Emission Control System using a Multi-Function Catalyzing Filter

Abstract

A multi-function filter is provided for use in emission control systems, for example, on the exhaust gas from an internal combustion engine. The filter has a substrate constructed using bonded fiber structures, which cooperate to form a highly uniform open cell network, as well as to provide a uniform arrangement of pores. The substrate typically is provided as a wall-flow honeycomb structure, and in one example, is manufactured using an extrusion process. In this way, the substrate has many channel walls, each having an inlet surface and an outlet surface. The inlet surface has a uniform arrangement of pores that form a soot capture zone, where soot and other particulate matter is captured from an exhaust gas. A gas conversion catalyst is disposed inside the channel wall, where one or more pollutants in the exhaust gas are converted to less harmful substances. Because of the uniform pore structure and open cell arrangement inside the channel wall, the filter is capable of being heavily loaded with catalyst, while avoiding undue increase in backpressure to the internal combustion engine.

Description

BACKGROUND

The field of the present invention is the construction and use of filters and catalyzing filters for pollution control in an emission control system. More particularly, the present invention relates to a multifunction filter for use with an internal combustion engine.

Internal combustion engines are essential to modern life. These engines power our cars, trucks, delivery vehicles, emergency generators, manufacturing equipment, farming equipment, and innumerable other machines and processes. Internal combustion engines typically are powered using a hydrocarbon fuel. Most often, this fuel is derived from crude oil, and is in the form of gasoline, diesel, or other liquid fuel. The internal combustion engine has evolved over time to provide excellent performance characteristics, extended durability, and low cost of operation. Due to these characteristics, the internal combustion engine continues to be a main power source for manufacturing, commercial, industrial, transportation, and residential use.

In operation, an internal combustion engine typically combines a hydrocarbon fuel with air, and ignites the mixture to generate an explosive power that is converted into a kinetic mechanical energy. Unfortunately, the burning of hydrocarbon fuels, and in particular fossil fuels, generates highly undesirable pollutants that harm the environment. For example, internal combustion engines generate volatile organic compounds, pollutant gases such as carbon monoxide and various derivatives of NOx, as well as soot and ash. Different types of internal combustion engines have different environmental impacts. For example, diesel engines typically generate far more soot than the gasoline powered engine, while having less environmental impact with NOx. Great strides have been made, primarily due to government regulation, to clean the exhaust from internal combustion engine systems. Larger internal combustion engines now typically have sophisticated engine control systems that monitor and adjust fuel-to-air ratios, as well as monitor other emission control characteristics. These engine control systems may adjust the engine to operate at a new performance or adjust a factor or add extra devices to the emission control system (i.e. after-treatment) to improve emission quality. Although the emission control systems are typically initially provide with a vehicle, additional emission control devices may be added to existing in-service vehicles by adding after-treatment devices. Hybrid vehicles generally fall in the same category when they are not operating on the battery powered mode, and therefore require emission controls when operating their internal combustion engine.

In a typical modern gasoline-powered passenger vehicle, several separate devices are provided for improved emissions control. In most cases, such systems are required to meet or exceed the regulatory emission limits. The vehicle may have 2, 3, or even more separate catalytic converters for converting various pollutant gases into less dangerous materials. In many countries, a gas powered passenger vehicle currently (2007) does not typically provide separate filtration for particulate matter or soot, even though some recent studies have highlighted the formation of nano-particle soot and secondary organic aerosol emissions from such engines. The vehicle also has a complex engine control system for monitoring air/fuel ratios, and making real-time adaptations to the engine and emission control system for improved emission control. For a typical diesel-powered truck, a large particulate filter is now used for trapping soot and ash, and a sophisticated burn off control system is used for periodically regenerating the filter. Such filtering requirements may apply to heavy duty, medium duty, or even light duty, depending on the particular regulatory jurisdiction. In the regeneration process, the filter is heated sufficiently to burn soot, sometimes in the presence of a catalyst, into relatively harmless exhaustible by-products. For engine systems requiring a greater degree of emission control, after-treatment devices may have to be installed, as in-engine modifications and controls are not enough to meet the regulatory emission limits. After filtration, an additional separate catalytic conversion devices or canisters are provided for oxidation of unburnt hydrocarbons, carbon monoxide and for NOx reduction. Additionally, sometimes cleanup catalyst systems are also needed to reduce leakage of criteria or toxic pollutants.

In some places, such as Europe, more stringent emission control standards require larger diesel delivery trucks to further reduce NOx emissions using systems such as Nox absorbers, lean Nox traps, or SCR (selective catalytic reduction). The SCR is either operated by the injection of hydrocarbon in the exhaust stream to reduce the NOx, or by injecting urea which decomposes to form NH₃. These trucks carry an additional refillable supply of urea (either in solution or solid state), which is introduced into the exhaust gas to generate ammonia. In some cases, technologies involving reformer systems and catalysts have been developed to generate on-board urea. The ammonia is reacted in a catalytic conversion device for converting NOx to relatively harmless byproducts, such as N₂.

Even today, a large volume of space is required for emission control devices and systems in both gasoline and diesel vehicles. In particular, most vehicles now require several separate units for the different aspects of after-treatment, for example for filtering and catalytic conversion, each consuming valuable volume in the vehicle, and limiting design options and making the design and manufacturing processes more complex. Further, adding these emission control systems, filters, and catalyzing devices add substantial expense to the cost of a new vehicle, as well as increase maintenance costs.

