDS catalyst 30”) disposed within thecanister 12. As will be described in greater detail below, theCDS catalyst 30 may include a single filtration media that is configured to form both particulate trapping and SCR functions. In additional exemplary embodiments, theCDS catalyst 30 may alternatively be replaced with a separate and dedicated particulate filter and SCR catalyst, if desired. The separate filter and SCR catalyst may be disposed within thecanister 12 or, alternatively, may be disposed within separate canisters. - In further embodiments, the
treatment device 28 may include anadditional catalyst 32 disposed within thecanister 12 downstream of theCDS catalyst 30. Theadditional catalyst 32 may be, for example, an SCR catalyst. In additional exemplary embodiments, theadditional catalyst 32 may include anupstream region 32A that functions as an SCR catalyst, and adownstream region 32B that functions as a cleanup catalyst such as, for example, a diesel oxidation catalyst or an ammonia oxidation catalyst. In an alternative embodiment, theadditional catalyst 32 may be a dedicated cleanup catalyst (e.g.,catalyst 32 may not provide SCR functionality). - The
CDS catalyst 30 may be configured to perform particulate trapping functions. In particular,CDS catalyst 30 may include filtration media configured to remove particulate matter from an exhaust flow. In one embodiment, the filtration media of theCDS catalyst 30 may embody a generally cylindrical deep-bed type of filtration media configured to accumulate particulate matter throughout a thickness thereof in a substantially homogenous manner. The filtration media may include a low density material having a flow entrance side and a flow exit side, and may be formed through a sintering process from metallic or ceramic particles. It is contemplated that the filtration media may alternatively embody a surface type of filtration media fabricated from metallic or ceramic foam, a wire mesh, or any other suitable material. - The
CDS catalyst 30 may also be configured to perform SCR functions. Specifically, the filtration media ofCDS catalyst 30 may be fabricated from or otherwise coated with a ceramic material such as titanium oxide, a base metal oxide such as vanadium and tungsten, zeolites, and/or a precious metal. With this composition, decomposed reductant entrained within an exhaust flow passing through theCDS catalyst 30 may be absorbed onto the surface of and/or within the filtration media, where the reductant may react with NOx (NO and NO2) in the exhaust gas to form water (H2O) and diatomic nitrogen (N2). It is contemplated thatCDS catalyst 30 may perform both particulate trapping and SCR functions throughout the media ofCDS catalyst 30 or, alternatively, in serial stages, as desired. If NO2 levels within the exhaust are sufficiently high, the exothermic reaction between the reductant and the NOx may assist in passively regenerating theCDS catalyst 30. - As described above, the
additional catalyst 32 may comprise anupstream region 32A and adownstream region 32B. In particular, a single substrate brick ofcatalyst 32 may include an upstream region (32A) located proximate and/or adjacent theCDS catalyst 30. Theupstream region 32A may be fabricated from or otherwise coated with a material that absorbs reductant onto its surface or otherwise internalizes reductant for reaction with NOx (NO and NO2) in the exhaust gas passing therethrough. Such a reaction may form water (H2O) and diatomic nitrogen (N2). Similarly, the substrate brick ofcatalyst 32 may include a downstream region (32B) located proximate and/or adjacent theoutlet 16. Thedownstream region 32B may be disposed adjacent to and downstream of theupstream region 32A, and may be coated with or otherwise contain a different catalyst than theupstream region 32A. Such catalysts may include an oxidation catalyst configured to oxidize residual reductant in the exhaust. - In exemplary embodiments in which the
downstream region 32B of theadditional catalyst 32 comprises an oxidation catalyst, such an exemplary oxidation catalyst may be, for example, a diesel oxidation catalyst (DOC) or an ammonia oxidation (AMOx) catalyst. Such oxidation catalysts may comprise any suitable substrate coated with or otherwise containing a catalyzing material, for example a precious metal, that catalyzes a chemical reaction to alter a composition of exhaust passing through the oxidation catalyst. In one embodiment, such an oxidation catalyst may include palladium, platinum, vanadium, or a mixture thereof that facilitates oxidation of residual ammonia gas and/or entrained reductant. Such catalysts may also facilitate the oxidation of NO in the exhaust to NO2. In another embodiment, theadditional catalyst 32 may alternatively or additionally perform particulate trapping functions (e.g., theadditional catalyst 32 may include a particulate trap such as a continuously regenerating technology particulate filter or a catalyzed continuously regenerating technology particulate filter), hydrocarbon oxidation functions, carbon monoxide oxidation functions, and/or other functions known in the art. - As shown in
