Abstract:
A regeneration method for a particulate filter includes estimating a quantity of particulate matter trapped within the particulate filter, comparing the quantity of particulate matter to a predetermined quantity, heating at least a portion of the particulate filter to a combustion temperature of the particulate matter, and introducing hydrocarbon fuel to the particulate filter. The hydrocarbon fuel facilitates combustion of the particulate matter to regenerate the particulate filter.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/705,712, filed on Aug. 3, 2005. The disclosure of the above application is incorporated herein by reference. 
    
    
     STATEMENT OF GOVERNMENT RIGHTS 
     This invention was produced pursuant to U.S. Government Contract No. DE-FC-04-03 AL67635 with the Department of Energy (DoE). The U.S. Government has certain rights in this invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to means for regenerating a heated particulate filter, and more particularly to such means which include a second energy source in combination with an electrical energy source. 
     BACKGROUND OF THE INVENTION 
     Exhaust gas from internal combustion engines, such as gasoline direct injection, homogeneous charge-compression ignition (HCCI), lean burn gasoline direct injection, alcohol fueled, and the like, includes particulate matter or soot that can contribute to environmental pollution. As such, an exhaust system of the engine may be fitted with a particulate filter that traps the particulate matter. After the engine has run for some time, the particulate filter needs to be cleared of the particulate matter through a regeneration process. 
     In one regeneration process, the particulate filter can be fitted with a microwave source that heats microwave absorbent spots located on a filter element within the particulate filter. The microwave absorbent spots heat to temperatures between about 500-900 deg. C. and ignite the particulate matter to burn it away. An undesirable aspect of this microwave heating method is that a microwave generator and antenna are only about 50% efficient in converting electrical energy to radiated microwave energy. As such, existing microwave heating methods require an undesirable amount of electrical energy in order to be effective. 
     Referring now  FIGS. 1-2 , simulation results are shown for a regeneration cycle of such a microwave heated particulate filter. The simulation assumes a filter substrate of the particulate filter is 7 ½ inches in diameter, 8 inches long, and has a channel density of 100 channels per square inch. The simulation assumes a radiated microwave power is 1000 watts (1 KW). 
     Referring now to  FIG. 1 , a graph  10  is shown having an x-axis  12  scaled in meters and a y-axis  14  scaled in degrees Kelvin (deg K). The x-axis  12  represents distance into inlet channels of the substrate. The y-axis  14  represents temperature of the accumulated particulate matter in the inlet channels. 
     A first line  16  indicates the temperatures of particulate matter in the inlet channels after the radiated microwave power has been turned on for eleven seconds. Peaks at locations  18  indicate locations of the microwave absorbent spots. A second line  20  indicates the temperatures of particulate matter in the inlet channels after the radiated microwave power has been turned on for sixty-one seconds. The radiated microwave power was turned off after the sixty-one seconds. The second line  20  shows that the temperatures of the particulate matter accumulated in the inlet channels are higher than in the first line  16 . 
     A third line  22  indicates the temperatures of the inlet channels fifty-nine seconds after the radiated microwave energy was turned off. It can be seen from the third line  22  that the temperatures of a substantial portion of the particulate matter are below the oxidation temperature of the particulate matter, which is between about 773 and 873 deg. K. (500 and 600 deg. C.). The third line  22  therefore indicates that the oxidation reaction in the accumulated particulate matter extinguished before substantially all of the particulate matter oxidized. 
     Referring now to  FIG. 2 , a graph  30  is shown that correlates with the graph  10  if  FIG. 1 . The graph  30  includes an x-axis  32  and a y-axis  34  scaled in meters (m). The x-axis  32  represents distance into the inlet channels. The y-axis  34  represents thickness of the accumulated particulate matter in the inlet channels. 
     A first line  36  indicates thicknesses of particulate matter on walls of the inlet channels after the radiated microwave power has been turned on for the eleven seconds. Valleys at positions  18  indicate the locations of the microwave absorbent spots. A second line  40  indicates thicknesses of particulate matter on the walls of the inlet channels after the radiated microwave power has been turned on for the sixty-one seconds. The radiated microwave energy was turned off after the sixty-one seconds. 
