Patent Application
20060242951
This disclosure pertains generally to refractory materials, and more particularly, to systems and methods for securing high-temperature refractory materials within an exhaust system.
Some exhaust system components are subjected to extreme environmental conditions, including high temperatures. Consequently, a variety of materials have been developed to withstand these high-temperatures, while performing important functions within the exhaust system. Such materials include a number of different ceramics and composite foams, which may form important components of exhaust system combustion burners.
Although ceramic and composite foams may be particularly well-suited for some conditions, including high temperatures, such foams have some disadvantages. For example, some ceramic foams may be brittle, and over time, the brittle foams may be damaged by repeated mechanical stress. In addition, the high temperature of the foam may damage adjacent structures, including foam retention devices, which may be less resistant to thermal damage. Damage to either the foam or adjacent foam retention devices may cause foam loosening and ultimate device failure. Therefore, improved foam retention devices are needed to prevent damage to the brittle foams and to withstand operational environmental conditions.
One ceramic support device is described in U.S. Pat. No. 6,077,483, issued to Locker on Jun. 20, 2000 (hereinafter “the '483 patent”). The '483 patent describes a honeycomb ceramic catalyst support. The support includes a substrate skin surrounding a catalyst core. The substrate skin is surrounded by a ceramic barrier coating.
Although the catalyst support of the '483 patent may provide suitable support for some materials, the support of the '483 patent has several disadvantages. The support of the '483 patent may not adequately protect materials that may be disposed between the catalyst and the exhaust system enclosures. As a result, these materials may degrade when exposed to high temperatures, as produced by exhaust system combustion burners. In addition, the support of the '483 patent may not provide adequate protection to brittle foam materials, as used in some exhaust system components.
The present disclosure is directed to overcoming one or more of the disadvantages of the prior art material retention devices.
One aspect of the present disclosure includes a combustion burner refractory material retention system. The system may include a tubular enclosure having a first section and a second section, wherein the first section has an internal cross-sectional area that is less than an internal cross-sectional area of the second section. A refractory material body may be disposed within the tubular enclosure second section. A first support layer may be disposed on a surface of the refractory material body, and at least one outer support layer may be disposed between the refractory material body and a wall of the tubular enclosure second section. The first support layer may form an insulating barrier between the refractory material body and the outer support layer. A cross-sectional area of the combined refractory material body and first support layer may be at least as large as the internal cross-sectional area of the tubular enclosure first section.
A second aspect of the present disclosure includes a method for securing a refractory material within an exhaust system burner unit. The method may include selecting a refractory material body, applying a first support layer to a surface of the refractory material body, applying at least one outer support layer to a surface of the first support layer, and positioning the refractory material body, first support layer, and at least one outer support layer within a burner tubular enclosure. The tubular enclosure may have a first section which has a first internal cross-sectional area and a second section which has a second internal cross-sectional area, wherein the first internal cross-sectional area is less than the second internal cross-sectional area. A cross-sectional area of the combined refractory material body and first support layer is at least as large as the first internal cross-sectional area.
A third aspect of the present disclosure includes a work machine. The work machine may include an engine, an exhaust system configured to receive an exhaust gas stream produced by the engine, and a burner unit configured to heat the exhaust gas stream. The burner unit may include a tubular enclosure having a first section and a second section, wherein the first section has an internal cross-sectional area that is less than an internal cross-sectional area of the second section. A refractory material body may be disposed within the tubular enclosure second section. A first support layer may be disposed on a surface of the refractory material body, and at least one outer support layer may be disposed between the refractory material body and a wall of the tubular enclosure second section. The first support layer may form an insulating barrier between the refractory material body and the outer support layer. A cross-sectional area of the combined refractory material body and first support layer may be at least as large as the internal cross-sectional area of the tubular enclosure first section.
A fourth aspect of the present disclosure includes a work machine. The work machine may include an engine, an exhaust system configured to receive an exhaust gas stream produced by the engine, and a burner unit configured to heat the exhaust gas stream. The burner unit may include a tubular enclosure having a first section and a second section, and a refractory material body may be disposed within the tubular enclosure second section. A first support layer may be disposed on a surface of the refractory material body, and at least one outer support layer may be disposed between the refractory material body and a wall of the tubular enclosure second section. The outer support layer may be insulated from the refractory material body and an interior of the tubular enclosure.