FIG. 1 , agap 34 may be maintained at the opposing ends ofcanister 12, proximate theinlet 14 andoutlet 16, respectively. Agap 34 may also be maintained between theCDS catalyst 30 and theadditional catalyst 32. Thegaps 34 may act as manifolds that facilitate substantially equal distribution of exhaust across faces of therespective catalysts canister 12. - It is contemplated that access to the
catalysts aftertreatment system 10 may be helpful in some situations. Thus, in exemplary embodiments,end portions canister 12 enclosing thegaps 34 at theinlet 14 andoutlet 16, respectively, may be removably connected to a center portion ofcanister 12 that encloses theCDS catalyst 30 and theadditional catalyst 32. For example, theend portions end portions various catalysts - One or more
removable couplings 26 may be connected to theend portions treatment device 28 from theaftertreatment system 10.Such couplings 26 may comprise any removable air-tight coupling device known in the art. In an exemplary embodiment,such couplings 26 may comprise one or more clamps, brackets, pieces of flexible tubing, and/or other like devices configured to facilitate a removable connection between thecanister 12 and other components of theaftertreatment system 10. In further exemplary embodiments, thecouplings 26 may embody cobra-head type couplings that are capable of bending through an angle of about 90 degrees.Such couplings 26 may have an elliptical opening at thecanister 12 and a circular opening at an opposite end of thecoupling 26. In still further embodiments, other types of couplings may be utilized, if desired. - As shown in
FIG. 1 , theaftertreatment system 10 may include a mixingtube 24 connected to theinlet 14 via one or more of thecouplings 26 described above. Theaftertreatment system 10 may also include areductant injector 36 fluidly connected to the mixingtube 24. In exemplary embodiments, thereductant injector 36 may be disposed upstream of the treatment device 28 (e.g., within an upstream end of the mixingtube 24 or within one of the coupling 26) and configured to inject a reductant into the exhaust flowing through the mixingtube 24. A gaseous or liquid reductant, most commonly a water/urea solution, ammonia gas, liquefied anhydrous ammonia, ammonium carbonate, an amine salt, or a hydrocarbon such as diesel fuel, may be sprayed or otherwise advanced by thereductant injector 36 into the exhaust passing through the mixingtube 24. For example, thereductant injector 36 may be disposed at any desired distance upstream of theCDS catalyst 30 to allow the injected reductant sufficient time to mix with exhaust and to sufficiently decompose before entering theCDS catalyst 30. In exemplary embodiments, an even distribution of sufficiently decomposed reductant within the exhaust passing through theCDS catalyst 30 may enhance NOX reduction therein. The distance between thereductant injector 36 and theinlet 14 of the canister 12 (e.g., the length of the mixing tube 24) may be based on a flow rate of exhaust passing throughaftertreatment system 10 and/or on a cross-sectional area of the mixingtube 24. In some exemplary embodiments, the distance between thereductant injector 36 and theinlet 14 of thecanister 12 may be 2 feet or more. - To enhance incorporation of the reductant with the exhaust, a
mixer 38 may be disposed within the mixingtube 24. In an exemplary embodiment, themixer 38 may include vanes or blades inclined to generate a swirling motion of the exhaust as it flows through the mixingtube 24. In another exemplary embodiment, themixer 38 may include a ring extending from internal walls of the mixingtube 24 radially inward a distance toward a longitudinal axis of the mixingtube 24. Such a ring may be configured to promote exhaust flow turbulence within the mixingtube 24, thereby assisting in incorporating the reductant into the exhaust. In either embodiment, themixer 38 may be disposed upstream or downstream (shown inFIG. 1 ) of thereductant injector 36. - The
aftertreatment system 10 may also include one or more probes situated to monitor operating characteristics and/or other parameters of theaftertreatment system 10. For example, afirst probe 40 may be situated within thegap 34 proximate theinlet 14 upstream of theCDS catalyst 30. In addition, asecond probe 42 may be situated within thegap 34 proximate theoutlet 16 downstream of theadditional catalyst 32. In one embodiment,first probe 40 may be a temperature probe configured to generate a first signal indicative of a temperature of the exhaust enteringCDS catalyst 30. The first signal may be utilized by a controller (not shown) to determine, among other things, an operating temperature and predicted efficiency of theCDS catalyst 30. Thesecond probe 42 may be utilized to detect a constituent of theexhaust exiting catalyst 32, for example a concentration of NOx or an amount of residual reductant. Thesecond probe 42 may generate a second signal indicative of this constituent, and the second signal may be utilized to determine, among other things, an actual effectiveness of theCDS catalyst 30 and/or theadditional catalyst 32. It is contemplated that at least one of theprobes aftertreatment system 10, and may be utilized for other purposes, if desired. - The
