Patent Publication Number: US-2022213822-A1

Title: Systems and methods for dynamic control of filtration efficiency and fuel economy

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 17/280,420, filed Mar. 26, 2021, which is a National Phase Application of PCT/US2018/053400, filed Sep. 28, 2018. The contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to aftertreatment systems for use with internal combustion (IC) engines. 
     BACKGROUND 
     Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Generally exhaust gas aftertreatment systems comprise any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust gas aftertreatment systems for diesel-powered IC engines comprise a selective catalytic reduction (SCR) system, including a catalyst formulated to convert NOx (NO and NO 2  in some fraction) into harmless nitrogen gas (N 2 ) and water vapor (H 2 O) in the presence of ammonia (NH 3 ). Aftertreatment systems may also include a filter such as a partial flow filter, configured to remove particulate matter (PM), for example, soot, dust, inorganic particles, etc. from the exhaust gas. Increasingly stringent PM emission standards require the filter to remove PM with high filtration efficiency. Filters having high filtration efficiency however, exert a high backpressure on exhaust gas flowing through the aftertreatment system which may reduce fuel economy of the engine. 
     SUMMARY 
     Embodiments described herein relate generally to systems and methods for controlling operation of an aftertreatment system for high filtration efficiency or high fuel economy based on an operating condition of an engine producing the exhaust gas. In particular, embodiments described herein relate to aftertreatment system that include a first filter, a second filter having a smaller pore size than the first filter positioned downstream of the first filter for providing high filtration efficiency, and a bypass conduit for selectively bypassing flow of the exhaust gas around the second filter when high fuel economy is desired while meeting PM emission standards. 
     In some embodiments, an aftertreatment system configured to reduce constituents of an exhaust gas produced by an engine comprises a first filter and a second filter disposed downstream of the first filter. A bypass conduit fluidly couples an exhaust gas flow path downstream of the first filter and upstream of the second filter to an exhaust gas flow path downstream of the second filter. A valve is operatively coupled to the bypass conduit, the valve moveable between a closed position in which the exhaust gas flows through the second filter, and an open position in which at least a portion of the exhaust gas flows through the bypass conduit so as to bypass the second filter. A controller is operatively coupled to the valve and is configured to determine whether a first filtration efficiency of the first filter is greater than a first filtration efficiency threshold or less than or equal to the first filtration efficiency threshold. The controller is configured to control the valve such that the valve is more closed when the first filtration efficiency is less than or equal to the first filtration efficiency threshold than when the first filtration efficiency is greater the first filtration efficiency threshold, such that a larger portion of the exhaust gas flows through the second filter when the first filtration efficiency is less than the first filtration efficiency threshold, the controlling of the valve causing the exhaust gas expelled into the environment from the aftertreatment system to have a PM count which is lower than a predetermined threshold. 
     In some embodiments, an aftertreatment system configured to reduce constituents of an exhaust gas produced by an engine comprises, a first filter, and a second filter disposed downstream of the first filter. A bypass conduit fluidly couples an exhaust gas flow path downstream of the first filter and upstream of the second filter to an exhaust gas flow path downstream of the second filter. A valve is operatively coupled to the bypass conduit. The valve is moveable between a closed position in which the exhaust gas flows through the second filter, and an open position in which at least a portion of the exhaust gas flows through the bypass conduit so as to bypass the second filter. A controller is operatively coupled to the valve. The controller is configured to determine whether the engine is operating in a high particulate matter operating condition or a low particulate matter operating condition. The controller is configured to control the valve such that the valve is more closed during the high particulate matter operating condition of the engine than during the low particulate matter operating condition of the engine, such that a larger portion of the exhaust gas flows through the second filter during the high particulate matter operating condition of the engine than during the low particulate matter operating condition of the engine, the controlling of the valve causing the exhaust gas expelled into the environment from the aftertreatment system to have a PM count which is lower than a predetermined threshold. 