Catalyst units 20, 24 and DPF 22 may include any suitable catalyst and/or filter type. For example, catalyst units 20, 24 may include, for example, oxidation catalysts, three-way catalysts, selective catalytic reduction system catalysts, and/or any other suitable catalyst. Further, exhaust system 16 may include additional catalysts, filters, additive supply devices, and/or other suitable exhaust system component, such as fuel-injectors, systems for adding oxidants or reductants, air-intake valves, exhaust valves, temperature sensors, gas sensors, forced-induction systems, and/or any other suitable exhaust system component.
Burner unit 26 may include a number of suitable burner unit types. For example, burner unit 26 may include a number of different fuel combustors, which may be configured to heat exhaust gas stream 14 to a selected temperature. Burner unit 26 may produce heat by combustion of a number of different fuels, such as diesel fuel or gasoline. Further, the fuel may be supplied to burner unit 26 using a number of suitable fuel-supply systems including, for example, various valves, injectors, atomizers, and/or any other suitable fuel-supply system. In addition, the fuel may be mixed with air provided by any suitable air supply system to facilitate combustion.
Burner unit 26 may be configured to heat exhaust gas stream 14 and one or more components of exhaust system 16 to a selected temperature. The desired temperature may be selected to facilitate one or more exhaust system functions. Such exhaust system functions may include, for example, control of one or more catalyst operations or regeneration of one or more exhaust system components. In one embodiment, burner unit 26 may be configured to heat DPF 22 and/or one or more downstream catalysts 24 to facilitate regeneration of DPF 22 and/or one or more downstream catalysts 24. For example, in one embodiment, burner unit 26 may be configured to heat DPF 22 to a temperature that may facilitate removal of soot and/or other deposits from DPF 22. In one embodiment, burner unit 26 may be configured to heat DPF 22 and/or other components of exhaust system 16 to temperatures up to 650° Celsius, to temperatures up to 900° Celsius, to temperatures up to 1200° Celsius, to temperatures up to 1500° Celsius, or to temperatures up to 1700° Celsius.
As shown in
As shown, burner unit 26 is positioned next to exhaust passage 18, and a portion of tubular member 28 may be disposed within exhaust passage 18 to facilitate heating of exhaust gas stream 14. It some embodiments, a larger portion of tubular member 28 and/or other components of burner unit 26 may be disposed within exhaust passage 18. For example, in one embodiment, the portion of tubular member 28, which includes refractory material unit 30, may be disposed within exhaust passage 18.
Refractory material body 32 may include a number of suitable materials. For example, refractory material body 32 may be produced from a number of suitable metals, ceramics, and/or composite materials. The specific materials may be selected based on a variety of properties including, for example, thermal conductivity, heat resistance, strength, fracture toughness, brittleness, cost, machinability, corrosion resistance, and/or any other physical, chemical, and/or thermal property.
In one embodiment, refractory material body 32 may be produced from a material that is able to withstand high temperatures without melting or structural degradation. For example, refractory material body 32 may be produced from a number of different ceramic, metal, and/or composite materials configured to withstand temperatures of up to 1000° Celsius, up to 1200° Celsius, up to 1400° Celsius, up to 1600° Celsius, or up to 1800° Celsius.
In one embodiment, refractory material body 32 may include one or more ceramic materials. Numerous suitable ceramics may be selected to produce all or part of refractory material body 32, and the specific ceramic may be selected based on a number of factors including, for example, machinability, heat resistance, and/or any desired physical property. Suitable ceramics may include, for example, silicon carbide (SiC), yittria-stabilized zirconia, yittria-stabilized zironia alumina, cordierite, kyanite, sodium zirconium phosphate, mullite zirconia, lithium silicate, and/or high purity alumina.
In one embodiment, refractory material body 32 may include one or more refractory metals. For example, suitable refractory metals may include niobium, tantalum, tungsten, rhenium, molybdenum, as well as other transition metals. Further, various combinations of metals may be selected to produce a suitable refractory material body 32. In addition, refractory material body 32 may include one or more ceramics produced from one or more refractory metals. For example, suitable ceramics may include various oxides, borides, carbides, and/or silicides of one or more metals. Further, refractory material body 32 may include a variety of suitable composite materials, including combinations of metals and/or ceramics.
