U.S. patent application number 11/225273 was filed with the patent office on 2006-03-16 for management of thermal fluctuations in lean nox adsorber aftertreatment systems.
Invention is credited to Richard Ancimer, Mark E. Dunn, Jonathan M.S. Harris, Olivier Lebastard.
Application Number | 20060053776 11/225273 |
Document ID | / |
Family ID | 32991668 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060053776 |
Kind Code |
A1 |
Ancimer; Richard ; et
al. |
March 16, 2006 |
Management of thermal fluctuations in lean NOx adsorber
aftertreatment systems
Abstract
A method and apparatus manage heat in exhaust gas in an
aftertreatment system that employs a lean NOx adsorber. A
de-sulfation hot line and cooling line are employed to control
exhaust gas temperatures for adsorption, regeneration and
de-sulfation cycles of the aftertreatment system where each cycle
can require different chemical and exhaust gas temperatures
independent of the engine operation. The method and apparatus
include a SOx adsorber to provide greater system durability.
Inventors: |
Ancimer; Richard;
(Vancouver, CA) ; Harris; Jonathan M.S.;
(Vancouver, CA) ; Lebastard; Olivier; (Burnaby,
CA) ; Dunn; Mark E.; (Vancouver, CA) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET
SUITE 3400
CHICAGO
IL
60661
US
|
Family ID: |
32991668 |
Appl. No.: |
11/225273 |
Filed: |
September 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/CA04/00390 |
Mar 11, 2004 |
|
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11225273 |
Sep 13, 2005 |
|
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Current U.S.
Class: |
60/286 ; 60/295;
60/301 |
Current CPC
Class: |
F01N 2610/04 20130101;
F01N 3/0871 20130101; F01N 2610/03 20130101; F01N 3/323 20130101;
F01N 2570/14 20130101; F01N 3/0878 20130101; F01N 3/2093 20130101;
F01N 3/0885 20130101; F01N 2430/085 20130101; F02B 37/00 20130101;
F02M 26/15 20160201; F01N 3/2046 20130101; F01N 3/0807 20130101;
B01D 53/96 20130101; F01N 2570/04 20130101; Y02T 10/22 20130101;
B01D 53/9454 20130101; F01N 3/0205 20130101; F01N 3/05 20130101;
F01N 3/0842 20130101; F01N 2240/02 20130101; F01N 2270/02 20130101;
Y02A 50/20 20180101; F01N 3/085 20130101; F01N 3/043 20130101; F01N
3/2006 20130101; F01N 5/04 20130101; F01N 3/0814 20130101; F01N
13/009 20140601; F01N 3/02 20130101; Y02A 50/2344 20180101; Y02C
20/10 20130101; F01N 2240/30 20130101; Y02T 10/12 20130101; F01N
3/32 20130101 |
Class at
Publication: |
060/286 ;
060/295; 060/301 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 14, 2003 |
CA |
2,422,164 |
Dec 17, 2003 |
CA |
2,453,689 |
Claims
1. An aftertreatment system for treating NOx found in exhaust gas
produced during combustion of a fuel within a combustion chamber of
an operating internal combustion engine, said aftertreatment system
comprising: an exhaust line for directing said exhaust gas from
said engine and through said aftertreatment system, said exhaust
line comprising a cooling line and a hot line for managing exhaust
gas temperature during an adsorption cycle and a regeneration
cycle; a lean NOx adsorber disposed in said exhaust line; a
catalyst capable of oxidizing a reductant and directing said
oxidized reductant into said exhaust gas; a reductant line for
delivering a reductant from a reductant store to said catalyst; a
reductant flow control disposed in said reductant line for
controlling flow of said reductant into said exhaust line; and a
flow control for controlling flow of exhaust gas through said hot
line and cooling line, wherein said exhaust line is capable of
delivering exhaust gas from said catalyst to said lean NOx
adsorber.
2. The aftertreatment system of claim 1 wherein said catalyst is
disposed in said exhaust line.
3. The aftertreatment system of claim 2 wherein said cooling line
and said hot line are between said catalyst and said NOx
adsorber.
4. The aftertreatment system of claim 2 wherein said cooling line
is longer than said hot line.
5. The aftertreatment system of claim 2 further comprising a
turbine disposed in said cooling line.
6. The aftertreatment system of claim 5 wherein said turbine drives
an air blower disposed in an air dilution line and connected to
compress air and direct the compressed air into said cooling
line.
7. The aftertreatment system of claim 2 further comprising an air
blower disposed in an air dilution line for compressing and
directing air into said cooling line.
8. The aftertreatment system of claim 2 further comprising a heat
exchanger disposed in said cooling line.
9. The aftertreatment system of claim 2 further comprising a
close-coupled catalyst in said exhaust line upstream of said
catalyst, said reductant line capable of delivering reductant to
said exhaust line upstream of said close-coupled catalyst.
10. The aftertreatment system of claim 2 wherein said reductant
line delivers said reductant to said exhaust line upstream of said
catalyst.
11. The aftertreatment system of claim 2 wherein said exhaust line
comprises a by-pass line capable of directing said exhaust gas
around said catalyst.
12. The aftertreatment system of claim 2 further comprising a SOx
adsorber disposed in said exhaust line to remove SOx from said
exhaust gas before said exhaust gas passes through said NOx
adsorber during The adsorption cycle.
13. The aftertreatment system of claim 12 wherein said exhaust line
further comprises a sulfur line for bypassing said exhaust gas
around said NOx adsorber when regenerating said SOx adsorber and a
flow control for controlling flow of exhaust gas through said
sulfur line.
14. The aftertreatment system of claim 12 wherein said hot line is
a reverse flow line capable of alternating flow of said exhaust gas
where said NOx adsorber is upstream of said SOx adsorber.
15. The aftertreatment system of claim 2 wherein a cooling line
length is chosen relative to a hot line length such that more
exhaust gas heat is dissipated through said cooling line than would
occur through said hot line.
16. The aftertreatment system of claim 2 wherein a cooling line
material is chosen such that more exhaust gas heat is dissipated
through said cooling line than would occur through said hot
line.
17. A method of operating an aftertreatment system for removing NOx
from exhaust gas generated by combustion of a fuel in at least one
combustion chamber of an internal combustion engine, said method
comprising an adsorption cycle, a regeneration cycle and a
de-sulfation cycle: during said adsorption cycle: cooling said
exhaust gas to within a predetermined adsorption temperature range
when said exhaust gas is above said adsorption temperature range,
directing said cooled exhaust gas through an exhaust line to a lean
NOx adsorber disposed in said exhaust line, during said
regeneration cycle: directing a first portion of said exhaust gas
through a bypass line around said lean NOx adsorber; oxidizing at
least a second portion of said exhaust gas to a lambda value of
less than or equal to 1, heating said at least said second portion
of said exhaust gas to within a predetermined regeneration
temperature range when said at least said second portion of said
exhaust gas is below said regeneration temperature range; directing
said oxidized and heated exhaust gas through said lean NOx
adsorber, during said de-sulfation cycle: oxidizing said exhaust
gas to a lambda value of less than or equal to 1, heating said
exhaust gas to within a predetermined de-sulfation temperature
range when said exhaust gas is below said de-sulfation temperature
range directing said oxidized and heated exhaust gas through said
lean NOx adsorber.
18. The method of claim 17 wherein, during said adsorption cycle,
said exhaust gas is cooled by introducing air into said exhaust
gas.
19. The method of claim 17 wherein, during said adsorption cycle,
said exhaust gas is cooled by directing said exhaust gas through a
turbine.
20. The method of claim 19 wherein said turbine is employed to
drive a blower for directing air into said exhaust line upstream of
said NOx adsorber.
21. The method of claim 17 wherein, during said adsorption cycle,
said exhaust gas is cooled by expanding said exhaust gas.
22. The method of claim 17 wherein, during said adsorption cycle,
said exhaust gas is cooled by directing said exhaust gas through a
heat exchanger.
23. The method of claim 17 wherein, during said adsorption cycle,
said exhaust gas is cooled by routing said exhaust line through a
cooling line.
24. The method of claim 17 wherein said at least said second
portion of said exhaust gas does not include said first portion of
said exhaust gas.
25. The method of claim 17 wherein, during said de-sulfation cycle,
a portion of said exhaust gas is directed through a bypass line
around said lean NOx adsorber.
26. The method of claim 17 wherein, during said adsorption cycle,
said exhaust gas is directed through a SOx adsorber disposed in
said exhaust line prior to directing said exhaust gas through said
NOx adsorber.
27. The method of claim 17 wherein said exhaust gas is heated and
oxidized by passing said exhaust gas through a catalyst with a
reductant introduced into said exhaust gas.
28. The method of claim 17 wherein said reductant is selected from
the group consisting of hydrocarbons, hydrogen, and combinations
thereof.
