Abstract:
A method for altering an operating condition of a filter includes actively increasing the temperature of the filter to a desired temperature below a regeneration temperature and sensing a filter operating condition at about the desired temperature. The method also includes comparing the sensed filter operating condition to an expected filter operating condition range and actively increasing the temperature of the filter to the regeneration temperature in response to the comparison.

Description:
TECHNICAL FIELD 
   The present disclosure relates generally to a particulate filter and, more particularly, to a strategy for regenerating a filter. 
   BACKGROUND 
   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 both gaseous and solid material, such as, for example, particulate matter. Particulate matter may include ash and unburned carbon particles called soot. 
   Due to increased environmental concerns, some engine manufacturers have developed systems to treat engine exhaust after it leaves the engine. Some of these systems employ exhaust treatment devices, such as particulate traps, to remove particulate matter from the exhaust flow. A particulate trap may include filter material designed to capture particulate matter. After an extended period of use, however, the filter material may become partially saturated with particulate matter, thereby hindering the particulate trap&#39;s ability to capture particulates. 
   The collected particulate matter may be removed from the filter material through a process called regeneration. A particulate trap may be regenerated by increasing the temperature of the filter material and the trapped particulate matter above the combustion temperature of the particulate matter, thereby burning away the collected particulate matter. This increase in temperature may be effectuated by various means. For example, some systems may employ a heating element to directly heat one or more portions of the particulate trap (e.g., the filter material or the external housing). Other systems have been configured to heat exhaust gases upstream of the particulate trap. The heated gases then flow through the particulate trap and transfer heat to the filter material and captured particulate matter. Such systems may alter one or more engine operating parameters, such as the ratio of air to fuel in the combustion chambers, to produce exhaust gases with an elevated temperature. Alternatively, such systems may heat the exhaust gases upstream of the particulate trap with, for example, a burner disposed within an exhaust conduit leading to the particulate trap. 
   One such system is disclosed by U.S. Pat. No. 4,651,524, issued to Brighton on Mar. 24, 1987 (“the &#39;524 patent”). The &#39;524 patent discloses an exhaust treatment system configured to increase the temperature of exhaust gases with a burner. 
   While the system of the &#39;524 patent may increase the temperature of the particulate trap, the regeneration device of the &#39;524 patent is not configured to assess whether an exothermic event may occur within the filter prior to actively initiating a regeneration event. As a result, such systems may cause the filter to overheat during regeneration, thereby damaging the filter. 
   The disclosed regeneration assembly is directed toward overcoming one or more of the problems set forth above. 
   SUMMARY OF THE INVENTION 
   In an exemplary embodiment of the present disclosure, a method for altering an operating condition of a filter includes actively increasing the temperature of the filter to a desired temperature below a regeneration temperature and sensing a filter operating condition at about the desired temperature. The method also includes comparing the sensed filter operating condition to an expected filter operating condition range and actively increasing the temperature of the filter to the regeneration temperature in response to the comparison. 
   In another exemplary embodiment of the present disclosure, a method of preventing damage to a filter during regeneration includes actively increasing the temperature of the filter to a desired temperature below a regeneration temperature and sensing a filter operating condition at about the desired temperature. The method also includes comparing the sensed filter operating condition to an expected filter operating condition range and maintaining the filter at the desired temperature for a desired period of time. The method further includes actively increasing the temperature of the filter to the regeneration temperature in response to the comparison. 
   In yet another exemplary embodiment of the present disclosure, an exhaust treatment system of a power source includes a filter having a housing with an inlet, a regeneration device fluidly connected to the inlet of the housing, and at least one sensor configured to sense an operating characteristic of the filter. The exhaust treatment system also includes a controller in communication with the regeneration device and the at least one sensor. The controller is configured to controllably increase the temperature of the filter to a desired temperature below a regeneration temperature. The controller is also configured to compare a sensed filter operating condition to an expected filter operating condition range at about the desired temperature, and actively increase the temperature of the filter to the regeneration temperature in response to the comparison. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagrammatic illustration of an engine having an. exhaust treatment system according to an exemplary embodiment. 
       FIG. 2  is a flowchart of a filter regeneration method according to an exemplary embodiment. 
   

   DETAILED DESCRIPTION 
     FIG. 1  illustrates an exhaust treatment system  10  connected to a power source  12 . 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. 
