U.S. patent application number 14/561699 was filed with the patent office on 2016-06-09 for method and system for removing ash within a particulate filter.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Kenneth John Behr, Mira Bumbaroska, Joseph Lyle Thomas, Michiel J. Van Nieuwstadt.
Application Number | 20160160723 14/561699 |
Document ID | / |
Family ID | 55974396 |
Filed Date | 2016-06-09 |
United States Patent
Application |
20160160723 |
Kind Code |
A1 |
Thomas; Joseph Lyle ; et
al. |
June 9, 2016 |
METHOD AND SYSTEM FOR REMOVING ASH WITHIN A PARTICULATE FILTER
Abstract
Methods and systems are provided for injecting water to reduce
an ash load on a PF. In one example, a method may include injecting
water from a reservoir to between a PF and a three-way catalyst in
order to reduce an ash load.
Inventors: |
Thomas; Joseph Lyle;
(Kimball, MI) ; Van Nieuwstadt; Michiel J.; (Ann
Arbor, MI) ; Behr; Kenneth John; (Farmington Hills,
MI) ; Bumbaroska; Mira; (Waterford, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
55974396 |
Appl. No.: |
14/561699 |
Filed: |
December 5, 2014 |
Current U.S.
Class: |
60/274 ;
60/295 |
Current CPC
Class: |
Y02T 10/22 20130101;
F01N 3/101 20130101; F01N 9/002 20130101; F01N 2900/1406 20130101;
F01N 2610/00 20130101; Y02T 10/12 20130101; F01N 2900/08 20130101;
Y02T 10/47 20130101; F01N 3/0232 20130101; F01N 3/04 20130101; F01N
3/021 20130101; F01N 3/0293 20130101; Y02T 10/40 20130101 |
International
Class: |
F01N 3/10 20060101
F01N003/10; F01N 3/023 20060101 F01N003/023; F01N 3/029 20060101
F01N003/029 |
Claims
1. A method, comprising: injecting water from a reservoir to
between a particulate filter and a three-way catalyst, the
particulate filter located downstream of the three-way
catalyst.
2. The method of claim 1, wherein the injecting is responsive to an
exhaust pressure signal between the three-way catalyst and the
particulate filter being above a threshold pressure.
3. The method of claim 1, wherein the injecting is responsive to a
particulate filter temperature being above a threshold
temperature.
4. The method of claim 1, wherein the three-way catalyst comprises
a porous substrate coated with one or more precious metals, the
three-way catalyst configured to convert one or more emissions in
exhaust gas flowing through the three-way catalyst, and wherein the
particulate filter comprises a mesh structure with less precious
metal coating, the particulate filter configured to trap soot in
exhaust gas flowing through the particulate filter.
5. The method of claim 1, wherein the injecting is responsive to an
estimated ash load after a soot regeneration has been
completed.
6. The method of claim 5, wherein the estimated ash load is based
on an exhaust pressure after the soot regeneration, and further
comprising adjusting a water injection amount based on the
estimated ash load.
7. The method of claim 5, wherein the soot regeneration is
performed responsive to an exhaust gas pressure between the
three-way catalyst and the particulate filter being above a
threshold exhaust gas pressure.
8. A system, comprising: an engine with a plurality of cylinders;
an engine exhaust emission control device comprising a particulate
filter positioned downstream of a three-way catalyst brick; an
exhaust gas pathway coupling an engine exhaust manifold to the
engine exhaust emission control device; an injector fluidically
coupled to a water reservoir via a conduit, the injector
fluidically coupled between the three-way catalyst brick and the
particulate filter; a pressure sensor coupled between the three-way
catalyst brick and the particulate filter; and a controller having
computer readable instructions stored on non-transitory memory for:
estimating an ash load in the particulate filter based on a
pressure measured by the pressure sensor; and injecting water via
the injector responsive to the estimated ash load exceeding a
threshold ash load.
9. The system of claim 8, further comprising an EGR pathway coupled
to the exhaust gas pathway upstream of the emission control device,
and wherein the instructions further comprise instructions for
adjusting an EGR flow rate responsive to the injection of
water.
10. The system of claim 8, wherein the three-way catalyst brick and
the particulate filter are housed in a common housing of the
emission control device and separated via an air gap, and wherein
the common housing includes a boss positioned between the three-way
catalyst brick and the particulate filter to accommodate the
injector, the injector positioned to inject water into the air
gap.
11. The system of claim 8, wherein the water reservoir is coupled
to one or more of a charge air cooler and an air conditioner, the
water reservoir is replenished via condensate from one or more of
the charge air cooler and the air conditioner.
12. The system of claim 8, wherein the three-way catalyst brick and
the particulate filter are housed in separate housings and
fluidically coupled via the exhaust pathway, and wherein the
injector is coupled to the exhaust pathway between the three-way
catalyst brick and the particulate filter.
13. The system of claim 12, wherein the estimated ash load is
determined following completion of a regeneration of the
particulate filter.
14. A method of an engine, comprising: combusting fuel in the
engine via spark ignition and directing exhaust gas from the engine
to a particulate filter; responsive to an exhaust gas pressure
upstream of the particulate filter exceeding a first threshold
pressure, regenerating the particulate filter to remove particulate
matter stored on the particulate filter; and responsive to the
exhaust gas pressure upstream of the particulate filter exceeding a
second threshold pressure following completion of the regeneration,
injecting water between the particulate filter and a three-way
catalyst upstream of the particulate filter to remove ash from the
particulate filter.
15. The method of claim 14, wherein the exhaust pressure is
measured between the three-way catalyst and the particulate
filter.
16. The method of claim 15, wherein regenerating the particulate
filter includes increasing an exhaust gas temperature to at least a
threshold temperature for a predetermined duration, where the
exhaust gas temperature and predetermined duration are determined
based at least in part on a particulate matter load on the
particulate filter.
17. The method of claim 16, further comprising determining that the
regeneration has reached completion when the exhaust gas
temperature has been maintained at least at the threshold
temperature for the predetermined duration.
18. The method of claim 16, wherein the exhaust gas temperature is
increased as a result of an increase in engine load.
19. The method of claim 14, wherein the first threshold pressure is
greater than the second threshold pressure.
20. The method of claim 14, further comprising injecting water to
between the three-way catalyst and the particulate filter when a
particulate filter temperature exceeds a threshold particulate
filter temperature.
Description
FIELD
[0001] The present description relates generally to methods and
systems for removing ash within an emission control device.
BACKGROUND/SUMMARY
[0002] The exhaust gas emitted from an internal combustion engine
may include a heterogeneous mixture that may contain gaseous
emissions such as carbon monoxide (CO), unburned hydrocarbons (HC),
nitrogen oxides (NO.sub.x), and condensed phase materials (liquids
and solids) that constitute particulate matter (PM). Transition and
primary group metal catalysts typically coat a catalyst support
along with substrates to provide an engine exhaust system the
ability to convert some, if not all of these exhaust components
into other compounds.
[0003] Exhaust aftertreament systems may include a three-way
catalyst (TWC) and a particulate filter (PF). The TWC provides a
passage for gaseous emissions to flow through and undergo oxidation
and reduction reaction with the catalytic components. The TWC may
not comprise a binding element, whereas the PF may comprise a
binding element to capture PM.
[0004] Over time, the PF may become full and a regeneration
operation may be used to remove trapped particulates. The
regeneration involves increasing the temperature of the particulate
filter to a relatively high temperature, such as above 600.degree.