29. The method of claim 28 wherein said reductant includes a
hydrocarbon selected from the group consisting of natural gas,
diesel, methane, ethane, butane, propane, and combinations thereof.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation of International
Application No. PCT/CA2004/000390, having an international filing
date of Mar. 11, 2004, entitled "Management of Thermal Fluctuations
in Lean NO.sub.x Adsorber Aftertreatment Systems". International
Application No. PCT/CA2004/000390 claimed priority benefits, in
turn, from Canadian Patent Application No. 2,422,164 filed Mar. 14,
2003 and from Canadian Patent Application No. 2,453,689 filed Dec.
17, 2003. International Application No. PCT/CA2004/000390 is hereby
incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates to methods and apparatuses for
managing exhaust gas heat over the range of operating conditions
required by a lean NOx adsorber aftertreatment system.
BACKGROUND OF THE INVENTION
[0003] Emissions controls for internal combustion engines are
becoming increasingly important in transportation and energy
applications. Oxides of nitrogen (NOx) are of particular concern.
NOx forms during combustion in internal combustion engines.
[0004] A lean NOx adsorber (LNA) can be employed to remove NOx from
exhaust gas. LNAs reduce NOx by trapping the NOx in a catalyst
washcoat. NOx trapping in the LNA is referred to herein as
adsorption. The NOx stored in the washcoat is reduced to nitrogen
gas (N.sub.2) periodically. This reduction process is referred to
as regeneration or a regeneration cycle.
[0005] Where sulfur is found in the engine fuel or where
sulfur-containing engine lubricating oil has leaked into the
combustion chamber, oxides of sulfur can also be trapped within the
LNA washcoat. As discussed in, by way of example, U.S. Pat. No.
6,393,834, sulfur poisoning of LNAs from oxides of sulfur in the
exhaust gas can interfere with the ability of the LNA to remove
NOx. Removing these oxides of sulfur periodically during operation
of the engine helps to maintain the efficiency of the LNA.
Processes employed to remove sulfur compounds are referred to as
de-sulfation. Regeneration and de-sulfation cycles both require a
low oxygen potential (or "rich") environment to be effective.
Regeneration, de-sulfation and removal of NOx each work best when
the exhaust gas temperature is within a different range.
[0006] The acid-based chemistry of the washcoat dictates the
temperature ranges at which the LNA washcoat effectively traps NOx
and SOx. In general, trapped sulfate compounds are more stable than
trapped nitrate compounds. That is, the ability of the LNA washcoat
to store sulfates extends to higher temperature ranges than is the
case for NOx. For similar reasons, the temperature at which
de-sulfation proceeds tends to be higher than the temperature
required for regeneration.
[0007] "De-sulfation temperature" is used herein to refer to that
relatively high temperature at which sulfur is effectively released
from the LNA washcoat. The performance of current LNA washcoats
tends to deteriorate, mainly due to sintering, when exposed to
temperatures in excess of 700.degree. C. Exceeding 700.degree. C.
by a significant margin increases the rate of deterioration.
De-sulfation temperatures can approach and exceed 700.degree. C.
leading to poor long-term performance of the LNA.
[0008] For regeneration of the LNA, a regeneration temperature
which is less than the de-sulfation temperature is generally
preferred.
[0009] During the adsorption phase, the exhaust gas is lean and NOx
is being trapped within the LNA. Lower exhaust gas temperatures can
be tolerated during the adsorption phase and are selected to allow
the LNA to adsorb NOx over a suitable range of the engine map.
Preferred exhaust gas temperatures during an adsorption cycle can
overlap with regeneration temperatures and are generally lower than
de-sulfation temperatures (all of which can depend on the washcoat
composition, the reductant chosen and other factors within the
aftertreatment system).
[0010] In light of the range of preferred exhaust gas temperatures
that depend on the aftertreatment control sought for the LNA,
flexibility in providing those temperatures over the range of
potential engine operating conditions is important. Control over
the temperature to which the LNA is exposed can both extend the
life of the LNA and improve its effectiveness at removing NOx from
internal combustion engine exhaust gas. Moreover, the faster the
regeneration or de-sulfation temperatures are reached within the
exhaust gas and then returned to preferred adsorption cycle
temperatures, the less the fuel penalty for regeneration or
de-sulfation and the less NOx delivered from the engine as a result
of these cycles.
[0011] Oxidation of a reductant in the exhaust gas, referred to
here as in-line oxidation, can provide the heat and reductants to
either regenerate or de-sulfate an LNA as well as create the
reduced oxygen potential environment for de-sulfation. Oxidation
can be promoted by a catalyst. The catalyst should be located in
close enough proximity to the engine that exhaust gas temperatures
are sufficient to cause the catalyst to "light-off" at engine out
temperatures yet still be proximate enough to the LNA to provide
rich exhaust gas regeneration temperatures or de-sulfation
temperatures. However, the LNA reactive capacity (the ability of
the LNA to trap NOx) is relatively low at the temperature needed
for the effective operation of the reformer/oxidation catalyst.
Therefore, consideration should be given to ensure that exhaust gas
passing through the LNA during an adsorption cycle is cool enough
(for example, placed distant from the engine) to allow the LNA to
operate efficiently over a wide range of engine operating
conditions.
[0012] All references to "upstream" and "downstream" herein
describe the relative position of components of the aftertreatment
in relation to the direction of the flow of exhaust gas during an
adsorption cycle of the LNA aftertreatment system (which may not be
the same as the flow during a regeneration cycle or de-sulfation
cycle), unless otherwise stated.
[0013] The present technique provides methods and apparatuses for
managing exhaust gas temperature using an LNA over a wide range of
engine operating conditions.
SUMMARY OF THE INVENTION
[0014] This present technique manages exhaust gas heat into an LNA
during adsorption, de-sulfation and regeneration cycles of the LNA.
One aspect of the present technique provides a hot route that
shortcuts or provides a bypass route around, a cooling path between
the LNA and an oxidation catalyst. Another aspect of the present
technique provides a long route or cooling route through the
aftertreatment system. The coding route allows the exhaust gas to
cool where needed. Another aspect provides a cooling route with a
heat exchanger between an oxidation catalyst and an LNA for cooling
the exhaust gas as needed. Another aspect of the present technique
provides a cooling route with a turbine between an oxidation
catalyst and a LNA for cooling the exhaust and extracting energy
from the exhaust gas heat. This energy can be employed, in another
aspect of the present technique, to introduce air into the exhaust
gas stream to cool the exhaust (by dilution) when needed. Another
aspect of the present technique provides for a sulfur trap to
manage sulfur in the aftertreatment system.
[0015] An aftertreatment system treats NOx found in exhaust gas
produced during combustion of a fuel within a combustion chamber of
an operating internal combustion engine. The system comprises:
[0016] an exhaust line for directing the exhaust gas from the
engine; [0017] a lean NOx adsorber disposed in the exhaust line;
[0018] a first catalyst disposed in the exhaust line upstream of
the LNA, the catalyst capable of oxidizing a reductant in the
exhaust gas; [0019] a reductant line for delivering a reductant
from a reductant store to the catalyst; [0020] a reductant flow
control disposed in the reductant line for controlling flow of the
reductant into the exhaust line; and [0021] a flow control for
controlling flow of exhaust gas through the hot line and the
cooling line. The exhaust line is capable of delivering exhaust gas
from the first catalyst to the lean NOx adsorber.
[0022] In one embodiment of the aftertreatment system, the cooling
line and the hot line are placed between the catalyst and the NOx
adsorber. The cooling line is preferably longer than the exhaust
line.
[0023] The system can further comprise a turbine, disposed within
the cooling line, which drives an air blower disposed in an air
dilution line for compressing and directing air into the cooling
line.
[0024] In one embodiment of the system, an air blower disposed in
an air dilution line can compress and direct air into the cooling
line. A heat exchanger can also be disposed in the cooling
line.
[0025] The aftertreatment system can further comprise a
close-coupled catalyst in the exhaust line upstream of the system's
first catalyst. The reductant line delivers reductant to the
exhaust line, upstream of the close-coupled catalyst. In another
embodiment, the reductant line delivers reductant upstream of the
first catalyst.
[0026] In a further embodiment of the system, the exhaust line can
comprise a bypass line employed to direct exhaust gas around the
first catalyst.
[0027] The aftertreatment system can further comprise a SOx
adsorber, disposed in the exhaust line relative to the NOx
adsorber, to remove SOx from the exhaust gas before it passes
through the NOx adsorber. In a preferred embodiment, the exhaust
line further comprises a sulfur line for bypassing exhaust gas
around the NOx adsorber when regenerating the SOx adsorber, and a
flow control for controlling exhaust gas flow through the sulfur
line.
