U.S. patent application number 13/197848 was filed with the patent office on 2011-11-24 for exhaust treatment system with hydrocarbon lean nox catalyst.
Invention is credited to Timothy Jackson, Adam J. Kotrba, Gabriel Salanta.
Application Number | 20110283685 13/197848 |
Document ID | / |
Family ID | 47629842 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110283685 |
Kind Code |
A1 |
Kotrba; Adam J. ; et
al. |
November 24, 2011 |
Exhaust Treatment System With Hydrocarbon Lean NOx Catalyst
Abstract
A system for treating an exhaust stream from an engine includes
a main exhaust passageway adapted to receive the exhaust stream
from the engine. A side branch is in communication with the main
exhaust passageway. A regeneration unit is positioned within the
side branch for combusting a fuel and heating the exhaust flowing
through the main exhaust passageway. A lean NO.sub.x catalyst is
positioned within the main exhaust passageway downstream of the
regeneration unit. A reductant injector is positioned downstream of
the regeneration unit and upstream of the lean NO.sub.x catalyst to
inject reductant particles into the exhaust stream. A controller
operates the regeneration unit to increase the exhaust temperature
as well as operates the reductant injector to reduce NO.sub.x
within the lean NO.sub.x catalyst.
Inventors: |
Kotrba; Adam J.;
(Laingsburg, MI) ; Salanta; Gabriel; (Ann Arbor,
MI) ; Jackson; Timothy; (Dexter, MI) |
Family ID: |
47629842 |
Appl. No.: |
13/197848 |
Filed: |
August 4, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12430194 |
Apr 27, 2009 |
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13197848 |
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61433297 |
Jan 17, 2011 |
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Current U.S.
Class: |
60/286 |
Current CPC
Class: |
Y02T 10/12 20130101;
F01N 3/0842 20130101; F01N 2610/03 20130101; F01N 13/009 20140601;
F01N 3/025 20130101; F01N 3/0821 20130101; F01N 3/106 20130101;
Y02T 10/24 20130101; F01N 3/035 20130101; F01N 2240/14 20130101;
F01N 3/2066 20130101 |
Class at
Publication: |
60/286 |
International
Class: |
F01N 3/18 20060101
F01N003/18 |
Claims
1. A system for treating an exhaust stream from an engine, the
system comprising: a main exhaust passageway adapted to receive the
exhaust stream from the engine; a side branch in communication with
the main exhaust passageway; a regeneration unit positioned within
the side branch for combusting a fuel and heating the exhaust
flowing through the main exhaust passageway; a lean NO.sub.x
catalyst positioned within the main exhaust passageway downstream
of the regeneration unit; a reductant injector positioned
downstream of the regeneration unit and upstream of the lean
NO.sub.x catalyst to inject reductant particles into the exhaust
stream; and a controller to operate the regeneration unit to
increase the exhaust temperature as well as operate the reductant
injector to reduce NO.sub.x within the lean NO.sub.x catalyst.
2. The system of claim 1, further including an oxidation catalyst
and a particulate filter positioned within the main exhaust
passageway downstream of the regeneration unit and upstream of the
reductant injector.
3. The system of claim 2, further including a selective catalytic
reduction device positioned downstream of the lean NO.sub.x
catalyst.
4. The system of claim 3, wherein the oxidation catalyst and the
particulate filter are positioned in a first housing, the lean
NO.sub.x catalyst and the selective catalytic reduction device
being positioned in a second housing spaced apart from the first
housing.
5. The system of claim 1, wherein the lean NO.sub.x catalyst
includes a catalyst coated particulate filter.
6. The system of claim 5, wherein the reductant injector is
positioned downstream of the oxidation catalyst and further
including a selective catalytic reduction device positioned
downstream of the lean NO.sub.x catalyst.
7. The system of claim 1, wherein the reductant injector includes
an aerosol generator for heating and injecting reductant.
8. The system of claim 7, wherein the aerosol generator supplies
reductant particles having a size less than one micron in
diameter.
9. The system of claim 1, further including an oxidation catalyst
and a particulate filter positioned within the main exhaust
passageway downstream of the lean NO.sub.x catalyst.
10. The system of claim 1, further including a hydrocarbon injector
positioned downstream of the regeneration unit and upstream from an
oxidation catalyst to inject a hydrocarbon into the exhaust
stream.
11. The system of claim 1, further including a particulate filter
having a selective catalytic reduction material coating, the coated
filter being positioned downstream of the lean NO.sub.x
catalyst.
