Abstract:
A reductant reservoir for an emission control system has a pump assembly with an intake adapted to withdraw reductant from the reservoir, a heating element associated with the pump assembly for heating reductant and an outlet for delivering heated reductant to the emission control system. A nozzle assembly ejects a portion of heated reductant into the reservoir to thaw frozen reductant.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to an emission control system for diesel and other lean-burn engines and, more particularly to an improved reductant storage system. Current emission control regulations necessitate the use of catalysts in the exhaust systems of automotive vehicles in order to convert regulated exhaust constituents such as carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx), produced during the operation of the engine, into unregulated exhaust gas. 
         [0002]    Vehicles equipped with diesel and lean-burn gasoline engines can offer the benefit of increased fuel economy, however, the control of NOx emissions in such systems is challenging due to the high content of oxygen in the exhaust gas. Selective Catalytic Reduction (SCR) catalysts, in which NOx is continuously reduced to nitrogen (N 2 ) over a catalyst typically composed of base metals through active injection of a reductant, such as ammonia rich urea, into the exhaust gas mixture entering the catalyst, are known to achieve high NOx conversion efficiency. 
         [0003]    In the systems described thus far, the ammonia rich urea is an aqueous solution which is stored in an aqueous urea reservoir in the vehicle and is delivered to an injector, located in the exhaust system of the vehicle, via fluid lines and a pump. The urea typically has a freezing temperature in the range of 12 degrees Fahrenheit, which may present winter challenges to the operation of the SCR system. Systems which include heating elements in a submersible pump module within the reservoir have been found to operate in a less than satisfactory manner as have resistor grid heating mats within the reservoir due to poor heat transfer throughout the fluid. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    The present invention is directed to an emission control system for diesel and other lean-burn engines and, more particularly to an improved reductant storage system. Selective Catalytic Reduction (SCR) catalysts, in which NOx is continuously reduced to nitrogen (N 2 ) over a catalyst typically composed of base metals, through active injection of a reductant such as ammonia rich urea into the exhaust gas mixture entering the catalyst, are known to achieve high NOx conversion efficiency. 
         [0005]    The reductant, which may be ammonia rich urea, is an aqueous solution which is stored in a reductant reservoir in the vehicle. The fluid is delivered to an injector, in communication with the exhaust system of the vehicle, via fluid lines and a pump. The urea solution typically has a freezing temperature in the range of 12 degrees Fahrenheit, which may present winter challenges to the operation of the SCR system. The system herein described includes a reservoir which, in an exemplary embodiment includes an in-tank, or partially submersible reductant pump assembly having a heating element associated therewith. The heating element operates to heat the liquid in the reservoir to avoid freezing, or to thaw frozen reductant during cold weather operation. Also associated with the pump assembly is a fluid sprayer which operates to draw fluid over the heating element and disperse the fluid through nozzles exiting from the exterior of the pump. The fluid spray disperses heated fluid throughout the reservoir resulting in circulation of the fluid into colder regions which are otherwise unaffected by the heating element. The result is more efficient thawing of the reductant. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0007]      FIG. 1  is a schematic view of an emission control system for an internal combustion engine, which embodies features of the present invention; 
           [0008]      FIG. 2  is a sectional view through a reductant reservoir of the emission control system of  FIG. 1 ; 
           [0009]      FIG. 3  is a top view of the reductant reservoir of the emission control system of  FIG. 1  with a reductant spray pattern illustrated thereon 
           [0010]      FIG. 4  is a sectional view through a second embodiment of the reductant reservoir of the emission control system of  FIG. 1 ; and 
           [0011]      FIG. 5  is a schematic, sectional view of the pump assembly of the reductant reservoir of  FIGS. 2-4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0012]    Illustrated in  FIG. 1 , an emission control system  10  for diesel and other lean-burn engines  12 , commonly used in motor vehicle applications, is shown. The emission control system includes a Selective Catalytic Reduction (SCR) catalyst  14 , in which the NOx component of the engine exhaust gas is continuously reduced to nitrogen (N 2 ) over a catalyst typically composed of base metals, through active injection of a reductant, such as ammonia rich urea, into the exhaust gas mixture entering the catalyst. The reductant is stored in a reductant reservoir  16 ,  FIGS. 2 and 3 , and is delivered by pump  18  to an injector  20  located upstream of the SCR catalyst  14  through fluid line  22 . 
