Abstract:
A system for ventilating a crankcase of an internal combustion engine includes an exhaust system having a treatment element, and the treatment element includes a catalyst configured to assist in passively regenerating a filter of the exhaust system. The system for ventilating the crankcase also includes first flow path configured to transmit a first flow from the crankcase to a port upstream of the filter, and a second flow path configured to transmit a second flow from a combustion chamber of the internal combustion engine to the exhaust system. The catalyst is configured to treat a combined flow comprising the first flow and the second flow.

Description:
PRIORITY DATA  
       [0001]     This application is a continuation-in-part of U.S. application Ser. No. 11/152,069, filed Jun. 15, 2005. 
     
    
     TECHNICAL FIELD  
       [0002]     The present disclosure relates generally to an exhaust treatment system and, more particularly, to an exhaust treatment system having a regeneration device.  
       BACKGROUND  
       [0003]     Internal combustion engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous compounds, which may include nitrous oxides (NOx), and solid particulate matter. Particulate matter may include soluble organic fraction, soot (unburned carbon), and/or hydrocarbons.  
         [0004]     Due to increased attention on the environment, exhaust emission standards have become more stringent, and the amount of gaseous compounds emitted to the atmosphere from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of these engine emissions is exhaust gas recirculation (EGR). EGR systems recirculate the exhaust gas byproducts into the intake air supply of the internal combustion engine. The exhaust gas directed to the engine cylinder reduces the concentration of oxygen within the cylinder and increases the specific heat of the air/fuel mixture, thereby lowering the maximum combustion temperature within the cylinder. The lowered maximum combustion temperature and reduced oxygen concentration can slow the chemical reaction of the combustion process and decrease the formation of NOx.  
         [0005]     In many EGR applications, the exhaust gas is passed through a particulate filter and catalyst containing precious metals. The particulate filter may capture a portion of the solid particulate matter carried by the exhaust. After a period of use, the particulate filter may become saturated and may require cleaning through a regeneration process wherein the particulate matter is purged from the filter. In addition, the catalyst may oxidize a portion of the unburned carbon particulates contained within the exhaust gas and may convert sulfur present in the exhaust to sulfate (SO3).  
         [0006]     As shown in U.S. Pat. No. 6,427,436 (the &#39;436 patent), a filter system can be used to remove particulate matter from a flow of engine exhaust gas before a portion of the gas is fed back to an intake air stream of the engine. Specifically, the &#39;436 patent discloses an engine exhaust filter containing a catalyst and a filter element. A portion of the filtered exhaust is extracted downstream of the filter and is directed to an intake of the engine through a recirculation loop.  
         [0007]     Although the filter system of the &#39;436 patent may protect the engine from harmful particulate matter, the system may not be configured to direct a flow of exhaust gas from a crankcase of the engine to the exhaust filter for treatment, and the exhaust filter may not be configured for passive regeneration during engine operation.  
         [0008]     The disclosed exhaust treatment system is directed to overcoming one or more of the problems set forth above.  
       SUMMARY OF THE INVENTION  
       [0009]     In one embodiment of the present disclosure, a system for ventilating a crankcase of an internal combustion engine includes an exhaust system having a treatment element, and the treatment element includes a catalyst configured to assist in passively regenerating a filter of the exhaust system. The system for ventilating the crankcase also includes first flow path configured to transmit a first flow from the crankcase to a port upstream of the filter, and a second flow path configured to transmit a second flow from a combustion chamber of the internal combustion engine to the exhaust system. The catalyst is configured to treat a combined flow comprising the first flow and the second flow.  
         [0010]     In another embodiment of the present disclosure, a method of controlling exhaust gases of an internal combustion engine includes pressurizing a crankcase of the internal combustion engine, releasing a pressurized flow from the crankcase, and combining the pressurized flow with a main exhaust flow from a combustion chamber of the internal combustion engine to form a combined flow. The method further includes treating the combined flow with a filter and passively regenerating at least a portion of the filter.  
