US20080155972A1

US20080155972A1 - Exhaust treatment system

Info

Publication number: US20080155972A1
Application number: US11/646,514
Authority: US
Inventors: James Joshua Driscoll; Praveen Shivshankar Chavannavar; Cho Y. Liang; Thomas Edward Paulson; Michael L. Woods
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 2006-12-28
Filing date: 2006-12-28
Publication date: 2008-07-03
Also published as: WO2008082467A1

Abstract

An exhaust gas treatment system of an internal combustion engine includes a selective catalytic reduction catalyst fluidly connected to the internal combustion engine, an oxidation catalyst fluidly connected upstream of the selective catalytic reduction catalyst, and a particulate filter fluidly connected upstream of the selective catalytic reduction catalyst. The exhaust gas treatment system further includes a recirculation line configured to direct a portion of an exhaust flow of the internal combustion engine toward an inlet of the engine.

Description

TECHNICAL FIELD

The present disclosure relates generally to an exhaust treatment system and, more particularly, to an exhaust treatment system having a selective catalytic reduction (“SCR”) catalyst.

BACKGROUND

Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may emit an exhaust flow containing a complex mixture of solid, liquid, and gaseous components. For example, the gaseous components of the exhaust flow may include compounds such as nitrous oxides (“NOx”) and CO, and the solid and/or liquid components of the flow may include soluble organic fraction, soot, and/or unburned hydrocarbons. Together, the soluble organic fraction, soot, and unburned hydrocarbons emitted by internal combustion engines is generally referred to as particulate matter.
The Environmental Protection Agency regulates the emissions released into the atmosphere from such engines based on the type, size, and/or class of engine. These exhaust emission standards continue to become more stringent, and engine manufacturers have begun to use catalytic exhaust treatment systems to comply with these regulations. In such systems, a reductant, such as urea or ammonia, may be injected into the exhaust gas upstream of an SCR catalyst, and the catalyst materials within the SCR catalyst may reduce NOx carried by the exhaust gas in the presence of the reductant. In addition, a particulate filter may capture a portion of the particulate matter carried by the exhaust.
The effectiveness of an SCR catalyst is based on its ability to convert NOx carried in the exhaust gas to N₂and other gaseous species such as O₂and H₂O. Maintaining the SCR catalyst within a desired temperature range and providing it with a flow of exhaust gas having approximately a one-to-one ratio of NO to NO₂are both factors that assist in maximizing the NOx conversion rate of the SCR catalyst. The exhaust gas leaving the engine, however, typically contains a much higher percentage of NO than NO₂. Thus, exhaust treatment systems often include an oxidation catalyst disposed upstream of the SCR catalyst to assist in oxidizing the NO present in the exhaust gas. Oxidizing the NO may increase the amount of NO₂present in the exhaust gas entering the SCR catalyst and may facilitate achieving a one-to-one ratio of NO to NO₂.
An exhaust treatment system for controlling the NOx and particulate matter emissions of an internal combustion engine is illustrated in U.S. Pat. No. 6,928,806 (“the '806 patent”). Specifically, the '806 patent discloses an oxidation catalyst, an SCR catalyst coupled downstream of the oxidation catalyst, and a particulate filter coupled downstream of the SCR catalyst.
Although the system disclosed in the '806 patent may assist in removing particulate matter and reducing the NOx content of the exhaust gas, the SCR catalyst of the '806 patent is disposed upstream of the particulate filter and is, therefore, particularly susceptible to fouling from, for example, particulate matter carried in the exhaust flow.
In addition, the system of the '806 patent fails to take advantage of the benefits associated with the use of exhaust gas recirculation (“EGR”) to direct at least a portion of the exhaust gas into the intake air supply of the engine. The use of EGR may assist in reducing the concentration of oxygen within the cylinder and increasing the specific heat of the air/fuel mixture, thereby reducing the amount of NOx produced by the engine. The use of EGR in combination with SCR catalyst technology may also assist in improving the fuel economy of the engine system and may increase the amount of NO₂produced by the engine relative to NO. The system of the '806 patent is not configured to direct any portion of the exhaust gas back to the intake of the engine to reduce NOx formation, improve fuel economy, or increase the quantity of NO₂produced by the engine.
The disclosed exhaust treatment system is directed to overcoming one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one embodiment of the present disclosure, an exhaust gas treatment system of an internal combustion engine includes an SCR catalyst fluidly connected to the internal combustion engine, an oxidation catalyst fluidly connected upstream of the SCR catalyst, and a particulate filter fluidly connected upstream of the SCR catalyst. The exhaust gas treatment system further includes a recirculation line configured to direct a portion of an exhaust flow of the internal combustion engine toward an inlet of the engine.
In another embodiment of the present disclosure, an exhaust gas treatment system of an internal combustion engine includes an SCR catalyst fluidly connected to the internal combustion engine, an oxidation catalyst fluidly connected upstream of the SCR catalyst, and a particulate filter fluidly connected upstream of the SCR catalyst. The system further includes a low pressure exhaust gas recirculation loop.
In yet another embodiment of the present disclosure, a method of an exhaust flow of an internal combustion engine includes filtering the exhaust flow with a particulate filter, oxidizing the exhaust flow with an oxidation catalyst, catalytically reducing NOx contained in the filtered oxidized flow with an SCR catalyst, and directing a portion of the exhaust flow to an inlet of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an engine having an exhaust treatment system according to an exemplary embodiment of the present disclosure.

