Patent Publication Number: US-2010111779-A1

Title: Exhaust treatment device

Description:
TECHNICAL FIELD 
     The present disclosure is directed to an exhaust treatment device and, more particularly, to an exhaust treatment device including a housing, at least a portion of which is double-walled. 
     BACKGROUND 
     Exhaust systems often include components that operate at relatively high temperatures. For example, exhaust after-treatment components, such as catalytic converters and particulate filters, often include an exhaust treatment material (e.g., the catalyst or the filter material) enclosed in a canister or housing. During operation, the canisters may not only experience relatively high temperatures, but may also transfer thermal energy to nearby objects. 
     For a number of reasons, it may be desirable to provide such high temperature exhaust treatment devices and yet not have the outer surfaces of such devices become excessively heated. One such reason may be to prevent heat damage of components installed nearby the canister. 
     Exhaust treatment devices have been developed with features for reducing the transfer of thermal energy to other objects. For example, U.S. Patent Application Publication No. 2007/0238008, issued to Hogan et al., discloses a heat shield for reducing transfer of heat from an exhaust treatment device to an undercarriage of the vehicle. 
     While the &#39;008 publication provides a heat shield for reducing heat transfer to other vehicle components, the shield does not reduce heat transfer to non-vehicle objects. In addition, while it may be desirable to reduce heat transfer to objects near the exhaust treatment device, it may also be desirable to retain heat within the exhaust treatment device, as many such devices operate well at elevated temperatures. With a heat shield on only one side, the device disclosed in the &#39;008 publication is not particularly well configured for retaining heat. 
     The present disclosure is directed at improvements in existing thermal transfer reduction technologies for exhaust treatment devices. 
     SUMMARY  
     In one aspect, the present disclosure is directed to an exhaust treatment device including an exhaust treatment material and a housing in which the exhaust treatment material is contained. The housing may include a double wall substantially surrounding the exhaust treatment material. The double wall may include an inner wall and an outer wall, the outer wall having an inner surface that is polished. 
     In another aspect, the present disclosure is directed to an exhaust treatment device including an exhaust treatment material and a housing in which the exhaust treatment material is contained. At least a portion of the housing may include a double wall, including an inner wall and an outer wall defining therebetween an enclosed space in which there is a substantial vacuum. 
     In another aspect, the present disclosure is directed to an exhaust treatment device including an exhaust treatment material and a housing in which the exhaust treatment material is contained. At least a portion of the housing may include a double wall, including an inner wall and an outer wall. The device may further include a layer of thermally reflective material affixed to an inner surface of the outer wall. 
     In another aspect, the present disclosure is directed to an exhaust system including an exhaust treatment device. The exhaust system may include an exhaust conduit configured to carry exhaust gases produced by an exhaust-producing engine, and an exhaust treatment device. The exhaust treatment device may include an exhaust treatment material and a housing in which the exhaust treatment material is contained. The housing may include a double wall substantially surrounding the exhaust treatment material, wherein the double wall includes an inner wall and an outer wall, the outer wall having an inner surface that is polished. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic, partial cross-sectional illustration of an exhaust system according to an exemplary disclosed embodiment. 
         FIG. 2  is a diagrammatic, cross-sectional illustration of an exhaust treatment device according to an exemplary disclosed embodiment. 
         FIG. 3  is a diagrammatic, cross-sectional illustration of an exhaust treatment device according to another exemplary disclosed embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 1  illustrates an exhaust system  10  including an exhaust treatment device  12 . Exhaust system  10  may include an exhaust conduit  14  configured to carry exhaust gases produced by an exhaust-producing engine  16 . Exhaust system  10  and engine  16  may be associated with a machine powered by engine  16 . Such machines may include mobile machines, such as vehicles (e.g., passenger vehicles, cargo trucks, construction equipment), or stationary machines, such as electrical power generation sets (e.g., an electric power generator driven by a combustion engine). Engine  16  may be any type of exhaust producing engine. For example, engine  16  may be a gasoline, diesel, or gaseous fuel burning engine. Alternatively, engine  16  could be an alternative fuel-burning engine (e.g., ethanol, biodiesel, etc.). 
     Exhaust treatment device  12  may be an after-treatment device. “After-treatment” is a term commonly used to refer to exhaust treatments, e.g., catalytic conversion or particulate filtration, that are carried out after the exhaust leaves the engine. Exhaust treatment device  12  may include an exhaust treatment material  18  and a housing  20  in which exhaust treatment material  18  may be contained. In some embodiments, exhaust treatment material  18  may include a catalyst. Exhaust treatment material  18  may include any kind of catalyst, including, for example, oxidation catalysts (e.g., a diesel oxidation catalyst or DOC), and/or a reduction catalyst (e.g., a selective catalytic reduction or SCR catalyst). In some embodiments, exhaust treatment material  18  may include a particulate filter. In certain embodiments, more than one exhaust treatment material may be included and/or combined. For example, housing  20  may contain both a catalyst and a particulate filter, or a catalytic particulate filter (e.g., a filter having a coating of catalytic material). 
     Exhaust treatment device  12  may have an inlet  22  at which the upstream side of exhaust conduit  14  connects to exhaust treatment device  12 , and an outlet  24  at which the downstream side of exhaust conduit  14  connects to exhaust treatment device  12 . At least a portion of housing  20  may include a double wall  26  including an inner wall  28  and an outer wall  30 . In some embodiments, double wall  26  may substantially surround exhaust treatment material  18 , as shown in  FIG. 1 . As also shown in  FIG. 1 , in some embodiments, double wall  26  may enclose all parts of exhaust treatment device  12  between inlet  22  and outlet  24 . 