C., in order to burn the accumulated particulates into ash.
[0005] A potential drawback with the regeneration process is ash
accumulation subsequent to the regeneration process in
spark-ignited engines. The high-exhaust temperatures of
spark-ignited engines (e.g., 550.degree. C.) vaporize the water
released after combustion, thereby disabling the ability for water
to sweep the ash from the exhaust pathway. This is generally in
contrast to diesel engines where the water is not vaporized due to
lower exhaust temperatures (e.g., 90.degree. C.) and is able to
reduce the ash load. One example attempt to address ash build up
includes injecting air to reduce ash accumulation, such as
described in Sorensen et al. in U.S. Patent No. 2011/0120090.
Therein, an oxygen injection is used to further burn an ash
accumulation and remove it from the PF.
[0006] However, the inventors herein have also recognized potential
issues with such systems. As one example, an oxygen injection
upstream of a PF may increase an exhaust gas temperature above a
threshold that may degrade the filter. By injecting air to initiate
a regeneration, the regeneration temperature may be more difficult
to regulate and increase a PF temperature to a temperature in which
the PF may be degraded.
[0007] In one example, the issues described above may be addressed
by a method for injecting water from a reservoir to between a
catalyst brick and a particulate filter. In this way, the water
injection carries the ash toward the back and out of the PF and
simultaneously maintains an exhaust gas temperature within a range
that does not degrade the PF. Further, the water injection can
increase the PF capacity to capture emission particles.
[0008] The above discussion includes recognitions made by the
inventors and not admitted to be generally known. Thus, it should
be understood that the summary above is provided to introduce in
simplified form a selection of concepts that are further described
in the detailed description. It is not meant to identify key or
essential features of the claimed subject matter, the scope of
which is defined uniquely by the claims that follow the detailed
description. Furthermore, the claimed subject matter is not limited
to implementations that solve any disadvantages noted above or in
any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a schematic diagram of an engine with a
three-way catalyst (TWC) upstream of a particulate filter (PF).
[0010] FIG. 2 shows a flow chart illustrating an exemplary method
for regenerating a particulate filter and performing direct
injection between the TWC and the PF.
[0011] FIG. 3 shows a flow chart demonstrating an exemplary method
for direct injecting a fluid at a space between the TWC and the
PF.
[0012] FIG. 4 shows a graph illustrating a variety of engine
conditions for initiating a water injection.
DETAILED DESCRIPTION
[0013] The following description relates to a method for injecting
water to reduce an ash load on a particulate filter (PF) surface
nearest to a location between the PF downstream of a three-way
catalyst (TWC). The PF and TWC may be located in an engine exhaust
emission control device. The engine exhaust emission control device
may include an injector port and a pressure sensor. Further, the
water injection may be used to maintain a PF temperature.
[0014] A PF may capture and store soot. The soot load may decrease
exhaust flow through the PF and as the soot load increases, the
exhaust flow through the PF may by impeded enough to create an
undesired amount of backpressure that can decrease engine
efficiency. In order to reduce such backpressure, a PF regeneration
may occur responsive to an exhaust gas pressure being greater than
a threshold exhaust gas pressure. As the PF undergoes a
regeneration, a portion of the soot is converted into a gas and a
separate portion is converted into ash. The ash may accumulate onto
the PF nearest a space between the TWC and the PF. After a number
of PF regenerations (e.g., 100), the ash load may cause increased
exhaust backpressure and/or reduce soot trapping and regeneration
effectiveness. However, because the exhaust backpressure increase
may be caused by either the high soot load prior to regeneration or
the high ash load following the regeneration, the present
application provides for, in one example, a method carried out by a
controller of a control system for differentiating the two causes
of increased backpressure along with a method for injecting water
into a space between the PF and the TWC based on the
differentiation.
[0015] FIG. 1 is a schematic diagram showing one cylinder of
multi-cylinder engine 10, which may be included in a propulsion
system of an automobile. Engine 10 may be controlled at least
partially by a control system including controller 12 and by input
from a vehicle operator 132 via an input device 130. In this
example, input device 130 includes an accelerator pedal and a pedal
position sensor 134 for generating a proportional pedal position
signal PP. Combustion chamber (i.e., cylinder) 30 of engine 10 may
include combustion chamber walls 32 with piston 36 positioned
therein. In some embodiments, the face of piston 36 inside cylinder
30 may have a bowl. Piston 36 may be coupled to crankshaft 40 so
that reciprocating motion of the piston is translated into
rotational motion of the crankshaft. Crankshaft 40 may be coupled
to at least one drive wheel of a vehicle via an intermediate
transmission system. Further, a starter motor may be coupled to
crankshaft 40 via a flywheel to enable a starting operation of
engine 10.
[0016] Combustion chamber 30 may receive intake air from intake
manifold 44 via intake passage 42 and may exhaust combustion gases
via exhaust passage 48. Intake manifold 44 and exhaust passage 48
can selectively communicate with combustion chamber 30 via
respective intake valve 52 and exhaust valve 54. In some
embodiments, combustion chamber 30 may include two or more intake
valves and/or two or more exhaust valves.
[0017] Intake valve 52 may be controlled by controller 12 via
electric valve actuator (EVA) 51. Similarly, exhaust valve 54 may
be controlled by controller 12 via EVA 53. Alternatively, the
variable valve actuator may be electro hydraulic or any other
conceivable mechanism to enable valve actuation. During some
conditions, controller 12 may vary the signals provided to
actuators 51 and 53 to control the opening and closing of the
respective intake and exhaust valves. The position of intake valve
52 and exhaust valve 54 may be determined by valve position sensors
55 and 57, respectively. In alternative embodiments, one or more of
the intake and exhaust valves may be actuated by one or more cams,
and may utilize one or more of cam profile switching (CPS),
variable cam timing (VCT), variable valve timing (VVT) and/or
variable valve lift (VVL) systems to vary valve operation. For
example, cylinder 30 may alternatively include an intake valve
controlled via electric valve actuation and an exhaust valve
controlled via cam actuation including CPS and/or VCT.
[0018] Fuel injector 66 is shown coupled directly to combustion
chamber 30 for injecting fuel directly therein in proportion to the
pulse width of signal FPW received from controller 12 via
electronic driver 68. In this manner, fuel injector 66 provides
what is known as direct injection of fuel into combustion chamber
30. The fuel injector may be mounted in the side of the combustion
chamber or in the top of the combustion chamber, for example. Fuel
may be delivered to fuel injector 66 by a fuel system (not shown)
including a fuel tank, a fuel pump, and a fuel rail.
[0019] Ignition system 88 can provide an ignition spark to
combustion chamber 30 via spark plug 92 in response to a spark
advance signal SA from controller 12, under select operating
modes.
[0020] Intake passage 42 may include throttles 62 and 63 having
throttle plates 64 and 65, respectively. In this particular
example, the positions of throttle plates 64 and 65 may be varied
by controller 12 via signals provided to an electric motor or
actuator included with throttles 62 and 63, a configuration that is
commonly referred to as electronic throttle control (ETC). In this
manner, throttles 62 and 63 may be operated to vary the intake air
provided to combustion chamber 30 among other engine cylinders. The
positions of throttle plates 64 and 65 may be provided to
controller 12 by throttle position signals TP. Intake passage 42
may include a mass air flow sensor 120 and a manifold air pressure
sensor 122 for providing respective signals MAF and MAP to
controller 12.
