U.S. patent application number 12/965525 was filed with the patent office on 2012-06-14 for exhaust system having doc regeneration strategy.
Invention is credited to Duncan J. Arrowsmith, James J. DRISCOLL.
Application Number | 20120144802 12/965525 |
Document ID | / |
Family ID | 46197950 |
Filed Date | 2012-06-14 |
United States Patent
Application |
20120144802 |
Kind Code |
A1 |
DRISCOLL; James J. ; et
al. |
June 14, 2012 |
EXHAUST SYSTEM HAVING DOC REGENERATION STRATEGY
Abstract
An exhaust system for use with a combustion engine is disclosed.
The exhaust system may have an exhaust passage configured to
receive a flow of exhaust from the combustion engine, and an
oxidation catalyst disposed within the exhaust passage. The exhaust
system may also have a fuel injector configured to selectively
inject fuel into the exhaust at a location upstream of the
oxidation catalyst, a temperature sensor configured to generate a
signal indicative of a temperature of exhaust flowing through the
exhaust passage, and a controller in communication with the fuel
injector and the temperature sensor. The controller may be
configured to make a determination based on the signal that an
oxide layer has formed on the oxidation catalyst, and to regulate
operation of the fuel injector to inject fuel and reduce the oxide
layer based on the determination.
Inventors: |
DRISCOLL; James J.; (Dunlap,
IL) ; Arrowsmith; Duncan J.; (Lincoln, GB) |
Family ID: |
46197950 |
Appl. No.: |
12/965525 |
Filed: |
December 10, 2010 |
Current U.S.
Class: |
60/274 ; 60/286;
60/295 |
Current CPC
Class: |
F01N 3/2033 20130101;
F01N 2610/02 20130101; F01N 2610/03 20130101; Y02T 10/47 20130101;
F01N 3/0253 20130101; Y02T 10/40 20130101; F01N 3/103 20130101;
Y02T 10/12 20130101; Y02T 10/26 20130101; F01N 9/00 20130101 |
Class at
Publication: |
60/274 ; 60/286;
60/295 |
International
Class: |
F01N 3/20 20060101
F01N003/20; F01N 3/023 20060101 F01N003/023; F01N 3/18 20060101
F01N003/18 |
Claims
1. An exhaust system for a combustion engine, comprising: an
exhaust passage configured to receive a flow of exhaust from the
combustion engine; an oxidation catalyst disposed within the
exhaust passage; a fuel injector configured to selectively inject
fuel into the exhaust at a location upstream of the oxidation
catalyst; a temperature sensor configured to generate a signal
indicative of a temperature of exhaust flowing through the exhaust
passage; and a controller in communication with the fuel injector
and the temperature sensor, the controller being configured to:
make a determination based on the signal that an oxide layer has
formed on the oxidation catalyst; and regulate operation of the
fuel injector to inject fuel and reduce the oxide layer based on
the determination.
2. The exhaust system of claim 1, wherein the controller is
configured to make the determination that an oxide layer has formed
when the signal indicates a temperature of exhaust flowing through
the exhaust passage has exceeded a threshold temperature.
3. The exhaust system of claim 2, wherein the controller is
configured to make the determination that an oxide layer has formed
when the signal indicates the temperature of exhaust flowing
through the exhaust passage has remained above the threshold
temperature for a threshold period of time.
4. The exhaust system of claim 2, wherein the threshold temperature
is a temperature at which about 60-100% of the oxidation catalyst
is covered by the oxide layer.
5. The exhaust system of claim 4, wherein the fuel injected by the
fuel injector to reduce the oxide layer changes an air-to-fuel
ratio of the flow of exhaust by less than about 5%.
6. The exhaust system of claim 4, wherein the fuel injected by the
fuel injector to reduce the oxide layer raises temperatures by less
than about 30.degree. C.
7. The exhaust system of claim 4, wherein the fuel injected by the
fuel injector during a single burst to reduce the oxide layer is
about 100 to 1000 ppm in the flow of exhaust, and the controller is
configured to continue the injections at about five minute
intervals as long as the temperature of exhaust flowing through the
exhaust passage remains above the threshold temperature.
8. The exhaust system of claim 2, wherein the controller is
configured to regulate operation of the fuel injector to inject
fuel when the signal indicates the exhaust flowing through the
exhaust passage is cooling.