     A third line  42  indicates thicknesses of particulate matter on the walls of the inlet channels fifty-nine seconds after the radiated microwave energy was turned off. The third line  42  shows that the thicknesses of particulate matter between about 0.01 m and 0.05 m (see inside dashed circle  44 ) into the inlet channels changed little from the first line  36 . Since the particulate matter did not combust in that region it is apparent that that region of the inlet channels did not regenerate. 
     From  FIGS. 1 and 2  it can be seen that the heated particulate filter is unable to completely regenerate without undesirably providing it with additional electrical energy. The additional electrical energy could be used to heat more and/or larger microwave absorbent spots and/or continue the radiated microwave power for longer than the sixty-one seconds. Any of these options could undesirably discharge a charging system and/or battery associated with the engine. 
     SUMMARY 
     A regeneration method for a particulate filter includes estimating a quantity of particulate matter trapped within the particulate filter, comparing the quantity of particulate matter to a predetermined quantity, heating at least a portion of the particulate filter to a combustion temperature of the particulate matter, and introducing hydrocarbon fuel to the particulate filter. The hydrocarbon fuel facilitates combustion of the particulate matter to regenerate the particulate filter. 
     A particulate filter regeneration system includes a control module. A sensor communicates with the control module and generates a signal indicative of a quantity of particulate matter within the particulate filter. A heat source is controlled by the control module and heats at least a portion of the particulate filter to a combustion temperature of the particulate matter. A fuel injector is controlled by the control module and delivers hydrocarbon fuel to the particulate filter. The control module estimates the quantity of particulate matter based on the sensor signal, compares the quantity of particulate matter to a predetermined quantity, and delivers hydrocarbon fuel via the fuel injector to facilitate combustion of the particulate matter and regeneration of the particulate filter. 
     A regenerative particulate filter system includes a control module and a engine including an exhaust manifold and at least one fuel injector that is controlled by the control module. The system also includes a particulate filter including first channels in communication with the exhaust manifold, second channels in communication with an exhaust gas outlet of the particulate filter, and a filter substrate positioned between the first and second inlet channels and collecting at least a portion of particulate matter particulate matter carried by exhaust gas from the engine. Microwave absorbent spots are positioned on the filter substrate. A microwave source that is controlled by the control system heats the microwave absorbent spots to at least a combustion temperature of the particulate matter. The control module estimates a quantity of particulate matter collected on the filter substrate based on an amount of fuel delivered by the at least one injector and consumed by the engine. The control module compares the estimated quantity of particulate matter to a predetermined quantity. The control module turns on the microwave source based on the comparison. The control module controls the at least one fuel injector to dispense a predetermined quantity of hydrocarbon fuel based on the estimated quantity of particulate matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a graph depicting simulation results of a particulate filter regeneration cycle of the prior art; 
         FIG. 2  is a graph depicting simulation results of a particulate filter regeneration cycle of the prior art; 
         FIG. 3  is a block diagram of an engine system that includes a hydrocarbon (HC) -enhanced particulate filter regeneration system; 
         FIG. 4  is a cross-sectional view of a particulate filter; and 
         FIG. 5  is a flow chart of a method for using an HC-enhanced particulate filter regeneration system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the term module, circuit and/or device refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
     Turning now to  FIG. 3 , a block diagram is shown of an engine  50  connected to a heated particulate filter  52 . The depicted engine  50  is a four-cylinder engine  50 , however it is appreciated by those skilled in the art that the engine  50  can have any number of cylinders. In some embodiments the engine  50  is a diesel engine. The engine  50  includes fuel injectors  54 - 1 , . . . ,  54 - 4 , referred to collectively as the fuel injectors  54 , that deliver fuel to respective cylinders. The fuel injectors  54  can deliver fuel directly into the cylinders of the engine  50 . An exhaust manifold  56  receives unfiltered exhaust gas from the engine  50  and directs the unfiltered exhaust gas through a collector pipe  58 . An outlet of the collector pipe  58  connects to an inlet  60  of the heated particulate filter  52 . 