         [0011]     In yet another embodiment of the present disclosure, a method of controlling exhaust gases of an internal combustion engine includes releasing a pressurized flow of exhaust from a crankcase of the internal combustion engine, directing the pressurized flow of exhaust to a catalyst, and treating at least a portion of the pressurized flow of exhaust with a filter. The method also includes passively regenerating at least a portion of the filter. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a diagrammatic illustration of an engine having an exhaust treatment system according to an exemplary embodiment of the present disclosure.  
         [0013]      FIG. 2  is a diagrammatic illustration of an engine having an exhaust treatment system according to another exemplary embodiment of the present disclosure.  
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  illustrates a power source  12  having an exemplary exhaust treatment system  10 . The power source  12  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. The power source  12  may, alternately, include another source of power such as a furnace or any other source of power known in the art.  
         [0015]     The exhaust treatment system  10  may be configured to direct exhaust gases out of the power source  12 , treat the gases, and introduce a portion of the treated gases into an intake  21  of the power source  12 . The exhaust treatment system  10  may include an energy extraction assembly  22  and a treatment element  19 . The treatment element  19  may include, for example, a regeneration device  20 , a filter  16 , and/or a catalyst  18 . The exhaust treatment system  10  may further include a recirculation line  24  fluidly connected between the filter  16  and the catalyst  18 , and a flow cooler  26 . The exhaust treatment system  10  may still further include a flow sensor  28 , a mixing valve  30 , a compression assembly  32 , and an aftercooler  34 .  
         [0016]     A flow of exhaust produced by the power source  12  may be directed from the power source  12  to components of the exhaust treatment system  10  by flow lines  15 . It is understood that the power source  12  may include one or more combustion chambers (not shown) fluidly connected to an exhaust manifold. In such an exemplary embodiment, the flow lines  15  may be configured to transmit a flow of exhaust from the combustion chambers to the components of the exhaust treatment system  10  via the exhaust manifold. The flow lines  15  may include pipes, tubing, and/or other exhaust flow carrying means known in the art. The flow lines  15  may be made of alloys of steel, aluminum, and/or other materials known in the art. The flow lines  15  may be rigid or flexible, and may be capable of safely carrying high temperature exhaust flows, such as flows having temperatures in excess of 700 degrees Celsius (approximately 1,292 degrees Fahrenheit).  
         [0017]     The energy extraction assembly  22  may be configured to extract energy from, and reduce the pressure of, the exhaust gases produced by the power source  12 . The energy extraction assembly  22  may be fluidly connected to the power source  12  by one or more flow lines  15  and may reduce the pressure of the exhaust gases to any desired pressure. The energy extraction assembly  22  may include one or more turbines  14 , diffusers, or other energy extraction devices known in the art. In an exemplary embodiment wherein the energy extraction assembly  22  includes more than one turbine  14 , the multiple turbines  14  may be disposed in parallel or in series relationship. It is also understood that in an embodiment of the present disclosure, the energy extraction assembly  22  may, alternately, be omitted. In such an embodiment, the power source  12  may include, for example, a naturally aspirated engine. As will be described in greater detail below, a component of the energy extraction assembly  22  may be configured in certain embodiments to drive a component of the compression assembly  32 .  