9. The exhaust system of claim 1, further including an exhaust
treatment device disposed within the exhaust passage downstream of
the oxidation catalyst.
10. The exhaust system of claim 9, wherein the exhaust treatment
device is one of a particulate filter configured to regenerate in
the presence of NO.sub.2 generated by the oxidation catalyst or a
reduction device configured to reduce a constituent of the exhaust
in the presence of NO and NO.sub.2 generated by the oxidation
catalyst.
11. A method of operating an exhaust system, comprising: directing
exhaust through an oxidation catalyst; making a determination that
an oxide layer has formed on the oxidation catalyst; and
selectively introducing a burst of fuel into exhaust directed
through the oxidation catalyst to reduce the oxide layer based on
the determination.
12. The method of claim 11, wherein making the determination
includes determining that a temperature of the exhaust has exceeded
a threshold temperature.
13. The method of claim 12, wherein making the determination
further includes determining that the temperature of the exhaust
has remained above the threshold temperature for a threshold period
of time.
14. The method of claim 12, wherein the threshold temperature is a
temperature at which about 60-100% of the oxidation catalyst is
covered with the oxide layer.
15. The method of claim 14, wherein selectively introducing bursts
of fuel increases an air-to-fuel ratio of the exhaust by less than
about 5%.
16. The method of claim 14, wherein selectively introducing bursts
of fuel increases a temperature of the exhaust by less than about
30.degree. C.
17. The method of claim 14, wherein the fuel injected during a
single burst of fuel is about 100 to 1000 ppm in the exhaust, and
the method further includes continuing to introduce bursts of fuel
at about five minute intervals as long as the temperature of the
exhaust remains above the threshold temperature.
18. The method of claim 11, wherein selectively introducing bursts
of fuel includes selectively introducing bursts of fuel when the
exhaust is cooling.
19. The method of claim 11, further including directing exhaust
from the oxidation catalyst through at least one of a particulate
filter and a reduction catalyst.
20. A power system, comprising: an internal combustion engine
configured to combust fuel and generate a flow of exhaust; an
exhaust passage leading from the internal combustion engine to the
atmosphere; an oxidation catalyst disposed within the exhaust
passage to convert NO to NO.sub.2; a particulate filter disposed
downstream of the oxidation catalyst configured to passively
regenerate in the presence of the NO.sub.2; a fuel injector
configured to selectively inject fuel into the exhaust passage at a
location upstream of the oxidation catalyst; a temperature sensor
configured to generate a signal indicative of a temperature of
exhaust flowing through the exhaust passage; and a controller in
communication with the fuel injector and the temperature sensor,
the controller being configured to: make a determination based on
the signal that temperature indicative of formation of an oxide
layer on the oxidation catalyst has been exceeded; and regulate
operation of the fuel injector to inject fuel and reduce the oxide
layer based on the determination, wherein the fuel injected by the
fuel injector changes an air-to-fuel ratio of the exhaust by less
than 5% and raises a temperature of the exhaust by less than
30.degree. C.
Description
TECHNICAL FIELD
[0001] The present disclosure is directed to an exhaust system and,
more particularly, to an exhaust system having a strategy for
regenerating a diesel oxidation catalyst (DOC).
BACKGROUND
[0002] Diesel oxidation catalysts (DOCs) are commonly used in the
exhaust systems of internal combustion engines to facilitate
different emission reduction processes. For example, DOCs can be
used to create a desired ratio of NO to NO.sub.2 in an engine's
exhaust stream that enhances NO.sub.X reduction within a downstream
selective catalytic reduction (SCR) device. In another example,
DOCs can be used to increase an overall amount of NO.sub.2 in the
exhaust stream passing through a diesel particulate filter (DPF) to
lower a combustion temperature of particulate matter trapped in the
DPF and thereby enhance passive regeneration of the DPF.
[0003] Although effective as exhaust treatment tools, DOCs can also
be problematic under some conditions. That is, it has been found
that the active catalytic materials of a DOC, which commonly
include precious materials such as Platinum, can become less active
when exposed to high temperatures. Consequently, as the DOC cools
after reaching high temperatures or operates for an extended period
of time at the high temperatures, the DOC is less capable of
generating NO.sub.2.
[0004] The reduced functionality of a DOC after exposure to high
temperatures mentioned above is discussed in a journal article
titled "Inverse Hysteresis During The NO Oxidation on Pt Under Lean
Conditions," written by W. Hauptmann et al. and published on Sep.