aftertreatment system 10 of the present disclosure may be applicable to any engine configuration requiring the treatment of exhaust where component packaging is an important issue. While known aftertreatment systems utilize a DOC catalyst upstream of an SCR catalyst for converting NO to NO2, such DOC catalysts are typically disposed in large canisters, and due to the precious metals utilized in DOC catalysts, such catalysts are costly. Theaftertreatment system 10 of the present disclosure, on the other hand, operates without using a DOC catalyst upstream of thetreatment device 28. As a result, the disclosedsystem 10 takes up less space downstream of theengine 22, and is less expensive, less complicated, and easier to package on vehicles utilizing theengine 22 than known systems. - To compensate for the conversion of NO to NO2 provided by the upstream DOC catalyst of known aftertreatment systems, the
engine 22 of the present disclosure may be calibrated to generate exhaust having increased NOx levels (thereby increasing the amount of NO2 in the exhaust) and decreased soot levels. For example, the timing of in-cylinder fuel injections may be advanced, the pressure of such injections may be increased, the flow of recirculated exhaust gas into theengine 22 may be reduced or eliminated, and/or the throughput of thecompressor 20 and/or theturbocharger 18 may be increased in order to facilitate generating such exhaust. The elevated NOx levels resulting from such engine calibration may ensure passive regeneration of theCDS catalyst 30 due to the exothermic reduction reaction at the SCR catalyst contained therein, and may also increase the fuel efficiency of theengine 22. Such NOx levels may be, for example, between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr. In further exemplary embodiments, such NOx levels may be greater than approximately 10 g NOx/kW-hr. Due to such calibration, theengine 22 may generate exhaust having a NO2 to NO ratio of approximately 1 to 2. In addition, such engine calibration may result in an improvement in fuel efficiency and a reduction in soot production by theengine 22. The exhaust flow through theaftertreatment system 10 will now be described. - Referring to
FIG. 1 , theengine 22 may generateuncatalyzed exhaust 44 containing a complex mixture of air pollutants including, among other things, NOX and soot. Theexhaust 44 may pass from theengine 22, through theturbocharger 18, via theexhaust line 23. Theuncatalyzed exhaust 44 may then enter the mixingtube 24, where reductant may be injected into theexhaust 44 by thereductant injector 36 upstream ofmixer 38. The swirl and/or turbulence of theexhaust 44 promoted bymixer 38 may be utilized to entrain and distribute reductant within theexhaust 44. As the swirling and/or turbulent flow of exhaust and reductant passes along the length of the mixingtube 24, the reductant may continue to homogenize within theuncatalyzed exhaust 44, and the reductant may begin to decompose into ammonia. Thus, the length and location of the mixingtube 24, together with themixer 38, may promote decomposition of the injected reductant. - The
uncatalyzed exhaust 44 may be directed from the mixingtube 24 into thecanister 12 via theinlet 14. Theexhaust 44 may flow frominlet 14 into thegap 34 upstream ofCDS catalyst 30, and due to the change in cross-sectional area and/or volume between the mixingtube 24 and theend portion 46, theuncatalyzed exhaust 44 may expand upstream of theCDS catalyst 30. Such expansion may facilitate a substantially equal distribution of theexhaust 44 across a face of theCDS catalyst 30. By the time theexhaust 44 reaches theCDS catalyst 30, the bulk of the reductant may be decomposed, thereby facilitating NOx reduction within theCDS catalyst 30 and theadditional catalyst 32. - The
CDS catalyst 30 may treat theuncatalyzed exhaust 44 as theexhaust 44 passes through theCDS catalyst 30. For example, particulate matter may be removed from theexhaust 44, and NOx within theexhaust 44 may react with the reductant at the SCR catalyst. In particular, theexhaust 44 may be catalytically reduced by the SCR catalyst to form water and diatomic nitrogen. As a result, theCDS catalyst 30 may form a first treated exhaust from theuncatalyzed exhaust 44. Such a first treated exhaust may be, for example, exhaust that has undergone a catalytic reduction process in which NO has been formed from NO2. The first treated exhaust may exit theCDS catalyst 30 and enter theadditional catalyst 32, where catalytic reduction of NOx contained in the first treated exhaust may occur and residual reductant carried by the first treated exhaust may be absorbed. For example, in embodiments in which theadditional catalyst 32 comprises an SCR catalyst, the SCR catalyst may catalytically reduce the first treated exhaust. As a result, the SCR catalyst of theadditional catalyst 32 may form a second treated exhaust from the first treated exhaust. Such a second treated exhaust may be, for example, treated exhaust that has undergone an additional catalytic reduction process in which NO has been formed from NO2. - In exemplary embodiments, the