         [0018]     In an exemplary embodiment, the regeneration device  20  of the treatment element  19  may be fluidly connected to the energy extraction assembly  22  via flow line  15 , and may be configured to increase the temperature of an entire flow of exhaust produced by the power source  12  to a desired temperature. The desired temperature may be, for example, a regeneration temperature of the filter  16 . Accordingly, the regeneration device  20  may be configured to assist in actively regenerating the filter  16 . Alternatively, in another exemplary embodiment the regeneration device  20  may be configured to increase the temperature of only a portion of the entire flow of exhaust produced by the power source  12 . The regeneration device  20  may include, for example, a fuel injector and an ignitor (not shown), heat coils (not shown), and/or other heat sources known in the art. Such heat sources may be disposed within the regeneration device  20  and may be configured to assist in increasing the temperature of the flow of exhaust through convection, combustion, and/or other methods. In an exemplary embodiment in which the regeneration device  20  includes a fuel injector and an ignitor, it is understood that the regeneration device  20  may receive a supply of a combustible substance and a supply of oxygen to facilitate combustion within the regeneration device  20 . The combustible substance may be, for example, gasoline, diesel fuel, reformate, and/or any other combustible substance known in the art. The supply of oxygen may be provided in addition to the relatively low pressure flow of exhaust gas directed to the regeneration device  20  through flow line  15 . In an exemplary embodiment, the supply of oxygen may be carried by a flow of gas directed to the regeneration device  20  from downstream of the compression assembly  32  via a supply line  40 . In such an embodiment, the flow of gas may include, for example, recirculated exhaust gas and ambient air. It is understood that, in an exemplary embodiment of the present disclosure, the supply line  40  may be fluidly connected to an outlet of the compression assembly  32 . In an exemplary embodiment, the regeneration device  20  may be dimensioned and/or otherwise configured to be housed within an engine compartment or other compartment of a work machine (not shown) to which the power source  12  is attached. In such an embodiment, the regeneration device  20 , may be desirably calibrated in conjunction with, for example, the filter  16 , the energy extraction assembly  22 , the catalyst  18 , and/or the power source  12 . Calibration of the regeneration device  20  may include, for example, among other things, adjusting the rate, angle, and/or atomization at which fuel is injected into the regeneration device  20 , adjusting the flow rate of the oxygen supplied, adjusting the intensity and/or firing pattern of the ignitor, and adjusting the length, diameter, mounting angle, and/or other configurations of a housing of the regeneration device  20 . Such calibration may reduce the time required to regenerate the filter  16  and the amount of fuel or other combustible substances needed for regeneration. Either of these results may improve the overall efficiency of the exhaust treatment system  10 . It is understood that the efficiency of the exhaust treatment systems  10 ,  100  described herein may be measured by a variety of factors including, among other things, the amount of fuel used for regeneration, the length of the regeneration period, and the amount (parts per million) of pollutants released to the atmosphere.  
         [0019]     As shown in  FIG. 1 , the filter  16  of the treatment element  19  may be connected downstream of the regeneration device  20 . The filter  16  may have a housing  25  including an inlet  23  and an outlet  31 . In an exemplary embodiment, the regeneration device  20  may be disposed outside of the housing  25  and may be fluidly connected to the inlet  23  of the housing  25 . In another exemplary embodiment, the regeneration device  20  may be disposed within the housing  25  of the filter  16 . The filter  16  may be any type of filter known in the art capable of extracting matter from a flow of gas. In an embodiment of the present disclosure, the filter  16  may be, for example, a particulate matter filter positioned to extract particulates from an exhaust flow of the power source  12 . The filter  16  may include, for example, a ceramic substrate, a metallic mesh, foam, or any other porous material known in the art. These materials may form, for example, a honeycomb structure within the housing  25  of the filter  16  to facilitate the removal of particulates. As discussed above, the particulates may be, for example, soluble organic fraction, hydrocarbons, and/or soot.  
         [0020]     In an exemplary embodiment of the present disclosure, a portion of the exhaust produced by the combustion process may leak past piston seal rings within a crankcase (not shown) of the power source  12 . This portion of the exhaust, often called “blow-by gases” or simply “blow-by” may contain one or more of the exhaust gas components discussed above. In addition, because the crankcase is partially filled with lubricating oil being agitated at high temperatures, the blow-by gases may also contain oil droplets and oil vapor. The blow-by gases may build up within the crankcase over time, thereby increasing the pressure within the crankcase. In such an embodiment, a ventilation line  42  may be fluidly connected to the crankcase of the power source  12 .  
