Abstract:
A filter media is disclosed. The filter media includes a plurality of channels separated by porous sidewalls extending longitudinally from a first end to a second end. The plurality of channels includes a plurality of first channels and a plurality of second channels. The first channels are open at both the first end and the second end and have a first width. The second channels are closed at the first end and open at the second end and have a second width greater than the first width.

Description:
TECHNICAL FIELD  
       [0001]    The present disclosure relates generally to a partial flow filter, and more particularly, to a partial flow exhaust filter. 
       BACKGROUND  
       [0002]    Internal combustion engines exhaust a complex mixture of chemical species as a byproduct of the combustion process. In diesel engines, the condensed phase chemical species are composed of three main fractions, namely, elemental carbon and inorganic ash (solid), soluble organic fraction (SOF and liquid), and sulphate particulates (liquid). Due to heightened environmental concerns, exhaust emission standards have become increasingly stringent over the years. As part of these emission standards, regulations prescribe the amount of chemical species that can be emitted from an engine depending on the type, size, and/or class of the engine. One method used by engine manufacturers to comply with these regulations is to remove the offending chemical species from the exhaust flow of the engine. Different techniques are typically used to remove solid phase and gaseous phase chemical species from the exhaust flow. One common method used to remove solid phase (and to some extent, liquid phase) particulate matter contained in the exhaust is to capture and oxidize these particulate matter using diesel particulate filters (DPF). 
         [0003]    DPF&#39;s are typically located along the path of the exhaust flow and they operate by forcing the exhaust flow through a filter media of the DPF. There are many types of filter media that have been used in DPF&#39;s. Ceramic wall-flow monoliths are by far the most common type of filter elements used in DPF&#39;s. A ceramic wall-flow filter element has parallel channels (called “honeycomb” structure) alternately plugged at each end in order to force the exhaust gases through the porous ceramic walls. That is, channels that are exposed at the inlet end (called “inlet channels”) are plugged at the outlet end, and channels that are plugged at the inlet end (called “outlet channels”) are exposed at the outlet end. Therefore, exhaust gases that enter the inlet channels at the inlet end are forced to percolate through the walls of the filter element to the outlet channels in order to exit the filter element. Thus, the walls of the filter media act as a filter. These filter elements are commonly made of ceramic materials, such as cordierite (a synthetic ceramic composition having the formula 2MgO-2Al 2 O 3 -5SiO 2 ), that are characterized by good porosity, high temperature resistance and good mechanical strength. The ceramic walls of the filter media block some or all of the particulate matter in the exhaust while allowing the exhaust gases to flow through. Over time, the particulate matter may clog the filter media, impeding the flow of gas through it, resulting in increased pressure drop across the filter (engine back pressure) and reduced engine efficiency. Filter regeneration is one way to remove the particulate build up within the filter media. Regeneration is the process of increasing the temperature of the filter media until the organic components of the particulate matter such as the soot and the soluble organic fraction (SOF) that accumulates in the filter media oxidize. The regeneration process exposes the filter media to large temperature cycles that negatively impact the durability of the filter media. 
         [0004]    U.S. Pat. No. 4,417,908 (the &#39;908 patent) to Pitcher, Jr. describes a honeycomb filter element that decreases the back pressure generated by the filter without sacrificing filtration efficiency. The filter media of the &#39;908 patent reduces backpressure by increasing the number of inlet channels as opposed to the outlet channels. The increased number of inlet channels increases the surface area of the inlet channel walls through which the exhaust gases can percolate into the outlet channels. The increased surface area delays clogging of filter media and hence, pressure build up. 
         [0005]    While the filter media of the &#39;908 patent may delay back pressure buildup, the accumulating soot in the filter media may eventually increase back pressure and require regeneration to maintain engine efficiency. By increasing the surface area available for soot accumulation, the filter element of the &#39;908 patent may increase the quantity of soot that has to be burned off during regeneration. This increased quantity of soot burned during regeneration may increase the high temperature exposure and the temperature gradients in the filter element, thereby negatively impacting its durability. The present disclosure is directed to solving one or more of the problems set forth above. 
       SUMMARY OF THE INVENTION  
       [0006]    In one aspect, a filter media is disclosed. The filter media includes a plurality of channels separated by porous sidewalls extending longitudinally from a first end to a second end. The plurality of channels includes a plurality of first channels and a plurality of second channels. The first channels are open at both the first end and the second end and have a first width. The second channels are closed at the first end and open at the second end and have a second width greater than the first width. 