FIG. 2 is a diagrammatic illustration of an engine having an exhaust treatment system according to another exemplary embodiment of the present disclosure.

FIG. 3 is a diagrammatic illustration of an engine having an exhaust treatment system according to still another exemplary embodiment of the present disclosure.

FIG. 4 is a diagrammatic illustration of an engine having an exhaust treatment system according to yet another exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates a power source 12 having an exemplary exhaust treatment system 10. The power source 12 may include an engine, such as, for example, a diesel engine, a gasoline engine, a natural gas engine, or any other engine apparent to one skilled in the art. The power source 12 may alternatively include another source of power, such as a furnace or any other source of power known in the art.
The exhaust treatment system 10 may be configured to direct exhaust gases out of the power source 12, treat the gases, and introduce a portion of the treated gases into an inlet 21 of the power source 12. The exhaust treatment system 10 may include, for example, an NOx trap 35, an energy extraction assembly 22, a regeneration device 20, an oxidation catalyst 18, a filter 16, an SCR catalyst 19, and/or a clean-up catalyst 33. The exhaust treatment system 10 may further include a recirculation line 24 fluidly connected between the filter 16 and the SCR catalyst 19. Alternatively, the recirculation line 24 may be fluidly connected between the oxidation catalyst 18 and the filter 16, between the SCR catalyst 19 and the clean-up catalyst 33, or downstream of the clean-up catalyst 33. The exhaust treatment system 10 may still further include a flow cooler 26, a flow sensor 28, a mixing valve 30, a compression assembly 32, and an aftercooler 34.
A flow of exhaust produced by the power source 12 may be directed from the power source 12 to components of the exhaust treatment system 10 by flow lines 15. It is understood that the power source 12 may include one or more combustion chambers (not shown) fluidly connected to an exhaust manifold. In such an exemplary embodiment, the flow lines 15 may be configured to transmit a flow of exhaust from the combustion chambers to the components of the exhaust treatment system 10 via the exhaust manifold. The flow lines 15 may include pipes, tubing, and/or other exhaust flow carrying means known in the art. The flow lines 15 may be made of alloys of steel, aluminum, and/or other materials known in the art. The flow lines 15 may be rigid or flexible, and may be capable of safely carrying high temperature exhaust flows, such as flows having temperatures in excess of 700 degrees Celsius (approximately 1,292 degrees Fahrenheit).
The NOx trap 35 may be any type of NOx adsorber or absorber known in the art, such as, for example, a lean NOx trap, and may contain catalyst materials capable of absorbing, adsorbing, and/or otherwise storing oxides of nitrogen. Such catalyst materials may include, for example, aluminum, platinum, rhodium, barium, cerium, and/or alkali metals, alkaline-earth metals, rare-earth metals, or combinations thereof. The catalyst materials may be situated within the NOx trap 35 so as to maximize the surface area available for NOx absorption, and the catalyst materials may be located on a substrate of the NOx trap 35. Substrate configurations may include, for example, a honeycomb, mesh, or any other configuration known in the art. The NOx trap 35 may be capable of storing NOx over a wide range of exhaust temperatures and may be configured to store NOx at relatively low exhaust temperatures, such as, for example, below 200 degrees Celsius. Such exhaust temperatures may occur during power source start-up or in low-load operating conditions. For example, it may be difficult for the SCR catalyst 19 to reduce or otherwise convert NOx at such low temperatures; thus, the NOx trap 35 may be particularly helpful in meeting government NOx emissions regulations at low temperatures. The NOx trap 35 may, however, store NOx more effectively at elevated exhaust temperatures. For example, the ability of the NOx trap 35 to adsorb NOx may be maximized when the exhaust gas temperatures between approximately 300 degrees Celsius and approximately 400 degrees Celsius. Accordingly, in an exemplary embodiment, the NOx trap 35 may be fluidly connected proximate an outlet 43 of the power source 12 such that the exhaust gases entering the NOx trap 35 may undergo relatively little convective cooling. It is understood that the outlet 43 may be an outlet of an exhaust manifold of the power source 12.
The energy extraction assembly 22 may be configured to extract energy from, and reduce the pressure of, the exhaust gases produced by the power source 12. The energy extraction assembly 22 may be fluidly connected to the power source 12 by one or more flow lines 15 and may reduce the pressure of the exhaust gases to any desired pressure. The energy extraction assembly 22 may include one or more turbines 14, diffusers, or other energy extraction devices known in the art. In an exemplary embodiment wherein the energy extraction assembly 22 includes more than one turbine 14, the multiple turbines 14 may be disposed in parallel or in series relationship. It is also understood that in an embodiment of the present disclosure, the energy extraction assembly 22 may alternatively be omitted. In such an embodiment, the power source 12 may include, for example, a naturally aspirated engine. As will be described in greater detail below, a component of the energy extraction assembly 22 may be configured in certain embodiments to drive a component of the compression assembly 32. It is understood that, in an exemplary embodiment, the energy extraction assembly 22 may include a heat exchanger and/or other components required to form and/or facilitate, for example, a Rankine cycle or a Brayton cycle.
In an exemplary embodiment, the regeneration device 20 of the exhaust treatment system 10 may be fluidly connected to the energy extraction assembly 22 via flow line 15 and may be configured to increase the temperature of an entire flow of exhaust produced by the power source 12 to a desired temperature. The desired temperature may be, for example, a regeneration temperature of the filter 16. Accordingly, the regeneration device 20 may be configured to assist in actively regenerating the filter 16. Alternatively, in another exemplary embodiment, the regeneration device 20 may be configured to increase the temperature of only a portion of the entire flow of exhaust produced by the power source 12. The regeneration device 20 may include, for example, a fuel injector and an ignitor (not shown), heat coils (not shown), and/or other heat sources known in the art. Such heat sources may be disposed within the regeneration device 20 and may be configured to assist in increasing the temperature of the flow of exhaust through convection, combustion, and/or other methods.
