Diesel aftertreatment systems

Abstract

A method for improving NOx conversion efficiency of a Nox-reducing catalyst by determining an accurate amount of reductant required is presented. The method includes calculating an initial reductant injection amount based on a steady state amount of NOx in the engine feedgas and adjusting the initial amount to compensate for transient NOx emissions. The compensation is initiated in response to an engine transient, such as impending acceleration or deceleration. This method further results in improved vehicle fuel economy.

1 . A method for controlling a Nox-reducing catalyst coupled downstream of an internal combustion engine, comprising: 
 calculating a desired amount of reductant based on a measure of engine transient behavior; and    injecting said calculated desired amount of reductant into the lean exhaust gas aftertreatment device.    
     
     
         2 . The method as set forth in  claim 1  wherein the engine is a diesel engine.  
     
     
         3 . The method as set forth in  claim 1  wherein the NOx-reducing catalyst is an ALNC.  
     
     
         4 . The method as set forth in  claim 3  wherein said reductant is hydrocarbon.  
     
     
         5 . The method as set forth in  claim 1  wherein the Nox-reducing catalyst is an SCR catalyst.  
     
     
         6 . The method as set forth in  claim 5  wherein said reductant is urea.  
     
     
         7 . The method as set forth in  claim 1  wherein said measure of engine transient behavior comprises a measure of engine deceleration.  
     
     
         8 . The method a set forth in  claim 1  wherein said measure of engine transient behavior is based on a rate of change of pedal position.  
     
     
         9 . The method as set forth in  claim 1  wherein said measure of engine transient behavior is based a rate of change of engine speed.  
     
     
         10 . The method as set forth in  claim 1  wherein said measure of engine transient behavior is based a rate of change of engine fuel injection amount.  
     
     
         11 . The method as set forth in  claim 1  wherein said measure of engine transient behavior is based a rate of change of engine load.  
     
     
         12 . The method as set forth in  claim 1  wherein said measure of engine transient behavior is filtered.  
     
     
         13 . A method for controlling a NOx-reducing catalyst coupled downstream of an internal combustion engine, comprising: 
 calculating an initial reductant amount;    adjusting said initial reductant amount to compensate for engine transient behavior; and    injecting said adjusted initial amount of reductant into the exhaust gas aftertreatment device.    
     
     
         14 . The method as set forth in  claim 13  wherein the NOx-reducing catalyst is an ALNC.  
     
     
         15 . The method as set forth in  claim 14  wherein said reductant is hydrocarbon.  
     
     
         16 . The method as set forth in  claim 13  wherein the NOx-reducing catalyst is an SCR catalyst.  
     
     
         17 . The method as set forth in  claim 16  wherein said reductant is urea.  
     
     
         18 . The method as set forth in  claim 13  wherein the engine is a diesel engine.  
     
     
         19 . The method as set forth in  claim 13  wherein said initial amount of reductant is based on a steady state estimate of an amount of NOx in an engine exhaust gas.  
     
     
         20 . The method as set forth in  claim 13  wherein said engine transient behavior is measured by calculating a rate of change of pedal position.  
     
     
         21 . The method as set forth in  claim 13  wherein said engine transient behavior is measured by calculating a rate of change of engine fuel injection amount.  
     
     
         22 . The method as set forth in  claim 13  wherein said engine transient behavior is measured by calculating a rate of change of engine speed.  
     
     
         23 . The method as set forth in  claim 13  wherein said engine transient behavior is measured by calculating a rate of change of engine load.  
     
     
         24 . A system for reducing NOx emissions in an engine exhaust gas mixture, Comprising: 
 a NOx-reducing catalyst coupled downstream of the engine; and    a controller injecting reductant into said NOx-reducing catalyst wherein said amount of injected reductant is based on a measure of engine transient behavior.    
     
     
         25 . A method for improving efficiency of a NOx reducing catalyst coupled downstream of an internal combustion engine, comprising: 
 providing an indication of an impending engine transient; and    adjusting an amount of reductant injection into the NOx-reducing catalyst to compensate for variations in engine feedgas Nox caused by said engine transient.    
     