         [0007]    In another aspect, a particulate filter is disclosed. The particulate filter includes a housing and a filter media with a first end and a second end positioned within the housing. The filter media includes a plurality of first channels extending from the first end to the second end. Each first channel has substantially rectangular cross-sectional shape and is open at both the first end and the second end. The filter media also includes a plurality of second channels extending from the first end to the second end. Each second channel of the plurality of second channels is closed at the first end and open at the second end, and adjacent to a first channel of the plurality of first channels. Each second channel also has a substantially octagonal cross-sectional shape. 
         [0008]    In yet another aspect, a method of filtering exhaust gas of an internal combustion engine is disclosed. The method includes directing the exhaust gas into a first channel extending from an inlet end to an outlet end. The first channel has a first cross-sectional area and is open at both the inlet end and the outlet end. The method also includes passing a first portion of the exhaust gas into a second channel. The second channel is adjacent to the first channel and has an inlet end and an outlet end. The second channel is closed at the inlet end and open at the outlet end and has a second cross-sectional area greater than the first cross-sectional area. The method further includes directing the first portion of the exhaust gas out of the outlet end of the second channel, and directing a portion of the exhaust gas out of the outlet end of the first channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is an illustration of an exemplary disclosed engine system; 
           [0010]      FIG. 2  is a cut away illustration of the diesel particulate filter (DPF) of  FIG. 1 ; 
           [0011]      FIG. 3  is an illustration of an embodiment of the filter media of the DPF of  FIG. 1 ; 
           [0012]      FIG. 4  is a cross-sectional illustration of the DPF of  FIG. 1 ; 
           [0013]      FIG. 5  is an illustration of a magnified view of the filter media of the DPF of  FIG. 1 ; 
           [0014]      FIGS. 6A-6D  are illustrations of another embodiment of the filter media of the DPF of  FIG. 1 ; 
           [0015]      FIG. 7A  illustrates the flow fraction filtered as a function of orifice size in an embodiment of the filter media of the DPF of  FIG. 1 ; and 
           [0016]      FIG. 7B  illustrates the pressure drop as a function of orifice size in an embodiment of the filter media of the DPF of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0017]      FIG. 1  illustrates an engine system  100 . Engine system  100  may have, among other systems, a power source  10 , and an induction system  14 , and an exhaust system  12 . Power source  10  may include an engine such as, for example, a diesel engine, a gasoline engine, a natural gas engine, or any other engine apparent to one skilled in the art. Fuel may be combusted in power source  10  to produce mechanical power. Combustion of the fuel may produce exhaust gas  25 . The exhaust gas  25  may be exhausted to the atmosphere through the exhaust system  12 . 
         [0018]    Induction system  14  may be configured to introduce compressed air into a combustion chamber (not shown) of power source  10 . Induction system  14  may include components configured to introduce compressed air and fuel into the power source. These components may include any components known in the art such as, valves, air coolers, air cleaners, control system, etc. 
         [0019]    Exhaust system  12  may be configured to direct hot exhaust gas  25  from power source  10  to the atmosphere. Exhaust system  12  may include components that are configured to extract power from exhaust gas  25 . These components may include a turbocharger  18 . Turbocharger  18  may consist of a turbine  18 A connected to a compressor  18 B by a shaft. The turbine  18 A may receive exhaust gas  25  from the power source  10  causing a turbine wheel to rotate. This rotation may drive the compressor  18 B, compressing air in induction system  14 . 
         [0020]    Exhaust gas  25  may also contain solid particulate matter and various chemicals in liquid or gaseous form. The solid particulate matter may include combustible organic constituents (such as elemental carbon) and incombustible inorganic constituents (such as ash). Some of the exhaust gas constituents may be regulated by regulatory agencies, and hence may need to be removed/reduced before exhaust gas  25  is released to the atmosphere. Exhaust system  12  may include components that may be configured to separate these regulated constituents from exhaust gas  25 . These components may include, among others, one or more filters. These filters may include a diesel particulate filter (DPF)  30 , and a catalytic converter  16 . 