As shown in FIG. 1, the filter 16 of the exhaust treatment system 10 may be connected downstream of the regeneration device 20. The filter 16 may have a housing 25 including an inlet 23 and an outlet 31. In an exemplary embodiment, the regeneration device 20 may be disposed outside of the housing 25 and may be fluidly connected to the inlet 23 of the housing 25. In another exemplary embodiment, the regeneration device 20 may be disposed within the housing 25 of the filter 16. The filter 16 may be any type of filter known in the art capable of extracting matter from a flow of gas. In an embodiment of the present disclosure, the filter 16 may be, for example, a particulate matter filter positioned to extract particulates from an exhaust flow of the power source 12. The filter 16 may include, for example, a ceramic substrate, a metallic mesh, foam, or any other porous material known in the art. These materials may form, for example, a honeycomb structure within the housing 25 of the filter 16 to facilitate the removal of particulates. As discussed above, the particulates may be, for example, soluble organic fraction, hydrocarbons, and/or soot.
In an exemplary embodiment of the present disclosure, a portion of the exhaust produced by the combustion process may leak past piston seal rings within a crankcase 45 of the power source 12. This portion of the exhaust, often called “blow-by gases” or simply “blow-by,” may contain one or more of the exhaust gas components discussed above. In addition, because the crankcase 45 is partially filled with lubricating oil being agitated at high temperatures, the blow-by gases may also contain oil droplets and oil vapor. The blow-by gases may build up within the crankcase 45 over time, thereby increasing the pressure within the crankcase 45. In such an embodiment, a ventilation line 42 may be fluidly connected to the crankcase 45 of the power source 12.
The ventilation line 42 may comprise piping, tubing, and/or other exhaust flow carrying means known in the art and may be structurally similar to the flow lines 15 described above. The ventilation line 42 may include, for example, a check valve 44 and/or any other valve assembly known in the art. The check valve 44 may be configured to assist in controllably regulating a flow of fluid through the ventilation line 42. The ventilation line 42 may be configured to direct the blow-by gases from the crankcase 45 to a location upstream of the filter 16, such as, for example, a port 46 of the flow line 15. For example, the ventilation line 42 may assist in directing the portion of exhaust gas from the crankcase 45 to a port 46 disposed upstream of the regeneration device 20. By directing the blow-by gases upstream of the filter 16 and/or the regeneration device 20, the contaminants contained in the blow-by gases may be substantially removed without contaminating the supercharger, turbocharger, or various power source components.
The oxidation catalyst 18 of the exhaust treatment system 10 may be located between the regeneration device 20 and the filter 16, and may contain catalyst materials useful in collecting, absorbing, adsorbing, and/or converting hydrocarbons, carbon monoxide, and/or oxides of nitrogen contained in a flow. Such catalyst materials may include, for example, aluminum, platinum, palladium, rhodium, barium, cerium, and/or alkali metals, alkaline-earth metals, rare-earth metals, or combinations thereof. The catalyst materials may be situated within the oxidation catalyst 18 so as to maximize the surface area available for the collection and/or conversion of the flow components discussed above. The oxidation catalyst 18 may include, for example, a ceramic substrate, a metallic mesh, foam, or any other porous material known in the art, and the catalyst materials may be located on, for example, a substrate of the oxidation catalyst 18. The oxidation catalyst 18 may, for example, assist in oxidizing one or more components of the exhaust flow, such as, for example, particulate matter, hydrocarbons, and/or carbon monoxide. The oxidation catalyst 18 may also be configured to oxidize NO contained in the exhaust gas, thereby converting it to NO₂. Thus, the oxidation catalyst 18 may assist in achieving a desired ratio of NO to NO₂upstream of the SCR catalyst 19. As mentioned above, this desired ratio may be, for example, approximately one to one.
As illustrated in FIG. 2, in an additional exemplary embodiment of the present disclosure, a filter 36 of the exhaust treatment system 100 may include catalyst materials useful in collecting, absorbing, adsorbing, and/or converting hydrocarbons, carbon monoxide, and/or oxides of nitrogen contained in a flow. In such an embodiment, the oxidation catalyst 18 (FIG. 1) may be omitted. The catalyst materials may include, for example, any of the catalyst materials discussed above with respect to the oxidation catalyst 18 (FIG. 1). The catalyst materials may be situated within the filter 36 so as to maximize the surface area available for collection and/or conversion. For example, the catalyst materials may be located on a substrate of the filter 36. The catalyst materials may be added to the filter 36 by any conventional means, such as, for example, coating or spraying, and the substrate of the filter 36 may be partially or completely coated with the materials.
In the embodiment shown in FIG. 2, the catalyst materials disposed on the substrate of the filter 36 may assist in passively regenerating the filter 36 during power source operation. As the power source 12 operates, particulates and other components of the power source exhaust may be trapped by the filter substrate. The exhaust flow may reach temperatures in excess of, for example, 300 degrees Celsius during normal operation of the power source 12 (i.e., without operating the power source 12 in a manner so as to increase the temperature of the exhaust by, for example, wastegating or other conventional methods), and the exhaust gas may increase the temperature of at least a portion of the filter substrate through convective heat transfer. At such temperatures, the components of the power source exhaust trapped by the substrate of the filter 36 may begin to react with the catalyst material located on the substrate. In particular, the catalyst material may passively regenerate a portion of the filter 36 by oxidizing particulate matter trapped by the filter substrate as well as carbon monoxide and/or hydrocarbons contained in the exhaust flow. Oxidation may occur at a passive regeneration temperature of the filter 36 in which the catalyst material is hot enough to react with the components of the exhaust flow without additional heat being provided by, for example, the regeneration device 20. Such passive regeneration temperatures may be below the active regeneration temperature of the filter 36.
