Exhaust treatment system and method

Abstract

An exhaust treatment system includes a catalytic device configured to receive an exhaust flow and an injector upstream of the catalytic device in an exhaust flow direction that injects a reductant into the exhaust flow. A controller is configured to determine a change in an amount of NOx and a change in an amount of the reductant downstream of the catalytic device due to a change in an amount of the reductant injected by the injector. The controller is configured to determine a slip factor corresponding to a relative weight of a NOx slip rate exiting the catalytic device compared to a reductant slip rate exiting the catalytic device, and determine a dosing command for providing to the injector based at least in part on the slip factor, and the change in the amount of NOx and the change in the amount of the reductant downstream of the catalytic device.

What is claimed is: 
     
         1 . An exhaust treatment system comprising:
 a catalytic device configured to receive a flow of exhaust;   an injector disposed upstream of the catalytic device in an exhaust flow direction, the injector being configured to inject a reductant into the flow of exhaust;   a controller in communication with the injector, the controller being configured to:
 determine a change in an amount of NOx and a change in an amount of the reductant downstream of the catalytic device due to a change in an amount of the reductant injected by the injector; 
 determine a slip factor corresponding to a relative weight of a NOx slip rate exiting the catalytic device compared to a reductant slip rate exiting the catalytic device; 
 determine a dosing command based at least in part on the slip factor, and the change in the amount of NOx and the change in the amount of the reductant downstream of the catalytic device; and 
 provide the dosing command to the injector. 
   
     
     
         2 . The exhaust treatment system of  claim 1 , wherein the controller is further configured to:
 determine a first parameter by dividing the change in the amount of NOx downstream of the catalytic device by the change in the amount of the reductant injected by the injector;   determine a second parameter by dividing the change in the amount of the reductant downstream of the catalytic device by the change in the amount of the reductant injected by the injector; and   determine the dosing command based on the first parameter and the second Parameter.   
     
     
         3 . The exhaust treatment system of  claim 2 , wherein the controller is further configured to:
 determine a change in a first ratio of an amount of NOx exiting the catalytic device to an amount of NOx upstream of the catalytic device to determine the change in the amount of NOx, wherein the first parameter corresponds to a first slope of the first ratio relative to an amount of the reductant injected by the injector; and   determine a change in a second ratio of an amount of the reductant exiting the catalytic device to an amount of the reductant upstream of the catalytic device to determine the change in the amount of the reductant downstream of the catalytic device, wherein the second parameter corresponds to a second slope of the second ratio relative to an amount of the reductant injected by the injector.   
     
     
         4 . The exhaust treatment system of  claim 2 , wherein the controller is further configured to scale the first parameter and the second parameter using the slip factor, add the scaled first and second parameters to obtain a net parameter, and determine the dosing command using the net parameter. 
     
     
         5 . The exhaust treatment system of  claim 4 , wherein the controller is further configured to determine an amount of NOx upstream of the catalytic device and multiply the net parameter by the amount of NOx upstream of the catalytic device to determine the dosing command. 
     
     
         6 . The exhaust treatment system of  claim 1 , wherein the controller is further configured to determine the change in the amount of NOx and the change in the amount of the reductant downstream of the catalytic device using at least one physics-based model of the catalytic device. 
     
     
         7 . The exhaust treatment system of  claim 6 , wherein:
 the at least one physics-based model includes a baseline physics-based model and an offset physics-based model; and   the controller is further configured to estimate a baseline amount of NOx and a baseline amount of the reductant exiting the catalytic device using the baseline physics-based model, and to predict an offset amount of NOx and an offset amount of the reductant exiting the catalytic device due to the change in the amount of injected reductant using the offset physics-based model.   
     
     
         8 . The exhaust treatment system of  claim 7 , wherein the controller is further configured to determine the change in the amount of NOx based on the baseline amount of NOx and the offset amount of NOx, and to determine the change in the amount of the reductant downstream of the catalytic device based on the baseline amount of the reductant and the offset amount of the reductant. 
     
     
         9 . The exhaust treatment system of  claim 1 , wherein the controller is further configured to determine the slip factor based on at least one of user input, a look-up table, a map, or a formula. 
     
     
         10 . The exhaust treatment system of  claim 1 , wherein the controller is further configured to increase the slip factor when the controller determines that a lower NOx slip rate is desired and decrease the slip factor when the controller determines that a lower reductant slip rate is desired. 
     
