U.S. patent application number 11/545803 was filed with the patent office on 2007-08-02 for nox adsorber aftertreatment system for internal combustion engines.
Invention is credited to Scott Cole, Rahul Mital, Bradlee J. Stroia.
Application Number | 20070175206 11/545803 |
Document ID | / |
Family ID | 31886526 |
Filed Date | 2007-08-02 |
United States Patent
Application |
20070175206 |
Kind Code |
A1 |
Mital; Rahul ; et
al. |
August 2, 2007 |
NOx adsorber aftertreatment system for internal combustion
engines
Abstract
The present invention provides for an NOx adsorber
aftertreatment system for internal combustion engines which
utilizes a parallel arrangement of an adsorber catalyst and a
bypass. The exhaust flow from the engine is routed through the
adsorber during lean operation. At a predetermined regeneration
time (for example, when the adsorber catalyst is 20% full), the
exhaust gas flow is reduced through the parallel leg that contains
the adsorber catalyst to be regenerated (e.g., 20% through the
catalyst leg, 80% of the flow to the bypass leg). A quantity of
hydrocarbon is injected into the reduced-flow catalyst leg in order
to make the mixture rich. Since the flow has been reduced in this
leg, only a small fraction of the amount of hydrocarbon that would
have been required to make the mixture rich during full flow is
required. This will result in a substantial reduction in the fuel
penalty incurred for regeneration of the adsorber catalyst. Once
the leg has been regenerated, the exhaust flow is switched to flow
100% through the adsorber leg.
Inventors: |
Mital; Rahul; (Columbus,
IN) ; Stroia; Bradlee J.; (Columbus, IN) ;
Cole; Scott; (Columbus, IN) |
Correspondence
Address: |
KRIEG DEVAULT LLP
ONE INDIANA SQUARE
SUITE 2800
INDIANAPOLIS
IN
46204-2079
US
|
Family ID: |
31886526 |
Appl. No.: |
11/545803 |
Filed: |
October 10, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10651055 |
Aug 28, 2003 |
7117667 |
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11545803 |
Oct 10, 2006 |
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10192897 |
Jul 11, 2002 |
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10651055 |
Aug 28, 2003 |
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Current U.S.
Class: |
60/286 ; 60/285;
60/288; 60/295 |
Current CPC
Class: |
F01N 2410/12 20130101;
F01N 3/085 20130101; F01N 2250/12 20130101; Y02A 50/2344 20180101;
F01N 3/0821 20130101; F01N 3/0814 20130101; F01N 13/009 20140601;
B01D 53/96 20130101; F01N 3/0878 20130101; Y02T 10/40 20130101;
F01N 2250/14 20130101; F01N 3/035 20130101; F01N 2610/14 20130101;
F01N 3/0871 20130101; F01N 2250/02 20130101; Y02A 50/20 20180101;
F01N 3/36 20130101; F01N 9/00 20130101; F01N 13/011 20140603; F01N
2570/04 20130101; Y02T 10/47 20130101; F01N 2570/14 20130101; F01N
3/0842 20130101; F01N 3/38 20130101; F01N 2610/03 20130101 |
Class at
Publication: |
060/286 ;
060/285; 060/295; 060/288 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Claims
1-31. (canceled)
32. An engine exhaust aftertreatment system comprising: parallel
exhaust flow paths; a NOx aftertreatment component disposed in each
of the flow paths; a reducing agent catalyst positioned downstream
of the parallel flow paths and through which exhaust flow from the
parallel flow paths is constrained to pass; a SOx aftertreatment
component; and a particulate aftertreatment component; wherein the
system regulates exhaust flow through the parallel exhaust flow
paths and is operable in a rich mode wherein the system consumes a
reduced amount of reducing agent attributable to the regulation of
exhaust flow.
33. A system according to claim 31 wherein the reduced amount of
reducing agent is attributable to exhaust flow in a first flow path
being increased exhaust flow in a second flow path being decreased.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention generally relates to internal
combustion engines and, more particularly, to an NOx adsorber
aftertreatment system for internal combustion engines.