Although at least a portion of the particulate matter contained within the filter 36 may be oxidized and/or removed therefrom through passive regeneration, it is understood that, as shown in FIG. 2, an exemplary exhaust treatment system 100 of the present disclosure may, nonetheless, include a regeneration device 20. Utilizing a catalyzed filter 36 in conjunction with a regeneration device 20 may assist in increasing the interval between active regenerations. Increasing this interval may reduce the amount of, for example, fuel burned during operation of the power source 12 and, thus, may reduce the cost of operating the machine to which the power source 12 is connected. An exhaust treatment system 100 including both a catalyzed filter 36 and a regeneration device 20 may also enable filter manufacturers to include less catalyst material (such as, for example, precious metals) in the filter 36, thereby reducing the cost of the filter 36 and the overall cost of the exhaust treatment system 100.
Referring again to FIG. 1, the SCR catalyst 19 of the exhaust treatment system 10 may be any selective catalytic reduction catalyst known in the art and may be, for example, a urea-based or an ammonia-based catalyst. The SCR catalyst 19 may be, for example, a vanadium and titanium-type, a platinum-type, or a zeolite-type SCR catalyst, and may include a substrate containing one or more of these metals and configured to assist in reducing NOx. For example, the SCR catalyst 19 may be capable of maintaining the NOx emissions of the exhaust treatment system 10 below approximately 0.2 grams/horsepower-hour, in compliance with future government regulations. The SCR catalyst 19 may have an optimum or peak NOx conversion rate when the ratio of NO to NO₂entering the SCR catalyst 19 is approximately one to one. The SCR catalyst 19 may be most effective at temperatures between approximately 200 degrees Celsius and approximately 500 degrees Celsius. As used herein, the term “conversion rate” is defined as the rate at which NOx is catalytically converted to N₂through a reduction reaction.
As mentioned above, the SCR catalyst 19 may be configured to reduce NOx in the presence of a reductant, such as, for example, urea or ammonia. Accordingly, the exhaust treatment system 10 may include an injector 37, a pump 39, a storage device 41, and/or any other components required to deliver reductant upstream of the SCR catalyst 19 and/or otherwise facilitate NOx reduction. In an exemplary embodiment, the injector 37 may be any type of fluid injector configured to deliver a flow of aqueous reductant. The injector 37 may be configured to at least partially atomize the flow of reductant as it is delivered, thereby facilitating mixing of the reductant with, for example, an exhaust flow of the power source 12. The pump 39 may be configured to draw reductant from the storage device 41 and pressurize the reductant upstream of the injector 37. Although not shown in FIG. 1, it is understood that one or more control valves maybe used in conjunction with the pump 39 to meter the flow of reductant supplied to the injector 37. Moreover, the control valves, pump 39, and/or the injector 37 may be electrically connected to and controlled by a controller (not shown).
As shown in FIG. 1, the clean-up catalyst 33 may be fluidly connected downstream of the SCR catalyst 19. The clean-up catalyst 33 may be configured to capture, store, and/or convert unreacted reductants that may slip past the SCR catalyst 19. In addition, it is understood that in some operating conditions, a quantity of NOx carried by the exhaust flow may not be converted to N₂by the SCR catalyst 19. Such conditions may include, for example, when the SCR catalyst 19 is below the optimum NOx conversion temperature range discussed above (between approximately 200 degrees Celsius and approximately 500 degrees Celsius), when the ratio of NO to NO₂is not approximately one to one, and when substantially all of the NOx conversion sites of the SCR catalyst substrate are occupied. In such conditions, the clean-up catalyst 33 may also assist in, for example, collecting and/or storing NOx. In an exemplary embodiment, the clean-up catalyst 33 may be an NOx trap similar to the NOx trap 35 discussed above.
The recirculation line 24 may be disposed between the filter 16 and the SCR catalyst 19, and may be configured to assist in directing a portion of the exhaust flow from the filter 16 to the inlet 21 of the power source 12. As discussed above, the recirculation line 24 may alternatively be fluidly connected between the oxidation catalyst 18 and the filter 16, between the SCR catalyst 19 and the clean-up catalyst 33, or downstream of the clean-up catalyst 33. The recirculation line 24 may comprise piping, tubing, and/or other exhaust flow carrying means known in the art, and may be structurally similar to the flow lines 15 described above. The portion of the exhaust flow directed to the power source 12 by the recirculation line 24 may assist in reducing the concentration of oxygen within, for example, one or more combustion chambers of the power source 12 and may assist in increasing the specific heat of the air/fuel mixture therein, thereby lowering the maximum combustion temperature within the one or more combustion chambers. The lowered maximum combustion temperature and reduced oxygen concentration may slow the chemical reaction of the combustion process and decrease the formation of NOx by the power source 12.
The flow cooler 26 may be fluidly connected to the filter 16 via the recirculation line 24 and may be configured to cool the portion of the exhaust flow passing through the recirculation line 24. The flow cooler 26 may include a liquid-to-air heat exchanger, an air-to-air heat exchanger, or any other type of heat exchanger known in the art for cooling an exhaust flow. In an alternative exemplary embodiment of the present disclosure, the flow cooler 26 may be omitted.
The mixing valve 30 may be fluidly connected to the flow cooler 26 via the recirculation line 24 and may be configured to assist in regulating the flow of exhaust through the recirculation line 24. It is understood that in an exemplary embodiment, a check valve (not shown) may be fluidly connected upstream of the flow cooler 26 to further assist in regulating the flow of exhaust through the recirculation line 24. The mixing valve 30 may be a spool valve, a shutter valve, a butterfly valve, a check valve, a diaphragm valve, a gate valve, a shuttle valve, a ball valve, a globe valve, or any other valve known in the art. The mixing valve 30 may be actuated manually, electrically, hydraulically, pneumatically, or in any other manner known in the art. The mixing valve 30 may be in communication with the controller mentioned above (not shown) and may be selectively actuated in response to one or more predetermined conditions.
