Method and system for NOx reduction

• US 6,427,439 B1
• Filed: 07/13/2000
• Issued: 08/06/2002
• Est. Priority Date: 07/13/2000
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Xu, Lifeng, Hammerle, Robert Henry, Wu, Ching-Hsong George
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, DIEM T
• Application Number:
  US09/615,427
• Time in Patent Office: 754 Days
• Field of Search: 602/74, 602/85, 602/86, 602/95, 603/01
• US Class Current: 60/286
• 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 2570/18 Ammonia
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 2900/0408 using a feed-back loop
• CPC Class Codes: F01N 3/208 Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
• CPC Class Codes: F02D 41/1462 with determination means using an estimation
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies

Abstract

A system and method for controlling reductant injection upstream of a selective reduction catalyst (SCR) to overcome NO_X inhibiting effects by injecting reductant in an amount proportional to engine out NO_X concentration when the NO_X concentration is above a predetermined level and injecting predetermined amounts of reductant into the SCR catalyst when engine out NO_X concentration is below the predetermined level such as when the engine is idling or decelerating.

Claims

1. A method for controlling reductant injection into an engine exhaust stream upstream of a selective reduction catalyst coupled to said engine, the method comprising the steps of:

determining a NO_X concentration level upstream of said catalyst;

controlling the amount of reductant injected into the engine exhaust stream proportional to the NO_X concentration if the NO_X concentration level is greater than a predetermined NO_X concentration level; and

injecting a predetermined amount of reductant into the engine exhaust stream if the NO_X concentration level is less than said predetermined NO_X concentration level and the amount of ammonia in the catalyst is less than the ammonia storage capacity of the catalyst.

2. The method of claim 1 comprising the additional steps of:

determining the exhaust gas flow rate;

reducing the value of a variable Q, indicative of catalyst ammonia storage capacity, by an amount proportional to said NO_X concentration level and said flow rate if said NO_X concentration is greater than said predetermined NO_X concentration level.

3. The method of claim 2 comprising the additional steps of:

determining catalyst temperature; and

injecting said predetermined amount of reductant into the exhaust stream only if the value of the variable Q is less than a catalyst temperature dependent value indicative of the ammonia storage capacity of said catalyst.

4. The method of claim 1 comprising the additional steps of:

determining a NO_X conversion value; and

if said NO_X concentration is greater than said predetermined NO_X concentration level and said NO_X conversion value is less than a threshold value increasing the amount of reductant injected by a predetermined amount; and

if said NO_X concentration is greater than said predetermined NO_X concentration level and said NO_X conversion value is greater than said threshold value, reducing the amount of reductant injected by a second predetermined amount.

5. The method of claim 4 comprising the additional steps of:

determining the exhaust gas flow rate;

reducing the value of a variable Q, indicative of catalyst ammonia storage capacity, by an amount proportional to said NO_X concentration level and said flow rate if said NO_X concentration is greater than said predetermined NO_X concentration level.

6. The method of claim 4 comprising the additional steps of:

determining catalyst temperature; and

injecting a predetermined amount of reductant into the exhaust stream if the NO_X concentration level is less than said predetermined NO_X concentration level and the value of the variable Q is less than a temperature dependent value indicative of the ammonia storage capacity of said catalyst.

7. The method of claim 1 comprising the additional steps of:

determining an ammonia concentration level downstream of said catalyst;

determining catalyst temperature; and

increasing the amount of reductant injected by a predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level; and

decreasing the amount of reductant injected by a second predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level.

8. The method of claim 1 comprising the additional steps of:

determining an ammonia concentration level downstream of said catalyst; and

increasing the amount of reductant injected by a predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level; and

reducing the amount of reductant injected by a second predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level.

9. The method of claim 7 comprising the additional steps of:

increasing the amount of reductant injected by a predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level; and

reducing the amount of reductant injected by a second predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level.

10. The method of claim 7 comprising the additional step of:

limiting the amount of reductant injected to a predetermined percentage of the catalyst ammonia storage capacity, whenever said NO_X concentration level is less than said predetermined NO_X concentration level and said ammonia concentration level is less than said ammonia slippage level.

11. The method of claim 8 comprising the additional steps of:

determining whether the reductant being used is urea and whether the catalyst temperature is below a predetermined temperature; and

performing the steps of claim 8 only if the reductant is not urea or the catalyst temperature is greater than said predetermined temperature.

