Abstract:
A particulate matter (PM) filter includes filter walls having inlet ends and outlet ends. First adjacent pairs of the filter walls define inlet channels. Second adjacent pairs of the filter walls define outlet channels. Outlet end plugs are arranged in the inlet channels adjacent to the output ends. Inlet end plugs arranged in the outlet channels spaced from the inlet ends.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/037,181, filed on Mar. 17, 2008, which is incorporated herein by reference in its entirety. 
     
    
     STATEMENT OF GOVERNMENT RIGHTS 
       [0002]    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 
       [0003]    The present disclosure relates to particulate matter (PM) filters. 
       BACKGROUND 
       [0004]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. 
         [0005]    Diesel engines combust fuel in the presence of air to produce power. The combustion of fuel produces exhaust gas that contains particulate matter (PM). The PM may be filtered from the exhaust gas using a PM filter. Over time, the PM may accumulate within the PM filter and may restrict the flow of exhaust gas through the PM filter. PM that has collected within the PM filter may be removed by a process referred to as regeneration. During regeneration, PM within the PM filter may be combusted. 
         [0006]    Regeneration may involve heating the PM filter to a combustion temperature of the PM. There are various ways to perform regeneration including modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, using resistive heating coils, and/or using microwave energy. 
         [0007]    Diesel PM combusts when temperatures above a combustion temperature such as 600° C. are attained. The start of combustion causes a further increase in temperature. Once the PM is ignited, the burning PM may be used to regenerate the rest of the filter. In other words, cascading flame front moves from the inlet to the outlet of the PM filter. While spark-ignited engines typically have low oxygen levels in the exhaust gas stream, diesel engines have significantly higher oxygen levels. While the increased oxygen levels make fast regeneration of the PM filter possible, it may also pose some problems. 
         [0008]    Referring now to  FIG. 1 , a PM filter system  10  for regenerating a PM filter is shown. The PM filter system  10  includes a heater  12 . The PM filter system  10  further includes a particular matter filter  14  that includes walls  16 - 1 ,  16 - 2 , . . . , and  16 - 6  (collectively walls  16 ). Some pairs of the adjacent walls  16  define outlet channels and may include an inlet end plug. Other pairs of adjacent walls define inlet channels and may include an outlet end plug. 
         [0009]    In particular, adjacent walls  16 - 1  and  16 - 2 ,  16 - 3  and  16 - 4 , and  16 - 5  and  16 - 6  define outlet channels and include an inlet end plugs  18 - 1 ,  18 - 2 , and  18 - 3 , respectively (collectively inlet end plugs  18 ). Adjacent walls  16 - 2  and  16 - 3 ,  16 - 4  and  16 - 5  include define inlet channels and include outlet end plugs  20 - 1  and  20 - 2 , respectively (collectively outlet end plugs  20 ). 
         [0010]    In use, exhaust flows through the heater  12  and into inlet channels of the filter  14 . The exhaust flows from the inlet channels through the walls  16  into adjacent outlet channels. PM is filtered as the exhaust gas passes through the walls  16  and builds up on the walls  16  in the inlet channels. PM also builds up in the inlet channels in areas around the outlet end plugs  20 . 
         [0011]    Referring now to  FIGS. 2-4 , regeneration within the PM filter system  10  is shown. In  FIG. 2 , when the heater  12  is turned on, PM adjacent to the heater begins burning in a burning zone. The substrate temperature in areas beyond the burning zone may be less than the PM ignition temperature. Therefore, there is no regeneration in these areas at this time. 
         [0012]    In  FIG. 3 , the burning zone moves along the length of the PM filter  14 . Regeneration of the PM continues as long as the burning zone temperature is above the PM ignition temperature. In  FIG. 4 , if the burning zone temperature falls below the PM ignition temperature, the filter  14  will not be regenerated fully. In other words, PM may remain in portions of the filter  14  that are adjacent to the outlet end plugs  20 . 
         [0013]    To avoid this situation, the heater  12  may be turned on to heat the PM filter to a higher initial temperature. The higher temperatures may tend to decrease the durability of the PM filter. 
       SUMMARY 
       [0014]    A particulate matter (PM) filter includes filter walls having inlet ends and outlet ends. First adjacent pairs of the filter walls define inlet channels. Second adjacent pairs of the filter walls define outlet channels. Outlet end plugs are arranged in the inlet channels adjacent to the output ends. Inlet end plugs arranged in the outlet channels spaced from the inlet ends. 