         [0021]    Catalytic converter  16  may be a device configured to chemically convert some of the constituents of exhaust gas into less harmful constituents. For example, catalytic converter  16  may reduce oxides of nitrogen in exhaust gas  25  to nitrogen and oxygen, oxidize carbon monoxide in exhaust gas  25  to less harmful carbon dioxide, and oxidize un-burnt hydrocarbons in exhaust gas  25  to carbon dioxide and water. Catalytic converter may include a substrate through which exhaust gas  25  may be flown through. The substrate may include a catalyst deposited thereon, to facilitate the oxidation and reduction reactions. Although  FIG. 1  depicts catalytic converter  16  to be located downstream of turbocharger  18  and DPF  30  to be located upstream of the turbocharger  18 , in general, catalytic converter  16  and DPF  30  may be located either upstream or downstream of turbocharger  18 . Catalytic converter  16  may typically be located downstream of DPF  30 . However, it is contemplated that other arrangements are possible. 
         [0022]    DPF  30  may separate some of the solid and liquid particulate matter (“particulate matter”) from exhaust gas  25 .  FIG. 2  illustrates a cutaway view of DPF  30 . DPF  30  may include a housing  32  enclosing a filter media  40 . Although a cylindrical housing is depicted in  FIG. 2 , housing  32  may be of any shape. Housing  32  may be made of any material, such as steel, that may reliably withstand the temperatures and constituents of exhaust gas  25 . In some embodiments, heaters may also be embedded in DPF  30  to heat filter media  40  to regeneration temperature. Filter media  40  may be positioned within housing  32  such that exhaust gas  25  flowing through DPF  30  flows through filter media  40 . Exhaust gas  25  may enter filter media  40  at an inlet end  44  and exit filter media  40  at outlet end  42 . 
         [0023]    Filter media  40  may have a porous structure. In some embodiments, filter media  40  may be made of a porous material such as cordierite or silicon carbide, while in other embodiments, filter media  40  may be made of a metallic mesh or a metallic foam. The porous nature of filter media  40  may filter some of the particulate matter from the exhaust gas  25  passing through it. Due to this filtering of particulate matter, the particulate matter content of exhaust gas  25  exiting filter media  40  at outlet end  42  may be less than particulate matter content of exhaust gas  25  entering filter media  40  at inlet end  44 . 
         [0024]      FIG. 3  illustrates an embodiment of filter media  40 . Filter media  40  may have a cylindrical shape, with length  82  and diameter  80  suited to fit within the cylindrical DPF housing  32 . However, other shapes of filter media  40  are also contemplated. Length  82  and diameter  80  may have any value depending upon the application. Filter media  40  may include multiple parallel channels  46  running in a longitudinal direction. Alternating adjacent channels  46  may be plugged at the inlet end  44  of filter media  40  to create inlet channels  46   a  and outlet channels  46   b.  Inlet channels  46   a  may be channels  46  with the inlet end  44  open and outlet channels  46   b  may be channels  46  with the inlet end  44  plugged. Inlet channels  46   a  and outlet channels  46   b  may together create a checker board pattern of channels  46  at inlet end  44 . 
         [0025]      FIG. 4  shows a cross-sectional view of DPF  30  showing filter media  40 . Inlet channels  46   a  and outlet channels  46   b  may be separated by porous side walls  50  having thickness  54 . Outlet channels  46   b  may have their outlet ends  42  open. Inlet channels  46   a,  on the other hand, may have their outlet end  42  plugged. Some of the plugged outlet ends  42  of inlet channels  46   a  may have an orifice  52  associated therewith. Orifice  52  may be an opening that may fluidly connect inlet channel  46   a  to the down stream side of DPF  30 . In some embodiments, orifice  52  may be included in the plugged outlet ends  42  of all inlet channels  46   a.  While in other embodiments, orifice  52  may only be included in the plugged outlet ends  42  of selected inlet channels  46   a.  For instance, every alternate inlet channel  46   a.  Orifice  52  may be a substantially circular opening in some embodiments, while in other embodiments, orifice  52  may have other shapes. The size of orifice  52  may vary with application and the desired filter performance. In some embodiments, orifice  52  may be a small opening while in other embodiments, orifice  52  may occupy the entire outlet end  42  of an inlet channel  46   a.  In these embodiments, the outlet end  42  of inlet channels  46   a  may also be open like the outlet end of outlet channels  46   b.  It is also contemplated that, in some embodiments, orifice  52  included in different inlet channels may have different sizes. For instance, the size of an orifice  52  may be function of its distance from the center of the filter media  40 . Some of the factors that may determine the size of orifice  52  will be described more in subsequent paragraphs. 