[0021] Further, in the disclosed embodiments, an exhaust gas
recirculation (EGR) system may route a desired portion of exhaust
gas from exhaust passage 48 to intake passage 44 via high pressure
EGR (HP-EGR) passage 140 or low pressure EGR (LP-EGR) passage 150.
The amount of EGR provided to intake passage 44 may be varied by
controller 12 via HP-EGR valve 142 or LP-EGR valve 152. Further, an
EGR sensor 144 may be arranged within the HP-EGR passage and may
provide an indication of one or more of pressure, temperature, and
concentration of the exhaust gas. Alternatively, the EGR may be
controlled through a calculated value based on signals from the MAF
sensor (upstream), MAP (intake manifold), MAT (manifold gas
temperature) and the crank speed sensor. Further, the EGR may be
controlled based on an exhaust O.sub.2 sensor and/or an intake
oxygen sensor (intake manifold). Under some conditions, the EGR
system may be used to regulate the temperature of the air and fuel
mixture within the combustion chamber. FIG. 1 shows a high pressure
EGR system where EGR is routed from upstream of a turbine of a
turbocharger to downstream of a compressor of a turbocharger and a
low pressure EGR system where EGR is routed from downstream of a
turbine of a turbocharger to upstream of a compressor of the
turbocharger. In some embodiments, engine 10 may include only an
HP-EGR system or only an LP-EGR system. In further embodiments,
engine 10 may not include a turbocharger.
[0022] As such, engine 10 may further include a compression device
such as a turbocharger or supercharger including at least a
compressor 162 arranged along intake manifold 44. For a
turbocharger, compressor 162 may be at least partially driven by a
turbine 164 (e.g., via a shaft) arranged along exhaust passage 48.
For a supercharger, compressor 162 may be at least partially driven
by the engine and/or an electric machine, and may not include a
turbine. Thus, the amount of compression provided to one or more
cylinders of the engine via a turbocharger or supercharger may be
varied by controller 12. Further, turbine 164 may include wastegate
166 to regulate the boost pressure of the turbocharger. Similarly,
intake manifold 44 may include valved bypass 167 to route air
around compressor 162.
[0023] Emission control devices 71 and 72 are shown arranged along
exhaust passage 48 downstream of exhaust gas sensor 126. Devices 71
and 72 may be a selective catalytic reduction (SCR) system, three
way catalyst (TWC), NO.sub.x trap, various other emission control
devices, or combinations thereof. In the example illustrated in
FIG. 1, device 71 is a TWC and device 72 is a particulate filter
(PF). In some embodiments, the TWC 71 and the PF 72 may be housed
in a common housing of an emission control device 74 (as shown in
FIG. 1) and separated via an air gap. In alternative embodiments,
emission control system housing 74 may be dispensed with and the
TWC and PF each housed in separate housings and fluidically coupled
via the exhaust passage (not shown in FIG. 1). Further, in some
embodiments, during operation of engine 10, emission control
devices 71 and 72 may be periodically reset by operating at least
one cylinder of the engine within a particular air/fuel ratio.
[0024] Exhaust gas sensor 126 is shown coupled to exhaust passage
48 upstream of emission control device 74. Further, sensor 127 is
shown coupled to exhaust passage 48 between a particulate filter 72
and a three-way catalyst 71 via a boss 76 located in exhaust
control device 74. Sensor 128 is shown coupled to exhaust passage
48 downstream of particulate filter 72. Sensors 127 and 128 may
measure an exhaust pressure upstream and downstream of the
particulate filter 72 to determine a pressure drop across the
particulate filter (also referred to as the exhaust delta
pressure). If the exhaust delta pressure is greater than a
threshold exhaust delta pressure, it may indicate that particulate
matter (e.g., soot) and/or ash have accumulated on the particulate
filter to a high enough degree to impede desired exhaust flow
through the particulate filter. In response to the large pressure
drop across the particulate filter, a particulate filter
regeneration to burn off particulate matter and/or a water
injection to remove built up ash may be performed, as described in
more detail below. In alternative embodiments, sensor 128 may not
be included and sensor 127 may be an absolute or gauge pressure
sensor.
[0025] The three-way catalyst comprises a porous substrate coated
with one or more precious metals. The three-way catalyst is
configured to convert one or more emissions in exhaust gas flowing
through the three-way catalyst. The particulate filter comprises a
mesh structure. In some examples, the particulate filter may
comprise one or more precious metals, wherein a precious metal mass
of the particulate filter is less than a precious metal mass of the
three-way catalyst. As an example, if the three-way catalyst
comprises 100 g of precious metals, then the particulate filter may
comprise 25 g of precious metals. In some examples, a four-way
catalyst may be used in place of the three-way catalyst, the
four-way catalyst may include the particulate filter integrated
with the three way catalyst. The particulate filter is configured
to trap soot in exhaust gas flowing through the particulate
filter.
[0026] Reservoir 70 may store water in one example. In other
examples, reservoir 70 may store another suitable fluid or a fluid
mixture (e.g., water and methanol/ethanol/glycol) in order to
reduce the freezing point of the water. Conduit 75 and water
injector 73 fluidically couple the reservoir 70 to an air gap
between the TWC 71 and the PF 72. The boss 76 accommodating
pressure sensor 127 may also accommodate water injector 73, wherein
the injector is positioned to inject water between the TWC and the
PF. In alternative embodiments, separate bosses may be used to
house the water injector 73 and the pressure sensor 127. The water
injector may be controlled via signals sent from a controller
(e.g., controller 12). Water injection into the air gap between the
TWC 71 and the PF 72 may be responsive to a pressure sensor
measurement being greater than a threshold pressure (e.g., pressure
sensor 127 measures an exhaust gas pressure greater than a
threshold exhaust gas pressure). The water injection may further be
responsive to a PF regeneration temperature being greater than a
threshold regeneration temperature.
[0027] Controller 12 is shown in FIG. 1 as a microcomputer,
including microprocessor unit 102, input/output ports 104, an
electronic storage medium for executable programs and calibration
values shown as read only memory chip 106 in this particular
example, random access memory 108, keep alive memory 110, and a
data bus. Controller 12 may receive various signals from sensors
coupled to engine 10, in addition to those signals previously
discussed, including measurement of inducted mass air flow (MAF)
from mass air flow sensor 120; engine coolant temperature (ECT)
from temperature sensor 112 coupled to cooling sleeve 114; a
profile ignition pickup signal (PIP) from Hall effect sensor 118
(or other type) coupled to crankshaft 40; throttle position (TP)
from a throttle position sensor; and absolute manifold pressure
signal, MAP, from sensor 122. Engine speed signal, RPM, may be
generated by controller 12 from signal PIP. Manifold pressure
signal MAP from a manifold pressure sensor may be used to provide
an indication of vacuum, or pressure, in the intake manifold. Note
that various combinations of the above sensors may be used, such as
a MAF sensor without a MAP sensor, or vice versa. During
stoichiometric operation, the MAP sensor can give an indication of
engine torque. Further, this sensor, along with the detected engine
speed, can provide an estimate of charge (including air) inducted
into the cylinder. In one example, sensor 118, which is also used
as an engine speed sensor, may produce a predetermined number of
equally spaced pulses every revolution of the crankshaft.
[0028] Storage medium read-only memory 106 can be programmed with
computer readable data representing instructions executable by
processor 102 for performing the methods described below as well as
other variants that are anticipated but not specifically
listed.