Governments are continually strengthening emission control standards, and requiring manufacturers to reduce carbon monoxide, NOx, and particulate emission. With the addition of each new regulation, manufacturers are further pressured to add more emission devices, enlarge current emission devices, and provide for more sophisticated emission control systems. Accordingly, over time the volume, cost, and design limitations presented by implementing emission standards becomes a substantial burden on any vehicle manufacturer. Further, these additional emission control devices may negatively affect fuel efficiency. Although these engines will be cleaner, they put additional strain on the world's resources, and contribute to further emission of carbon dioxide, which has been linked to global climate change.

Therefore, there exists a need to provide emission control devices that can efficiently meet current and evolving emission standards, while minimizing the overall size, cost, and complexity of the emission control system.

SUMMARY

Briefly, the present invention provides a multi-function filter for use in emission control systems, for example, on the exhaust gas from an internal combustion engine. The filter has a substrate constructed using bonded fiber structures, which cooperate to form a highly uniform open cell network, as well as to provide a uniform arrangement of pores. The substrate typically is provided as a wall-flow honeycomb structure, and in one example, is manufactured using an extrusion process. In this way, the substrate has many channel walls, each having an inlet surface and an outlet surface. The inlet surface has a uniform arrangement of pores that form a soot capture zone, where soot and other particulate matter is captured from an exhaust gas. A gas conversion catalyst is disposed inside the channel wall, where one or more pollutants in the exhaust gas are converted to less harmful substances. Because of the uniform pore structure and open cell arrangement inside the channel wall, the filter is capable of being heavily loaded with catalyst, while avoiding undue increase in backpressure to the internal combustion engine.

In one example, the multi-function filter has a single soot collection zone and a single gas-conversion zone. The gas conversion zone may be inside the channel wall, adjacent to the inlet surfaces, or adjacent to the outlet surfaces. Accordingly, the position of the gas conversion zone, as well as the particular catalyst or combination of catalysts, may be selected to support a wide range of emission control requirements. For example, the gas conversion zone may be constructed as an oxidation catalyst, a soot-regeneration catalyst, a NOx reduction catalyst, or a slip catalyst. In the gas conversion zone, a catalyst may be evenly loaded, or may be loaded according to a gradient. The gas conversion zone may also have multiple catalysts layered onto the fiber structures according to known processes.

In another example, the multi-function filter has two or more gas conversion zones. These zones may be layered within a channel wall, or may be positioned in separate locations in the filter. In one construction, a first catalyst is applied toward the inlet end of the substrate, and another catalyst is applied toward the outlet end of the substrate. In this way, the channel areas nearer the inlet act as a first gas conversion zone, while the channel areas nearer the outlet act as a second gas conversion zone. In yet another example, the soot collection zone and a gas conversion zone share the same channel area. In this regard, a soot-regeneration catalyst may be disposed in the soot collection area to assist in lower temperature soot burn-off. In another case, a gas conversion catalyst may be disposed in the soot collection area to assist in generating transient molecules that are consumed in other downstream processes. In another illustration, a gas conversion catalyst may be disposed in the soot collection area to assist in converting a pollutant gas to a less harmful substance, thereby increasing the overall conversion efficiently of the filter.

In operation, the multi-function filter may be provided in a single device, which is typically in the from of a can. In this way, a single can is able to both effectively trap soot, as well as enable highly efficient catalytic conversion processes. Since the filter may be heavily loaded with catalyst, the filter exhibits greatly improved conversion efficiencies, even for relatively slow reactions; has an extended useful life, even in processes where catalyst is consumed; and provides sufficient catalyst surface area to meet stringent new emission standards. Since all this is done in a single can, the engine control system is simplified, less expensive, and easier to design into new vehicles. Importantly, even as a single can solution, the multi-function filter does not cause undue backpressure to the engine, and avoids undesirable channeling effects when loading and unloading soot.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the following figures. The components within the figures are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views. It will also be understood that certain components and details may not appear in the figures to assist in more clearly describing the invention.

FIG. 1 is a simplified block diagram of a emission control system in accordance with the present invention;

FIG. 2 is a flow chart of an emission control system in accordance with the present invention;

FIG. 3 is a substrate for a multi-function filter in accordance with the present invention;

FIG. 4 is an enlarged sectional view of a channel wall structure for the substrate illustrated in FIG. 3;

FIG. 5 is an enlarged sectional view of a channel wall structure for the substrate illustrated in FIG. 3;

FIG. 6 is an enlarged sectional view of a portion of a single channel wall for the substrate illustrated in FIG. 3;

FIG. 7 is an illustration of a bonded fiber arrangement providing highly uniform pore structures;

FIG. 8 is a scanning electron microscope photograph showing a bonded fiber arrangement providing highly uniform pore structures;

FIG. 9 is an illustration of a bonded fiber arrangement providing highly uniform pore structures;

FIG. 10 is a block diagram showing a process for filtering and catalyzing an exhaust gas using a multifunction filter in accordance with the present invention;

FIG. 11 is a functional block diagram of a wall flow multifunction filter in accordance with the present invention;

