U.S. patent application number 12/685016 was filed with the patent office on 2010-12-30 for selective catalytic reduction exhaust aftertreatment system and engine incorporating the same.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS, INC.. Invention is credited to Jianwen Li, Rahul Mital.
Application Number | 20100326059 12/685016 |
Document ID | / |
Family ID | 43379244 |
Filed Date | 2010-12-30 |
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United States Patent
Application |
20100326059 |
Kind Code |
A1 |
Mital; Rahul ; et
al. |
December 30, 2010 |
SELECTIVE CATALYTIC REDUCTION EXHAUST AFTERTREATMENT SYSTEM AND
ENGINE INCORPORATING THE SAME
Abstract
In one exemplary embodiment of the present invention, an exhaust
aftertreatment system is disclosed. The system includes an
oxidation catalyst (OC) that is configured to receive an exhaust
gas flow from an engine. The system also includes an uncoated
particulate filter (PF) that is configured to receive the exhaust
gas flow from the OC. The system further also includes an exhaust
fluid (EF) dosing device configured for dosing of an EF into the
exhaust gas flow upstream of the uncoated PF. Still further, the
system includes a selective catalyst reduction (SCR) catalyst that
is configured to receive the exhaust gas flow from the uncoated PF,
wherein the OC, uncoated PF and SCR catalyst comprise an exhaust
aftertreatment system. A urea injector may be provided as the EF
dosing device and arranged to inject urea, for example, into the
exhaust gases upstream of the uncoated PF.
Inventors: |
Mital; Rahul; (Rochester
Hills, MI) ; Li; Jianwen; (West Bloomfield,
MI) |
Correspondence
Address: |
Cantor Colburn LLP-General Motors
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS,
INC.
Detroit
MI
|
Family ID: |
43379244 |
Appl. No.: |
12/685016 |
Filed: |
January 11, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61220667 |
Jun 26, 2009 |
|
|
|
Current U.S.
Class: |
60/297 ; 29/890;
60/299; 60/303 |
Current CPC
Class: |
F01N 3/0222 20130101;
F01N 3/2828 20130101; F01N 3/035 20130101; F01N 3/281 20130101;
F01N 2610/03 20130101; F01N 2610/02 20130101; Y02T 10/12 20130101;
Y10T 29/49345 20150115; F01N 3/103 20130101; F01N 13/0093 20140601;
Y02T 10/24 20130101; F01N 13/009 20140601; F01N 13/0097 20140603;
F01N 3/2066 20130101 |
Class at
Publication: |
60/297 ; 60/299;
60/303; 29/890 |
International
Class: |
F01N 3/035 20060101
F01N003/035; F01N 3/10 20060101 F01N003/10; B21D 51/16 20060101
B21D051/16 |
Claims
1. An exhaust aftertreatment system, comprising: an oxidation
catalyst (OC) that is configured to receive an exhaust gas flow
from an engine; an uncoated particulate filter (PF) that is
configured to receive the exhaust gas flow from the OC; an exhaust
fluid (EF) dosing device configured for dosing of an EF into the
exhaust gas flow upstream of the uncoated PF; and a selective
catalytic reduction (SCR) catalyst that is configured to receive
the exhaust gas flow from the uncoated PF, wherein the OC, EF
dosing device, uncoated PF and SCR catalyst comprise an exhaust
aftertreatment system.
2. The exhaust aftertreatment system of claim 1, further comprising
a second OC that is configured to receive the exhaust gas flow from
the SCR catalyst.
3. The exhaust aftertreatment system of claim 1, wherein the
uncoated PF and SCR catalyst are housed in a single housing.
4. The exhaust aftertreatment system of claim 1, wherein the
uncoated PF and SCR catalyst are each housed in a separate
housing.
5. The exhaust aftertreatment system of claim 2, wherein the
uncoated PF, SCR catalyst and second OC are housed in a single
housing.
6. The exhaust aftertreatment system of claim 2, wherein the SCR
catalyst and second OC are each located on a metal or ceramic
substrate, or a combination thereof
7. The exhaust aftertreatment system of claim 6, wherein SCR
catalyst and second OC are each located on a monolithic,
flow-through substrate.
8. The exhaust aftertreatment system of claim 1, further comprising
an HC dosing device located upstream of the OC.
9. The exhaust aftertreatment system of claim 1, wherein the EF
dosing device comprises a urea injector.
10. An internal combustion engine and exhaust aftertreatment
system, comprising: an internal combustion engine comprising an
exhaust treatment system, the exhaust treatment system comprising:
an oxidation catalyst (OC) that is configured to receive an exhaust
gas flow from the engine; an uncoated particulate filter (PF) that
is configured to receive the exhaust gas flow from the OC; an
exhaust fluid (EF) dosing device configured for dosing of an EF
into the exhaust gas flow upstream of the uncoated PF; and a
selective catalytic reduction (SCR) catalyst that is configured to
receive the exhaust gas flow from the PF.
11. The exhaust aftertreatment system for an internal combustion
engine of claim 10, further comprising a second OC that is
configured to receive the exhaust gas flow from the SCR
catalyst.
12. The exhaust aftertreatment system for an internal combustion
engine of claim 10, wherein the uncoated PF and SCR catalyst are
housed in a single housing.
13. The exhaust aftertreatment system for an internal combustion
engine of claim 10, wherein the uncoated PF and SCR catalyst are
each housed in a separate metal housing.