Refractory material body 32 may include a number of suitable macroscopic configurations. For example, refractory material body 32 may include a foam material, a solid material, or a solid material with one or more openings. The specific configuration may be selected based on desired physical properties including strength, porosity, thermal conductivity, and/or density. Further, the configuration may also be selected to control the flow of air and/or heat through refractory material body 32.
In one embodiment, refractory material body 32 may include a foam material. A variety of suitable foam structures are available, and the specific foam composition and structure may be selected based on desired weight, cost, thermal conductivity, strength, surface area, fracture resistance, desired application, and/or other physical, chemical, and/or thermal properties. In one embodiment, the foam material may include an open-cell structure configured to facilitate the flow of gases and/or heat through the material. Further, the foam structure may be configured to facilitate dispersion of a flame produced within burner unit 26. For example, in one embodiment, the foam may include a reticulated structure, which may provide a tortuous flow path through the material, whereby the tortuous flow path may disperse a flame produced within burner unit 26.
Suitable foam materials may be selected based on desired material properties. For example, in one embodiment, a ceramic foam may be selected based on a desired degree of porosity. In one embodiment, the ceramic foam may have a porosity between about 60% and about 95% by volume. Further, in one embodiment the ceramic foam may have a porosity of at least 80% by volume. Any suitable material may be selected as along as the material has a desired heat resistance, thermal conductivity, and provides a desired degree of flame dispersion.
Suitable foam materials may be produced using a number of processes. For example, suitable foam materials may be produced by depositing a ceramic material on a suitable preform. Suitable preforms may include, for example, reticulated polymer foams. The ceramic material may be deposited on the preform using a number of suitable processes, including physical vapor deposition (PVD), chemical vapor deposition (CVD), and/or chemical vapor infiltration (CVI) techniques, and the reticulated polymer foam may be pyrolized after deposition of the ceramic material to leave a porous ceramic foam. Refractory material body 32 may be produced using any suitable process as long as the process provides the desired material structure and properties.
As noted above, one or more supporting layers 34, 36 may be disposed on a surface of refractory material body 32. In one embodiment, the one or more supporting layers 34, 36 may include at least two layers. Further, as shown in the embodiment of
First supporting layer 34 may include a number of suitable materials. For example, first supporting layer 34 may include a number of suitable ceramics, ceramic-fiber mats, refractory metals, and/or composite materials. The specific material may be selected based on the material's thermal conductivity, stability at high temperatures, strength, thermal expansion properties, ability to bond with refractory material body 32 or outer supporting layers 36, and/or any other suitable properties. Any suitable material may be selected for first supporting layer 34.
In one embodiment, first supporting layer 34 may be selected to have a certain thermal expansion coefficient. For example, first supporting layer 34 may be selected to have thermal expansion properties that are similar to the thermal expansion properties of refractory material body 32. Furthermore, first supporting layer 34 may be selected to have thermal expansion properties which may minimize thermal stresses exerted by first supporting layer 34 on refractory material body 32.
In addition, first supporting layer 34 may be selected based on certain mechanical properties. For example, first supporting layer 34 may be selected to have a certain strength, density, and/or fracture toughness. First supporting layer 34 may be configured to protect refractory material body 34 from vibrations and/or impact during use. Further, first supporting layer 34 may be configured to absorb compressive forces produced by tubular member 28 and/or outer supporting layers 36 and to prevent damage to refractory material body 32.
Further, first supporting layer 34 may be selected to insulate outer supporting layers 36 from refractory material body 32 and/or gases located within tubular member 28. In one embodiment, first supporting layer 34 may be selected to have a certain thermal conductivity. Particularly, first supporting layer 34 may be produced from a material having a lower thermal conductivity than a material used to produced refractory material body 32.
Additionally or alternatively, first supporting layer 34 may include a ceramic material. The specific ceramic material may be selected based on desired strength, thermal conductivity, cost, and compatibility with refractory material body 32. For example, in one embodiment, first supporting layer 34 may include the same ceramic material used to produce refractory material body 32. Any suitable ceramic material may be selected.