[0029] As described above, FIG. 1 shows only one cylinder of a
multi-cylinder engine, and that each cylinder may similarly include
its own set of intake/exhaust valves, fuel injector, spark plug,
etc.
[0030] As described previously, injector 73 provides water to
between the TWC 71 and the PF 72. This method may be used to reduce
an ash load on the surface of the PF nearest the TWC. Functions of
the system are determined by controller 12 and are further
explained in FIG. 2.
[0031] FIG. 2 is a flow chart illustrating an exemplary method for
regenerating a particulate filter and injecting water between the
TWC and the PF that may be carried by a control system including
the controller and processor in combination with one or more
sensors, one or more actuators, and/or one or more other hardware
components such as the described engine exhaust system. Portions of
the actions described in the routine of FIG. 2 may be structurally
formed as instructions stored in non-transitory memory.
[0032] Continuing with FIG. 2, the water injection may either
decrease an ash load on the PF surface nearest the space between
the TWC and the PF or decrease a PF temperature in order to prevent
PF degradation. For example, the ash may accumulate on the PF in a
region that is closer to the TWC, or more upstream, in some
examples. As described above, the injection between the TWC and the
PF may include water. In some examples, the injection may also be
accomplished with a fluid mixture (e.g., water and
methanol/ethanol/glycol). The mixture may be injected during
instances where water would otherwise be frozen (e.g., engine cold
start) as determined by the controller.
[0033] Method 200 will be described herein with reference to
components and systems depicted in FIG. 1, particularly, regarding
TWC 71, PF 72, water reservoir 70, water injector 73, pressure
sensors 127 and 128, emission control device 74, turbine 164,
wastegate 166, and exhaust pathway 48. Method 200 may be carried
out by a controller (e.g., controller 12) according to
computer-readable media stored thereon. In some examples, method
200 may be performed in a spark-ignition engine, and as such during
execution of the method, fuel in the engine may be combusted via
spark ignition and exhaust gas from the engine may be directed to
the particulate filter. It should be understood that the method 200
may be applied to other systems of a different configuration
without departing from the scope of this disclosure.
[0034] Method 200 may begin at 202, wherein engine operating
conditions may be estimated and/or measured. The engine operating
conditions may include, but are not limited to an exhaust gas
temperature, an engine load and speed, an exhaust gas pressure, and
a commanded air/fuel ratio. At 204, the method includes measuring
the exhaust gas pressure between the TWC and the PF. In one
example, there are no other components between a pressure sensor
and the TWC in the upstream direction, and the pressure sensor and
the PF in the downstream direction, other than injector 75. In
other examples, additional components may be added, if desired. In
some examples where the TWC and PF are housed in a common housing,
the exhaust gas pressure may be measured at an air gap within the
housing between the TWC and PF. In other examples where the TWC and
PF are housed in separate housings coupled via an exhaust passage,
the exhaust gas pressure may be measured at the exhaust passage
between the TWC and PF. The exhaust gas pressure may be measured by
a gauge pressure sensor or an absolute pressure sensor. For
example, pressure sensor 127, accommodated via boss in the housing
between the TWC and the PF, may measure an exhaust gas pressure in
the air gap, as explained above with respect to FIG. 1. As another
example, emission control device 74 may house delta pressure
sensors 127 and 128, wherein pressure sensor 127 measures an
exhaust gas pressure in an air gap and pressure sensor 128 measures
an exhaust gas pressure downstream of the PF, as explained above
with respect to FIG. 1.
[0035] At 206, the method includes comparing the exhaust gas
pressure between the TWC and the PF to a first threshold exhaust
pressure. The first threshold exhaust pressure may be a suitable
pressure that indicates a relatively high level of soot and/or ash
has accumulated on the PF. For example, a soot load greater than
the threshold soot load may impede exhaust flow through the PF. In
one example, if the exhaust gas pressure is measured by a
gauge/absolute pressure sensor, then the first threshold exhaust
pressure may be a first threshold gauge/absolute exhaust pressure.
In another example, if the delta exhaust pressure is measured by
upstream and downstream pressure sensors, then the first threshold
exhaust pressure may be a first threshold delta exhaust pressure.
If the exhaust pressure is greater than the first threshold exhaust
pressure, then the method proceeds to 210, which will be explained
in more detail below. Briefly, as explained above, the exhaust
pressure may be greater than the first threshold exhaust pressure
due to a soot load and/or an ash load being greater than a
threshold, and as a result a PF regeneration may be carried out to
burn off the accumulated soot. This PF regeneration demand may be
based on a soot load on the PF exceeding a threshold soot load. On
the other hand, if the exhaust pressure is less than the first
threshold exhaust pressure, then the method proceeds to 208. At
208, the method includes maintaining current engine operating
parameters and not conducting a PF regeneration. The method may
exit.
[0036] At 210, the method includes determining if regeneration
conditions are met. The PF regeneration may be either passive or
active. If the regeneration is passive, the regeneration conditions
may include a vehicle speed exceeding a threshold vehicle speed
(e.g., 40 mph) and/or an engine load exceeding a threshold engine
load. If the passive regeneration conditions are not met, then the
method proceeds to 208. At 208, the method includes maintaining
current engine operating parameters, as described above. The method
may return to continue to monitor for conditions suitable for
performing the regeneration.
[0037] If the regeneration is active, engine operating parameters
may be purposely adjusted to increase exhaust gas temperature to a
temperature high enough to initiate combustion of the stored soot
on the PF. The engine operating parameters that may be varied may
include one or more of increasing an oxygen content in the intake
air and/or exhaust (e.g., by adjusting a throttle position),
retarding spark, and delaying fuel injection timing. In some
examples, the regeneration may be carried out only if the current
operating parameters allow for the changes listed above and/or if
such changes will actually result in a high enough exhaust
temperature to perform the regeneration. For example, the
regeneration may not be performed during a cold engine start. If
the active regeneration parameters are not met, then the method
proceeds to 208. Further, the regeneration may occur during a
subsequent iteration of the method 200 when the active regeneration
conditions are met. In alternative embodiments, a controller (e.g.,
controller 12) may signal for the active regeneration adjustments
to occur regardless of current engine operating parameters. At 208,
the method includes maintaining current engine operating
parameters, as described above. The method may exit.
[0038] If either the passive or active regeneration conditions are
met, the method proceeds to 212, wherein the regeneration is
performed. During the regeneration, the air/fuel ratio may be
leaned, spark may be retarded, and/or the fuel injection may be
delayed in order to increase an exhaust gas temperature. The
hotter, lean exhaust gas may allow the PF to combust and self-burn
the stored soot. As a result, if the exhaust gas oxygen content and
temperature increase, then the faster the PF self-burns and
regenerates the soot. For a given exhaust gas temperature under
regeneration conditions, a total duration of regeneration may be
based on a total soot load stored on the PF. The total soot load on
the PF may be estimated based on a difference between the exhaust
gas pressure and the first threshold exhaust pressure, for example,
or based on engine operating parameters since a previous PF
regeneration has occurred. The exhaust gas pressure greater than
the first threshold exhaust pressure indicates a PF regeneration
demand and that the soot load on the PF is greater than a threshold
soot load. Therefore, as the difference between the exhaust gas
pressure and the first threshold exhaust pressure increases, the
estimated soot load on the PF increases (e.g., the increasing soot
load further impedes the flow of exhaust gas through the PF and
increases exhaust backpressure). As a result, as the estimated soot
load increases and/or the exhaust gas temperature decreases, the
total duration of regeneration increases. Further, as the estimated
soot load decreases and/or the exhaust gas temperature increases,
the total duration of regeneration decreases.