   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  44  of the power source  12 . The exhaust treatment system  10  may include an energy extraction assembly  22 , a regeneration device  14 , a filter  16 , a recirculation line  32  fluidly connected downstream of the filter  16 , and a flow cooler  34 . The exhaust treatment system  10  may further include a mixing valve  36 , a compression assembly  40 , and an aftercooler  46 . 
   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  18 . The flow lines  18  may include pipes, tubing, and/or other exhaust flow carrying means known in the art. The flow lines  18  may be made of alloys of steel, aluminum, and/or other materials known in the art. The flow lines  18  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). 
   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  18  and may reduce the pressure of the exhaust gases to any desired pressure. The energy extraction assembly  22  may include one or more turbines  24 , 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  24 , the multiple turbines  24  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  40 . 
   In an exemplary embodiment, the regeneration device  14  may be fluidly connected to the energy extraction assembly  22  via a flow line  18 , 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 . Alternatively, the desired temperature may be a temperature less than a regeneration temperature of the filter  16 . Accordingly, the regeneration device  14  may be configured to assist in regenerating the filter  16 . The regeneration device  14  may be in communication with a controller  50 , as illustrated by control line  60 . 
   The regeneration device  14  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  14 , 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  14  includes a fuel injector and an ignitor, it is understood that the regeneration device  14  may receive a supply of a combustible substance and a supply of oxygen to facilitate combustion within the regeneration device  14 . 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  14  through flow line  18 . In an exemplary embodiment, the supply of oxygen may be carried by a flow of gas directed to the regeneration device  14  from downstream of the compression assembly  40 . In such an embodiment, the flow of gas may include, for example, recirculated exhaust gas and ambient air. 
   As shown in  FIG. 1 , the filter  16  may be connected downstream of the regeneration device  14 . The filter  16  may have a housing  25  including an inlet  26  and an outlet  28 . 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. The particulates may be, for example, soot. 
   In an exemplary embodiment of the present disclosure, a filter  16  of the exhaust treatment system  10  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. 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 filter  16  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  16 . The catalyst materials may be added to the filter  16  by any conventional means, such as, for example, coating or spraying, and the substrate of the filter  16  may be partially or completely coated with the materials. It is understood that the catalyst materials described above may be capable of oxidizing hydrocarbons in certain conditions. 
   The recirculation line  32 , fluidly connected downstream of the filter  16  and upstream of an exhaust system outlet  30 , may be configured to assist in directing a portion of the exhaust flow from the filter  16  to the inlet  44  of the power source  12 . The recirculation line  32  may comprise piping, tubing, and/or other exhaust flow carrying means known in the art, and may be structurally similar to the flow lines  18  described above. 
   The flow cooler  34  may be fluidly connected to the filter  16  via the recirculation line  32 , and may be configured to cool the portion of the exhaust flow passing through the recirculation line  32 . The flow cooler  34  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  34  may be omitted. 
   The mixing valve  36  may be fluidly connected to the flow cooler  34  via the recirculation line  32  and may be configured to assist in regulating the flow of exhaust through the recirculation line  32 . It is understood that in an exemplary embodiment, a check valve (not shown) may be fluidly connected upstream of the flow cooler  34  to further assist in regulating the flow of exhaust through the recirculation line  32 . The mixing valve  36  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  36  may be actuated manually, electrically, hydraulically, pneumatically, or in any other manner known in the art. The mixing valve  36  may be in communication with the controller  50  via control line  61 , and may be selectively actuated in response to one or more predetermined conditions. 
   The mixing valve  36  may also be fluidly connected to an ambient air intake  38  of the exhaust treatment system  10 . Thus, the mixing valve  36  may be configured to control the amount of exhaust flow entering the compression assembly  40  relative to the amount of ambient air flow entering the compression assembly  40 . For example, as the amount of exhaust flow passing through the mixing valve  36  is desirably increased, the amount of ambient air flow passing through the mixing valve  36  may be proportionally decreased and vice versa. 
   The compression assembly  40  may include a compressor  42  configured to increase the pressure of a flow of gas to a desired pressure. The compressor  42  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  40  may include more than one compressor  42 , and the multiple compressors  42  may be disposed in parallel or in series relationship. A compressor  42  of the compression assembly  40  may be connected to a turbine  24  of the energy extraction assembly  22 , and the turbine  24  may be configured to drive the compressor  42 . In particular, as hot exhaust gases exit the power source  12  and expand against the blades (not shown) of the turbine  24 , components of the turbine  24  may rotate and drive the connected compressor  42 . 