     
         11 . The exhaust treatment system of  claim 1 , wherein the controller is further configured to measure a temperature of the flow of exhaust and determine the slip factor based on the measured temperature. 
     
     
         12 . The exhaust treatment system of  claim 11 , wherein:
 the controller is in communication with a database storing a correlation between the slip factor and a standard deviation of the temperature based on a limit on the reductant slip rate; and   the controller is further configured to determine the slip factor using the correlation.   
     
     
         13 . The exhaust treatment system of  claim 1 , further comprising:
 a database storing the slip factor after shutdown of the engine;   wherein the controller is further configured to, during start-up of the engine, use the slip factor stored in the database after shutdown of the engine.   
     
     
         14 . The exhaust treatment system of  claim 1 , wherein the change in the amount of the injected reductant is an increase by at least 10%. 
     
     
         15 . The exhaust treatment system of  claim 1 , wherein the catalytic device is a selective catalytic reduction device. 
     
     
         16 . A method of controlling an injection of a reductant into a flow of exhaust from an engine using a controller, the method comprising:
 injecting the reductant into the flow of exhaust with an injector disposed upstream from a catalytic device, the injector and the catalytic device being disposed in an exhaust system for the engine;   passing the flow of exhaust through the catalytic device;   determining, using the controller, a first amount of NOx and a first amount of the reductant in the flow of exhaust at an exit of the catalytic device based at least in part on a first dosing rate of the reductant;   determining, using the controller, a second amount of NOx and a second amount of the reductant in the flow of exhaust at the exit of the catalytic device based at least in part on a second dosing rate of the reductant, the first dosing rate of the reductant being different from the second dosing rate of the reductant;   determining, using the controller, a slip factor corresponding to a relative weight of a NOx slip rate exiting the catalytic device compared to a reductant slip rate exiting the catalytic device;   determining, using the controller, a dosing command based at least in part on the slip factor, the difference between the second amount of NOx and the first amount of NOx, and the difference between the second amount of the reductant and the first amount of the reductant; and   providing, using the controller, the dosing command to the injector.   
     
     
         17 . The method of  claim 16 , further comprising:
 determining, using the controller, a first parameter by dividing the difference between the second amount of NOx and the first amount of NOx by the difference between the second dosing rate and the first dosing rate; and   determining, using the controller, a second parameter by dividing the difference between the second amount of the reductant and the first amount of the reductant by the difference between the second dosing rate and the first dosing rate;   wherein the dosing command is further determined based on the first and second parameters.   
     
     
         18 . A non-transitory computer readable storage device storing instructions that are executable by at least one processor of a computer to cause the computer to perform a method for controlling an injection of reductant into a flow of exhaust from an engine, the method comprising:
 determining a change in an amount of NOx and a change in an amount of a reductant downstream of a catalytic device due to a change in an amount of the reductant injected by an injector disposed upstream of the catalytic device in an exhaust flow direction;   determining a slip factor corresponding to a relative weight of a NOx slip rate exiting the catalytic device compared to a reductant slip rate exiting the catalytic device;   determining a dosing command based at least in part on the slip factor, the change in the amount of NOx, and the change in the amount of the reductant downstream of the catalytic device; and   causing a change in the amount of the reductant injected by the injector based on the dosing command.   
     
     
         19 . The non-transitory computer readable storage device of  claim 18 , wherein the change in the amount of the injected reductant is a change from a first dosing rate to a second dosing rate, the first dosing rate of the reductant being different from the second dosing rate of the reductant, and the method further comprises:
 determining a first amount of NOx and a first amount of the reductant in the flow of exhaust downstream of the catalytic device based at least in part on the first dosing rate of the reductant;   determining a second amount of NOx and a second amount of the reductant downstream of the catalytic device based at least in part on the second dosing rate of the reductant;   determining the change in the amount of NOx as a difference between the second amount of NOx and the first amount of NOx; and   determining the change in the amount of the reductant as a difference between the second amount of the reductant downstream of the catalytic device and the first amount of the reductant downstream of the catalytic device.   
     
     
         20 . The non-transitory computer readable storage device of  claim 19 , wherein the method further comprises:
 measuring a temperature of the flow of exhaust; and   determining the slip factor based on the measured temperature.