[0039] However, the regeneration may be halted due to a change in
engine operating parameters. As an example for a passive
regeneration, the regeneration may be halted and/or interrupted due
to an engine load being less than a threshold load. As the engine
load decreases, the air/fuel ratio becomes richer and as a result,
the PF self-burn does not receive an amount of oxygen sufficient to
keep the self-burn active. Therefore, instances may occur where the
PF regeneration is an incomplete PF regeneration (e.g., the
regeneration is interrupted).
[0040] At 214, the method includes determining if the PF
regeneration is complete. A complete PF regeneration may be based
on running a regeneration for a predetermined period of time (e.g.,
10 minutes), reaching a PF regeneration temperature (e.g.,
800.degree. C.), reducing a soot load to a relatively low load, or
a combination of all three. If it is determined that a regeneration
is incomplete, then the method proceeds to 216. At 216, the method
includes determining if the regeneration was interrupted based on
conditions described above (e.g., an engine load dropping below a
threshold engine load). If the regeneration was not interrupted,
then the method proceeds to 212 and continues to perform the
regeneration.
[0041] However, if the regeneration is complete or if the
regeneration was interrupted, then the method proceeds to 218. At
218, the method includes measuring an exhaust pressure between the
TWC and the PF (e.g., at the air gap), similar to the process
described above with respect to 204 in order to estimate an ash
load on the PF surface nearest the space between the TWC and the
PF. As explained previously, as exhaust flows through the emission
control device (e.g., emission control device 74), soot is stored
on a PF (e.g., PF 72). The soot may block the flow of exhaust gas
through the PF, and create exhaust backpressure (e.g., increased
exhaust pressure upstream of the PF). In response to the increased
backpressure, signaled by an exhaust pressure being greater than a
first threshold exhaust pressure, the controller (e.g., controller
12) may signal for a regeneration. As the regeneration is
performed, the soot is burned into ash, which may accumulate on the
upstream PF surface. As the ash accumulates over a number of PF
regenerations (e.g., 100), the ash load may increase enough to
cause exhaust backpressure. Therefore, the exhaust pressure
measurement may be used to detect either a regeneration demand or a
water injection demand depending on when the exhaust pressure
signal is queried. As a result, the exhaust pressure may be
measured prior to a regeneration event as well as immediately
following the PF regeneration in order to determine if the
backpressure is a result of the soot load being greater than the
threshold soot load or the ash load being greater than the
threshold ash load. As used herein, the term "immediately" may
include a suitable duration of time after regeneration has been
determined to have completed or interrupted but before soot begins
to rebuild on the PF, such as within 5 minutes or less of a PF
regeneration.
[0042] At 220, the measured exhaust pressure is compared to a
second threshold exhaust pressure. In one embodiment, the second
threshold exhaust pressure may be equal to the first threshold
exhaust pressure. In a second embodiment, the second threshold
exhaust pressure may be based on an expected exhaust gas pressure.
The expected exhaust gas pressure may be based on the previous PF
regeneration. For example, if the PF regeneration was interrupted,
then the expected exhaust pressure may be higher than an expected
exhaust pressure for a completed PF regeneration. Further, the
expected exhaust pressure may be based on a PF regeneration
temperature and/or a PF regeneration duration. In other words, as
the PF regeneration duration and/or temperature increases, the
expected exhaust gas pressure decreases. If the exhaust pressure is
less than the second threshold exhaust pressure, then the ash load
is not greater than a threshold ash load and no water injection
occurs. The method proceeds to 208 and maintains current engine
operating parameters, as described above. The method may exit.
[0043] If the exhaust pressure measurement following the PF
regeneration is greater than the second threshold exhaust pressure,
then the ash load may be greater than the threshold ash load and be
causing the pressure backflow. The method proceeds to 222.
[0044] An ash load greater than the threshold ash load causes the
exhaust gas pressure to be greater than the second threshold
exhaust pressure by impeding exhaust flow through the PF, and thus
the ash load exceeding the threshold ash load may be determined by
the controller based on the exhaust pressure measurement occurring
only at the selected timing as described above. In other examples,
the ash load may be predicted to be greater than the threshold ash
load after a predetermined number of PF regenerations (e.g., 100).
Further, in some examples the ash load may be estimated to exceed
the threshold based on an estimated ash load production. The
estimated ash load production may be based on an estimated PF soot
load prior to regeneration and the PF regeneration temperature and
the PF regeneration duration. The estimated ash load production
increases as the estimated soot load burned increases. The
predicted ash load may increase as one or more of the estimated
soot load increases, the PF regeneration temperature increases,
and/or the PF regeneration duration increases.
[0045] As an example, a vehicle may begin a PF regeneration in
response to a high soot load on a PF (e.g., 0.5 kg). The vehicle
may adjust operating parameters in order to increase exhaust gas
temperature to a PF regeneration temperature (e.g., 650.degree.
C.). However the PF regeneration may be interrupted and thus the
regeneration may be incomplete. The vehicle may be able to estimate
an amount of soot burned based on the regeneration temperature and
duration. Considering the regeneration is not complete (e.g., 0.2
kg soot remains on the PF) and all burned soot is not converted
into ash (e.g., 0.5 kg of burned soot converts to 0.05 kg ash), a
conversion factor may be used to estimate a newly formed ash load
based on the regeneration conditions (e.g., 0.3 kg of soot may be
burned resulting in 0.03 kg of ash). The ash loads may be added up
over time (e.g., after each regeneration event) to allow the
controller to predict when the next water injection to reduce an
ash load may occur.
[0046] At 222, the method includes determining if water injection
conditions are met. The water injection conditions may include
determining if water is available based on a temperature
measurement or volume measurement in a water reservoir (e.g.,
reservoir 70). The temperature measurement may be used to determine
if the water is liquid phase water or frozen water (e.g., ice). The
volume measurement may be conducted by an appropriate gauge volume
sensor and may be used to determine if enough water is present for
the injection. Further, the water injection conditions may further
include measuring an exhaust gas temperature. As an example, it may
be preferred to inject water during conditions where the exhaust
gas temperature is less than a threshold exhaust gas temperature
(e.g., 100.degree. C.). An injection where the exhaust gas
temperature is less than the threshold exhaust gas temperature
allows the water to remain in the liquid phase and wash the ash
from the surface of the PF nearest the TWC to the end of the PF. If
the exhaust gas temperature is greater than the threshold exhaust
gas temperature, then the water may vaporize upon injection and
become unable to reduce the ash load. If water injection conditions
are not met, then the method proceeds to 224. At 224, the method
includes continuing to monitor the injection parameters until the
water injection conditions are met.
[0047] If injection conditions are met, the method proceeds to 226
and injects water. As an example, a water injection duration and/or
volume may be adjusted based on an estimated ash load described
above, wherein as the estimated ash load increases, the water
injection duration and/or volume may also increase. As another
example, a water injection duration and/or volume may be based on a
specific duration of injection regardless of the estimated ash load
(e.g., 30 seconds). In one example, the water injection may be
based on a predetermined value, regardless of the estimated ash
load, wherein the water injection reduces the ash load to a
relatively low amount an attenuates the exhaust backpressure. In
another example, the water injection may be performed at a
predetermined water injection rate such as 5 kg/hr. The water
injection may wash the ash that has accumulated on the upstream
surface of the PF to the back of the PF and eventually to
atmosphere. The method proceeds to 228.
