System and method for mitigating potential for formation of urea deposits in an engine exhaust system during cold ambient conditions

Abstract

A device and method for catalytic reduction of NOx in gaseous products of a combustion process before entry into the atmosphere. The gaseous and particulate products of a combustion process flow radially through a radial flow particulate filter element ( 24 ) that is effective to trap particulate matter, and are then directed axially through a collector ( 26 ). An injector ( 30 ) introduces a reductant into an axial end of the collector for entrainment with axial flow through the collector in a direction away from the injector. Flow leaving the collector is directed through an SCR catalyst ( 40 ) where catalytic reduction of NOx occurs.

1 . An internal combustion engine comprising:
 an exhaust system through which exhaust gas created by combustion in engine combustion chambers passes to atmosphere and which comprises an after-treatment device for treating the exhaust gas before the exhaust gas leaves the exhaust system;   an injector for injecting a liquid phase reductant for the after-treatment device's treatment of the exhaust gas into the exhaust system upstream of the after-treatment device for entrainment with, and vaporization in, flow of the exhaust gas through the exhaust system;   and one or more electric heater elements for heating a surface that may be wetted by the liquid phase to a temperature that is high enough to prevent reductant from coming out of the liquid phase and depositing on the surface.   
     
     
         2 . An engine as set forth in  claim 1  in which the after-treatment device comprises an SCR catalyst, and further including a supply of urea solution for the injector to inject as the liquid phase. 
     
     
         3 . An engine as set forth in  claim 2  in which the injector comprises a body that is received in a bore of a boss and a nozzle through which urea solution is sprayed into the exhaust gas flow, and in which a heater element is disposed on the boss for heating the boss. 
     
     
         4 . An engine as set forth in  claim 2  in which a heater element is disposed on a portion of a wall of the exhaust system that circumscribes the exhaust gas flow and is downstream of the boss. 
     
     
         5 . An engine as set forth in  claim 2  in which a heater element is disposed on a portion of a wall of the exhaust system that circumscribes the exhaust gas flow and is upstream of the boss. 
     
     
         6 . An engine as set forth in  claim 2  in which the exhaust system comprises structure disposed in the path of urea spray from the nozzle for deflecting/dispersing/breaking up at least some portion of the spray before that portion of the spray can contact the surface, and in which a heater element is disposed on a wall of the exhaust system that circumscribes the exhaust gas flow at the location of the structure. 
     
     
         7 . An engine as set forth in  claim 6  in which the exhaust system further comprises a mixer downstream of the structure, and a heater element is disposed on the wall of the exhaust system at the location of the mixer. 
     
     
         8 . An engine as set forth in  claim 2  in which a temperature sensor is disposed to measure temperature of exhaust gas upstream of the injector, and in which a controller for the one or more heater elements uses that measurement to control operation of the one or more heater elements. 
     
     
         9 . A method for mitigating the deposit of reductant out of liquid phase on a surface of an internal combustion engine exhaust system through which exhaust gas created by combustion in engine combustion chambers passes to atmosphere and which comprises an after-treatment device for treating the exhaust gas before the exhaust gas leaves the exhaust system, and an injector for injecting liquid phase reductant for the after-treatment device's treatment of the exhaust gas into the exhaust system upstream of the after-treatment device for entrainment with, and vaporization in, flow of the exhaust gas through the exhaust system, the method comprising:
 operating one or more electric heater elements to heat a surface that may be wetted by the liquid phase to a temperature that is high enough to prevent reductant from coming out of the liquid phase and depositing on the surface.   
     
     
         10 . A method as set forth in  claim 9  in which the step of operating one or more electric heater elements comprises operating an electric heater element disposed on a boss having a bore within which a body of the injector is received. 
     
     
         11 . A method as set forth in  claim 9  in which the step of operating one or more electric heater elements comprises operating an electric heater element disposed on a portion of a wall of the exhaust system that circumscribes the exhaust gas flow and is downstream of the boss. 
     
     
         12 . A method as set forth in  claim 9  in which the step of operating one or more electric heater elements comprises operating an electric heater element disposed on a portion of a wall of the exhaust system that circumscribes the exhaust gas flow and is upstream of the boss. 
     
     
         13 . A method as set forth in  claim 9  in which the step of operating one or more electric heater elements comprises operating an electric heater element disposed on a portion of a wall of the exhaust system that circumscribes the exhaust gas flow at the location of structure disposed in the path of urea spray from the nozzle for deflecting/dispersing/breaking up at least some portion of the spray before that portion of the spray can contact the surface. 
     
     
         14 . A method as set forth in  claim 13  in which the step of operating one or more electric heater elements comprises operating an electric heater element disposed on a portion of a wall of the exhaust system that circumscribes the exhaust gas flow at the location of a mixer downstream of the structure. 
     
     
         15 . A method as set forth in  claim 9  further comprising measuring temperature of exhaust gas upstream of the injector, using the measured temperature to selectively allow and disallow the injector to inject urea solution and to selectively operate the one or more heater elements.