Patent Publication Number: US-2011072805-A1

Title: Electrically heated diesel oxidation catalyst

Description:
BACKGROUND 
     Embodiments described herein relate to a system, method and device for heating exhaust gas. More specifically, embodiments described herein relate to a system, method and device for heating exhaust gas to create a regeneration event at a diesel particulate filter. 
     Exhaust gas aftertreatment systems in diesel vehicles are located downstream of the engine for treating exhaust gases emitted from the engine. The aftertreatment systems typically include a diesel oxidation catalyst, and a diesel particulate filter. Particulate matter from the exhaust gas accumulates on the diesel particulate filter, and if left unchecked, can create a back pressure in the aftertreatment system. 
     A regeneration event is the periodic oxidation of the collected particulate matter in the aftertreatment system during routine diesel engine operation. When the diesel particulate filter of the exhaust system experiences a build-up of particulate matter, the particulate matter is oxidized to “regenerate” the filter. Regeneration is typically initiated by increasing engine load and activating a post-injection of diesel fuel into the exhaust stream. This post-injection provides sufficient heat to oxidize the trapped particulate matter within the diesel particulate filter. 
     Exhaust gas is a relatively poor conductor of heat. As such, the loading of the engine must be increased to provide a sufficiently heated exhaust gas to initiate the regeneration downstream at the diesel particulate filter. During low speed and low load operation of the engine, the resulting exhaust gas may not have a sufficiently high temperature to initiate the regeneration. 
     SUMMARY 
     An exhaust gas aftertreatment system for a vehicle having an engine includes a fluid passageway extending from the engine to an ambient for fluidly communicating exhaust gas. A diesel particulate filter is disposed on the fluid passageway downstream of the engine. Disposed downstream of the engine and upstream of the diesel particulate filter is an electric diesel oxidation catalyst having a substrate. A first electrode and a second electrode are attached to the electric diesel oxidation catalyst. The first electrode selectively delivers current through the catalyst substrate to the second electrode to generate heat at the catalyst substrate. 
     A method of regenerating an exhaust aftertreatment system of an engine having a diesel particulate filter includes the steps of providing a fluid passageway from the engine to an ambient, providing a substrate upstream of the diesel particulate filter, and heating the substrate electrically. The method of regeneration also includes the steps of heating the exhaust gas flowing through the heated substrate, and delivering the heated exhaust gas to the diesel particulate filter to initiate regeneration. 
     An electric diesel oxidation catalyst for an exhaust aftertreatment system of an engine includes a housing that substantially encloses a substrate. The housing has an inlet and an outlet configured for permitting a flow of exhaust gas through the housing. A first electrode extends through the housing and is configured for providing an electric current to the substrate. A second electrode extends from the housing and is configured for receiving the electric current from the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of an exhaust aftertreatment system having an electric diesel oxidation catalyst located downstream of an engine. 
         FIG. 2  is a schematic indicating the direction of flow of exhaust gas through the electric diesel oxidation catalyst. 
         FIG. 3  is a section view of the electric diesel oxidation catalyst taken along line A-A of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-3 , an exhaust gas aftertreatment system is indicated generally at  10 , and has an exhaust pipe assembly  12  extending from an engine  14  to an outlet  16 , such as the outlet to an ambient  18 . The exhaust pipe assembly  12  forms a fluid passageway  20  for the flow of exhaust gas F from the engine  14  to the ambient  18 . 
     A first portion  22  of the exhaust pipe assembly  12  extends from the engine  14  to an electric diesel oxidation catalyst (EDOC)  24 . A second portion  26  of the exhaust pipe assembly  12  extends from the EDOC  24  to a diesel oxidation catalyst (DOC)  28 , which is upstream of diesel particulate filter (DPF)  30 . A third portion  27  of the exhaust pipe  12  assembly extends from the DPF  30  to the outlet  16 . Other portions of the exhaust pipe may be disposed between various components on the aftertreatment system  10 , such as between the engine  14  and an exhaust brake  29 , between the exhaust brake and the EDOC  24 , or between the DOC  28  and the DPF  30 . 