16, 2009 ("the Hauptmann article"). In the Hauptmann article, a
method of regenerating a DOC is also discussed. In particular, the
Hauptmann article describes how cooling the DOC slowly over an
extended period of time in an exhaust flow containing a high
concentration of NO can improve subsequent performance of the
DOC.
SUMMARY
[0005] One aspect of the present disclosure is directed to an
exhaust system for use with a combustion engine. The exhaust system
may include an exhaust passage configured to receive a flow of
exhaust from the combustion engine, and an oxidation catalyst
disposed within the exhaust passage. The exhaust system may also
include a fuel injector configured to selectively inject fuel into
the exhaust at a location upstream of the oxidation catalyst, a
temperature sensor configured to generate a signal indicative of a
temperature of exhaust flowing through the exhaust passage, and a
controller in communication with the fuel injector and the
temperature sensor. The controller may be configured to make a
determination based on the signal that an oxide layer has formed on
the oxidation catalyst, and to regulate operation of the fuel
injector to inject fuel and reduce the oxide layer based on the
determination.
[0006] Another aspect of the present disclosure is directed to a
method of operating an exhaust system. The method may include
directing exhaust through an oxidation catalyst, and making a
determination that an oxide layer has formed on the oxidation
catalyst. The method may further include selectively introducing a
burst of fuel into exhaust directed through the oxidation catalyst
to reduce the oxide layer based on the determination.
BRIEF DESCRIPTION OF THE DRAWING
[0007] FIG. 1 is a schematic and diagrammatic illustration of an
exemplary disclosed power system; and
[0008] FIG. 2 is a graph illustrating an operation of the power
system of FIG. 1.
DETAILED DESCRIPTION
[0009] FIG. 1 illustrates an exemplary power system 10. For the
purposes of this disclosure, power system 10 is depicted and
described as a diesel-fueled internal combustion engine. However,
it is contemplated that power system 10 may embody any other type
of combustion engine such as, for example, a gasoline engine or a
gaseous fuel-powered engine burning compressed or liquefied natural
gas, propane, or methane. Power system 10 may include an engine
block 12 that at least partially defines a plurality of combustion
chambers 14 provided with fuel via a plurality of fuel injectors
15. It is contemplated that power system 10 may include any number
of combustion chambers 14 and that combustion chambers 14 may be
disposed in an "in-line" configuration, a "V" configuration, or in
any other conventional configuration.
[0010] Multiple separate sub-system may be included within power
system 10. For example, power system 10 may include an air
induction system 16, an exhaust system 18, and a control system 20.
Air induction system 16 may be configured to direct air into
combustion chambers 14 of power system 10 to mix with fuel from
injectors 15 for subsequent combustion. Exhaust system 18 may
exhaust byproducts of the combustion to the atmosphere. Control
system 20 may regulate operations of air induction and exhaust
systems 16, 18 to reduce the production of regulated constituents
and/or their discharge to the atmosphere.
[0011] Air induction system 16 may include multiple components that
cooperate to condition and introduce compressed air into combustion
chambers 14. For example, air induction system 16 may include an
air cooler 22 located downstream of one or more compressors 24.
Compressors 24 may be connected to pressurize inlet air directed
through cooler 22. A throttle valve (not shown) may be located
upstream and/or downstream of compressors 24 to selectively
regulate (i.e., restrict) the flow of inlet air into power system
10. A restriction on the flow of inlet air may result in less air
entering power system 10 and, thus, affect an air-to-fuel ratio of
power system 10. It is contemplated that air induction system 16
may include different or additional components than described above
such as, for example, variable valve actuators associated with each
combustion chamber 14, filtering components, compressor bypass
components, and other known components that may be selectively
controlled to affect the air-to-fuel ratio of power system 10, if
desired. It is further contemplated that compressors 24 and/or
cooler 22 may be omitted, if a naturally aspirated power system 10
is desired.
[0012] Exhaust system 18 may include multiple components that
condition and direct exhaust from combustion chambers 14 to the
atmosphere. For example, exhaust system 18 may include an exhaust
passage 26, one or more turbines 28 driven by exhaust flowing
through passage 26, and a plurality of exhaust treatment devices
fluidly connected within passage 26 at a location downstream of
turbines 28. It is contemplated that exhaust system 18 may include
different or additional components than described above such as,
for example, exhaust gas recirculation (EGR) components, bypass
components, an exhaust compression or restriction brake, an
attenuation device, and other known components, if desired.