[0028] An aftertreatment system is disclosed, for treating NOx
found in exhaust gas produced during combustion of a fuel within a
combustion chamber of an operating internal combustion engine. The
system comprises: [0029] an exhaust line for directing the exhaust
gas from the engine and through the aftertreatment system; [0030] a
lean NOx adsorber disposed in the exhaust line; [0031] a first
catalyst disposed in the exhaust line, the catalyst capable of
oxidizing a reductant in the exhaust gas; [0032] a reductant line
for delivering the reductant from a reductant store to the exhaust
line upstream of the catalyst; [0033] a reductant flow control
disposed in the reductant line for controlling flow of the
reductant into the exhaust line; [0034] a SOx adsorber disposed in
the exhaust line; [0035] a sulfur line capable of bypassing exhaust
gas around the NOx adsorber; [0036] a flow control for controlling
flow of exhaust gas through the sulfur line wherein the exhaust
line delivers exhaust gas from the catalyst and the SOx adsorber to
the lean NOx adsorber.
[0037] In a preferred embodiment, the system further comprises a
sulfur line for bypassing exhaust gas around the NOx adsorber, and
a flow control for controlling exhaust gas flow through the sulfur
line.
[0038] A method is also provided of operating an internal
combustion engine equipped with an aftertreatment system for
removing NOx from exhaust gas. The method comprises an adsorption
cycle, a regeneration cycle and a de-sulfation cycle.
[0039] During the adsorption cycle the exhaust gas is cooled to
within a predetermined adsorption temperature range when the
exhaust gas is above the adsorption temperature range. The cooled
exhaust gas is directed through an exhaust line to a lean NOx
adsorber disposed in the exhaust line.
[0040] During the regeneration cycle, the exhaust gas is oxidized
to a lambda value of less than or equal to 1, the exhaust gas is
heated to within a predetermined regeneration temperature range
when the exhaust gas is below the regeneration temperature range,
and the oxidized and heated exhaust gas is directed through the
lean NOx adsorber.
[0041] During the de-sulfation cycle, the exhaust gas is oxidized
to a lambda value of less than or equal to 1, the exhaust gas is
heated to within a predetermined de-sulfation temperature range
when the exhaust gas is below the de-sulfation temperature range;
and the oxidized and heated exhaust gas is directed through the
lean NOx adsorber.
[0042] In preferred embodiments of the method, cooling the exhaust
gas during the adsorption cycle, can further comprise one or more
of introducing air into the exhaust gas, expanding the exhaust gas,
and directing exhaust gas through a heat exchanger or through a
turbine. In a preferred example, the turbine is employed to drive a
blower for directing air into the exhaust line upstream of the NOx
adsorber.
[0043] In additional preferred embodiments, cooling the exhaust gas
can further comprise routing the exhaust through a cooling line, or
directing a portion of the exhaust gas through the lean NOx
adsorber or directing the exhaust gas through a SOx adsorber
disposed in the exhaust line prior to directing the exhaust gas
through the NOx adsorber.
[0044] In another embodiment of the method, exhaust gas is heated
and oxidized by passing the exhaust gas through a catalyst with a
reductant introduced into the exhaust gas.
[0045] The method can be practiced such that the reductant
comprises one or more of hydrocarbons, hydrogen, and/or
combinations thereof. In preferred embodiments, the hydrocarbon
comprises one or more of natural gas, diesel, methane, ethane,
butane, propane, and/or combinations thereof.
[0046] Further aspects of the present technique and features of
specific embodiments of the present technique are described
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] In drawings which illustrate non-limiting embodiments of the
present technique:
[0048] FIG. 1 is a graph demonstrating flow of exhaust gas and
temperature over the range of engine operating conditions with
adsorption (normal cycle), regeneration and de-sulfation zones.
[0049] FIG. 2 is a schematic diagram of a first embodiment of the
present aftertreatment system.
[0050] FIG. 3 is a schematic diagram of a second embodiment of the
present aftertreatment system.
[0051] FIG. 4 is a schematic diagram of a generalized embodiment of
the present aftertreatment system.
[0052] FIG. 5 is a schematic diagram of a third embodiment of the
present aftertreatment system.
[0053] FIG. 6 is a schematic diagram of a fourth embodiment of the
present aftertreatment system.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0054] A method of and apparatus for managing exhaust gas heat in a
LNA aftertreatment system, are disclosed. The LNA is employed to
treat exhaust gases created during combustion of a fuel in an
engine's combustion chamber. Relatively low exhaust gas
temperatures (less than 450.degree. C. by way of example) are
typically needed for effective operation of the LNA. However, high
temperatures and a reducing atmosphere are also needed
periodically. These requirements are independent of engine speed
and load conditions. Thus, a means to independently control the
temperature at the LNA is desirable for effective system
operation.
[0055] When needed, the exhaust gas is cooled from the engine by
passing the exhaust gas through a cooling line which could embody a
heat exchanger, a long route (long as compared to an exhaust gas
route provided for where hot exhaust gas is desired), or a turbine
driven blower, by way of example. When a reduced oxygen potential
environment is desired, a reductant, which can comprise, for
example, methane, other hydrocarbons or hydrogen, can be introduced
into the exhaust line and oxidized. This reduces the exhaust gas
and elevates the temperature of the exhaust gas.
[0056] FIG. 1 provides a graph of the flow of exhaust gas plotted
against temperature. The area within curve 800 defines an example
range of flow/temperature properties for exhaust gas exiting an
engine block over operating conditions of the engine. The area
within curve 802 defines a range of target properties for the
exhaust gas directed into a catalyst during regeneration. The area
within curve 804 defines a range of target properties for the
exhaust gas passing through an LNA during an adsorption cycle
(normal cycle). The area within curve 806 defines a range of target
properties for the exhaust gas through an LNA during
de-sulfation.
[0057] Care should be taken to ensure that temperatures are not so
high as to excessively reduce the durability or effective life of
the LNA. Therefore, while curve 806 allows for effective
de-sulfation, it may not be desirable to allow exhaust gases within
the LNA to be at the highest temperatures within the range,
depending on the properties of the LNA. Point A is a typical
midpoint operating condition for the engine.
[0058] FIG. 2 is a schematic diagram showing an aftertreatment
system according to one embodiment of the present technique.
Exhaust lines flow from the engine and through the aftertreatment
system and are made up of a number of branches or alternate lines
for controlling aftertreatment of the exhaust gases. These include
lead line 12, line 12a, hot line 49 and bypass line 20. Lead line
12 carries exhaust gases flowing in the direction of arrow 14 from
engine block 10 to a NOx aftertreatment system where it can be
directed through alternate lines that generally make up an exhaust
line. In the aftertreatment system, lead line 12 carries exhaust
gases to LNA 16, as indicated by arrow 14. Lead line 12 branches to
line 12a and hot line 49 which bounds line 12a.
[0059] Gases exiting LNA 16 are delivered to an outlet through lead
line 12. Catalyst 18 is disposed in lead line 12 upstream of LNA
16.
[0060] The term "exhaust line" is used herein to include lines that
carry exhaust gas within the aftertreatment system and into and out
of the aftertreatment system.
[0061] Lead line 12 also branches to bypass line 20, which is
capable of carrying a portion of the exhaust gases around LNA 16,
as may be desirable while LNA 16 is being regenerated or
de-sulfated. The exhaust gas can be directed through bypass line 20
as indicated by arrow 22 by opening bypass valve 24. Bypass valve
24 can be disposed anywhere along bypass line 20.
[0062] Valves 24 and 30 are provided to help control the flow of
exhaust gas through lead line 12 during regeneration and
de-sulfation.
[0063] Optional close-coupled catalyst 32 is provided in lead line
12 physically proximate to engine block 10. A reductant, preferably
methane or another hydrocarbon or hydrogen, can be introduced just
prior to catalyst 18 and/or catalyst 32. Reductant valves 34 and 36
are disposed in respective main line 38 and close-coupled line 40,
each of which connect back to store 44 from which reductant is
supplied.
[0064] Hot line 49 bypasses line 12a of the exhaust line running
between catalyst 18 and LNA 16. Valves 51 and 57 are disposed in
hot line 49 and line 12a, respectively. Arrow 53 indicates flow
direction in hot line 49.
[0065] Temperature sensor 58 is employed to measure temperatures
before catalyst 18 and LNA 16 as shown by the respective
intersection points of sensor feed lines 60 and 62 within lead line
12. Data flow is indicated by data direction lines 63. Sensor 58
feeds temperature information to controller 64 through feed line 66
as indicated by data direction line 67. Feed line 70 provides
engine data to controller 64 as indicated by data direction line
71. Controller 64 operates valves 24, 30, 34, 36, 51 and 57 through
feed line 72 as indicated by data direction lines 75.
[0066] FIG. 3 shows an aftertreatment system according to a second
embodiment of the present technique. As in the embodiment shown in
FIG. 2, exhaust gas is directed, as indicated by arrow 14, to LNA
16 from engine block 10 through exhaust lines that include lead
line 12 and hot line 86. A reductant can be introduced into lead
line 12 through line 38 as controlled by valve 36 from store 44.
Catalyst 18 is available downstream of the junction of line 38 and
lead line 12 to allow for the exhaust gas to be heated and oxidized
across catalyst 18 as needed. Exhaust gas temperature is further
controlled by turbine-driven blower 82 disposed in lead line 12.