treatment device 28 may be characterized by a NOx conversion efficiency greater than approximately 95 percent. As used herein with regard to the SCR catalysts of thetreatment device 28, the term “NOx conversion efficiency” means the percentage of NOx contained by the exhaust that is catalytically reduced to N2 upon passing through the SCR catalysts or thetreatment device 28. Further, unless otherwise specified, the NOx conversion efficiency values discussed herein are associated with treatment devices at or near the beginning of their useful life. In exemplary embodiments, theCDS catalyst 30 may be characterized by a NOx conversion efficiency of approximately 90 percent or less. TheCDS catalyst 30 may provide such a NOx conversion efficiency while producing advantageous levels of backpressure upstream of thetreatment device 28 and while having a size suitable for packaging in theaftertreatment system 10 of theengine 22. In such exemplary embodiments, the SCR catalyst of theadditional catalyst 32 may be characterized by a NOx conversion efficiency of at least approximately 50 percent. In further exemplary embodiments, the SCR catalyst of theadditional catalyst 32 may be characterized by a NOx conversion efficiency of between approximately 50 percent and approximately 80 percent. Thus, the respective NOx conversion efficiencies of the SCR catalysts may combine to result in a NOx conversion efficiency of thetreatment device 28 greater than approximately 95 percent. Such NOx conversion efficiency levels may be required to comply with exhaust emission standards. - In addition, exemplary treatment device embodiments including a
CDS catalyst 30 having a NOx conversion efficiency of approximately 90 percent or less, and anadditional catalyst 32 having an SCR catalyst with a NOx conversion efficiency of between approximately 50 percent and approximately 80 percent, may be capable of oxidizing a greater amount of soot per unit volume of exhaust than, for example, a treatment device including a single CDS catalyst having a NOx conversion efficiency of approximately 95 percent. It is understood that, for example, passive soot regeneration may improve inversely with NOx conversion to N2. This relationship is a result of NO2 being consumed by the passive soot oxidation reaction and the NOx reduction reactions taking place at the one or more SCR catalysts of thetreatment device 28. For example, lower levels of NOx reduction at theCDS catalyst 30 may allow for higher levels of soot reduction on the substrate of theCDS catalyst 30. Such NOx reduction may be furthered and/or completed at theadditional catalyst 32 in order to achieve a NOx conversion efficiency of the treatment device greater than approximately 95 percent. - In embodiments in which the
additional catalyst 32 further comprises one of a DOC catalyst and an AMOx catalyst, the second treated exhaust may pass from the SCR catalyst of theadditional catalyst 32 to the downstream oxidation catalyst of theadditional catalyst 32. The oxidation catalyst may catalytically oxidize the second treated exhaust. In particular, as the second treated exhaust passes through the oxidation catalyst, residual reductant entrained within the second treated exhaust may be oxidized. After treatment within theadditional catalyst 32, the exhaust may pass through thegap 34 proximate theend portion 48, and may be discharged to the atmosphere or other downstream exhaust system components via theoutlet 16. - The
aftertreatment system 10 may be simple, compact, and relatively inexpensive. For example, theaftertreatment system 10 may be simple and compact because it may utilize only a single canister having catalysts that provide multiple functions. In addition, theCDS catalyst 30 may provide both particulate trapping and NOx reduction functionality, while theadditional catalyst 32 may provide NOx reduction and oxidation functionality. The simplicity of theaftertreatment system 10 may result in a lower cost solution to exhaust aftertreatment and may require less packaging space than known systems. - It will be apparent to those skilled in the art that various modifications and variations can be made to the
aftertreatment system 10 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 aftertreatment 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 equivalent.
Claims (20)
1. An aftertreatment system for an internal combustion engine, comprising:
a treatment device including a combined particulate filter and SCR catalyst, the combined particulate filter and SCR catalyst treating uncatalyzed exhaust from the internal combustion engine comprising between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr.