     The DPF  30  is a filter constructed from a very high temperature resistant material. The DPF  30  catches and holds particulate matter entrained within the exhaust gases discharged into the exhaust aftertreatment system  10 . The DPF  30  is periodically regenerated to limit increases in exhaust aftertreatment system  10  back pressure and to maintain engine  14  efficiency. 
     The DOC  28  is a flow-through device that includes a substrate, typically a ceramic or a metal covered with a catalyst. As the exhaust gases F flow through the DOC  28 , carbon monoxide, gaseous hydrocarbons and liquid hydrocarbon particles (unburned fuel and oil) are oxidized, thereby reducing emissions. 
     Upstream of the DPF  30  and the DOC  28  is the EDOC  24 . The EDOC  24  has a housing  32  that substantially encloses a substrate  34  having a structure that permits the flow of exhaust gas F through the substrate and that is distributed within the cross-section of the EDOC, for example a grid-shape, a swirl-shape, a honeycomb-shape, a circuitous-shape, a mesh-shape, or any other shape. The substrate  34  is made of metal, however other highly conductive materials are possible. 
     The housing  32  may be generally cylindrical or have any other shape that permits the flow of exhaust gas F from an inlet  36  to an outlet  38  and through the substrate  34 . The first portion  22  of the pipe assembly  12  provides the fluid passageway  20  for the flow of exhaust gas F into the EDOC  24  at the inlet  36 , and the second portion  26  of the pipe assembly provides the fluid passageway for the flow of exhaust gas F out of the EDOC at the outlet  38 . The housing  32  of the EDOC  24  may be metal, however other materials are possible. 
     A first electrode  40  is electrically connected to a power source on the vehicle, such as the engine  14 , with a first transmission wire  42 . The first electrode  40  extends through the housing of the EDOC  24 , and may extend generally the radius or generally half the width of the EDOC, however other lengths of extension into the EDOC are possible. The first electrode  40  contacts the substrate  34  generally at the cross-sectional center C of the EDOC  24  and the substrate. An isolator sleeve  44  is disposed about the first electrode  40  to prevent the contact of the first electrode with the housing  32  of the EDOC  24 . The isolator sleeve  44  co-extends with the first electrode  40  less than the entire length of the first electrode  40  so that a portion of the first electrode is exposed. When current is run to the first electrode  40 , the current is isolated from the housing  32  and the current is directed to the general cross-sectional center C of the EDOC  24 . 
     A second electrode  46  extends from the housing  32  of the EDOC  24  and is also electrically connected to the engine  14  with a second transmission wire  48 . While the second electrode  46  extends from the housing, it is also possible that the second electrode  46  may contact the substrate  34 . 
     The first electrode  40  does not contact the second electrode  46 , but instead the electrodes are spaced from each other and separated by the substrate  34  within the EDOC  24 . The electrodes  40 ,  46  may also be spaced from each other a distance D along the length of the EDOC  24 . The first electrode  40  delivers current from the engine  14  through the substrate  34  to the second electrode  48 . It is possible that the selective introduction of current into the EDOC  24  can be at the activation of a user or an automatic activation, such as by an engine control module. 
     When the current flows from the first electrode  40 , through the substrate  34 , and to the second electrode  48 , heat is created at the substrate. When current is delivered to the general cross-sectional center C of the substrate  34 , the heat created is generally uniform across the substrate  34 . The exhaust gases F that flow through the EDOC  24  are heated by the substrate  34  and the housing  32 , and the heated exhaust gases flow to the DOC  28  and to the DPF  30 . At the DPF  30 , the heated exhaust gases F provide sufficient heat to initiate regeneration of the DPF. 
     While the aftertreatment system  10  of  FIG. 1  has the EDOC  24  located upstream of the DOC  28 , it is possible that if the EDOC  24  achieves a sufficient exhaust gas temperature, that the aftertreatment system may include only the EDOC with no downstream DOC. Further, it is possible that more than one EDOC  24  can be used to increase the exhaust gas temperature. 
     By electrically heating the EDOC  24 , the DPF  30  on the aftertreatment system  10  can be regenerated without having to increase the loading on the engine  14 , which allows regeneration at low engine speed and low engine loading.