The specific ceramic used to produce first supporting layer 34 may be selected based on the desired structure and/or physical properties. For example, in one embodiment, the ceramic may be selected to have a desired strength, flexibility, compressibility, and/or ductility. Further, the specific ceramic may be selected to have a certain porosity. For example, in one embodiment, refractory material body 32 and first supporting layer 34 may both include ceramic materials, and the ceramic included in first supporting layer 34 may have a porosity which is lower than the porosity of refractory material body 32. The lower porosity ceramic included in first supporting layer 34 may produce desired physical properties, including a certain strength, which may provide protection and support for refractory material body 32. In one embodiment, first supporting layer may include a ceramic having a porosity less than 20% by volume, less than 15% by volume, less than 10% by volume, or less than 5% by volume.
First supporting layer 34 may be produced using a number of suitable processes. For example, in one embodiment, refractory material body 32 may include a ceramic foam material, such as SiC, and first supporting layer 34 may be produced from a ceramic precursor powder, such as a SiC precursor. The powder may be combined with one or more liquids to produce a slurry, which may be applied to a surface of refractory material body 32.
The slurry may be applied to a surface of refractory material body 32 using a number of suitable techniques. For example, the slurry may be applied by dipping refractory material body 32 into the slurry, by brushing the slurry onto certain sections of refractory material body 32, or by applying the slurry with a spatula or similar instrument. Further, if refractory material body 32 includes a foam material, the slurry may infiltrate the pores of the foam to a certain depth, thereby binding to refractory material body 32. For example, in one embodiment, the slurry may infiltrate refractory material body 32 to a depth between about 1 mm and about 10 mm.
Numerous other suitable processes may be selected to apply first supporting layer 34 to refractory material body 32. For example, first supporting layer 34 may be produced using a variety of suitable processing techniques including, for example, tape casting and/or tape calendaring. In tape casting and tape calendaring, a ceramic material may be produced as a strip or patch of material, which may be applied to a surface of refractory material body 32. Alternatively or additionally, the material used to produce first supporting layer 34 may be bonded to refractory material body 32 using a variety of high-temperature adhesives, such as Ceramacast 673N SiC based casting material or Ceramabond 813A alumina-silica paste, which are produced by Aremco.
Further, first supporting layer 34 may be produced using a number of suitable casting or coating materials. For example, as noted above, a variety of high-temperature adhesives may be applied to the surface of refractory material body 32. In one embodiment, an adhesive, casting material, high-temperature paint, and/or coating material may be applied to a surface of refractory material body 32, and the adhesive, casting material, high-temperature paint, and/or coating material may form first supporting layer 34. For example, suitable materials may include Aremco's Ceramcast 673N SiC based casting material or PyroPaint 634 SiC. The Ceramcast 673N or PyroPaint 634 SiC material may be applied to a surface of refractory material body 32 and optionally heat treated to form a suitable first supporting layer 34.
In one embodiment, it may be desirable to apply first supporting layer 34 to certain sections of refractory material body 32. Therefore, part of refractory material body 32 may be masked to expose only the surface to which first supporting layer 34 should be applied. In one embodiment, first supporting layer 34 may be applied only to a circumference of refractory material body 32.
After applying first supporting layer 34 to refractory material body 32, it may be desirable to further treat first supporting layer 34 and/or refractory material body 32. Further treatment may facilitate bonding of first supporting layer 34 to refractory material body 32. Additionally, further treatment may facilitate formation of a desired structure, composition, and/or physical or thermal properties within first supporting layer 34. In one embodiment, the treatment may include heat treatment of first supporting layer 34 and/or refractory material body 32.
First supporting layer 34 and refractory material body 32 may be heat treated using any suitable process. For example, in one embodiment, the heat treatment may include sintering the materials in an oven or furnace. The specific sintering conditions including, for example, ramp rate, hold time, and/or sintering temperature may be selected based on a number of factors, including the specific materials included in refractory material body 32 and first supporting layer 34, desired effects of the sintering process, and/or the material size. Any suitable heat treatment may be selected to produce a material having desired physical properties.
Refractory material unit 30 may also include one or more outer supporting layers 36. Outer supporting layers 36 may be configured to further insulate tubular member 28 from refractory material body 32, to prevent vibration of refractory material body 32, and to further secure refractory material body 32 within tubular member 28. Outer supporting layers 36 may include a single layer of material or may include multiple layers.
