Patent attributes
Various embodiments of an apparatus, system, and method are disclosed for reducing NOx emissions on an SCR catalyst. For example, according to one representative embodiment, an apparatus for reducing NOx emissions in an engine exhaust includes a NOx reduction target module that is configured to determine a NOx reduction requirement that includes an amount of NOx in the exhaust gas stream to be reduced on a selective catalytic reduction (SCR) catalyst. The apparatus also includes an ammonia target module that is configured to determine an ammonia addition requirement that includes an amount of ammonia added to the exhaust gas stream to achieve the NOx reduction requirement. The apparatus also includes a reductant target module that is configured to determine a reductant injection requirement that includes an amount of reductant added to the exhaust gas stream to achieve the ammonia addition requirement. The apparatus further includes a reductant limiting module that is configured to determine whether at least one reductant limiting condition is met and to limit the amount of reductant added in response to the at least one reductant limiting condition if the at least one reductant limiting condition has been met.
