Abstract: Systems and method are disclosed in which a portion of an exhaust gas stream is received into an exhaust outlet flow path downstream of a first selective catalytic reduction (SCR) catalyst and upstream of a second SCR catalyst. The removed portion is treated with a diagnostic SCR catalyst element and an NH3 concentration composition of the treated removed portion is determined. The NH3 concentration is used to control injection of reductant upstream of the first SCR catalyst.

Abstract: An apparatus for controlling engine operations to a low NOx output amount at low selective catalytic reduction (SCR) temperature values and alternatively for controlling engine operations in an EGR cooler bypass regime at low engine load levels is described. The apparatus includes a controller that interprets a present speed and a present load of an engine, that determines an engine operating region in response to the present speed and the present load, and that provides an EGR cooler bypass command that provides EGR cooler bypass flow in response to the engine operating region being a first, low load, region. The controller operates the engine with supplemental NOx management in response to the engine operating region being a second, intermediate load, region. The controller operates the engine without either of the EGR cooler bypass or the supplemental NOx management in response to the engine operating region being a third region.