Method and apparatus for regenerating a NOx trap and a particulate trap

Abstract

An apparatus comprises an emission abatement device and a ratio oscillator. The emission abatement device comprises a NOx trap and a particulate trap. The ratio oscillator is configured to oscillate a ratio of the oxygen content and regenerative agent content of a flow advanced to the emission abatement device so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles. An associated method is disclosed.

Description

FIELD OF THE DISCLOSURE

The present disclosure relates generally to methods and apparatus for treatment of emissions present in exhaust gas.

BACKGROUND OF THE DISCLOSURE

Emission abatement devices are used to treat emissions present in exhaust gas. For example, there are NOx traps and particulate traps. NOx traps are used to trap oxides of nitrogen (i.e., NOx) and particulate traps are used to trap particulate matter. From time to time, the NOx traps and particulate traps are “regenerated” to purge them of the components trapped thereby for further use of the traps.

SUMMARY OF THE DISCLOSURE

According to an aspect of the present disclosure, there is provided an apparatus comprising an emission abatement device and a ratio oscillator. The emission abatement device comprises a NOx trap and a particulate trap. The ratio oscillator is configured to oscillate a ratio of the oxygen content and regenerative agent content of a flow advanced to the emission abatement device so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles. An associated method is disclosed.

The above and other features of the present disclosure will become apparent from the following description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram showing an apparatus for oscillating injection of a regenerative agent into a flow of exhaust gas for regeneration of a downstream NOx trap and particulate trap of an emission abatement device; and

FIG. 2 is an exemplary graph showing oscillation of a ratio of the oxygen content and regenerative agent content of the exhaust gas flow advanced to the emission abatement device.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives following within the spirit and scope of the invention as defined by the appended claims.

Referring to FIG. 1, there is shown an apparatus 10 for regenerating a NOx trap 12 and a particulate trap 14 of an emission abatement device 16. The traps 12, 14 may be separate components as in option 1 of FIG. 1 or may be portions of an integrated device as in option 2 of FIG. 1.

The apparatus 10 includes a ratio oscillator 18. The ratio oscillator 18 is configured to oscillate a ratio of the oxygen content and regenerative agent content of a flow advanced to the emission abatement device 16 so as to alternately partially regenerate the NOx trap 12 and the particulate trap 14 for a plurality of cycles until completion of regeneration of the traps 12, 14. As such, a given quantity of regenerative agent is used to regenerate both the NOx trap 12 and the particulate trap 14. Performance of such “double duty” by a given quantity of regenerative agent reduces overall consumption of the regenerative agent. In addition, by dividing regeneration of the particulate trap 14 into a plurality of events, a potentially damaging increase in the temperature of the particulate trap 14 is avoided.

The ratio oscillator 18 oscillates the ratio of the flow advanced to the emission abatement device 16 between higher and lower agent levels (e.g., between relatively agent-rich and relatively agent-lean levels). The NOx trap 12 is partially regenerated with the regenerative agent each time that the ratio is at a higher agent level. In addition, an oxidation catalyst 19 (“OC”), such as a diesel oxidation catalyst, upstream from or integrated with the particulate trap 14 oxidizes a portion of the regenerative agent to generate heat and elevate the temperature of the particulate trap 14 each time that the ratio is at a higher agent level. Indeed, the oxidation catalyst 19 oxidizes regenerative agent so as to generate heat for elevating the temperature of the particulate trap 14 whenever there is oxygen and an amount of regenerative agent at the catalyst 19 (i.e., not just when the regenerative agent is at a higher agent level).

The particulate trap 14 is partially regenerated with oxygen present in the flow and with heat generated by the catalyst 19 each time that the ratio is at a lower agent level. As such, each partial regeneration cycle includes commencing partial regeneration of the NOx trap 12 and interrupting partial regeneration of the particulate trap 14 upon commencement of partial regeneration of the NOx trap 12. Each partial regeneration cycle further includes commencing partial regeneration of the particulate trap 14 and interrupting partial regeneration of the NOx trap 12 upon commencement of partial regeneration of the particulate trap 14.

The regenerative agent thus serves as a NOx-reducing agent for reducing NOx at the NOx trap 12 and serves as an oxidizable agent to be oxidized at the catalyst 19 to generate heat for regeneration of the particulate trap 14. As such, the agent may take a variety of forms. For example, the agent may be a hydrocarbon fuel (e.g., diesel, gasoline, propane, alcohol, methanol), hydrogen (H₂), carbon monoxide (CO), and/or other fuels. In such a case, the ratio of the oxygen content and the regenerative agent content of the flow may be the “lambda value” or corresponding air-to-fuel ratio of the flow advanced to the emission abatement device 16.

When the traps 12, 14 are separate components as in option 1 of FIG. 1, the particulate trap 14 may be positioned upstream from the NOx trap 12. In addition, the catalyst 19 may be positioned upstream from the particulate trap 14 or integrated into the particulate trap 14.

When the traps 12, 14 are combined in an integrated device as in option 2 of FIG. 1, the catalyst 19 may be a separate component upstream from the integrated device or integrated into the integrated device.