2. The aftertreatment system of claim 1 , further comprising a reductant injector disposed upstream of the treatment device and configured to inject a reductant into the uncatalyzed exhaust.
3. The aftertreatment system of claim 2 , further comprising a mixing tube connected to an inlet of the treatment device, the reductant injector being fluidly connected to the mixing tube.
4. The aftertreatment system of claim 3 , further comprising a mixer disposed within the mixing tube.
5. The aftertreatment system of claim 1 , further comprising an additional catalyst disposed downstream of the combined particulate filter and SCR catalyst.
6. The aftertreatment system of claim 5 , wherein the additional catalyst comprises an SCR catalyst.
7. The aftertreatment system of claim 6 , wherein the additional catalyst further comprises one of an ammonia oxidation catalyst and a diesel oxidation catalyst.
8. The aftertreatment system of claim 5 , wherein the combined particulate filter and SCR catalyst and the additional catalyst are disposed within a single canister.
9. An aftertreatment system for an internal combustion engine, comprising:
a treatment device including a first SCR catalyst disposed on a particulate filter substrate, and a second SCR catalyst downstream of the first SCR catalyst, the first SCR catalyst treating uncatalyzed exhaust from the internal combustion engine, wherein the treatment device is characterized by a NOx conversion efficiency greater than approximately 95 percent.
10. The aftertreatment system of claim 9 , wherein the first and second SCR catalysts are disposed within a single canister, the canister including at least one removable end portion configured to provide access to at least one of the first and second SCR catalysts.
11. The aftertreatment system of claim 9 , wherein and the first SCR catalyst is characterized by a NOx conversion efficiency of approximately 90 percent or less.
12. The aftertreatment system of claim 9 , wherein the second SCR catalyst is characterized by a NOx conversion efficiency between approximately 50 percent and approximately 80 percent.
13. The aftertreatment system of claim 9 , further comprising one of an ammonia oxidation catalyst and a diesel oxidation catalyst downstream of the second SCR catalyst.
14. The aftertreatment system of claim 9 , further comprising a substrate having an upstream region and a downstream region, the second SCR catalyst being disposed on the upstream region of the substrate, and one of an ammonia oxidation catalyst and a diesel oxidation catalyst being disposed on the downstream region of the substrate.
15. The aftertreatment system of claim 9 , further comprising a mixing tube connected to an inlet of the treatment device, and a reductant injector fluidly connected to the mixing tube upstream of the inlet.
16. The aftertreatment system of claim 15 , further comprising a mixer disposed within the mixing tube downstream of the reductant injector and upstream of the inlet.
17. An exhaust treatment method, comprising:
generating exhaust with an internal combustion engine, the exhaust comprising between approximately 7 g NOx/kW-hr and approximately 10 g NOx/kW-hr;
directing the exhaust uncatalyzed from the internal combustion engine to a combined particulate filter and SCR catalyst; and
catalytically reducing NOx in the exhaust with the combined particulate filter and SCR catalyst, the combined particulate filter and SCR catalyst forming a first treated exhaust.
18. The method of claim 17 , further comprising catalytically reducing the first treated exhaust with an additional SCR catalyst disposed downstream of the combined particulate filter and SCR catalyst, the additional SCR catalyst forming a second treated exhaust.
19. The method of claim 18 , further comprising catalytically oxidizing the second treated exhaust with one of an ammonia oxidation catalyst and a diesel oxidation catalyst.
20. The method of claim 17 , wherein the uncatalyzed exhaust generated by the engine is characterized by a NO2 to NO ratio of approximately 1 to 2.
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CN2012103165581A CN102966413A (en) | 2011-08-31 | 2012-08-30 | Nachbehandlungssystem |
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US20160356200A1 (en) * | 2013-11-15 | 2016-12-08 | Robert Bosch Gmbh | Exhaust gas post treatment device |
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US10022672B2 (en) | 2014-03-13 | 2018-07-17 | Umicore Ag & Co. Kg | Catalyst system for gasoline combustion engines, having three-way catalysts and SCR catalyst |
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US10443465B2 (en) * | 2014-08-12 | 2019-10-15 | Jaguar Land Rover Limited | Engine exhaust system and control system for an engine exhaust system |
US20180163600A1 (en) * | 2016-12-13 | 2018-06-14 | Caterpillar Inc. | Compact hydrocarbon dosing and mixing system and method |
US20190383189A1 (en) * | 2018-06-13 | 2019-12-19 | Deere & Company | Exhaust gas treatment system with improved low temperature performance |
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