         [0021]     The ventilation line  42  may comprise piping, tubing, and/or other exhaust flow carrying means known in the art and may be structurally similar to the flow lines  15  described above. The ventilation line  42  may include, for example, a check valve  44  and/or any other valve assembly known in the art. The check valve  44  may be configured to assist in controllably regulating a flow of fluid through the ventilation line  42 .  
         [0022]     The contaminants contained in blow-by gases are harmful to the environment, and emissions concerns make direct atmospheric venting a poor option under most, if not all, operating conditions. In addition, directing blow-by gases back to the intake side of, for example, a compressor in a supercharger or turbocharger can result in fouling of the compressor wheel in a relatively short time period. Thus, the ventilation line  42  may be configured to direct the blow-by gases from the crankcase to a location upstream of the filter  16  such as, for example, a port  46  of the flow line  15 . For example, the ventilation line  42  may assist in directing the portion of exhaust gas from the crankcase to a port  46  disposed upstream of the regeneration device  20 . By directing the blow-by gases upstream of the filter  16  and/or the regeneration device  20 , the harmful contaminants contained in the blow-by gases may be substantially removed prior to contaminating the supercharger, turbocharger, or various power source components.  
         [0023]     In addition, in conventional exhaust treatment systems a cleaning device, such as, for example, an oil filter or other conventional blow-by filter may be fluidly connected to a ventilation line and configured to remove components of the blow-by flow. In such systems, the cleaning device may require periodic servicing and may increase the cost of the overall exhaust treatment system. By directing the blow-by gases upstream of the filter  16  and/or the regeneration device  20 , as shown, for example,  FIG. 1 , the exhaust treatment system  10  of the present disclosure may eliminate the need for such cleaning devices, thereby eliminating the need to service an extra component and minimizing the cost of the system  10 .  
         [0024]     The exhaust treatment system  10  may further include a catalyst  18  disposed downstream of the filter  16 . The catalyst  18  may contain catalyst materials useful in collecting, absorbing, adsorbing, and/or storing hydrocarbons, oxides of sulfur, and/or oxides of nitrogen contained in a flow. Such catalyst materials may include, for example, aluminum, platinum, palladium, rhodium, barium, cerium, and/or alkali metals, alkaline-earth metals, rare-earth metals, or combinations thereof. The catalyst materials may be situated within the catalyst  18  so as to maximize the surface area available for the collection of, for example, hydrocarbons. The catalyst  18  may include, for example, a ceramic substrate, a metallic mesh, foam, or any other porous material known in the art, and the catalyst materials may be located on, for example, a substrate of the catalyst  18 .  
         [0025]     As illustrated in  FIG. 2 , in an additional exemplary embodiment of the present disclosure, a filter  36  of the exhaust treatment system  100  may include catalyst materials useful in collecting, absorbing, adsorbing, and/or storing hydrocarbons, oxides of sulfur, and/or oxides of nitrogen contained in a flow. In such an embodiment, the catalyst  18  ( FIG. 1 ) may be omitted. The catalyst materials may include, for example, any of the catalyst materials discussed above with respect to the catalyst  18  ( FIG. 1 ). The catalyst materials may be situated within the filter  36  so as to maximize the surface area available for absorption, adsorption, and or storage. The catalyst materials may be located on a substrate of the filter  36 . The catalyst materials may be added to the filter  36  by any conventional means such as, for example, coating or spraying, and the substrate of the filter  36  may be partially or completely coated with the materials. It is understood that the presence of catalyst materials, such as, for example, platinum and/or palladium, upstream of the recirculation line  24  may result in the formation of sulfate in the exhaust treatment system  100 . Accordingly, to minimize the amount of sulfate formed in the exemplary embodiment of  FIG. 2 , only minimal amounts of catalyst materials may be incorporated into the filter  36 .  
