Combustion driven ammonia generation strategies for passive ammonia SCR system

摘要

A method for controlling ammonia generation in an exhaust gas feedstream output from an internal combustion engine equipped with an exhaust aftertreatment system including a first aftertreatment device includes executing an ammonia generation cycle to generate ammonia on the first aftertreatment device. A desired air-fuel ratio output from the engine and entering the exhaust aftertreatment system conducive for generating ammonia on the first aftertreatment device is determined. Operation of a selected combination of a plurality of cylinders of the engine is selectively altered to achieve the desired air-fuel ratio entering the exhaust aftertreatment system.

主权项

1. A method for controlling ammonia generation in an exhaust gas feedstream output from an internal combustion engine equipped with an exhaust aftertreatment system including a first aftertreatment device, comprising:
determining whether an ammonia generation cycle is necessary based on a monitored engine operation parameter, an exhaust gas feedstream parameter and an exhaust aftertreatment system parameter; executing the ammonia generation cycle to generate ammonia on the first aftertreatment device when the ammonia generation cycle is determined to be necessary, said ammonia generation cycle comprising:
determining a desired air-fuel ratio of the engine to generate an engine-out exhaust gas feedstream conducive for generating ammonia on the first aftertreatment device; andselectively altering operation of a selected combination of a plurality of cylinders of the engine such that the desired air-fuel ratio of the engine is achieved, comprising intermittently operating the selected combination of the plurality of cylinders at:
an air-fuel ratio that is at least stoichiometric to generate ammonia production on the first aftertreatment device; andan air-fuel ratio that is lean of stoichiometric to reduce carbon monoxide breakthrough caused by operation at the air-fuel ratio that is at least stoichiometric,wherein the average of the air-fuel ratio that is at least stoichiometric and the air-fuel ratio that is lean of stoichiometric is equal to the desired air-fuel ratio; and discontinuing the ammonia generation cycle when the ammonia generation cycle is determined to not be necessary based on the monitored engine operation parameter, the exhaust gas feedstream parameter and the exhaust aftertreatment system parameter.