[0048] At 228, the method includes optionally adjusting current
engine operating parameters to increase mass flow of exhaust
through the PF to assist in the removal of the ash. In one
embodiment, where the TWC is downstream of a LP-EGR system, the
adjusting may include opening a wastegate and/or partially or fully
closing an EGR valve in order to flow higher pressure and/or more
exhaust through the TWC and the PF. However, this may only be
performed when an engine dilution demand is met in order to
maintain desired exhaust emission levels, for example. By
decreasing the EGR flow rate the likelihood of removing the ash
from the back of the PF may be increased. The method may then
exit.
[0049] FIG. 2 described an exemplary method of regenerating a PF
and injecting water between a TWC and a PF to decrease an ash load
on the PF surface nearest the space between the TWC and the PF.
FIG. 3 will now describe a method to inject water in order to
maintain a PF temperature and/or reduce an ash load on the PF
surface nearest the space between a TWC and a PF. The routine of
FIG. 3 may be performed in combination with the routine of FIG. 2,
in one example.
[0050] FIG. 3 is a flow chart illustrating an example method 300
for injecting water between a particulate filter (PF) and a
three-way catalyst (TWC), wherein the PF is downstream of the
TWC.
[0051] Method 300 will be described herein with reference to
components and systems depicted in FIG. 1, particularly, regarding
TWC 71, PF 72, water reservoir 70, water injector 73, pressure
sensors 127 and 128, and emission control device 74. Method 300 may
be carried out by a controller (e.g., controller 12) according to
computer-readable media stored thereon. It should be understood
that the method 300 may be applied to other systems of a different
configuration without departing from the scope of this
disclosure.
[0052] Method 300 may begin at 302, wherein engine operating
conditions may be estimated and/or measured. The engine operating
conditions may include, but are not limited to an exhaust gas
temperature, an engine load and/or speed, an exhaust pressure, and
a commanded air/fuel ratio. At 304, the method 300 includes
estimating if a PF temperature exceeds a threshold PF temperature.
A PF temperature greater than the threshold PF temperature (e.g., a
temperature above 1000.degree. C.) may cause irreversible
degradation to the PF. The PF temperature may be directly measured
by a temperature sensor in one example, or it may be inferred from
operating conditions, such as exhaust temperature, air-fuel ratio,
soot load on the PF, etc. The threshold PF temperature may be
higher than the temperature the PF typically reaches during a
regeneration event. If the PF temperature is greater than the
threshold PF temperature, then the method proceeds to 310, which
will be described below. However, if the PF temperature is less
than the threshold PF temperature, then the method proceeds to
306.
[0053] At 306, the method includes comparing an ash load on the PF
surface nearest the space between the TWC and the PF to a threshold
ash load. The ash load may be estimated based on an estimated ash
load production, as described above. Determining the ash load
includes measuring an exhaust pressure in the air gap via a
pressure sensor and comparing the measured exhaust pressure to a
second threshold exhaust gas pressure. As described above, the
pressure sensor may be a gauge, an absolute, or a delta pressure
sensor. If the measured exhaust pressure is greater than the second
threshold exhaust gas pressure, then the ash load may be greater
than the threshold ash load.
[0054] In an alternative embodiment, determining the ash load being
greater than the threshold ash load may be based on a number of
miles driven (e.g., 1000 miles) or driving over a threshold speed
for a period of time (e.g., 40 mph over 100 hours).
[0055] If the ash load is greater than the threshold ash load, then
the method proceeds to 310. If the ash load is less than the
threshold ash load, then the method proceeds to 308. At 308, the
method includes maintaining current engine operating parameters and
the fluid injection does not occur. The method may exit.
[0056] At 310, the method includes determining if injection
conditions are met. The injection conditions may include a water
availability (e.g., enough water present in reservoir or water is
liquid), as described above. If a reservoir is does not have a
sufficient volume of water for injection, the reservoir may be
replenished via an external service port. In alternative
embodiments, the reservoir may be replenished via a condensate
formed in a charge air cooler. The charge air cooler may be
fluidically coupled to the water reservoir, wherein the condensate
from the charge air cooler flows to the water reservoir responsive
to a fluid volume gauge in the reservoir. Further, in some
embodiments, an air conditioner drip tube may be fluidically
coupled to the water reservoir, wherein the condensate from the air
conditioner flow to the water reservoir responsive to the fluid
volume gauge in the reservoir. The method proceeds to 314 if water
injection conditions are met. However, the method proceeds to 312
if the conditions are not met and the controller maintains current
engine operating parameters as described above with respect to
308.
[0057] At 314, the method includes injecting water into a space
(e.g., air gap or exhaust passage) between the TWC and the PF. The
injecting is responsive to a pressure signal being above a
threshold pressure, as described above. Further, the injecting may
be responsive to a particulate filter temperature being above a
threshold temperature. The water injection impinges on the front
surface of the PF and washes the ash to the back of the PF. The
exhaust gas then blows the ash out the PF and through the tailpipe
and into the atmosphere.
[0058] Serendipitously, the water injection maximizes the PF
capacity to capture more soot. This may be due to the water
providing the PF with an increased adhesive surface area. Further,
the water may provide improved capturing of NO.sub.x and CO due to
its polarity and ability to hydrogen bond to the gases. The amount
of water injected may be determined based on the estimated ash
load, as described above. The method proceeds to 316.
[0059] At 316, the method includes adjusting engine parameters in
response to the water injection. This may include but is not
limited to decreasing an EGR flow rate only if an engine dilution
demand is met, as described above. The method may exit.
[0060] FIG. 3 illustrated an exemplary method for utilizing a water
injection to either maintain a PF temperature or to decrease an ash
load on the PF surface nearest the space between a TWC and a PF.
FIG. 4 will now graphically illustrate conditions during a PF
regeneration and events leading to a water injection.
[0061] FIG. 4 illustrates plot 400 of various engine conditions
affecting a water injection. It should be understood that the
examples presented in FIG. 4 are illustrative in nature, and other
outcomes are possible. For example, additional or alternative
engine parameters may affect a regeneration occurrence. PF
temperature has been omitted from FIG. 4.
[0062] FIG. 4 represents an example of an active regeneration,
wherein a controller may adjust engine parameters to initiate a PF
regeneration (e.g., run engine lean, delay fuel injection, and/or
retard spark). However, in alternative embodiments, the
regeneration may be only passive, only active, or a combination
thereof. If regeneration is passive, the controller may not signal
an adjustment to initiate the passive PF regeneration.
[0063] The graphs in FIG. 4 represent various operating parameters
and resultant engine controls for reducing an ash load on the PF
surface nearest the space between a TWC and a PF via a water
injection into a space between the TWC and the PF. The x-axis
represents time and the y-axis represents the respective engine
condition being demonstrated. On plot 400, graph 402 represents a
soot load, graph 404 represents an exhaust gas temperature and line
405 represents a minimum threshold exhaust gas temperature to begin
a PF regeneration, graph 406 represents an exhaust pressure and
line 408 represents a threshold exhaust pressure, graph 410
represents an ash load and line 411 represents a threshold ash
load, and graph 412 represents a water injection. In the example
illustrated in FIG. 4, the threshold exhaust pressure 408
represents the first threshold exhaust pressure and the second
threshold exhaust pressure, wherein the second threshold exhaust
pressure is equal to the first threshold exhaust pressure.