14. The exhaust aftertreatment system for an internal combustion
engine of claim 11, wherein the uncoated PF, SCR catalyst and
second OC are housed in a single housing.
15. The exhaust aftertreatment system for an internal combustion
engine of claim 11, wherein the SCR catalyst and second OC are each
located on a separate metal or ceramic substrate, or a combination
thereof.
16. The exhaust aftertreatment system for an internal combustion
engine of claim 15, wherein the SCR catalyst and second OC are each
located on the same monolithic, flow-through substrate.
17. The exhaust aftertreatment system for an internal combustion
engine of claim 10, further comprising an HC dosing device located
upstream of the OC.
18. The exhaust aftertreatment system for an internal combustion
engine of claim 10, wherein the EF dosing device comprises a urea
injector.
19. A method of making an exhaust aftertreatment system,
comprising: providing an oxidation catalyst (OC) that is configured
to receive an exhaust gas flow from an engine; fluidly connecting
an uncoated particulate filter (PF) to the OC to receive the
exhaust gas flow from the OC; fluidly connecting an exhaust fluid
(EF) dosing device upstream of the uncoated PF for dosing of an EF
into the exhaust gas flow; and fluidly connecting a selective
catalytic reduction (SCR) catalyst to receive the exhaust gas flow
from the uncoated PF, wherein the OC, EF dosing device, uncoated PF
and SCR catalyst comprise an exhaust aftertreatment system.
20. The method of claim 19, further comprising fluidly connecting a
second OC to receive the exhaust gas flow from the SCR catalyst.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to provisional patent
application Ser. No. 61/220,667 filed on Jun. 26, 2009, which is
hereby incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] Exemplary embodiments of the present invention are related
to exhaust gas treatment systems, and, more specifically, to an
exhaust gas treatment system for lean-burn internal combustion
engines and vehicles incorporating the same.
BACKGROUND
[0003] Manufacturers of internal combustion engines must satisfy
customer demands and meet various regulations for reduced emissions
and improved fuel economy. One example of a way to improve fuel
economy is to operate an engine at an air/fuel ratio that is lean
(excess oxygen) of stoichiometry. Examples of lean-burn engines
include compression-ignition (diesel) and lean-burn spark-ignition
engines. However, while a lean-burn engine has improved fuel
economy, they tend to have higher nitrogen oxides (NO.sub.X)
emissions. The commercial application of lean-burn engines is
limited due to a lack of effective methods to remove sufficient
NO.sub.X from the lean exhaust stream before it exits the tail pipe
to meet regulations. Thus, efficient reduction of NO.sub.X from
lean-burn gasoline and diesel exhaust before it exits the tail pipe
is important to meet future emission standards and improve vehicle
fuel economy.
[0004] Reduction of NO.sub.X emissions from an exhaust stream
including excess oxygen is a challenge for vehicle manufacturers.
It is estimated that compliance with Bin 5 regulations in the
United States may require an aftertreatment system for diesel and
gasoline engines capable of 70-90% NO.sub.X conversion efficiency
on the FTP (Federal Test Procedure) cycle based on currently
anticipated engine-out NO.sub.X levels. Such conversion efficiency
must be obtained at a variety of operating temperatures ranging
between 200-550.degree. C. during various parts of the
aforementioned FTP cycle or, for example, the US06 Federal Test
Procedure.
[0005] Several potential aftertreatment systems have been proposed
for vehicle applications. These systems employ various exhaust
aftertreatment devices. One such aftertreatment system employs a
urea selective catalyst reduction (SCR) catalyst and a NO.sub.X
reductant, e.g., urea, that is injected upstream of the catalyst
and is converted to ammonia that is used to reduce NO.sub.X to
N.sub.2. Use of urea as a reductant necessitates a urea
distribution infrastructure and an on-vehicle monitoring system for
this secondary fluid, and may have potential problems in cold
weather climates due to the relatively high freezing point
(-12.degree. C.) of the urea solution. NO.sub.X storage catalysts
typically require large catalyst volumes, large amounts of
platinum-group metals and low sulfur fuel for efficient storage
operation. Such systems require periodic catalyst regeneration
involving fuel injection or injection of reductants to regenerate
the storage material of the catalyst.
[0006] While systems that employ SCR catalysts have been used for
NO.sub.X reduction in exhaust gas flow streams having excess
oxygen, packaging of the various catalysts has been problematic,
particularly in relatively smaller vehicles having relatively
shorter wheelbases, due the reduced space available to package the
desired combinations of catalysts. For example, in some of the
smaller heavy duty vehicles, it is desirable to package the SCR
last where it is farthest from the engine and the exhaust system
operating temperatures are lowest, in order to minimize thermal
degradation of the SCR catalyst materials and thereby maximize the
operating life of the SCR catalyst. While this arrangement is
desirable, there is generally not enough room to package the SCR
last while also providing the needed mixing length for conversion
of the injected urea into ammonia, particularly if the system also
employs one or more additional exhaust treatment devices for the
reduction of NO.sub.X or oxidation or reduction of other exhaust
constituents, including carbon monoxide (CO), various hydrocarbons
(HC), particulate matter (PM) and the like.
