Methods for engine exhaust NOx control using no oxidation in the engine

1. Apparatus for reducing NOx emissions in a powertrain comprising an internal combustion engine including a combustion chamber, the apparatus comprising:

an aftertreatment system; and

an aftertreatment system control module configured to:

monitor an actual exhaust gas feedstream ratio of NO 2 to NO;

monitor a desired exhaust gas feedstream ratio of NO 2 to NO;

compare the actual and the desired exhaust gas feedstream ratios of NO 2 to NO;

initiate NO 2 generation selectively to increase the actual exhaust gas feedstream ratio of NO 2 to NO by injecting a fuel mass into the combustion chamber after a primary combustion event to generate HO2, wherein said generated HO 2 oxidizes NO present in the combustion chamber to generate NO 2 sufficient to increase the actual exhaust gas feedstream ratio of NO 2 to NO at the desired exhaust gas feedstream ratio of NO 2 to NO.

2. Method for reducing NOx emissions in a powertrain comprising an internal combustion engine including a combustion chamber and an aftertreatment system, the method comprising:

monitoring an actual exhaust gas feedstream ratio of NO 2 to NO;

monitoring a desired exhaust gas feedstream ratio of NO 2 to NO;

comparing the actual and the desired exhaust gas feedstream ratios of NO 2 to NO; and

selectively initiating a NO 2 generation cycle to increase the actual exhaust gas feedstream ratio of NO 2 to NO based upon the comparison of the actual and the desired exhaust gas feedstream ratios of NO 2 to NO comprising injecting fuel mass into the combustion chamber after a primary combustion event to generate HO 2 , wherein said generated HO 2 oxidizes NO present in the combustion chamber to generate NO 2 sufficient to increase the actual exhaust gas feedstream ratio of NO 2 to NO.

3. The method of claim 2 , wherein monitoring the desired exhaust gas feedstream ratio of NO 2 to NO comprises:

monitoring operation of the engine;

determining a desired engine NOx aftertreatment device based upon the operation of the engine; and

selecting the desired exhaust gas feedstream ratio of NO 2 to NO based on the desired engine NOx aftertreatment device.

4. The method of claim 3 , wherein determining the desired engine NOx aftertreatment device comprises:

utilizing a NOx treatment catalyst and a lean NOx trap during periods of cold start operation and engine operation lean of stoichiometry;

wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO comprises:

during said periods of cold start operation and engine operation lean of stoichiometry, selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially all NO 2 for storing NO 2 on said lean NOx trap.

5. The method of claim 3 , wherein determining the desired engine NOx aftertreatment device comprises:

utilizing a urea-selective catalytic reduction device during periods of warm-up of said aftertreatment system and engine operation lean of stoichiometry;

wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO comprises:

during said periods of warm-up of said aftertreatment system and engine operation lean of stoichiometry, selecting the desired exhaust gas feedstream ratio of NO 2 to NO to substantially a one to one molar ratio of NO 2 to NO.

6. The method of claim 3 , wherein the desired engine NOx aftertreatment device comprises an upstream oxidation catalyst including platinum group metals.

7. The method of claim 2 further comprising:

generating HO 2 from the injected fuel mass into the combustion chamber after a primary combustion event; and

utilizing the generated HO 2 to oxidize NO present in the combustion chamber to generate NO 2 .

8. Method for reducing NOx emissions in a powertrain comprising an internal combustion engine including a combustion chamber and an aftertreatment system, the method comprising:

monitoring an actual exhaust gas feedstream ratio of NO 2 to NO;

monitoring a desired exhaust gas feedstream ratio of NO 2 to NO;

comparing the actual and the desired exhaust gas feedstream ratios of NO 2 to NO; and

selectively initiating a NO 2 generation cycle based upon the comparison of the actual and the desired exhaust gas feedstream ratios of NO 2 to NO comprising injecting extra fuel mass after the primary combustion event into a plurality of cylinders less than the total number of cylinders in a multi-cylinder engine when the desired exhaust gas feedstream ratio of NO 2 to NO is less than substantially all NO 2 .

9. Method for reducing NOx emissions in a powertrain comprising an internal combustion engine including a combustion chamber and an aftertreatment system, the method comprising:

monitoring operation of the engine;

determining an actual exhaust gas feedstream ratio of NO 2 to NO;

determining a desired engine NOx aftertreatment device based upon the operation of the engine;

selecting a desired exhaust gas feedstream ratio of NO 2 to NO based on the desired engine NOx aftertreatment device;

comparing the actual and the desired exhaust gas feedstream ratios of NO 2 to NO;

injecting a fuel mass into the combustion chamber after a primary combustion event to generate HO 2 ; and

utilizing the generated HO 2 to oxidize NO present in the combustion chamber to generate NO 2 sufficient to establish the actual exhaust gas feedstream ratio of NO 2 to NO at the desired exhaust gas feedstream ratio of NO 2 to NO.