[0064] Plot 400 will be described herein with reference to
components and systems depicted in FIG. 1, particularly, water
reservoir 70, conduit/water injector 73, TWC 71, PF 72, exhaust
pressure sensors 127 and 128, and exhaust aftertreatment system 74.
The parameters illustrated in plot 400 may be measured by a
controller (e.g., controller 12), according to computer-readable
media stored thereon.
[0065] Prior to T1, the soot load increases, as seen with respect
to graph 402. As the soot accumulates on the PF, the exhaust gas
pressure increases, as shown on graph 406. The soot load may be
increasing due to an increased engine load and as a result, the
exhaust gas temperature increases, as shown with respect to graph
404. The ash load remains constant and below the threshold ash load
as no new soot is being regenerated into ash, shown by graph 410.
The water injection remains disabled, shown by graph 412.
[0066] At T1, the exhaust pressure increases to the threshold
exhaust pressure and as a result, the controller may begin
signaling adjustments to begin a PF regeneration. The exhaust gas
temperature is greater than the minimum threshold exhaust gas
temperature to begin the PF regeneration due to the adjustments
signaled by the controller to begin a regeneration (e.g.,
increasing air intake, delaying fuel injection, and/or retarding
spark). After T1 and prior to T2, the exhaust temperature continues
to increase beyond the minimum threshold exhaust gas temperature.
The minimum threshold regeneration exhaust gas temperature may be
based on a threshold PF regeneration temperature (e.g., 600.degree.
C.). As described above, the PF regeneration efficacy may be
dependent on the exhaust gas temperature, the soot load, and/or the
duration of regeneration. Further, the duration of regeneration may
be based on the soot load, the exhaust gas temperature, and/or
engine parameters (e.g., engine speed, engine load, engine
temperature, etc.). As an example, the duration of regeneration and
the exhaust gas temperature may be inversely related for a given
soot load, wherein as the exhaust temperature increases, the
duration of regeneration decreases.
[0067] The soot load remains high until the exhaust gas temperature
increases to a relatively high temperature. The high exhaust gas
temperature (e.g., 900.degree. C.) is a temperature greater than a
low exhaust gas temperature (e.g., 550.degree. C.). The exhaust
pressure decreases to a pressure below the threshold exhaust gas
pressure. However, the regeneration duration may be based on a
calculation comprising the regeneration temperature and the soot
load, as described above, in order to reduce the soot load to a
relatively low amount, wherein the regeneration duration is
independent of the exhaust pressure. The exhaust gas temperature
begins to decrease as the soot load decreases in order to improve
fuel economy (e.g. air/fuel ratio returns to stoichiometric, fuel
injection timing is not delayed, and/or spark is no longer
retarded). Once the PF has reached the threshold PF regeneration
temperature, it may self-burn and no longer demand the exhaust gas
temperature to be greater than the minimum threshold exhaust gas
temperature to begin the PF regeneration. The ash load increases
over the length of the regeneration as the soot is converted to
ash. The rate of ash load increase is not equivalent to the rate of
soot load decrease, as the conversion of soot to ash is not 1:1
(e.g., burning soot produces gas particles). The newly formed ash
load is not above the threshold ash load, and therefore the exhaust
pressure remains below the threshold exhaust pressure. As a result,
the water injection remains disabled.
[0068] At T2, the PF regeneration ends and the soot load is low.
The exhaust gas temperature decreases. The exhaust gas pressure
remains below the threshold exhaust gas pressure. The ash load
remains below the threshold ash load, therefore, the water
injection remains disabled. After T2 and prior to T3, the exhaust
gas pressure increases as the soot load on the PF increases. The
ash load remains constant due to the soot not being regenerated
into ash, as described above. The exhaust gas temperature begins to
increase and the water injection remains disabled.
[0069] At T3, the exhaust pressure increases to a pressure greater
than the threshold exhaust gas pressure due to the increasing soot
load. As a result, the controller signals regeneration adjustments
to increase the exhaust gas temperature, as described above. The
ash load remains constant and below the threshold ash load due to
the soot load not yet converting into ash. At T3 and prior to T4,
the exhaust gas temperature increases to a temperature
substantially equal to the minimum threshold exhaust gas
temperature to begin the PF regeneration (e.g., 600.degree. C.) and
remains at that temperature. As a result, the PF regeneration
duration is greater than the PF regeneration duration discussed
above. This may be due to a lower exhaust gas temperature (e.g.,
600.degree. C. compared to 900.degree. C.). The lower exhaust gas
temperature may not heat the PF to a desired regeneration
temperature as quickly as a higher exhaust gas temperature. As a
result, the regeneration may take a longer period of time. Further,
the ash load rate of accumulation is decreased due to the longer
regeneration. The exhaust gas temperature begins to decrease after
a duration of time, however, the regeneration continues until the
soot load is low, as described above.
[0070] At T4, the regeneration is complete and soot load is
relatively low. The exhaust temperature is decreasing to a
relatively low temperature. The exhaust pressure has deceased to a
pressure below the threshold exhaust gas pressure. However, the
reduction in the exhaust gas pressure is less than the reduction in
the prior regeneration due to the ash load increasing over
successive regenerations. However, the ash load remains below the
threshold ash load and the water injection is disabled. After T4
and prior to T5, the exhaust gas pressure increases due to an
increasing soot load on the PF. The exhaust temperature continues
to decrease. The ash load remains constant and below the threshold
ash load. Therefore, the water injection remains disabled.
[0071] At T5, the exhaust gas pressure reaches the threshold
exhaust gas pressure. In response to the exhaust gas pressure being
greater than or equal to the threshold exhaust gas pressure, the
controller signals adjustments to being the PF regeneration, as
described above. The signaled adjustments cause the exhaust gas
temperature to increase. The exhaust gas temperature increases to a
temperature greater than a nominal exhaust temperature (e.g.,
550.degree. C.). The exhaust pressure continues to increase. The
ash load does not increase due to the soot load not yet being
converted into ash. The water injection remains disabled. After T5
and prior to T6, the exhaust gas temperature increases to a
temperature greater than the minimum threshold exhaust gas
temperature to begin the PF regeneration. In this example, the
exhaust gas temperature may be less than the temperature of the
first regeneration (e.g., between T1 and T2) and greater than the
temperature of the second regeneration (e.g., between T3 and T4).
Therefore, the regeneration duration between T5 and T6 is greater
than the regeneration duration between T1 and T2 and less than the
regeneration duration between T3 and T4. Once the PF reaches the
threshold PF regeneration temperature, the soot load begins to
decrease. As the soot load decreases, the exhaust pressure
decreases and the ash load increases. However, the ash load
increases to an ash load greater than the threshold ash load,
therefore, the exhaust pressure is unable to decrease below the
threshold exhaust gas pressure despite the PF regeneration. The
regeneration continues until the soot reaches a relatively low
load, as described above.
[0072] At T6, the regeneration is disabled and the soot load is
relatively low. The exhaust gas temperature returns to the nominal
exhaust gas temperature. The exhaust gas pressure between the TWC
and the PF remains greater than the threshold exhaust gas pressure
due to the ash load being relatively high. In other words, the
regeneration was initiated responsive to an exhaust gas pressure
being greater than the threshold exhaust gas pressure. However, the
exhaust gas pressure being greater than the threshold exhaust gas
pressure following a PF regeneration no longer signals the PF
regeneration, rather, it may signal an ash load being greater than
a threshold ash load. As a result, the water injection is
initiated. After T6 and prior to T7, the water injection continues
at a constant rate over a predetermined period of time. In
alternative examples, the water injection rate may be adjustable
based on the estimated ash load on the PF, as described above. The
exhaust pressure decreases below the threshold exhaust gas
pressure. However, the water injection continues until the ash load
decreases to a relatively low load. The exhaust gas temperature
remains at a relatively low temperature. The soot load increases at
a low rate.