[0013] Each turbine 28 may be located to receive exhaust discharged
from combustion chambers 14, and may be connected to one or more
compressors 24 of air induction system 16 by way of a common shaft
30 to form a turbocharger. As the hot exhaust gases exiting power
system 10 move through turbine 28 and expand against vanes (not
shown) thereof, turbine 28 may rotate and drive the connected
compressor 24 to pressurize inlet air. In one embodiment, turbine
28 may be a variable geometry turbine (VGT) or include a
combination of variable and fixed geometry turbines. VGTs are a
type of turbocharger having geometry adjustable to attain different
aspect ratios, such that adequate boost pressure may be supplied to
combustion chambers 14 under a range of operational conditions. As
a flow area of turbine 28 changes, the air-to-fuel ratio and thus
the performance of power system 10 may also change. Alternatively,
a fixed geometry turbocharger with or without an electronically
controlled wastegate may be included, if desired.
[0014] The treatment devices of exhaust system 18 may receive
exhaust from turbine 28 and reduce or remove constituents of the
exhaust. In one example, the exhaust treatment devices may include
one or more of a diesel particulate filter (DPF) 32 and a selective
catalytic reduction (SCR) device 34. A particulate filter is a
device designed to trap particulate matter and typically consists
of a wire mesh or ceramic honeycomb medium. As exhaust laden with
particulate matter passes through the filter, the particulate
matter is blocked by the filter and suspended from the exhaust
flow. SCR device 34 may include a catalyst substrate 36 located
downstream from an injector 38. A pressurized gaseous or liquid
reductant, most commonly urea (NH.sub.2).sub.2CO or a water/urea
mixture may be selectively advanced into the exhaust upstream of
catalyst substrate 36 by injector 38. An onboard reductant supply
40 and a pressurizing device 42 may be associated with injector 38
to provide the pressurized reductant. As the injected reductant is
adsorbed onto a surface of catalyst substrate 36, the reductant may
react with NOx (NO and NO.sub.2) in the exhaust gas to form water
(H.sub.2O) and diatomic nitrogen (N.sub.2).
[0015] The performance of particulate trap 32 and/or SCR device 34
may be enhanced by an upstream-located diesel oxidation catalyst
(DOC) 44. In particular, as DPF 32 operates, particulate matter may
build up therein and, if unaccounted for, eventually restrict the
exhaust flow through DPF 32 by an undesired amount. Accordingly,
DPF 32 may be selectively regenerated to reduce the amount of
particulate matter buildup. To initiate regeneration of DPF 32, the
temperature of the particulate matter entrained within DPF 32 must
be elevated above a combustion threshold temperature at which the
trapped particulate matter is burned away, for example above about
600.degree. C. Under most conditions, however, this threshold
temperature is not achieved naturally. DOC 44, as will be explained
in more detail below, may generate an amount of NO.sub.2 in the
exhaust flow passing through DPF 32 that helps to lower the
combustion threshold temperature to a level that allows combustion
of trapped particulate matter under normal operating conditions.
This type of regeneration may be known as passive regeneration.
Similarly, the reduction process performed by SCR device 34 may be
most effective when a concentration of NO to NO.sub.2 supplied to
SCR device is about 1:1, and DOC 44 may help provide this
concentration.
[0016] DOC 44 may include a porous ceramic honeycomb structure or a
metal mesh substrate coated with a material, for example a washcoat
containing precious metals, that catalyzes a chemical reaction to
alter the composition of the exhaust. For example, DOC 44 may
include a washcoat of palladium, platinum, vanadium, or a mixture
thereof that facilitates the conversion of a portion of the NO
already existing in the exhaust flow of power system 10 to
NO.sub.2. The exhaust flow having an increased amount of NO.sub.2
may then be directed into DPF 32 to facilitate passive regeneration
therein and/or into SCR device 34 to facilitate the reduction of
NO.sub.X.
[0017] As described above, the precious metal/active catalytic
component of a DOC can become less active after exposure to high
temperatures. In particular, it has been determined that when
exposed to high temperatures for an extended period of time, a DOC
can become coated with an oxide layer due to the NO.sub.2 it
generates, the oxide layer resulting in decreased performance of
the DOC. This phenomenon is depicted in FIG. 2. Specifically, FIG.