         [0026]     It is also understood that the catalyst materials described above with respect to  FIGS. 1 and 2  may be capable of oxidizing one or more components of an exhaust flow such as, for example, particulate matter, hydrocarbons, and/or carbon monoxide. Thus, in the embodiment shown in  FIG. 1 , a portion of the particulate matter, hydrocarbons, and/or carbon monoxide contained within the exhaust flow may be permitted to travel back to the power source  12  without being oxidized by the catalyst materials. Although the catalyst materials discussed above may assist in the formation of sulfate, the presence of these catalyst materials, either on a substrate of the filter  36  ( FIG. 2 ) or in the catalyst  18  ( FIG. 1 ), may improve the overall emissions characteristics of the exhaust treatment system  10 ,  100  by, for example, removing hydrocarbons from the treated exhaust flow.  
         [0027]     It is further understood that in the embodiment shown in  FIG. 2 , the catalyst materials disposed on the substrate of the filter  36  may assist in passively regenerating the filter  36  during power source operation. As the power source  12  operates, particulates and other components of the power source exhaust may be trapped by the filter substrate. The exhaust flow may reach temperatures in excess of, for example, 300 degrees Celsius during normal operation of the power source  12  (i.e., without operating the power source  12  in a manner so as to increase the temperature of the exhaust by, for example, wastegating or other conventional methods), and the exhaust gas may increase the temperature of at least a portion of the filter substrate through convective heat transfer. At such temperatures, the components of the power source exhaust trapped by the substrate of the filter  36  may begin to react with the catalyst material located on the substrate. In particular, the catalyst material may passively regenerate a portion of the filter  36  by oxidizing particulate matter trapped by the filter substrate as well as carbon monoxide and/or hydrocarbons contained in the exhaust flow. Oxidation may occur at a passive regeneration temperature of the filter  36  in which the catalyst material is hot enough to react with the components of the exhaust flow without additional heat being provided by, for example, the regeneration device  20 . Such passive regeneration temperatures may be below the regeneration temperature of the filter  36 .  
         [0028]     Although at least a portion of the particulate matter contained within the filter  36  may be oxidized and/or removed therefrom through passive regeneration, it is understood that, as shown in  FIG. 2 , an exemplary exhaust treatment system  100  of the present disclosure may, nonetheless, include a regeneration device  20 . Utilizing a catalyzed filter  36  in conjunction with a regeneration device  20  may assist in increasing the interval between active regenerations. Increasing this interval may reduce the amount of, for example, fuel burned during operation of the power source  12 , and may, thus, reduce the cost of operating the machine to which the power source  12  is connected. An exhaust treatment system  100  including both a catalyzed filter  36  and a regeneration device  20  may also enable filter manufacturers to include less catalyst material (such as, for example, precious metals) in the filter  36 , thereby reducing the cost of the filter  36  and the overall cost of the system  100 .  
         [0029]     Referring again to  FIG. 1 , the exhaust treatment system  10  may further include a recirculation line  24  fluidly connected downstream of the filter  16 . The recirculation line  24  may be disposed between the filter  16  and the catalyst  18  and may be configured to assist in directing a portion of the exhaust flow from the filter  16  to the inlet  21  of the power source  12 . The recirculation line  24  may comprise piping, tubing, and/or other exhaust flow carrying means known in the art and may be structurally similar to the flow lines  15  described above. In an embodiment in which the exhaust treatment system  100  ( FIG. 2 ) includes a filter  36  containing catalyst materials, the recirculation line  24  may be disposed downstream of the filter  36  and upstream of an exhaust system outlet  17 .  
         [0030]     The flow cooler  26  may be fluidly connected to the filter  16  via the recirculation line  24  and may be configured to cool the portion of the exhaust flow passing through the recirculation line  24 . The flow cooler  26  may include a liquid-to-air heat exchanger, an air-to air heat exchanger, or any other type of heat exchanger known in the art for cooling an exhaust flow. In an alternative exemplary embodiment of the present disclosure, the flow cooler  26  may be omitted.  