     In some embodiments, an aftertreatment system for reducing constituents of an exhaust gas produced by an engine comprises a first filter and a second filter positioned downstream of the first filter. A controller is operably coupled to the first and second filters and is configured to determine a first filtration efficiency of the first filter during operation of the aftertreatment system. In response to the first filtration efficiency being equal to or greater than a first filtration efficiency threshold, the controller is configured to generate a fault code instructing a user to remove the second filter from the aftertreatment system. 
     In some embodiments, a valve comprises a plurality of rings comprising a first ring defining a plurality of first openings, and a second ring defining a plurality of second openings. The second ring abuts the first ring. The valve is moveable between a closed position and an open position. In the closed positioned, the plurality of first openings are misaligned with the plurality of second openings to prevent a fluid from flowing through the plurality of first and second openings. In the open position, the second ring is rotated relative to the first ring such that the plurality of first openings are aligned with the plurality of second openings allowing the fluid to flow therethrough. 
     In some embodiments, an aftertreatment system configured to reduce constituents of an exhaust gas produced by an engine comprises a first filter and a second filter disposed downstream of the first filter. A bypass conduit fluidly couples at least one of an exhaust gas flow path upstream of the first filter to an exhaust gas flow path between the first filter and the second filter or an exhaust gas flow path between the first filter and the second filter to an exhaust gas flow path downstream of the second filter. A valve is operatively coupled to the bypass conduit, the valve moveable between a closed position in which the exhaust gas flows through the second filter, and an open position in which at least a portion of the exhaust gas flows through the bypass conduit so as to bypass the second filter. A controller is operatively coupled to the valve. The controller is configured to determine whether the engine is operating in a high PM operating condition or a low PM operating condition. The controller is configured to control the valve such that the valve is more closed during the high PM operating condition of the engine than during the low PM operating condition of the engine, such that a larger portion of the exhaust gas flows through the second filter during the high PM operating condition of the engine than during the low PM operating condition of the engine, the controlling of the valve causing the exhaust gas expelled into the environment from the aftertreatment system to have a PM count which is lower than a predetermined threshold. 
     It should be appreciated that all combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the subject matter disclosed herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several implementations in accordance with the disclosure and are therefore not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings. 
         FIG. 1  is a schematic illustration of an aftertreatment system, according to an embodiment. 
         FIG. 2  is a schematic flow diagram of an example method to control filtration efficiency of an aftertreatment system, according to an embodiment. 
         FIG. 3A  is a schematic block diagram of an aftertreatment system, according to another embodiment. 
         FIG. 3B  is a schematic block diagram of an aftertreatment system, according to another embodiment. 
         FIG. 4  is a schematic block diagram of an embodiment of a control circuitry that may be included in the aftertreatment system of  FIG. 3A or 3B . 
         FIG. 5  is a plot of a filter flow restriction vs filtration efficiency for an example filter. 
         FIG. 6  is a schematic illustration of an aftertreatment system, according to yet another embodiment. 
         FIG. 7A  is a side perspective view of a portion of an aftertreatment system showing a first filter, a second filter and a bypass conduit, according to an embodiment;  FIG. 7B  is a side perspective view of a valve disposed in the bypass conduit of the aftertreatment system of  FIG. 7A . 
         FIG. 8A  is a side view of the portion of the aftertreatment system of  FIG. 7A  with the valve being in a closed position, and  FIG. 8B  shows the valve in an open position. 
         FIG. 9  is a schematic illustration of an aftertreatment system, according to still another embodiment. 
         FIG. 10  is a plot of overall filtration efficiency of an aftertreatment system including a first filter and a second filter positioned downstream of the first filter. 
         FIGS. 11A-11B  are schematic flow diagrams of a method for dynamically controlling filtration efficiency of an aftertreatment system, and fuel economy of an engine fluidly coupled to an aftertreatment system, according to an embodiment. 
