Exhaust gas aftertreatment systems

Abstract

A system for effective NOx control in a diesel or other lean burn internal combustion engine is presented. The system includes a urea-based SCR catalyst having an oxidation catalyst coupled upstream of it and an ALNC coupled upstream of the oxidation catalyst. This system configuration results in improved NOx conversion due to faster SCR catalyst warm-up and higher operating temperatures. Additionally, placing the ALNC upstream of the oxidation catalyst prevents hydrocarbon slip into the SCR catalyst at low exhaust gas temperatures. Also, system reliability is improved by adding an auxiliary NOx aftertreatment device.

1 - 5 . (canceled)  
   
   
       6 . A method for controlling a temperature of an oxidation catalyst coupled downstream of an Active Lean NOx catalyst (ALNC), comprising: 
 providing an indication that the ALNC temperature is above a first predetermined temperature; and    in response to said indication controlling the temperature of the oxidation catalyst by adjusting an amount of reductant in an exhaust gas mixture entering the ALNC.    
   
   
       7 . A method for controlling a temperature of an oxidation catalyst coupled downstream of an Active Lean NOx catalyst (ALNC) during cold start, comprising: 
 providing an indication that the ALNC temperature is above a first predetermined temperature; and    in response to said indication adjusting an amount of reductant in an exhaust gas mixture entering the ALNC thereby raising the temperature of the oxidation catalyst above a second predetermined temperature.    
   
   
       8 . A method for controlling a temperature of an oxidation catalyst coupled downstream of an Active Lean NOx catalyst (ALNC) during cold start, comprising: 
 injecting a predetermined amount of reductant into an exhaust gas stream entering the ALNC when the oxidation catalyst temperature is above a predetermined temperature; and    increasing reductant injection into the ALNC thereby causing the oxidation catalyst temperature to reach said predetermined temperature otherwise.    
   
   
       9 - 10 . (canceled)