[0007] Therefore, it would be desirable to develop exhaust
aftertreatment systems that provide the needed NO.sub.X conversion
under excess oxygen (lean burn) conditions using an SCR catalyst,
and that can be packaged on vehicles having relatively short
wheelbases and small space envelopes. It would also be desirable to
locate the SCR last while also including other exhaust treatment
devices within the space available on the vehicle while providing
the necessary NO.sub.X reduction efficiency.
SUMMARY OF THE INVENTION
[0008] In one exemplary embodiment of the present invention, an
exhaust aftertreatment system is disclosed. The system includes an
oxidation catalyst (OC) that is configured to receive an exhaust
gas flow from an engine. The system also includes an uncoated
particulate filter (PF) that is configured to receive the exhaust
gas flow from the OC. The system further also includes an exhaust
fluid (EF) dosing device configured for dosing of an EF into the
exhaust gas flow upstream of the uncoated PF. Further, the system
includes an SCR catalyst that is configured to receive the exhaust
gas flow from the PF, wherein the OC, uncoated PF, EF dosing device
and SCR catalyst comprise an exhaust aftertreatment system.
[0009] In another exemplary embodiment of the present invention, an
internal combustion engine and exhaust aftertreatment system is
disclosed. The internal combustion engine includes an exhaust
aftertreatment system. The exhaust aftertreatment system includes
an OC that is configured to receive an exhaust gas flow from the
engine. The exhaust aftertreatment system also includes an uncoated
PF that is configured to receive the exhaust gas flow from the OC.
The system further also includes an exhaust fluid (EF) dosing
device configured for dosing of an EF into the exhaust gas flow
upstream of the uncoated PF. Still further, the system also
includes an SCR catalyst that is configured to receive the exhaust
gas flow from the PF wherein the OC, uncoated PF, EF dosing device
and SCR catalyst comprise an exhaust aftertreatment system.
[0010] In yet another exemplary embodiment of the present
invention, a method of making an exhaust aftertreatment system is
disclosed. The method includes providing an OC that is configured
to receive an exhaust gas flow from an engine. The method also
includes fluidly connecting an uncoated PF to the OC to receive the
exhaust gas flow from the OC. The method further includes fluidly
connecting an EF dosing device upstream of the PF for dosing an EF
into the exhaust gas flow. Further, the method includes fluidly
connecting an SCR catalyst to receive the exhaust gas flow from the
PF, wherein the OC, EF dosing device, PF and SCR catalyst comprise
an exhaust aftertreatment system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other features, advantages and details appear, by way of
example only, in the following description of embodiments, the
description referring to the drawings in which:
[0012] FIG. 1 is a schematic illustration of an exemplary
embodiment of an internal combustion engine and exhaust gas
treatment system as disclosed herein; and;
[0013] FIG. 2 is a schematic illustration of a second exemplary
embodiment of an internal combustion engine and exhaust gas
treatment system as disclosed herein.
DESCRIPTION OF THE EMBODIMENTS
[0014] Referring now to FIGS. 1 and 2, schematic diagrams depict
exemplary embodiments of an internal combustion engine 10 that is
particularly suitable for use in many types of motorized vehicles
1, such as automobiles, light trucks, marine vehicles, ATVs and the
like, as well as numerous fixed installation applications, such as
generators, pumps and the like. Engine 10 includes an exhaust
aftertreatment system 2, including a plurality of exhaust
aftertreatment devices. These exemplary embodiments of exhaust
aftertreatment system 2 include an OC 14, such as a diesel
oxidation catalyst, that is used to oxidize certain constituents of
exhaust gas flow 4. OC 14 is located upstream of PF 26, such as a
diesel particulate filter (DPF), that is used to filter PM from the
exhaust gas flow 4. OC 14 may also be used for regeneration of PF
26 by generation of heat for oxidation of the PM, as described
herein. Exhaust aftertreatment system 2 also includes a urea
selective catalyst reduction (SCR) catalyst 28 located downstream
of an uncoated PF 26. Optionally, system 2 may also include a
second OC 40 downstream of SCR catalyst 28 to oxidize any remaining
HC and reduce the possibility of HC, ammonia or CO slip through the
system, i.e. passage through the system without being converted.
The physical spacing of OC 14 and SCR catalyst 28 by the uncoated
PF 26 provides greater distance over which the urea may vaporize
and mix and be converted to ammonia through thermolysis and
hydrolysis reactions, thereby improving the conversion efficiency
of the urea and providing sufficient opportunity for this reaction
to occur, thus enhancing the NO.sub.X conversion ability of SCR
catalyst 28. The heat resulting from the oxidation reactions in OC
14 further facilitates the urea conversion. The location of OC 14
just upstream of PF 26 increases the efficiency of usage of
post-injected fuel, since post-injected fuel is used only for
generating heat, and this arrangement places OC 14 in close
proximity to PF 26, thereby reducing heat losses from the fuel
usage and increasing the efficiency of PF 26, as well as engine 10
or vehicle 1, or both of them, in cases where the fuel is drawn
from the vehicle fuel tank.
[0015] Exhaust aftertreatment system 2 may be used with any
internal combustion engine and engine control system 3. An
exemplary engine 10 and control system 3 includes a conventional
four-cycle diesel, gasoline or natural gas fueled internal
combustion engine and electronic engine control module (ECM) 5. The
engine 10 may include a compression-ignition or diesel engine
having an operating regime such that it is primarily a lean-burn
engine and is operated on an air/fuel mixture where the amount of
fuel is lower or leaner than the stoichiometric amount required for
combustion, or from another perspective, where the oxygen exceeds
the stoichiometric amount. Alternately, engine 10 may include an
engine employing any one of a number of engine control strategies
that operate lean of stoichiometry, e.g., homogeneous-charge
compression-ignition engines and lean-burn spark-ignition engines.
