Apparatus and method of operating an injector for an exhaust gas aftertreatment apparatus

Abstract

A method for operating an exhaust aftertreatment system injector to prevent coking includes steps of injecting fuel for heating the aftertreatment devices, when not injecting fuel, flowing air to purge and cool the nozzle to prevent carbon deposits when exhaust gas temperature is low, and substantially stop air flow to allow passive heating of the nozzle by the exhaust for oxidation of any accumulated carbon when exhaust temperature is high enough to support oxidation. Preferably, the nozzle has a catalytic material coating to reduce the temperature necessary for oxidation of the coking material.

What is claimed is: 
     
         1 . A method of operating an injector for an exhaust gas aftertreatment apparatus to avoid coke deposits, the injector nozzle having a catalyst coating, the method comprising the steps of:
 selectively injecting a hydrocarbon fluid into an exhaust gas flow to increase the temperature of the exhaust flow;   when not injecting hydrocarbon, causing air to flow through the injector nozzle when an exhaust gas temperature is below a threshold temperature; and,   when not injecting hydrocarbon, substantially stopping the flow of air through the injector nozzle when the exhaust gas temperature is above the threshold temperature.   
     
     
         2 . The method as in  claim 1 , further comprising:
 monitoring a condition of the aftertreatment apparatus;   monitoring an exhaust gas temperature; and,   responsive to the condition of the aftertreatment apparatus and responsive to the exhaust gas temperature, controlling the injection of hydrocarbon in the exhaust gas flow.   
     
     
         3 . The method as in  claim 1 , comprising the step of causing air to flow through the injector immediately following injecting hydrocarbon to purge residual hydrocarbon from the injector. 
     
     
         4 . The method as in  claim 1 , wherein the flow of air through the injector nozzle when the exhaust gas temperature is above the threshold temperature is substantially stopped until the exhaust gas temperature is below the threshold temperature. 
     
     
         5 . The method as in  claim 1 , wherein the flow of air through the injector nozzle when the exhaust gas temperature is above the threshold temperature is substantially stopped for a predetermined time interval.