Exhaust treatment system implementing selective doc bypass

Abstract

An exhaust treatment system for use with a power system is disclosed. The exhaust treatment system may have an SCR device ( 32 ), and an oxidation device ( 26 ) located upstream of the SCR device ( 32 ) to convert NO to NO2. The exhaust treatment system may also have an exhaust passageway ( 14 ) extending from an exhaust source ( 10 ) to the oxidation device ( 26 ), and a bypass passageway ( 24 ) extending from the exhaust passageway at a location upstream of the oxidation device to the exhaust passageway at a location downstream of the oxidation device ( 26 ). The exhaust treatment system may further have a valve element ( 20 ) configured to selectively direct exhaust from the exhaust source ( 10 ) through the oxidation device ( 26 ) and through the bypass passageway ( 24 ), at least one sensor configured to sense operating parameters of the exhaust source ( 10 ), and a controller ( 36 ) in communication with the valve element ( 20 ). The controller ( 36 ) may be configured to move the valve element ( 20 ) in response to an estimated ratio of NO to NO2 based on sensed operating parameters of the exhaust source ( 10 ).

1 . An exhaust treatment system, comprising:
 an SCR device;   an oxidation device located upstream of the SCR device to convert NO to NO 2 ;   an exhaust passageway extending from an exhaust source to the oxidation device;   a bypass passageway extending from the exhaust passageway at a location upstream of the oxidation device to the exhaust passageway at a location downstream of the oxidation device;   a valve element configured to selectively direct exhaust from the exhaust source through the oxidation device and through the bypass passageway;   at least one sensor configured to sense operating parameters of the exhaust source; and   a controller in communication with the valve element, the controller being configured to move the valve element in response to an estimated ratio of NO to NO 2  based on sensed operating parameters of the exhaust source.   
   
   
       2 . The exhaust treatment system of  claim 1 , wherein the controller includes a map stored in a memory thereof relating the exhaust source operating parameters to an amount of NO and an amount of NO 2  produced by the exhaust source. 
   
   
       3 . The exhaust treatment system of  claim 1 , wherein the exhaust source operating parameters include at least one of fuel/air settings, operating speed, load, and fuel injection profile. 
   
   
       4 . The exhaust treatment system of  claim 1 , wherein the valve element includes a three-way valve located at the junction of the bypass passageway and the exhaust passageway upstream from the oxidation device. 
   
   
       5 . The exhaust treatment system of  claim 1 , wherein the valve element includes a two-way valve located within the bypass passageway. 
   
   
       6 . The exhaust treatment system of  claim 1 , wherein:
 the controller has stored in a memory thereof a virtual model of the exhaust treatment system; and   the valve element is moved based on the estimated ratio of NO to NO 2  in the exhaust gas and the virtual model.   
   
   
       7 . The exhaust treatment system of  claim 1 , wherein a greater amount of exhaust is directed through the DOC when the amount of NO 2  in the exhaust is less than the amount of NO in the exhaust. 
   
   
       8 . The exhaust treatment system of  claim 7 , wherein a greater amount of exhaust is directed through the bypass passageway when the amount of NO 2  in the exhaust is greater than the amount of NO in the exhaust. 
   
   
       9 . The exhaust treatment system of  claim 1 , wherein the oxidation device includes a substrate coated with a precious metal. 
   
   
       10 . A method of treating exhaust, comprising:
 generating a flow of exhaust;   treating at least a portion of the flow of exhaust by a catalyst;   directing the flow of exhaust through an SCR device;   estimating a ratio of NO to NO 2  in the flow of exhaust based on sensed operating parameters of a power source that generates the flow of exhaust; and   changing an amount of the at least a portion in response to the estimation.   
   
   
       11 . The method of  claim 10 , wherein estimating includes referencing a known relationship between power source operating parameters and the production of NO and NO 2 . 
   
   
       12 . The method of  claim 11 , wherein the power source operating parameters include at least one of fuel/air settings, operating speed, load, and fuel injection profile. 
   
   
       13 . The method of  claim 12 , wherein changing an amount of the at least a portion includes estimating the amount of the at least a portion based on the ratio of NO to NO 2  and the predicted behavior of the catalyst. 
   
   
       14 . The method of  claim 10 , further including increasing the amount of the at least a portion when an amount of NO in the exhaust directed to the SCR device exceeds an amount of NO 2  in the exhaust directed to the SCR device. 
   
   
       15 . The method of  claim 14 , further including decreasing the amount of the at least a portion when the amount of NO 2  in the exhaust directed to the SCR device exceeds the amount of NO in the exhaust directed to the SCR device. 
   
   
       16 . A power system, comprising:
 a power source configured to combust a fuel/air mixture and generate power and a flow of exhaust;   an SCR device;   an exhaust passageway fluidly communicating the power source with the SCR device;   an oxidation device to convert NO to NO 2  located in the exhaust passageway between the power source and the SCR device;   a bypass passageway extending from the exhaust passageway at a location upstream of the oxidation device to the exhaust passageway at a location downstream of the oxidation device;   a valve element configured to selectively direct exhaust from the power source through the oxidation device and through the bypass passageway;   at least one sensor configured to sense operating parameters of the exhaust source; and   a controller in communication with the valve element, the controller being configured to move the valve element in response to an estimated ratio of NO to NO 2  based on sensed operating parameters of the power source.   
   
   
       17 . The power system of  claim 16 , wherein the controller includes a map stored in a memory thereof relating power source operating parameters to an amount of NO and an amount of NO 2  produced by the power source. 
   
   
       18 . The power system of  claim 17 , wherein the power source operating parameters include at least one of fuel/air settings, operating speed, load, and fuel injection profile. 
   
   
       19 . The power system of  claim 16 , wherein a greater amount of exhaust is directed through the DOC when an amount of NO 2  in the exhaust is less than an amount of NO in the exhaust. 
   
   
       20 . The power system of  claim 19 , wherein a greater amount of exhaust is directed through the bypass passageway when the amount of NO 2  in the exhaust is greater than the amount of NO in the exhaust.