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.

Description

FIELD

The present description relates generally to methods and systems for removing ash within an emission control device.

BACKGROUND/SUMMARY

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_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.

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.

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° C., in order to burn the accumulated particulates into ash.

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° 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° 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.

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.

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.

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

FIG. 1 shows a schematic diagram of an engine with a three-way catalyst (TWC) upstream of a particulate filter (PF).

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.

FIG. 3 shows a flow chart demonstrating an exemplary method for direct injecting a fluid at a space between the TWC and the PF.

FIG. 4 shows a graph illustrating a variety of engine conditions for initiating a water injection.

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

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.

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.

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.

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 O₂ 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.

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.

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_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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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).

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° 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.

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.

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.

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.

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.

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° 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.

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° 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.

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.

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.

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.

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.

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.

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° 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.

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.

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).

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.

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.

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.

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_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.

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.

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.

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.

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.

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.

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.

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.

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° 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.

The soot load remains high until the exhaust gas temperature increases to a relatively high temperature. The high exhaust gas temperature (e.g., 900° C.) is a temperature greater than a low exhaust gas temperature (e.g., 550° 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.

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.

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° 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° C. compared to 900° 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.

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.

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° 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.

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.

At T7, the water injection is deactivated due to the ash load reaching the relatively low load.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.