Engine 10 includes one or more reciprocating pistons attached to a
crankshaft, which is operably attached to a driveline or powertrain
of vehicle 1 to deliver tractive torque to the driveline. During
operation, internal combustion processes in engine 10 generate an
exhaust gas feedstream or flow that travels in the direction
illustrated by arrow 4 and contains regulated constituents as
combustion by-products, and that must be transformed by the
aftertreatment system prior to release from the system 2, such as
to an external environment. The constituents of exhaust gas flow 4
produced by engine 10 under lean combustion conditions include HC,
CO, NO.sub.X, and PM, among others.
[0016] Exhaust aftertreatment system 2 is an integrated system
intended to treat the regulated constituents of the exhaust gas
flow 4 to produce a flow that includes unregulated constituents, or
regulated constituents in amounts that may be released from the
system to the external environment, such as by reducing amounts of
the regulated constituents to acceptable levels or by chemically
converting them to unregulated materials that may be released. An
exhaust manifold 11, or manifolds, and associated conduits 13
entrain and direct the exhaust gas flow 4 to and through the
exhaust aftertreatment system 2. Referring to FIGS. 1-2, the
exhaust aftertreatment systems 2 described herein, including the
components or devices thereof described herein, employ technologies
having various capabilities for treating the constituent elements
of the exhaust gas feedstream, including oxidation, selective
catalytic reduction, HC (e.g., fuel) or reductant (e.g., urea)
dosing and particulate filtering, as further described herein. The
devices are fluidly and operably connected in series and in fluid
communication with one another using known pipes or conduits 13 and
connectors to contain and channel the exhaust gas flow 4 through
exhaust aftertreatment system 2.
[0017] Referring again to the exemplary embodiments of FIGS. 1 and
2, the OC 14 is in fluid communication with the engine 10 and, with
reference to the exhaust gas flow 4, is located downstream from
engine 10 and is configured to oxidize certain constituents of the
exhaust gas flow 4 to produce unregulated by-products or
constituents that are adapted for further treatment in other
components of exhaust aftertreatment system 2, as described herein.
Generally, the OC 14 is a flow-through device, as described herein,
that consists of a metal or ceramic monolith or substrate having a
honeycomb-like structure that includes a plurality of generally
parallel, longitudinally-extending, interconnected cells that
provide a network comprising a plurality of flow channels for
receiving exhaust gas flow 4 and are separated by a corresponding
network of cell walls. The substrate has a large surface area along
the cell walls. The cell walls have a washcoat that includes a
porous ceramic matrix with a surface that is coated with a
catalytically active amount of a Pt group metal catalyst. Suitable
platinum group metals include Pt, Pd, Rh, Ru, Os or Ir, or a
combination thereof. Of these, Pt or Pd, or combinations thereof,
including alloys thereof, are particularly useful. Those that
include both Pt and Pd are particularly useful, such as those
having Pt:Pd ratios of about 2:1 to about 4:1. As the exhaust gas
flow 4 traverses the length of the OC 14, particularly the flow
channels and the washcoated cell walls, the platinum group metal
catalyst catalyzes the oxidation of CO to CO.sub.2, as well as
catalyzing the oxidation of various HC, including gaseous HC's and
liquid HC particles, including unburned fuel or oil, or fuel or
other HC reactants that are introduced into exhaust gas
aftertreatment system to form CO.sub.2 and H.sub.2O, thereby
reducing harmful emissions. In one configuration, during an
advanced combustion operation of the engine, the control system 3,
including ECM 5, may be used to cause combustion resulting in a
higher level of HC in the exhaust gas flow 4 than is generated
during normal combustion. The OC 14 is configured to catalyze the
decomposition of at least a portion of the increased amounts of HC
in order to reduce, or alternately to prevent, the HC in the
exhaust gas flow from reaching the SCR catalyst 28 and poisoning
this device by reducing its ability to catalyze NO.sub.X, or from
reaching the external environment by release from the exhaust
aftertreatment system 2.
[0018] The OC 14, such as a diesel oxidation catalyst (DOC) in the
case of an exhaust aftertreatment system 2 for a diesel engine 10,
may be configured to convert various regulated exhaust constituents
to other regulated or unregulated exhaust constituents through
oxidation. For example, the OC 14 may be configured to oxidize HC
to carbon dioxide (CO.sub.2) and water (H.sub.20), convert CO to
carbon dioxide (CO.sub.2) convert sulfur dioxide (SO.sub.2) to
sulfur trioxide (SO.sub.3) and/or sulfuric acid (H.sub.2SO.sub.4)
and convert nitrogen oxide (NO) to nitrogen dioxide (NO.sub.2), or
otherwise. Exemplary oxidation reactions contemplated with the OC
14 are provided below:
HC+O.sub.2.dbd.CO.sub.2+H.sub.20 (1)
CO+ 1/20O.sub.2.dbd.CO.sub.2 (2)
2SO.sub.2+O.sub.2.dbd.2SO.sub.3 (3)
SO.sub.3+H.sub.2O.dbd.H.sub.2SO.sub.4 (4)
NO+ 1/20O.sub.2.dbd.NO.sub.2 (5)
[0019] It should be appreciated that the OC 14 may be configured to
perform any one of the above conversions, combinations of the above
conversions, or even all of the above conversions, depending on the
reactant compounds and their concentrations found in the exhaust
gas flow 4, the temperature of OC 14, and the platinum group metals
selected as the catalyst. Other oxidations are contemplated as
well, such as oxidation of aldehydes, polycyclic aromatic
hydrocarbons or otherwise. Further, the reactions in OC 14 may be
used to reduce the odor of certain emission components.
