US20130180231A1

US20130180231A1 - Exhaust aftertreatment system

Info

Publication number: US20130180231A1
Application number: US13/350,272
Authority: US
Inventors: Yong Miao; Julian C. Tan
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2012-01-13
Filing date: 2012-01-13
Publication date: 2013-07-18
Also published as: CN103206288A; DE102013200245A1

Abstract

In one exemplary embodiment of an exhaust aftertreatment system, the system includes an oxidation catalyst configured to receive an exhaust gas flow from an internal combustion engine and a particulate filter positioned downstream of the oxidation catalyst, the particulate filter comprising a substrate. The system also includes a nitrogen oxide adsorbing catalyst applied to a downstream portion of the substrate and a selective catalytic reduction device positioned downstream of the nitrogen oxide adsorbing catalyst, wherein the selective catalytic reduction device is configured to remove nitrogen oxides from the exhaust gas flow.

Description

FIELD OF THE INVENTION

The subject invention relates to internal combustion engines, and, more particularly, to exhaust aftertreatment systems for internal combustion engines.

BACKGROUND

An engine control module of an internal combustion engine controls the mixture of fuel and air supplied to combustion chambers of the engine. After the air/fuel mixture is ignited, combustion takes place and the combustion gases exit the combustion chambers through exhaust valves. The combustion gases are directed by an exhaust manifold to a catalyst (or “catalytic converter”) and/or other exhaust aftertreatment systems.
During certain engine operating conditions combustion gases may enter the exhaust system while components of the aftertreatment system, such as the catalyst, are not yet heated to operating temperatures at which they can adequately reduce regulated exhaust gas constituents. The issue is typically greatest following a cold engine startup. Cold exhaust system components can have large thermal masses that act as heat sinks, thereby slowing down heating of the exhaust system and the catalysts contained therein. Therefore, following startup, a slow temperature rise in exhaust system components can lead to undesirable emission levels, due to the corresponding slow response and light-off (i.e. activation) of the catalyst(s).

SUMMARY OF THE INVENTION

In one exemplary embodiment of the invention, an exhaust aftertreatment system includes an oxidation catalyst configured to receive an exhaust gas flow from an internal combustion engine and a particulate filter positioned downstream of the oxidation catalyst, the particulate filter comprising a substrate. The system also includes a nitrogen oxide adsorbing catalyst applied to a downstream portion of the substrate and a selective catalytic reduction device positioned downstream of the nitrogen oxide adsorbing catalyst, wherein the selective catalytic reduction device is configured to remove nitrogen oxides from the exhaust gas flow.
In another exemplary embodiment of the invention, an internal combustion engine includes an oxidation catalyst in fluid communication with an exhaust manifold and a particulate filter configured to receive an exhaust gas flow from the oxidation catalyst. The internal combustion engine also includes a nitrogen oxide adsorbing catalyst configured to receive the exhaust flow from the particulate filter and a selective catalytic reduction device configured to receive the exhaust flow from the nitrogen oxide adsorbing catalyst, wherein the configuration of the nitrogen oxides catalyst and the selective catalytic reduction catalyst enable adsorption of nitrogen oxides by the nitrogen oxide adsorbing catalyst during a start up period, release of the nitrogen oxides after the start up period and removal the nitrogen oxides from the exhaust flow by the selective catalytic reduction catalyst as the nitrogen oxides are released by the nitrogen oxide adsorbing catalyst.
The above features and advantages and other features and advantages of the invention are readily apparent from the following detailed description of the invention when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and details appear, by way of example only, in the following detailed description of embodiments, the detailed description referring to the drawings in which

FIG. 1 illustrates an exemplary schematic view of an internal combustion engine including an exemplary exhaust aftertreatment system; and

