NOx CONTROL SYSTEMS AND METHODS FOR CONTROLLING NOx EMISSIONS

Abstract

An exhaust aftertreatment system comprising a selective reduction catalyst, a NO x sensor or an NH 3 sensor, a urea injector, and a dosing control unit, wherein the dosing control unit calculates the rate of urea injection by estimating the concentrations of NO and NO 2 in the exhaust downstream of the SCR catalyst.

1 . A method for minimizing NO x  in an exhaust stream from an engine having an exhaust aftertreatment system comprising a urea solution injector and a catalyst, the method comprising:
 collecting engine operating parameters;   measuring NO x  concentrations in the exhaust stream;   estimating a NO concentration and a NO 2  concentration in the exhaust stream using the engine operating parameters and the measured NO x  concentration;   estimating a fractional surface coverage of NH 3  in the catalyst;   calculating an amount of urea solution needed to minimize NO x  emissions using the estimate of the NO concentration and the estimate of the NO 2  concentration in the exhaust and the estimate of fractional surface coverage of NH 3  in the catalyst; and   injecting an amount of urea solution into the exhaust stream.   
     
     
         2 . The method of  claim 1 , wherein the engine is a diesel engine. 
     
     
         3 . The method of  claim 1 , wherein the engine parameters are selected from the group consisting of engine speed, engine load, engine temperature, exhaust gas temperature, exhaust flow rate, and exhaust pressure. 
     
     
         4 . The method of  claim 1 , wherein a state estimator is used to calculate the quantity of urea solution needed to minimize NO x  emissions. 
     
     
         5 . A method for minimizing NO x  in an exhaust stream from an engine having an exhaust aftertreatment system comprising a urea solution injector and a catalyst, the method comprising:
 collecting engine operating parameters;   measuring NH 3  concentrations in the exhaust stream;   estimating a NO concentration and a NO 2  concentration in the exhaust stream using the engine operating parameters and the measured NH 3  concentration;   estimating a fractional surface coverage of NH 3  in the catalyst;   calculating an amount of urea solution needed to minimize NO x  emissions using the estimate of the NO concentration and the NO 2  concentration in the exhaust and the estimate of fractional surface coverage of NH 3  in the catalyst; and   injecting an amount of urea solution into the exhaust stream.   
     
     
         6 . The method of  claim 5 , wherein the engine is a diesel engine. 
     
     
         7 . The method of  claim 5 , wherein the engine parameters are selected from the group consisting of engine speed, engine load, engine temperature, exhaust gas temperature, exhaust flow rate, and exhaust pressure. 
     
     
         8 . The method of  claim 5 , wherein a state estimator is used to calculate the quantity of urea solution needed to minimize NO x  emissions.