Patent Application
20060283176
The present disclosure relates generally to methods and apparatus for treatment of emissions present in exhaust gas.
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.
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.
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
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
When the traps 12, 14 are combined in an integrated device as in option 2 of
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
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
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.