Carbon monoxide (CO) may be generated as a by-product of each partial regeneration of the particulate trap 14 (i.e., during each phase involving lower levels of regenerative agent such as agent-lean phases). CO is useful as a reducing agent to reduce NOx in the NOx trap 12. In addition, each partial regeneration of the particulate trap 14 generates heat which raises the temperature of the NOx trap 12 (e.g., to about 600° C.). Such temperature elevation of the NOx trap 12 facilitates desulfation of the NOx trap 12 during phases involving higher levels of regenerative agent (e.g., agent-rich phases).

Referring to FIG. 2, there is shown a graph illustrating oscillation of the ratio of the oxygen content and regenerative agent content of the flow over time. The ratio is shown in FIG. 2 as both the agent-to-oxygen ratio (solid line) to highlight the regenerative agent content and as the inverse oxygen-to-agent ratio (dashed line) to highlight the oxygen content. As such, an increase in the agent-to-oxygen ratio represents an increase in the regenerative agent content of the flow delivered to the emission abatement device 16. Conversely, an increase in the oxygen-to-agent ratio represents an increase in the oxygen content of the flow delivered to the emission abatement device 16.

Illustratively, the ratio waveform is generally sinusoidal. It is within the scope of this disclosure for the ratio waveform to be other than sinusoidal (e.g., a step waveform or near step waveform). Regardless of the particular shape of the ratio waveform, the ratio waveform has a plurality of adjacent peaks 20 and valleys 22, each adjacent peak and valley producing one cycle. Such peaks 20 and valleys 22 in the ratio waveform achieve oscillation of the ratio to alternately partially regenerate the NOx trap 12 and particulate trap 14 for the plurality of cycles until completion of regeneration of the traps 12, 14.

Referring back to FIG. 1, the emission abatement device 16 is contained in an exhaust gas passageway 24 for conducting exhaust gas (“EG”) through the traps 12, 14. The exhaust gas is generated by an exhaust gas source such as an internal combustion engine 26 (e.g., diesel engine) fluidly coupled to the passageway 24. The ratio oscillator 18 is configured, for example, as an agent injection system that is fluidly coupled to the passageway 24 and that oscillates injection of regenerative agent into exhaust gas flowing through the passageway 24 between higher and lower agent levels so as to alternately partially regenerate the NOx trap 12 and the particulate trap 14 for the plurality of cycles. The regenerative agent delivered to the emission abatement device 16 is thus a combination of the injected regenerative agent and any regenerative agent already present in the exhaust gas [e.g., unburned hydrocarbon fuel, hydrogen (H₂), carbon monoxide (CO)]. It is within the scope of this disclosure for the lower agent level to be zero or non-zero.

As an agent injection system, the ratio oscillator 18 includes a controller 27 electrically coupled to a flow control device 28 via an electrical line 29 and electrically coupled to a pump 30 via an electrical line 31. The controller 27 is configured to control operation of the pump 30 to cause regenerative agent to be pumped from an agent supply 32 past the flow control device 28 and injected into the exhaust gas passageway 20. The controller 27 is configured to control operation of the flow control device 28 to cause the flow control device 28 to oscillate injection of the regenerative agent into the passageway 20 between higher and lower agent levels, thereby oscillating the ratio of the oxygen content and regenerative agent content of the exhaust gas flow in the passageway 20 to the emission abatement device 16.

Exemplarily, the flow control device 28 is a valve. The valve may take a variety of configurations. For example, it may be a rotatable flapper valve. In other cases, it may be a solenoid valve movable between opened and closed positions in response to energization and de-energization of the solenoid valve.

The agent supply 32 may be a fuel supply to supply fuel. More particularly, the agent supply 32 may be a hydrocarbon fuel supply to supply hydrocarbon fuel, a hydrogen supply to supply to H₂, and/or a CO supply to supply CO. In the particular case where the engine 22 is a diesel engine onboard a vehicle, the supply 32 may be a diesel fuel supply due to the ready availability of diesel fuel already onboard the vehicle.

It is within the scope of this disclosure for the ratio oscillator 18 to be coupled to the engine 26 by a line 40 to inject the regenerative agent into one or more cylinders of the engine 26 in addition to or instead of injecting the regenerative agent into the exhaust gas passageway 24. In particular, the ratio oscillator 18 may inject the regenerative agent into exhaust gas present in the cylinder(s) just before the exhaust gas is discharged from the cylinder(s). The regenerative agent is thus discharged from the engine 26 with the exhaust gas into the exhaust gas passageway 24 for delivery to the emission abatement device 16.

It is further within the scope of this disclosure for the ratio oscillator 18 to oscillate injection of regenerative agent into exhaust gas of the engine 26 in response to at least one of a flow of air introduced into the engine 26, an engine out lambda value measured by a lambda sensor 42 electrically coupled to the controller 27 by an electrical line 44, and an engine map 46 of the engine 26. The engine map 46 may be integrated into the controller 27 or be separate from the controller 27 as part of some other device such as the engine control unit. It is within the scope of this disclosure for the controller 27 to be integrated into or be separate from the engine control unit.