12. The system of claim 1, wherein the reductant injector injects
an internal combustion engine fuel.
13. The system of claim 12, wherein the regeneration unit is
positioned immediately upstream of the lean NO.sub.x catalyst to
provide exhaust at a temperature high enough to burn carbon
deposits from active sites within the lean NO.sub.x catalyst.
14. A system for treating an exhaust stream from an engine, the
system comprising: an exhaust passageway adapted to receive the
exhaust stream from the engine; a burner for combusting a fuel and
heating the exhaust flowing through the exhaust passageway; a lean
NO.sub.x catalyst positioned within the exhaust passageway
downstream of the burner; a reductant injector positioned upstream
of the burner and upstream of the lean NO.sub.x catalyst to inject
reductant particles into the exhaust stream; and a controller to
operate the burner to increase the exhaust temperature as well as
operate the injector to reduce NO.sub.x within the lean NO.sub.x
catalyst.
15. The system of claim 14, further including a particulate filter
having a selective catalytic reduction material coating, the coated
filter being positioned downstream of the lean NO.sub.x
catalyst.
16. The system of claim 14, wherein the reductant injector includes
an aerosol generator for heating and injecting a hydrocarbon
reductant.
17. The system of claim 16, wherein the aerosol generator supplies
reductant particles having a size less than one micron in
diameter.
18. The system of claim 14, wherein the reductant includes an
alcohol based fuel.
19. The system of claim 14, wherein the burner includes a shell
around which an exhaust and reductant mixture flows, the burner
generating a flame positioned within the shell.
20. A system for treating an exhaust stream from an engine, the
system comprising: an exhaust passageway adapted to receive the
exhaust stream from the engine; a burner for combusting a fuel and
heating the exhaust flowing through the exhaust passageway; a lean
NO.sub.x catalyst positioned within the exhaust passageway in
direct receipt of the exhaust heated by the burner prior to passing
through another catalyst; a hydrocarbon injector positioned
downstream of the burner and upstream of the lean NO.sub.x catalyst
to inject hydrocarbon into the exhaust stream; and a controller to
operate the burner to increase the exhaust temperature to a
predetermined magnitude for burning carbon deposits positioned at
active sites within the lean NO.sub.x catalyst.
21. The system of claim 20, wherein the hydrocarbon includes an
alcohol based fuel.
22. The system of claim 20, wherein the hydrocarbon includes diesel
fuel.
23. The system of claim 20, further including an oxidation catalyst
and a particulate filter positioned within the main exhaust
passageway downstream of the regeneration unit.
24. The system of claim 20, wherein the reductant injector includes
an aerosol generator for heating and injecting the hydrocarbon.
25. The system of claim 24, wherein the aerosol generator supplies
reductant particles having a size less than one micron in diameter.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/430,194, filed on Apr. 27, 2009. This
application claims the benefit of U.S. Provisional Application No.
61/433,297 filed on Jan. 17, 2011. The entire disclosures of the
above applications are incorporated herein by reference.
FIELD
[0002] The present disclosure generally relates to a system for
treating exhaust gases. More particularly, a device for increasing
an exhaust gas temperature upstream of a hydrocarbon lean NO.sub.x
catalyst is discussed.
BACKGROUND
[0003] In an attempt to reduce the quantity of NO.sub.X and
particulate matter emitted to the atmosphere during internal
combustion engine operation, a number of exhaust aftertreatment
devices have been developed. A need for exhaust aftertreatment
systems particularly arises when diesel combustion processes are
implemented. Typical aftertreatment systems for diesel engine
exhaust may include one or more of a diesel particulate filter
(DPF), a selective catalytic reduction (SCR) system, a hydrocarbon
(HC) injector, and a diesel oxidation catalyst (DOC).
[0004] During engine operation, the DPF traps soot emitted by the
engine and reduces the emission of particulate matter (PM). Over
time, the DPF becomes loaded and begins to clog. Periodic
regeneration or oxidation of the trapped soot in the DPF is
required for proper operation. To regenerate the DPF, relatively
high exhaust temperatures in combination with an ample amount of
oxygen in the exhaust stream are needed to oxidize the soot trapped
in the filter.
[0005] The DOC is typically used to generate heat to regenerate the
soot loaded DPF. When hydrocarbons (HC) are sprayed over the DOC at
or above a specific light-off temperature, the HC will oxidize.