FIG. 2 is a perspective view of a portion of the exemplary exhaust aftertreatment system of FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
FIG. 1 is a schematic diagram of an embodiment of an engine system 100. The engine system 100 includes an internal combustion engine 102, an exhaust system 104 and an engine controller 106. The exhaust system 104 includes an exhaust manifold 108, an exhaust aftertreatment system 110 and an exhaust conduit 112. Cylinders 116 are located in the internal combustion engine 102, wherein the cylinders 116 receive a combination of combustion air and fuel. The combustion air/fuel mixture is combusted resulting in reciprocation of pistons (not shown) located in the cylinders 116. The reciprocation of the pistons rotates a crankshaft (not shown) to deliver motive power to a vehicle powertrain (not shown) or to a generator or other stationary recipient of such power (not shown) in the case of a stationary application of the internal combustion engine 102. The combustion of the air/fuel mixture causes a flow of exhaust gas 118 through the exhaust manifold 108 and into the exhaust gas aftertreatment system 110, wherein the exhaust aftertreatment system 110 may include an oxidation catalyst 119, a particulate filter 120, a nitrogen oxide adsorbing catalyst (“NAC”) 122 and a selective catalytic reduction (“SCR”) device 124. The exhaust aftertreatment system 110 reduces, oxidizes, traps or otherwise treats various regulated constituents of the exhaust gas 118, such as nitrogen oxides (“NOx”), carbon monoxide (“CO”), hydrocarbon (“HC”) and particulates prior to its release to the atmosphere.
In addition, the exhaust aftertreatment system 110 and a fluid supply 125 are operationally coupled to and controlled by engine controller 106. The engine controller 106 collects information regarding the operation of the internal combustion engine 102 from sensors 128 a-128 n, such as temperature (intake system, exhaust system, engine coolant, ambient, etc.), pressure, exhaust flow rates, NOx concentrations and, as a result, may adjust the amount of an emission reducing fluid, such as urea or ammonia gas, injected into the exhaust aftertreatment system 110. As used herein the term controller refers to an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. In an exemplary embodiment, the exhaust gas flow 118 is received by the oxidation catalyst 119, which may be closely-coupled, to the engine exhaust manifold to minimize heat loss. The particulate filter 120 is configured to remove particulate matter or soot from the exhaust gas flow 118. In an embodiment, the NAC 122 may be a NOx absorbing coating applied to a downstream portion of the particulate filter 120 substrate, where the NAC 122 adsorbs NOx at a first temperature and releases NOx at a second temperature. The first temperature is lower than a threshold and the second temperature is higher than the threshold. After the NOx is released at the second temperature by the NAC, the SCR device 124 receives the exhaust gas 118 and is sufficiently heated to remove NOx from the exhaust. In an embodiment, the SCR device 124 simultaneously removes NOx from the exhaust gas flow 118 as the NAC 122 releases the NOx.
With continuing reference to FIG. 1, during a startup period for the exemplary internal combustion engine system 102, components of the exhaust aftertreatment system 110, such as the SCR device 124, are relatively “cool” and can take time to be warmed up to an operating temperature. Specifically, when heated to its operating temperature, the SCR device 124 removes NOx more effectively from the exhaust gas flow 118. Accordingly, a method and apparatus are provided for the exhaust aftertreatment system 110 to enable the SCR device 124 to remove NOx from the exhaust gas flow 118 after being heated at or above a threshold operating temperature, thereby reducing emissions. As discussed herein, the operating temperature for the SCR device 124 is a temperature or range of temperatures where the device is able to remove a sufficient amount of NOx, to achieve selected targets.
FIG. 2 is a perspective view of a portion of the exemplary exhaust aftertreatment system 110. As depicted, the exhaust aftertreatment system 110 receives the exhaust gas flow 118 into the oxidation catalyst 119, which may be a diesel oxidation catalyst (DOC). The Exhaust gas flows into the particulate filter 120, which may be a diesel particulate filter. The oxidation catalyst 119 is configured to oxidize selected pollutants, such as carbon monoxide and hydrocarbon, from the exhaust gas flow 118, while the particulate filter 120 is configured to remove soot and other particulates. In an embodiment, the NAC 122 is downstream of the particulate filter 120 and is configured to adsorb or capture NOx from the exhaust gas flow 118 at a first temperature. Further, the NAC 122 is also configured to release the adsorbed NOx at a second temperature that is higher than the first temperature. The exemplary NAC 122 is a coating of suitable material applied to a downstream portion of a substrate of the particulate filter 120. Exemplary materials for the coating include, but are not limited to, basic metal oxides (γ-Al₂O₃, CeO₂, MgO, MgO/Al₂O₃, BaO/Al₂O₃, K₂O/Al₂O₃) and metal exchanged zeolites (Na-exchanged