Diesel Engine Nox Reduction

Abstract

An engine system for treating nitrogen oxides present in an exhaust gas generated by the combustion of fuel. The engine system includes one or more long breathing lean nitrogen oxide traps that is/are configured to store at least a portion of the nitrogen oxide in the exhaust gas when the lean nitrogen oxide trap operates in an absorption mode. The lean nitrogen oxide trap is also configured for the conversion of the nitrates stored by the lean nitrogen oxide trap during a regeneration event. The engine-out nitrogen oxide levels may be reduced to extend the duration of the absorption process, thereby reducing both the frequency of regeneration events and the associated fuel penalty. The system may include primary and secondary exhaust gas recirculation systems, with exhaust gas from the secondary system being returned to the engine cylinder to reduce the level of nitrogen oxides in that exhaust gas.

1 . An engine system for treating nitrogen oxides present in an exhaust gas generated by the combustion of fuel, the engine system comprising:
 a diesel engine configured to generate the exhaust gas by the combustion of a fuel, the diesel engine calibrated for the generated exhaust gas to have, at least periodically, an engine-out nitrogen oxide level of less than around 100 parts-per-million;   a lean nitrogen oxide trap configured to store at least a portion of the nitrogen oxide in the exhaust gas when the lean nitrogen oxide trap operates in an absorption mode, the lean nitrogen oxide trap configured for the conversion of a plurality of nitrates stored by the lean nitrogen oxide trap during a regeneration event, the adsorption process being, at least periodically, at least three times longer than that of a conventional LNT operating under similar conditions.   
     
     
         2 . The engine system of  claim 1 , further including a primary exhaust gas recirculation system configured for at least a portion of the exhaust gas generated by the diesel engine to be circulated to an intake manifold of the diesel engine, the exhaust gas circulated to the intake manifold being used to lower a temperature attained during the combustion of fuel by the diesel engine to reduce the engine-out nitrogen oxide level. 
     
     
         3 . The engine system of  claim 2 , further including a secondary exhaust gas recirculation system configured to recirculate at least a portion of the exhaust gas that has exited the lean nitrogen oxide trap to a location upstream of the diesel engine. 
     
     
         4 . The engine system of  claim 3 , wherein the secondary exhaust gas recirculation system is configured to recirculate at least a portion of the exhaust gas exiting the lean nitrogen oxide trap while the lean nitrogen oxide trap is undergoing a regeneration event. 
     
     
         5 . The engine system of  claim 3 , wherein the secondary exhaust gas recirculation system does not recirculate exhaust gas during the absorption process in the lean nitrogen oxide trap. 
     
     
         6 . The engine system of  claim 3 , wherein exhaust gas delivered by the secondary exhaust gas recirculation system is supplied to at least one cylinder of the diesel engine that is operating in a low temperature combustion mode, the level of nitrogen oxide of the supplied exhaust gas being lowered by the combustion of the fuel in the at least one cylinder. 
     
     
         7 . An engine system for treating nitrogen oxides present in an exhaust gas generated by the combustion of fuel by an engine, the engine system comprising:
 a primary exhaust gas recirculation system configured for at least a portion of the exhaust gas generated by the diesel engine to be circulated to an intake manifold of the engine;   at least one injector configured to inject a fuel into the exhaust gas;   a plurality of lean nitrogen oxide traps; and   a secondary exhaust gas recirculation system configured to recirculate at least a portion of the exhaust gas that exits one or more of the lean nitrogen oxide traps to a location upstream of the engine.   
     
     
         8 . The engine system of  claim 7 , wherein the plurality of lean nitrogen oxide traps includes a first lean nitrogen oxide trap and a second lean nitrogen oxide trap, and wherein at least one of the first and second lean nitrogen oxide traps is configured to operate in an absorption mode for at least a portion of the time while the other of the first and second lean nitrogen oxide traps undergoes a regeneration event. 
     
     
         9 . The engine system of  claim 8 , wherein the plurality of lean nitrogen oxide traps are configured to store at least a portion of the nitrogen oxide in the exhaust gas when at least one of the plurality of lean nitrogen oxide trap operates in an absorption mode, each of the plurality of lean nitrogen oxide traps configured for the conversion of a plurality of nitrates stored by the lean nitrogen oxide trap during a regeneration event, the adsorption process being, at least periodically, at least three times longer than that of a conventional LNT operating under similar conditions. 
     
     
         10 . The engine system of  claim 8 , wherein exhaust gas delivered by the secondary exhaust gas recirculation system is supplied to at least one cylinder of the engine that is operating in a low temperature combustion mode, the level of nitrogen oxide of the supplied exhaust gas being lowered by the combustion of the fuel in the at least one cylinder. 
     
     
         11 . The engine system of  claim 7 , wherein the engine system is configured for exhaust gas exiting each of the plurality of lean nitrogen oxide traps that are undergoing an absorption process to flow along an exhaust line, and wherein exhaust gas exiting each of the plurality of lean nitrogen oxide traps that are undergoing a regeneration event are diverted into the secondary exhaust gas recirculation system. 
     
     
         12 . The engine system of  claim 11 , wherein the plurality of lean nitrogen oxide traps are simultaneously undergoing an absorption process at least approximately 75% of the time that the engine is operating. 
     
     
         13 . The engine system of  claim 11 , wherein the secondary exhaust gas recirculation system is configured to deliver exhaust gas to a portion of an intake line upstream of a compressor.