     The heated particulate filter  52  includes a filter substrate  62  that is formed to include a plurality of inlet channels  64 - 1  and outlet channels  64 - 2 , referred to collectively as the channels  64 . The filter substrate  62  can be formed from a porous material, such as cordierite and/or silicon carbide, which is tolerant of exhaust and particulate filter regeneration temperatures. The inlet channels  64 - 1  include associated downstream plugs  66  that prevent the unfiltered exhaust gas from reaching an outlet plenum  68 . The inlet channels  64 - 1  have ends that are open to an inlet plenum  70 . 
     The outlet channels  64 - 2  include associated upstream plugs  72  that prevent the unfiltered exhaust gas and particulate matter  74  from entering the outlet channels  64 - 2 . The outlet channels  64 - 2  have ends that are open to the outlet plenum  68 . 
     In operation, the unfiltered exhaust gas enters the inlet channels  64 - 1 . The particulate matter  74  is too large to pass through walls of the filter substrate  62  and becomes trapped in the inlet channels  64 - 1 . Filtered exhaust gas exits through the outlet channels  64 - 2  and passes through the outlet plenum  68  before reaching an outlet  76 . 
     Turning briefly to  FIG. 4 , a cross-section view of the heated particulate filter  52  is shown along a section line . A-A of  FIG. 1 . The cross-section shows an end view of the channels  64 . The channels  64  can have a density between 100-300 channels per square inch. 
     Returning now to  FIG. 3 , the heated particulate filter  52  includes a heat source for heating at least a portion of the particulate matter  74  until it oxidizes, thereby clearing the particulate matter  74  from the inlet channels  64 - 1  and regenerating the heated particulate filter  52 . The heat source can be inductive, resistive, arc, microwave, or any other heat source now known or developed later. 
     In the system of  FIG.3 , the heat source is a microwave heat source. A microwave E-probe antenna  80  selectively radiates microwave energy into the heated particulate filter  52 . The inlet channels  64 - 1  Include microwave absorbent spots  82  that are positioned on the walls of the inlet channels  64 - 1 . The microwave absorbent spots  82  are formed from one or more materials such as silicon carbide (SiC), indium tin oxide (ITO), and/or iron, and reach at least the combustion temperature of the particulate matter  74  when they are radiated with the microwave energy. 
     Once the particulate matter  74  reaches its combustion temperature and begins to oxidize, the heat source is turned off to conserve energy. The oxidation reaction can thereafter be maintained by hydrocarbons, e.g. gasoline or diesel fuel, which is delivered into the inlet channels  64 - 1  in accordance with a method described later. 
     The heated particulate filter  52  includes metallic screens and/or honeycombs  91  that allow exhaust gas to pass through while attenuating microwave energy that escapes from the heated particulate filter  52 . 
     A microwave generation module  90  receives electrical energy from an alternator  92  and/or electrical subsystem that are powered by the engine  50 . The microwave generation module  90  converts the electrical energy to microwave energy in accordance with a regeneration command from an engine control module (ECM)  94 . A coaxial cable  95  connects the microwave generation module  90  to the E-probe antenna  80 . The coaxial cable  95  can be s semi-rigid coaxial cable  95 . 
     A temperature sensor  96  generates a temperature signal based on the temperature of the filter substrate  62 . The temperature signal can be communicated to the microwave generation module  90 . 
     In some embodiments the ECM  94  can receive an upstream pressure signal from an upstream pressure transducer  97  that is mounted at the inlet  60 . The ECM  94  can also receive a downstream pressure signal from a downstream pressure transducer  98  that is mounted at the outlet  76 . The ECM  94  can determine a differential pressure across the inlet  60  and the outlet  76  by determining a difference between the upstream and downstream pressure signals. The differential pressure is indicative of a quantity of particulate matter  74  that is accumulated on the walls of the inlet channels  64 - 1 . In some embodiments the upstream pressure transducer  97  and the downstream pressure transducer  98  can be substituted with a single differential pressure transducer that communicates a differential pressure signal to the ECM  94 . 