         [0026]    Exhaust gas  25  enters inlet channels  46   a  of filter media  40  at the inlet end  44 . Some exhaust gas  25  may also enter outlet channel  46   b  through porous walls of plugged inlet end  44  of outlet channel  46   b.  A portion of exhaust gas  25  in the inlet channels  46   a  may percolate into the outlet channels  46   b  through the porous side walls  50  of inlet channel  46   a.  Orifice  52  at the outlet end  42  of inlet channel  46   a  may restrict the free flow of exhaust gas  25  through inlet channel  46   a.  This restriction to the flow may also force an additional portion of exhaust gas  25  through the porous side walls  50  into outlet channels  46   b.  The remaining portion of exhaust gas  25  may exit inlet channels  46   a  through orifice  52 . Decreasing thickness  54  of side wall  50  may increase the portion of exhaust gas  25  that percolates into outlet channels  46   b.  Increasing size of orifice  52  may also decrease the portion of exhaust gas  25  that is forced through side walls  50 . 
         [0027]      FIG. 5  is an illustration of a magnified view of side wall  50  of filter media  40 . When exhaust gas  25  percolates through the porous side walls  50  of inlet channels  46   a,  some of particulate matter  48  is filtered by side walls  50 . This filtration may be the result of a number of mechanisms. In some embodiments, mean pore size of filter media  40  may be smaller than a mean size of particulate matter  48 . In these embodiments, the filter media  40  may only allow exhaust gas  25  to pass through its pores while blocking larger particulate matter  48 . Thus, particulate matter  48  may be deposited on side walls  50  through sieving. As particulate matter  48  builds up on side wall  50 , the accumulated particulate matter  48  may also filter exhaust gas  25  leading to more particulate matter accumulation. In some embodiments of filter media  40 , the mean pore size of filter media  40  may be larger than the mean diameter of particulate matter  48 . In these embodiments, particulate matter  48  may be deposited on side walls  50  through a combination of depth filtration mechanisms which are driven by various force fields. For example, the force fields may be related to velocity or concentration gradients of exhaust gas  25 . 
         [0028]    A portion of particulate matter  48  present in exhaust gas  25  may, thus, be filtered while percolating through side walls  50  of filter media  40 . The remaining portion of particulate matter  48  may pass through DPF  30  along with the portion of exhaust gas  25  exiting filter media  40  through orifice  52 . A ratio of the amount of particulate matter  48  filtered by filter media  40  to the total amount of particulate matter  48  present in exhaust gas  25  may be a measure of filtration efficiency of DPF  30 . The portion of particulate matter  48  escaping with exhaust gas  25  passing through orifice  52  may contribute to a reduction in filtration efficiency of DPF  30 . The amount of exhaust gas  25  flowing through orifice  52 , and the amount of escaping particulate matter  48  may increase with size of orifice  52 . Therefore, filtration efficiency may decrease with orifice size. 
         [0029]    As particulate matter  48  accumulates in filter media  40 , the resistance to exhaust flow through DPF  30  may increase. This resistance to exhaust flow may, in turn, increase the pressure of exhaust gas  25  in filter media  40  (“back pressure”). The increase in back pressure may adversely affect the performance of power source  10 . Continued accumulation of particulate matter  48  may eventually clog the pores of side walls  50  thereby preventing further percolation of exhaust gas  25  through side walls  50 . The increase in back pressure associated with clogging may in some instances cause catastrophic failure of exhaust system  12 . The ability of exhaust gas  25  to exit filter media  40  through orifice  52 , may however, prevent catastrophic failure of exhaust system  12 . 
         [0030]    When the back pressure, resulting from particulate matter  48  build up in DPF  30 , affects engine performance, DPF  30  may be regenerated. Regeneration is the process of oxidizing (that is, burning) a part of the particulate matter  48  accumulated in the filter media  40 . During regeneration, the combustible portion of the accumulated particulate matter  48  may be oxidized to carbon dioxide or carbon monoxide. Oxidation of the combustible part of particulate matter  48  may occur at a regeneration temperature between about 550° C. and 650° C. or by the oxidation of carbon by NO 2  at a temperature above about 225° C. In some embodiments, this regeneration temperature may be decreased using a catalyst. The accumulated particulate matter may be heated to the regeneration temperature using a variety of ways. In some embodiments, a heater embedded in DPF  30  or filter media  40  may be used to raise the temperature of accumulated particulate matter  48 . In some embodiments, the temperature of the exhaust gas  25  may be increased when a regeneration event is triggered. The temperature of exhaust gas  25  may be increased in a number of ways. For instance, a regeneration assist system (not shown) located upstream of DPF  30  may be used to heat exhaust gas  25 . 