[0073] At T7, the water injection is deactivated due to the ash
load reaching the relatively low load.
[0074] In this way, an ash load accumulated onto a surface of a PF
nearest a space between the PF filter downstream of the TWC may be
decreased. Further, the water injection may enhance the filtering
abilities of the PF by increasing its adhesive surface area and
providing hydrogen bonds for regulated emission gases. The
technical effect of performing the water injection in the space
between the TWC and the PF is to decrease the ash load accumulated
over PF regenerations to a level less than a threshold ash load.
Further, the water injection may be responsive to a PF filter
temperature above a threshold PF temperature. The water injection
may decrease the PF filter temperature above the threshold PF
temperature in order to prevent PF degradation.
[0075] In an embodiment, method for an engine comprises injecting
water from a reservoir to between a particulate filter and a
three-way catalyst, the particulate filter located downstream of
the three-way catalyst. Additionally or alternatively, the
injecting is responsive to an exhaust pressure signal between the
three-way catalyst and the particulate filter being above a
threshold pressure. The method may further include the injecting
being responsive to a particulate filter temperature being above a
threshold temperature. Additionally or alternatively, the injecting
is responsive to an estimated ash load after a soot regeneration
has been completed, wherein the estimated ash load is based on an
exhaust pressure after the soot regeneration, and further
comprising adjusting a water injection amount based on the
estimated ash load.
[0076] The method, additionally or alternatively, may include the
three-way catalyst comprises a porous substrate coated with one or
more precious metals, the three-way catalyst configured to convert
one or more emissions in exhaust gas flowing through the three-way
catalyst, and wherein the particulate filter comprises a mesh
structure without a precious metal coating, the particulate filter
configured to trap soot in exhaust gas flowing through the gas
particulate filter. Additionally of alternatively, the soot
regeneration is performed responsive to an exhaust gas pressure
between the three-way catalyst and the particulate filter being
above a threshold exhaust gas pressure.
[0077] An embodiment of an engine comprises an engine with a
plurality of cylinders, an engine exhaust emission control device
comprising a particulate filter positioned downstream of a catalyst
brick, an exhaust gas pathway coupling an engine exhaust manifold
to the engine exhaust emission control device, an injector
fluidically coupled to a water reservoir via a conduit, the
injector fluidically coupled between the catalyst brick and the
particulate filter, a pressure sensor coupled between the catalyst
brick and the particulate filter, and a controller having computer
readable instructions stored on non-transitory memory for
estimating an ash load in the particulate filter based on a
pressure measured by the pressure sensor and injecting water via
the injector responsive to the estimated ash load exceeding a
threshold ash load. The system, additionally or alternatively, may
comprise an EGR pathway coupled to the exhaust pathway upstream of
the emission control device, and wherein the instructions further
comprise instructions for adjusting an EGR flow rate responsive to
the injection of water.
[0078] The system may further include the three-way catalyst brick
and the particulate filter being housed in a common housing of the
emission control device and separated via an air gap, and wherein
the common housing includes a boss positioned between the three-way
catalyst brick and the gas particulate filter to accommodate the
injector, the injector positioned to inject water into the air gap,
wherein the boss may further accommodate the injector. Additionally
or alternatively, the system may include the three-way catalyst
brick and the particulate filter being housed in separate housings
and fluidically coupled via the exhaust pathway, and wherein the
injector is coupled to the exhaust pathway between the three-way
catalyst brick and the particulate filter. The system, additionally
or alternatively, may include the estimated ash level being
determined following completion of a regeneration of the
particulate filter.
[0079] Another method for an engine comprises combusting fuel in
the engine via spark ignition and directing exhaust gas from the
engine to a particulate filter, regenerating the particulate filter
to remove particulate matter stored on the particulate filter
responsive to exhaust gas pressure upstream of the particulate
filter exceeding a first threshold pressure, and injecting water
between the particulate filter and a three-way catalyst upstream of
the particulate filter to remove ash from the particulate filter
responsive to the exhaust gas pressure upstream of the particulate
filter exceeding a second threshold pressure following completion
of the regeneration. The method, additionally or alternatively, may
include the exhaust pressure being measured between the three-way
catalyst and the particulate filter.
[0080] Additionally or alternatively, the method may include
regenerating the particulate filter, wherein the regenerating
includes increasing exhaust gas temperature to at least a threshold
temperature for a predetermined duration, where the exhaust gas
temperature and predetermined duration are determined based at
least in part on a particulate matter load on the particulate
filter. The method, additionally or alternatively, may include
determining that the regeneration has reached completion when the
exhaust gas temperature has been maintained at least at the
threshold temperature for the predetermined duration.
[0081] Additionally or alternatively, the method may include the
exhaust gas temperature being increased as a result of an increase
in engine load. The method may further include the first threshold
pressure being greater than the second threshold pressure. The
method, additionally or alternatively, may include injecting water
to between the three-way catalyst and the particulate filter when a
particulate filter temperature exceeds a threshold particulate
filter temperature.
[0082] Note that the example control and estimation routines
included herein can be used with various engine and/or vehicle
system configurations. The control methods and routines disclosed
herein may be stored as executable instructions in non-transitory
memory and may be carried out by the control system including the
controller in combination with the various sensors, actuators, and
other engine hardware. The specific routines described herein may
represent one or more of any number of processing strategies such
as event-driven, interrupt-driven, multi-tasking, multi-threading,
and the like. As such, various actions, operations, and/or
functions illustrated may be performed in the sequence illustrated,
in parallel, or in some cases omitted. Likewise, the order of
processing is not necessarily required to achieve the features and
advantages of the example embodiments described herein, but is
provided for ease of illustration and description. One or more of
the illustrated actions, operations and/or functions may be
repeatedly performed depending on the particular strategy being
used. Further, the described actions, operations and/or functions
may graphically represent code to be programmed into non-transitory
memory of the computer readable storage medium in the engine
control system, where the described actions are carried out by
executing the instructions in a system including the various engine
hardware components in combination with the electronic
controller.
[0083] It will be appreciated that the configurations and routines
disclosed herein are exemplary in nature, and that these specific
embodiments are not to be considered in a limiting sense, because
numerous variations are possible. For example, the above technology
can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine
types. The subject matter of the present disclosure includes all
novel and non-obvious combinations and sub-combinations of the
various systems and configurations, and other features, functions,
and/or properties disclosed herein.
[0084] The following claims particularly point out certain
combinations and sub-combinations regarded as novel and
non-obvious. These claims may refer to "an" element or "a first"
element or the equivalent thereof. Such claims should be understood
to include incorporation of one or more such elements, neither
requiring nor excluding two or more such elements. Other
combinations and sub-combinations of the disclosed features,
functions, elements, and/or properties may be claimed through
amendment of the present claims or through presentation of new
claims in this or a related application. Such claims, whether
broader, narrower, equal, or different in scope to the original
claims, also are regarded as included within the subject matter of
the present disclosure.
* * * * *