         FIG. 12  is a schematic block diagram of a computing device which may be used as the controller shown in  FIG. 3A-3B, 4, 6 or 9 , according to an embodiment. 
     
    
    
     Reference is made to the accompanying drawings throughout the following detailed description. In the drawings, similar symbols typically identify similar components unless context dictates otherwise. The illustrative implementations described in the detailed description, drawings, and claims are not meant to be limiting. Other implementations may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and made part of this disclosure. 
     DETAILED DESCRIPTION 
     Embodiments described herein relate generally to systems and methods for controlling operation of an aftertreatment system for high filtration efficiency or high fuel economy based on an operating condition of an engine producing the exhaust gas. In particular, embodiments described herein relate to aftertreatment systems that include a first filter, a second filter having a smaller pore size than the first filter and positioned downstream of the first filter for providing high filtration efficiency, and a bypass conduit for selectively bypassing flow of the exhaust gas around the second filter when high fuel economy is desired while meeting PM emission standards. 
     Increasingly stringent PM emission standards on exhaust gas emitted from aftertreatment systems require that filters included in aftertreatment systems remove PM with high filtration efficiency. For example, China is implementing very strict regulations on PM emission from aftertreatment systems. Conventional aftertreatment systems only allow a short preconditioning time which creates challenges in the ash limited filter performance. Filters included in conventional aftertreatment systems may have open pores which allow a large amount of PM (e.g., soot or ash) to flow therethrough during the preconditioning phase, for example, when the aftertreatment system is operated for the first time or after regeneration of the filter when there is no PM, or negligible amount of PM trapped in the filter. This allows a large amount of PM to flow through the filter during the preconditioning phase. While the PM accumulation in the filter over time reduces the porosity of the filter and eventually increases the filtration efficiency of the filter to a desirable level, the passage of the higher amount of PM through the filter during the preconditioning phase is undesirable. Filters having high filtration efficiency can address the PM issue. However, such filters exert a high backpressure on the exhaust gas flowing through the aftertreatment system which reduces fuel economy of the engine. Moreover, conventional aftertreatment systems typically include the filter located upstream of a location of an SCR system. This allows PM generated from the decomposition of reductant into the SCR system or to pass out of the aftertreatment system unfiltered, increasing the PM count. In some arrangements, reductant insertion can increase PM count downstream of the filter by 400%-600% due to reductant insertion and reaction with the exhaust gas in the SCR system. 
     Various embodiments of the systems and methods described herein provide benefits including, for example: (1) providing a high filtration efficiency during and after the preconditioning phase or during high PM operating condition of an engine by disposing a second smaller pore size filter downstream or upstream of a first larger pore size filter; (2) reducing PM count during reductant insertion in the exhaust gas by disposing the second filter downstream of an SCR system of the aftertreatment system; (3) providing high filtration efficiency during high PM operating conditions and providing high fuel economy during low PM operating conditions while meeting emission standards by selectively bypassing at least a portion of the exhaust gas around the second filter (4) allowing installation in existing aftertreatment systems with minimum modifications; and/or (5) reducing durability concerns by allowing selective removal of the second filter from the aftertreatment system. 
       FIG. 1  is a schematic illustration of an aftertreatment system  100 , according to an embodiment. The aftertreatment system  100  is configured to receive an exhaust gas from an engine (e.g., a diesel engine, a gasoline engine, a natural gas engine, a dual fuel engine, a biodiesel engine, an E-85 engine, or any other suitable engine) and reduce constituents of the exhaust gas such as, for example, NOx gases, CO, hydrocarbons, etc. The aftertreatment system  100  may comprise a reductant storage tank  110 , a reductant insertion assembly  120 , a housing  101 , a first filter  140 , a second filter  142  and a SCR system  150 . 