         [0013]    In an exemplary embodiment of the invention the reductant reservoir  16  includes an in-tank, or partially submersible reductant pump assembly  24  having a delivery module  26  associated with a fluid uptake or base  28  which extends axially from a location adjacent to the bottom  30  of the reservoir  16  to the top  32  thereof. The base  28  includes an annular mounting ring  34  which secures the pump assembly  24  to the reservoir through engagement with opening  36  in reservoir top  32 . A reductant intake  38  is located in base  28  preferably adjacent to the bottom  30  of the tank to assure efficient scavenging of the reductant  40 . The reductant  40  which may be an aqueous urea formulation typically has a freezing temperature in the range of 12 degrees Fahrenheit. A heating element  42  is associated with the pump assembly  24  and operates to warm and/or thaw the reductant  40  during cold weather operation of the vehicle. In a preferred embodiment, the heating element  42  is associated with the base  28 ,  FIG. 2 , and heats the reductant drawn into the pump assembly through reductant intake  38 . The heating element  42  may also heat the base  28  resulting in localized heating of the reductant  40  surrounding the base. 
         [0014]    Also associated with the pump assembly is a fluid spray assembly including, in an exemplary embodiment, a nozzle spray ring  44 . The spray ring  44  is disposed about the upper portion of the base  28  near the upper fluid level  29  of the reductant, and is operated in association with the pump  18  and the heating element  42  to spray heated, liquid reductant  41 , through one or more nozzles  43 , about the interior of the reductant reservoir in a spray pattern  46  which is configured to move heated fluid within the reservoir radially outwardly from the centrally located pump assembly  24  to the outer regions of the reservoir to warm and/or thaw reductant throughout the reservoir using the heat generated by the heating element  42 . The fluid spray disperses heated fluid throughout the reservoir resulting in heat transfer from the warmer fluid into colder regions which are otherwise unaffected by the heating element. The result is more efficient thawing of the reductant. It may be desirable to augment the heat delivered to the already heated fuel in order to improve the warm/thaw capability of the present invention. In such an instance it is contemplated that the nozzle spray ring may also include a supplemental heating element operable to further heat the fluid exiting the nozzle spray ring  44 . 
         [0015]    In another exemplary embodiment of the invention illustrated in  FIGS. 4 and 5 , in which like elements of the invention are illustrated with the same numbers as already described, a fluid circulation assembly has a nozzle circulation ring  144  disposed about the circumference of the base  28 , below the upper fluid level  29  of the reservoir  16 . The circulation ring  144  may be disposed at any location axially along the base  28  and is preferably located adjacent to the reductant intake  38 . The circulation ring is operated in association with the pump  18  and the heating element  42  to inject heated, liquid reductant  41  into the reductant to establish fluid circulation which operates to move heated fluid within the reservoir radially outwardly from the centrally located pump assembly  24  to the outer regions of the reservoir to warm and/or thaw reductant throughout the reservoir using the heat generated by the heating element  42 . The fluid circulation disperses heated fluid throughout the reservoir resulting in heat transfer from the warmer fluid into colder regions which are otherwise unaffected by the heating element. The result is more efficient thawing of the reductant. It may be desirable to augment the heat delivered to the already heated fuel in order to improve the warm/thaw capability of the present invention. In such an instance it is contemplated that the nozzle spray ring may also include a supplemental heating element operable to further heat the fluid exiting the nozzle spray ring  144 . 
         [0016]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.