         [0031]     The mixing valve  30  may be fluidly connected to the flow cooler  26  via the recirculation line  24  and may be configured to assist in regulating the flow of exhaust through the recirculation line  24 . It is understood that in an exemplary embodiment, a check valve (not shown) may be fluidly connected upstream of the flow cooler  26  to further assist in regulating the flow of exhaust through the recirculation line  24 . The mixing valve  30  may be a spool valve, a shutter valve, a butterfly valve, a check valve, a diaphragm valve, a gate valve, a shuttle valve, a ball valve, a globe valve, or any other valve known in the art. The mixing valve  30  may be actuated manually, electrically, hydraulically, pneumatically, or in any other manner known in the art. The mixing valve  30  may be in communication with a controller (not shown) and may be selectively actuated in response to one or more predetermined conditions.  
         [0032]     The mixing valve  30  may also be fluidly connected to an ambient air intake  29  of the exhaust treatment system  10 . Thus, the mixing valve  30  may be configured to control the amount of exhaust flow entering a flow line  27  relative to the amount of ambient air flow entering the flow line  27 . For example, as the amount of exhaust flow passing through the mixing valve  30  is desirably increased, the amount of ambient air flow passing through the mixing valve  30  may be proportionally decreased and vise versa.  
         [0033]     As shown in  FIG. 1 , the flow sensor  28  may be fluidly connected to the recirculation line  24  downstream of the flow cooler  26 . The flow sensor  28  may be any type of mass air flow sensor such as, for example, a hot wire anemometer or a venturi-type sensor. The flow sensor  28  may be configured to sense the amount of exhaust flow passing through the recirculation line  24 . It is understood that the flow cooler  26  may assist in reducing fluctuations in the temperature of the portion of the exhaust flow passing through the recirculation line  24 . Reducing temperature fluctuations may also assist in reducing fluctuations in the volume occupied by a flow of exhaust gas since a high temperature mass of gas occupies a greater volume than the same mass of gas at a low temperature gases. Thus, sensing the amount of exhaust flow through the recirculation line  24  at positions downstream of the flow cooler  26  (i.e. at a relatively controlled temperature) may result in more accurate flow measurements than measurements taken upstream of the flow cooler  26 . It is further understood that the flow sensor  28  may also include, for example, a thermocouple (not shown) or other device configured to sense the temperature of the exhaust flow.  
         [0034]     The flow line  27  downstream of the mixing valve  30  may direct the ambient air/exhaust flow mixture to the compression assembly  32 . The compression assembly  32  may include a compressor  13  configured to increase the pressure of a flow of gas a desired pressure. The compressor  13  may include a fixed geometry type compressor, a variable geometry type compressor, or any other type of compressor known in the art. In the exemplary embodiment shown in  FIG. 1 , the compression assembly  32  may include more than one compressor  13  and the multiple compressors  13  may be disposed in parallel or in series relationship. A compressor  13  of the compression assembly  32  may be connected to a turbine  14  of the energy extraction assembly  22  and the turbine  14  may be configured to drive the compressor  13 . In particular, as hot exhaust gases exit the power source  12  and expand against the blades (not shown) of the turbine  14 , components of the turbine  14  may rotate and drive the connected compressor  13 . Alternatively, in an embodiment in which the turbine  14  is omitted, the compressor  13  may be driven by, for example, the power source  12 , or by any other drive known in the art. It is also understood that in a non-pressurized air induction system, the compression assembly  32  may be omitted.  
         [0035]     The aftercooler  34  may be fluidly connected to the power source  12  via the flow line  27  and may be configured to cool a flow of gas passing through the flow line  27 . In an exemplary embodiment, this flow of gas may be the ambient air/exhaust flow mixture discussed above. The aftercooler  34  may include a liquid-to-air heat exchanger, an air-to air heat exchanger, or any other type of flow cooler or heat exchanger known in the art. In an exemplary embodiment of the present disclosure, the aftercooler  34  may be omitted if desired.  