This reaction is highly exothermic and the exhaust gases are heated
during light-off. The heated exhaust gases are used to regenerate
the DPF.
[0006] Under many engine operating conditions, however, the exhaust
gas is not hot enough to achieve a DOC light-off temperature of
approximately 300.degree. C. As such, DPF regeneration does not
passively occur. Furthermore, NO.sub.X adsorbers and selective
catalytic reduction systems typically require a minimum exhaust
temperature to properly operate.
[0007] A burner may be provided to heat the exhaust stream upstream
of the various aftertreatment devices. Known burners have
successfully increased the exhaust temperature of internal
combustion engines for automotive use. Some Original Equipment
Manufacturers have resisted implementation of prior burners due to
their size and cost. Furthermore, other applications including
diesel locomotives, stationary power plants, marine vessels and
others may be equipped with relatively large diesel compression
engines. The exhaust mass flow rate from the larger engines may be
more than ten times the maximum flow rate typically provided to the
burner. While it may be possible to increase the size of the burner
to account for the increased exhaust mass flow rate, the cost,
weight and packaging concerns associated with this solution may be
unacceptable. Therefore, a need may exist in the art for an exhaust
treatment system equipped with a hydrocarbon lean NO.sub.x catalyst
and a device to increase the temperature of the exhaust output from
an engine while minimally affecting the cost, weight, size and
performance of the exhaust system. It may also be desirable to
minimally affect the pressure drop and/or back pressure associated
with the use of a burner.
SUMMARY
[0008] This section provides a general summary of the disclosure,
and is not a comprehensive disclosure of its full scope or all of
its features.
[0009] A system for treating an exhaust stream from an engine
includes a main exhaust passageway adapted to receive the exhaust
stream from the engine. A side branch is in communication with the
main exhaust passageway. A regeneration unit is positioned within
the side branch for combusting a fuel and heating the exhaust
flowing through the main exhaust passageway. A lean NO.sub.x
catalyst is positioned within the main exhaust passageway
downstream of the regeneration unit. A reductant injector is
positioned downstream of the regeneration unit and upstream of the
lean NO.sub.x catalyst to inject reductant particles into the
exhaust stream. A controller operates the regeneration unit to
increase the exhaust temperature as well as operates the reductant
injector to reduce NO.sub.x within the lean NO.sub.x catalyst.
[0010] A system for treating an exhaust stream from an engine
includes a burner for combusting a fuel and heating the exhaust
flowing through an exhaust passageway. A lean NO.sub.x catalyst is
positioned within the exhaust passageway downstream of the burner.
A reductant injector is positioned upstream of the burner and
upstream of the lean NO.sub.x catalyst to inject reductant
particles into the exhaust stream. A controller operates the burner
to increase the exhaust temperature as well as operates the
injector to reduce NO.sub.x within the lean NO.sub.x catalyst.
[0011] A system for treating an exhaust stream from an engine
includes a burner for combusting a fuel and heating the exhaust
flowing through an exhaust passageway. A lean NO.sub.x catalyst is
positioned within the exhaust passageway in direct receipt of the
exhaust heated by the burner prior to passing through another
catalyst. A hydrocarbon injector is positioned downstream of the
burner and upstream of the lean NO.sub.x catalyst to inject
hydrocarbon into the exhaust stream. A controller operates the
burner to increase the exhaust temperature to a predetermined
magnitude for burning carbon deposits positioned at active sites
within the lean NO.sub.x catalyst.
[0012] Further areas of applicability will become apparent from the
description provided herein. The description and specific examples
in this summary are intended for purposes of illustration only and
are not intended to limit the scope of the present disclosure.
DRAWINGS
[0013] The drawings described herein are for illustrative purposes
only of selected embodiments and not all possible implementations,
and are not intended to limit the scope of the present
disclosure.
