Abstract:
A method and apparatus for initiating regeneration in a particulate trap including the steps of locating structures in the particulate trap in areas that generate particulate build up, generating microwaves, absorbing microwaves with the particulate build up, and controlling the microwaves to initiate a burn off of particulates.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a diesel particulate trap. More specifically, the present invention relates to a method and apparatus for regenerating a diesel particulate trap using microwave radiation.  
         BACKGROUND OF THE INVENTION  
         [0002]    Increased regulation has reduced the allowable levels of particulates generated by diesel engines. The particulates can generally be characterized as a soot that is captured and reduced by particulate filters or traps. Present particulate filters or traps contain a separation medium with tiny pores that capture particles. As trapped material accumulates in the particulate trap, resistance to flow in the particulate trap increases, generating backpressure. The particulate trap must then be regenerated to burn off the particulates/soot in the particulate trap to eliminate the backpressure and allow air flow through the particulate trap. Past practices of regenerating a particulate trap utilized an energy source such as a burner or electric heater to generate combustion in the particulates. Particulate combustion in a diesel particulate trap by these past practices has been found to be difficult to control and may result in an excessive temperature rise.  
         SUMMARY OF THE INVENTION  
         [0003]    The present invention is a method and apparatus for regenerating a particulate trap using microwave energy. The present invention in the preferred embodiment uses concentrated particulate matter ignited by microwave radiation to initiate the burn off of particles/soot in a particulate trap. The particulates are concentrated in desired areas in the particulate trap using structures such as tabs or walls.  
           [0004]    The present invention includes a particulate trap placed in the exhaust flow of a diesel engine. A microwave source may be operatively coupled to a wave guide, and a focus ring may be used to direct the microwaves to particulate matter or microwave absorbing materials. The concentrated particulate matter or microwave-absorbing material generates heat in response to incident microwaves to burn off particulates. Materials transparent to microwaves are preferably used for the basic construction of the particulate trap housing and other areas in the particulate trap where it would be inefficient to absorb microwave energy. By strategically locating structures to accumulate particulate matter and/or microwave absorbing materials, microwaves may be used efficiently at the locations they are most needed to initiate the burn off of particulates and heat catalyst materials. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 is a diagrammatic drawing of a wall flow monolith particulate trap.  
         [0006]    [0006]FIG. 2 is a diagrammatic drawing of the microwave regeneration system of the present invention.  
         [0007]    [0007]FIG. 3 is a diagrammatic drawing illustrating a particulate trap of the present invention.  
         [0008]    [0008]FIG. 4 is a plot detailing the exhaust gas velocity, flame front, and heat release generated by the end plug heating illustrated in FIG. 3. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0009]    [0009]FIG. 1 is a diagrammatic drawing of a typical wall flow monolith particulate trap  10  “particulate trap” used in diesel applications. The particulate trap  10  includes alternating closed cells/channels  14  and open cells/channels  12 . Exhaust gases such as those generated by a diesel engine enter the closed end channels  14 , depositing particulate matter  16  and exiting through the open channels  12 . The particulate trap  10  structure is preferably comprised of a porous ceramic honeycomb wall of chordierite material, but any ceramic honeycomb material is considered within the scope of the present invention.  
         [0010]    [0010]FIG. 2 is a diagrammatic drawing of the microwave system  22  of the present invention. The system  22  includes a particulate trap  10  placed in the exhaust flow of a diesel engine. A microwave power source  26  and microwave antenna  28  may be operatively coupled to a wave guide  30 , and an optional focus ring  32  to direct the microwaves to the particulate trap  10 . In alternate embodiments of the present invention, the microwave antenna  28  is directly coupled to the housing of the particulate trap  10 .  
         [0011]    Concentrated particulate deposits generate heat in response to incident microwaves to initiate the burn off of particulates in the particulate trap  10 . Materials such as chordierite that are transparent to microwaves are preferably used for the basic construction of the particulate trap  10  housing and other areas in the particulate trap  10  where it would be inefficient to absorb microwave energy. As the chordierite does not absorb microwave energy, the microwaves will “bounce” around until they are incident upon the particulate deposits. The temperature of the particulate trap  10  may be regulated by the timed build up of particulates and by controlling the application of the microwave energy. A metallic honeycomb  32  may be fitted to the particulate trap  10  to block microwaves exiting the particulate trap  10 .  
         [0012]    [0012]FIG. 3 is a diagrammatic drawing of a particulate trap configured with structures  40  to collect particulate matter. The structures  40  will accumulate matter in preferred locations in the particulate trap  10 . Diesel exhaust filled with particulates flows through the particulate trap, depositing particulates  42  upon walls  44  of the particulate trap  10  with concentrations of particulate matter occurring around the structures  40  and end plug  46 . The microwave field density will inherently focus on the most microwave absorbent materials. In the present invention, the most absorbent materials in the particulate trap  10  are the particulate concentrations around the mid-channel structures  40  and the end plug  46 . The particulate concentrations create a hot spot or ignition point for the microwave energy that burns off particulates deposited on the walls  44  of the particulate trap  10 . Microwaves incident upon particulate deposits initiate the burn off of the particulates  42  to clear the walls  44  of the particulate trap  10 , as seen by waves  50  that represent the flame front of the particulate burn off. The ignition of a relatively small amount of particulates, that are ignited by the particulate concentrations, will be leveraged to burn a relatively large amount of particulates. The present invention is self regulating in temperature, as energy absorption by the deposits of particulate matter will stop as the particulates combust. Accordingly, the microwave energy will be absorbed by the next largest carbon deposit within the particulate filter. This pattern of microwave absorption and particulate combustion uniformly initiates the regeneration process within the particulate filter.  
         [0013]    [0013]FIG. 4 illustrates the performance of the particulate trap shown in FIG. 3. The exhaust gas velocity shown as plot  60  will decrease as a function of the distance of the closed end channel. The heat shown as plot  62  generated by the particulate heat release will initially be localized mid-channel and near the end plug  46 , and then propagate as a burn-off flame front shown by arrows  64  and  66 .  
         [0014]    The preferred structures  40  used to generate the build up of particulate matter have been show as walls in the present invention, but any structure that may generate a concentration of particulate matter in a particulate trap is considered within the scope of the present invention. The structures include, but are not limited walls, tabs, points, arrays of prominences, and other similar structures.  
         [0015]    It is to be understood that the invention is not limited to the exact construction illustrated and described above, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.