Outer supporting layers 36 may be produced from a number of suitable materials. For example, outer supporting layers 36 may include a number of suitable heat-resistant mats. The specific mat material may be selected based on desired physical properties including, for example, strength, heat resistance, specific heat, thermal expansion coefficients, flexibility, compressibility, and/or thermal conductivity. The mat material may also be selected based on manufacturability and/or cost.
In one embodiment, outer supporting layers 36 may include a heat-resistant mat including a refractory fiber material. A number of suitable refractory fiber materials may be selected including, for example, alumina silicate, aluminoborosilicate, and/or vermiculite. The mat may further include combinations of various refractory-fiber materials and/or other additives, such as binders and/or fillers.
The materials included in outer supporting layers 36 may be selected based on desired expansion during heating. For example, in one embodiment, outer supporting layers 36 may include an intumescent material, which may expand when heated. Further, expansion of an intumescent material may produce compressive forces on first supporting layer 34 and/or refractory material body 32, thereby preventing vibration or loosening of refractory material body 32. In another embodiment, outer supporting layer 36 may include a non-intumescent material, which may have little or no expansion at elevated temperatures. A non-intumescent material may be selected to prevent additional compression of refractory material body 32 during heating. For example, refractory material body 32 may be secured by first supporting layer 34 and outer supporting layers 36, and additional compressive forces may not be necessary. Further, in some embodiments, a non-intumescent material may be selected to prevent excessive compressive forces, which may damage refractory material body 32.
Tubular member 28 may include one or more shapes, which may facilitate retention of refractory material body 32 within a region of tubular member 28. For example, as shown in
In one embodiment, tubular member 28 and first supporting layer 34 may be configured to isolate outer supporting layers 36 from hot gases within tubular member 28. For example, in the embodiment of
Indentation 38 may have a number of suitable configurations. For example, in one embodiment, indentation 38 may be configured to deflect hot gas within proximal section 37. Particularly, indentation 38 may be configured to deflect hot gases away from outer supporting layer 36, thereby protecting outer supporting layer 36 from excessive heat produced within burner unit 26.
In another embodiment, tubular member 28 may further include one or more surface openings 40, which may provide fluid communication between outer supporting layers 36 and gases located outside of tubular member 28. Surface openings 40 may be positioned at any suitable location along tubular body 28. Further, surface openings 40 may be configured to facilitate convection and/or conduction of heat away from outer supporting layers 36, thereby reducing the temperature of outer supporting layers 36. Alternatively or additionally, surface openings 40 may be configured to cool first supporting layer 32 and/or peripheral regions of refractory material body 32. Cooling of first supporting layer 32 and/or certain regions of refractory material body 32 may also reduce the temperature of outer supporting layers 36.
It should be noted, that although tubular member 28, 28′ is shown as a cylindrical tube, a number of suitable shapes may be available for tubular member 28. For example, tubular member 28, 28′ may include a square, rectangular, or oval cross-sectional area. Further, refractory material body 32 and supporting layers 34, 36 may also include a number of suitable shapes, which may facilitate placement of refractory material body 34, 36 within tubular member 28.
For example,
The present disclosure provides a exhaust system refractory material retention system. The retention system of the present disclosure may be used to secure any exhaust system component that may be exposed to high temperatures.
The retention system of the present disclosure may include any refractory material 32, including ceramic foams used in exhaust system combustion burners. The ceramic foam may be covered with one or more supporting layers 34, 36. The supporting layers 34, 36 may be produced from a number of readily-available and cost-effective materials, while protecting the foam from vibration and impact during on-highway or off highway use.
In addition, the retention system of the present disclosure may prevent thermal damage to outer supporting layers 36. The system of the present disclosure may insulate outer supporting layers 36 from refractory material 32 and high-temperature gases within combustion burners. The system may also include peripherally located openings, which may improve cooling of outer supporting layers 36 by lower-temperature gases. Protection of outer supporting layer 36 may reduce or prevent degradation of outer supporting layers 36. In turn, refractory material 32 may be protected from loosening, thereby reducing device failure rates and replacement costs.
It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed systems and methods without departing from the scope of the disclosure. Other embodiments of the disclosed systems and methods will be apparent to those skilled in the art from consideration of the specification and practice of the embodiments disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.