FIG. 12 is a flowchart of a process of forming a multifunction filter in accordance with the present invention;

FIG. 13 is a block diagram of a wall flow multifunction filter having multiple gas phase reaction zones; and

FIG. 14 is a flowchart of a process of making a substrate for a multifunction filter in accordance with the present invention;

DETAILED DESCRIPTION

Referring now to FIG. 1, emission control system 10 is illustrated. Emission control system 10 is constructed for use with an internal combustion engine to provide pollution control. As such, emission control system 10 advantageously may be used with gasoline, diesel, or other hydrocarbon-based internal combustion engine systems. Since the design and construction of engines, engine control systems, and general exhaust system components are well known, these will not be described in detail. Emission system 10 has internal combustion engine 12 operating, for example, on diesel or gasoline fuel. Engine 12 emits an untreated exhaust gas containing various pollutants, such as particulate matter, volatile organic compounds (VOC), and pollutant gases. The untreated exhaust gas 19 is received into multi-function filter 14. The multi-function filter 14 is a single discrete device for both filtering particulate matter from the untreated gas, and for facilitating catalytic conversion of one or more pollutant gases. Advantageously, exhaust 21 from multi-function filter 14 is a filtered and catalyzed exhaust gas that complies with new and evolving emission control standards. Importantly, the filtering and catalyzing process has been enabled within a single multifunction filter assembly, reducing the size, complexity or cost of the other emission control devices in the exhaust systems. Accordingly, the multifunction filter 14 consumes less space in a vehicle, may be more conveniently integrated into vehicle aesthetics, and simplifies construction, maintenance, and repair.

In some cases, a gas-phase additive 18 will be mixed with the untreated exhaust gas in mixing chamber 19. This gas-phase additive reacts with one or more gases in the untreated exhaust gas 19 to create an intermediate substance that may be more readily catalyzed or otherwise removed within the multifunction filter 14. Although emission control system 10 is illustrated with a single multifunction filter 14, it will be appreciated that other catalysts and filters may be provided in the overall exhaust path. Emission control system 10 also has engine control system 16 for managing the individual components of emission control system 10. For example, engine control system 16 may communicate with engine 12 to determine performance characteristics, may monitor the multifunction filter 14, and may make adjustments to improve overall pollution control or engine performance. In one example, engine control system 16 may monitor for an undue increase in back pressure in the multifunction filter 14, and in response, initiate a burn-off process to unload accumulated soot. It will be appreciated that engine control system 16 may monitor several aspects of emission control system, and may make adjustments according to the specific engine and exhaust design. Since the design and implementation of engine control systems is well known, engine control system 16 will not be described in detail.

Multifunction filter 14 has been constructed in a way that provides for both 1) highly efficient soot capture, as well as 2) enabling highly efficient gas catalyzing processes, while maintaining desirable back pressure, soot loading, soot unloading, and burn of characteristics. In this way, emission control system 10 provides the first known multi-function filter capable of meeting stringent particulate and pollution control standards evolving in Europe, the United States, and in other countries around the world. Advantageously, use of the multifunction filter 14 provides exceptional particulate and pollution control, while allowing internal combustion engines to meet performance requirements. For example, since multifunction filter 14 has exceptional back pressure characteristics, an associated internal combustion engine is able to more efficiently operate, and thereby maintaining or improving its fuel economy. In this way, the multi-function filter 14 may enable vehicles to emit cleaner exhaust, without the typical degradation to fuel economy. Use of the disclosed multifunction filter 14 thereby protects the earth's atmosphere by providing for effective pollution control, and at the same time helps to reduce dependency on carbon-based fuels by enabling better fuel efficiencies.

Multifunction filter 14 may be better understood with reference to FIG. 2, where a process 50 is described for operation on multifunction filter 14. Multifunction filter 14 receives gas and particulate matter from an internal combustion engine as shown in block 52. In some cases, an additive may be reacted with the gas according to the particular gas-phase chemistry requirements as shown in block 54. Typically, additive mixing is achieved in a mixing chamber prior to the gas being received into multifunction filter 55. In one example, the additive is urea, which is decomposed to form ammonia by the heat from the exhaust. It will be appreciated that other catalyst processes may be used to facilitate improved ammonia formation. The ammonia (decomposed urea) is received into multifunction filter 55, where it reacts with nitrogen oxides in a reduction reaction to produce harmless nitrogen gas. It will also be appreciated that other additives may be used for creating other intermediate products for the removal of other pollutant gases according to application needs.