and Ba-exchanged faujasite, such as NaY and BaY, as well as Cu-exchanged and Fe-exchanged Beta). As depicted, an assembly 200 allowing close coupling to the engine exhaust manifold 108 includes the oxidation catalyst 119, the particulate filter 120 and the NAC 122. As discussed herein, close coupled components are close in proximity to an exhaust exit of the internal combustion engine 102 to reduce a length of at least a portion of an exhaust gas flow path. Further, close coupled components are placed substantially adjacent or proximate one another to cause a reduced exhaust flow path between components. Close coupled components reduce thermal degradation (i.e., heat loss) caused by exhaust gas flow along longer flow paths and resultant thermal mass and, accordingly, provide more rapid heating of components to operating temperatures due to shorter overall flow paths. In other embodiments, the oxidation catalyst 119, the particulate filter 120 and the NAC 122 are separate components, wherein the NAC 122 is applied to a substrate downstream of, and separate from, the particulate filter 120.
An emission fluid injector 202 is positioned downstream of the close couple assembly 200 to inject an emission fluid, such as urea, to assist the SCR device 124 in reduction of NOx constituents in the exhaust gas flow 118. A mixer may be located in an exhaust conduit 204 to improve distribution and mixing of the emission fluid. The SCR device 124 is configured to receive the exhaust gas flow 118 mixed with emission fluid and reduce the NOx in the exhaust gas. After NOx and other exhaust gas components are removed, the exhaust gas 118 flows downstream to other aftertreatment devices or into the atmosphere, depending on the application. The exemplary SCR device 124 is configured to remove NOx from exhaust at or above a threshold operating temperature, such as about 150 degrees C. In other embodiments, the operating temperature is at or above about 175 degrees C. In yet other embodiments, the operating temperature is at or above about 200 degrees C. At lower exhaust flow rates, the temperature for initiating urea injection is about 150 degrees C. At higher exhaust flow rates, the temperature for urea injection is higher, such as about 175 to about 200 degrees C.
An exemplary start up period begins when a “cool” engine (i.e., not warmed up) is started. In embodiments, certain components are not sufficiently heated to operate efficiently during the start up period. Specifically, the SCR device 124 may not remove NOx at a desired rate, such as to reduce levels to meet certain regulations or targets, during the start up period. Thus, in an embodiment, the NAC 122 is configured to adsorb NOx from the exhaust gas flow 118 during the start up period. After the start up period, the NAC 122 is heated and can no longer adsorb NOx. In addition, after the start up period, the NAC 122 releases the adsorbed NOx pollutants for treatment by the SCR device 124, wherein the SCR device 124 has been heated to an operating temperature to remove NOx. For example, following a cold startup, the SCR device 124 and the NAC 122 are substantially cool and the NAC 122 adsorbs NOx at or below its “release” temperature. The release temperature is a temperature at which the NAC 122 slows or stops adsorbing NOx and begins to release adsorbed NOx. After the start up period, the NAC 122 and SCR device 124 are above a threshold temperature (i.e., about equal to the release temperature of the NAC and the operating temperature of the SCR), wherein the NAC 122 releases the NOx and the SCR device 124 is heated and able to remove NOx from the exhaust gas. In embodiments, the first temperature is below about 100 degrees C. and the second temperature is equal to or greater than about 150 degrees C. In the example, the NAC 122 and SCR device 124 are heated from below about 100 degrees C. to about 150 degrees C. during the start up period, wherein the components are at or above 150 degrees C. after the start up period.
The embodiments depicted in FIGS. 1 and 2 are configured to substantially “match” the temperatures of the NAC 122 and SCR device 124, wherein NAC 122 and SCR device 124 are both heated by the exhaust gas to a selected temperature or threshold where the NAC 122 releases NOx for removal by the SCR device 124 after the start up period. In addition, the depicted arrangement does not have a filter positioned between the NAC 122 and SCR device 124. Accordingly, the arrangement enables the temperature of the exhaust gas 118 flow to be substantially matched or similar at the NAC 122 and SCR device 124 by not having devices that act as heat sinks between the components. For example, the NAC 122 adsorbs NOx while the exhaust gas flow heats the NAC 122 and SCR device 124. The SCR device 124 then receives the released NOx for treatment from the NAC 122 after the start up period, when the temperatures of the NAC 122 and SCR device 124 are both heated and substantially matched to improve emissions reduction. Accordingly, the arrangement depicted in FIGS. 1 and 2 substantially matches the temperatures of the NAC 122 and SCR device 124 to improve NOx reduction during and after the engine's start up period.
While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the application.