   The aftercooler  46  may be fluidly connected to the power source  12 , and may be configured to cool a flow of gas passing to the intake  44 . In an exemplary embodiment, this flow of gas may be the ambient air/exhaust flow mixture discussed above. The aftercooler  46  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  46  may be omitted if desired. 
   The exhaust treatment system  10  may also include a plurality of sensors  48  configured to collect data corresponding to various operating characteristics of a device. The sensors  48  may measure, for example, pressure, flow, temperature, particulate content, and/or other operating characteristics known in the art. In an exemplary embodiment of the present disclosure, at least one sensor  48  may be connected to the power source  12  and may be configured to measure temperature, speed, fuel quantity consumed, and/or other power source  12  operating characteristics. In another exemplary embodiment, a sensor  48  may be disposed proximate the inlet  26  of the filter  16 , and another sensor  48  may be disposed proximate the outlet  28 . Such sensors  48  may be configured to measure temperature, pressure, and/or other filter operating characteristics. It is understood that such sensors  48  may assist in measuring, for example, a pressure drop and/or a change in temperature across the filter  16 , and that such measurements may correspond to sensed exhaust flow characteristics. The exhaust treatment system  10  may further include a sensor  48  disposed within the filter  16  configured to measure any of the filter operating characteristics mentioned above. The sensor  48  disposed within the filter  16  may also be configured to measure the quantity of soot contained within the filter  16 . As illustrated by data lines  54 ,  56 ,  58 , and  62  shown in  FIG. 1 , the sensors  48  described above may be in communication with the controller  50 , and may be configured to send data thereto. It is understood that the sensor locations, types, and functions described herein are merely exemplary, and that the sensors  48  may have locations, may be of types, and may have functions other than those listed above. 
   The controller  50  may be, for example, an electronic control module, a system computer, a central processing unit, or other data storage and manipulation device known in the art. The controller  50  may be configured to send and receive data. The controller  50  may also store data received from the sensors  48  and from various operator interfaces  52 . The controller  50  may be configured to manipulate stored and/or received data using stored algorithms, stored exhaust treatment system component limits, and/or preset maps. In an exemplary embodiment, the controller  50  may be configured to control a regeneration event based on sensed operating characteristics, expected filter operating characteristics, and/or filter design limits. 
   Operator interfaces  52  may be located in an operator compartment of a work machine to which the exhaust treatment system  10  is connected, but can be located elsewhere. Such operator interfaces  52  may include, but are not limited to, levers, switches, buttons, foot petals, joysticks, control wheels, touchpads, LCD displays, computer screens, and keyboards. The operator interfaces  52  may be in communication with the controller  50  via a communication line  64 , and may be useful in notifying the operator of, for example, an operating characteristic of the filter  16 , the regeneration device  14 , and/or the power source  12 . 
   INDUSTRIAL APPLICABILITY 
   The exhaust treatment system  10  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 system  10  may be useful in reducing the amount of harmful exhaust emissions discharged into the environment. The exhaust treatment system  10  may also be capable of purging the portions of the exhaust gas captured by components of the system through a regeneration process. The exhaust treatment system  10  may further be configured to assess the condition of the filter  16  before actively beginning regeneration. Such an assessment may reduce the potential for damage to the filter  16  caused by uncontrolled regeneration. As used herein, the term “active regeneration” refers to using a regeneration device or some other heat source to initiate the burning and/or combustion of, for example, soot contained within a filter. Alternatively, “passive regeneration” refers to burning and/or combusting, for example, soot contained within a filter without supplying additional heat to a flow of exhaust gas with regeneration devices or other heat sources. 
   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 a mixture of 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 exhaust flow may be directed from the power source  12  through the energy extraction assembly  22 . The hot exhaust flow may expand on the blades of the turbines  24  of the energy extraction assembly  22 , and this expansion may reduce the pressure of the exhaust flow while assisting in rotating the turbine blades. 
   The reduced pressure exhaust flow may pass through the regeneration device  14  to the filter  16 . The regeneration device  14  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 . 