         [0031]    A regeneration event may be triggered depending upon the amount of accumulated particulate matter  48  in DPF  30 . In some embodiments, the amount of accumulated particulate matter  48  may be directly measured (for instance, by using a RF measuring device), while in other embodiments, a threshold value of back pressure may trigger regeneration. During uncontrolled regeneration, the combustible portion of accumulated particulate matter  48  burns, resulting in a rapid increase in temperature, sometimes exceeding 650° C. Due to non-uniform deposition of particulate matter  48  on filter media  40 , the temperature of some regions of filter media  40  may be significantly higher than other regions causing a large temperature gradient in filter media  40  during regeneration. These high temperatures and temperature gradients may result in filter media  40  damage. In some applications, filter media  40  may be cooled during regeneration by the stream of exhaust gas  25 . Increasing amounts of accumulated particulate matter  48  in filter media  40  may increase the temperature and duration of regeneration. The ability of exhaust gas  25  to cool filter media  40  during regeneration may also be compromised by increasing particulate matter  48  build up. The portion of particulate matter  48  exiting filter media  40  may decrease the accumulation of particulate matter  48  in filter media  40 , thereby decreasing the possibility of filter damage during regeneration and decreasing the frequency at which regeneration may be required. 
         [0032]    Regeneration clears accumulated particulate matter  48  from filter media  40  by converting them into gaseous compounds. The incombustible portion of particulate matter  48  (for example, ash), however, does not get removed by regeneration. This portion of particulate matter  48  gets removed from filter media  40  along with the portion of exhaust gas  25  passing through orifice  52 . Increasing size of orifice  52  allows this incombustible particulate matter  48  to be removed from filter media  40  easily. 
         [0033]    Therefore, increasing filtration efficiency (that is, reducing the amount of particulate matter released from DPF  30 ) may favor a small orifice  52 . While lower back pressure, lower regeneration temperature and duration, lower frequency of regeneration, and lower ash buildup in the DPF  30  may favor a larger orifice  52  size. The choice of orifice size in an application may, thus, involve a tradeoff between these and other factors. In general, orifice size may vary from a smallest size that may be reliably produced in filter media  40  to the size of inlet channel  46   a.    
         [0034]    In general, decreased side wall thickness  54  may increase filtration efficiency. However, the strength of the filter media  40  may be adversely affected. Decreasing side wall thickness may also increase cost and complexity of fabrication. In general, any side wall thickness  54  may be used in an application. Side wall thickness  54  selected for an application may depend on performance, strength, cost, and other factors. 
         [0035]    The size of inlet channel  46   a,  outlet channel  46   b,  and side wall thickness  54  may also depend on the application. In some embodiments, inlet channels  46   a  and outlet channels  46   b  may be substantially equally sized. The size of these channels may also be designed to achieve the required filtration efficiency while reducing back pressure and regeneration temperature. In some embodiments, inlet channel  46   a  and/or outlet channel  46   b  may be tapered. That is, the width of these channels may vary along a length of the channel. 