The exhaust gas is received into multifunction filter 55. The multifunction filter 55 performs two distinct functions within a single substrate: first, highly effective soot capture; and second, it hosts an efficient gas-phase process. In its filtering role, multifunction filter 55 collects particulate matter using a highly uniform arrangement of pores. This highly uniform arrangement of pores has a relatively narrow distribution of pore sizes, as well as a generally open, inter-connected pore structure. This means that soot may be captured in a regular and uniform manner, and in some cases acts as an especially efficient cake filtering structure. With such a highly organized and arranged pore structure and size distribution, a very uniform loading of soot is achieved as shown in block 59. In a similar manner, this same pore structure contributes to a highly uniform unloading of soot as shown in block 61. Uniform loading and unloading is advantageous, as it reduces undesirable channeling effects within the filter. In previous filters, channeling effects occur within a filter as pores fill with trapped soot. In these filters, since there is a wide distribution of pore sizes, and many pore paths are blocked, exhaust gases initially move along a path of least resistance, which typically will be through some set of relatively aligned and large pores. Operating in this state, the filter has a very low back pressure. However, as these initial pore networks clog with trapped soot, the exhaust gas is forced to take alternative paths. While these paths are being established, the filter's backpressure may undergo an undesirable and sizeable increase, and the overall performance of the emission control system declines. This temporary spike in backpressure wreaks havoc on the overall emission control system, complicating design and implementation, and causes irregular emission control performance. For example, the control strategies used for regenerating such filters are often under-utilizing the filter to make sure no backpressure spikes are observed. In contrast, the more regular and uniform distribution provided in multifunction filter 55 avoids much of his channeling effect, thereby maintaining efficiency over the loading and unloading process. The open pore structure of multifunction filter 55 also allows gases to flow more uniformly and freely into internal areas of the multifunction filter. It also makes the porosity inside the wall fully accessible for catalyst loading and gas permeation.

Within the multifunction filter 55, the filtered gas is reacted with one or more catalysts that have been disposed on the internal arrangement of pores. The arrangement of pores within the multifunction filter is also a generally uniform arrangement, and is constructed as a highly open cell network of pores. Typically, a washcoat is disposed on to the substrate surface, which facilitates better adhesion and distribution of the catalyst or catalysts. Advantageously, the uniform nature of the pore structure within the multifunction filter enables a uniform loading of the washcoat and catalyst as shown in block 65. Further, because of the open pore, interconnected pore network, the washcoat and catalyst may be disposed at very high loading levels. These high loading levels are highly advantageous for efficient catalyst processes, as well as desirable to assure long-term survivability. It will also be appreciated that multifunction filter 55 may have a single catalyst for reacting a single pollutant gas, or may have multiple catalysts arranged for reacting multiple pollutant gases. The gas expelled from the multifunction filter 55 has been filtered and reacted as shown in block 67. An engine control system 69 may monitor various aspects of process 50, and a make adaptations for improved emission control or engine performance.

Referring now to FIG. 3, a substrate 100 is illustrated. In one example, substrate 100 may advantageously be used in a multifunction filter, such as multifunction filter 14 described with reference to FIG. 1. While substrate 100 may be manufactured in alternative ways, extrusion has been found to be a particularly efficient and effective process. Generally, the extrusion process mixes together fibers or fiber precursors with pore formers, plasticizers, and fluids to form an extrudable mixture at the proper rheology. The extrudable mixture is then forced through the die of an extruder, thereby generating a green substrate having a honeycomb form. The green substrate is first dried to remove fluids, and then further heated to remove pore formers, volatile organic and inorganic materials, and finally to form a bonded fibrous structure.

It is this bonded fibrous structure that enables the multifunction filter to efficiently act as both a filter and a catalyzing substrate. The bonded fibrous structure is identifiable in its finished form by the uniform arrangement of pores, and the relatively narrow distribution of pore sizes. Although there is a high degree of uniformity, different zones of substrate 100 may have different uniform arrangements. For example, the extrusion process may provide for one geometry of pore structure at or near the surface of each channel wall, while a somewhat different, yet uniform, pore structure may exist more towards the inside or middle of each channel wall. Indeed, these differences in zone pore structures may beneficially be used to adapt substrates for particular filtering and catalytic requirements. The pore-structure can be altered in a controlled fashion by changing the raw material inputs, and the processing processes and parameters during extrusion and sintering.

The bonded fibrous structure may be manufactured in different ways. For example the bonded fibrous structure may be constructed as an arrangement of individual fiber or fiber-like structures that are bonded together at overlapping nodes. In another example, fiber structures include individual fibers, fibers formed into multi-fiber bundles or multi-fiber clumps. These collections of fiber structures bond with other fibers, bundles, or clumps to form a bonded fibrous structure having a highly desirable open, inter-connected pore network. It will also be appreciated that the bonded fibrous structure may use fiber strands in the extrudable mixture, which are then bonded to other fibers during sintering, or the extrudable mixture may have precursors to the fiber or fiber-like structure, whereby the fibers or fiber-like structures form during the sintering process. It will also be understood that the fibers or fiber-like structures may be formed from different materials. For example, organics, carbon, oxides, carbides, nitrides, metals, steels, or metal alloys may be used as the fiber or fiber precursors. It will also be understood that the bond between fibers, fiber bundles, or the fiber-like structures may be ceramic, glass, liquid state sintered, solid state centered, or another type of sintering bond. For the multifunction filter, it is the unique functional characteristics of the resulting bonded structure that is most meaningful, since there are many ways to commercially manufacture such a fibrous bonded, often extruded honeycomb, structure.

Further detailed discussion of extruding and sintering a bonded fibrous substrate may be found in U.S. patent application Ser. No. 11/323,429, filed Dec. 30, 2005, and entitled An Extruded Porous Substrate and Products using the Same, which is incorporated herein in its entirety. As illustrated in FIG. 3, substrate 100 has many channels formed in a honeycomb pattern. This honeycomb may have a channel density of, for example, 100 to 900 cells per square inch. In some cases where high flow rates are required, even smaller cell densities, as low as 10 cells per square inch, may be used as well. It will be understood that other cell densities may be used for other particular applications. In a particular construction, substrate 100 has alternating channels blocked or plugged at each end. In this way, an inlet channel 107 receives a gas flow, and the gas flows through channel walls into one or more output channels 109. The gas then continues down the outlet channel until it is exhausted. Generally, this type of channel arrangement is referred to as a “wallflow” filter construction.

