Apparatus, system, and method for reducing NO x emissions on an SCR catalyst

• US 8,256,208 B2
• Filed: 04/30/2009
• Issued: 09/04/2012
• Est. Priority Date: 04/30/2008
• Status: Active Grant

• Current Assignee: Cummins Incorporated
• Original Assignee: Cummins Incorporated
• Inventors: Wills, Joan M., Chi, John N., Wang, Weiwen, Garimella, Phanindra, Frazier, Timothy R., Ofoli, Abdul R., Hill, Joe V., Farrell, Lisa A., Currier, Neal W., Yezerets, Aleksey, Osburn, Andy
• Primary Examiner(s): Tran, Binh Q
• Application Number:
  US12/433,586
• Publication Number:
  US 20100024390A1
• Time in Patent Office: 1,223 Days
• Field of Search: 602/74, 602/76, 602/80, 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 2259/4566 for use in transportation means
• CPC Class Codes: B01D 53/86 Catalytic processes
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• 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 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: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

According to one representative embodiment, an apparatus for reducing NO_x emissions in an engine exhaust gas stream of an engine system having a selective catalytic reduction (SCR) system with an SCR catalyst positioned downstream of a reductant injector includes a NO_x reduction target module and a reductant module. The NO_x reduction target module is configured to determine a NO_x reduction requirement, which includes an amount of NO_x in the exhaust gas stream to be reduced on the SCR catalyst. The reductant module is configured to determine the amount of reductant added to the exhaust gas stream to achieve the NO_x reduction requirement. The amount of reductant added to the exhaust gas stream is a function of at least one ammonia storage characteristic of the SCR catalyst, at least one reductant-to-ammonia conversion characteristic, and a conversion capability of an AMOX catalyst in exhaust receiving communication with the SCR catalyst.

Claims

1. An apparatus for reducing NO_x emissions in an engine exhaust gas stream of an engine system having a selective catalytic reduction (SCR) system with an SCR catalyst positioned downstream of a reductant injector, 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; and

a reductant module configured to determine the amount of reductant added to the exhaust gas stream to achieve the NO_x reduction requirement;

wherein the amount of reductant added to the exhaust gas stream is a function of at least one ammonia storage characteristic of the SCR catalyst, at least one reductant-to-ammonia conversion characteristic, and an ammonia conversion efficiency of an ammonia oxidation (AMOX) catalyst in exhaust receiving communication with the SCR catalyst.

2. The apparatus of claim 1, wherein the at least one ammonia storage characteristic comprises at least one of an estimated amount of ammonia stored on the SCR catalyst, an estimated amount of ammonia slipping from the SCR catalyst, and an estimated maximum ammonia storage capacity of the SCR catalyst.

3. The apparatus of claim 1, wherein the at least one reductant-to-ammonia conversion characteristic comprises at least one of the distance between the SCR catalyst and the reductant injector, the conversion efficiency of reductant to ammonia, and the conversion efficiency of reductant to constituents other than ammonia.

4. The apparatus of claim 1, wherein the conversion capability of the AMOX catalyst is a function at least one of the temperature of the AMOX catalyst, an AMOX catalyst degradation factor, and a tailpipe ammonia slip target.

5. The apparatus of claim 1, wherein the amount of reductant added to the exhaust gas stream is a function of a physical condition of the SCR catalyst the condition of the SCR catalyst.

6. The apparatus of claim 5, wherein the physical condition of the SCR catalyst is represented by at least one of a degradation factor of the SCR catalyst and a maximum NO_x conversion efficiency of the SCR catalyst.

7. The apparatus of claim 1, further comprising an on-board diagnostics module configured to determine whether a maximum NO_x reduction efficiency of the SCR catalyst is less than a predetermined threshold.

