Exhaust system having mid-reducer NOx sensor

Abstract

An exhaust system for a combustion engine is disclosed. The exhaust system may have a housing connected to receive a flow of exhaust. The exhaust system may also have a first catalyst disposed within the housing to reduce the concentration of an exhaust constituent, and a second catalyst disposed within the housing downstream of the first catalyst to further reduce the concentration of the exhaust constituent. The exhaust system may further have a sensor disposed between the first and second catalysts to generate a signal indicative of the concentration of the exhaust constituent at the location between the first and second catalysts. The exhaust system may additionally have a controller in communication with the sensor to receive the signal. The controller may determine, based on the received signal, the concentration of the exhaust constituent at a location downstream of the second catalyst.

1 . An exhaust system, comprising:
 a housing connected to receive a flow of exhaust;   a first catalyst disposed within the housing to reduce the concentration of an exhaust constituent;   a second catalyst disposed within the housing downstream of the first catalyst to further reduce the concentration of the exhaust constituent;   a sensor disposed between the first and second catalysts to generate a signal indicative of the concentration of the exhaust constituent at the location between the first and second catalysts; and   a controller in communication with the sensor to receive the signal and determine, based on the received signal, the concentration of the exhaust constituent at a location downstream of the second catalyst.   
   
   
       2 . The exhaust system of  claim 1 , wherein the constituent is an oxide of nitrogen. 
   
   
       3 . The exhaust system of  claim 2 , wherein the first and second catalysts are SCR catalysts. 
   
   
       4 . The exhaust system of  claim 3 , wherein the first and second catalysts have substantially the same reducing capacity. 
   
   
       5 . The exhaust system of  claim 1 , wherein the concentration of the exhaust constituent at the location downstream of the second catalyst is determined based further on an estimated production of the constituent. 
   
   
       6 . The exhaust system of  claim 5 , wherein the controller includes a map stored in a memory thereof, the map relating a power source parameter to the estimated production of the constituent. 
   
   
       7 . The exhaust system of  claim 5 , wherein the estimated production of the constituent and the signal provide an indication of the effectiveness of the first catalyst. 
   
   
       8 . The exhaust system of  claim 7 , wherein:
 the effectiveness of the second catalyst is assumed to be about the same as the effectiveness of the first catalyst; and   the concentration of the exhaust constituent at the location downstream of the second catalyst is determined based further on the assumed effectiveness of the second catalyst.   
   
   
       9 . The exhaust system of  claim 1 , further including a second sensor located upstream of the first catalyst to generate a second signal indicative of a constituent production, wherein the concentration of the exhaust constituent at the location downstream of the second catalyst is determined based further on the second signal. 
   
   
       10 . The exhaust system of  claim 1 , wherein the concentration of the constituent downstream of the second catalyst is less than a sensitivity of the sensor. 
   
   
       11 . A method of determining the concentration of an exhaust constituent, comprising:
 receiving a flow of exhaust;   reducing the concentration of the exhaust constituent within the flow of exhaust;   measuring the reduced concentration of the exhaust constituent;   further reducing the concentration of the exhaust constituent within the flow of exhaust; and   determining the further reduced concentration of the exhaust constituent based on the measured reduced concentration.   
   
   
       12 . The method of  claim 11 , wherein the constituent is an oxide of nitrogen. 
   
   
       13 . The method of  claim 11 , wherein:
 reducing the concentration includes removing about 50% of the constituent from the exhaust flow; and   further reducing the concentration includes removing about 50% of the remaining constituent from the already reduced exhaust flow.   
   
   
       14 . The method of  claim 11 , further including estimating a production of the constituent, wherein determining the further reduced concentration is based further on the estimated production. 
   
   
       15 . The method of  claim 14 , wherein the estimated production and the measured reduction provide an indication of the amount of constituent reduced in the reducing step. 
   
   
       16 . The method of  claim 15 , further including equating the amount of constituent reduced in the further reducing step to the indicated amount of constituent reduced in the reducing step, wherein determining the further reduced concentration is based further on the amount of constituent reduced in the further reducing step. 
   
   
       17 . The method of  claim 11 , further including measuring a production of the constituent, wherein determining the further reduced concentration is based further on the measured production. 
   
   
       18 . A power system, comprising:
 a combustion engine configured to combust a fuel/air mixture and produce a power output and a flow of exhaust;   a conduit connected to receive the flow of exhaust;   a first NOx catalyst disposed within the conduit to reduce the concentration of NOx in the flow of exhaust;   a second NOx catalyst disposed within the conduit downstream of the first NOx catalyst to further reduce the concentration of NOx in the exhaust flow;   a sensor disposed between the first and second NOx catalysts to generate a signal indicative of the concentration of NOx at a location between the first and second NOx catalysts; and   a controller in communication with the sensor to receive the signal and determine, based on the received signal and a production of NOx, the concentration of NOx at a location downstream of the second NOx catalyst, wherein the concentration of NOx at the location downstream of the second NOx catalyst is less than a sensitivity of the sensor.   
   
   
       19 . The power system of  claim 18 , wherein:
 the control is configured to determine an effectiveness of the first NOx reducing catalyst based on the NOx production and the signal;   the effectiveness of the second NOx reducing catalyst is assumed to be about the same as the effectiveness of the first NOx reducing catalyst; and   the concentration of the exhaust constituent at the location downstream of the second NOx reducing catalyst is determined based further on the assumed effectiveness of the second NOx reducing catalyst.   
   
   
       20 . The power system of  claim 18 , further including a second sensor located between the combustion engine and the first NOx reducing catalyst to generate a second signal indicative of the NOx production amount, wherein the concentration of the exhaust constituent at the location downstream of the second NOx reducing catalyst is determined based further on the second signal.