   A portion of the filtered exhaust flow may be extracted downstream of the filter  16 . The extracted portion of the exhaust flow may enter the recirculation line  32 , and may be recirculated back to the power source  12 . Catalyst materials contained within the filter  16  may assist in oxidizing the hydrocarbons and soluble organic fraction carried by the flow. After passing through the filter  16 , the filtered exhaust flow may exit the exhaust treatment system  10  through the exhaust system outlet  30 . 
   The recirculated portion of the exhaust flow may pass through the flow cooler  34 . The flow cooler  34  may reduce the temperature of the portion of the exhaust flow, and the mixing valve  36  may be configured to regulate the ratio of recirculated exhaust flow to ambient inlet air passing to the compression assembly  40 . The compressors  42  may increase the pressure of the flow, thereby increasing the temperature of the flow. The compressed flow may pass through the flow line  18  to the aftercooler  46 , which may reduce the temperature of the flow before the flow enters the intake  44  of the power source  12 . 
   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 controller  50  may determine that it is necessary to regenerate the filter  16  once the filter&#39;s storage abilities are reduced to unsatisfactory levels. As shown by the control strategy  66  illustrated in  FIG. 2 , the sensors  48  may sense operating characteristics of the power source  12 , the filter  16 , and/or the exhaust treatment system  10 , generally (Step  68 ), and may send data representing these sensed characteristics to the controller  50 . Reference will be made to  FIG. 2  for the duration of this disclosure. It is understood, however, that any discussion of the components of the exhaust treatment system  10  will be made with reference to  FIG. 1 . 
   The controller  50  may use the information sent from the sensors  48  in conjunction with an algorithm or other preset criteria, such as, for example, maps and/or soot loading models, to determine whether the filter  16  has become saturated and is in need of regeneration (Step  70 ). In an exemplary embodiment, trigger values corresponding to one or more of the sensed operating characteristics may be saved in a memory of the controller  50 . Such trigger values may include, for example, a maximum pressure drop across the filter  16 , a maximum increase in temperature across the filter  16 , a maximum engine temperature, a maximum quantity of fuel consumed, and a maximum soot load in the filter  16 . The soot loading of the filter  16  may be calculated or estimated by the controller  50 . Alternatively, the soot loading may be measured using one or more sensors  48  disposed within the filter  16 . It is understood that a maximum elapsed run time may also be used as a trigger value. If none of the above trigger values has been met (Step  70 : No), the controller  50  may not initiate the regeneration process and the sensors  48  may continue to sense operating characteristics. Once one of the above trigger values has been reached, the controller  50  may send appropriate signals to components of the exhaust treatment system  10  to begin the regeneration process (Step  70 : Yes). 
   The controller  50  may send a control signal to ignite, or otherwise activate, the regeneration device  14 . It is understood that the regeneration device  14  may controllably increase the temperature of an exhaust flow, thereby increasing the temperature of the filter  16  through convection. Activating the regeneration device  14  may, for example, increase the temperature of the filter media to a desired sub-temperature (Step  72 ). The sub-temperature may be a desired temperature less than a regeneration temperature of the filter  16 . In an exemplary embodiment, the sub-temperature may be in the range of approximately 300° Celsius to approximately 500° Celsius. As will be described in greater detail below, actively increasing the temperature of the filter  16  to a sub-temperature within this exemplary range may enable the controller  50  to evaluate the conditions of the filter  16  before increasing its temperature to the regeneration temperature and potentially damaging the filter  16 . 
   It is understood that increasing the temperature of the exhaust flow may also be accomplished by using other structures and methods. For example, in an embodiment of the present disclosure (not shown), the timing of the opening of the exhaust valves in the power source combustion chambers may be modified to increase exhaust flow temperature. In particular, the exhaust valves may be controlled to open several degrees before the commencement of an exhaust stroke of the power source  12 . In another exemplary embodiment (not shown), a fuel injection cycle of the power source  12  may be modified to increase the exhaust flow temperature. In an additional exemplary embodiment, the position of the mixing valve  36  may be manipulated to increase the temperature of the exhaust flow entering the filter  16 . 