         [0036]     The exhaust treatment system  10  may further include a condensate drain  38  fluidly connected to the aftercooler  34 . The condensate drain  38  may be configured to collect a fluid, such as, for example, water or other condensate formed at the aftercooler  34 . It is understood that such fluids may consist of, for example, condensed water vapor contained in recycled exhaust gas and/or ambient air. In such an exemplary embodiment, the condensate drain  38  may include a removably attachable fluid tank (not shown) capable of safely storing the condensed fluid. The fluid tank may be configured to be removed, safely emptied, and reconnected to the condensate drain  38 . In another exemplary embodiment, the condensate drain  38  may be configured to direct the condensed fluid to a fluid container (not shown) and/or other component or location on the work machine. Alternatively, the condensate drain  38  may be configured to direct the fluid to the atmosphere or to the surface by which the work machine is supported.  
       INDUSTRIAL APPLICABILITY  
       [0037]     The exhaust treatment systems  10 ,  100  of the present disclosure may be used with any combustion-type device such as, for example, an engine, a furnace, or any other device known in the art where the recirculation of reduced-particulate exhaust into an inlet of the device is desired. The exhaust treatment systems  10 ,  100  may be useful in reducing the amount of harmful exhaust emissions discharged to the environment and reducing or substantially eliminating the amount of sulfate produced during treatment of the exhaust gas. The exhaust treatment systems  10 ,  100  may also be capable of purging the portions of the exhaust gas captured by components of the system through a regeneration process.  
         [0038]     As discussed above, the combustion process may produce a complex mixture of air pollutants. These pollutants may exist in solid, liquid, and/or gaseous form. In general, the solid and liquid pollutants may fall into the three categories of soot, soluble organic fraction, and sulfates. The soot produced during combustion may include carbonaceous materials, and the soluble organic fraction may include unburned hydrocarbons that are deposited on or otherwise chemically combined with the soot. The sulfates produced in the combustion process may be formed from sulfur molecules contained within the fuel and may be released in the form of SO2. This SO2 may react with oxygen molecules contained within the exhaust flow to form SO3. As explained above, SO2 may also be converted into SO3 in the presence of, for example, platinum, palladium, and/or other rare earth metals used as catalyst materials in conventional catalysts. It is understood that the combustion process may also produce small amounts of SO3.  
         [0039]     In a conventional exhaust treatment system, a portion of the SO3 produced may be released to the atmosphere through an outlet of the exhaust system. The exhaust treatment systems  10 ,  100  of the present disclosure, however, may substantially reduce the formation of sulfates by minimizing the amount of platinum, palladium, and/or other precious earth metals used. The operation of the exhaust treatment systems  10 ,  100  will now be explained in detail. Unless otherwise noted, the exhaust treatment system  10  of  FIG. 1  will be referred to for the duration of the disclosure.  
         [0040]     The power source  12  may combust a mixture of fuel, recirculated exhaust gas, and ambient air to produce mechanical work and an exhaust flow containing the gaseous compounds discussed above. The exhaust flow may be directed, via flow line  15 , from the power source  12  through the energy extraction assembly  22 . The hot exhaust flow may expand on the blades of the turbines  14  of the energy extraction assembly  22 , and this expansion may reduce the pressure of the exhaust flow while assisting in rotating the turbine blades.  
         [0041]     The reduced pressure exhaust flow may pass through the regeneration device  20  to the filter  16 . The regeneration device  20  may be deactivated during the normal operation of the power source  12 . As the exhaust flow passes through the filter  16 , a portion of the particulate matter entrained with the exhaust flow may be captured by the substrate, mesh, and/or other structures within the filter  16 .  
         [0042]     A portion of the filtered exhaust flow may be extracted downstream of the filter  16  and upstream of the catalyst  18 . The extracted portion of the exhaust flow may enter the recirculation line  24  and may be recirculated back to the power source  12 . The remainder of the filtered exhaust flow may pass through the catalyst  18 . The catalyst materials contained within the catalyst may assist in oxidizing the hydrocarbons and soluble organic fraction carried by the filtered flow. After passing through the catalyst  18 , the remainder of the filtered exhaust flow may exit the exhaust treatment system  10  through an exhaust system outlet  17 .  