     The housing  101  defines an internal volume within which the components of the aftertreatment system  100 , i.e., the first filter  140 , the second filter  142  and the SCR system  150  are positioned. The housing  101  may be formed from a rigid, heat-resistant and corrosion-resistant material, for example stainless steel, iron, aluminum, metals, ceramics, or any other suitable material. The housing  101  may have any suitable cross-section, for example circular, square, rectangular, oval, elliptical, polygonal, or any other suitable shape. 
     An inlet conduit  102  is fluidly coupled to an inlet of the housing  101  and structured to receive exhaust gas from the engine and communicate the exhaust gas to an internal volume defined by the housing  101 . Furthermore, an outlet conduit  104  may be coupled to an outlet of the housing  101  and structured to expel treated exhaust gas into the environment (e.g., treated to remove PM such as soot and ash by the first and/or second filters  140  and  142  and/or reduce constituents of the exhaust gas such as NOx gases included in the exhaust gas). 
     A first sensor  103  may be positioned in the inlet conduit  102 . The first sensor  103  may comprise a NOx sensor configured to measure an amount of NOx gases included in the exhaust gas flowing into the aftertreatment system  100  and may include a physical NOx sensor or a virtual NOx sensor. In other embodiments, the first sensor  103  may comprise an exhaust gas flow rate sensor. In various embodiments, a temperature sensor, a pressure sensor, an oxygen sensor or any other sensor may also be positioned in the inlet conduit  102  so as to determine one or more operational parameters of the exhaust gas flowing through the housing  101  of the aftertreatment system  100 . 
     A second sensor  105  may be positioned in the outlet conduit  104 . The second sensor  105  may comprise a second NOx sensor configured to determine an amount of NOx gases expelled into the environment after passing through the SCR system  150 . In other embodiments, the second sensor  105  may comprise a PM sensor configured to determine an amount of PM (e.g., soot or ash included in the exhaust gas exiting the filter  140 ). In still other embodiments, the second sensor  105  may comprise an ammonia sensor configured to measure an amount of ammonia in the exhaust gas flowing out of the SCR system  150 , i.e., determine the ammonia slip. This may be used as a measure of determining a catalytic efficiency of the SCR system  150 , adjust an amount of reductant to be inserted into the SCR system  150 , and/or adjust a temperature of the SCR system  150  so as to allow the SCR system  150  to effectively use the ammonia for catalytic decomposition of the NOx gases included in the exhaust gas flowing therethrough. In some embodiments, an ammonia oxidation (AMOx) catalyst may be positioned downstream of the SCR system  150 , for example, in the outlet conduit  104  so as to decompose any unreacted ammonia in the exhaust gas downstream of the SCR system  150 . 
     In some embodiments, the aftertreatment system  100  may also include an oxidation catalyst  130  (e.g., a diesel oxidation catalyst) disposed upstream of the first filter  140 , for example, in the housing  101 . The oxidation catalyst  130  may be configured to oxidize unburnt hydrocarbons and/or carbon monoxide included in the exhaust gas to CO 2 . 
     The SCR system  150  includes an SCR catalyst formulated to decompose constituents of an exhaust gas flowing therethrough. In some embodiments, the SCR system  150  may comprise a selective catalytic reduction filter (SCRF), or any other aftertreatment component configured to decompose constituents of the exhaust gas (e.g., NOx gases such as such nitrous oxide, nitric oxide, nitrogen dioxide, etc.), flowing through the housing  101  in the presence of a reductant, as described herein. 
     Any suitable SCR catalyst may be used such as, for example, rhodium, cerium, iron, manganese, copper, vanadium based catalyst, any other suitable catalyst, or a combination thereof. The SCR catalyst may be disposed on a suitable substrate such as, for example, a ceramic (e.g., cordierite) or metallic (e.g., kanthal) monolith core which can, for example, define a honeycomb structure. A washcoat can also be used as a carrier material for the SCR catalyst. Such washcoat materials may comprise, for example, aluminum oxide, titanium dioxide, silicon dioxide, any other suitable washcoat material, or a combination thereof. The exhaust gas (e.g., diesel exhaust gas) can flow over and/or about the SCR catalyst such that any NOx gases included in the exhaust gas are further reduced to yield an exhaust gas which is substantially free of NOx gases. 