[0020] OC 14 may be housed within a separate housing 15, including
a metal housing, such as a metal can having an inlet opening and
outlet opening, or otherwise, configured for providing support and
directing fluid flow to the OC 14, as shown in FIGS. 1 and 2. The
housing 15 may comprise any suitable shape or size including a
cylindrically shaped compartment. In an exemplary embodiment,
housing 15 for OC 14 was generally cylindrical in shape having a
volume of about 5.0 liters with a tapered inlet and outlet and
associated mounting flanges to size the cylinder wall down for
engagement with and fluid coupling to respective exhaust conduits
with their associated mounting flanges. The compartment, as well as
other compartments described herein, further may include attachment
features, such as a cylindrical inlet pipe located proximate an
inlet opening and a cylindrical outlet pipe located proximate an
outlet opening of the compartment for fluid coupling of OC 14 to an
exhaust pipe and/or another component of the exhaust aftertreatment
system 2. It should be appreciated that OC 14, including the
housing 15, may include one or more additional components for
facilitating operation of OC 14, or exhaust aftertreatment system
2, or control system 3, including, but not limited to, various gas
or temperature sensors, injectors (urea or fuel injectors) or
otherwise. Such additional features may be particularly
advantageous for monitoring characteristics of the exhaust gas flow
4, such as the flow rate of certain emission constituents (e.g.,
particulate matter or otherwise), which may be particularly
advantageous for determining the necessity of initiating certain
system processes, such as, for example, the regeneration of PF 26
or SCR catalyst 28.
[0021] PF 26 is a wall-flow-device that consists of a ceramic
monolith or substrate having a honeycomb-like structure that
includes a plurality of generally parallel,
longitudinally-extending, interconnected cells that provide a
network comprising a plurality of flow channels for exhaust gas
flow 4 and are separated by a corresponding network of porous cell
walls. The substrate has a large surface area along the cell walls.
Alternating adjacent cells have one of the inlet or outlet plugged
such that an alternating array of inlets is plugged with inlets of
the immediately adjacent cells being open, and an alternating array
of outlets is plugged with outlets of the immediately adjacent
cells being open. The structure has open pores in the cell walls.
Thus, the exhaust gas flow 4 passes into the plurality of inlets
and is forced through the porous cell walls and into the adjacent
outlet cells where it then flows out the plurality of unplugged
outlets. The pores permit the gaseous constituents to pass through
the cell walls while the PM is entrapped within the pores, thereby
providing the PM filtering action of PF 26. PF 26 may have a
predetermined amount of porosity selected to selectively filter PM
within the exhaust gas flow 4 over a range of predetermined exhaust
gas flow rates within exhaust aftertreatment system 2, with the
pore size selected to be smaller than a predetermined particle size
of the PM that exists within exhaust gas flow 4. In an exemplary
embodiment, the average pore size is selected to be smaller than
the average size of the PM particles. For example, in gasoline
fueled engines, the average particle size of the PM is generally
smaller than the average particle size of PM in diesel engines,
hence the pore size of PF 26 used in gasoline engines may be
selected to be smaller than the average pore size of PF 26 used in
diesel engines (e.g., DPF). Any suitable pore size may be used. Any
suitable material may be used for PF 26, including various high
temperature ceramic materials. In an exemplary embodiment, PF 26
may include a ceramic material comprising cordierite or alumina, or
a combination thereof. In an exemplary embodiment, PF 26 is
uncoated, that is, it is not treated with a material that is
configured to catalyze the oxidation or reduction of the
constituents of exhaust gas flow 4.
[0022] The SCR catalyst 28 may be provided, for example, as a
washcoat disposed on a ceramic flow-through monolith or substrate
having a honeycomb-like structure that includes a plurality of
generally parallel, longitudinally-extending, interconnected cells
that provide a network comprising a plurality of flow channels for
exhaust gas flow 4 and are separated by a corresponding network of
cell walls. The substrate has a large surface area along the cell
walls. The washcoat includes a reduction catalyst disposed on a
ceramic matrix. The washcoat may be disposed along the cell walls
in any suitable configuration. For example, it may be located
proximate the cell inlets or the cell outlets, or a combination of
them, or along the entire length of the cells. The washcoat
includes a porous matrix with a surface that is coated with a
catalytically active amount of a suitable reduction catalyst. The
ceramic wall-flow monolith may be made from any suitable ceramic,
including cordierite or alumina or the like.
[0023] PF 26 and SCR catalyst 28 are adapted to provide reduction
of NO.sub.X (SCR catalyst 28) and collection and conversion of PM
(PF 26) over most of the operating temperature range of exhaust
aftertreatment system 2 and engine 10, including typical exhaust
treatment system operating temperatures of from about 302.degree.
