Methods for monitoring and/or controlling the performance of selective catalytic reduction devices

Abstract

Method for controlling and/or monitoring the performance of selective catalytic reduction devices (SCR) and systems incorporating the same are provided. Systems can include a SCR configured to receive reductant at a variable dosing rate, an upstream NOx sensor, and a downstream NOx sensor. Methods can include correlating a SCR reductant dosing signal direction with a SCR downstream NOx signal direction, and determining one or more of NOx breakthrough through the SCR and reductant slip through the SCR. Methods can further comprise identifying reductant slip through the SCR using an upstream NOx sensor signal and a downstream NOx sensor signal. Methods can further comprise comparing an upstream NOx signal to a downstream NOx signal, determining a system objective, and adapting the SCR reductant dosing rate to achieve the system objective in order to identify a faulty upstream NOx sensor.

What is claimed is: 
     
         1 . A method for monitoring the performance of a selective catalytic reduction device (SCR) of an exhaust gas treatment system, wherein the system includes a SCR configured to receive reductant at a variable dosing rate and a downstream NO x  sensor disposed downstream from the SCR, the method comprising:
 correlating a SCR reductant dosing signal direction with a SCR downstream NO x  signal direction to determine an operating correlation; and   determining one or more of NO x  breakthrough through the SCR and reductant slip through the SCR using the operating correlation;   
       wherein a negative operating correlation indicates a change in NO x  breakthrough through the SCR and a positive operating correlation indicates a change in reductant slip through the SCR, and the upstream NO x  signal is measured by the upstream NO x  sensor and the downstream NO x  signal is measured by the downstream NO x  sensor. 
     
     
         2 . The method of  claim 1 , further comprising determining a reductant loading of the SCR subsequent to correlating, wherein a reductant loading of the SCR is underloaded while determining a negative operating correlation and a reductant loading of the SCR is overloaded while determining a positive operating correlation. 
     
     
         3 . The method of  claim 1 , wherein a positive operating correlation comprises an increasing SCR reductant dosing signal direction and an increasing downstream NO x  signal direction, and indicates an increased reductant slip through the SCR. 
     
     
         4 . The method of  claim 1 , wherein a positive operating correlation comprises a decreasing SCR reductant dosing signal direction and a decreasing downstream NO x  signal direction, and indicates a decreased reductant slip through the SCR. 
     
     
         5 . The method of  claim 1 , wherein a negative operating correlation comprises an increasing SCR reductant dosing signal direction and a decreasing downstream NO x  signal direction, and indicates a decreased NO x  breakthrough through the SCR. 
     
     
         6 . The method of  claim 1 , wherein a negative operating correlation comprises a decreasing SCR reductant dosing signal direction and an increasing downstream NO x  signal direction, and indicates an increased NO x  breakthrough through the SCR. 
     
     
         7 . The method of  claim 1 , wherein correlating the SCR reductant dosing signal direction with the SCR downstream NO x  signal direction occurs while the SCR is in steady state. 
     
     
         8 . A method for controlling a selective catalytic reduction device (SCR) of an exhaust gas treatment system, wherein the system includes a SCR configured to receive reductant at a variable dosing rate, wherein reductant dosing is controlled by an SCR chemical model to achieve a desired SCR NO x  reduction yield by using one or more SCR reductant dosing signals and one or more upstream SCR NO x  signals to determine one or more of SCR reductant loading and SCR NO x  reduction yield, an upstream NO x  sensor disposed upstream from the SCR, and a downstream NO x  sensor disposed downstream from the SCR, the method comprising:
 determining one or more of a SCR reductant loading and a SCR NO x  reduction yield via the SCR chemical model using the upstream NO x  signal and the reductant dosing signal;   identifying reductant slip through the SCR using the SCR chemical model;   adapting the reductant dosing rate to reduce reductant slip through the SCR;   subsequently correlating the SCR reductant dosing signal direction with the SCR downstream NO x  signal direction to determine an operating correlation; and   identifying NO x  breakthrough through the SCR using the operating correlation;   
       wherein the upstream NO x  signal is measured by the upstream NO x  sensor, the downstream NO x  signal is measured by the downstream NO x  sensor, and the reductant dosing signal comprises one or more of a measured flow rate of reductant delivered to the SCR, a reductant dosing rate commanded by the SCR chemical model, a reductant dosing mass commanded by the SCR chemical model, and a reductant dosing volume commanded by the SCR chemical model. 
     
     
         9 . The method of  claim 8 , wherein the SCR reductant dosing signal direction comprises a decreasing signal direction, and the SCR downstream NO x  signal direction comprises an increasing signal direction. 
     
     
         10 . The method of  claim 8 , wherein the upstream NO x  sensor is faulty and incorrectly sensing a NO x  value below the actual NO x  process value. 
     
     
         11 . The method of  claim 8 , further comprising determining an underloaded reductant loading of the SCR subsequent to correlating the SCR reductant dosing signal direction with the SCR downstream NO x  signal direction. 
     
     
         12 . The method of  claim 8 , further comprising adapting the reductant dosing rate to reduce NO x  breakthrough, subsequent to identifying NO x  breakthrough through the SCR. 
     
     
         13 . The method of  claim 8 , further comprising identifying the upstream NO x  sensor as faulty, subsequent to identifying NO x  breakthrough through the SCR. 
     
     
         14 . The method of  claim 8 , wherein correlating the SCR reductant dosing signal direction with the SCR downstream NO x  signal direction occurs while the SCR is in steady state. 
     
     
         15 . A method for detecting a faulty sensor of an exhaust gas treatment system, wherein the system includes a selective catalytic reduction device (SCR) configured to receive reductant at a variable dosing rate, an upstream NO x  sensor disposed upstream from the SCR, and a downstream NO x  sensor disposed downstream from the SCR, the method comprising:
 comparing an upstream NO x  signal to a downstream NO x  signal;   determining a system objective;   adapting the SCR reductant dosing rate to achieve the system objective;   correlating a SCR reductant dosing signal direction to the downstream NO x  signal direction to determine if the system objective has been at least partially achieved; and   identifying an upstream NO x  sensor fault if the system objective has not been at least partially achieved;   
       wherein the upstream NO x  signal is measured by the upstream NO x  sensor and the downstream NO x  signal is measured by the downstream NO x  sensor. 
     
     
         16 . The method of  claim 15 , further comprising determining one or more of a SCR reductant loading and a SCR NO x  reduction yield via an SCR chemical model using the upstream NO x  signal and the reductant dosing signal prior to adapting the SCR reductant dosing rate. 
     
     
         17 . The method of  15 , wherein the system objective comprises reducing reductant slip through the SCR, and adapting the SCR reductant dosing comprises lowering the reductant dosing rate. 
     
     
         18 . The method of  17 , wherein the SCR reductant loading is below about 10%. 
     
     
         19 . The method of  17 , wherein the upstream NO x  sensor fault comprises a measuring a NO x  signal below the actual NO x  process value. 
     
     
         20 . The method of  claim 15 , wherein correlating the SCR reductant dosing signal direction with the SCR downstream NO x  signal direction occurs while the SCR is in steady state.