Exhaust system implementing SCR and EGR

• US 20090193794A1
• Filed: 01/31/2008
• Published: 08/06/2009
• Est. Priority Date: 01/31/2008
• Status: Active Grant

• Current Assignee: Caterpillar Incorporated
• Original Assignee: Caterpillar Incorporated
• Inventors: Robel, Wade J., Driscoll, James J.
• Granted Patent: US 8,151,558 B2
• Time in Patent Office: Days
• US Class Current: 60/295
• CPC Class Codes: F01N 2570/18 Ammonia
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 3/0821 combined with particulate filters catalysed diesel particulate filters F01N3/035
• CPC Class Codes: F02B 37/00 Engines characterised by provision of pumps driven at least for part of the time by exhaust
• CPC Class Codes: F02M 26/15 in relation to engine exhaust purifying apparatus

Abstract

An exhaust system for use with an engine is disclosed. The exhaust system may have an exhaust passageway, a reduction catalyst located within the exhaust passageway, and a particulate filter located within the exhaust passageway upstream of the reduction catalyst. The exhaust system may also have an oxidation catalyst located within the exhaust passageway upstream of the reduction catalyst to provide a desired ratio of NO:NO₂ to the reduction catalyst, and an exhaust gas recirculation loop. The exhaust gas recirculation loop may be situated to receive exhaust from the exhaust passageway at a location upstream of the oxidation catalyst and downstream of the particulate filter.

Claims

1. An exhaust system, comprising:

an exhaust passageway;

a reduction catalyst located within the exhaust passageway;

a particulate filter located within the exhaust passageway upstream of the reduction catalyst;

an oxidation catalyst located within the exhaust passageway upstream of the reduction catalyst to provide a desired ratio of NO;

NO₂ to the reduction catalyst; and

an exhaust gas recirculation loop situated to receive exhaust from the exhaust passageway at a location upstream of the oxidation catalyst and downstream of the particulate filter.

2. The exhaust system of claim 1, further including an injector located to inject reductant into the exhaust passageway upstream of the reduction catalyst, wherein the exhaust gas recirculation loop is situated to receive exhaust from the exhaust passageway at a location upstream of both the oxidation catalyst and the injector.

3. The exhaust system of claim 2, wherein the injector is located downstream of the oxidation catalyst.

4. The exhaust system of claim 2, wherein at least part of the particulate filter is catalyzed to reduce NO_X.

5. The exhaust system of claim 4, wherein:

the injector is a first injector;

the oxidation catalyst is a first oxidation catalyst; and

the exhaust system further includes;

a second injector located to inject reductant into the exhaust passageway upstream of the particulate filter; and

second oxidation catalyst located downstream of the particulate filter and upstream of the location from which the exhaust gas recirculation loop receives exhaust to remove residual reductant from the exhaust.

6. The exhaust system of claim 5, further including a third oxidation catalyst located upstream of the second injector to convert NO to NO₂.

7. The exhaust system of claim 6, further including a fourth oxidation catalyst located downstream of the reduction catalyst to remove residual reductant.

8. The exhaust system of claim 1, further including a regeneration device located upstream of the particulate filter.

9. The exhaust system of claim 1, wherein the oxidation catalyst is a first oxidation catalyst and the exhaust system further includes a second oxidation catalyst located downstream of the reduction catalyst to oxidize residual reductant.

10. The exhaust system of claim 1, further including a hydrolysis catalyst located upstream of the reduction catalyst.

11. The exhaust system of claim 1, wherein the oxidation catalyst is a first oxidation catalyst, and the exhaust system further includes a second oxidation catalyst located upstream of the particulate filter.

12. The exhaust system of claim 11, wherein:

the first oxidation catalyst is coated to provide a desired ratio of NO;

NO₂ to the reduction catalyst; and

the second oxidation catalyst is coated to convert only enough NO to NO₂ for regeneration of the particulate filter.

13. An exhaust system, comprising:

an exhaust passageway;

a reduction catalyst located within the exhaust passageway;

a particulate filter located within the exhaust passageway upstream of the reduction catalyst;

an injector located to inject reductant into the exhaust passageway upstream of the reduction catalyst; and

an exhaust gas recirculation loop situated to receive exhaust from the exhaust passageway at a location upstream of the injector and downstream of the particulate filter.

14. The exhaust system of claim 13, further including a regeneration device located upstream of the particulate filter.

15. The exhaust system of claim 13, further including an oxidation catalyst located downstream of the reduction catalyst to oxidize residual reductant.

16. The exhaust system of claim 13, further including a hydrolysis catalyst located upstream of the reduction catalyst.

17. The exhaust system of claim 13, further including an oxidation catalyst located upstream of the particulate filter to convert only enough NO to NO₂ for regeneration of the particulate filter.

18. A power system, comprising:

an engine;

an exhaust passageway extending from the engine to the atmosphere;

an SCR catalyst located within the exhaust passageway;

an injector located to inject urea into the exhaust passageway upstream of the SCR catalyst;

a diesel particulate filter located within the exhaust passageway upstream of the SCR catalyst;

a diesel oxidation catalyst located within the exhaust passageway upstream of the SCR catalyst and the injector; and

an exhaust gas recirculation loop situated to receive exhaust from the exhaust passageway at a location upstream of both the injector and the diesel oxidation catalyst, and downstream of the diesel particulate filter.

19. The power system of claim 18, wherein at least part of the diesel particulate filter is catalyzed to reduce NO_X.

20. The power system of claim 19, wherein:

the injector is a first injector;

the diesel oxidation catalyst is a first diesel oxidation catalyst coated to provide a desired ratio of NO;

NO₂ to the SCR catalyst; and

the exhaust system further includes;

a second injector located to inject urea into the exhaust passageway upstream of the diesel particulate filter;

an ammonia oxidation catalyst located downstream of the diesel particulate filter and upstream of the location from which the exhaust gas recirculation loop receives exhaust to remove residual urea from the exhaust; and

a second diesel oxidation catalyst located upstream of the second injector to convert enough NO to NO₂ for regeneration of the diesel particulate filter and to provide a desired ratio of NO;

NO₂ to the catalyzed diesel particulate filter.