A washcoat and catalyst is applied to substrate 100 for converting one or more pollutant gases to a less harmful substance. The substrate may host a single type of catalyst, either in a relatively even loading from the inlet side 111 to the outlet side 112, or may be applied with a gradient loading. In this way, a heavier loading may be provided toward one end, while a lesser loading is applied at the other end. Also, the substrate is capable of hosting two or more different catalysts. In one example, a first catalyst is disposed toward the inlet side 101 of the filter, and the second catalyst may be disposed toward the outlet end 102. In this way, the first catalyst may be injected or received through the inlet side 101 openings, and the second catalyst may be injected or received through the outlet side 102 openings. In another example, multiple catalysts may be layered on the fiber structures, or, cell walls may have multiple zones, with each zone having its own catalytic purpose. As an illustration, the surface adjacent to an inlet wall may have a catalyst for assisting in lower temperature soot burn-off, the interior of the channel wall may have a catalyst to assist in NOx reduction, and an area adjacent to the outlet wall may have a cleanup or oxidation catalyst. In this way, a single substrate may efficiently provide or multiple catalytic processes.

FIG. 4 shows an enlarged cross-section of part of the honeycomb structure of substrate 100. Enlargement 110 shows inlet channel 107 adjacent to several output channels, including outlet channel 109. Each of the channel walls 111 is a bonded fibrous structure. Each inlet channel wall has a zone 113 having a particulate loading area having a highly uniform pore structure. For convenience, since soot is the most common particulate, this will be general referred to as a soot capture zone. However, it will be appreciated that other particulates may be used. Typically, the soot capture zone extends from the surface of the channel wall into the initial set of pores. The depth of the soot capture zone will generally be a function of the pore-size, which can be set by changing the size or shape of pore-formers and fibers etc. For example, a larger pore arrangement will result in a fiber structure that acts more like a depth filter, whereas an arrangements of smaller pores will function more as a cake filter. Within this soot capture zone the bonded fibrous structure has a pore structure arranged for an even loading or unloading of soot. This even loading reduces undesirable channeling effects for an operating multifunction filter. Each of the channel walls also has a gas-phased zone in an interior area. The gas-phased zone also has a highly uniform open pore structure, although the structure may vary from the pore structure in the soot capture zone. The open pore structure within the gas-phase zone enables an unusually heavy loading of washcoat and catalyst. In this way a highly efficient and survivable multifunction filter may be made. Often, the catalyst of choice is platinum, although other catalysts may be used. It will also be appreciated that more than one type of washcoat or more than one type of catalyst may be used. In this way, a single multifunction filter is able to filter and react to or more pollutant gases. The soot collection zone may also be coated in the same or a different catalyst. For example, the soot collection zone may also be coated with a washcoat and platinum, which assists in low temperature soot oxidation, although other catalysts may be selected that also help in the regeneration of soot.

A further enlargement of the channel wall structure is illustrated in FIG. 5. Here, a single inlet channel 200 is illustrated. Channel 200 has channel walls 201 having a soot capture zone 204 and a gas phase zone 202. As illustrated, gas is received into the inlet channel, which then moves through channel walls 201 into an outlet channel. Particulate matter is captured on the soot capture zone 204, while the filtered gas moves into the gas-phase zone 202. In the gas-phase zone, a tortuous gas flow occurs within the uniform open cell network, allowing efficient contact of pollutant gas molecules with the catalyst active surfaces. Upon contact, the pollutant gases are converted to less harmful components. The filtered and reacted gas then moves from the channel walls into adjacent outlet channels, and is then expelled from the multifunction filter.

FIG. 6 shows yet a further enlargement of a channel wall 225 for a multifunction filter substrate. Filter wall 225 is constructed as a bonded fibrous substrate 227. The bonded fibrous substrate 227 has two distinct zones, which may or may not be contiguous. A first soot capture zone 229 has a highly uniform pore structure and arrangement, as well as a reasonably narrow pore-size distribution. A second gas-phase conversion zone 231 is found within the channel wall. The gas-phase zone also has a highly uniform pore structure, although the pore structure may be different from that of the soot capture zone 229. Exhaust gas is received at the inlet channel wall, typically from an internal combustion engine. The exhaust gas typically has both particulate matter and pollutant gases. The exhaust gas first passes through the soot capture zone 209, where the soot 233 is captured at or near the surface of the inlet channel wall. The filtered gas continues through to the gas-phase zone 231, where the gas pollutant molecules contact catalyst, and are converted to less harmful gases. For example, CO may be converted to CO₂ in an oxidation process, or NOx may be converted in a NOx reduction process. The filtered and reacted gas is then exhausted into outlet channel 235. Optionally, another gas conversions zone 232 may be layered in the channel wall. The second zone may be used to support conversions of a second pollutant gas. In this way, the first gas zone 231 may convert a first pollutant, such as NOx, and the second gas zone 232 may convert a second pollutant, such as CO or VOCs. Although the second gas zone 232 is illustrated downstream from the first gas zone, it will be appreciated that it may be located upstream, for example, adjacent the soot collection zone 229.