8. A method for reducing NO_x emissions in an engine exhaust gas stream of an engine system flowing from an engine of the engine system to a tailpipe of the engine system, the engine system having a selective catalytic reduction (SCR) catalyst and a urea injector upstream of the SCR catalyst, the method comprising:

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 an ammonia oxidation (AMOX) catalyst conversion capability;

determining an ammonia storage modifier;

determining an ammonia addition requirement, the ammonia addition requirement comprising an amount of ammonia added to the exhaust gas stream to achieve the NO_x reduction requirement, the ammonia addition requirement being at least partially dependent on the AMOX catalyst conversion capability and the ammonia storage modifier;

determining urea-to-ammonia and urea-to-isocyanic acid conversion factors;

determining a urea injection requirement based at least partially on the urea-to-ammonia and urea-to-isocyanic acid conversion factors, the urea injection requirement comprising an amount of urea added to the exhaust gas stream to achieve the ammonia addition requirement;

determining whether at least one urea limiting condition is met, and modifying the urea injection requirement if the at least one urea limiting condition is met; and

injecting urea into the exhaust stream according to the urea injection requirement.

9. The method of claim 8, wherein the ammonia storage modifier is based at least partially on the estimated amount of ammonia stored on the SCR catalyst, the estimated amount of ammonia slipping from the SCR catalyst, and the estimated maximum ammonia storage capacity of the SCR catalyst.

10. The method of claim 8, wherein the urea-to-ammonia and urea-to-isocyanic acid conversion factors is based at least partially on the distance between the SCR catalyst and the urea injector, a conversion efficiency of urea to ammonia, and a conversion efficiency of urea to isocyanic acid.

11. An engine system, comprising:

an internal combustion engine generating an exhaust gas stream;

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

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

a controller comprising;

a feedforward component configured to determine a reductant dosing rate corresponding to a desired level of NO_x reduction on the SCR catalyst during steady-state operating conditions of the internal combustion engine;

a feedback-type component configured to modify the reductant dosing rate based at least partially on a physical degradation of the SCR catalyst; and

an ammonia storage component configured to modify the reductant dosing rate based at least partially on a desired ammonia storage level on the SCR catalyst, wherein the desired ammonia storage level represents an ammonia storage level that accommodates transient changes in NO_x emissions during transient operating conditions of the internal combustion engine.

12. The system of claim 11, further comprising an AMOX catalyst downstream of the SCR catalyst, wherein the feedback-type component is further configured to modify the reductant dosing rate based at least partially on a physical degradation of the AMOX catalyst.

13. The system of claim 11, wherein the reductant is urea, the urea reducing in part to ammonia and in part to isocyanic acid prior to entering the SCR catalyst, and wherein the urea dosing rate is based at least partially on a first conversion efficiency of urea to ammonia and a second conversion efficiency of urea to isocyanic acid.

14. The system of claim 11, wherein the feedback-type component is further configured to modify the reductant dosing rate based at least partially on the occurrence of at least one reductant limiting condition.

15. The system of claim 14, wherein the at least one reductant limiting condition comprises at least one of an exhaust gas temperature limit, an ammonia slip limit, and an SCR catalyst bed temperature limit.

16. The system of claim 11, wherein the desired ammonia storage level is based at least partially on a maximum ammonia storage capacity of the SCR catalyst.

17. The system of claim 12, wherein the desired ammonia storage level is based at least partially on a maximum ammonia storage capacity of the SCR catalyst and a maximum NH₃ conversion capability of the AMOX catalyst.

18. The system of claim 11, wherein the controller comprises an on-board diagnostics (OBD) component configured to determine whether the SCR system is capable of reducing the NO_x emissions in the exhaust gas stream to an amount below a predetermined threshold.

19. The system of claim 18, further comprising an OBD interface communicable in electrical communication with the controller, wherein the controller alerts the OBD interface when the OBD component determines that the SCR system is not capable of reducing the NO_x emissions in the exhaust gas stream to an amount below the predetermined threshold.

20. The system of claim 18, wherein the determination of whether the SCR system is capable of reducing the NO_x emissions in the exhaust gas stream to an amount below a predetermined threshold is based at least partially on the physical degradation of the SCR catalyst.

21. The system of claim 11, wherein the SCR system comprises a NO_x sensor embedded within the SCR catalyst.

22. The system of claim 21, wherein the SCR catalyst comprises a pair of spaced-apart catalyst beds extending a length of the SCR catalyst, the catalyst beds defining a space between the beds, and wherein the embedded NO_x sensor is at least partially positioned in the space between the beds.