BACKGROUND OF THE INVENTION
[0002] As environmental concerns have led to increasingly strict
regulation of engine emissions by governmental agencies, reduction
of nitrogen-oxygen compounds (NOx) in exhaust emissions from
internal combustion engines has become increasingly important.
Current indications are that this trend will continue.
[0003] Future emission levels of diesel engines will have to be
reduced in order to meet Environmental Protection Agency (EPA)
regulated levels. In the past, the emission levels of U.S. diesel
engines have been regulated according to the EPA using the Federal
Test Procedure (FTP) cycle, with a subset of more restrictive
emission standards for California via the California Air Resources
Board (CARB). For example, the Tier II emission standards, which
are being considered for 2004, are 50% lower than the Tier I
standards. Car and light truck emissions are measured over the FIT
75 test and expressed in gm/mi. Proposed Ultra-Low Emissions
Vehicle (ULTEV) emission levels for light-duty vehicles up to model
year 2004 are 0.2 gm/mi NOx and 0.08 gm/mi particulate matter (PM).
Beginning with the 2004 model year, all light-duty Low Emission
Vehicles (LEVs) and ULEVs in California would have to meet a 0.05
gm/mi NOx standard to be phased in over a three year period. In
addition to the NOx standard, a full useful life PM standard of
0.01 gm/mi would also have to be met.
[0004] Traditional methods of in-cylinder emission reduction
techniques such as exhaust gas recirculation (EGR) and injection
rate shaping by themselves will not be able to achieve these low
emission levels required by the standard. Aftertreatment
technologies will have to be used, and will have to be further
developed in order to meet the future low emission requirements of
the diesel engine.
[0005] Some promising aftertreatment technologies to meet future
NOx emission standards include lean NOx catalysts, Selective
Catalytic Reduction (SCR) catalysts, and Plasma Assisted Catalytic
Reduction (PACR). Current lean NOx catalyst technologies will
result in the reduction of engine out NOx emissions in the range of
10 to 30 percent for typical conditions. Although a promising
technology, SCR catalyst systems require an additional reducing
agent (aqueous urea) that must be stored in a separate tank, which
opens issues of effective temperature range of storage (to
eliminate freezing) as well as distribution systems that must be
constructed for practical use of this technology. PACR is similar
to lean NOx in terms of reduction efficiency but is more expensive
due to plasma generator. These technologies, therefore, have
limitations which may prevent their use in achieving the new
emissions requirements.
[0006] NOx adsorber catalysts have the potential for great NOx
emission reduction (60-90%). The NOx adsorber is one of the most
promising NOx reduction technologies. During lean-bum operation of
the engine, the trap adsorbs nitrogen oxide in the form of stable
nitrates. Under stoiciometric or rich conditions, the nitrate is
thermodynamically unstable and the stored nitrogen oxides are
released and subsequently catalytically reduced. Therefore, the
operation cycle alternates between lean and rich conditions around
the catalyst. During lean operation the catalyst stores the NOx and
during rich operation the NOx is released and reduced to No.
However, to make the conditions around the catalyst rich, a
significant amount of hydrocarbon (HC) needs to be injected. The
amount of HC required for reduction is only a small fraction of the
total hydrocarbon injected, resulting in a significant fuel
penalty. If the HC required to make. conditions rich can be
reduced, the fuel penalty can be brought down substantially.
[0007] An additional problem is the need for a diesel oxidation
catalyst downstream from the NOx adsorber. The diesel oxidation
catalyst oxidizes any unburned hydrocarbon that slips through the
adsorber before the exhaust gases are released to the atmosphere.
The need for a diesel oxidation catalyst negatively affects system
cost and system package size.
[0008] Furthermore, some diesel engines include a catalytic soot
filter to trap the soot generated by the engine. This soot is
carcinogenic to living beings. Such catalytic soot filters often
become clogged with the trapped particulate matter owing to the
fact that they require high temperatures to regenerate. It is
difficult to attain these high temperatures in the engine exhaust
stream at low loads.