Blower 82 accepts exhaust gas, expands and cools the gas to extract
energy from the gas, and uses that energy to direct air through
line 84 and valve 80 as indicated by arrow 94 (in the embodiment
shown) to lead line 12 downstream of turbine-driven blower 82 and
upstream of LNA 16.
[0067] The exhaust line includes hot line 86. Flow through hot line
86 is controlled by valve 90. Flow through line 91 is controlled by
valve 88, as indicated by arrow 92.
[0068] FIG. 4 shows a generalized schematic diagram of an
aftertreatment system according to the present technique. FIG. 4
illustrates three possible cooling loops to be attached between
catalyst 18 and LNA 16 downstream of hot line 142. Flow through hot
line 142 is controlled by valve 140. Exhaust lines in this
embodiment include lead line 12, hot line 142 and cooling lines
144, 146 and 148. Cooling lines, 144, 146 and 148, include
components of the exhaust line within the aftertreatment system.
Heat exchanger route 144 has a heat exchanger disposed in lead line
12. Turbine route 146 has turbine 152 for converting heat energy of
the exhaust gas (to a turbocharger by way of example). Long route
148 has an extended lead line 12 extended to allow for cooling of
exhaust gas prior to delivering the exhaust gas to catalyst 16.
Long route 148 and turbine route 146 are versions of the
embodiments provided in FIGS. 2 and 3 respectively. One or more of
the cooling lines, 144, 146 and 148, or other embodiments disclosed
herein, could be incorporated into a LNA aftertreatment system.
[0069] Exhaust gas is generated by combustion events within one or
more combustion chambers disposed upstream of lead line 12 in
engine block 10. Exhaust gas results from the combustion of fuel.
For example, the fuel could be hydrogen, a hydrocarbon such as
natural gas, diesel or gasoline, or a mixed fuel that includes such
fuels as natural gas or methane or other hydrocarbons. Combustion
of a fuel that combines hydrogen and a hydrocarbon fuel such as
natural gas, diesel or a mixed hydrocarbon is also contemplated.
The fuel is, in general, either directly injected into the
combustion chamber or pre-mixed with a quantity of air to create a
fumigated charge. In each case, spark ignition, hot surface
ignition or compression ignition is utilized to initiate the
combustion process within the combustion chamber.
[0070] During an adsorption cycle of the aftertreatment system, it
is desirable to maintain flow and exhaust gas temperature, within
the area bounded by curve 804 to help ensure adequate removal of
NOx from exhaust gas within the lean, oxygen rich, exhaust gas
environment. Considering the range of operating temperatures and
flow rates for exhaust gas generated during an adsorption cycle, an
adsorption cycle of the aftertreatment system requires cooling of
the exhaust gas from the engine prior to the LNA over at least a
portion of operating conditions. This can be accomplished by
causing at least a significant portion of the exhaust gas to flow
through a cooling line upstream from LNA 16.
[0071] During an adsorption cycle, LNA 16, under relatively cool,
lean (oxygen rich) operating conditions, that is with an excess of
oxygen available in the exhaust gas, will drive NOx to
(NO.sub.3).sub.2 by way of: NO + 1 2 .times. O 2 .times. .times. (
Pt ) .fwdarw. NO 2 ( 1 ) X .times. O + 2 .times. NO 2 + 1 2 .times.
O 2 .fwdarw. X .function. ( NO 3 ) 2 ( 2 ) ##EQU1## where X is in a
washcoat (this is described further below).
[0072] Considering the embodiment of FIG. 2 again, valves 24 and 51
are closed and exhaust gas flows along lead line 12, including line
12a. The exhaust gases cool down in traveling along the extended
route provided by line 12a. That is, a cooling period through line
12 may be required to ensure that the exhaust temperature falls
into area 804. The exhaust gas, at its desired temperature, passes
through LNA 16 which removes NOx.
[0073] The extended route between block 10 and LNA 16 helps to
provide for a relatively cool exhaust gas during adsorption. The
route length provided by line 12a and exhaust line material(s)
employed upstream from LNA 16 are selected to allow the exhaust
temperature to fall within area 804 across the range of operating
loads. Alternatively, if the engine rarely operates within the
highest temperature portions of area 800, the resulting NOx slip
can be acceptable for a reduced length or more flexibility in
choice of materials for line 12a.
[0074] In the embodiment of FIG. 3, the cooling loop, rather than
an extended line from catalyst 18 to LNA 16, includes
turbine-driven blower 82 disposed in lead line 12. Heat employed to
drive turbine-driven blower 82 and cool exhaust gas prior to LNA 16
is employed to drive a compressor drawing in air through line 84,
past valve 80 and into lead line 12. The exhaust gas is diluted and
cooled with cooler intake air. Valves, 90, 88 and 80 can be
employed to adjust the temperature of the exhaust gases being
delivered into LNA 16. Valve 88 is optional. The turbine in turbine
driven blower 82 can also be employed to drive a shaft if desired
to generate work for other purposes.
[0075] FIG. 4 shows an embodiment having a generalized cooling
loop. Here the exhaust gas route between catalyst 18 and LNA 16 is
shown in cooling loops 144, 146 and 148. Specifically, a turbine is
shown in cooling loop 146. While employed for providing air
dilution in the embodiment discussed for FIG. 3, it could be
employed to extract energy from the exhaust gas heat to drive a
generator or other such applications.
[0076] Also, air dilution from an independent air compressor could
be directed in to the exhaust line. This compressor could be driven
by a independent electric motor or other independent energy source.
Here, the turbine could be eliminated.
[0077] The engine coolant or other coolant (such as air) could be
incorporated in a heat exchanger 150 to draw heat away from the
exhaust gas when needed, as demonstrated in cooling loop 144.
Cooling loop 148 is an extension of lead line 12. These methods can
be employed to drive down exhaust gas temperature to provide for an
adsorption cycle of the subject aftertreatment system.
[0078] Eventually LNA 16 becomes less effective at removing NOx as
X(NO.sub.3).sub.2 uses up adsorbing sites in LNA 16. As such,
periodic regeneration is required to remove NOx. Controller 64
determines when LNA 16 needs regenerating.
[0079] During regeneration, the following provides a set of
reactions found across catalyst 18 where methane is the reductant:
CH 4 + 2 .times. O 2 .fwdarw. CO 2 + 2 .times. H 2 .times. O ( 3 )
CH 4 + 1 2 .times. O 2 .fwdarw. CO + 2 .times. H 2 ( 4 ) CH 4 + H 2
.times. O .fwdarw. CO + 3 .times. H 2 ( 5 ) CO + H 2 .times. O CO 2
+ H 2 ( 6 ) ##EQU2## where reaction (6) can be held in equilibrium
depending on exhaust gas temperature. Note also, that equation (3)
can occur but is not preferred. The CO and H.sub.2 generated
according to equations (4) through (6) are then employed for
regeneration, for example, as follows: X .function. ( NO 3 ) 2
.fwdarw. X .times. O + 2 .times. NO + 3 2 .times. O 2 ( 7 ) X
.function. ( NO 3 ) 2 .fwdarw. X .times. O + 2 .times. NO 2 + 1 2
.times. O 2 ( 8 ) NO + H 2 .fwdarw. H 2 .times. O + 1 2 .times. N 2
( 9 ) NO 2 + 2 .times. H 2 .fwdarw. 1 2 .times. N 2 + 2 .times. H 2
.times. O ( 10 ) NO + CO .function. ( Rh ) .fwdarw. 1 2 .times. N 2
+ CO 2 ( 11 ) NO 2 + 2 .times. CO .fwdarw. 1 2 .times. N 2 + 2
.times. CO 2 ( 12 ) ##EQU3## where X is provided in a washcoat. A
lambda less than or equal to 1, which denotes a low oxygen
potential in the exhaust gas, favors reactions (7) through (12);
this is not the case, in general, when lambda is above 1.
[0080] In general, a regeneration strategy can be employed
targeting a regeneration flow and temperature of exhaust gas
through the LNA. Catalyst 18 helps provides a hot and rich
environment as is desirable to ensure regeneration. A reductant
provided to catalyst 18 during regeneration is oxidized and
reformed to provide an exhaust gas environment that has a low
oxygen potential and includes effective reductants (from the
catalyst or from reductant store 44) for regeneration such as CO
and hydrogen.