2 illustrates a first curve 200 representing operation of a typical
DOC during an initial operation of a corresponding power source as
the power source heats up, and a second curve 210 representing
operation of the same DOC after an extended period of time at
elevated temperatures and during cooling of the power source. As
can be seen from comparison of these curves, the typical DOC will
initially perform well and convert an increasing amount of NO to
NO.sub.2 until exhaust temperatures reach about 180.degree. C. Once
exhaust temperatures reach about 180.degree. C. and continue to
increase, however, the conversion efficiency of the typical DOC may
reduce. And, the conversion efficiency drops dramatically as the
DOC cools after extended operation at elevated temperatures. For
example, when cooling from about 250.degree. C. to about
200.degree. C., the efficiency shown in curve 210 may be about half
of the initial efficiency shown in curve 200. Further, if reheated
before sufficient cooling has occurred, the efficiency of the
typical DOC will follow the reduced efficiency curve 210 rather
than curve 200.
[0018] To help ensure prolonged operation of DOC 44 at a desired
level, an injector 46 may be disposed at a location upstream of DOC
44 and configured to selectively inject bursts of a hydrocarbon,
for example diesel fuel, into exhaust passage 26. When the
hydrocarbon comes into contact with the oxide layer on the metallic
substrate of DOC 44, a chemical reaction may occur that removes or
otherwise reduces the oxide layer. An onboard hydrocarbon supply 48
and a pressurizing device 50 may be associated with injector 46 to
provide the pressurized hydrocarbon.
[0019] Control system 20 may include components configured to
regulate the treatment of exhaust from power system 10 prior to
discharge to the atmosphere. Specifically, control system 20 may
include a controller 52 in communication with one or more exhaust
sensors 54, injector 38, and injector 46. Based on input from
exhaust sensor 54 and/or other input, controller 52 may determine
an amount of NO.sub.X being produced by power system 10, a
performance of SCR device 34, the formation of the oxide layer on
DOC 44, a desired amount of urea that should be sprayed by injector
38 into the exhaust flow, a desired amount of hydrocarbon that
should be sprayed by injector 46 into the exhaust flow, and/or
other similar control parameters. Controller 52 may then regulate
operation of injectors 38 and 46 such that the desired amounts of
urea and hydrocarbon are sprayed into the exhaust flow upstream of
catalyst substrate 36 and DOC 44, respectively.
[0020] Controller 52 may embody a single or multiple
microprocessors, field programmable gate arrays (FPGAs), digital
signal processors (DSPs), etc. that include a means for controlling
an operation of power system 10 in response to signals received
from the various sensors. Numerous commercially available
microprocessors can be configured to perform the functions of
controller 52. It should be appreciated that controller 52 could
readily embody a microprocessor separate from that controlling
other non-exhaust related power system functions, or that
controller 52 could be integral with a general power system
microprocessor and be capable of controlling numerous power system
functions and modes of operation. If separate from the general
power system microprocessor, controller 52 may communicate with the
general power system microprocessor via datalinks or other methods.
Various other known circuits may be associated with controller 52,
including power supply circuitry, signal-conditioning circuitry,
actuator driver circuitry (i.e., circuitry powering solenoids,
motors, or piezo actuators), communication circuitry, and other
appropriate circuitry.
[0021] Exhaust sensor 54 of control system 20 may be configured to
generate a signal indicative of formation of the oxide layer on the
metallic substrate of DOC 44. In one embodiment, exhaust sensor 54
may be a temperature sensor configured to generate a signal
corresponding to a temperature of the exhaust passing through DOC
44, and send this signal to controller 52. In this example, when
the signal corresponds with an exhaust temperature above a
threshold temperature, controller 52 may make a determination that
it is likely that the oxide layer has formed. The threshold
temperature may be about 180-250.degree. C. and correspond with
about 60-100% of the substrate of DOC 44 being covered by the oxide
layer. In another example, when the signal indicates that the
exhaust temperature has remained above the threshold temperature
for a threshold period of time, controller 52 may make the
determination that the oxide layer has formed. The threshold period
of time may be about 2-30 seconds. It is contemplated that exhaust
sensor 54 may be a type of sensor other than a temperature sensor,
if desired, and that controller 52 may be configured to similarly
make the determination regarding formation of the oxide layer based
on the corresponding signal(s) from that sensor. For example,
exhaust sensor 54 could alternatively embody a NO.sub.X sensor
configured to detect an amount of NO and/or NO.sub.2 in the exhaust
exiting DOC 44, with controller 52 then being configured to
determine formation of the oxide layer based on the sensed
conversion performance of DOC 44. In another example, exhaust
sensor 54 could alternatively embody a particulate filter sensor
configured to generate signals indicative of lower than expected
regeneration rates of DPF 32 as determined by an amount of soot
detected within or downstream of DPF 32, and/or a pressure
differential across DPF 32.