[0014] FIG. 1 is a schematic depicting a system for controlling the
temperature of an exhaust from an engine;
[0015] FIG. 2 is a sectional side view of a portion of the exhaust
aftertreatment system depicted in FIG. 1 including a miniature
regeneration unit;
[0016] FIG. 3 is a cross-sectional view of an alternate
regeneration unit;
[0017] FIG. 4 is a cross-sectional view of an alternate
regeneration unit;
[0018] FIG. 5 is a cross-sectional view of an engine aftertreatment
system including a flow diverter;
[0019] FIG. 6 is a perspective view of the aftertreatment system
including the flow diverter;
[0020] FIG. 7 is a partial perspective view of a portion of another
alternate regeneration unit;
[0021] FIG. 8 is a cross-sectional view of another alternate
regeneration unit;
[0022] FIGS. 9-13 are perspective views depicting alternate inlet
tube portions of the regeneration unit;
[0023] FIG. 14 is a sectional view depicting another alternate
exhaust aftertreatment system;
[0024] FIGS. 15-19 depict alternate exhaust aftertreatment systems
including a regeneration unit and a hydrocarbon lean NO.sub.x
catalyst; and
[0025] FIGS. 20 and 21 depict alternate exhaust gas aftertreatment
systems including a burner and a hydrocarbon lean NO.sub.x
catalyst.
[0026] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0027] Example embodiments will now be described more fully with
reference to the accompanying drawings.
[0028] FIG. 1 depicts an exhaust gas aftertreatment system 10 for
treating the exhaust output by an exemplary engine 12 to a main
exhaust passageway 14. An intake passage 16 is coupled to engine 12
to provide combustion air thereto. A turbocharger 18 includes a
driven member (not shown) positioned in an exhaust stream. During
engine operation, the exhaust stream causes the driven member to
rotate and provide compressed air to intake passage 16 prior to
entry into engine 12.
[0029] Exhaust aftertreatment system 10 also includes a miniature
regeneration unit 26 positioned downstream from turbocharger 18 and
upstream from a number of exhaust aftertreatment devices. In the
exemplary aftertreatment system depicted in FIG. 1, the
aftertreatment devices include a hydrocarbon injector 28, a diesel
oxidation catalyst 30 and a diesel particulate filter 32.
[0030] Regeneration unit 26 is positioned within a side branch
portion 34 of system 10 in communication with main exhaust
passageway 14. Regeneration unit 26 may be used to heat the exhaust
passing through passageway 14 to an elevated temperature that will
enhance the efficiency of DOC 30 and allow regeneration of DPF
32.
[0031] Regeneration unit 26 may include one or more injectors 36
for injecting a suitable fuel and an oxygenator. The fuel may
include hydrogen or a hydrocarbon. Injector 36 may be structured as
a combined injector that injects both the fuel and oxygenator, as
shown in FIG. 1, or may include separate injectors for the fuel and
the oxygenator (FIG. 11). A control module 38 is provided to
monitor and control the flows through the injector 36 and the
ignition of fuel by a first igniter 42 using any suitable
processor(s), sensors, flow control valves, electric coils,
etc.
[0032] Regeneration unit 26 includes a housing 50 constructed as a
multi-piece assembly of fabricated metal components. Housing 50
includes an inlet tube 52, a cylindrically-shaped body 54, and an
outlet tube 56. An inlet header 58 is fixed to inlet tube 52. Inlet
header 58 is fixed to side branch portion 34 and encloses one of
its ends. Other single or multi-piece inlet assemblies are also
contemplated as being within the scope of the present disclosure.
An annular volume 62 exists in a space between an inner surface 64
of side branch portion 34 and an outer surface of housing 50.
[0033] An injector mount 65 is fixed to inlet tube 52 and/or inlet
header 58 to provide an attachment mechanism for injector 36. A
nozzle portion 66 of injector 36 extends into inlet tube 52 such
that atomized fuel may be injected within a primary combustion
chamber 68 at least partially defined by an inner cylindrical
surface 70 of body 54. Injector 36 includes a fuel inlet 72 and an
air inlet 74. Fuel inlet 72 is in communication with a fuel
delivery system 76 including a fuel tank 78, a fuel filter 80, a
fuel pump 82 and a fuel block 84 interconnected by a fuel line 86.
Operation of the components of fuel delivery system 76 selectively
provides hydrocarbon to injector 36.
[0034] A secondary air system 90 includes a secondary air filter 92
and a MAF sensor 94. A compressor 96 is in receipt of air that is
passed through secondary air filter 92 and MAF sensor 94.
Compressor 96 may include a portion of a supercharger, a
turbocharger or a stand-alone electric compressor. Output from
compressor 96 is provided to air inlet 74. When exhaust heating is
desired, fuel is injected via fuel inlet 72 and the oxygenator is
provided via air inlet 74 to inject a stream of atomized fuel.
First igniter 42 is mounted to side branch portion 34 downstream of
inlet header 58 and is operable to combust the fuel provided by
injector 36 within primary combustion chamber 68.
