Liquid Reductant Dosing Module with Heating Device

Abstract

A liquid reductant dosing module for a combustion exhaust system is disclosed comprising an enclosed reservoir comprising a top, a bottom, one or more sides, an inlet, and an outlet. A resistive wire rod heater is disposed in that reservoir, comprising a hollow member extending along a first axis between the bottom of the reservoir and the top of the reservoir. Along that member there is disposed resistive metal wire such that when electric current is applied to the resistive metal wire, a greater portion of electric power is distributed as heat proximate to the bottom of the reservoir than is distributed as heat proximate to the top of the reservoir.

1 . A liquid reductant dosing module for a combustion exhaust treatment system comprising:
 (a) an enclosed reservoir comprising a top, a bottom, one or more sides, an inlet, and an outlet; and   (b) a resistive wire rod heater disposed in said reservoir, comprising:
 (1) a hollow member extending along a first axis between the bottom of said reservoir and the top of said reservoir; 
 (2) resistive metal wire disposed along said member such that when electric current is applied to said resistive metal wire, a greater portion of electric power is distributed as heat proximate to the bottom of said reservoir than is distributed as heat proximate to the top of said reservoir. 
   
     
     
         2 . A liquid reductant dosing module according to  claim 1  wherein there is a greater density of resistive metal wire disposed along said member proximate to the bottom of said reservoir than is disposed along said member proximate to the top of said reservoir. 
     
     
         3 . A liquid reductant dosing module according to  claim 1  wherein resistive metal wire disposed along said member proximate to the bottom of said reservoir has a greater resistivity than resistive metal wire disposed along said member proximate to the top of said reservoir. 
     
     
         4 . A liquid reductant dosing module according to  claim 1  wherein resistive metal wire is disposed along said member such that when current is applied to said resistive metal wire, 0 to 10 percent of the heat generated by such current is distributed along a zone of said member proximate to the top of said reservoir, 60 to 80 percent of the heat generated by such current is distributed along a zone of said member proximate to the bottom of said reservoir, and 20 to 30 percent of the heat generated by such current is distributed along a zone of said member between the zone proximate to the top and the zone proximate to the bottom of said reservoir. 
     
     
         5 . A liquid reductant dosing module according to  claim 1  wherein resistive metal wire is disposed along said hollow member such that when current is applied to said resistive metal wire, 0 to 1 watts/in 2  is distributed along a zone of said hollow member proximate to the top of said reservoir, 8 to 10 watts/in 2  is distributed along a zone of said hollow member proximate to the bottom of said reservoir, and 2.5 to 3.5 watts/in 2  is distributed along a zone of said member between the zone proximate to the top and the zone proximate to the bottom of said reservoir. 
     
     
         6 . A liquid reductant dosing module according to  claim 1  wherein said inlet is located proximate to the bottom of said reservoir. 
     
     
         7 . A liquid reductant dosing module according to  claim 1  wherein said outlet comprises a pickup tube extending along a second axis, which may be the same as or different than said first axis, extending between the bottom of said reservoir and the top of said reservoir, said pickup tube having an open end proximate to the bottom of said reservoir. 
     
     
         8 . A liquid reductant dosing module according to  claim 7  wherein said pickup tube is disposed inside said hollow member. 
     
     
         9 . A liquid reductant dosing module according to  claim 1  wherein said hollow member is stainless steel. 
     
     
         10 . A liquid reductant dosing module according to  claim 4  wherein the resistivity of the resistive metal wire along a zone of said member proximate to the top of said reservoir is 0 ohm-m to 0.25 ohm-m, the resistivity of the resistive metal wire along a zone of said member proximate to the bottom of said reservoir is 1.5 ohm-m to 2.5 ohm-m, and the resistivity of the resistive metal wire along a zone of said member between the zone proximate to the top and the zone proximate to the bottom of said reservoir is 0.25 ohm-m to 0.5 ohm-m. 
     
     
         11 . A liquid reductant dosing module according to  claim 1  wherein said wire material has a resistivity of 1 ohm-m to 1.5 ohm-m. 
     
     
         12 . A liquid reductant dosing module according to  claim 2  wherein said wire material has a resistivity of 1 ohm-m to 1.5 ohm-m. 
     
     
         13 . A liquid reductant dosing module according to  claim 1  wherein said wire material has a positive temperature resistivity coefficient ranging from 0.1 ohm-m/° C. to 0.15 ohm-m/° C. 
     
     
         14 . A liquid reductant dosing module according to  claim 1 , further comprising a Wheatstone bridge control circuit to control the current applied to said resistive wire. 
     
     
         15 . A liquid reductant dosing module according to  claim 1 , further comprising a heat sink member in thermal contact with said heater in said zone proximate to the bottom of said reservoir. 
     
     
         16 . A liquid reductant dosing module according to  claim 5 , further comprising a heat sink member in thermal contact with said heater in said zone proximate to the bottom of said reservoir such that when current is applied to said resistive metal wire, 0.5 to 1.5 watts/in 2  is distributed through the combined surface area of said heat sink member and said hollow member along the zone of said hollow member proximate to the bottom of said reservoir. 
     
     
         17 . A liquid reductant dosing module according to  claim 1 , further comprising a deflector to inhibit convectional movement of liquid reductant from proximate the bottom of said reservoir toward the top of said reservoir. 
     
     
         18 . A liquid reductant dosing module for a combustion exhaust treatment system comprising:
 (a) an enclosed reservoir comprising a top, a bottom, one or more sides, an inlet, and an outlet;   (b) a rod heater disposed in said reservoir extending along a first axis between the bottom of said reservoir and the top of said reservoir; and   (c) a heat deflector member disposed circumferentially around said rod header proximate to the bottom of said rod heater, configured to inhibit upward convective heat transfer in said liquid reductant.   
     
     
         19 . A liquid reductant dosing module according to  claim 18  wherein said inlet is located proximate to the bottom of said reservoir. 
     
     
         20 . A liquid reductant dosing module according to  claim 18  wherein said outlet comprises a pickup tube extending along a second axis, which may be the same as or different than said first axis, extending between the bottom of said reservoir and the top of said reservoir, said pickup tube having an open end proximate to the bottom of said reservoir. 
     
     
         21 . A liquid reductant dosing module according to  claim 20  wherein said pickup tube is disposed inside said hollow member. 
     
     
         22 . A liquid reductant dosing module according to  claim 18  wherein said heat deflector member comprises a top member having an opening therein disposed circumferentially around said hollow member and at least one side member attached to and extending downward from said top member such that there is a space between said hollow member and said at least one side member. 
     
     
         23 . A liquid reductant dosing module according to  claim 22 , further comprising a bottom member having an opening therein disposed circumferentially around said hollow member and attached to said at least one side member. 
     
     
         24 . A liquid reductant dosing module according to  claim 23  wherein at least one of said top member, said at least one side member, and said bottom member has at least one opening therein through which liquid reductant can pass. 
     
     
         25 . A liquid reductant dosing module according to  claim 24  wherein said at least one opening through which liquid reductant can pass has a filter medium disposed therein.