[0022] It is further contemplated that sensor 54 may alternatively
embody a virtual sensor. A virtual sensor may produce a
model-driven estimate based on one or more known or sensed
operational parameters of power system 10 and/or DOC 44. For
example, based on a known operating speed, load, temperature, boost
pressure, ambient conditions (humidity, pressure, temperature),
and/or other parameter of power system 10, a model may be
referenced to determine formation of the oxide layer on DOC 44.
Similarly, based on a known or estimated NOx production of power
system 10, a flow rate of exhaust exiting power system 10, and/or a
temperature of the exhaust, the model may be referenced to
determine the formation of the oxide layer. As a result, the signal
directed from sensor 54 to controller 52 may be based on calculated
and/or estimated values rather than direct measurements, if
desired. It is contemplated that rather than a separate element,
these virtual sensing functions may be accomplished by controller
52, if desired.
[0023] When controller 52 determines that it is likely that the
oxide layer has formed on the substrate of DOC 44, controller 52
may selectively cause injector 46 to inject one or more bursts of
hydrocarbon into the exhaust at a location upstream of DOC 44. For
example, after the temperature of the exhaust at DOC 44 exceeds
180.degree. C. and/or remains above 180.degree. C. for at least 2
seconds, controller 52 may energize injector 46 to inject an amount
of hydrocarbon necessary to remove or otherwise reduce the
corresponding oxide layer. In one embodiment, the amount of
hydrocarbon injected during a single oxide-dissolving event may be
about 100-1000 ppm or about 1/100-1/1000 of a total amount of fuel
consumed (i.e., including fuel used for normal combustion purposes)
by power system 10 during the event, and have an injection duration
of about 5-300 seconds. This amount of hydrocarbon may serve
primarily to remove some or all of the oxide layer and have little
affect on the air-to-fuel ratio or the temperature of exhaust
within passage 26. For example, the injected hydrocarbon may raise
the air-to-fuel ratio of the exhaust within passage 26 by less than
about 5% and increase a temperature of the exhaust by less than
about 30.degree. C. In one example, the injection of hydrocarbon
has been shown to remove the oxide layer to less than about 20% of
the substrate surface of DOC 44 in as little as about 5-300
seconds, depending on the application.
[0024] In one embodiment, controller 52 may delay the injections of
hydrocarbon until the exhaust temperatures have peaked and cooling
of the exhaust is observed. This cooling may correspond, for
example, with idling of power system 10 or a particular segment of
an excavation cycle such as a dump or return segment that requires
less output from power system 10. Controller 52 may determine that
temperatures have peaked and the exhaust is cooling when controller
52 detects a temperature drop of about 5-20.degree. C. over a one
minute time period.
[0025] Under some conditions, the exhaust temperatures of power
system 10 may remain elevated for extended periods of time. During
operation in these conditions, controller 52, after triggering the
initial hydrocarbon injections according to the strategy outlined
above, may continue to inject bursts of hydrocarbon as long as
exhaust temperatures remain elevated. For example, after the
initial burst of hydrocarbon, injector 46 may be controlled to
inject subsequent bursts of hydrocarbon about every five
minutes.
INDUSTRIAL APPLICABILITY
[0026] The exhaust system of the present disclosure may be
applicable to any power system having an oxidation catalyst, where
continued performance at a desired level is important. The
performance of DOC 44 may be extended through selective injections
of hydrocarbon into the exhaust flow of power system 10 at a
location upstream of DOC 44 when it is determined to be likely that
an oxide layer has formed on DOC 44. Operation of power system 10
will now be described.