     In various embodiments, the aftertreatment system  100  may also include other aftertreatment components such as, for example, ammonia oxidation catalysts, mixers, baffle plates, or any other suitable aftertreatment component. 
     A reductant port (not shown) may be positioned on a sidewall of the housing  101  and structured to allow insertion of a reductant therethrough into the internal volume defined by the housing  101 . The reductant port may be positioned upstream of the SCR system  150  (e.g., to allow reductant to be inserted into the exhaust gas upstream of the SCR system  150 ) or over the SCR system  150  (e.g., to allow reductant to be inserted directly on the SCR system  150 ). In other embodiments in which the reductant is inserted upstream of the SCR system  150 , mixers, baffles, vanes or other structures may be positioned upstream of the SCR system  150  so as to facilitate mixing of the reductant with the exhaust gas. 
     The reductant storage tank  110  is structured to store a reductant. The reductant is formulated to facilitate decomposition of the constituents of the exhaust gas (e.g., NOx gases included in the exhaust gas). Any suitable reductant can be used. In some embodiments, the exhaust gas comprises a diesel exhaust gas and the reductant comprises a diesel exhaust fluid. For example, the diesel exhaust fluid may comprise urea, an aqueous solution of urea, or any other fluid that comprises ammonia, by-products, or any other diesel exhaust fluid as is known in the arts (e.g., the diesel exhaust fluid marketed under the name ADBLUE®). For example, the reductant may comprise an aqueous urea solution having a particular ratio of urea to water. In particular embodiments, the reductant can comprise an aqueous urea solution including 32.5% by volume of urea and 67.5% by volume of deionized water, including 40% by volume of urea and 60% by volume of deionized water, or any other suitable ratio of urea to deionized water. 
     A reductant insertion assembly  120  is fluidly coupled to the reductant storage tank  110 . The reductant insertion assembly  120  is configured to selectively insert the reductant into the SCR system  150  or upstream thereof (e.g., into the inlet conduit  102 ) or a mixer (not shown) positioned upstream of the SCR system  150 . The reductant insertion assembly  120  may comprise various structures to facilitate receipt of the reductant from the reductant storage tank  110  and delivery to the SCR system  150 . 
     In various embodiments, the reductant insertion assembly  120  may also include one or more pumps (e.g., a diaphragm pump, a positive displacement pump, a centrifugal pump, a vacuum pump, etc.) for delivering the reductant to SCR system  150  at an operating pressure and/or flow rate. The reductant insertion assembly  120  may also include filters and/or screens (e.g., to prevent solid particles of the reductant or contaminants from flowing into the one or more pumps) and/or valves (e.g., check valves) to receive reductant from the reductant storage tank  110 . 
     Screens, check valves, pulsation dampers, or other structures may also be positioned downstream of the one or more pumps of the reductant insertion assembly  120  and configured to remove contaminants and/or facilitate delivery of the reductant to the SCR system  150 . In various embodiments, the reductant insertion assembly  120  may also comprise a bypass line structured to provide a return path of the reductant from the one or more pumps to the reductant storage tank  110 . A valve (e.g., an orifice valve) may be provided in the bypass line. In various embodiments, the reductant insertion assembly  120  may also comprise a blending chamber structured to receive pressurized reductant from a metering valve at a controllable rate. The blending chamber may also be structured to receive air (e.g., compressed air or portion of the exhaust gas), or any other inert gas (e.g., nitrogen), for example, from an air supply unit so as to deliver a combined flow of the air and the reductant to the SCR system  150  through the reductant port. 