[0035] Side branch portion 34 intersects exhaust passageway 14 at
an angle A of substantially 30 degrees. The flame produced by
regeneration unit 26 extends into exhaust passageway 14 at
substantially the same angle.
[0036] An elongated aperture 110 extends through a pipe 112
defining main exhaust passageway 14. A portion of body 54 and
outlet tube 56 are positioned within exhaust passageway 14. Exhaust
provided from engine 12 impinges on housing 50 and cools it during
operation of regeneration unit 26. Furthermore, because housing 50
minimally intrudes within passageway 14, exhaust back pressure is
also minimally increased. It should also be appreciated that side
branch portion 34 and injector 36 minimally radially outwardly
extend from pipe 112. Such an arrangement allows an Original
Equipment Manufacturer to more easily package the miniature
regeneration unit on the vehicle.
[0037] In the present aftertreatment system, first igniter 42 also
includes an ion sensor 44 coupled to a coil 46. Ion sensor 44 may
be in the form of an electrode positioned within combustion chamber
68. A voltage may be applied to the ion sensor to create an
electric field from the sensor to a ground such as housing 50. When
voltage is applied, an electric field radiates from the sensor to
the ground. If free ions are present in the field, a small ion
current may flow. The magnitude of the ion current provides an
indication of the density of the ions. Control module 38 detects
and receives signals from ion sensor 44 to determine the presence
or absence of a flame. Ion sensor 44 may also determine if igniter
42 is fouled.
[0038] Fouling may occur through deposition of soot, oil or other
contaminants. When igniter 42 is fouled, proper combustion may not
occur. Control module 38 is operable to supply and discontinue the
supply of fuel to fuel inlet 72, air to air inlet 74 and electrical
energy to igniter 42. Prior to initiating the supply of fuel and
air to injector 36, control module 38 determines whether igniter 42
has been fouled via the signal provided by ion sensor 44. If the
igniter is determined to be ready for operation, control module 38
may account for a number of engine and vehicle operating conditions
such as engine speed, ambient temperature, vehicle speed, engine
coolant temperature, oxygen content, mass air flow, pressure
differential across diesel particulate filter 32, and any number of
other vehicle parameters. If control module 38 determines that an
increase in exhaust gas temperature is desired, fuel and secondary
air are provided to injector 36. Coil 46 supplies electrical energy
to igniter 42 to initiate combustion within primary combustion
chamber 68.
[0039] Control module 38 may also evaluate a number of other
parameters including presence of combustion and temperature of the
exhaust gas within passageway 14 at a location downstream from
regeneration unit 26 to determine when to cease the supply of fuel
and air to injector 36. For example, control module 38 may receive
signals from one or more temperature sensors located within
regeneration unit 26, side branch portion 34 or within main
passageway 14 to perform a closed loop control by operating
regeneration unit 26 to maintain a desired temperature at a
particular location. If combustion unexpectedly extinguishes,
control module 38 ceases the supply of fuel. Other control schemes
are also within the scope of the present disclosure.
[0040] FIG. 3 depicts an alternate regeneration unit 26a coupled to
side branch portion 34. Regeneration unit 26a is substantially
similar to regeneration unit 26 except that the reduced or
necked-down outlet tube portion of housing 50 has been removed. As
such, like elements will be identified with an "a" suffix. Main
body portion 54a includes a substantially constant diameter that
terminates at an outlet opening 53a.
[0041] FIG. 4 depicts another alternate regeneration unit
identified at reference numeral 26b. Regeneration unit 26b is
substantially similar to regeneration unit 26 except that a length
L has been increased to cause a greater portion of housing 50b to
be positioned within exhaust passageway 14. Like elements will
include a "b" suffix. The location of igniter 42b has been changed
to be further from an end of nozzle 66.
[0042] FIGS. 5 and 6 depict another alternate arrangement including
a diverter plate 140 positioned within pipe 112 upstream of
miniature regeneration unit 26. Diverter plate 140 includes a
D-shaped aperture 142 extending therethrough. Diverter plate 140 is
positioned at an angle as depicted in FIG. 5 to urge exhaust
flowing through passageway 14 to flow toward and around housing 50.
The diverted exhaust flow transfers heat from regeneration unit 26
to the exhaust flowing through pipe 112.