F. (about 150.degree. C.) to about 1202.degree. F. (about
650.degree. C.). PF 26 is uncoated and is configured to filter soot
over the entire operating temperature range of engine 10,
including, but not limited to, typical ambient vehicle
storage/starting temperatures from about -40.degree. F. (about
-40.degree. C.) to about 120.degree. F. (about 49.degree. C.) to
operating temperatures up to about 1292.degree. F. (about
700.degree. C.). Passive regeneration of PF 26 and oxidation of the
soot particles occurs in the presence of NO.sub.X over the
temperature range of 482.degree. F. (250.degree. C.) to about
842.degree. F. (450.degree. C.), whereas active regeneration and
oxidation of the soot particles occurs in the presence of O.sub.2
at temperatures of about 500.degree. C. or more, and more
preferably over the temperature range of about 1112.degree. F.
(600.degree. C.) to about 1202.degree. F. (650.degree. C.).
[0024] The SCR catalyst washcoat includes a porous ceramic matrix
with a surface that is coated with a catalytically active amount of
a base metal catalyst, i.e., an amount sufficient to catalyze the
desired chemical reactions. Suitable base metal catalysts include
copper (Cu), chromium (Cr) or iron (Fe), or a combination thereof,
including alloys and compounds thereof. The porous matrix may
include any suitable porous matrix. Suitable porous matrices
include various zeolites. In the case of Cu catalysts, a suitable
zeolite is one known commercially as ZSM-5. The use of a base metal
catalyst allows conversion of the nitrogen oxides without the use
of precious metals. SCR catalyst 28 utilizes ammonia to reduce
NO.sub.X. For example, in an exemplary embodiment, a dosing device,
such as urea dosing device 17, is provided upstream from uncoated
PF 26 for introducing an exhaust fluid (EF), and in the case of
exhaust fluids used with diesel exhaust after treatment systems a
diesel EF (DEF), such as urea, to the exhaust gas flow stream 4,
such as through introduction of a urea solution into exhaust gas
flow 4. The EF is introduced upstream a sufficient distance from
uncoated PF 26 to permit the fluid, e.g. a urea solution, to react
in the exhaust gas flow 4 to form ammonia prior to entering SCR
catalyst 28. Below are exemplary conversion chemical reactions
contemplated with SCR catalyst 28:
[0025] Urea decomposition:
CO(NH.sub.2).sub.2+H.sub.2O.fwdarw.2NH.sub.3+CO.sub.2 (6)
[0026] NO.sub.X reduction reations in SCR catalyst 28:
6NO+4NH.sub.3.fwdarw.5N.sub.2+6H.sub.2O (7)
4NO+4NH.sub.3+O.sub.2.fwdarw.4N.sub.2+6H.sub.2O (8)
6NO.sub.2+8NH.sub.3.fwdarw.7N.sub.2+12H.sub.2O (9)
2NO.sub.2+4NH.sub.3+O.sub.2.fwdarw.3N.sub.2+6H.sub.2O (10)
NO+NO.sub.2+2NH.sub.3.fwdarw.2N.sub.2+3H.sub.2O (11)
[0027] It should be appreciated that the SCR catalyst 28 may be
configured to perform any one of the above conversions, or
combinations of the above conversions, including all of the above
conversions. SCR catalyst 28 begins to function as described above
at an operating temperature of at about 356.degree. F. (180.degree.
C.), and may be more preferably operated in the range of about
482.degree. F. (250.degree. C.) to about 1022.degree. F.
(550.degree. C.).
[0028] Referring to FIG. 2, PF 26 and SCR catalyst 28 may be
housed, for example, within a single housing 25, such as a metal
can, configured to provide support and direct the exhaust gas flow
4 into PF 26 and out of SCR catalyst 28. The housing 25 may have
any suitable shape or size including a cylindrical shape. The
housing 25 may also include attachment features located proximate
to an inlet opening, such as an inlet pipe, and an outlet opening,
such as an outlet pipe, for fluid coupling of housing 25 to an
exhaust pipe and/or other component of the exhaust aftertreatment
system 2. It should be appreciated that housing 25, may include one
or more additional components for facilitating operation of the
exhaust aftertreatment system 2, including, but not limited to,
various sensors, dosing devices (urea or fuel injectors) or
otherwise. Such additional features may be particularly
advantageous for monitoring characteristics of the exhaust gas flow
4, such as the amounts or flow rates of certain emission
constituents, which are particularly advantageous for control of
the exhaust aftertreatment system 2, including regeneration of PF
26.
[0029] Exhaust aftertreatment system 2 may optionally also include
singly, or in combination, additional exhaust aftertreatment
devices, including catalyzed or uncatalyzed particulate filters,
additional oxidation catalysts, catalyzed soot filters, soot
filters, NO.sub.X traps, NSR catalysts, partial hydrocarbon
oxidation catalysts, air pumps, external heating devices, precious
metal catalysts, sulfur traps, phosphorous traps, PO.sub.X
reformers and the like. Each of the additional exhaust
aftertreatment devices employs technologies having various
capabilities for treating the constituent elements of the exhaust
gas flow 4. These devices may be fluidly connected in series or
parallel using known pipes, conduits and connectors. In an
exemplary embodiment, as shown in FIGS. 1 and 2, exhaust
aftertreatment system 2 may include a second OC 40 to ensure the
oxidation of certain constituents in exhaust gas flow 4 and prevent
their release from the system, including unburned HC, ammonia, urea
or CO. Second OC 40 may be housed in a separate housing 45 (FIG.
