Apparatus, system, and method for NOx signal correction in feedback controls of an SCR system

• US 8,201,394 B2
• Filed: 04/30/2009
• Issued: 06/19/2012
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Chi, John N., Hill, Joe V.
• Primary Examiner(s): Tran, Binh Q
• Application Number:
  US12/433,705
• Publication Number:
  US 20100024393A1
• Time in Patent Office: 1,146 Days
• Field of Search: 602/74, 602/76, 602/77, 602/86, 602/95, 602/97, 603/01, 603/03
• US Class Current: 60/286
• CPC Class Codes: B01D 2251/2067 Urea
• CPC Class Codes: B01D 2255/91 NOx-storage component incorporated in the catalyst
• CPC Class Codes: B01D 2258/012 Diesel engines and lean burn gasoline engines
• CPC Class Codes: B01D 2258/014 Stoichiometric gasoline engines
• CPC Class Codes: B01D 2259/455 for transportable use
• CPC Class Codes: B01D 53/86 Catalytic processes
• CPC Class Codes: F01N 2560/021 for measuring or detecting ammonia NH3
• CPC Class Codes: F01N 2560/026 for measuring or detecting NOx
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2900/1616 NH3-slip from catalyst
• CPC Class Codes: F01N 3/106 Auxiliary oxidation catalysts
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: F01N 9/005 using models instead of sensors to determine operating characteristics of exhaust systems, e.g. calculating catalyst temperature instead of measuring it directly
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

For example, according to one representative embodiment, an apparatus for reducing NO_x emissions in an engine exhaust includes a NO_x reduction target module configured to determine a NO_x reduction requirement. The apparatus also includes a tailpipe NO_x module configured to determine a sensed amount of NO_x exiting the engine system and a signal correction algorithm module configured to determine a corrected amount of NO_x exiting the engine system based at least partially on the sensed amount of NO_x exiting the engine system. The apparatus also includes a feedback ammonia target module configured to determine a feedback ammonia addition requirement. The feedback ammonia addition requirement includes an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement in response to the corrected amount of NO_x exiting the engine system. The apparatus also includes a reductant target module that is configured to determine a reductant injection requirement.

Claims

1. An apparatus for reducing NO_x emissions in an engine exhaust gas stream of an engine system, 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;

a tailpipe NO_x module configured to determine a sensed amount of NO_x exiting the engine system and a predicted amount of NO_x exciting the engine system, the predicted amount of NO_x exiting the engine system being based at least partially on an analytical model;

a signal correction algorithm module configured to determine a corrected amount of NO_x exiting the engine system based at least partially on the sensed amount of NO_x exiting the engine system and an ammonia correction factor, wherein the ammonia correction factor is adjustable by dithering, and wherein dithering comprises comparing the sensed amount of NO_x exiting the engine system with the predicted amount of NO_x exiting the engine system adjusting the ammonia correction factor accordingly;

a feedback ammonia target module configured to determine a feedback ammonia addition requirement, the feedback ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement, wherein the feedback ammonia addition requirement is based at least partially on the corrected amount of NO_x exiting the engine system; 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 feedback ammonia addition requirement.

2. The apparatus of claim 1, wherein:

the signal correction algorithm comprises an ammonia correction factor; and

the corrected amount of NO_x exiting the engine system is a function of the sensed amount of NO_x exiting the engine system, an amount of ammonia exiting the engine system, and an ammonia correction factor.

3. The apparatus of claim 2, wherein the corrected amount of NO_x exiting the engine system is equal to the sensed amount of NO_x exiting the engine system minus the amount of ammonia exiting the engine system times the ammonia correction factor.

4. The apparatus of claim 2, wherein the amount of ammonia exiting the engine system is predicted based upon an analytical model.

5. The apparatus of claim 1, the apparatus further comprising a feedforward ammonia target module configured to determine a feedforward ammonia addition requirement, wherein the reductant injection requirement comprises an amount of reductant added to the exhaust gas stream to achieve a combination of the feedback and feedforward ammonia addition requirements.

6. The apparatus of claim 1, wherein the feedback ammonia addition requirement is based at least partially on a comparison between a desired amount of NO_x exiting the engine system and the corrected amount of NO_x exiting the engine system.

