Methods to protect selective catalyst reducer aftertreatment devices during uncontrolled diesel particulate filter regeneration

Abstract

The present invention is directed to a method to operate an electronically controlled internal combustion engine with an exhaust system equipped with a diesel particulate filter upstream of a selective catalyst reducer to protect the selective catalyst reducer from premature aging and failure caused by exhaust temperature heat generated during uncontrolled regeneration of the diesel particulate filter.

1 . A method to operate an electronically controlled internal combustion engine equipped with a Engine Control System (ECS) and an exhaust system with a Diesel Particulate Filter (DPF) having an inlet and an outlet, said DPF upstream of a Selective Catalytic Reducer (SCR) having an inlet and an outlets and at least one temperature sensor at said SCR inlet or DPF outlet electronically connected to said ECS to transmit data signals to said ECS indicative of temperature at said SCR inlet, said SCR in fluid connection with a urea source; said method to protect the SCR during uncontrolled DPF regeneration comprising:
 determining engine operating mode;   determining whether the DPF is regenerating;   sensing whether the SCR inlet temperature exceeds a predetermined threshold for a predetermined period of time:   introducing urea to said SCR in an amount sufficient to cool the SCR during DPF regeneration below said predetermined temperature threshold.   
   
   
       2 . The method of  claim 1 , further including a clean up catalyst to catalyze any excess ammonia slip. 
   
   
       3 . The method of  claim 1 , further including a dump valve responsive to commands from said ECS to reroute exhaust gas in said exhaust system to bypass said SCR during uncontrolled DPF regeneration. 
   
   
       4 . The method of  claim 3  wherein said dump valve is controlled by said ESC and actuated responsive to the introduction of urea if said SCR inlet temperature continues to exceed a predetermined threshold for a predetermined period of time. 
   
   
       5 . The method of  claim 1 , wherein said engine operating mode is engine idle. 
   
   
       6 . The method of  claim 1 , wherein said urea is introduced to said SCR by an injector in fluid communication with a urea source; said injector responsive to commands from said ECS. 
   
   
       7 . A method to operate an electronically controlled internal combustion engine equipped with an Engine Control System (ECS), an exhaust system equipped with a Diesel Particulate Filter (DPF) having an inlet and an outlet, said DPF positioned upstream of a Selective Catalytic Reducer having an inlet and an outlet, at least one temperature sensor at said SCR inlet electronically connected to said ECS to transmit data signals to said ECS indicative of temperature at said SCR inlet, and a protector to prevent overheating of the SCR during uncontrolled DPF regeneration, comprising:
 determining engine operating mode:   determining whether the DPF is regenerating;   sensing whether the SCR inlet temperature exceeds a predetermined threshold for a predetermined period of time;   actuating said protector to prevent overheating of said SCR during uncontrolled DPF regeneration.   
   
   
       8 . The method of  claim 7 , wherein said protector is comprised of a source of urea and an injector in fluid communication with said urea and said SCR to facilitate the introduction of an amount of urea in sufficient quantity over a sufficient period of time to cool the SCR inlet below a predetermined temperature for a predetermined period of time during uncontrolled DPF regeneration. 
   
   
       9 . The method of  claim 8 , further including a clean tip catalyst to catalyze any excess ammonia slip. 
   
   
       10 . The method of  claim 7 , wherein said protector is a dump valve actuated by said ECS to divert exhaust gas from said SCR during uncontrolled DPF regeneration; said dump valve responsive to commands from said ESC to divert exhaust from said SCR when said SCR inlet temperature exceeds a predetermined temperature for a predetermined period of time during uncontrolled DPF regeneration. 
   
   
       11 . The method of  claim 7 , wherein the engine operating mode is engine idle. 
   
   
       12 . The method of  claim 10 , wherein said dump valve vents said exhaust from said exhaust system.