[0009] There is therefore a need for an engine aftertreatment
system employing an NOx adsorber which reduces the fuel penalty
associated with these devices, allows for regeneration of the soot
filter, even at low loads, and reduces the system cost and package
size. The present invention is directed toward meeting this
need.
SUMMARY OF THE INVENTION
[0010] The present invention provides for an NOx adsorber
aftertreatment system for internal combustion engines which
utilizes a parallel arrangement of an adsorber catalyst and a
bypass. The exhaust flow from the engine is routed through the
adsorber during lean operation. At a predetermined regeneration
time (for example, when the adsorber catalyst is 20% full), the
exhaust gas flow is reduced through the parallel leg that contains
the adsorber catalyst to be regenerated (e.g., 20% through the
catalyst leg, 80% of the flow to the bypass leg). A quantity of
hydrocarbon is injected into the reduced-flow catalyst leg in order
to make the mixture rich. Since the flow has been reduced in this
leg, only a small fraction of the amount of hydrocarbon that would
have been required to make the mixture rich during full flow is
required. This will result in a substantial reduction in the fuel
penalty incurred for regeneration of the adsorber catalyst. Once
the leg has been regenerated, the exhaust flow is switched to flow
100% through the adsorber leg.
[0011] In one embodiment, a catalytic soot filter is positioned
upstream from the adsorber. The additional hydrocarbon used to
promote regeneration is injected into the catalytic soot filter.
The catalytic soot filter, when used in combination with the
adsorber, provides more time and surface area for the hydrocarbon
to react with the oxygen. The catalytic soot filter will
additionally reformulate some of the diesel fuel into hydrogen and
carbon monoxide, which have been shown to be better reductants than
diesel fuel.
[0012] In another embodiment, a catalytic soot filter is positioned
downstream from the adsorber. The heat generated by the
regenerating adsorber is transferred downstream to the soot filter,
thereby heating the soot filter above the temperature required for
regeneration. Additionally, any hydrocarbon that slips through the
adsorber is burned in the catalytic soot filter, further raising
the temperature. Such burning of the hydrocarbon slip in the
catalytic soot filter obviates the need for a diesel oxidation
catalyst, thereby reducing system cost and package size.
[0013] In another embodiment, a catalytic soot filter is positioned
upstream from the sulfur trap. The soot filter converts SO.sub.2 to
SO.sub.3, which is more readily trapped by the sulfur trap.
[0014] In one form of the invention, an internal combustion engine
aftertreatment system for treating exhaust gases exiting an engine
is disclosed, the system comprising a sulfur trap having a sulfur
trap input operatively coupled to the engine exhaust and having a
sulfur trap output, a catalytic soot filter having a soot filter
input operatively coupled to the sulfur trap output and having a
soot filter output, a valve system having a valve input operatively
coupled to the soot filter output, a first valve output and having
a second valve output, an adsorber having an adsorber input
operatively coupled to the first valve output and having an
adsorber output, a bypass pathway having a bypass input operatively
coupled to the second valve output and having a bypass output
operatively coupled to the adsorber output, and a diesel oxidation
catalyst having a DOC input operatively coupled to the adsorber
output and to the bypass output and having a DOC output.
[0015] In another form of the invention, an internal combustion
engine aftertreatment system for treating exhaust gases exiting an
engine is disclosed, the system comprising a valve system having a
valve input operatively coupled to the engine exhaust, a first
valve output and having a second valve output, an adsorber having
an adsorber input operatively coupled to the first valve output and
having an adsorber output, and a bypass pathway having a bypass
input operatively coupled to the second valve output and having a
bypass output operatively coupled to the adsorber output.
[0016] In another form of the invention, an internal combustion
engine aftertreatment system for treating exhaust gases exiting an
engine is disclosed, the system comprising a valve system having a
valve input operatively coupled to the engine exhaust, a first
valve output and having a second valve output, a catalytic soot
filter having a soot filter input operatively coupled to the valve
system output and having a soot filter output, an adsorber having
an adsorber input operatively coupled to the soot filter output and
having an adsorber output, and a bypass pathway having a bypass
input operatively coupled to the second valve output and having a
bypass output operatively coupled to the adsorber output.
