Patent ID: 8181450

Claim:
An apparatus for reducing NO x emissions in an engine exhaust gas stream, comprising: a NO x reduction target module configured to determine a NO x reduction requirement, the NO x reduction requirement comprising an amount of NO x in the exhaust gas stream to be reduced on a selective catalytic reduction (SCR) catalyst having a catalyst bed; an ammonia storage module configured to determine an ammonia storage modifier by comparing a current ammonia storage level and a target ammonia storage level, wherein the ammonia storage module comprises an ammonia adsorption look-up table and an ammonia desorption look-up table each including predetermined time constants corresponding to various reductant addition rates and SCR catalyst bed temperatures, wherein the ammonia storage module is configured to determine the current ammonia storage level by utilizing a time constant selected from one of the tables, and wherein the time constant is selected from the ammonia adsorption look-up table when the SCR catalyst is in an ammonia adsorption mode and from the ammonia desorption table when the SCR catalyst is in an ammonia desorption mode; an ammonia target module configured to determine an ammonia addition requirement, the ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO x reduction requirement, wherein the ammonia target module is communicable in data receiving communication with the ammonia storage module to receive the ammonia storage modifier, and wherein the ammonia target module is configured to add the ammonia storage modifier to the ammonia addition requirement; and a reductant target module configured to determine a reductant injection requirement, the reductant injection requirement comprising an amount of reductant added to the exhaust gas stream to achieve the ammonia addition requirement; wherein at least one of the NO x reduction target module, ammonia storage module, ammonia target module, and reductant target module comprises at least one of logic hardware and executable code, the executable code being stored on at least one non-transitory machine-readable storage media.