     
         26 . A system for reducing transient and steady-state NOx emissions in the exhaust gases of a vehicle powered by a diesel fueled internal combustion engine comprising: 
 a) a Nox-reducing catalyst downstream of said engine;    b) a source of liquid hydrocarbons;    c) a valve for introducing predetermined quantities of said hydrocarbons from said source into said exhaust gases upstream of said NOx-reducing catalyst pursuant to a command signal;    d) a plurality of vehicle sensors generating sensor signals indicative of at least one operating condition of said engine, said sensors including at least one transient operation sensor generating a signal prior to a transient operating condition of said engine and predictive of said transient operating condition;    e) an engine control unit having a plurality of programmed routines for 
 controlling said engine in response to said plurality of sensor signals, said routines including at least  
 (1) a first routine for generating a first command signal for introducing a first predetermined quantity of said hydrocarbons through said valve when said engine is operating at a steady state condition sufficient to reduce a portion of NOx emissions produced at the steady state condition, and  
 (2) a second routine activated when said at least one transient operating sensor generates said signal predictive of said transient operating condition, said second routine comprising: 
 i) calculating a second quantity of hydrocarbons sufficient to reduce a portion of the NOx emissions generated during a period in which said engine is operating in said transient operating condition and  
 ii) generating a second command signal for introducing said second predetermined quantity of said hydrocarbons through said valve during at least a portion of the period in which said engine is operating in said transient operating condition.  
 
   
     
     
         27 . The system of  claim 26  wherein said source of hydrocarbons comprises a diesel fuel tank of said vehicle.  
     
     
         28 . The system of  claim 26  wherein said transient operation sensor comprises an engine speed sensor.  
     
     
         29 . The system of  claim 26  wherein said transient operation sensor comprises a pedal position sensor.  
     
     
         30 . The system of  claim 26  wherein said transient operation sensor is indicative of a change in speed of said engine.  
     
     
         31 . The system of  claim 26  wherein said transient operation sensor is indicative of deceleration of said engine.  
     
     
         32 . The system of  claim 26  wherein said transient operation sensor is indicative of a change in load of said engine.  
     
     
         33 . The system of  claim 26  wherein said transient operating condition is controlled by the operator of said vehicle.  
     
     
         34 . A method for reducing NOx emissions present in the exhaust gases of an internal combustion engine comprising the steps of: 
 a) providing a source of liquid hydrocarbons;    b) providing a reducing catalytic converter downstream of said engine through which said exhaust gases pass;    c) sensing a set of engine operating parameters including at least a space velocity of the exhaust gases and a temperature of the exhaust gases;    d) calculating a first concentration of hydrocarbon and Nox emissions present in said exhaust gases based on said sensed engine operating parameters during a steady state operation of said engine;    e) determining an amount of said hydrocarbons sufficient to reduce a desired percentage of said NOx emissions when said exhaust gases leave said reducing catalytic converter during said steady state operation of said engine;    f) metering a quantity of said hydrocarbons into said exhaust gases upstream of said reducing catalytic converter sufficient to reduce said desired percentage of said NOx emissions during said steady state operation of said engine;    g) sensing a signal predictive of a transient operation state of said engine;    h) calculating the expected concentration of NOx emissions present in said exhaust gases while the engine is in said transient operation state based on said signal predictive of said transient operation state; and    i) metering an additional quantity of said hydrocarbons into said exhaust gases upstream of said reducing catalytic converter sufficient to reduce said expected concentration of NOx emissions during said transient engine operation state.    
     
     
         35 . The method of  claim 34  in which said internal combustion engine is a lean operating gasoline engine.  
     
     
         36 . The method of  claim 34  wherein said lean operating gasoline engine operates at an air-to-fuel ratio of at least 1.03.  
     
     
         37 . The method of  claim 34  wherein said signal predictive of a transient operating state of said engine indicates a change in engine fuel demand.  
     
     
         38 . The method of  claim 34  wherein said signal predictive of a transient operating state of said engine indicates a change in engine fueling rate.  
     
     
         39 . The method of  claim 34  wherein said signal predictive of a transient operating state of said engine indicates a change in a pedal position.  
     
     
         40 . The method of  claim 34  wherein said signal predictive of a transient operating state of said engine indicates a change in engine speed.  
     
     
         41 . The method of  claim 34  wherein said signal predictive of a transient operating state of said engine indicates a change in engine load.  
     
     
         42 . The method of  claim 34  wherein said signal predictive of a transient operating state of said engine indicates deceleration of said engine.  
     
     
         43 . The method of  claim 34  wherein said transient operating state of said engine is responsive to an operator inputted command.  
     
     
         44 . The method of  claim 34  wherein said sensed operating conditions include the air-to-fuel ratio of the engine.  
     
     
         45 . A method for reducing NO x  emissions produced by a vehicle powered by a diesel engine having an active lean NOx catalyst through which the exhaust gases pass and sensors for determining NO x  concentrations at steady state engine operating conditions, the improvement comprising the steps of: 
 a) sensing a pedal position sensor signal prior to an engine transient; and    b) injecting a set quantity of diesel fuel reductant into the exhaust gases of the engine sufficient to substantially react with transient emissions produced by the engine during said transient, the injection occurring at a time in advance of and not later than the time the engine produces the transient emissions.