[0081] As noted above, however, the regeneration temperature for
the exhaust gas may need to be hotter in general than the exhaust
gas leaving block 10 over some engine operating conditions--see
area 802. Therefore, during regeneration, it can be beneficial to
retain heat generated in catalyst 18 or block 10 in the exhaust gas
delivered to LNA 16. Where it was preferable to have LNA 16 well
after or otherwise thermally "distant" from block 10 during an
adsorption cycle, it can be desirable to reduce this thermal
distance during regeneration. As such, referring to FIG. 2,
reductant from catalyst 18 is directed to LNA 16 at appropriate
exhaust gas temperatures to provide for the sought regeneration
environment by way of line 12a. As catalyst 18 has been lit off to
reduce the exhaust gas environment, the resulting rise in exhaust
temperature during oxidation of the exhaust gas is sufficient
generally for regeneration of LNA 16. Therefore line 12a in general
should be sufficient to regenerate (NOx) LNA 16. If there is too
much heat loss through line 12a, then hot line 49 could be
employed. Note that the sensors (singular or plural) shown disposed
in the aftertreatment system prior to catalyst 18 and LNA 16 can be
employed to control flow through LNA 16 during regeneration. The
sensors could also be disposed after catalyst 18 as required.
[0082] It is also possible to use an off-line reformer for
directing a reductant into the exhaust line just prior to LNA 16.
This could make hot line 49 unnecessary. The reformer could heat
the exhaust gas as needed by providing a hot gas (such as air) with
the reductant. Such a system could also incorporate the benefits of
bypass 20 by reducing the amount of exhaust gas to be heated and
oxidized. Further, the cooling line can be employed to control
temperature during an adsorption cycle.
[0083] Referring to FIG. 2, an optional close-coupled catalyst 32
can be provided to increase exhaust gas temperatures when desired.
The proximity of catalyst 32 to engine block 10 helps ensure that
exhaust gas is not too cool to oxidize the exhaust gas environment.
Therefore, when the controller detects an exhaust gas temperature
below a threshold temperature, valve 34 will provide reductant
upstream of catalyst 32, heating and oxidizing the exhaust gas well
upstream of LNA 16. This is useful when the engine is operating at
low loads. In low load operation, the exhaust gas exiting block 10
is relatively cool. Extra catalyst 32 also helps to light off
catalyst 18, when needed. Catalyst 18 can be located at a position
in the exhaust gas path which is a compromise between being
proximate to LNA 16 and being proximate to block 10, while LNA 16
and block 10 are thermally removed from each other.
[0084] Referring to FIG. 3, a turbine driven blower is employed to
control temperature of exhaust gas between catalyst 18 and LNA 16.
Where exhaust gas is determined to be undesirably cool for
regeneration, the load on turbine driven blower 82 is reduced or
eliminated. Here, line 91 is provided to direct intake air through
valve 88 reducing or eliminating the load and therefore,
maintaining some of the exhaust gas temperature. Alternatively, or
in addition, hot line 86 can be employed to bypass turbine driven
blower 82 when exhaust gas heat needs to be maintained. As would be
apparent to a persons skilled in the technology involved here, the
system shown in FIG. 3 could operate with only hot line 86.
[0085] Referring to FIG. 4, cooling loops 144, 146 and 148 can be
employed to adjust exhaust gas heat where hot line 142 is available
to divert heated and oxidized exhaust gas around either turbine
152, heat exchanger 150 or the extension of lead line 12 from loop
148. In addition, combinations of the systems discussed above, in
parallel or in series can be employed.
[0086] As shown in FIG. 2, sensors can be placed in the
aftertreatment system to monitor temperature and, according to
those readings, control flow of exhaust gas during
regeneration.
[0087] A regeneration cycle targeted at regeneration of LNA 16,
will usually fail to de-sulfate LNA 16. Within LNA 16, X(SO.sub.x)
also uses up adsorbing sites that would otherwise be available to
remove NOx. Therefore, in order to maintain the efficiency of LNA
16, in addition to a regeneration cycle, a de-sulfation cycle is
also required periodically.
[0088] During a de-sulfation cycle, an example set of reaction
conditions across catalyst 18, where methane is the reductant,
comprises: CH 4 + 2 .times. O 2 .fwdarw. CO 2 + 2 .times. H 2
.times. O ( 13 ) CH 4 + 1 2 .times. O 2 .fwdarw. CO + 2 .times. H 2
( 14 ) ##EQU4##
[0089] The resulting rich and hot exhaust gas environment is
employed for de-sulfation as follows: X(SOx).fwdarw.SOx (15) where
X is in a washcoat.
[0090] As with regeneration, lambda should be low (quantitatively,
a value below one) to promote reaction 7.
[0091] In addition to providing a rich exhaust gas environment, the
temperature of the exhaust gas needs to be held at a temperature
sufficient for effective de-sulfation. The temperature required for
de-sulfation is higher than the temperature required for
regeneration and typically higher than the temperature of the
exhaust gas from block 10. In the embodiment of FIG. 2, when a
de-sulfation cycle is needed, hot line 49 is opened to shorten the
distance traveled by the exhaust gas by bypassing line 12a of line
12. This helps to ensure that the heat from the exhaust gas is not
dissipated significantly as the exhaust gas flows from catalyst 18
to LNA 16. As well, referring to FIGS. 3 and 4, if, in addition to
long route, heat exchanger 150 or turbine driven blower 82 or
turbine 152 are employed, the hot line 49 can bypass these heat
reducing systems as needed. The process is similar to that needed
for regeneration. However, the temperatures sought for de-sulfation
of LNA 16 are much higher referring to area 806 of FIG. 1.
[0092] The adsorption, regeneration and de-sulfation cycles can be
controlled through an open-loop control, based on selected
parameters from the engine map, or closed-loop control, based, in
part, on the exhaust gas temperature and the reactive capacity of
catalyst 18 at the given exhaust gas temperature. By way of
example, one open-loop control uses a calibration of the treatment
system over a range of engine operating conditions to estimate the
time required for LNA 16 to be regenerated or de-sulfated in light
of the properties of catalyst 18. In such embodiments, the
controller monitors such variables as the engine load and speed,
and then determines from a look-up table, the time needed for
regeneration or de-sulfation.
[0093] Open-loop control can be driven by such conditions as
torque, speed, intake manifold temperature, intake manifold
pressure, exhaust gas temperature and exhaust gas pressure prior to
the catalysts as well as other conditions known to persons skilled
in the technology involved here. The system can be calibrated such
that the engine operating conditions, which are indicative of NOx
and sulfur content in the exhaust gas, are employed to estimate
when regeneration or de-sulfation LNA is desirable.
[0094] The time required for de-sulfation is somewhat dependent on
an assumed range of sulfur content in the exhaust gases, which can
vary depending on such factors as the source of the fuel employed
in the engine and the source of the lubricating oils employed in
the engine.
[0095] A closed-loop control can be employed to determine when to
commence a regeneration or de-sulfation cycle and how to
efficiently operate each cycle in light of the aftertreatment
architecture chosen. By way of example, referring to one or more of
FIGS. 2 through 4, one such control strategy for selecting a
de-sulfation cycle can monitor NOx levels within lead line 12
downstream of LNA 16 over the course of many regeneration cycles.
When the capacity of the LNA falls below a predetermined level, the
controller can direct a de-sulfation cycle. The capacity of the LNA
can be measured between regeneration cycles. When the length of
time between regeneration cycles falls below a predetermined level,
then the controller will commence a de-sulfation cycle. The
controller can control exhaust gas flow and the introduction of
reductant to provide a de-sulfation strategy that helps to limit
the use of reductant. For regeneration cycle control, the NOx slip
through LNA 16 can be measured to select commencement of a
regeneration cycle.
[0096] During an adsorption, regeneration or de-sulfation cycle,
the exhaust gas is provided to the LNA as lean exhaust gas (during
adsorption) or as a rich exhaust gas (oxygen depleted environment)
and with a temperature appropriate for the adsorption, regeneration
or de-sulfation cycle, as the case may be.
[0097] The flow of exhaust gas through the NOx LNA during
regeneration is referred to as the regeneration flow herein. The
flow of exhaust gas through the LNA during de-sulfation is referred
to as de-sulfation flow herein.
[0098] Referring to FIG. 2, during a regeneration cycle or a
de-sulfation cycle, controller 64 determines a regeneration or
de-sulfation strategy based, generally, on the exhaust gas flow,
the exhaust gas temperature, a desired exhaust gas flow chosen
considering the reactive capacity of catalyst 18 at a given exhaust
gas temperature, and lambda of the exhaust gas from the engine. The
regeneration and de-sulfation strategy for a given regeneration
cycle or de-sulfation cycle can be done by an open-loop or
closed-loop strategy as discussed above. The regeneration and
de-sulfation strategy can be controlled by the quantity and rate of
the reductant introduced into the exhaust gas from store 44, and by
the amount of exhaust gas flow through hot line 49 dictated by
valve 51.
[0099] Optionally, a bypass can also be provided prior to catalyst
18. Bypass line 20 with flow controlled by valves 24 and 30 can
help to reduce the amount of exhaust gas that needs to be oxidized
or heated during either regeneration or de-sulfation. The goal is
to provide an exhaust gas environment wherein lambda is below or
equal to one and the temperature of the exhaust gas is high enough
to promote either reaction (7) through (12) or (15) as the case may
be. The reductants are oxidized to provide the energy required to
heat the exhaust gas.