The mixing valve 30 may also be fluidly connected to an ambient air intake 29 of the exhaust treatment system 10. Thus, the mixing valve 30 may be configured to control the amount of exhaust flow entering a flow line 27 relative to the amount of ambient air flow entering the flow line 27. For example, as the amount of exhaust flow passing through the mixing valve 30 is desirably increased, the amount of ambient air flow passing through the mixing valve 30 may be proportionally decreased and vice versa.
As shown in FIG. 1, the flow sensor 28 may be fluidly connected to the recirculation line 24 downstream of the flow cooler 26. The flow sensor 28 may be any type of mass air flow sensor, such as, for example, a hot wire anemometer or a venturi-type sensor. The flow sensor 28 may be configured to sense the amount of exhaust flow passing through the recirculation line 24. It is understood that the flow cooler 26 may assist in reducing fluctuations in the temperature of the portion of the exhaust flow passing through the recirculation line 24. Reducing temperature fluctuations may also assist in reducing fluctuations in the volume occupied by a flow of exhaust gas since a high temperature mass of gas occupies a greater volume than the same mass of gas at a low temperature. Thus, sensing the amount of exhaust flow through the recirculation line 24 at positions downstream of the flow cooler 26 (i.e., at a relatively controlled temperature) may result in more accurate flow measurements than measurements taken upstream of the flow cooler 26. It is further understood that the flow sensor 28 may also include, for example, a thermocouple (not shown) or other device configured to sense the temperature of the exhaust flow.
The flow line 27 downstream of the mixing valve 30 may direct the ambient air/exhaust flow mixture to the compression assembly 32. The compression assembly 32 may include a compressor 13 configured to increase the pressure of a flow of gas to a desired pressure. The compressor 13 may include a fixed geometry type compressor, a variable geometry type compressor, or any other type of compressor known in the art. In the exemplary embodiment shown in FIG. 1, the compression assembly 32 may include more than one compressor 13, and the multiple compressors 13 may be disposed in parallel or in series relationship. A compressor 13 of the compression assembly 32 may be connected to a turbine 14 of the energy extraction assembly 22, and the turbine 14 may be configured to drive the compressor 13. In particular, as hot exhaust gases exit the power source 12 and expand against the blades (not shown) of the turbine 14, components of the turbine 14 may rotate and drive the connected compressor 13. Alternatively, in an embodiment in which the turbine 14 is omitted, the compressor 13 may be driven by, for example, the power source 12, or by any other drive known in the art. It is also understood that in a nonpressurized air induction system, the compression assembly 32 may be omitted.
The aftercooler 34 may be fluidly connected to the power source 12 via the flow line 27 and may be configured to cool a flow of gas passing through the flow line 27. In an exemplary embodiment, this flow of gas may be the ambient air/exhaust flow mixture discussed above. The aftercooler 34 may include a liquid-to-air heat exchanger, an air-to-air heat exchanger, or any other type of flow cooler or heat exchanger known in the art. In an exemplary embodiment of the present disclosure, the aftercooler 34 may be omitted if desired.
The exhaust treatment system 10 may further include a condensate drain 38 fluidly connected to the aftercooler 34. The condensate drain 38 may be configured to collect a fluid, such as, for example, water or other condensate formed at the aftercooler 34. It is understood that such fluids may consist of, for example, condensed water vapor contained in recycled exhaust gas and/or ambient air. In such an exemplary embodiment, the condensate drain 38 may include a removably attachable fluid tank (not shown) capable of safely storing the condensed fluid. The fluid tank may be configured to be removed, safely emptied, and reconnected to the condensate drain 38. In another exemplary embodiment, the condensate drain 38 may be configured to direct the condensed fluid to a fluid container (not shown) and/or other component or location on the machine. Alternatively, the condensate drain 38 may be configured to direct the fluid to the atmosphere or to the surface by which the machine is supported.
As shown in FIGS. 1 and 2, the recirculation line 24 may form a low pressure EGR loop in which a portion of the exhaust gas is extracted downstream of the energy extraction assembly 22 and directed to the inlet 21. It is understood, however, that in an exemplary embodiment, the recirculation line 24 may form a high pressure EGR loop. In such an embodiment, the portion of the exhaust gas may be extracted upstream of the energy extraction assembly 22. For example, as shown in FIGS. 3 and 4, in additional exemplary embodiments, the recirculation line 24 may be connected downstream of the NOx trap 35 and upstream of the energy extraction assembly 22. FIG. 3 illustrates an exemplary embodiment including an oxidation catalyst separate from and upstream of a filter 36, and FIG. 4 illustrates an exemplary embodiment in which a filter 36 includes a catalyzed substrate and in which the oxidation catalyst 18 is omitted.
In the high pressure EGR loop embodiments of FIGS. 3 and 4, the recirculated exhaust gas may pass through the flow cooler 26 upstream of the flow sensor 28. The recirculated exhaust gas may then be combined with a compressed flow of ambient air at the mixing valve 30, and the combined flow may be directed to the aftercooler 34. It is understood that, in the high pressure EGR loop embodiments of FIGS. 3 and 4, one or more components of the exhaust treatment system 200, 300 may be omitted. In another exemplary embodiment of a high pressure EGR loop (not shown), the recirculation line 24 may be internal to the power source 12, thereby creating an internal EGR loop. In such an embodiment, at least the flow cooler 26 may be omitted. In still another high pressure EGR loop embodiment, the recirculation line 24 may be fluidly connected downstream of the power source 12 and upstream of the NOx trap 35.