[0043] FIG. 7 depicts a portion of another alternate regeneration
unit identified at reference numeral 26c. Regeneration unit 26c is
substantially similar to regeneration unit 26 except that outlet
tube 56c is increased in length and includes a plurality of
apertures 144 extending therethrough. The extended outlet tube
length and apertures 144 assure that the combustion flame is
properly maintained and directed during operation of regeneration
unit 26c. As exhaust flows through passageway 14, some of the
exhaust passes through apertures 144 creating a mixing effect
resulting in a more desirable temperature distribution, flame
stability and flame quality.
[0044] FIG. 8 depicts another alternate regeneration unit
identified at reference numeral 26d. Regeneration unit 26d includes
the components of regeneration unit 26 as well as an additional
housing portion 145 defining a secondary combustion chamber 146. A
second igniter 148 extends into secondary combustion chamber 146. A
plurality of apertures 149 extends through second housing 145 to
allow exhaust gas to enter secondary combustion chamber 146.
Enhanced exhaust heating and mixing may be achieved through the use
of regeneration unit 26d.
[0045] FIGS. 9-13 depict alternate inlet tube configurations that
may be used in lieu of inlet tube 52. Each of the modified inlet
tubes includes a plurality of circumferentially spaced apart
apertures 150 extending through an end wall 152. Apertures 150
allow exhaust gas flowing through passageway 14 to enter primary
combustion chamber 68. By providing oxygen into primary combustion
chamber 68 via apertures 150, the pressure of secondary air
provided by compressor 96 to injector 36 may be reduced. The cost
and size of compressor 96 may also be reduced.
[0046] Inlet tube 52e shown in FIG. 9 includes a plurality of flaps
156e attached at one end to end wall 152e. Flaps 156e are arranged
to induce gas passing through apertures 150e to swirl. FIG. 10
depicts rectangularly shaped apertures 150f with no flaps. FIG. 11
depicts a plurality of flaps 156g attached at a radial inner extent
of apertures 150g. Flaps 156g extend at an angle to exhaust flow in
a radially outward direction. FIG. 12 refers to another alternate
inlet tube assembly 52h having a plurality of apertures 150h and a
plurality of flaps 156h. Flaps 156h radially inwardly extend.
[0047] FIG. 13 shows a plurality of circular apertures 150i
circumferentially spaced apart from one another. No flaps partially
block the apertures. Each of the arrangements depicted in FIGS.
9-13 provide a substantially homogenous distribution of flow within
primary combustion chamber 68.
[0048] It is also contemplated that any one of the described
miniature regeneration unit arrangements including apertures 150
may be equipped with an injector 36j having a relocated secondary
air inlet 74j, to inject compressed air at a relatively low
pressure into annular volume 62, as shown in FIG. 14. Fuel inlet
72j positioned to inject atomized fuel within primary combustion
chamber 68j, as previously discussed. Some of the air injected into
annular volume 62j passes through apertures 150i and the remaining
portion of the secondary air passes over an outside surface of
housing 50j to cool miniature regeneration unit 26j.
[0049] FIG. 15 depicts a portion of another exhaust gas
aftertreatment system identified at reference numeral 200. System
200 is similar to system 10 depicted in FIG. 1. Accordingly, like
elements will retain their previously introduced reference
numerals. Exhaust gas aftertreatment system 200 includes a
reductant injector 202 positioned immediately downstream from DPF
32. The reductant injector may be configured as an aerosol
generator 202. Reductant injector 202 is supplied with a
hydrocarbon such as diesel fuel stored within fuel tank 78. In the
example shown in FIG. 15, a fuel line 204 supplies fuel from tank
78 to the reductant injector. Other internal combustion engine
fuels such as ethanol based fuels including E85, E93, or E95 may be
the reductant of choice and stored in a separate on-board
container.
[0050] Aerosol generator 202 includes an electrically powered
heating element. Reductant supplied via fuel line 204 is heated by
the heating element. It should be appreciated that the reductant
may or may not come into direct contact with a surface of the
heating element. Regardless of the arrangement, energy is
transferred from the heating element to the reductant to increase
the temperature and energy content of the reductant. The heated
reductant is injected into the exhaust stream downstream from DPF
32. Based on the nozzle design, reductant pressure and reductant
temperature, very small reductant droplets having a size less the
one micron are injected into exhaust passageway 14.
[0051] A lean NO.sub.X catalyst (LNC) 208 and a selective catalytic
reduction device (SCR) 210 are mounted within a common housing 214.