12. The method of claim 1 comprising the additional steps of:

determining a NO_X conversion value;

determining an ammonia concentration level downstream of said catalyst; and

increasing the amount of reductant injected by a predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level, said NO_X conversion value is less than a threshold value, and said ammonia concentration level is less than an ammonia slippage level; and

reducing the amount of reductant injected by a second predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level, said NO_X conversion value is greater than said threshold value, and said ammonia concentration level is greater than said ammonia slippage level.

13. The method of claim 12 comprising the additional steps of:

increasing the amount of reductant injected by a predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level; and

reducing the amount of reductant injected by a second predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level.

14. A system for controlling reductant injection into an internal combustion engine exhaust stream upstream of a catalyst coupled to said engine, comprising:

means for determining a NO_X concentration level upstream of said catalyst;

means for controlling reductant injection as a function of NO_X concentration if the NO_X concentration level is greater than a predetermined NO_X concentration level and for injecting a predetermined amount of reductant into the exhaust stream if the NO_X concentration level is less than said predetermined NO_X concentration level and the amount of ammonia in the catalyst is less than the catalyst ammonia storage capacity.

15. The system of claim 14 further comprising:

means for determining an ammonia concentration level downstream of said catalyst;

means for increasing the amount of reductant injected by a predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level and for decreasing the amount of reductant injected by a second predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level; and

means for increasing the amount of reductant injected by a predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level and for reducing the amount of reductant injected by a second predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level.

16. The system of claim 14 further comprising:

means for determining a NO_X conversion value;

means for determining an ammonia concentration level downstream of said catalyst;

means for increasing the amount of reductant injected by a predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level, said NO_X conversion value is less than a threshold value, and said ammonia concentration level is less than an ammonia slippage level and for reducing the amount of reductant injected by a second predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level, said NO_X conversion value is greater than said threshold value, and said ammonia concentration level is greater than said ammonia slippage level; and

means for increasing the amount of reductant injected by a predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level and for reducing the amount of reductant injected by a second predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level.

17. An article of manufacture comprising:

a computer storage medium having a computer program encoded therein for controlling reductant injection into the exhaust stream of an internal combustion engine, upstream of a selective reduction catalyst coupled to said engine, said computer storage medium comprising;

code for causing the computer to determine a NO_X concentration level upstream of said catalyst;

code for causing the computer to control the amount of reductant injected proportional to NO_X concentration if the NO_X concentration level is greater than a predetermined NO_X concentration level and to inject a predetermined amount of reductant if the NO_X concentration level is less than said predetermined NO_X concentration level and the amount of ammonia in the catalyst is less than the ammonia storage capacity of the catalyst.

18. The article of claim 17 further comprising:

code for causing the computer to determine a NO_X conversion value; and

code for causing the computer to increase the amount of reductant injected by a predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level and said NO_X conversion value is less than a threshold value and to reduce the amount of reductant injected by a second predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level and said NO_X conversion value is greater than said threshold value.

19. The article of claim 17 further comprising:

code for causing the computer to determine a NO_X conversion value;

code for causing the computer to determine an ammonia concentration level downstream of said catalyst;

code for causing the computer to increase the amount of reductant injected by a predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level, said NO_X conversion value is less than a threshold value, and said ammonia concentration level is less than an ammonia slippage level and to reduce the amount of reductant injected by a second predetermined amount if said NO_X concentration is greater than said predetermined NO_X concentration level, said NO_X conversion value is greater than said threshold value, and said ammonia concentration level is greater than said ammonia slippage level; and

code for causing the computer to increase the amount of reductant injected by a predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is less than an ammonia slippage level and to reduce the amount of reductant injected by a second predetermined incremental value if said NO_X concentration is less than said predetermined NO_X concentration level and said ammonia concentration level is greater than said ammonia slippage level.

20. A method for controlling reductant injection into an engine exhaust stream upstream of a catalyst coupled to said engine, the method comprising the steps of:

determining an engine-out NO_X concentration level;

controlling the amount of reductant injected into the engine exhaust stream as a function of the NO_X concentration if the NO_X concentration level is greater than a predetermined NO_X concentration level;

determining the exhaust gas flow rate;

reducing the value of a variable Q, indicative of catalyst reductant storage capacity, by an amount proportional to said NO_X concentration level and said flow rate if said NO_X concentration is greater than said predetermined NO_X concentration level.