7. The apparatus of claim 1, further comprising a calibrated NO_x module configured to determine a calibrated tailpipe NO_x sensor signal based at least partially on input from a tailpipe NO_x sensor and a condition of the tailpipe NO_x sensor, wherein the corrected amount of NO_x exiting the engine system is determined by the signal correction algorithm module based at least partially on the calibrated tailpipe NO_x sensor signal.

19. The apparatus of claim 1, wherein dithering to adjust the ammonia correction factor occurs only when the engine system is in an ammonia non-slip mode.

8. A method for reducing NO_x emissions in an engine exhaust gas stream of an engine system, the method comprising the steps of:

determining 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;

determining a feedback ammonia addition requirement, the feedback ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement in response to a corrected amount of NO_x exiting the engine system;

sensing an amount of NO_x exiting the engine system;

determining an amount of ammonia exiting the engine system;

determining an ammonia correction factor;

determining the corrected amount of NO_x exiting the engine system, the corrected amount of NO_x exiting the engine system is equal to the sensed amount of NO_x exiting the engine system minus the amount of ammonia exiting the engine system times the ammonia correction factor; and

determining a reductant injection requirement, the reductant injection requirement comprising an amount of reductant added to the exhaust gas stream to achieve the feedback ammonia addition requirement.

9. The method of claim 8, wherein the step of determining the corrected amount of NO_x exiting the engine system comprises applying the ammonia correction factor to the amount of ammonia exiting the engine system to compensate for ammonia cross-sensitivity of a sensed amount of NO_x exiting the engine system.

10. The method of claim 8, wherein the step of determining the corrected amount of NO_x exiting the engine system comprises performing dithering to adjust the ammonia correction factor so as to reduce transient error.

11. The method of claim 10, wherein dithering comprises comparing the sensed amount of NOx exiting the engine system with a predicted amount of NOx exiting the system based at least partially on an analytical model and adjusting the ammonia correction factor accordingly.

12. The method of claim 8, wherein determining the feedback ammonia addition requirement comprises comparing a desired amount of NO_x emissions exiting the engine system with the corrected amount of NO_x exiting the engine system.

13. A system for reducing NO_x emissions in an engine exhaust, the system comprising:

an internal combustion engine producing an exhaust gas stream;

a selective catalytic reduction (SCR) catalyst that reduces NO_x emissions in the exhaust gas stream in the presence of a reductant;

a reductant injector that injects reductant into the exhaust gas stream upstream of the SCR catalyst;

a tailpipe NO_x sensor configured to determine a sensed amount of NO_x exiting the engine system; and

a controller 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 the SCR catalyst;

a signal correction algorithm module configured to determine a corrected amount of NO_x exiting the engine system based at least partially on the sensed amount of NO_x exiting the engine system;

a calibrated NO_x module configured to determine a calibrated tailpipe sensor signal based at least partially on input from the tailpipe NO_x sensor and a condition of the tailpipe NO_x sensor, wherein the corrected amount of NO_x exiting the engine system is determined by the signal correction algorithm module based at least partially on the calibrated tailpipe NO_x sensor signal;

a feedback ammonia target module configured to determine a feedback ammonia addition requirement, the feedback ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement in response to a corrected amount of NO_x exiting the engine system; 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 feedback ammonia addition requirement.

14. The system of claim 13, wherein the signal correction algorithm module comprises an ammonia correction factor applied to the amount of ammonia exiting the engine system to compensate for ammonia cross-sensitivity of a measured amount of NO_x exiting the engine system so as to yield the corrected amount of NO_x exiting the engine system.

15. The system of claim 13, wherein dithering is applied by the signal correction algorithm module to adjust an ammonia correction factor so as to reduce transient error.

16. The system of claim 13, further comprising a NO_x sensor embedded within the SCR catalyst.

17. A method for extracting a tailpipe NO_x measurement from a tailpipe NO_x signal transmitted from a tailpipe NO_x sensor having an ammonia cross-sensitivity, the method comprising the steps of:

determining an amount of ammonia slipping from the tailpipe;

adjusting an ammonia correction factor periodically by dithering the amount of ammonia slipping from the tailpipe;

multiplying the amount of ammonia slipping from the tailpipe by the ammonia correction factor to yield a product term; and

subtracting the product term from the tailpipe NO_x signal to extract the tailpipe NO_x measurement.

18. The method of claim 17, wherein adjusting the ammonia correction factor periodically occurs only during an ammonia non-slip mode of an engine system comprising the tailpipe NO_x sensor.