[0100] During regeneration, regeneration flow includes a portion of
exhaust not diverted through bypass 20 that is oxidized and heated
and routed, in many cases, through line 12a.
[0101] De-sulfation flow is directed through hot line 49 so that it
retains more heat compared to the case where the exhaust gas is
routed through line 12a of line 12.
[0102] At commencement of a de-sulfation cycle, controller 64
causes valve 51 to open and valve 57 to close. The de-sulfation
flow bypasses line 12a to some extent, depending on the control
strategy chosen and the valve position chosen for valve 57 in line
12a. Bypass line 20 is helpful to ensure efficient regeneration and
de-sulfation; however, it is not mandatory. The system is capable
of providing full exhaust flow through the LNA during
de-sulfation.
[0103] Note that oxidation through the LNA with other reductants
such as hydrogen, methane or other hydrocarbons can also provide an
exotherm required to provide de-sulfation temperatures across the
LNA and the desired rich exhaust gas environment.
[0104] Using the variables considered above for open loop control
of the aftertreatment system, the controller is preferably
calibrated to direct flow of exhaust gas through the LNA and
reductant into the exhaust gas based on the engine speed and load
just prior to and during either regeneration or de-sulfation
cycles. Engine intake manifold temperature, intake air mass flow,
fuel flow or intake manifold pressure can also be employed as
indicators of exhaust gas properties that are useful for
controlling the de-sulfation cycle. A constant de-sulfation cycle
time can also be employed. This can be appropriate as the
de-sulfation cycle time is relatively long as compared to such
variables as the catalyst light off time and cycle variations
related to varying exhaust gas flow.
[0105] An open-loop strategy employs an engine calibration that
considers one or more engine operating conditions, each of which is
indicative of at least one of exhaust gas temperature, flow and
lambda value. The controller is calibrated to direct a desired flow
of exhaust gas through the LNA based on the characteristics of
catalyst 18 and LNA 16. A look-up table can be employed to
determine whether the exhaust gas flow exceeds the desired
regeneration or de-sulfation flow and, if so, controller 64 can
cause excess exhaust gas to be diverted around LNA 16 via bypass
line 20. The desired bypass flow is achieved by adjusting valves 24
and 30 to match the target de-sulfation flow though LNA 16.
[0106] The look-up table can also be employed to provide a desired
flow rate across hot line 49. As mentioned above, valve 51 can be
opened at the commencement of a de-sulfation or a regeneration
cycle to direct a significant portion of the regeneration or
de-sulfation flow through hot line 49. Valve 57 disposed in line
12a can provide additional control over the flow through hot line
49 during regeneration or de-sulfation.
[0107] Valves suitable for the purpose described for valves 51 and
57 are well known. For example, each valve described in the
embodiment of FIGS. 2 through 4 could be a simple two position
valve, a multi-position valve, or a variable position control
valve, with the choice of valve type being dictated by cost and the
desired degree of control. Also, one of valves 51 or 57 could be
eliminated, reducing control, but simplifying controls and reducing
costs and maintenance by removing a moving component. In each case,
the controller can adjust de-sulfation flow by splitting the flow
through line 12a and hot line 49.
[0108] With reference to the embodiment provided in the FIG. 2,
valves 51 can also be eliminated retaining an operable system.
Regeneration and de-sulfation flow and adsorption exhaust gas flow
control would need to consider that a portion of the de-sulfation
flow would be directed from catalyst 18 to LNA 16 through hot line
49 during the range of operating modes. By continuously splitting
the exhaust flow in this manner, the exhaust gas temperature can be
elevated at LNA 16. Another means could be provided, where desired,
for managing temperature to keep the exhaust gas below a target
temperature during an adsorption cycle. Alternatively, without
valve 57, there will be a quantity of exhaust gas flow through line
12a, and the controller would need to consider this. In each case,
closed-loop strategies can be combined with the above. In some
closed-loop strategies, temperature sensor 58 can be employed to
feed data to controller 64 that can be employed by controller 64 to
control the efficiency of the regeneration and de-sulfation
cycles.
[0109] The look-up table for an open-loop control can also provide
a target reductant concentration prior to catalyst 18 during
regeneration or de-sulfation. The engine operating conditions
provide information about the exhaust gas temperature, flow and
lambda of the exhaust gas from block 10. The temperature of the
exhaust gas can be employed to determine the amount of reductant
required in order to meet the target temperature range for the
exhaust gas during regeneration and de-sulfation cycles. This
target temperature range should be held below a temperature that
might damage the catalyst and above a temperature suitable for
efficient reformation of reductant and, therefore, regeneration or
de-sulfation of LNA 16. Moreover, the lambda of the exhaust gas,
estimated from the engine operating conditions, determines the
amount of reductant required to provide a sufficiently rich exhaust
gas environment to support efficient regeneration or
de-sulfation.
[0110] Referring again to FIG. 1, a closed-loop strategy could also
be employed wherein the temperature could be measured prior to or
after catalyst 18 (see sensor 58 shown before catalyst 18 in the
embodiment shown) and prior to LNA 16 through line 62. The load and
speed of the engine could be employed by the controller to
determine the exhaust gas flow based on look-up tables. A flow
meter within the exhaust line could also be employed for further
closed-loop control. The look-up table along with sensor
information can be employed to determine the flow of reductant to
be introduced into lead line 12 and how much flow of exhaust gas,
if any, to direct through valve 24 and line 20 during regeneration
or de-sulfation cycles to maintain a target regeneration or
de-sulfation flow and regeneration or de-sulfation temperature.
[0111] When exhaust gas flow is too high for catalyst 18 to allow
complete oxidation of methane or too high to de-sulfate
efficiently, some flow is directed into bypass line 20 until the
desired flow is met.
[0112] If temperature prior to LNA 16 is too high or too low, the
methane quantity can be adjusted to achieve the desired
de-sulfation temperature. This can also be done monitoring the
temperature into or out of catalyst 18.
[0113] As with the open-loop system above, de-sulfation flow
through hot line 49 can be determined by a calibration provided to
the controller that would include an engine map corresponding to a
flow split through hot line 49 and line 12a. This is dependent on
the control available to the controller resulting from the
availability and type of valves in line 12a and/or hot line 49.
Also, an open-loop control could be employed that would also
consider the temperature of the regeneration or de-sulfation flow
prior to LNA 16 and direct that de-sulfation flow through hot line
49 and line 12a to target the desired temperature required to
ensure efficient regeneration or de-sulfation of LNA 16. The
temperature can also be employed to control valve 36 to vary
reductant flow or quantity providing a hotter exhaust gas into LNA
16.
[0114] As noted above, a closed-loop strategy may be preferred
depending on cost and application considerations. The open-loop
strategy discussed above utilizes a calibration of the system that
provides a target reductant injection rate and quantity over a
regeneration and de-sulfation cycle that is based on the engine
operating parameters such as load and speed, and could eliminate
dynamic monitoring and the added complexity in hardware and
software for the system. However, the trade-off is that such a
strategy is more likely to regenerate or de-sulfate LNA 16
incompletely or less efficiently.
[0115] Controls, as described above, can also be employed to
control embodiments having a turbine-driven blower 82. Here,
however, control is needed to monitor the flow of air into lead
line 12 through valve 80 during adsorption cycles. During a
regeneration or de-sulfation cycle, valve 90 can be opened to
direct all or a portion of the flow around turbine driven blower
82, as desired to match the temperature requirement for exhaust gas
through LNA 16. Although, not shown in this embodiment, as would be
understood by persons skilled in the technology involved here, a
bypass could also be employed between catalyst 18 and LNA 16
(upstream of catalyst 18 and downstream of LNA 16). This bypass
would be employed in the same manner as described for the first
embodiment in FIG. 1.
[0116] In addition to hot line 86, line 91 could also be employed
to remove load from turbine driven blower 82 when there is a need
to maintain exhaust gas heat.
[0117] For the embodiment shown in FIG. 3 flow sensors through
valve 80 and temperature sensors within the line 12 could be
employed to provide closed-loop control for adsorption,
regeneration and de-sulfation cycles.
[0118] More generally, referring to FIG. 4, the three heat
exchangers or turbines could also be controlled as needed to
manipulate exhaust temperature through to LNA 16. Open or
closed-loop controls could control flow and temperature through the
exhaust line into LNA 16 to ensure the exhaust gas temperature
falls within a desired range regardless of the operating demands on
the engine and whether adsorption, regeneration or de-sulfation is
sought from the aftertreatment system.
[0119] To simplify the system, an alternative to using variable
flow control valves is to use two position valves (or for that
matter other multiple position valves). For example, for valves 24,
30, 51 and 57 the controller can elect from one of a plurality of
possible settings to control flow through lines 12, 20 and 49.