     There are three main physical processes by which thermal energy is transferred in such double wall configurations. These three main processes are conduction, convection, and radiation. The disclosed exhaust treatment device may include features that address each of these processes. Exhaust treatment device  12  may include several features that limit the transfer of thermal energy from inner wall  28  of the double-walled structure to outer wall  30 . That is, exhaust treatment device  12  may be configured to reduce the transfer of heat from the inside of exhaust treatment device  12  to outer wall  30  of exhaust treatment device  12 . 
     In order to address thermal conduction, exhaust treatment device  12  may have very few physical contact points between outer wall  30  and inner wall  28 . In some embodiments, exhaust treatment device  12  may be elongated, as shown in  FIG. 1 , and may include contact points between inner wall  28  and outer wall  30  only at the ends of exhaust treatment device  12 . For example, as shown in  FIGS. 2 and 3 , housing  20  may include an elongated canister  32 , including an upstream end wall  34 , a downstream end wall  36 , and one or more substantially longitudinal walls  38  connecting upstream end wall  34  to downstream end wall  36 . In certain embodiments, longitudinal walls  38  may be double-walled with outer wall  30  being connected to canister  32  only at upstream end wall  34  and downstream end wall  36  of canister  32 , as shown in  FIG. 2 . In other embodiments, longitudinal walls  38 , as well as upstream end wall  34  and downstream end wall  36  may all be double-walled, as shown in  FIG. 3 , thereby fully enclosing canister  32  from inlet  22  to outlet  24 . 
     In some embodiments, inner wall  28  and outer wall  30  may define therebetween an enclosed space  40  in which there is a substantial vacuum. Space  40  may be evacuated to create a substantial vacuum in order to reduce/prevent heat convection. The substantial vacuum in space  40  may be created using any suitable method. 
     Thermal radiation may be reduced using thermal reflection. For example, an inner surface  42  of outer wall  30  may be configured to be thermally reflective. In some embodiments, inner surface  42  of outer wall  30  may be in order to reflect thermal energy. For purposes of this disclosure, the term “polished” shall refer to a metal surface finish that has a substantially glossy or shiny appearance and provides the surface with increased thermally reflective properties as compared to an unfinished, bare metal surface. In other embodiments, a thermally reflective material may be affixed to inner surface  42  of outer wall  30 . Thermally reflective material may be affixed to inner surface  42  of outer wall  30  using, for example, adhesive, fasteners, or other means of attachment. In some embodiments, the thermally reflective material may include a metal foil. In one exemplary embodiment, the thermally reflective material may include a thin layer of fiberglass cloth  44 , which may have an aluminized surface  46  (e.g., an aluminum foil), as shown in  FIG. 3 . Alternatively (or additionally), other thermally reflective materials may be used. In some embodiments, such materials may be coated onto inner surface  42  of outer wall  30  of canister  32 . 
     In some embodiments, a minimal amount of insulating material may be provided in space  40  between inner wall  28  and outer wall  30  (e.g., the aforementioned fiberglass cloth  44 ). In other embodiments, such insulating material may be omitted. 
     The various thermal energy transfer reduction features disclosed herein may be embodied in any number of combinations. For example, although the accompanying figures show  FIG. 2  having a partial double wall structure and  FIG. 3  having a full double wall structure and also a thermally-reflective insulation layer (i.e., fiberglass cloth  44  with aluminized surface  46 ), embodiments are contemplated that combine a partial double wall structure with a thermally-reflective insulation layer. Also, exhaust treatment device may have any suitable shape and size. While  FIG. 1  shows a cylindrical canister  32  having tapered end portions,  FIGS. 2 and 3  illustrate cylindrical canisters  32  having squared-off upstream and downstream end walls  34  and  36 . However, other shapes are contemplated, such as oval, polygonal, etc. cross-sections. 
     INDUSTRIAL APPLICABILITY 
     The disclosed exhaust treatment device may be applicable to any exhaust treatment system configured to treat the exhaust of an engine. The features of the disclosed exhaust treatment device may be applicable to any high temperature exhaust treatment device. For example, some applications may include housings for exhaust treatment devices such as particulate filters (e.g., diesel particulate filters (DPF&#39;s)), catalysts, mufflers, etc. Other exemplary applications may include hydraulics canisters. 
     The disclosed double wall structure of the disclosed exhaust treatment device may reduce the loss of thermal energy from the exhaust treatment device and, in doing so, may prevent transfer of excessive amounts of thermal energy (and consequent damage and/or other problems) to nearby machine components and/or other objects. In addition, reducing loss of thermal energy may facilitate maintaining the temperature within the exhaust treatment device at a higher level, which may be desirable for some exhaust treatment materials, e.g., catalysts or particulate filters. 
     In some embodiments, the disclosed double wall structure of the exhaust treatment device may substantially surround the exhaust treatment material. This may protect objects on all sides of the disclosed exhaust treatment device from the transfer of heat from the exhaust treatment device. For example, not only may the disclosed exhaust treatment device be configured to transfer a reduced amount of thermal energy to nearby undercarriage components of a vehicle, but it may also transfer a reduced amount of thermal energy to objects on the ground under the vehicle. 
     It will be apparent to those having ordinary skill in the art that various modifications and variations can be made to the disclosed exhaust treatment device without departing from the scope of disclosed embodiments. Other embodiments of the disclosed system will be apparent to those having ordinary skill in the art from consideration of the specification and practice of the systems disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosed concept being indicated by the following claims and their equivalents.