CONVERSION OF NOx IN EXHAUST GAS

Abstract

A quantity of ammonia being consumed within an exhaust system of an internal combustion engine to reduce NOx in exhaust passing through the exhaust system by chemical reactions enabled by an SCR catalyst is calculated by processing, in accordance with an algorithm, certain data including data indicative of a quantity of NOx in exhaust upstream of where ammonia is being introduced into the exhaust system, data indicative of a quantity of NOx in exhaust downstream of the SCR catalyst, and data indicative of exhaust flow.

What is claimed is: 
     
         1 . An internal combustion engine comprising:
 combustion chambers within which fuel is combusted to operate the engine;   an intake system through which air for supporting combustion is introduced into the combustion chambers;   an exhaust system through which exhaust resulting from combustion in the combustion chambers passes to atmosphere and which comprises an SCR catalyst;   an ammonia delivery system for introducing ammonia into the exhaust system upstream of the SCR catalyst for entrainment with exhaust flow toward the SCR catalyst; and   a processor for processing certain data including data indicative of a quantity of NOx in exhaust upstream of where ammonia is being introduced into the exhaust system, data indicative of a quantity of NOx in exhaust downstream of the SCR catalyst, and data indicative of exhaust flow, in accordance with an algorithm to estimate a quantity of ammonia consumed by chemical reactions which are enabled by the SCR catalyst to reduce NOx to N 2  and H 2 O.   
     
     
         2 . The engine set forth in  claim 1  including a downstream NOx sensor providing the data indicative of a quantity of NOx in exhaust downstream of the SCR catalyst. 
     
     
         3 . The engine set forth in  claim 2  including an upstream NOx sensor providing the data indicative of a quantity of NOx in exhaust upstream of where ammonia is being introduced into the exhaust system. 
     
     
         4 . The engine set forth in  claim 3  including a diesel oxidation catalyst in the exhaust system upstream of the SCR catalyst, and in which the upstream NOx sensor is disposed to indicate a quantity of NOx in the exhaust upstream of the diesel oxidation catalyst. 
     
     
         5 . The engine set forth in  claim 1  in which the algorithm comprises a division calculation for dividing data indicative of a quantity of NOx in exhaust downstream of the SCR catalyst by data indicative of a quantity of NOx in exhaust upstream of where ammonia is being introduced into the exhaust system, a subtraction calculation for subtracting the division calculation from unity, and a multiplication calculation for multiplying the subtraction calculation a) by a quantity of ammonia which would have been consumed according to one or more chemical reactions in which at least ammonia and NOx are reactants in order to reduce NOx to the subtraction calculation, and b) by data indicative of exhaust flow through the SCR catalyst. 
     
     
         6 . The engine set forth in  claim 1  in which the chemical reactions comprise one or more of:
   4NO+4NH3+O2→4N2+6H2O
 
   NO+NO2+2NH3→2N2+3H2O
 
   6NO2+8NH3→7N2+12H2O.
 
 
     
     
         7 . The engine set forth in  claim 5  in which the algorithm further comprises a conversion calculation for converting the multiplication calculation to desired units of ammonia consumption. 
     
     
         8 . A method for estimating a quantity of ammonia being consumed by chemical reactions which are enabled by an SCR catalyst within an exhaust system of an internal combustion engine to reduce NOx in exhaust passing through the exhaust system to N 2  and H 2 O, the method comprising:
 processing certain data, including data indicative of a quantity of NOx in exhaust upstream of where ammonia is being introduced into the exhaust system, data indicative of a quantity of NOx in exhaust downstream of the SCR catalyst, and data indicative of exhaust flow, in accordance with an algorithm to estimate a quantity of ammonia consumed by chemical reactions enabled by the SCR catalyst within the exhaust system.   
     
     
         9 . The method set forth in  claim 8  comprising using a downstream NOx sensor to provide the data indicative of a quantity of NOx in exhaust downstream of the SCR catalyst. 
     
     
         10 . The method set forth in  claim 9  comprising using an upstream NOx sensor to provide the data indicative of a quantity of NOx in exhaust upstream of where ammonia is being introduced into the exhaust system. 
     
     
         11 . The method set forth in  claim 9  comprising using an upstream NOx sensor to provide the data indicative of a quantity of NOx in exhaust upstream both of where ammonia is being introduced into the exhaust system and of a diesel oxidation catalyst which is upstream of the SCR catalyst in the exhaust system. 
     
     
         12 . The method set forth in  claim 8  in which the processing comprises a division step of dividing data indicative of a quantity of NOx in exhaust downstream of the SCR catalyst by data indicative of a quantity of NOx in exhaust upstream of where ammonia is being introduced into the exhaust system, a subtraction step of subtracting a result of the division step from unity, and a multiplication step of multiplying a result of the subtraction step a) by a quantity of ammonia which would have been consumed according to chemical reactions in which at least ammonia and NOx are reactants in order to reduce NOx to the subtraction calculation and b) by data indicative of exhaust flow through the SCR catalyst. 
     
     
         13 . The method set forth in  claim 12  further comprising converting a result of the multiplying step to desired units of ammonia consumption. 
     
     
         14 . A system for estimating a quantity of ammonia consumed by selective catalytic reduction (SCR) of NOx in exhaust flow through an exhaust system, the system comprising:
 an SCR catalyst;   an ammonia supply;   an ammonia outlet through which ammonia from the ammonia supply is introduced into the exhaust flow;   a downstream NOx sensor providing data indicative of a quantity of NOx in exhaust flow downstream of the SCR catalyst;   a data source providing data indicative of a quantity of NOx in exhaust flow upstream of where ammonia is being introduced into the exhaust system; and   a processor for processing data from the downstream NOx sensor, data from the data source, and data indicative of exhaust flow, in accordance with an algorithm to estimate a quantity of ammonia consumed to reduce NOx to N 2  and H 2 O by chemical reactions enabled by the SCR catalyst.   
     
     
         15 . The system set forth in  claim 14  in which the algorithm comprises a division calculation for dividing data provided by the downstream NOx sensor by data provided by the data source, a subtraction calculation for subtracting the division calculation from unity, and a multiplication calculation for multiplying the subtraction calculation a) by a quantity of ammonia which would have been consumed according to one or more chemical reactions in which at least ammonia and NOx are reactants in order to reduce NOx to the subtraction calculation, and b) by data indicative of exhaust flow through the SCR catalyst. 
     
     
         16 . The system set forth in  claim 14  in which the data source comprises an upstream NOx sensor.