Selective NOx catalytic reduction system including an ammonia sensor

Abstract

An improved SCR system for controlling NOx levels in internal combustion engine exhaust, comprising a least one ammonia sensor disposed at an intermediate longitudinal location in an SCR catalyst and in communication with a System Control Module (SCM). The ammonia measurement permits calculation of ammonia storage on catalyst sites via a stored SCM algorithm. Locating the ammonia sensor midway in the catalyst allows for optimum control of NOx reduction and permits the portion of the catalyst downstream of the sensor to be treated as a slip catalyst, thus minimizing or eliminating the need for a second slip catalyst and housing, and reducing the size, volume, complexity, and cost of an SCR system. In-brick ammonia sensor permits the system to manage engine exhaust to a desired NOx conversion level and ammonia slip target value, thus minimizing the rate of consumption of ammonia while meeting required limits for NOx emissions.

1 . A system for control of nitrogen oxide concentrations in a stream of exhaust gas from an internal combustion engine, comprising:
 a) a first catalytic element disposed in said stream of exhaust gas for catalytically reducing nitrogen oxides to elemental nitrogen;   b) a second catalytic element disposed in said stream of exhaust gas downstream of said first catalytic element for further catalytic treatment of said exhaust gas;   c) a system for injecting an ammoniacal chemical reductant into said stream of exhaust gas ahead of said first and second catalytic elements; and   d) an ammonia sensor disposed in said stream of exhaust gas between said first and second catalytic elements for sensing ammonia concentrations in said stream of exhaust gas.   
   
   
       2 . A system in accordance with  claim 1  wherein said further catalytic treatment is selected from the processes consisting of reducing nitrogen oxides, oxidizing ammonia, and combinations thereof. 
   
   
       3 . A system in accordance with  claim 1  wherein said first and second catalytic elements are disposed in a single housing. 
   
   
       4 . A system in accordance with  claim 1  wherein said first and second catalytic elements are provided in a single monolithic catalytic brick, and wherein said ammonia sensor is disposed at an intermediate longitudinal location of said brick, which location defines portions of said brick upstream of said ammonia sensor as said first catalytic element and portions of said brick downstream of said ammonia sensor as said second catalytic element. 
   
   
       5 . A system in accordance with  claim 1  wherein said first catalytic element and second catalytic element are abuttingly disposed and have a well formed at the location of said abutting, and wherein said ammonia sensor is disposed in said well. 
   
   
       6 . A system in accordance with  claim 1  wherein said first catalytic element and said second catalytic element have a gap therebetween, and wherein said ammonia sensor is disposed in said gap. 
   
   
       7 . A system in accordance with  claim 1  wherein said ammoniacal chemical reductant is ammonia. 
   
   
       8 . A system in accordance with  claim 7  wherein said ammonia is derived by decomposition of urea. 
   
   
       9 . A system in accordance with  claim 8  wherein said urea is provided in the form of an aqueous solution. 
   
   
       10 . A system in accordance with  claim 1  further comprising a programmable controller responsive to signals from said ammonia sensor for regulating rate of injecting of said ammoniacal chemical reductant into said exhaust gas stream. 
   
   
       11 . A system in accordance with  claim 1  further comprising a second ammonia sensor disposed in said stream of exhaust gas after said second catalytic element. 
   
   
       12 . An internal combustion engine, comprising a system for control of nitrogen oxide concentrations in a stream of exhaust gas from said engine, wherein said system includes
 a first catalytic element disposed in said stream of exhaust gas for catalytically reducing nitrogen oxides to elemental nitrogen,   a second catalytic element disposed in said stream of exhaust gas downstream of said first catalytic element for further catalytic treatment of said exhaust,   a system for injecting an ammoniacal chemical reductant into said stream of exhaust gas ahead of said first and second catalytic elements, and   an ammonia sensor disposed in said stream of exhaust gas between said first and second catalytic elements for sensing ammonia concentrations in said stream of exhaust gas.   
   
   
       13 . An internal combustion engine in accordance with  claim 12  wherein said further catalytic treatment is selected from the processes consisting of reducing nitrogen oxides, oxidizing ammonia, and combinations thereof. 
   
   
       14 . An internal combustion engine in accordance with  claim 12  wherein said engine is selected from the group consisting of spark-ignited and compression-ignited.