[0017] In another form of the invention, an internal combustion
engine aftertreatment system for treating exhaust gases exiting an
engine is disclosed, the system comprising a valve system having a
valve input operatively coupled to the engine exhaust, a first
valve output and having a second valve output, an adsorber having
an adsorber input operatively coupled to the first valve output and
having an adsorber output, a bypass pathway having a bypass input
operatively coupled to the second valve output and having a bypass
output, and a catalytic soot filter having a soot filter input
operatively coupled to the adsorber output and the bypass output
and having a soot filter output.
[0018] In another form of the invention, an internal combustion
engine aftertreatment system for treating exhaust gases exiting an
engine, the system comprising a catalytic soot filter having a soot
filter input operatively coupled to the engine exhaust and having a
soot filter output, a sulfur trap having a sulfur trap input
operatively coupled to the filter output and having a sulfur trap
output, a valve system having a valve input operatively coupled to
the sulfur trap output, a first valve output and having a second
valve output, an adsorber having an adsorber input operatively
coupled to the first valve output and having an adsorber output, a
bypass pathway having a bypass input operatively coupled to the
second valve output and having a bypass output operatively coupled
to the adsorber output, and a diesel oxidation catalyst having a
DOC input operatively coupled to the adsorber output and to the
bypass output and having a DOC output.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic block diagram of a first preferred
embodiment system of the present invention.
[0020] FIG. 2 is a schematic block diagram of a second preferred
embodiment system of the present invention.
[0021] FIG. 3 is a process flow diagram illustrating a preferred
embodiment process of the present invention.
[0022] FIG. 4 is a schematic block diagram of a third preferred
embodiment system of the present invention.
[0023] FIG. 5 is a schematic block diagram of a fourth preferred
embodiment of the present invention.
[0024] FIG. 6 is a schematic block diagram of a fifth preferred
embodiment of the present invention.
[0025] FIG. 7 is a schematic block diagram of a sixth preferred
embodiment of the present invention.
DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to the
embodiment illustrated in the drawings and specific language will
be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is thereby
intended, and alterations and modifications in the illustrated
device, and further applications of the principles of the invention
as illustrated therein are herein contemplated as would normally
occur to one skilled in the art to which the invention relates.
[0027] Referring to FIG. 1, there is illustrated a schematic block
diagram of a first preferred embodiment of the present invention.
The system is designed to remove NOx compounds from the exhaust
stream of an internal combustion engine 12, such as a diesel
engine. The exhaust produced by the engine 12 exits the exhaust
manifold 14 of the engine and is passed through an optional sulfur
trap 16. NOx adsorber catalysts are extremely sensitive to the
level of sulfur in the fuel. The fuel and the lubrication oil of
the engine contain sulfur and therefore sulfur-oxygen compounds
(SOx) are contained in the exhaust gas. This SOx is adsorbed into
the NOx adsorber and reduces its capacity. Unlike NOx, SOx does not
regenerate under rich conditions within the operating temperature
range of the engine. Eventually the adsorber is filled up with
sulfate and becomes inactive. The optional sulfur trap 16 may
therefore be used to trap SOx compounds before they reach the NOx
adsorbers downstream.
[0028] The output of the sulfur trap 16 may be passed through an
optional catalytic soot filter 18 in order to trap any diesel soot
particulate matter that may be entrained in the exhaust gases. In
addition to trapping diesel soot particulate matter by physical
filtering, the catalytic soot filter also acts as a flow-through
oxidation catalyst by the addition of precious metal catalysts
which reduce the volatile organic fraction of the soot material by
the catalyzed oxidation reaction (e.g. C+Oxidant.fwdarw.CO). A
sensor 20 may be placed at the output of the soot filter 18 in
order to measure the temperature and air/fuel (A/F) ratio (lambda)
of the exhaust stream. The output of the optional sensor 20 is
provided to an electronic engine control module 22.
[0029] The engine controller 22 is additionally coupled to the
engine 12 for reading various engine sensor data, such as engine
position sensor data, speed sensor data, air mass flow sensor data,
fuel rate data, etc., as is known in the art. The engine controller
22 may further provide data to the engine 12 in order to control
the operating state of the engine 12, as is well known in the
art.