FIG. 7 shows a simplified diagram of a channel wall 250 similar to channel wall 225 described with reference to FIG. 6. Channel wall 250 has is positioned between an inlet channel 251 and an outlet channel 259. The channel wall 250 is a bonded fibrous substrate, having individual fibers 258, fiber bundles 257, and clumps of fibers 255 that are bonded together to form an open pore network. This open pore network further has a highly uniform pore arrangement, due to the consistent physical characteristics of the fibers or fiber like structures. Channel wall 250 has a soot capture zone 252 for capturing particulate matter and passing filtered gas into the gas-phase zone 254. The gas-phase zone also has a highly uniform pore structure, although the pore structure may be different than the pore structure in the soot capture zone 202. As exhaust gas passes through the gas-phase zone, pollutant molecules react with catalyst, forming less harmful gases. The surface adjacent the outlet channel has a pore structure similar to the soot capture zone, however is used primarily for structural support of the channel wall 250. In another example, a different catalyst may be disposed in the outlet side 256 as opposed to the catalyst in the gas-phase zone 254. In such a case, the outlet side 256 would act as a second gas-phase zone in the multifunction filter.

Referring now to FIG. 8, and scanning electron microscope (SEM) image of a channel wall 275 illustrated. Channel wall 275 is a cross-sectional view showing an inlet channel 276 and an outlet channel 284. The channel wall 275 is a bonded fibrous structure 276, having individual fibers 288, fiber bundles 284, and fiber clumps 289 bonded together in an open pore network. Although wall 275 uses fibers, it will be understood that other materials may be used to effect the functionality of fiber. For example, fiber-like structures may be introduced in an extrusion mix, with fiber-like structures formed during the sintering process. Accordingly, for the multifunction filter, it is the unique functional characteristics of the resulting bonded structure that is most meaningful, since there are many ways to commercially manufacture such a fibrous bonded structure. In operation, and exhaust gas is received from the inlet channel 276, which passes through the soot capture zone 277, where soot captures at or near the surface. The filtered gas continues through to the gas-phase zone 279, where gas molecules react with catalyst to form less harmful materials. The gas is then exhausted into outlet channel 284. The outside wall 281 provides additional structural integrity for the channel wall 275. As illustrated, the soot capture zone 277 has a highly uniform pore structure, but is different than the highly uniform pore structure in the gas-phase zone 279.

In manufacturing the multifunction filter for channel wall 275, mullite fibers were mixed with approximately 44 micron (325 mesh) particle size carbon as a pore former, colloidal silica, organic and inorganic binders and plasticizers, along with water. The mixture was aggressively and thoroughly mixed to an extrudable rheology. A piston/ram extruder was used to extrude a green substrate at 200 cells per square inch. The green substrate was dried in an RF oven, and then heated to about 1000 degrees Celsius for approximately 28 hours to burn out organic materials, and sintered at 1500 degrees Celsius for about one hour. After cooling, the multifunction filter can be coated with washcoat, have one or more catalysts applied, and be secured into a can, canister, or other container. Although a specific recipe for manufacturing a multifunction filter is described, it will be appreciated that many other fibers, fiber precursors, pore formers, plasticizers, bonding agents or precursors or fluids may be used. It will also be appreciated that other types of machines and processes may be used for mixing, extruding, drying, and sintering.

Referring now to FIG. 9, another cell wall 300 is illustrated. Cell wall 300 shows a cell wall loaded with washcoat and catalyst. Accordingly, fibers 306 are heavily loaded with washcoat and one or more types of catalyst. Even though the fibers, fiber bundles, and fiber clumps are heavily loaded with washcoat and catalyst, an effective soot capture zone 302 is present, and the gas-phase zone 304 allows for relatively unrestricted flow. In this way, even when fully loaded with catalyst and washcoat, a highly efficient multifunction filter is provided, with both excellent back pressure characteristics and effective emission control. It will be appreciated that washcoat and catalyst loading will be determined according to application specific requirements, including the level of conversion required within the filter, the size of the filter, the expected flows, and the expected life. Generally, the need for heavier catalyst loading will increase as more demanding emission requirements come into effect. The multi-function filter may be loaded with washcoat and catalyst at a loading rate of 10 grams per cubic foot, 20 grams per cubic foot, and 30 grams per cubic foot or more. In some instances, washcoat and catalyst loadings of 10 to 400 grams per cubic foot may be necessary. It will be appreciated that heavier catalyst loadings may be desirable to support multiple catalysts, to support conversions that consume or degrade catalyst, or to allow for more efficient conversions for slower reactions. By enabling a heavier loading of catalyst, the multifunction filter allows a single substrate to perform functions previously implemented only in multiple substrates in multiple devices. Importantly, even with these heavy load requirements, the resulting multifunction filter may operate with an impact on back pressure that is 0% to 50% increase over the back pressure of the filter without the washcoat and catalyst. This means, that even when fully loaded with washcoat and catalyst, the multi-function filter does not cause an undue backpressure to the engine. In this way, the overall engine system is able to maintain fuel efficiency and meet performance goals, even when the multifunction filter is heavily loaded.

