System and method for nox reduction optimization

Abstract

An engine controller determines the cost of operating a combustion engine and the cost of operating an emissions after-treatment device. Accordingly, the engine controller adjusts parameters for operation of the engine and the after-treatment device to ensure cost-effective use of the engine and the after-treatment device while complying with exhaust emissions requirements. In particular, the engine controller receives the price of fuel consumed by the engine and the price of reductant used by the after-treatment device to determine the respective cost of operation. Specifically, the fuel is diesel fuel used in a diesel engine; the reductant is urea use in a urea-based Selective Catalytic Reduction (SCR) system; and the regulated exhaust emissions is nitrogen oxide (NOx) emissions. The engine operating parameters may include cooled exhaust gas recirculation airflow, fuel injection timing, fuel injection pressure, and air-to-fuel ratio. The SCR system operating parameters may include the volume of urea injected.

What is claimed is: 
     
         1 . A system for controlling exhaust emissions from a combustion engine, the system comprising:
 a combustion engine adapted to produce a first mixture of exhaust emissions after combustion of fuel according one or more engine operating parameters;   an exhaust after-treatment device adapted to convert the first exhaust emissions to a second mixture of exhaust emissions according to one or more after-treatment parameters, and adapted to inject a reductant from a supply of the reductant into the first exhaust emissions; and   an engine controller adapted to control the engine and the after-treatment device, and adapted to determine the supply of the reductant,   wherein, according to the supply of the reductant, the engine controller at least one of adjusts the one or more engine operating parameters and adjusts the one or more after-treatment parameters.   
     
     
         2 . The system for controlling exhaust emissions from a combustion engine according to  claim 1 ,
 wherein the one or more engine operating parameters comprise at least one of a fuel injector timing, an air-to-fuel ratio, a fuel injection pressure, and a cooled exhaust gas recirculation airflow, and   wherein the one or more after-treatment parameters comprise a reductant injection volume.   
     
     
         3 . The system for controlling exhaust emissions from a combustion engine according to  claim 2 , wherein if the supply of the reductant falls below a threshold,
 the engine controller at least one of adjusts the one or more engine operating parameters and adjusts the one or more after-treatment parameters by at least one of retarding the fuel injector timing, decreasing the air-to-fuel ratio, decreasing the fuel injection pressure, increasing the cooled exhaust gas recirculation airflow, and decreasing the reductant injection volume.   
     
     
         4 . The system for controlling exhaust emissions from a combustion engine according to  claim 1 , wherein the reductant is urea. 
     
     
         5 . A method for controlling exhaust emissions from a combustion engine, the method comprising:
 determining a supply of a reductant for an exhaust after-treatment device; and   at least one of adjusting one or more engine operating parameters and adjusting one or more after-treatment parameters according to the supply of a reductant,   wherein the one or more engine operating parameters determine a first mixture of exhaust emissions after combustion of fuel by a combustion engine,   wherein the one or more after-treatment parameters determine a second mixture of exhaust emissions converted from the first exhaust emissions by the exhaust after-treatment device, and   wherein the exhaust after-treatment device injects the reductant from a supply of the reductant into the first exhaust emissions.   
     
     
         6 . The method for controlling exhaust emissions from a combustion engine according to  claim 5 ,
 wherein the one or more engine operating parameters comprise at least one of a fuel injector timing, an air-to-fuel ratio, a fuel injection pressure, and a cooled exhaust gas recirculation airflow, and   wherein the one or more after-treatment parameters comprise a reductant injection volume.   
     
     
         7 . The method for controlling exhaust emissions from a combustion engine according to  claim 6 , wherein if the supply of the reductant falls below a threshold, the step of at least one of adjusting the one or more engine operating parameters and adjusting the one or more after-treatment parameters includes at least one of retarding the fuel injector timing, decreasing the air-to-fuel ratio, decreasing the fuel injection pressure, increasing the cooled exhaust gas recirculation airflow, and decreasing the reductant injection volume. 
     
     
         8 . The method for controlling exhaust emissions from a combustion engine according to  claim 5 , wherein the reductant is urea.