INDUSTRIAL APPLICABILITY

The exhaust treatment systems 10, 100, 200, 300 of the present disclosure may be used with any combustion-type device, such as, for example, an engine, a furnace, or any other device known in the art, where the reduction of NOx emissions, the reduction of particulate matter emissions, and/or the recirculation of treated exhaust into an inlet of the device is desired. The exhaust treatment systems 10, 100, 200, 300 may be useful in reducing the amount of engine emissions (such as, for example, NOx and particulate matter) discharged into the environment. The exhaust treatment systems 10, 100, 200, 300 may also be capable of purging the portions of the exhaust gas captured by components of the system through a regeneration process.
The operation of the exhaust treatment systems 10, 100, 200, 300 will now be explained in detail. Unless otherwise noted, the exhaust treatment system 10 of FIG. 1 will be referred to for the duration of the disclosure.
The power source 12 may combust a mixture of fuel, recirculated exhaust gas, and ambient air to produce mechanical work and an exhaust flow. As discussed above, the exhaust flow includes a complex mixture of solid, liquid, and/or gaseous components. In general, the solid and liquid components of the exhaust flow may consist of soot, soluble organic fraction, and unburned hydrocarbons. The soot produced during combustion may include carbonaceous materials, and the soluble organic fraction may include unburned hydrocarbons that are deposited on or otherwise chemically combined with the soot. The gaseous components of the exhaust flow may consist of, among other things, NOx and CO.
The exhaust flow may be directed, via flow line 15, from the power source 12 through the NOx trap 35. The NOx trap 35 may store, absorb, adsorb, collect, and/or otherwise store NOx carried by the exhaust flow. The NOx trap 35 may be useful in removing NOx in, for example, low load or low temperature (start-up) operating conditions in which the SCR catalyst 19 may be less effective in catalytically reducing NOx. The reduced NOx exhaust may then be directed to the energy extraction assembly 22. The hot exhaust flow may expand on the blades of the turbines 14 of the energy extraction assembly 22, and this expansion may reduce the pressure of the exhaust flow while assisting in rotating the turbine blades.
The reduced pressure exhaust flow may pass through the regeneration device 20 to the oxidation catalyst 18. The regeneration device 20 may be deactivated during the normal operation of the power source 12. As the exhaust flow passes through the oxidation catalyst 18, the catalyst materials contained therein may assist in oxidizing the particulate matter, hydrocarbons, and/or carbon monoxide carried by the flow. The catalyst materials may also assist in oxidizing gaseous NO contained in the flow, thereby converting the NO to NO₂. The oxidation catalyst 18 may be coated and/or otherwise configured to yield a treated flow of exhaust having a desired ratio of NO to NO₂to optimize the NOx conversion rate of the SCR catalyst 19. As discussed above, this desired ratio may be approximately one to one.
As the exhaust flow exits the oxidation catalyst 18 and passes through the filter 16, at least a portion of the particulate matter entrained with the exhaust flow may be captured by the substrate, mesh, and/or other structures within the filter 16. As discussed above with respect to FIG. 2, in an exemplary embodiment, the catalyst materials of the oxidation catalyst 18 may be disposed on the substrate of the filter 36 and, in such an embodiment, the oxidation catalyst 18 may be omitted. Such a configuration may also allow for the passive regeneration of the filter 36 during operation of the power source 12.
With continued reference to FIG. 1, a portion of the filtered exhaust flow may be extracted downstream of the filter 16 and the remainder of the filtered exhaust flow may be directed to the SCR catalyst 19. Disposing the filter 16 upstream of the SCR catalyst 19 minimizes the amount of, for example, particulate matter entering the SCR catalyst 19, thereby reducing the fouling thereof. The injector 37 may inject a desirable quantity of reductant into the exhaust flow upstream of the SCR catalyst 19, and the amount of reductant injected may depend on, among other things, the mass flow, temperature, and NOx concentration of the filtered flow. The injection amount may be calculated and otherwise controlled by the controller mentioned above (not shown). The injected reductant may be substantially atomized and may mix substantially uniformly with the filtered flow upstream of the SCR catalyst 19.
The NOx carried by the filtered flow may be catalytically reduced by the SCR catalyst 19 in the presence of the injected reductant. In particular, the NOx molecules may be substantially entirely converted to, for example, N₂, CO₂, H₂O, and O₂by the SCR catalyst 19, and the SCR catalyst 19 may be configured to reduce the overall NOx emissions of the exhaust treatment system 10 to below 0.2 grams/horsepower-hour. The SCR catalyst 19 reduces NOx most effectively at temperatures between approximately 200 degrees Celsius and approximately 500 degrees Celsius, and the conversion rate of the SCR catalyst 19 will be maximized when the ratio of NO to NO₂is approximately one to one.
The clean-up catalyst 33 downstream of the SCR catalyst 19 may remove any unreacted reductant from the flow exiting the SCR catalyst 19. After passing through the clean-up catalyst 33, the treated exhaust flow may exit the exhaust treatment system 10 through an exhaust system outlet 17.
In the low pressure EGR loop embodiments of FIGS. 1 and 2, the extracted portion of the exhaust flow discussed above may enter the recirculation line 24 downstream of the energy extraction assembly 22 and may be recirculated back to the power source 12. Alternatively, with reference to FIGS. 3 and 4, in the exemplary high pressure EGR loop embodiments disclosed herein, a portion of the exhaust flow may be extracted upstream of the energy extraction assembly 22. With reference to FIG. 1, the recirculated portion of the exhaust flow may pass through the flow cooler 26. The flow cooler 26 may reduce the temperature of the portion of the exhaust flow before the portion enters the flow line 27. The mixing valve 30 may be configured to regulate the ratio of recirculated exhaust flow to ambient inlet air passing through flow line 27. As described above, the flow sensor 28 may assist in regulating this ratio.