10. The method of claim 9 , wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO based on the desired engine NOx aftertreatment device comprises:

during periods of cold start operation and engine operation lean of stoichiometry, selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially all NO 2 for storing NO 2 on a lean NOx trap.

11. The method of claim 9 , wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO based on the desired engine NOx aftertreatment device comprises:

during periods of hot start operation and engine operation lean of stoichiometry, selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially all NO 2 for storing NO 2 on a lean NOx trap.

12. The method of claim 9 , wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO based on the desired engine NOx aftertreatment device comprises:

during periods of warm-up of said aftertreatment system and engine operation lean of stoichiometry, selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially one to one.

13. The method of claim 9 , wherein said internal combustion engine is a homogeneous charge compression ignition engine.

14. The method of claim 9 , wherein said internal combustion engine is an stratified charge spark-ignition engine.

15. The method of claim 9 , wherein said internal combustion engine is a homogenous spark-ignition engine.

16. The method of claim 9 , wherein said internal combustion engine is a diesel engine.

17. Method for reducing NOx emissions in a powertrain comprising an internal combustion engine including a combustion chamber and an aftertreatment system, the method comprising:

monitoring an actual exhaust gas feedstream ratio of NO 2 to NO;

monitoring a desired exhaust gas feedstream ratio of NO 2 to NO, comprising:

monitoring operation of the engine;

determining a desired engine NOx aftertreatment device based upon the operation of the engine, comprising:

utilizing a NOx treatment catalyst and a lean NOx trap during periods of hot start operation and engine operation lean of stoichiometry;

wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO comprises:

during said periods of hot start operation and engine operation lean of stoichiometry, selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially all NO 2 for storing NO 2 on said lean NOx trap;

selecting the desired exhaust gas feedstream ratio of NO, to NO based on the desired engine NOx aftertreatment device:

comparing the actual and the desired exhaust gas feedstream ratios of NO 2 to NO; and

selectively initiating a NO 2 generation cycle based upon the comparison of the actual and the desired exhaust gas feedstream ratios of NO 2 to NO comprising injecting fuel mass into the combustion chamber after a primary combustion event.

18. Method for reducing NOx emissions in a powertrain comprising an internal combustion engine including a combustion chamber and an aftertreatment system, the method comprising:

monitoring an actual exhaust gas feedstream ratio of NO 2 to NO;

monitoring a desired exhaust gas feedstream ratio of NO 2 to NO, comprising:

monitoring operation of the engine:

determining a desired engine NOx aftertreatment device based upon the operation of the engine, comprising:

utilizing a hydrocarbon-selective catalytic reduction device during periods of warm-up of said aftertreatment system and engine operation lean of stoichiometry;

wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO comprises:

during periods of warm-up of said aftertreatment system and engine operation lean of stoichiometry, selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially all NO 2 ;

selecting the desired exhaust gas feedstream ratio of NO 2 to NO based on the desired engine NOx aftertreatment device;

comparing the actual and the desired exhaust gas feedstream ratios of NO 2 to NO; and

selectively initiating a NO 2 generation cycle based upon the comparison of the actual and the desired exhaust gas feedstream ratios of NO 2 to NO comprising injecting fuel mass into the combustion chamber after a primary combustion event.

19. The method of claim 18 , wherein said hydrocarbon-selective catalytic reduction system comprises a silver-alumina catalyst.

20. Method for reducing NOx emissions in a powertrain comprising an internal combustion engine including a combustion chamber and an aftertreatment system, the method comprising:

monitoring an actual exhaust gas feedstream ratio of NO 2 to NO;

monitoring a desired exhaust gas feedstream ratio of NO 2 to NO, comprising:

monitoring operation of the engine;

determining a desired engine NOx aftertreatment device based upon the operation of the engine, comprising:

utilizing a diesel particulate filter and an oxidation catalyst upstream of said diesel particulate filter;

wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO comprises:

selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially all NO 2 during warm-up of said aftertreatment device;

selecting the desired exhaust gas feedstream ratio of NO 2 to NO based on the desired engine NOx aftertreatment device;

comparing the actual and the desired exhaust gas feedstream ratios of NO 2 to NO; and

selectively initiating a NO 2 generation cycle based upon the comparison of the actual and the desired exhaust gas feedstream ratios of NO 2 to NO comprising injecting fuel mass into the combustion chamber after a primary combustion event.

21. The method of claim 20 , wherein selecting the desired exhaust gas feedstream ratio of NO 2 to NO to substantially all NO 2 during periods of warm-up of said aftertreatment device further comprises selecting the desired exhaust gas feedstream ratio of NO 2 to NO as substantially all NO 2 after warm-up of said aftertreatment device.