[0027] Referring to FIG. 1, air induction system 16 may pressurize
and force air or a mixture of air and fuel into combustion chambers
14 of power system 10 for subsequent combustion. The fuel and air
mixture may be combusted by power system 10 to produce a mechanical
work output and an exhaust flow of hot gases. The exhaust flow may
contain a complex mixture of air pollutants composed of gaseous
material, which can include oxides of nitrogen (NO.sub.X). As this
NO.sub.X-laden exhaust flow is directed from combustion chambers 14
through oxidation catalyst 44, some NO in the flow may be converted
to NO.sub.2.
[0028] After passing through oxidation catalyst 44, the exhaust
flow containing an increased amount of NO.sub.2 may be directed
through DPF 32 and SCR 34. As the exhaust passes through these
treatment devices, particulate matter in the exhaust may be removed
by DPF 32 and NO.sub.X in the exhaust may be reduced to innocuous
substances. As described above, the increased amount of NO.sub.2
generated by DOC 44 may facilitate passive regeneration of DPF 32
and enhance the reduction of NO.sub.X within SCR 34.
[0029] When temperatures of the exhaust flow passing through DOC 44
reach about 180.degree. C. and/or remain elevated above 180.degree.
C. for at least 2 sec., an oxide layer may form on the metallic
substrate of DOC 44. This oxide layer, if unaccounted for, may
decrease the performance of DOC 44. To maintain the desired level
of performance within DOC 44, the substrate of DOC 44 may need to
be selectively regenerated. Accordingly, controller 52 may monitor
the signals from exhaust sensor 54 (Step 300) and determine if
exhaust temperatures have remained above 180.degree. C. for at
least 2 seconds (Step 310). When controller 52 determines that the
conditions of step 310 have been satisfied (Step 310: Yes),
controller 52 may await the next exhaust cooling event (e.g., an
event where exhaust temperatures cool by about 5-20.degree. C.
within a one minute time period) (Step 310), and then initiate
regeneration of DOC 44 by causing injector 46 to selectively inject
bursts of hydrocarbon (i.e., diesel fuel) into the exhaust of
passage 26 at a location upstream of DOC 44 (Step 330). This
injected hydrocarbon, when it comes into contact with the oxide
layer, may facilitate a chemical reaction that removes the oxide
layer and restores functionality to DOC 44. As long as controller
52 determines that exhaust temperatures remain elevated (e.g.,
above 180.degree. C.), controller 52 may cause injector 46 to
inject additional bursts of hydrocarbon on a regular basis, for
example every five minutes (Step 340), without waiting for a
cooling event to occur.
[0030] Several aspects may be associated with power system 10. For
example, the disclosed injections of hydrocarbon may be capable of
dissolving the oxide layer of a DOC in a very short amount of time
with very little hydrocarbon. In particular, it has been shown that
a relatively small injection of hydrocarbon (i.e., about
1/100-1/1000 of a total amount of fuel consumed) may dissolve the
oxide layer in about 5-300 seconds, and do so with an efficiency of
about twenty times greater than using elevated concentrations of NO
alone. Accordingly, the disclosed system may be very responsive and
efficient. In addition, many power systems may already be equipped
with an exhaust-located fuel injector used to actively regenerate a
DPF and/or heat an SCR device. Accordingly, selective use of this
same fuel injector to regenerate a DOC may require little or no new
hardware.
[0031] It will be apparent to those skilled in the art that various
modifications and variations can be made to the system of the
present disclosure without departing from the scope of the
disclosure. Other embodiments will be apparent to those skilled in
the art from consideration of the specification and practice of the
system disclosed herein. For example, in addition to utilizing
injector 46 to increase an amount of hydrocarbon passing through
DOC 44 after formation of the oxide layer, it is contemplated that
the air/fuel ratio adjusting devices discussed above (e.g, the
throttle valve, the variable valve actuators, the VGT, etc.) may
also be utilized to help in removing the oxide layer. Further, it
is contemplated that, instead of utilizing injector 46 to inject
fuel and selectively remove the oxide layer from DOC 44, fuel
injectors 15 may additionally be utilized to inject the small
quantities of fuel required for the removal at a timing when the
injected fuel will not fully combust within cylinders 14 (e.g., in
a late post injection or during an injection when corresponding
cylinders 14 are disabled). When fuel injectors 15 are utilized to
regenerate DOC 44, injector 46, supply 48, and device 50 may be
omitted. It is intended that the specification and examples be
considered as exemplary only, with a true scope of the disclosure
being indicated by the following claims and their equivalents.
* * * * *