[0030] The flow of exhaust leaving the soot filter 18 is controlled
by a proportional control 3-way valve 24. As is known in the art, a
proportional control 3-way valve may be used to divide the flow of
a gas stream into two separate paths, wherein the percentage of the
total gas flow being directed to either path is controllable. In
the embodiment of FIG. 1, the proportional control 3-way valve 24
is coupled to the engine controller 22 in order to control the
relative proportions of exhaust gas flow routed to either output of
the valve 24.
[0031] The two outputs of the valve 24 are coupled to the
respective inputs of a pair of NOx adsorbers (catalytic converters)
26 and 28. Therefore, by providing control signals from the engine
controller 22 to the proportional control 3-way valve 24, the
percentage of the total exhaust flow from the engine 14 entering
either the adsorber 26 or the adsorber 28 may be precisely
controlled. A fuel injector 30 is positioned to inject a measured
quantity of fuel (hydrocarbon) into the exhaust gas flow entering
the adsorber 26. Similarly, a second fuel injector 32 is positioned
to inject a quantity of fuel into the exhaust gas flow entering
adsorber 28. Both injectors 30, 32 are controlled by the engine
controller 22 and are supplied with fuel from a pump 34 supplied by
the vehicle fuel tank 36. Preferably, the fuel pump 34 is a
low-cost diaphragm-type fuel pump. Two igniters 38 are provided to
ignite the fuel being injected by the injectors 30, 32 under the
control of the engine controller 22.
[0032] Because the exhaust flow is reduced in the adsorber leg
being regenerated, the amount of reductant required to burn off the
oxygen reduces. The concentration of reductant required for
reduction remains the same, but this amount is a small fraction of
the total reductant during full exhaust flow. It will be
appreciated that any flow ratios may be utilized during reduction
and regeneration and during normal flow, even though exemplary
flows are used herein for illustrative purposes. The optimum flow
ratios for any given system will depend upon the particular system
configuration.
[0033] The exhaust gases exiting the adsorbers 26 and 28 are
combined together before being input to an optional diesel
oxidation catalyst 40. Due to the pulse injection of relatively
large quantities of reductant (normally hydrocarbon) for short
periods during regeneration of the NOx adsorbers 26, 28 of the
present invention, some unburned hydrocarbon can slip through the
adsorber catalyst. The use of a diesel oxidation catalyst 40
downstream of the adsorbers 26, 28 virtually eliminates hydrocarbon
emission from the tailpipe. Such catalysts contain precious metals
in them that reduce the activation energy of hydrocarbon
combustion, such that the unburned hydrocarbon is oxidized to
carbon dioxide and water. The exhaust gases exiting the diesel
oxidation catalyst 40 may then exit the vehicle. An optional NOx
sensor 42 may be placed between the adsorbers 26, 28 and the diesel
oxidation catalyst 40 in order to directly measure the NOx levels
leaving the adsorbers 26 and 28. The output of the optional NOx
sensor 42 is provided to the engine controller 22.
[0034] Referring now to FIG. 2, there is illustrated a second
preferred embodiment of the present invention. The second
embodiment of the present invention is similar to the first
embodiment illustrated in FIG. 1, and like reference designators
refer to like components. In the second embodiment, the
proportional control 3-way valve is replaced with a pair of two-way
valves 50 and 52. Valve 50 controls the flow of exhaust gases into
the adsorber 26, while valve 52 controls the flow of exhaust gases
into adsorber 28. Each of the valves 50, 52 is coupled to the
engine controller 22 for control thereby.
[0035] The valves 50, 52 may comprise either variable flow rate
control valves or may comprise valves having a fixed number of flow
rate settings. For example, if the aftertreatment system design
dictates that the relative flow between adsorbers 26, 28 will
always be 20-80 during regeneration, then the valves 50, 52 may
have discrete settings that will allow the engine controller 22 to
switch them between reduced flow (20%) and max flow (80%) settings
in order to achieve the desired flow reduction in one of the
adsorbers 26, 28. Optionally, the valves 50, 52 may have variably
adjustable flow rates, such that the engine controller 22 can
infinitely adjust the flow percentage through each valve 50, 52 in
order to divide the exhaust flow between the adsorbers 26, 28 in
any desired proportion.