         [0036]      FIGS. 6A-6D  illustrates another embodiment of filter media  40 .  FIG. 6A  shows a cross-sectional view of filter media  40  of this embodiment, while  FIGS. 6B and 6C  shows side views of inlet end  44  and outlet end  42 , respectively.  FIG. 6D  shows a magnified view of the inlet end  44 . In the description below, reference is made to  FIGS. 6A-6D . In the embodiment depicted in  FIGS. 6A-6D , the outlet ends  42  of input channels  46   a  may be open (see  FIGS. 6A and 6C ) or partially open with a similar orifice as discussed previously. The size of inlet channel  46   a  may also smaller than the size of the outlet channel  46   b.  The inlet channel  46   a  may have a substantially rectangular shape, while outlet channel  46   b  may have a substantially octagonal shape (see  FIGS. 6B-6D ). In this disclosure, substantially rectangular shape is used generally to represent any quadrilateral shape (such as, rectangle, square, rhombus, parallelogram, trapezoid, irregular quadrilateral, etc.), and substantially octagonal shape is used generally to represent any eight sided shape (for example, regular octagon, irregular octagon, etc.). These sides may intersect each other at a sharp point or a curve. The width of a side of inlet channel  46   a  may be w i . This width w i  may be defined as the size of inlet channel  46   a.  The distance between opposite walls of the octagonal outlet channel  46   b  may be w o . This width w o  may be defined as the size of outlet channel  46   b.  Widths w i  and w o  may have any value. It should be pointed out that, due to the geometrical arrangement of inlet and outlet channels, when width w o  is √2 times w i , the octagon shape of outlet channels may collapse into a square shape. Thus, when w o =(√2×w i ), the geometrical arrangement of inlet and outlet channels of this embodiment may resemble the arrangement depicted in  FIG. 3 . In embodiments with tapered channels, inlet channel width w i  and/or outlet channel width w o  may vary along the length of length of the channel. 
         [0037]    As shown in  FIG. 6A , exhaust gas  25  may enter the inlet channel  46   a  at inlet end  44  and travel down the length of the channel towards outlet end  42 . The pressure of the exhaust gas in the channel may force a portion of exhaust gas  25  to percolate into adjacent outlet channels  46   b  through side wall  50 . As described earlier, particulate matter  48  may be separated from exhaust gas  25  as it passes through side wall  50 . A portion of particulate matter  48  may also escape filter media  40  through the open outlet ends  42  of inlet channels  46   a.  A larger proportion of exhaust gas  25  percolating into outlet channels  46   b  may increase the particulate matter  48  filtered by filter media  40 . Reducing the size of inlet channel  46   a  may force more exhaust gas  25  into outlet channels  46   b,  and thus increase filtration efficiency. However, back pressure may increase with decreasing inlet channel  46   a  size. Decreasing size of inlet channels  46   a  may also increase manufacturing complexity and therefore, cost. The inlet channel  46   a  and outlet channel  46   b  size in an embodiment may involve a tradeoff between the afore mentioned factors, and depend on the application. In some embodiments, the sizes of inlet channel  46   a  and outlet channel  46   b  may be such that w 0  is approximately equal to 1.7 to 2 times w i  (that is, w 0 ≈(1.7 to 2)×w i ). While computational fluid dynamic (CFD) simulations indicate that filter media  40  may have desirable characteristics when the ratio w o /w i  equals to about 1.7 to 2, it is contemplated that inlet and outlet channels  46   a,    46   b  may have other sizes. In some embodiments, some of the particulate matter that escapes DPF  30  may be captured by other filters downstream of DPF  30 . 
       INDUSTRIAL APPLICABILITY  
       [0038]    The disclosed embodiments relate to a partial flow filter to separate particulate matter from engine exhaust. The filter includes a porous filter media with multiple parallel channels running from an inlet end to an outlet end. Alternate adjacent channels of the filter media are plugged at the inlet end of the filter. These plugged channels may be open at the outlet end of the filter media. Some or all of the channels which are not plugged at the inlet end may include an orifice at the outlet end. The size of the orifice may be small or may be as large as the size of the channel. The size of the channels may also vary. Exhaust from an engine may be passed through the filter. These exhaust may enter the channels of the filter media that are open at the inlet end (inlet channels). Due to the pressure of exhaust gas in the inlet channel, some of the exhaust gas may percolate into the adjacent channels through the porous walls of the channel. During percolation through these porous walls, particulate matter contained in the exhaust may be filtered. The decreasing size of the inlet channels and/or decreasing size of the orifice may increase the amount of particulate matter filtered by the filter media and improve filter efficiency. However, small orifices and small inlet channels may increase the back pressure of filter and negatively affect engine efficiency. Therefore, the selection of orifice size and channel size in an application may involve application specific factors. To illustrate an application of the disclosed partial flow filter, an exemplary embodiment will now be described. 