LNC 208 is positioned upstream of SCR 210 to reduce NO.sub.X in an
oxygen rich environment. LNC 208 is a hydrocarbon lean NO.sub.X
catalyst configured to reduce NO.sub.X using a hydrocarbon as the
reductant. Aerosol generator 202 provides a number of design
advantages for exhaust aftertreatment system 200. The heated
aerosol mist of reductant exiting aerosol generator 202 is rapidly
dispersed throughout the exhaust exiting DPF 32. A minimized length
of exhaust conduit is required to provide a mixing zone for the
exhaust and reductant prior to entry into LNC 208. The small
reductant droplets interact with the porous surface of LNC 208 more
efficiently than larger droplets of reductant. Use of aerosol
generator 202 results in improved catalyst response from LNC 208.
The reduced size droplets also minimize the likelihood of damage to
LNC 208 through liquid impingement on the catalyst.
[0052] SCR 210 is positioned downstream from LNC 208 to further
reduce NO.sub.X and remove ammonia from the exhaust stream. As
depicted in FIG. 15, LNC 208 and SCR 210 may be positioned adjacent
to one another within common housing 214.
[0053] Reductant injector 202 may alternatively be configured as a
nozzle for supplying unheated and pressurized reductant. Injector
202 may supply an alcohol based internal combustion engine fuel.
Based on the volatility of these fuels, an aerosol generator or
vaporizer may not be needed to rapidly disperse the reductant in
the exhaust.
[0054] FIG. 16 depicts a portion of another alternate exhaust gas
aftertreatment system identified at reference numeral 300. System
300 is substantially similar to system 200. Accordingly, like
elements will be identified by their previously introduced
reference numerals. In the arrangement depicted in FIG. 16, the
diesel particulate filter has been moved downstream and combined
with the SCR. As such, a DPF having an SCR coating is depicted at
reference numeral 302. By moving the DPF further downstream, LNC
208 is positioned closer to engine 12 and miniature regeneration
unit 26. Accordingly, the temperature of exhaust entering LNC 208
should be greater than a like configuration where LNC 208 is
positioned further from the energy sources.
[0055] Exhaust gas aftertreatment system 10 takes advantage of the
relative position of miniature regeneration unit 26, diesel
oxidation catalyst 30 and aerosol generator 202 to maximize the
conversion efficiency of LNC 208. The NO.sub.X reduction efficiency
achieved by LNC 208 increases with the increase of exhaust
temperature. Furthermore, it should be appreciated that SCR coated
DPF 302 is positioned within sufficient proximity of miniature
regeneration unit 26 and diesel oxidation catalyst 30 to
selectively regenerate SCR/DPF 302 as required. By using aerosol
generator 202 to introduce the reductant, improved distribution and
mixing of the reductant with the exhaust gas occurs prior to
entering LNC 208. Efficient NO.sub.X reduction occurs. Aerosol
generator 202 further improves the operating characteristics of LNC
208 by injecting heated reductant. An undesirable reduction in the
exhaust temperature is avoided.
[0056] FIG. 17 depicts a portion of another alternate exhaust gas
aftertreatment system 400. Aftertreatment system 400 relocates LNC
208 further upstream closer to engine 12 and miniature regeneration
unit 26. This configuration increases NO.sub.X conversion
efficiency over a greater range of engine operating conditions
including cold starts. Miniature regeneration unit 26 adds heat to
the exhaust while aerosol generator 202 adds energy to the
reductant injected upstream of LNC 208. Regeneration unit 26 may be
positioned upstream of lean NO.sub.x catalyst 208 such that carbon
deposits may be periodically or continuously burned from the
catalyst's active sites. Regeneration of lean NO.sub.x catalyst 208
increases the NO conversion efficiency of aftertreatment system
400. It is contemplated that LNC 208 includes a silver-based
catalyst for use with alcohol-based reductants such as ethanol,
E85, E93, E95 and the like. Acetaldehyde is produced as the active
compound in NO reduction at temperatures greater than or equal to
300.degree. C. Through the use of aerosol generator 202, also known
as a vaporizer, the alcohol-based reductants may be broken down
prior to contact with the silver-based catalyst to cause NO
conversion to occur at temperatures lower than 300.degree. C. The
use of aerosol generator 202 also increases the overall conversion
efficiency at higher catalyst temperatures.