[0036] Referring now to FIG. 3, there is illustrated a preferred
embodiment process of the present invention. The process begins at
step 100, which represents the steady state operation of the engine
with exhaust gas flow split evenly between the adsorbers 26 and 28.
At step 102, the engine controller 22 determines whether either of
the adsorber 26, 28 catalysts need be regenerated. The decision
made at step 102 can be made under open-loop control, by using
stored catalyst adsorption maps in the engine controller 22. These
catalyst adsorption maps may be predetermined using empirical data
from laboratory tests utilizing the same or similar engine and
exhaust system. The regeneration decision at step 102 may also be
made under closed-loop control, wherein the engine controller 22
examines the data being produced by the NOx sensor 42 which is
proportional to the level of NOx being emitted at the output of the
adsorbers 26, 28.
[0037] If step 102 determines that the adsorbers 26, 28 need to be
regenerated (e.g. the adsorption efficiency has dropped to 80%),
then the process continues at step 104 in which the flow of exhaust
through the system is controlled such that the adsorber to be
regenerated receives a reduced level of exhaust flow. For example,
if the engine controller 22 determines that adsorber 26 needs to be
regenerated, then the flow of exhaust through the adsorber 26 can
be reduced to 20% of the total exhaust flow, with the remaining 80%
being routed through the adsorber 28. The relative proportions of
exhaust flow routed to either adsorber will depend upon various
system design parameters. The 20-80 split discussed herein is for
illustrative purposes only.
[0038] Control of the relative flow of exhaust gases through
adsorbers 26 and 28 is performed under control of the engine
controller 22 (for example, based upon the engine sensor parameters
being sent to the controller 22 (engine position sensor, speed
sensor, air mass flow sensor, fuel rate, etc.)) through operation
of either the proportional control 3-way valve 24 of the system of
FIG. 1 or through control of the dual 2-way valves 50, 52 of the
system of FIG. 2, which are adjusted to achieve the correct
predetermined exhaust flow velocity needed for regeneration of the
aftertreatment system.
[0039] Once the correct flow velocity has been achieved through
each of the adsorbers 26, 28, the process moves to step 106 in
which the engine controller 22 determines the temperature and
air/fuel ratio of the regeneration exhaust stream using the sensor
20. If the temperature of the exhaust stream is sufficient for
regeneration of the catalysts (according to a predetermined
temperature limit), then the process continues to step 110. If step
106 determines that the temperature of the regeneration exhaust
stream needs to be raised, then the process continues at step 108
in which the engine controller 22 causes the igniter 38 to be
activated in order to ensure ignition of the regeneration fuel
injection.
[0040] At step 110, the fuel injector 30, 32 in the leg being
regenerated is used to inject the required amount of fuel into the
exhaust stream as a reductant to completely regenerate the
catalysts within the adsorber. The injectors 30, 32 are controlled
by the engine controller 22. The exhaust fuel injector 30, 32 is
used to achieve a rich air/fuel ratio (lambda less than 1.0) in the
regeneration stream. Because of the reduced amount of exhaust gas
flowing through the regeneration leg, the quantity of fuel needed
to be injected by the injector 30, 32 is greatly reduced, thereby
significantly reducing the fuel penalty associated with adsorber
regeneration. This injected fuel will be ignited by the temperature
of the exhaust gas stream (possibly supplemented by the igniter 38)
in order to facilitate regeneration of the adsorber.