         [0039]    A diesel engine exhaust may be directed to a DPF  30 . The DPF  30  may contain a cylindrical filter media  40 . Filter media  40  may be made of a cordierite ceramic having a porosity of 38% and a micron hole size of  11 . Filter media  40  have a diameter  80  of about 7.5 inches and a length  82  of about 8 inches. Filter media  40  may include multiple parallel channels  46  running from an inlet end  44  to an outlet end  42 . Each channel  46  may be separated from adjacent channels by a wall having thickness  54  of about 0.012 inches. Alternate adjacent channels of filter media  40  may be plugged at inlet end  44  to create a checker board pattern of channels (as seen in  FIG. 3 ) at inlet end  44 . These channels are referred as outlet channels  46   b.  The outlet channels  46   b  may be open at outlet end  42  of filter media  40 . The channels  46  that are open at inlet end  44  (referred to as inlet channels  46   a ) may have an orifice  52  at the outlet end  42 . These inlet channels  46   a  may have a square cross-section with a width w i  of about 1.5 mm. The outlet channels  46   b  may have an octagonal cross-section, as illustrated in  FIG. 6A-6D , with width w o  being about 3 mm. 
         [0040]    Parametric CFD simulations were carried out on filter media  40  to determine the impact of orifice size on filter performance parameters. Keeping all variables of filter media  40  constant, orifice diameter was varied in each simulation. The ratio of the amount of exhaust flow percolating through side walls  50  to the total exhaust flow into DPF (“flow fraction filtered”), and the pressure drop across filter media  40 , were recorded in each case. Increasing values of flow fraction filtered may indicate increased particulate matter  48  filtration, and therefore, increased filtration efficiency. While increasing values of pressure drop across filter media  40  may indicate increasing back pressure, and therefore, decreasing engine performance. 
         [0041]      FIGS. 7A and 7B  illustrate the impact of orifice size on flow fraction filtered by, and pressure drop across, filter media  40 . At an orifice size of “0” (that is, the outlet end of inlet channels  46   a are closed) all the exhaust may be forced to percolate through side walls  50 . Thus, flow fraction filtered may be “ 1” (as indicated by  FIG. 7A ), when orifice size is “ 0 .”  FIG. 7B  indicates that the corresponding pressure drop across filter media  40  when orifice size is “ 0 ” to be 9 kilo Pascals (kPa). The impact on engine performance at a filter pressure drop of 9 kPa may be unacceptable for the application.  FIG. 7A  indicates the flow fraction filtered at the largest orifice size evaluated (when the inlet channel  46   a  is open at outlet end  42 ) to be approximately “0.2.” That is, when the inlet channel  46   a  is open at outlet end  42 , approximately 20% of exhaust flow percolates through side walls  50 .  FIG. 7B  indicates that the pressure drop associated with such a geometry may be about 3.5 Kpa. While this low value of pressure drop through filter media  40  may be attractive, the filtration efficiency associated with 20% of exhaust flow filtration may be unacceptable for some applications. 
         [0042]    In between these two extreme cases (that is, the case were orifice size is “0,” and the case where the outlet end of inlet channel is open),  FIG. 7A  indicates that increasing values of orifice size decreases the fraction of exhaust flow filtered.  FIG. 7B  indicates that the pressure drop across the filter media associated with this decreased amount of flow through the filter walls may also be correspondingly lower. Operating conditions (such as, amount of particulate matter that can be released to the atmosphere) and the efficiency requirements, may indicate acceptable values of flow fraction filtered and pressure drop for an application. Based on these acceptable values, an appropriate orifice size may be chosen. 
         [0043]    In some engine applications, complete removal of particulate matter from exhaust flow may not be required. The disclosed filter embodiments may enable the tradeoff of filter efficiency to decrease exhaust back pressure. The disclosed filter elements may be designed to achieve a desired filtration efficiency at a lower value of exhaust back pressure. Since all the exhaust gas flowing through the DPF may not be filtered, the amount of particulate matter accumulation in the filter media may also be lower. This lower particulate matter accumulation may decrease the temperature, temperature gradient, and time of exposure of the filter media to high temperature during regeneration. Lower particulate matter accumulation in the filter media may also decrease the frequency of regeneration, thereby decreasing the number of times the filter media is exposed to regeneration temperature. Since the outlet end of the inlet channels may also include an opening, incombustible particulate matter (ash) may be blown out of the filter media along with the exhaust flow, thereby reducing ash buildup in the filter media. This reduction in ash buildup may delay (or even eliminate) filter service needed to remove the accumulated ash, and thereby prolong filter life. 
         [0044]    It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed partial flow filter. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed partial flow filter. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.