   After increasing the filter temperature to the sub-temperature, the sensors  48  may continue to sense operating characteristics of the filter  16  at the sub-temperature (Step  74 ) and may send this data to the controller  50 . Based on this data, the controller  50  may determine whether the sensed values are within an expected range (Step  76 ) for the respective operating characteristics. For example, upon increasing the temperature of the exhaust flow entering the filter  16  to a sub-temperature of approximately 400° Celsius, the controller  50  may expect a measured outlet flow temperature between approximately 400° Celsius and approximately 405° Celsius when filter conditions are normal. It is understood that in exemplary normal filter conditions, substantially no oil or fuel may be present within the filter  16  and the amount of accumulated soot may be substantially below the design limits of the filter  16 . 
   If the sensed filter operating characteristics are within their respective expected ranges (Step  76 : Yes), the controller  50  may command the regeneration device  14  to increase the flow temperature, and thus, the filter temperature, to a regeneration temperature (Step  78 ). In an exemplary embodiment of the present disclosure, the regeneration temperature may be in the range of approximately 600° Celsius to approximately 650° Celsius. The regeneration device  14  may hold the flow temperature at the regeneration temperature while the filter  16  regenerates and the soot and other particulate matter trapped therein is burned away. 
   It is understood that in an exemplary embodiment of the present disclosure, the temperature of the filter  16  may be increased according to a desired filter temperature profile. In such an embodiment, the regeneration device  14  may increase the temperature of the exhaust flow in a stepwise manner. For example, the regeneration device  14  may raise the exhaust flow temperature from a sub-temperature of approximately 400° Celsius to a regeneration temperature of approximately 650° Celsius in increments of approximately 50° Celsius. The controller  50  may command the regeneration device  14  to maintain an increased temperature for a desired period of time in accordance with the desired filter temperature profile. Such a profile may, for example, assist in minimizing damage to the filter  16  caused by repeated regenerations over the life of the filter  16 . 
   The sensors  48  may continue to sense filter operating characteristics at the regeneration temperature (Step  80 ), and the controller  50  may determine whether the filter  16  has been sufficiently regenerated (Step  82 ) based on this sensed data. It is understood that the controller  50  may use, for example, pressure drop, temperature increase, regeneration elapsed time, quantity of fuel consumed, and/or other sensed operating characteristics in conjunction with stored algorithms and/or preset maps, such as soot loading models, to make this determination. 
   If the filter  16  has been sufficiently regenerated (Step  82 : Yes), the controller  50  will command the regeneration device  14  to deactivate (Step  84 ). If the filter  16  has not been sufficiently regenerated (Step  82 : No), the regeneration device  14  will continue to maintain the regeneration temperature, and the sensors  48  and the controller  50  will continue to evaluate the operating conditions of the filter  16  until it has been sufficiently regenerated. 
   Alternatively, if any of the operating characteristics measured at the sub-temperature are determined not to be within their respective expected ranges (Step  76 : No), the controller  50  may determine whether the sensed values are outside of the known design limits of the filter  16  (Step  86 ). For example, heating the exhaust flow to a sub-temperature of 400° Celsius may cause the temperature of the flow measured proximate the outlet  28  of the filter  16  to exceed the design limits of the filter  16  due to abnormal conditions within the filter  16 . It is understood that in exemplary abnormal filter conditions, oil and/or fuel may be present within the filter  16 . In addition, the amount of accumulated soot may be substantially above the design limits of the filter  16 . Such abnormal filter conditions may cause an uncontrolled regeneration to occur at the sub-temperature, thereby causing irreparable harm to the filter, such as, for example, cracking or melting. Evaluating filter operating conditions at sub-temperatures, however, may assist in mitigating and/or avoiding such harm. If the sensed values are outside of design limits, (Step  86 : Yes), the controller  50  may deactivate the regeneration device  14  (Step  88 ) and may send an alarm to and/or otherwise notify the operator (Step  90 ). Such an alarm may indicate that the filter  16  is damaged and requires replacing. 
   If the sensed operating characteristic values are outside of their respective expected limits, but are not outside of the design limits of the filter  16  (Step  86 : No), the controller  50  may command the regeneration device  14  to hold the filter  16  at the sub-temperature for a desired period of time (Step  92 ). Doing so may, for example, cause any oil and/or fuel accumulated within the filter  16  to burn away without causing harm to the filter  16 . The filter  16  may eventually return to normal conditions as determined by the continued sensing of filter operating characteristics at the sub-temperature (Step  74 ). 
   Other embodiments of the disclosed exhaust treatment system  10  will be apparent to those skilled in the art from consideration of the specification. For example, the exhaust treatment system  10  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.