Referring now to FIG. 10, a general process for using a multifunction filter is illustrated. In process 325 exhaust gas is received from an internal combustion engine as shown at block 326. In some cases, a gas-chemistry additive may be added as shown at 327. This additive is mixed with exhaust gas to form a material that is more easily reacted, filtered, or catalyzed within the multifunction filter 329. The gas is received into the multifunction filter 329 where a soot collection zone 331 first captures soot or other particles or particulate matter. The filtered gas is then passed into a gas-phase zone as shown at block 333. In gas-phase zone 333, pollutant gas molecules contact catalyst, and react to form less harmful materials. The filtered and reacted gas is then exhausted as shown at 335. It will be appreciated that gas reactions may start as soon as there is contact between the gas phase species and the solid phase catalyst. Depending on the flow rates, flow patterns, and turbulence, the reaction can be pore diffusion limited, mass transfer limited, or chemical concentration limited.

FIG. 11 shows a multifunction filter 400 having a single bonded fibrous substrate 402. The fibrous substrate 402 is heavily loaded with washcoat and catalyst as shown at block 404. Although the particular level of loading is application-specific, loads of 10 to 400 grams per cubic foot or more may be advantageously used. The multifunction filter 452 also has a set of soot collection zones 406, typically positioned on the surface walls for inlet channels of the filter. The multifunction filter 402 also has a set of gas reaction zones 408. These gas reaction zones are typically inside the channel walls of the multifunction filter. Prior to washcoat and catalyst loading, the fibrous substrate 402 typically has a porosity of about 55% to about 70%. It will be appreciated other porosities may be selected according to application needs. Importantly, loading or unloading soot from the soot collection zone has an insignificant channeling effect.

Referring now to FIG. 12, a process of making a multifunction filter is illustrated. Process 425 uses an extrusion process to extrude a honeycomb filter substrate as shown in block 428. This honeycomb substrate has a fiber arrangement on the surface walls particularly constructed to have a highly uniform pore structure for collecting target particular matter as shown at block 430. In this way, specific fiber diameters, sizes of pore formers, and amounts of organic material are selected to construct a pore structure for the target particular matter. Fibers are also arranged inside the walls to form a uniform open, inter-connected pore network for facilitating gas contact with the catalyst as shown at block 431. The fibrous substrate is made into a wallflow structure by plugging every other hole at each end as shown in block 432. The green substrate is dried and sintered into a bonded fibrous block as shown in 436. The substrate is then loaded with a heavy load of washcoat and catalyst as shown in block 438. In one example, the loading of washcoat and catalyst may exceed even 30 grams per cubic foot.

Referring now to FIG. 13, another wallflow multifunction filter 450 is illustrated. Multifunction filter 450 has a bonded fibrous substrate 452 as previously discussed. The multifunction filter 452 has a set of soot collection zones 465 arranged to capture soot in a highly uniform arrangement of pores. The multifunction filter 452 also has a set of gas-phase reaction zones. Here, the filter has multiple zones, with each zone having a catalyst for reacting a different pollutant gas. For example, zone 460 has a washcoat and catalyst for reacting a first pollutant gas, while zone 461 has a different catalyst for reacting another pollutant gas. Accordingly, an inlet gas 454 is filtered through one or more soot collection zones 465 and then received into the gas-phase reaction zones. Each zone reacts a different pollutant gas, thereby exhausting a filtered and dual reacted gas 456.

FIG. 14 shows a process 475 for manufacturing the multifunction filter 450 illustrated in FIG. 13. Process 475 extrudes the fibrous honeycomb filter substrate as shown in block 477. The extrusion process arranges fibers in the soot collection zone 479, as well as fibers in the gas-phase zone 481. Every other hole is plugged to form a wallflow structure 483, and the block is dried and sintered into a bonded fibrous substrate. A washcoat may be applied to the entire substrate, and then a first catalyst is applied through the inlet channels as shown at block 487. A second catalyst may be applied through the outlet channels as shown in block 489. In this way, a soot collection zone is at or near the surface of inlet channel walls, a first gas-phase zone exists inside channel walls, and a second gas-phase zone exists at a or near the outlet channel wall. It will be appreciated that other processes may be used for applying washcoat and catalyst to a bonded fibrous substrate.

With reference to FIGS. 1 through 14, a general multifunction filter has been described. This multifunction filter is intended to be adapted to particular and specific emission control requirements. For example, the multifunction filter may have its soot collection zone constructed for capturing one or more specific particle sizes, while the gas-phase zone may be arranged to support the loading of a specific washcoat and catalyst. Accordingly, the multifunction filters described in FIGS. 1 through 14 should not be limited to any particular structure, engine, fuel type, particular matter, or catalyst.

While particular preferred and alternative embodiments of the present intention have been disclosed, it will be appreciated that many various modifications and extensions of the above described technology may be implemented using the teaching of this invention. All such modifications and extensions are intended to be included within the true spirit and scope of the appended claims.

Claims

1. A multi-function wallflow filter, comprising: an arrangement of bonded fiber structures forming inlet and outlet channels that are separated by respective channel walls;a soot capture zone on at least some of the channel walls constructed to enable a highly uniform loading of soot;a gas-conversion zone inside at least some of the channel walls constructed to enable a highly uniform loading of a gas conversion catalyst;a catalyst in the gas-conversion zone for converting an undesirable exhaust gas to a more desirable exhaust gas.