         [0015]    In other features, the exhaust flows into the inlet channels, through the filter walls of the inlet channels to the outlet channels. Exhaust also flows into portions of the outlet channels between the inlet ends of the walls and the inlet end plugs. PM builds up in the portions during operation. 
         [0016]    A system comprises the PM filter and further comprises a heater that is arranged adjacent to the inlet ends of the filter walls. A control module selectively activates the heater to regenerate the PM filter. 
         [0017]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0019]      FIG. 1  is a side cross-sectional view of a PM filter assembly according to the prior art; 
           [0020]      FIG. 2  is a side cross-sectional view of the PM filter of  FIG. 1  and a graph of regeneration temperature during a first period after regeneration begins; 
           [0021]      FIG. 3  is a side cross-sectional view of the PM filter of  FIG. 1  and a graph of regeneration temperature during a second period after regeneration begins; 
           [0022]      FIG. 4  is a side cross-sectional view of the PM filter of  FIG. 1  and a graph of regeneration temperature during a third period after regeneration begins; 
           [0023]      FIG. 5  is a functional block diagram of an exemplary engine and exhaust system according to the present disclosure; 
           [0024]      FIG. 6  is a side cross-sectional view of a PM filter assembly with recessed inlet end plugs according to the present disclosure; 
           [0025]      FIG. 7  is a side cross-sectional view of the PM filter of  FIG. 6  and a graph of regeneration temperature during a first period after regeneration begins; 
           [0026]      FIG. 8  is a side cross-sectional view of the PM filter of  FIG. 6  and a graph of regeneration temperature during a second period after regeneration begins; and 
           [0027]      FIG. 9  is a side cross-sectional view of the PM filter of  FIG. 6  and a graph of regeneration temperature during a third period after regeneration begins. 
       
    
    
     DETAILED DESCRIPTION  
       [0028]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. 
         [0029]    The present disclosure describes systems and methods for improving the regeneration of front-heated, wall-flow PM filters. The PM filter according to the present disclosure uses recessed inlet end plugs to localize and increase PM accumulation in these areas. The accumulated PM improves the regeneration of the PM filter. 
         [0030]    The successful regeneration of front-heated PM (PM) filters depends on the amount of heat applied to an inlet of a wall-flow substrate. The peak temperature will determine if PM light-off is initiated. The amount of thermal mass will determine if the regeneration process will proceed down the entire substrate length. In other words, the heat applied to the inlet of the PM Filter is based on (exhaust heat) plus (localized PM exothermic heat) plus (any external heat source). 
         [0031]    Recessed inlet end plugs according to the present disclosure provide for PM accumulation at the inlet end of the PM filter adjacent to the heater element. This accumulation increases the localized PM exothermic heat at the inlet compared to non-recessed inlet end plugs. The increased energy can increase the likelihood that the burn-off propagates down the length of the PM Filter. This approach may tend to reduce the amount of heat supplied by the heater. 
         [0032]    In other words, heat applied to the inlet of the PM filter is based on (exhaust heat (which is the same as in  FIG. 1 )) plus (localized PM exothermic heat (which is increased due to the accumulated PM in the recessed inlet end plugs)+(external heat (which can be decreased)). 
         [0033]    As can be appreciated, the external heat may be supplied by any suitable method. For example only, heat can be supplied by modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, using resistive heating coils, and/or using microwave energy. The resistive heating coils may be zoned or unzoned. 
         [0034]    In  FIG. 5 , a functional block diagram of an exemplary engine and exhaust system  100  for a vehicle is shown. The engine and exhaust system  100  may include a diesel engine system  102 . While diesel engine system  102  is shown, the present disclosure is applicable to gasoline engine systems, homogenous charge compression ignition engine systems, and/or other engine systems. 
         [0035]    The diesel engine system  102  includes an engine  104  and an exhaust system  106 . The engine  104  combusts a mixture of air and diesel fuel to produce power (e.g., torque). The combustion of the air and fuel mixture produces exhaust gas that may be expelled from the engine  104  into the exhaust system  106 . The exhaust gas produced by the engine  104  may contain a mixture of gaseous compounds and PM that enters the exhaust system and may be treated therein prior to exiting the exhaust system  106 . 
         [0036]    The exhaust system  106  may include an exhaust manifold assembly  108 , an intermediate pipe assembly  110 , a PM filter assembly  112 , and a muffler assembly  114 . The PM filter assembly may include heater  124  that may be used to increase the heat of the PM filter during regeneration. 