[0041] Once regeneration of the leg is determined to be complete at
step 112 (e.g. after a predetermined amount of time has elapsed),
the process continues at step 114, where the engine controller 22
determines if both legs of the system have been regenerated. If
they have not, then the process continues at step 116, where the
engine controller 22 operates either the proportional control 3-way
valve 24 or the 2-way valves 50, 52 in order to route the majority
of the exhaust gas flow to the recently regenerated leg and to
reduce the amount of exhaust gases flowing through the leg which is
to be regenerated. The process is then returned to step 106 in
order to regenerate the next leg. If, on the other hand, step 114
determines that both legs have been regenerated, then the process
is returned to step 100 where the engine controller 22 operates the
proportional control 3-way valve 24 or the 2-way valves 50, 52 in
order to evenly split the exhaust gas flow through the adsorbers
26, 28.
[0042] As detailed hereinabove, the adsorber regeneration cycle
switches back and forth between the two sides of the exhaust as
necessary in order to keep the outlet exhaust stream purified of
excessive emissions. It will be appreciated that since dual exhaust
streams are being utilized, the regeneration cycle of the adsorber
does not necessarily have to be short. During the entire time that
the adsorber is being regenerated, the second adsorber is available
for cleaning the majority of the exhaust gas stream. It should also
be noted that the temperature of the regeneration exhaust gas
stream may also be controlled by adjustment of the proportional
control 3-way valve in conjunction with the igniter 38. By allowing
slightly more exhaust gas to pass into the regeneration side of the
exhaust, the temperature thereof may be raised.
[0043] Besides the aforementioned advantages in adsorber
regeneration, the arrangement of catalysts illustrated in FIGS. 1
and 2 of the present invention provides other benefits. Placing the
catalytic soot filter 18 before the adsorbers 26, 28 helps in
multiple ways. The catalytic soot filter 18 converts the NO in the
exhaust stream to NO.sub.2 which helps NOx storage-in the adsorber
26, 28. The catalytic soot filter 18. also prevents particulate
matter from clogging the adsorber system and it also helps increase
the temperature of the exhaust stream in order to make the adsorber
26, 28 more efficient.
[0044] In another embodiment, the sulfur trap 16 may be placed
downstream from the catalytic soot filter 18. By placing the
catalytic soot filter 18 upstream of the sulfur trap 16, the
catalytic soot filter 18 will convert SO.sub.2 to SO.sub.3, which
is more readily trapped by the sulfur trap 16.
[0045] Therefore, the system illustrated and described herein is
effective in addressing all legislatively-controlled emissions
including NOx, SOx and hydrocarbons. The adsorbers are used for
reduction of NOx levels and are more easily regenerated than in
prior art systems. The sulfur trap removes sulfur from the exhaust,
making the operation of the adsorber more efficient and longer
lasting. The catalytic soot filter traps particulate soot from the
exhaust stream. Finally, the diesel oxidation catalyst cleans up
any leftover hydrocarbons exiting the adsorbers, thereby allowing
the exhaust emitted by the system of the present invention to meet
or exceed the requirements of the various legislative bodies.
[0046] Referring now to FIG. 4, there is illustrated a third
preferred embodiment of the present invention. The third embodiment
of the present invention is similar to the first embodiment
illustrated in FIG. 1, and like reference designators refer to like
components. In the third embodiment, the adsorber 28 and injector
32 are replaced by a simple bypass tube 29. During lean operation
of the engine 12, the entire exhaust flow is routed through the
adsorber 26 under control of the 3-way valve 24. As in the first
preferred embodiment, when the adsorber 26 efficiency falls to a
predetermined level (e.g. 80% efficiency), the 3-way valve 24 is
adjusted to route a majority of the exhaust flow through the bypass
tube 29. As in the first preferred embodiment, the adsorber 26 may
then be regenerated by the injection of hydrocarbon through the
fuel injector 30.
[0047] After the adsorber 26 has been regenerated, the valve 24 is
adjusted to route all of the exhaust flow through the adsorber 26.
In this manner, the regeneration cycle can be switched back and
forth between full flow through the adsorber 26 and partial
adsorber bypass through the tube 29 in order to keep the outlet
exhaust stream purified of excessive emissions. Since the bypass
tube 29 contains no adsorber, the regeneration cycle needs to be
kept short in order to keep NOx emissions to acceptable levels.