     The ECM  94  provides an injector drive signal to respective ones of the fuel injectors  54 . The duration of each injector drive signal corresponds to operating conditions of the engine  50  such as intake air flow, throttle pedal position, and engine temperature, and determines the amount of fuel that is delivered to the corresponding cylinder of the engine  50 . The amount of fuel delivered to the engine and the operating conditions of the engine are indicative of the amount of particulate matter  74  that the engine  50  will generate. The ECM  94  can therefore integrate the expected particulate matter  74  generation rate over time to determine the amount of particulate matter  74  on the walls of the inlet channels  64 - 1  at any time. The ECM  94  can use the differential pressure across the heated particulate filter  52  and/or the particulate matter  74  integration method to determine when the heated particulate filter  52  needs to be regenerated and to determine how much particulate matter  74  is accumulated in the inlet channels  64 - 1 . 
     Turning now to  FIG. 5 , a method  100  is shown for regenerating the heated particulate filter (PF)  52 . The method  100  can be implemented as a software subroutine and stored as computer instructions in a computer memory located in the ECM  94  and/or the microwave generation module  90 . The method  100  can then be executed periodically by a microprocessor that is connected to the memory. 
     The method  100  begins in start block  101  and control immediately proceeds to decision block  102 . In decision block  102 , control determines whether the inlet channels  64 - 1  are loaded with the particulate matter  74 . The inlet channels  64 - 1  are deemed to be loaded when a predetermined quantity of particulate matter  74  is accumulated in the inlet channels  64 - 1 . If the inlet channels  64 - 1  are not loaded, control proceeds to exit block  104  and terminates. On the other hand, if control determines that the inlet channels  64 - 1  are loaded then control proceeds to block  105 . In block  105  control turns on the heat source, such as the microwave E-probe antenna  80 , to begin heating the accumulated particulate matter  74 . Control then proceeds to decision block  106 . Control can turn the heat source on for an amount of time that is a predetermined time, an amount of time that is a function of the exhaust gas conditions from the engine  50 , and/or an amount of time that is a function of the temperature of the filter substrate  62 . Examples of exhaust gas conditions include an exhaust gas temperature and/or an exhaust flow rate. 
     In block  106 , control determines whether the exhaust gas conditions are such that they may extinguish or otherwise prevent the accumulated particulate matter  74  from oxidizing. If the exhaust temperature is above a predetermined exhaust temperature, and/or if the exhaust gas flow rate is below a predetermined flow rate, then control proceeds to exit block  104  and terminates. On the other hand, if the exhaust temperature is below the predetermined exhaust temperature, and/or if the exhaust gas flow rate is above the predetermined flow rate, then control proceeds to block  108 . 
     In block  108 , control determines an amount of HC to deliver into the inlet channels  64 - 1 . The ECM  94  can deliver the HC by turning on one or more of the fuel injectors  54  during an exhaust stroke of the cylinder associated with the energized fuel injector(s). The amount of HC that the ECM  94  delivers can be based on the exhaust gas conditions, the amount of particulate matter  74  accumulated in the inlet channels  64 - 1 , and or the temperature of the filter substrate  62 . The amount of particulate matter  74  accumulated in the inlet channels  64 - 1  can be determined by the differential pressure method and/or the integration method described above. After determining the amount of HC to deliver in block  108 , control proceeds to block  110  and delivers the HC. 
     In some embodiments, a waiting step can be included between blocks  105  and  110 . The waiting step ensures that the heat source has ample time to elevate the temperature of the accumulated particulate matter  74  to its combustion temperature. This ensures that the HC will combust and contribute to oxidizing the accumulated particulate matter  74 . 
     By delivering HC to the inlet channels  64 - 1  during regeneration, the method  100  reduces the electrical energy needed by the heat source of the heated particulate filter  52 . The heat source can be turned off once the HC begins to combust and oxidize the accumulated particulate matter  74 . Delivering HC to the inlet channels  64 - 1  will also accelerate the particulate matter  74  oxidation and prevent the oxidation reaction from being extinguished by the exhaust gas. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.