Engine-out NOx virtual sensor using cylinder pressure sensor

Apparatus for estimating NOx creation in a combustion process of a four-stroke internal combustion engine including a variable volume combustion chamber defined by a piston reciprocating within a cylinder between top-dead center and bottom-dead center points, intake and exhaust passages, and intake and exhaust valves controlled during repetitive, sequential exhaust, intake, compression and expansion strokes of said piston, said apparatus comprising:

• a pressure sensor generating pressure sensor readings representing conditions within said combustion chamber;
• a NOx estimation module including logic operations comprising:
• monitoring said pressure sensor readings;
• modeling a mass fraction burn value for combustion within the combustion chamber based upon said pressure sensor readings, wherein said mass fraction burn value indexes a crank angle at which a selected percentage of injected fuel is burned in a combustion cycle;
• estimating a state of combustion within the combustion chamber based upon the mass fraction burn value, the state of combustion comprising a combustion phasing and a combustion strength;
• and
• estimating NOx creation with a non-linear function based upon said state of combustion;
• and
• an aftertreatment system receiving an exhaust gas flow from said engine and modulating aftertreatment based upon said NOx creation estimate.