2. The multi-function filter according to claim 1, wherein the soot capture zone comprises the bonded fiber structures arranged to form a highly uniform set of pores that are exposed at the surface of the channel walls of the multi-function filter.

3. The multi-function filter according to claim 1, wherein the gas-conversion zone comprises the bonded fiber structures arranged to form a highly uniform set of pores inside the channel walls of the multi-function filter.

4. The multi-function filter according to claim 1, wherein the bonded fiber structures are one selected from the group consisting of: individual fibers bonded at intersecting nodes, fiber bundles cooperating with each other or individual fibers, and elongated polycrystalline fiber-like structures.

5. The multi-function filter according to claim 1, wherein the bonded fiber structures have a fiber composition comprising a metal, a ceramic, SiC, AlO3, or mullite.

6. The multi-function filter according to claim 1, wherein the channels are arranged in a honeycomb pattern.

7. The multi-function filter according to claim 1, wherein the channels are extruded in a honeycomb pattern.

8. The multi-function filter according to claim 1, wherein the soot capture zone consists of side walls of inlet channels.

9. The multi-function filter according to claim 1, wherein the soot capture zone comprises a cake filter on the side wall of respective inlet channels.

10. The multi-function filter according to claim 1, wherein the soot capture zone extends into the channel wall.

11. The multi-function filter according to claim 1, wherein the soot capture zone comprises side walls of inlet channels, and the side walls further comprise fibers arranged according to frictional contact with die openings of an extrusion machine.

12. The multi-function filter according to claim 1, wherein the gas-conversion zone comprises an open cell network arranged to generate a tortuous flow path for an exhaust gas.

13. The multi-function filter according to claim 1, wherein the gas-conversion zone comprises a substrate structure of bonded fibers or fiber-like structures.

14. The multi-function filter according to claim 1, wherein the gas-phase zone comprises more than about 20 grams/cu. ft. of the gas-conversion catalyst.

15. The multi-function filter according to claim 1, further comprising a second gas-conversion zone having a second gas-conversion catalyst.

16. The multi-function filter according to claim 15 wherein the first gas conversion zone is adjacent to the gas inlet of the multifunction filter and the second gas conversion zone is adjacent to the outlet of the multifunction filter.

17. The multi-function filter according to claim 15, wherein the first gas conversion zone is inside at least some of the channel walls, and the second gas conversion zone comprises side walls of at least some of the outlet channels.

18. The multi-function filter according to claim 1, wherein the soot capture zone and the gas conversion zone coexist in the same area of the multi-function filter.

19. An emission control system for an internal combustion engine, comprising: an inlet for receiving an exhaust gas, the exhaust gas comprising particulate matter and an undesirable pollutant gas;a fibrous substrate comprised of an organized arrangement of bonded fiber-structures for receiving the exhaust gas;a particulate matter filtering zone on the fibrous substrate for collecting the particulate matter;a gas conversion zone in the fibrous substrate that is loaded with a gas-conversion catalyst selected to convert the pollutant gas to a more desirable gas; andan engine control system for adjusting the internal combustion engine according to measured performance.

20. The emission control system according to claim 19, further including a second gas conversion zone in the fibrous substrate that is loaded with a second gas-conversion catalyst selected to convert a second pollutant gas to a more desirable gas.

21. The emission control system according to claim 19, further including a regeneration catalyst in the particulate matter filtering zone for assisting in conversion of soot during a regeneration process

22. The emission control system according to claim 19, wherein the fibrous substrate is constructed from individual fibers bonded at intersecting nodes; fiber bundles cooperating with each other or individual fibers; or elongated polycrystalline fiber-like structures.

23. A multi-function filter assembly, comprising: an arrangement of bonded fiber structures forming a substrate;a single can for holding the substrate, the can having an inlet and an outlet;a plurality of input and output channels in the substrate and separated by respective channel walls to form a wall-flow arrangement;a washcoat material disposed in the filter substrate; anda catalyst material disposed on the washcoat.

24. The emission control system according to claim 23, wherein the substrate is constructed from individual fibers bonded at intersecting nodes; fiber bundles bonded to other fiber bundles or individual fibers; or elongated polycrystalline fiber-like structures bonded together.

25. The multi-function filter assembly according to claim 23, wherein the substrate exhibits an insignificant level of channeling effect during soot loading.

26. The multi-function filter assembly according to claim 23, wherein the substrate exhibits an insignificant level of channeling effect during soot unloading.

27. The multi-function filter assembly according to claim 23, wherein the washcoat and catalyst, in the aggregate, are loaded to more than 10 gram/cu. ft in the substrate.

28. The multi-function filter assembly according to claim 23, wherein the washcoat and catalyst, in the aggregate, are loaded to more than 30 gram/cu. ft in the substrate.

29. The multi-function filter assembly according to claim 23, wherein the washcoat and catalyst, in the aggregate, are loaded to more than 50 gram/cu. ft in the substrate.

30. The multi-function filter assembly according to claim 23, wherein the washcoat and catalyst, in the aggregate, are loaded to up to 400 gram/cu. ft in the substrate.