1), such as that described above for OC 14, or alternately, may be
housed together with SCR 28, or PF 26 and SCR catalyst 28, in a
single housing 25 (FIG. 2).
[0030] Referring to FIG. 1, uncoated PF 26 and SCR catalyst 28 may
also may be housed, for example, within separate housings 25.1,
25.2 respectively, such as metal cans, configured to provide
support and direct the exhaust gas flow 4 into, through and out of
these devices. The housings 25 may have any suitable shape or size
including a cylindrical shape as described above in conjunction
with housing 15. In an exemplary embodiment, housings 25.1 (PF 26)
and 25.2 (SCR catalyst 28) were generally cylindrical in shape
having volumes of about 8.7 liters and 13.2 liters, respectively,
with tapered inlets and outlets to size the cylinder wall down for
engagement with and fluid coupling to respective exhaust conduits.
Housings 25.1 and 25.2 may each also include attachment features
located proximate to an inlet opening, such as an inlet pipe, and
an outlet opening, such as an outlet pipe, for fluid coupling of
the devices to an exhaust pipe and/or other component of the
exhaust aftertreatment system 2. It should be appreciated that
housings 25.1 and 25.2 may include one or more additional
components for facilitating operation of the exhaust aftertreatment
system 2, including, but not limited to, various sensors, dosing
devices (urea or fuel injectors) or otherwise.
[0031] The aftertreatment system includes sensing devices and
systems that are signally connected to and in signal communication
with control system 3, including ECM 5. The sensing devices may
include a NO.sub.X sensor 12 operative to sense exhaust gases
exiting the engine 10, a temperature sensor 27 operative to measure
temperature of exhaust gases or a pressure sensor (not shown) to
sense restriction of the porous passageways of cell walls of PF 26
by accumulation of PM. The NO.sub.X sensor 12 preferably comprises
a sensor operative to generate an electrical signal correlatable to
a parametric value for NO.sub.X concentration in the exhaust gas
flow 4, and further operative to generate a second electrical
signal correlatable to a parametric value for air/fuel ratio of the
exhaust gas feedstream, from which oxygen content can be
determined. The exhaust gas sensing device 22 may optionally
include a second NO.sub.X sensor, operative to generate an
electrical signal correlatable to a parametric value for NO.sub.X
concentration in the exhaust gas feedstream, a temperature sensor
or a pressure sensor, or a combination thereof. Alternately,
NO.sub.X sensor 12 can comprise a virtual sensing device, wherein
NO.sub.X concentration in the exhaust gas flow 4 is determined
based upon engine operating conditions, which is a known
technique.
[0032] The exhaust aftertreatment system 2 optionally includes a HC
dosing device 16 for injecting a controlled amount of HC reductant
upstream of OC 14. An exemplary HC dosing device includes a fuel
injector, such as a diesel fuel injector in the case where engine
10 is a diesel engine, for injecting diesel fuel into exhaust gas
flow 4. In an exemplary embodiment, the fuel line 30 from engine 10
provides pressurized fuel to a controllable pressure regulator
device 32, such as a valve, the output of which is fluidly
connected through conduit 34 to the HC dosing device 16. The HC
dosing device 16 and pressure regulator device 32 are both operably
connected to and in signal communication with control system 3,
including ECM 5, which is adapted to control timing and quantity
(e.g., mass flow) of HC injection, typically in the form of vehicle
fuel, to the exhaust gas flow 4. Alternately, hydrocarbons from a
hydrocarbon reservoir (not shown) or reformer device (not shown)
may be used.
[0033] Referring to FIGS. 1 and 2, in exemplary embodiments,
exhaust aftertreatment system 2 also includes an exhaust fluid (EF)
dosing device 17, such as, for example, a urea injector, for
injecting a controlled amount of EF 19 as a reductant upstream of
the uncoated PF 26 from an EF reservoir 23 through conduit 21. As
used herein, the term EF includes urea in all forms, including
aqueous solutions, and may also include the use of ammonia
(NH.sub.3) as a reductant, since the urea decomposes to produce
ammonia as a reaction by-product, and it is the ammonia that is
used as a reactant species in the catalytic reactions that occur in
SCR catalyst 28. It may also include other materials that can be
used to provide ammonia directly for injection into exhaust gas
flow 4, or that provide ammonia, either directly or indirectly,
upon injection into exhaust gas flow 4. An example of a suitable EF
reservoir 23 is a urea tank. The EF dosing device 17 is operably
connected to and in signal communication with ECM 5, which is
adapted to control timing and quantity of EF 19 injection into the
exhaust gas flow 4. When urea is used as the reductant, injection
should occur sufficiently upstream from uncoated PF 26 to enable
the decomposition of the urea to ammonia prior to entry into SCR
catalyst 28.
[0034] The control system 3 preferably comprises a distributed
control module architecture including a plurality of control
modules adapted to provide coordinated control of the various
vehicle systems including the powertrain system described herein.
The control system is operable to monitor inputs from sensing
devices, synthesize pertinent information, and execute algorithms
to control various actuators to meet operator demands and achieve
control targets, including such parameters as fuel economy,
emissions, performance, drivability, and protection of hardware.