         [0037]    Exhaust gas produced by the engine  104  flows through the exhaust manifold assembly  108  to the PM filter assembly  112  via the intermediate pipe assembly  110 . Exhaust gas exiting the PM filter assembly  112  flows through the muffler assembly  114  and is released to the atmosphere through a tailpipe  118 . The intermediate pipe assembly  110  may include exhaust gas after treatment systems, such as but not limited to, a diesel oxidation catalyst (DOC) assembly and a selective catalytic reduction (SCR) assembly. 
         [0038]    The PM filter assembly  112  filters PM from the exhaust gas flowing through the PM filter assembly  112 . PM may accumulate within the PM filter assembly  112  during a process referred to as loading and thereby restrict the flow of exhaust gas through the PM filter assembly  112 . PM that has accumulated within the PM filter assembly  112  may be removed by regeneration. During regeneration, heat is used to combust the PM present in the PM filter assembly  112 . 
         [0039]    The vehicle may include a control module  130  that monitors sensors  132  such as intake air temperature (IAT), manifold absolute pressure (MAP), mass air flow (MAF), engine speed, coolant temperature, throttle position, and other parameters. The control module  130  adjusts actuators  134  such as an ignition system, an electric throttle, a fuel injection system, and other engine systems. The control module  130  may also determine when the PM filter requires regeneration and actuate the heater  124 . 
         [0040]    Referring now to  FIG. 6 , a PM filter assembly  210  for regenerating a PM filter is shown. The PM filter assembly  210  includes a heater  212 . For example only, the heater  212  may include a resistive heater. The heater may be turned on and off by the control module. The PM filter assembly  210  further includes a PM filter  214  that includes walls  216 - 1 ,  216 - 2 , . . . , and  216 - 6  (collectively walls  216 ). The walls  216  may be arranged adjacent and generally parallel to each other. 
         [0041]    In particular, adjacent walls  216 - 1  and  216 - 2 ,  216 - 3  and  216 - 4 , and  216 - 5  and  216 - 6  define outlet channels and include recessed inlet end plugs  218 - 1 ,  218 - 2 , and  218 - 3 , respectively (collectively recessed inlet end plugs  18 ). Adjacent walls  216 - 2  and  216 - 3 ,  216 - 4  and  216 - 5  define inlet channels and include outlet end plugs  220 - 1  and  220 - 2 , respectively (collectively outlet end plugs  220 ). The recessed inlet end plugs  18  may be recessed from the inlet ends of the walls  216  by any suitable distance to achieve a desirable amount of PM buildup during a desired regeneration interval. The distance may be limited in part by the corresponding reduction in wall area available for the exhaust gas to transition from the inlet channel to the outlet channel. 
         [0042]    In use, exhaust flows through the heater  212  and into inlet channels formed by walls  216  that do not have recessed inlet end plugs  218 . In addition, exhaust flows into portions  219  of the outlet channels formed by walls  216  that have recessed inlet end plugs  218 . As a result, PM accumulates in the portions  219  of the outlet channels. 
         [0043]    The exhaust gas flows from the inlet channels into adjacent outlet channels. The exhaust gas also flows into the portions  219  of the outlet channels and then into the inlet channels. PM is filtered as the exhaust passes through the walls  216  and builds up on the walls  216 . PM also builds up in areas around the outlet end plugs  220 . 
         [0044]    Referring now to  FIGS. 7-9 , regeneration within the PM filter system  210  is shown. In  FIG. 7 , when the heater  212  is turned on, PM adjacent to the heater  212  begins burning in a burning zone. The PM in the portions  219  contributes to the regeneration heat in the burning zone. As a result, less external heat needs to be applied by the heater for a given target regeneration temperature. 
         [0045]    The substrate temperature in areas beyond the burning zone may be less than the PM ignition temperature. In  FIG. 8 , the burning zone moves and creates a wavefront along the length of the PM filter. Regeneration of the PM continues as long as the burning zone temperature is above the PM ignition temperature. In  FIG. 9 , since the burning zone continues to propagate down the length of the PM filter, the filter  214  is regenerated fully. The heater  212  may be turned off before regeneration completes. 
         [0046]    Benefits of the proposed system and method include improved regeneration robustness to engine operating conditions. There is also the potential for reduced heating requirements of the heater since the PM accumulated in the recessed inlet end plugs of the outlet channels can be used to increase regeneration heat while external heat from the heater can be reduced. By reducing the heat from the external heater, the durability of the PM filter may tend to increase. 
         [0047]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.