[0048] The third embodiment system of FIG. 4 has certain advantages
over the first embodiment system. In the first embodiment system,
the regeneration operation has to e performed twice in each cycle
since there is a catalyst mounted in each leg. Use of the third
embodiment system therefore leads to less injections of
regeneration hydrocarbon and additional fuel savings. Of course,
NOx is not stored in the bypass tube 29 during regeneration, thus
the system efficiency of the third embodiment is slightly less than
for the first and second embodiments. The third embodiment,
however, has the advantage of less hardware by requiring one less
adsorber, fuel injector and ignitor. The third embodiment also
utilizes a simpler control strategy because of the need to
regenerate only a single adsorber.
[0049] Referring now to FIG. 5, there is illustrated a fourth
preferred embodiment of the present invention. The fourth
embodiment of the present invention is similar to the third
embodiment illustrated in FIG. 4, and like reference designators
refer to like components. In the fourth embodiment, the catalytic
soot filter 18 is moved to a position upstream from the adsorber 26
and downstream of the fuel injector 30.
[0050] As discussed hereinabove, catalytic soot filters 18 require
high temperatures in order to regenerate. It is difficult to attain
these high temperatures in the exhaust stream during low load
operation of the engine 12. Under these conditions, the soot filter
18 eventually becomes clogged with soot. By placing the soot filter
18 upstream from the adsorber 26 and downstream from the fuel
injector 30 as shown in the fourth embodiment, the catalytic soot
filter 18 also receives the injected hydrocarbon and is regenerated
by combustion of this hydrocarbon. Placement of the catalytic soot
filter 18 in this position also provides more time and surface area
for the introduced hydrocarbon to react with oxygen, thereby more
completely burning the hydrocarbon. More complete hydrocarbon
combustion will possibly eliminate the need for the diesel
oxidation catalyst 40, thereby reducing exhaust system cost and
package size.
[0051] Furthermore, the catalytic soot filter 18 will reformulate
some of the diesel fuel into hydrogen and carbon monoxide, which
have been shown to be better reductants than diesel fuel. This
improvement in reduction will result in more complete regeneration
of the catalytic soot filter 18 and adsorber 26 and/or a shorter
regeneration time.
[0052] Referring now to FIG. 6, there is illustrated a fifth
preferred embodiment of the present invention. The fifth embodiment
of the present invention is similar to the third embodiment
illustrated in FIG. 4, and like reference designators refer to like
components. In the fifth embodiment, the diesel oxidation catalyst
40 is removed from the system and the catalytic soot filter 18 is
positioned downstream from the adsorber 26.
[0053] As discussed hereinabove, catalytic soot filter 18 requires
high temperatures in order to regenerate. It is difficult to attain
these high temperatures in the exhaust stream during low load
operation of the engine 12. Under these conditions, the soot filter
18 eventually becomes clogged with soot. By placing the soot filter
18 downstream from the adsorber 26 as shown in the fifth
embodiment, heat generated in the adsorber 26 due to the combustion
of the introduced hydrocarbon serves to raise the temperature of
the catalytic soot filter 18 sufficiently to accomplish
regeneration.
[0054] Furthermore, any hydrocarbon that slips unburned through the
adsorber 26 will oxidize in the soot filter 18, thereby generating
further heat to encourage regeneration of the soot filter 18.
Because the hydrocarbon slip is oxidized in the soot filter 18, the
diesel oxidation catalyst 40 of the prior embodiments is no longer
required. Elimination of the diesel oxidation catalyst 40 reduces
the exhaust system cost and package size.
[0055] Referring now to FIG. 7, there is illustrated a sixth
preferred embodiment of the present invention. The sixth embodiment
of the present invention is similar to the third embodiment
illustrated in FIG. 4, and like reference designators refer to like
components. In the sixth embodiment, the catalytic soot filter 18
is positioned upstream from the sulfur trap 16. Placement of the
catalytic soot filter 18 in this position enhances the efficiency
of the sulfur trap, as the soot filter converts SO.sub.2 to
SO.sub.3, which is more readily trapped by the sulfur trap.
[0056] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown
and described and -that all changes and modifications- that come
within the spirit of the invention are desired to be protected.
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