The distributed controller architecture includes ECM 5, and User
Interface (UI) 7 which is operably connected to and in signal
communication with other devices through which a vehicle operator
typically controls or directs operation of the vehicle and
powertrain. Devices through which a vehicle operator provides input
to the UI 7 typically include an accelerator pedal, a brake pedal,
transmission gear selector, and, vehicle speed cruise control. Each
of the aforementioned control modules and devices communicate with
other control modules, devices, sensors, and actuators via a
high-speed local area network (LAN) bus, shown generally as item 6.
The LAN bus 6 allows for structured communication of control
parameters and commands between the various processors, control
modules, and devices. The specific communication protocol utilized
is application-specific. The LAN bus and appropriate protocols
provide for robust messaging and multi-control module interfacing
between the aforementioned control modules and other control
modules providing functionality such as antilock brakes, traction
control, and vehicle stability.
[0035] The ECM 5 comprises a central processing unit signally
electrically connected to volatile and non-volatile memory devices
via data buses. The ECM 5 is operably attached to and in signal
communication with sensing devices and other output devices to
monitor and control operation of the engine 10 and exhaust
aftertreatment system 2, as shown. The output devices preferably
include subsystems necessary for proper control and operation of
the engine, including, by way of example, an air intake system, a
fuel injection system, a spark-ignition system (when a
spark-ignition engine is used, e.g., a homogeneous charge
compression ignition engine), an exhaust gas recirculation (EGR)
system, and an evaporative control system. The engine sensing
devices include devices operable to monitor engine operation,
external conditions, and operator command, and are typically
signally attached to the ECM 5 via wiring harnesses.
[0036] Algorithms stored in the non-volatile memory devices are
executed by the central processing unit and are operable to monitor
inputs from the sensing devices and execute engine control and
diagnostic routines to control operation of the engine, using
preset calibrations. Use of the ECM 5 to control and diagnose
operation of various aspects of the internal combustion engine 10
is well known to one skilled in the art. However, the ECM 5 may be
adapted to exploit the unique advantages of exhaust aftertreatment
system 2 as described herein, to maximize the reduction of NO.sub.X
under various operating regimes of engine 10, and also to maintain
acceptable levels of NO.sub.X reduction during operation of vehicle
1 and engine 10, including during regeneration of PF 26 or SCR
catalyst 28.
[0037] The engine 10 and exhaust aftertreatment system 2 provide a
combination where the performance of the exhaust aftertreatment
system is not constrained due to space limitation on the vehicle
which can be provided at a cost competitive with existing treatment
systems with a NO.sub.X conversion efficiency sufficient to meet
Bin 5 and FTP cycle tailpipe regulations. In many existing designs,
although it would be desirable, there is not enough room to package
the SCR last while providing sufficient mixing length for DEF
(e.g., urea) injection. These include, for example, short
wheelbase, heavy-duty trucks that require the use of exhaust
treatment devices that are capable of processing significant
exhaust volumes, but have limited space in which to package the
necessary exhaust treatment devices between the axles. As an
example, the exhaust aftertreatment system 2 of this invention
enables the packaging of a 5 liter OC 14, a 8.7 liter uncoated DPF
26 and a 13.2 liter SCR catalyst 28 forward of the rear axle. The
exhaust aftertreatment system 2 of this invention provides such an
aftertreatment system, where SCR catalyst 28 is located downstream
of PF 26 within the space envelope available on the vehicle and
without compromising NO.sub.X conversion efficiency. Packaging SCR
catalyst 28 after PF 26 has the advantage that it would see lower
exhaust temperatures under all operating conditions including
regenerations, particularly as compared to other systems where the
SCR is upstream of the DPF in a single can. The wall flow substrate
of PF 26 provides the mixing environment needed to ensure NH.sub.3
uniformity at the face of the SCR catalyst 28. PF 26 also provides
some NH.sub.3 storage capability in the uncoated wall-flow
substrate, which will also enhance the NO.sub.X reduction
capability of SCR catalyst 28. PF 26 will be closer to the engine
which will be better for thermal management, particularly the
retention of heat for use in PF 26 to decompose PM. The NO.sub.X
will all react first with soot providing an improved catalytic
reduction temperature (CRT) effect, resulting in longer
regeneration intervals, improved fuel economy and PF durability. In
addition, the use of second OC 40 downstream of SCR catalyst 28 can
be added to control any HC, urea, ammonia or CO slip. Since PF 26
has no washcoat or platinum group metals, the associated cost
saving from PF 26 can be used, for example, to provide second OC
40, without increasing the cost of exhaust aftertreatment system 2,
relative to conventional exhaust aftertreatment systems. The need
for urea mixers in exhaust conduits 13 will be minimized in this
arrangement due to the space available for conversion of urea prior
to reaching SCR catalyst 28 and the mixing effect realized from the
wall-flow substrate of PF 26, which will result in further
reductions of cost relative to conventional aftertreatment systems.
The back pressure due to the wall-flow substrate of PF 26 provides
high flow uniformity of urea/ammonia at the inlet of PF 26. Since
exhaust gas flow 4 is forced through the substrate walls, this
provides sufficient opportunity for the EF to mix even further and
so by the time it will reach the SCR catalyst 28 inlet, the
NH.sub.3 distribution will be substantially homogeneous.
[0038] 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 as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the present
application.
* * * * *