While the concepts of the present disclosure have been illustrated and described in detail in the drawings and foregoing description, such illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only the illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.

There are a plurality of advantages of the concepts of the present disclosure arising from the various features of the systems described herein. It will be noted that alternative embodiments of each of the systems of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of a system that incorporate one or more of the features of the present disclosure and fall within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A method, comprising the steps of:

oscillating a ratio of the oxygen content and regenerative agent content of a flow advanced to an emission abatement device comprising a NOx trap and a particulate trap, and

alternately partially regenerating the NOx trap and the particulate trap for a plurality of cycles in response to the oscillating step.

2. The method of claim 1, wherein:

the oscillating step comprises operating a valve so as to oscillate injection of a hydrocarbon fuel into exhaust gas advanced to the emission abatement device, and

the regenerating step comprises (i) partially regenerating the NOx trap with the injected fuel and other regenerative agent present in the exhaust gas each time the ratio is at a higher fuel level, (ii) generating heat each time the ratio is at a higher fuel level, and (iii) partially regenerating the particulate trap with oxygen present in the exhaust gas and with the generated heat each time the ratio is at a lower fuel level.

3. The method of claim 1, wherein the oscillating step comprises oscillating the ratio of the oxygen content and regenerative agent content of exhaust gas advanced to the emission abatement device.

4. The method of claim 1, wherein the oscillating step comprises oscillating injection of regenerative agent into exhaust gas advanced to the emission abatement device.

5. The method of claim 4, wherein the injection oscillating step comprises operating a valve so as to oscillate injection of the regenerative agent into the flow of exhaust gas.

6. The method of claim 4, wherein the injection oscillating step comprises oscillating injection of a fuel into the exhaust gas.

7. The method of claim 1, wherein:

the oscillating step comprises oscillating the ratio between higher and lower agent levels, and

the regenerating step comprises (i) partially regenerating the NOx trap when the ratio is at a higher agent level and (ii) partially regenerating the particulate trap when the ratio is at a lower agent level.

8. The method of claim 7, wherein:

the regenerating step further comprises generating heat when the ratio is at a higher agent level, and

the step of partially regenerating the particulate trap comprises partially regenerating the particulate trap with the generated heat and oxygen present in the flow.

9. The method of claim 1, wherein the regenerating step comprises (i) commencing partial regeneration of the NOx trap and interrupting partial regeneration of the particulate trap upon commencement of partial regeneration of the NOx trap and (ii) commencing partial regeneration of the particulate trap and interrupting partial regeneration of the NOx trap upon commencement of partial regeneration of the particulate trap.

10. An apparatus, comprising:

a NOx trap and a particulate trap,

an exhaust gas passageway in which the NOx trap and the particulate trap are positioned, and

an agent injection system configured to oscillate injection of a regenerative agent into the exhaust gas passageway between higher and lower agent levels so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles.

11. The apparatus of claim 10, wherein the agent injection system comprises an agent supply, a flow control device positioned to control flow of the agent from the agent supply to the exhaust gas passageway, and a controller coupled to the flow control device to vary operation thereof to oscillate injection of the regenerative agent.

12. The apparatus of claim 10, wherein the agent injection system comprises a fuel supply to supply fuel as the injected regenerative agent.

13. The apparatus of claim 10, wherein the agent injection system comprises a valve operable to oscillate injection of the regenerative agent.

14. The apparatus of claim 13, wherein the agent injection system comprises a controller coupled to the valve to vary operation of the valve to oscillate injection of the regenerative agent.

15. An apparatus, comprising:

an emission abatement device comprising a NOx trap and a particulate trap, and

a ratio oscillator configured to oscillate a ratio of the oxygen content and regenerative agent content of a flow advanced to the emission abatement device so as to alternately partially regenerate the NOx trap and the particulate trap for a plurality of cycles.

16. The apparatus of claim 15, wherein the ratio oscillator is configured to oscillate the ratio between higher and lower agent levels so as to partially regenerate the NOx trap each time that the ratio is at a higher agent level and to partially regenerate the particulate trap each time that the ratio is at a lower agent level.

17. The apparatus of claim 16, wherein the emission abatement device comprises a catalyst associated with the particulate trap to elevate the temperature of the particulate trap in the presence of oxygen and regenerative agent.

18. The apparatus of claim 15, wherein:

the emission abatement device is positioned in an exhaust gas passageway, and

the ratio oscillator comprises a fuel supply to supply a fuel, a valve fluidly coupled to the fuel supply and fluidly coupled to the exhaust gas passageway at a location upstream from the emission abatement device, and a controller coupled to the valve to vary operation thereof to oscillate injection of the fuel into the exhaust gas passageway.

19. The apparatus of claim 15, further comprising an engine fluidly coupled to the emission abatement device, wherein the ratio oscillator is configured to oscillate injection of a regenerative agent into exhaust gas of the engine in response to at least one of a flow of air introduced into the engine, the lambda value of the exhaust gas, and a map of the engine.

20. The apparatus of claim 15, further comprising an engine fluidly coupled to the emission abatement device, wherein the ratio oscillator is coupled to the engine to inject a fuel into the engine.