Engine-out NOx virtual sensor using cylinder pressure sensor

1. Method 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, comprising:

monitoring engine sensor inputs comprising a cylinder pressure within the combustion chamber;

modeling a mass fraction burn value for combustion within the combustion chamber based upon said engine sensor inputs, 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 within the combustion chamber with a non-linear function based upon said state of combustion.

2. The method of claim 1 wherein estimating NOx creation within the combustion chamber with the non-linear function based upon said state of combustion comprises:

partitioning a speed-torque profile for the engine into a plurality of zones; and

estimating NOx creation within the combustion chamber with the non-linear function based upon said state of combustion for each partitioned zone.

3. The method of claim 1 wherein the non-linear function includes a plurality of input parameters comprising:

a crank angle wherein a predetermined percentage of a fractional pressure rise in said combustion chamber is achieved;

a maximum pressure achieved within said combustion chamber;

a crank angle wherein said maximum pressure is achieved;

an air-fuel ratio; and

a percentage of cylinder intake comprising exhaust gas recirculation flow.

4. The method of claim 1 wherein the non-linear function includes a plurality of input parameters comprising:

an estimated temperature of burned charge within said cylinder;

a crank angle wherein a predetermined percentage of a fractional pressure rise in said combustion chamber is achieved;

a percentage of intake comprising exhaust gas recirculation flow;

an air-fuel ratio; and

a fuel rail pressure.

5. The method of claim 1 wherein the non-linear function includes a plurality of input parameters comprising:

an estimated average temperature within said combustion chamber;

a crank angle wherein a predetermined percentage of a fractional pressure rise in said combustion chamber is achieved;

a percentage of intake comprising exhaust gas recirculation flow;

an air-fuel ratio; and

a fuel rail pressure.

6. The method of claim 1 wherein the non-linear function includes a plurality of input parameters comprising at least one of:

an estimated average temperature within said combustion chamber;

a crank angle wherein a predetermined percentage of a fractional pressure rise in said combustion chamber is achieved;

an engine speed;

a fuel energy content;

an oxygen sensor measurement; and

a fuel rail pressure.

7. The method of claim 1 wherein the non-linear function includes a plurality of input parameters comprising at least one of:

an estimated average temperature within said combustion chamber;

a crank angle wherein a predetermined percentage of a fractional pressure rise in said combustion chamber is achieved;

an engine speed;

a fuel energy content;

an oxygen sensor measurement; and

a start of fuel injection crank angle.

8. The method of claim 1 , further comprising controlling aftertreatment devices based upon said estimated NOx creation.

9. The method of claim 1 , wherein modeling said mass fraction burn value comprises calculating a total heat released for a given crank angle based upon said cylinder pressure.

10. The method of claim 1 , wherein modeling said mass fraction burn value includes analyzing said cylinder pressure through spectral analysis comprising a Fast Fourier Transform.

11. The method of claim 1 , further comprising modifying a result of said estimated NOx creation based upon a dynamic engine factor.

12. The method of claim 11 , wherein said dynamic engine factor comprises a filter discriminating NOx estimates generated during transitory engine operation.

13. The method of claim 11 , wherein said dynamic engine factor comprises a NOx creation rate estimate utilized to estimate effects of transitory engine operation.

14. 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.

15. The apparatus of claim 14 , wherein said logic operations further comprise a dynamic engine filter modulating NOx estimates based upon transient operation of said engine.

16. The apparatus of claim 14 , wherein said aftertreatment system comprises a lean NOx trap, and wherein modulating aftertreatment comprises scheduling regeneration events.

17. The apparatus of claim 14 , wherein said aftertreatment system comprises a selective catalytic reduction device, and wherein modulating aftertreatment comprises dosing urea injection based upon said NOx creation estimation.

18. The apparatus of claim 14 , further comprising:

monitoring an average temperature within said combustion chamber; and

wherein estimating said NOx creation is further based upon said average temperature.

19. The apparatus of claim 18 , wherein monitoring said average temperature comprises:

monitoring a maximum pressure achieved within said combustion chamber;

monitoring a volume of the cylinder at an instant said maximum pressure is achieved;

monitoring a charge flow into said cylinder; and

determining said average temperature based upon said maximum pressure, said volume, and said charge flow.