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Emission control system using a multi-function catalyzing filter

This application is related to 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.

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.

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.

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;