Claims

What is claimed is:

1. An exhaust aftertreatment system, comprising:

an oxidation catalyst configured to receive an exhaust gas flow from an internal combustion engine;

a particulate filter positioned downstream of the oxidation catalyst, the particulate filter comprising a substrate;

a nitrogen oxide adsorbing catalyst applied to a downstream portion of the substrate; and

a selective catalytic reduction device positioned downstream of the nitrogen oxide adsorbing catalyst, wherein the selective catalytic reduction device is configured to remove nitrogen oxides from the exhaust gas flow.

2. The exhaust aftertreatment system of claim 1, wherein the nitrogen oxide adsorbing catalyst adsorbs nitrogen oxides below a threshold temperature during a start up period for the internal combustion engine and releases the nitrogen oxides above the threshold temperature, wherein the second temperature is greater than the first temperature.

3. The exhaust aftertreatment system of claim 1, wherein the selective catalytic reduction device removes nitrogen oxides at an operating temperature that is greater than its temperature following a start up period for the internal combustion engine.

4. The exhaust aftertreatment system of claim 1, wherein a temperature of the exhaust gas flow is substantially matched between the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device.

5. The exhaust aftertreatment system of claim 1, wherein the configuration of the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device enable adsorption of nitrogen oxides by the nitrogen oxide adsorbing catalyst during a start up period, release of the nitrogen oxides after the start up period and removal of the nitrogen oxides simultaneously by the selective catalytic reduction device from the exhaust gas flow as the nitrogen oxides are released by the nitrogen oxide adsorbing catalyst.

6. The exhaust aftertreatment system of claim 1, comprising an emission fluid injector positioned in a flow path between the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device.

7. The exhaust aftertreatment system of claim 1, wherein the oxidation catalyst and the particulate filter are closely coupled to the internal combustion engine.

8. An internal combustion engine comprising:

an oxidation catalyst in fluid communication with an exhaust manifold;

a particulate filter configured to receive an exhaust gas flow from the oxidation catalyst;

a nitrogen oxide adsorbing catalyst configured to receive the exhaust flow from the particulate filter; and

a selective catalytic reduction device configured to receive the exhaust flow from the nitrogen oxide adsorbing catalyst, wherein the configuration of the nitrogen oxides catalyst and the selective catalytic reduction catalyst enable adsorption of nitrogen oxides by the nitrogen oxide adsorbing catalyst during a start up period, release of the nitrogen oxides after the start up period and removal the nitrogen oxides from the exhaust flow by the selective catalytic reduction catalyst as the nitrogen oxides are released by the nitrogen oxide adsorbing catalyst.

9. The internal combustion engine of claim 8, wherein the nitrogen oxide adsorbing catalyst adsorbs nitrogen oxides below a threshold temperature during a start up period for the internal combustion engine and releases the nitrogen oxides after the start up period above the threshold temperature.

10. The internal combustion engine of claim 8, wherein the selective catalytic reduction device removes nitrogen oxides at an operating temperature that is greater than its temperature during the start up period.

11. The internal combustion engine of claim 8, wherein a temperature of the exhaust gas flow is substantially matched between the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device.

12. The internal combustion engine of claim 8, comprising an emission fluid injector positioned in a flow path between the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device.

13. The internal combustion engine of claim 8, wherein the oxidation catalyst, the particulate filter and the nitrogen oxide adsorbing catalyst are closely coupled to the internal combustion engine.

14. An exhaust aftertreatment system, comprising:

a selective catalytic reduction device configured to remove nitrogen oxides from the exhaust gas flow received from the nitrogen oxide adsorbing catalyst, wherein a temperature of the exhaust gas flow is substantially matched between the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device.

15. The exhaust aftertreatment system of claim 14, wherein the nitrogen oxide adsorbing catalyst adsorbs nitrogen oxides below a threshold temperature during a start up period for the internal combustion engine and releases the nitrogen oxides above the threshold temperature.

16. The exhaust aftertreatment system of claim 15, wherein the selective catalytic reduction device removes nitrogen oxides at about the second temperature.

17. The exhaust aftertreatment system of claim 14, wherein the configuration of the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device enable adsorption of nitrogen oxides by the nitrogen oxide adsorbing catalyst during a start up period of the internal combustion engine, release of the nitrogen oxides after the start up period and removal of the nitrogen oxides from the exhaust flow as the nitrogen oxides are released by the nitrogen oxide adsorbing catalyst.

18. The exhaust aftertreatment system of claim 14, comprising an emission fluid injector positioned in a flow path between the nitrogen oxide adsorbing catalyst and the selective catalytic reduction device.

19. The exhaust aftertreatment system of claim 14, wherein the nitrogen oxide adsorbing catalyst is applied to a downstream portion of a substrate of the particulate filter.

20. The exhaust aftertreatment system of claim 19, wherein the oxidation catalyst and the particulate filter are closely coupled to the internal combustion engine.