The mixing valve 30 may permit the ambient air/exhaust flow mixture to pass to the compression assembly 32 where the compressors 13 may increase the pressure of the flow, thereby increasing the temperature of the flow. The compressed flow may pass through the flow line 27 to the aftercooler 34, which may reduce the temperature of the flow before the flow enters the inlet 21 of the power source 12. As discussed above, recirculating a portion of the exhaust flow back to the power source 12 assists in reducing the overall NOx produce thereby.
Over time, soot produced by the combustion process may collect in the filter 16 and may begin to impair the ability of the filter 16 to store particulates. The flow sensor 28 and other sensors (not shown) sense parameters of the power source 12 and/or the exhaust treatment system 10. Such parameters may include, for example, engine speed, engine temperature, exhaust flow temperature, exhaust flow pressure, and particulate matter content. The controller (not shown) may use the information sent from the sensors in conjunction with an algorithm or other preset criteria to determine whether the filter 16 has become saturated and is in need of regeneration. Once this saturation point has been reached, the controller may send appropriate signals to components of the exhaust treatment system 10 to begin the regeneration process. A preset algorithm stored in the controller may assist in this determination and may use the sensed parameters as inputs. Alternatively, regeneration may commence according to a set schedule based on fuel consumption, hours of operation, and/or other variables.
The signals sent by the controller may alter the position of the mixing valve 30 to desirably alter the ratio of the ambient air/exhaust flow mixture. These signals may also activate the regeneration device 20. Upon activation, oxygen and a combustible substance, such as, for example, fuel, may be directed to the regeneration device 20. The regeneration device 20 may ignite the fuel and may increase the temperature of the exhaust flow passing to the filter 16 to a desired temperature for regeneration. This temperature may be in excess of 700 degrees Celsius (approximately 1,292 degrees Fahrenheit) in some applications, depending on the type and size of the filter 16. At these temperatures, soot contained within the filter 16 may be burned away to restore the storage capabilities of the filter 16.
As discussed above, disposing the filter 36 upstream of the SCR catalyst 19 may reduce or substantially eliminate fouling of the SCR catalyst 19 caused by, for example, particulate matter carried by the exhaust flow. Minimizing SCR catalyst fouling may assist in maximizing the number of available NOx conversion sites on the substrate of the SCR catalyst 19, thereby maximizing the ability of the SCR catalyst 19 to convert NOx carried by the exhaust flow to, for example, N₂.
It is understood that systems employing an SCR catalyst for NOx conversion may provide for reduced NOx emissions to the environment. For example, as mentioned above, the SCR catalyst 19 may be capable of maintaining the NOx emissions of the exhaust treatment system 10 described herein below approximately 0.2 grams/horsepower-hour, in compliance with future government regulations. Because the SCR catalyst 19 is capable of obtaining such low levels of NOx emissions, reducing the amount of NOx produced by the power source 12 by, for example, recirculating at least a portion of the exhaust gas, may no longer be necessary. Thus, due to the presence of the SCR catalyst 19, the EGR loop may instead be used to assist in improving, for example, the fuel economy of the power source 12 and/or the exhaust treatment system 10, generally. In particular, a system combining an SCR catalyst with EGR methods and components may enable the user to employ, for example, power source control techniques to improve fuel economy. Such techniques may include, for example, advancing fuel injection timing, modifying the actuation of combustion chamber intake valves, and/or altering fuel (rail) pressure.
In addition, recirculating a portion of the exhaust flow back to the power source 12 may increase the amount of NO₂produced by the power source 12 during combustion. Such an increase may result in an exhaust flow having a higher ratio of NO₂to NO at the outlet 43 of the power source 12 than an exhaust flow produced by a power source of an exhaust treatment system not utilizing EGR. Obtaining this higher ratio of NO₂to NO through combustion may reduce the oxidation requirements of the oxidation catalyst 18 during operation. As a result, a smaller, less expensive oxidation catalyst 18 having less precious metals, may be used. The use of such an oxidation catalyst 18 may, thus, reduce the overall cost of the exhaust treatment system 10 and may reduce the overall footprint of the system 10 within, for example, a crowded engine compartment of a machine to which the power source 12 is connected. In addition, obtaining this higher ratio of NO₂to NO may be particularly advantageous at low temperatures (such as those occurring at start-up or during low load conditions) where the ability of the oxidation catalyst 18 to oxidize NO to NO₂is diminished.
Other embodiments of the disclosed exhaust treatment system 10, 100, 200, 300 will be apparent to those skilled in the art from consideration of the specification. For example, the system 10, 100, 200, 300 may include additional filters, such as, for example, a sulfur trap, disposed upstream of the filter 16. The sulfur trap may be useful in capturing sulfur molecules carried by the exhaust flow. It is intended that the specification and examples be considered as exemplary only, with the true scope of the invention being indicated by the following claims.