Valve 30 can be fully open or partially open. Valves 24, 51 and 57
can be closed or open. Therefore, controller 70 can select a
position for each valve according to the engine operating
parameters in order to match exhaust flow through line 12 to a
pre-determined target value. That is, at low speed and load, valve
30 and 51 are open fully, and valves 24 and 57 are closed. At
higher loads and speeds, valves 24, 30 and 51 are fully opened and
valve 57 can be closed. At still higher speeds and loads, valve 30
is partially open and valves 24 and 51 are opened while valve 57
can be opened or closed.
[0120] As would be understood by persons skilled in the technology
involved here, valves employed in the aftertreatment systems shown
could be any suitable flow control mechanism and need not be
limited to valves.
[0121] Other valve configurations can be employed as well. More
flexibility for the controller to manage flow during adsorption,
regeneration and de-sulfation cycles helps the controller to meet a
target pre-determined flow for each cycle. A trade-off is that such
flexibility can result in a system that requires more expensive
valves and more complicated software to control those valves.
[0122] FIG. 5 shows an additional embodiment of the present
technique. Here, a second LNA is added: SOx adsorber 100. Exhaust
lines include lead line 12, bypass line 20, line 12a, hot line 49
and sulfur line 106. To control flow through SOx adsorber 100,
valves 102 and 104 are employed to control exhaust gas flow through
LNA 16 or around LNA 16 by way of sulfur line 106. Valves 108 and
110 are employed to control bypass flow (where desired) around LNA
16, catalyst 18 and SOx adsorber 100. Note here, as mentioned
above, as a demonstration of an alternative flow control
architecture, the bypass control valves 108 and 110 are both in
bypass line 20 where one of these valves was in lead line 12 in the
embodiment demonstrated in FIG. 2 above.
[0123] The embodiment shown in FIG. 5 is a version of the
embodiment shown in FIG. 2 which has been modified to include SOx
adsorber 100. SOx adsorber 100 extends the time between
de-sulfation cycles. LNA 16 still needs periodic de-sulfation.
However, SOx adsorber 100 in line 12a removes most of the Sox. The
concentration of sulfur compounds in exhaust gas passing through
LNA 16 during an adsorption cycle is small. The structure shown
however, still needs to allow for de-sulfation of both LNA 16 and
the SOx LNA 100.
[0124] LNA 16 can be de-sulfated substantially as described above.
The heat required to effect de-sulfation is provided by catalyst
18, reductant from reductant store 44 (introduced through line 42
and valve 36) and hot line 49 ensuring heat in the exhaust is
maintained for de-sulfation of the LNA.
[0125] A SOx adsorber regeneration cycle (like LNA regeneration
cycles, designed to release the primary trapped component--sulfur
compounds in this case--periodically to free up the adsorber for
further adsorption), needs to also be incorporated. When SOx
adsorber 100 is "full", exhaust gas is oxidized with reaction of
reductant from store 44 across catalyst 18. The resulting rich
exhaust gas environment through SOx adsorber 100 releases sulfur
into the exhaust gas flowing from SOx adsorber 100. This is
designed to happen when exhaust gas temperatures are within a range
similar for release of NOx from LNA 16. This can allow regeneration
of NOx and SOx adsorbers at the same time as long as released
sulfur is directed around LNA 16. Here a line directly from
catalyst 18 to LNA 16 would be needed to provide relatively
sulfur-free exhaust gas required for regeneration of LNA 16. Some
of that same exhaust gas would be directed to SOx adsorber 100 and
the resulting sulfur-rich exhaust gas would be passed out of the
aftertreatment system via line 106. That is, the resulting exhaust
gas is routed through valve 104 and from the system along line 106.
In the embodiment shown, it is important that valve 102 be closed
to avoid release of sulfur rich exhaust gas through LNA 16 during a
SOx adsorber regeneration cycle.
[0126] The regeneration of NOx and SOx adsorbers could occur in
series where the exhaust gas is heated as required for regeneration
of SOx adsorber and bypassed through sulfur line 106 immediately
after which the exhaust gas is passed through LNA 16 once the
regeneration of the SOx adsorber is complete and little sulfur is
directed to LNA 16 for a regeneration cycle of this catalyst.
[0127] Bypass line 20 can also be employed to help with efficiency
during SOx adsorber regeneration cycles by directing some exhaust
gas through bypass line 20 thereby reducing the energy required to
heat the remaining exhaust gas through line 12a.
[0128] A clean-up catalyst, not shown, can optionally be provided
to ensure that hydrogen sulfide released during SOx adsorber
regeneration or during de-sulfation is converted to a sulfate.
[0129] Note, in this embodiment, that it is less important to
include hot line 49, employed to de-sulfate LNA 16. As the periods
between de-sulfation cycles of LNA 16 are increased considerably
with the introduction of the SOx adsorber 100, the loss in
efficiency of additional heating for the exhaust gas for
de-sulfation to make up for greater heat loss by routing the
exhaust gas through line 12a is less important.
[0130] In general, an appropriately sized SOx adsorber, could, by
way of example, increase the time between de-sulfation cycles of
LNA 16 by a factor of 50. By way of example, the SOx adsorber,
depending on the fuel employed, could be sized one-quarter of the
size relative to the LNA. As noted above, the SOx adsorber could be
selected to allow for a SOx adsorber regeneration temperature range
similar to the NOx adsorber regeneration temperature thus reducing
complication in the system by allowing for similar conditions for
two different processes. Also, where exhaust flow can be reversed
or separated to flow through SOx adsorber and NOx adsorber
separately from the same catalyst, by way of example, then
regeneration of both of these adsorbers can occur at the same
time.
[0131] Sulfur line 106 is not essential to the system, however,
without it, regeneration of SOx adsorber should either be avoided
or should employ a reverse flow strategy like the one taught for
the embodiment discussed below (see FIG. 6 and the accompanying
discussion).
[0132] FIG. 6 shows a further embodiment of the present technique
that includes bypass line 20 with valves 108, 110 and, in the
exhaust line, catalyst 18, SOx adsorber 100 and LNA 16. This
embodiment also includes lead line 12 that branches into reverse
flow line 208. Exhaust gas flow through line 208 is controlled by
valves 200 and 204. In general, exhaust lines include lead line 12,
bypass line 20, line 208 and reverse flow exit 202.
[0133] Valve 201 controls flow out of reverse flow exit 202. Valve
206 controls flow out of lead line 12. Reductant store 44 is
provided with reductant line 42. Valve 36 controls flow of the
reductant to the catalyst when regeneration and de-sulfation are
required.
[0134] In operation, during an adsorption cycle, exhaust gas flows
from engine block 10 through line 12 and SOx adsorber 100, LNA 16
and out through valve 206. Valves 108, 201 and 204 are closed
forcing exhaust gas to flow through valve 206 and out of the
aftertreatment system. Control of the system can be as described
above.
[0135] When a regeneration cycle is required, flow is maintained
through catalyst 18 where valve 36 is opened to introduce
reductant. The rich, heated exhaust gas can be directed into LNA 16
through valve 204 and out of the system through line 202. As
discussed above, some exhaust gas can be directly bypassed around
catalyst 18 via line 20.
[0136] When the system controller chooses to de-sulfate LNA 16,
valves 36 and 204 are opened. Valves 108 and 110 can be opened if
bypass of some exhaust gas is preferred. During de-sulfation of LNA
16, exhaust gas flows from catalyst 18, where with the introduction
of a reductant to catalyst 18, the exhaust gas is oxidized, heated
and bypassed through valve 204 and line 208 to LNA 16. Valve 206 is
closed, routing the exhaust gas through LNA 16. Eventually, the
exhaust gas with sulfur from LNA 16 is directed from lead line 12
to line 202 and through valve 200 out of the aftertreatment
system.
[0137] Similarly, exhaust gas is routed in the same direction
during regeneration of SOx adsorber 100. Heated exhaust gas is
directed to SOx adsorber 100 by way of line 208 through valve 204
and LNA 16. After releasing sulfur in SOx adsorber 100, the exhaust
gas is expelled from the system by way of line 202 through valve
200.
[0138] This embodiment could operate with a closed-loop system. A
sensor could be placed within the aftertreatment architecture to
monitor sulfur slip or NOx slip from SOx adsorber 100 or LNA 16 for
determining when these adsorbers need to be regenerated or
de-sulfated, after which the valves would be appropriately
controlled. The sensor could also measure flow rates through parts
of the aftertreatment system to help target the flow requirements
through parts of the system during adsorption, de-sulfation and
regeneration cycles. As well, the system could be calibrated to
take advantage of an open-loop control strategy that determines or
estimates the flow rate of exhaust gas and engine operating
conditions to approximate when regeneration cycles should occur and
when de-sulfation cycles should occur.
[0139] During regeneration and de-sulfation cycles where bypass
line 20 is employed, the NOx levels out of line 12 can increase
substantially, as the engine is continuing to operate without NOx
treatment of the exhaust gas routed through bypass line 20. Once
regeneration and de-sulfation are complete, however, NOx quickly
falls as exhaust gas is routed through recently regenerated and
de-sulfated LNA 16. Therefore, as well as a desire to reduce fuel
consumption (consumption of methane), short regeneration and
de-sulfation cycles also limit the amount of NOx emitted during
de-sulfation through bypass line 20. The longer the period of time
needed for regeneration and de-sulfation cycles, the more
cumulative exhaust gas flows through bypass line 20.