[0057] If desired, an optional SCR (not shown) may be positioned
immediately downstream from LNC 208 to conduct additional NO.sub.X
conversion and ammonia reduction. System 400 includes hydrocarbon
injector 28 being positioned downstream from LNC 208 and upstream
from DOC 30 and DPF 32. DOC 30 and DPF 32 are shown positioned in a
common housing 402. To regenerate DPF 32, controller 38 selectively
causes hydrocarbon injector 28 to inject a reductant such as diesel
fuel into the exhaust stream downstream of LNC 208 and upstream
from DOC 30.
[0058] FIG. 18 depicts another alternate exhaust gas aftertreatment
system 500. Aftertreatment system 500 is substantially similar to
aftertreatment system 300. Accordingly, like elements will retain
their previously introduced reference numerals. More particularly,
system 500 differs from system 300 in that system 500 includes a
diesel particulate filter having a lean NO.sub.X catalyst coating
instead of an SCR coated DPF. Packaging space and cost may be
reduced by implementing the solutions shown in aftertreatment
system 300 and aftertreatment system 500.
[0059] During operation of LNC DPF 502, an exothermic chemical
reaction takes place. The release of energy aids in regeneration of
soot captured by the diesel particulate filter. Furthermore,
regeneration of the DPF may occur simultaneously with desulfation
of the hydrocarbon LNC. SCR 210 is positioned downstream from
LNC/DPF 502 to remove ammonia and further reduce NO.sub.X.
[0060] FIG. 19 shows another alternate exhaust gas aftertreatment
system 600. Exhaust gas aftertreatment system 600 is substantially
similar to aftertreatment system 500. These systems are
substantially the same other than aerosol generator 202 is replaced
with a second reductant injector 602. Second reductant injector 602
is plumbed in communication with a supplemental storage tank 604. A
second reductant such as an alcohol based fuel is stored within
tank 604 and selectively supplied to second reductant injector 602.
Alcohol based fuels such as E85, E93 and E95 provide an enhanced
NO.sub.X reduction efficiency when compared to the use of diesel
fuel as a reductant. An injector may be used to inject the alcohol
based fuel instead of an aerosol generator due to the low vapor
pressure of the second reductant. Filling tank 604 with a readily
available alcohol based fuel is considered to be desirable when
compared to storing and dispensing a source of ammonia such as
urea.
[0061] FIG. 20 depicts another exhaust gas aftertreatment system
700 equipped with LNC 208 and SCR/DPF 302 packaged in a common
housing 702. Aerosol generator 202 is positioned in communication
with exhaust passageway 14 upstream of a burner 704. Burner 704 is
configured such that all of the exhaust travelling through
passageway 14 passes through burner 704 to an inlet 706 of housing
702. System 700 operates such that the atomized reductant provided
by aerosol generator 202 is heated by burner 704 but not combusted
by the flame produced within burner 704. As such, a reductant laden
and heated exhaust is provided to inlet 706 to achieve an improved
operating range and better cold start performance of LNC 208.
Burner 704 is configured with a shell 708 to achieve this function.
The burner generates a combustion flame within shell 708. The
reductant and exhaust mixture passes over an outer surface of shell
708 to allow heat transfer to the exhaust without combusting the
reductant.
[0062] FIG. 21 depicts another exhaust gas aftertreatment system
identified at reference numeral 800. System 800 is substantially
similar to system 700 with the exception that aerosol generator 202
is replaced with a secondary reductant injector 802. Secondary
reductant injector 802 is supplied with a secondary reductant such
as an alcohol based fuel stored in a supplemental reductant tank
804. Injected secondary reductant mixes with exhaust travelling
through exhaust passageway 14 and is heated by burner 704. The
heated reductant and exhaust is supplied to LNC 208 and SCR/DPF 302
to reduce undesirable NO.sub.X emissions.
[0063] The foregoing description of the embodiments has been
provided for purposes of illustration and description. It is not
intended to be exhaustive or to limit the disclosure. Individual
elements or features of a particular embodiment are generally not
limited to that particular embodiment, but, where applicable, are
interchangeable and can be used in a selected embodiment, even if
not specifically shown or described. Additional alternate exhaust
gas aftertreatment systems are also contemplated as being within
the scope of the present disclosure. For example, previous
configurations described as having an aerosol generator may also be
configured to include a more typical reductant injector for
supplying reductant into the exhaust at its ambient temperature.
The same may also be varied in many ways. Such variations are not
to be regarded as a departure from the disclosure, and all such
modifications are intended to be included within the scope of the
disclosure.
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