Combustion driven ammonia generation strategies for passive ammonia SCR system
First Claim
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; and
selectively 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; and
an 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.
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Abstract
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.
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Citations
20 Claims
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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:
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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; and selectively 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; and an 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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. 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 three-way catalytic device and an ammonia-selective catalytic reduction device, comprising:
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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 three-way catalytic 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 including nitric oxide, carbon monoxide, hydrogen and unburned hydrocarbons that enters the exhaust aftertreatment system and converts to ammonia on the three-way catalytic device; selectively 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; and an 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; wherein selectively altering operation of the selected combination of the plurality of cylinders of the engine comprises one of; operating all cylinders of the engine to dither around the desired air-fuel ratio; and operating each of a selected combination of a plurality of cylinders of the engine at a biased air-fuel ratio and each of the remaining cylinders at an un-biased air-fuel ratio resulting in operation at an average air-fuel ratio of the selected combination of the plurality of cylinders and the remaining cylinders that 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. - View Dependent Claims (15, 16, 17, 18, 19)
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20. An exhaust aftertreatment system for an internal combustion engine, comprising:
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a catalytic device formulated to produce ammonia from an exhaust gas feedstream that includes nitric oxide, carbon monoxide, hydrogen and unburned hydrocarbons, the catalytic device close-coupled to an exhaust manifold of the internal combustion engine and fluidly coupled to an ammonia-selective catalytic reduction device located downstream of the catalytic device; a control module; 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 catalytic device when the ammonia generation cycle is determined to be necessary; determining a desired air-fuel ratio of the engine to generate an engine-out exhaust gas feedstream conducive for generating ammonia on the catalytic device; and 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 catalytic device; and an 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.
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Specification