[0140] Catalyst 18 is generically described as a bed that promotes
the relevant reactions noted above to provide a desired exhaust gas
with a lambda below or equal to one and at or above the
regeneration or de-sulfation temperature, as the case may be. As
this catalyst needs to heat exhaust gas quickly to a very high
temperature, it also needs to be selected from materials able to
withstand the temperature needed for the exhaust gas and be capable
of heating exhaust gas to those temperatures quickly. A metal
substrate for carrying the catalyst is generally preferred, rather
than, for example, a ceramic substrate, if the metal substrate
improves thermal response to catalyst 18. As noted above, the
quicker the thermal response, the faster the regeneration or
de-sulfation cycle can be completed, thereby reducing the amount of
untreated exhaust gas allowed to flow through bypass line 20 where
employed.
[0141] Catalyst 18 can be a partial oxidation catalyst that
partially oxidizes a reductant (such as methane) and reforms that
reductant--see reactions (4) through (6) for the methane
example.
[0142] Catalyst 18 can also be a back-to-back oxidation catalyst
and reformer sharing a common boundary surface. Such catalysts
first oxidize reductant until the oxygen potential is reduced
sufficiently. These two catalysts, the oxidation catalyst and
reformer, can also be disposed in line 12 in series and need not
share a common boundary surface. Also, a combination reformer and
oxidation catalyst that integrates the reformer and oxidation
catalyst together in a mixed catalyst could be employed. Each
option provides trade-offs between cost and efficiency.
[0143] An oxidation catalyst can be a component of catalyst 18, and
can be an oxidization catalyst suitable for oxidizing the exhaust
gas to reduce the oxygen content. By way of example, a suitable
oxidation catalyst can promote the following reactions: C x .times.
H y + ( x + y 4 ) .times. .times. O 2 .function. ( Pt ) .fwdarw. x
.times. CO 2 + y 2 .times. H 2 .times. O C x .times. H y + ( x + y
4 ) .times. .times. O 2 .function. ( Pd ) .fwdarw. x .times. CO 2 +
y 2 .times. H 2 .times. O C x .times. H y + x 2 .times. O 2
.function. ( Pd ) .fwdarw. x .times. CO + y 2 .times. H 2 CO + 1 2
.times. O 2 .fwdarw. CO 2 ##EQU5## By way of example only, for the
operating conditions known for this application, a suitable
washcoat formulation comprises Al.sub.2O.sub.3. Other suitable
washcoat formulations can also be employed, as would be understood
by persons skilled in the technology involved here.
[0144] A reformer can be a component of catalyst 18. Reformers
suitable for this application are well known. The reformer is
preferably suitable to convert a hydrocarbon with water to CO and
H.sub.2. By way of example, the reformer can be a precious
metal-based catalyst with washcoat materials including
Al.sub.2O.sub.3.
[0145] FIG. 2 shows an additional catalyst, close-coupled catalyst
32, positioned near engine block 10. Some systems can include such
a catalyst disposed close to the engine to ensure that the exhaust
gas is hot enough to support oxidation of reductant. That is, there
are some aftertreatment system designs that would benefit from
employing a close-coupled catalyst near the engine block so that
the exhaust gas temperature under low load and/or speed or idle
conditions can be prevented from falling below a threshold limit at
which stable oxidation of methane in catalyst 18 would be
compromised. The close-coupled catalyst is typically physically
smaller than catalyst 18 and therefore more easily accommodated
near the engine. It would not replace catalyst 18. A larger
catalyst allows the system to take advantage of higher exhaust gas
flows to provide quick de-sulfation cycles. Therefore, under such
conditions, there are advantages in having close-coupled catalyst
32 near engine block 10 with line 40 feeding methane into the
exhaust gas prior to such catalyst. Catalyst 32 oxidizes the
reductant provided from store 44 to heat the exhaust gas to a
temperature suitable to allow catalyst 18 to light off
satisfactorily.
[0146] Note also that the close-coupled catalyst could be placed
prior to a turbine, and the heated exhaust gas, partly heated in
the turbine, could be employed to help drive the turbine for
greater flexibility for the engine.
[0147] As noted above, the adsorption, regeneration, and
de-sulfation cycles are dependent on the exhaust gas temperature.
For example, for regeneration and de-sulfation it is important that
the exhaust gas introduced into catalyst 18 has a temperature above
a minimum temperature to ensure that the catalyst is "lit-off"
initially. One strategy for ensuring an appropriate exhaust gas
temperature from the combustion chamber is to choose a combustion
strategy or combustion timing that ensures either relatively late
heat release, as might be the case with spark ignited engines, for
regeneration or de-sulfation cycles, or by ensuring quick heat
release at higher loads for adsorption. Also, a delayed or second
direct injection of fuel into the combustion chamber late in the
power stroke when regeneration or de-sulfation is required will
help heat the exhaust gas from engine block 10. This can also
reduce NOx levels with associated benefits during regeneration or
de-sulfation cycles as a quantity of exhaust gas could be directed
through the bypass line without NOx treatment. A reduced NOx level
has benefits here. Other strategies are well known to persons
skilled in the technology involved here.
[0148] As hydrocarbons or hydrogen can be effective reductants,
store 44 can be the fuel storage tanks if the engine is fueled by
the reductant. For example, for natural gas engines, natural gas
can be employed as the reductant.
[0149] Also, valves 34 and 36 can be injectors that directly inject
a suitable reductant, such as methane, into lead line 12. Injectors
would provide greater control over the timing and quantity of
methane and, therefore, greater control over the duration of the
regeneration or de-sulfation cycles.
[0150] LNA 16 typically adsorbs and stores NOx in the catalyst
washcoat while operating under lean conditions and NO.sub.2 can be
released and reduced to N.sub.2 under rich operating conditions
when a de-sulfation mixture, that includes hydrogen and rich
exhaust gas, is passed through the LNA. As noted above, the
following shows typical operation of the LNA under lean conditions:
NO + 1 2 .times. O 2 .function. ( Pt ) .fwdarw. NO 2 XO + 2 .times.
NO 2 + 1 2 .times. O 2 .fwdarw. X .function. ( NO 3 ) 2 ##EQU6##
and under rich conditions: X .function. ( NO 3 ) 2 .fwdarw. X
.times. O + 2 .times. NO + 3 2 .times. O 2 X .function. ( NO 3 ) 2
.fwdarw. X .times. O + 2 .times. NO 2 + 1 2 .times. O 2 NO + CO
.function. ( Rh ) .fwdarw. 1 2 .times. N 2 + CO 2 2 .times. NO 2 +
4 .times. H 2 .fwdarw. N 2 + 4 .times. H 2 .times. O ##EQU7## where
X is provided in the washcoat and is typically an alkali (for
example, K, Na, Li, Ce), an alkaline earth (for example, Ba, Ca,
Sr, Mg) or a rare earth (for example, La, Yt).
[0151] A further advantage can be realized if a fuel that combines
a reductant such as methane and hydrogen as two major components of
the fuel is employed. By way of example, natural gas with 10% to
50% hydrogen might be appropriate as an engine fuel and appropriate
for regeneration or de-sulfation cycles. Such a fuel could then be
utilized in the embodiments discussed wherein the hydrogen
introduced with the fuel prior to the oxidation catalyst could help
to light off those catalysts and help to provide an exhaust gas
environment with a lambda less than or equal to 1. Further, by
providing a quantity of hydrogen into the exhaust stream, the
burden on catalyst 18 is reduced. Less reforming is required for
de-sulfation due to the presence of hydrogen in the injected
fuel.
[0152] Reductants that could be employed include such things as
diesel fuel, gasoline or other hydrocarbons as well as natural gas,
methane, ethane, propane, butane or hydrogen or combinations of
these fuels.
[0153] Whenever flow is referred to in this disclosure, it is the
mass or molar flow rate of the gas in question.
[0154] Exhaust gas recirculation (EGR) can also be utilized to help
reduce NOx emissions during regeneration or de-sulfation cycles
when a bypass line is opened. Increased EGR rates during
regeneration or de-sulfation can reduce NOx generated in the
combustion chamber, resulting in less NOx flowing through bypass
line 20 and into the atmosphere. Further, increases in EGR can also
be employed to reduce the concentration of oxygen in the exhaust
gas during regeneration or de-sulfation, reducing, in turn, the
burden on the oxidation catalyst to reduce oxygen during a
regeneration or de-sulfation cycle as well as reduce the amount of
reductant needed to burn off oxygen.
[0155] While particular elements, embodiments and applications of
the present invention have been shown and described, it will be
understood, of course, that the invention is not limited thereto
since modifications can be made by those skilled in the art without
departing from the scope of the present disclosure, particularly in
light of the foregoing teachings.
* * * * *