Control of selective catalytic reduction

• US 8,578,705 B2
• Filed: 07/18/2007
• Issued: 11/12/2013
• Est. Priority Date: 07/20/2006
• Status: Active Grant

• Current Assignee: Ricardo UK Limited (Ricardo PLC)
• Original Assignee: Ricardo UK Limited (Ricardo PLC)
• Inventors: Sindano, Hector, Rogers, Ben, Noble, Andy, Keenan, Matthew, Mortimer, Phil
• Primary Examiner(s): Bomberg, Kenneth
• Assistant Examiner(s): MATTHIAS, JONATHAN R
• Application Number:
  US12/374,150
• Publication Number:
  US 20090301066A1
• Time in Patent Office: 2,309 Days
• Field of Search: 602/86, 602/95, 603/01, 603/03
• US Class Current: 60/295
• CPC Class Codes: F01N 2900/0402 using adaptive learning
• CPC Class Codes: F01N 2900/0408 using a feed-back loop
• CPC Class Codes: F01N 2900/0411 using a feed-forward control
• 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: F02D 2041/141 using a feed-forward control element
• CPC Class Codes: F02D 2200/0802 Temperature of the exhaust gas treatment apparatus
• CPC Class Codes: F02D 2200/0806 NOx storage amount, i.e. amount of NOx stored on NOx trap
• CPC Class Codes: F02D 41/005 according to engine operating conditions
• CPC Class Codes: F02D 41/027 to purge or regenerate the exhaust gas treating apparatus
• CPC Class Codes: F02D 41/1402 Adaptive control
• CPC Class Codes: F02D 41/146 the characteristics being an NOx content or concentration
• CPC Class Codes: F02D 41/1462 with determination means using an estimation
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A method of controlling a rate of introduction of a NO_x reducing substance or precursor to a catalyst component. The method comprises obtaining the amount of NO_x entering the catalyst component, modeling the amount of NO_x reducing substance or precursor in the catalyst component and controlling the rate of introduction of the NO_x reducing substance or precursor to reduce NO_x.

Claims

1. An apparatus comprising a controller configured to control the rate of an introduction component for providing a NO_x reducing precursor to a catalyst component, the controller:

obtaining an amount of NO_x entering the catalyst component from a NO_x sensor,

modeling an amount of NO_x reducing substance or precursor in the catalytic component to react with the NO_x obtained by the NO_x sensor, and

controlling the rate of the introduction component to produce NO_x reducing substance or precursor to reduce NO_x,

wherein an optimum NO_x reducing precursor introduction rate, Mu_inj_rate_opt, satisfies the relation;

Mu_inj_rate_opt=(ku·

Mnox_rate−

Mu_stored/Tau_rel)/X

wherein ku is the amount of NO_x reducing substance required to reduce one mole of NO_x;

Mu_stored is the mass of NO_x reducing precursor stored in the catalyst;

Tau_rel is a time constant for the rate of NO_x reducing precursor release from the catalyst; and

Mnox_rate is the mass flow rate of NO_x emission entering the catalyst component, and X is the fraction of introduced NO_x reducing precursor that immediately decomposes into NH₃.

2. The apparatus as claimed in claim 1 further comprising a catalyst component.

3. An engine comprising an apparatus as claimed in claim 2.

4. A method of controlling a rate of introduction of a NO_x reducing precursor to a catalyst component, comprising:

obtaining the amount of NO_x entering the catalyst component without monitoring the amount of NO_x leaving the catalyst component, modeling the amount of NO_x reducing substance or precursor in the catalyst component and controlling the rate of introduction of the NO_x reducing precursor to reduce NO_x,

wherein the step of modeling the amount of NO_x reducing substance or precursor further comprises;

modeling the amount of introduced NO_x reducing precursor converted into NO_x reducing substance dependent on a catalyst component temperature;

modeling the amount of NO_x reducing precursor stored in the catalyst component dependent on the catalyst component temperature; and

modeling the amount of stored NO_x reducing precursor released dependent on the catalyst component temperature;

wherein an optimum NO_x reducing precursor introduction rate, Mu_inj_rate_opt, satisfies the relation;

Mu_inj_rate_opt=(ku·

Mnox_rate−

Mu_stored/Tau_rel)/X

wherein ku is the amount of NO_x reducing substance required to reduce one mole of NO_x;

Mu_stored is the mass of NO_x reducing precursor stored in the catalyst;

Tau_rel is a time constant for the rate of NO_x reducing precursor release from the catalyst; and

Mnox_rate is the mass flow rate of NO_x emission entering the catalyst component and X is the fraction of introduced NO_x reducing precursor that immediately decomposes into NH₃.

5. The method as claimed in claim 4 wherein the rate of introduction is controlled such that the NO_x entering the catalyst component is reduced by the NO_x reducing substance.

6. The method as claimed in claim 4 in which the rate of introduction is controlled such that substantially all of the NO_x reducing substance is used up in the catalyst component.

7. The method as claimed in claim 4 further comprising the step of controlling the amount of NO_x entering the catalyst component to use up substantially all of the NO_x reducing substance in the catalyst component.

8. The method as claimed in claim 7 wherein the amount of NO_x entering the catalyst component is controlled by varying exhaust gas recirculation.

9. The method as claimed in claim 4 in which the amount of NO_x entering the catalyst component is obtained from a model based on a measure of the exhaust temperature entering the catalyst component from an engine, and engine load.

10. The method as claimed in claim 9 in which the amount of NO_x entering the catalyst component is stored in a look up table as a function of temperature and load.

11. The method as claimed in claim 10 in which the temperature comprises engine in-cylinder peak temperature derived from at least one of engine coolant temperature, intake air temperature, manifold pressure, start of injection, injected fuel mass, exhaust gas recirculation and engine speed.

12. The method as claimed in claim 9 in which the amount of NO_x entering the catalyst component is further modeled dependent on correction for transient operation.

13. The method as claimed in claim 4 in which the amount of NO_x entering the catalyst component is obtained from a sensor.

14. The method as claimed in claim 4 further comprising modeling the catalyst component temperature based on a measure of the temperature of exhaust entering the catalyst component.

15. The method as claimed in claim 4 in which the rate of introduction is further controlled to maintain the amount of NO_x reducing precursor stored in the catalyst component above a buffer threshold.

16. The method as claimed in claim 4 in which the NO_x reducing substance comprises ammonia and the NO_x reducing precursor comprises urea.

17. The method as claimed in claim 4 in which the catalyst component comprises a selective catalytic reduction component.

18. The method as claimed in claim 4, wherein the precursor comprises urea and/or one or more intermediate ammonia related compounds.