Claims

1. An exhaust gas treatment system of an internal combustion engine, comprising:

a selective catalytic reduction catalyst fluidly connected to the internal combustion engine;

an oxidation catalyst fluidly connected upstream of the selective catalytic reduction catalyst;

a particulate filter fluidly connected upstream of the selective catalytic reduction catalyst; and

a recirculation line configured to direct a portion of an exhaust flow of the internal combustion engine toward an inlet of the engine.

2. The system of claim 1, further including at least one component configured to inject a flow of reductant upstream of the selective catalytic reduction catalyst.

3. The system of claim 1, wherein the recirculation line is fluidly connected one of downstream of the oxidation catalyst, downstream of the particulate filter, or downstream of the selective catalytic reduction catalyst.

4. The system of claim 1, wherein the recirculation line is fluidly connected downstream of an energy extraction assembly of the exhaust gas treatment system.

5. The system of claim 1, wherein the oxidation catalyst is disposed on a substrate of the particulate filter.

6. The system of claim 1, wherein the oxidation catalyst is configured to maintain a desired ratio of NO to NO₂in an exhaust flow of the internal combustion engine.

7. The system of claim 1, further including an NOx trap fluidly connected upstream of the oxidation catalyst.

8. The system of claim 7, wherein the NOx trap is disposed between an outlet of the internal combustion engine and an energy extraction assembly of the exhaust gas treatment system.

9. The system of claim 1, further including a catalyst fluidly connected downstream of the SCR catalyst.

10. The system of claim 1, further including a ventilation line fluidly connected to a crankcase of the internal combustion engine.

11. The system of claim 1, further including an energy extraction assembly configured to reduce the pressure of an exhaust flow of the internal combustion engine.

12. An exhaust gas treatment system of an internal combustion engine, comprising:

a low pressure exhaust gas recirculation loop.

13. The system of claim 12, wherein a component of the low pressure exhaust gas recirculation loop is fluidly connected one of downstream of the oxidation catalyst, downstream of the particulate filter, or downstream of the selective catalytic reduction catalyst, and the component is configured to direct a portion of an exhaust flow of the internal combustion engine toward an inlet of the internal combustion engine.

14. The system of claim 12, wherein the oxidation catalyst is disposed on a substrate of the particulate filter.

15. The system of claim 12, wherein the oxidation catalyst is configured to maintain a desired ratio of NO to NO₂in an exhaust flow of the internal combustion engine.

16. The system of claim 12, further including an NOx trap fluidly connected upstream of the oxidation catalyst.

17. The system of claim 12, further including a catalyst fluidly connected downstream of the selective catalytic reduction catalyst.

18. A method of an exhaust flow of an internal combustion engine, comprising:

filtering the exhaust flow with a particulate filter;

oxidizing the exhaust flow with an oxidation catalyst;

catalytically reducing NOx contained in the filtered oxidized flow with a selective catalytic reduction catalyst; and

directing a portion of the exhaust flow to an inlet of the internal combustion engine.

19. The method of claim 18, further including collecting NOx contained within the exhaust flow with an NOx trap fluidly connected upstream of the selective catalytic reduction catalyst.

20. The method of claim 18, further including removing reductant from the exhaust flow with a catalyst fluidly connected downstream of the selective catalytic reduction catalyst.