         [0043]     The embodiment of the exhaust treatment system  10  illustrated in  FIG. 1  may be preferable to conventional systems since, although the exhaust treatment system  10  contains a separate catalyst  18 , the catalyst  18  is downstream of the recirculation line  24 . As a result, any of the SO3 produced by the rare earth metals contained within the catalyst  18  exits through the outlet  17  and is not recirculated through the exhaust treatment system  10 . It is understood, however, that since the catalyst  18  is downstream of the recirculation line  24 , a portion of the hydrocarbons produced during the combustion process may be recirculated back to the power source  12 .  
         [0044]     In the exemplary embodiment illustrated in  FIG. 2 , the filter  36  may contain catalyst materials such as platinum. The catalyst materials may be disposed on a substrate of the filter  36  and may substantially oxidize the particulate matter, hydrocarbons, and/or carbon monoxide contained within the exhaust flow. Such a configuration may result in the production of substantially less sulfate in the recirculated filtered exhaust flow than conventional exhaust treatment systems containing a separate catalyst upstream of a filter. Such a configuration may also allow for the passive regeneration of the filter  36  during operation of the power source  12 .  
         [0045]     Referring again to  FIG. 1 , the recirculated portion of the exhaust flow may pass through the flow cooler  26 . The flow cooler  26  may reduce the temperature of the portion of the exhaust flow before the portion enters the flow line  27 . The mixing valve  30  may be configured to regulate the ratio of recirculated exhaust flow to ambient inlet air passing through flow line  27 . As described above, the flow sensor  28  may assist in regulating this ratio.  
         [0046]     The mixing valve  30  may permit the ambient air/exhaust flow mixture to pass to the compression assembly  32  where the compressors  13  may increase the pressure of the flow, thereby increasing the temperature of the flow. The compressed flow may pass through the flow line  27  to the aftercooler  34 , which may reduce the temperature of the flow before the flow enters the inlet  21  of the power source  12 .  
         [0047]     Over time, soot produced by the combustion process may collect in the filter  16  and may begin to impair the ability of the filter  16  to store particulates. The flow sensor  28  and other sensors (not shown) sense parameters of the power source  12  and/or the exhaust treatment system  10 . Such parameters may include, for example, engine speed, engine temperature, exhaust flow temperature, exhaust flow pressure, and particulate matter content. A controller (not shown) may use the information sent from the sensors in conjunction with an algorithm or other pre-set criteria to determine whether the filter  16  has become saturated and is in need of regeneration. Once this saturation point has been reached, the controller may send appropriate signals to components of the exhaust treatment system  10  to begin the regeneration process. A preset algorithm stored in the controller may assist in this determination and may use the sensed parameters as inputs. Alternatively, regeneration may commence according to a set schedule based on fuel consumption, hours of operation, and/or other variables.  
         [0048]     The signals sent by the controller may alter the position of the mixing valve  30  to desirably alter the ratio of the ambient air/exhaust flow mixture. These signals may also activate the regeneration device  20 . Upon activation, oxygen and a combustible substance, such as, for example, fuel may be directed to the regeneration device  20 . The regeneration device  20  may ignite the fuel and may increase the temperature of the exhaust flow passing to the filter  16  to a desired temperature for regeneration. This temperature may be in excess of 700 degrees Celsius (approximately 1,292 degrees Fahrenheit) in some applications, depending on the type and size of the filter  16 . At these temperatures, soot contained within the filter  16  may be burned away to restore the storage capabilities of the filter  16 .  
         [0049]     Other embodiments of the disclosed exhaust treatment system  10 ,  100  will be apparent to those skilled in the art from consideration of the specification. For example, the system  10 ,  100  may include additional filters such as, for example, a sulfur trap disposed upstream of the filter  16 . The sulfur trap may be useful in capturing sulfur molecules carried by the exhaust flow. It is intended that the specification and examples be considered as exemplary only, with the true scope of the invention being indicated by the following claims.