     The aftertreatment system  100  may also comprise a reductant injector fluidly coupled to the reductant insertion assembly  120  and configured to insert the reductant (e.g., a combined flow of reductant and compressed air) into the SCR system  150 . In various embodiments, the reductant injector may comprise a nozzle having predetermined diameter. In various embodiments, the reductant injector may be positioned in the reductant port and structured to deliver a stream or a jet of the reductant into the internal volume of the housing  101  so as to deliver the reductant to the SCR system  150 . 
     In various embodiments, the reductant insertion assembly  120  may also comprise a dosing valve, for example positioned within a reductant delivery line for delivering the reductant from the reductant insertion assembly  120  to the SCR system  150 . The dosing valve can comprise any suitable valve, for example a butterfly valve, a gate valve, a check valve (e.g., a tilting disc check valve, a swing check valve, an axial check valve, etc.), a ball valve, a spring loaded valve, an air assisted injector, a solenoid valve, or any other suitable valve. The dosing valve may be selectively opened to insert a predetermined quantity of the reductant for a predetermined time into the SCR system  150  or upstream therefrom. 
     The first filter  140  is configured to remove PM (e.g., soot, debris, inorganic particles, etc.) from the exhaust gas. In various embodiments, the first filter  140  may include a ceramic filter. In particular embodiments, the first filter  140  may include a partial flow filter (e.g., a ceramic partial filter). In other embodiments, the first filter  140  may include a metallic partial flow filter. In still other embodiments, the first filter  140  may include a cordierite filter which can, for example, be an asymmetric filter. In yet other embodiments, the first filter  140  may be catalyzed. 
     The second filter  142  is disposed downstream of the first filter  140 . While shown as being disposed upstream of the SCR system  150 , in other embodiments, the second filter  142  may be disposed downstream of the SCR system  150 . The second filter  142  may include a ceramic filter, a partial flow filter, a cordierite filter or any other filter as described with respect to the first filter  140 . In some embodiments, the second filter  142  may include an uncoated filter. 
     In various embodiments, the first filter  140  may have a first pore size which is larger than a second pore size of the second filter  142  such that the second filter  142  has a higher filtration efficiency than a first filtration efficiency of the first filter  140 . For example, certain emissions standards (e.g., in Europe or China) may place very high restrictions on PM emission from aftertreatment systems. During a preconditioning stage (e.g., when the aftertreatment system  100  is new or after regeneration of the first filter  140 ) the first filter  140  may have a porosity which allows a larger amount of PM to pass therethrough then is allowable by emission standards. Positioning the second filter  142  having a small pore size and thereby, a higher filtration efficiency than the first filtration efficiency of the first filter  140  downstream of the first filter  140 , allows filtering of a higher amount of PM from the exhaust gas than would be possible by the first filter  140 . For example, the first filter  140  may have a first filtration efficiency of 70%, and the second filter may  142  may have a second filtration efficiency of 90% such that the aftertreatment system  100  has an overall filtration efficiency of 1−(1−70%)×(1−90%)=97%, higher than each of the filters  140  and  142  alone, thereby effectively meeting PM emission standards. 
     Over time as the exhaust gas continues to flow through the aftertreatment system  100 , the first filter  140  may become increasingly clogged with PM which causes a decrease in its porosity and increase in its filtration efficiency. Over time, the first filtration efficiency of the first filter  140  reaches a first efficiency threshold at which the first filter  140  is able to meet PM emission standards. The first filtration efficiency may be based on a pressure drop across the first filter  140  (e.g., measured using a differential pressure sensor) and an exhaust gas flow rate of the exhaust gas, for example, a ratio of the pressure drop to the exhaust gas flow rate. 
     While the first filter  140  becomes increasingly clogged with PM resulting in an increase in its filtration efficiency, the second filter  142  also becomes increasingly clogged. This causes an increase in the backpressure on the exhaust gas causing a decrease in fuel economy of the engine. The second filter  142  may be removably coupled to the aftertreatment system  100 , such that in response to first filtration efficiency first filter  140  reaching the first efficiency threshold, the second filter  142  may be removed from the aftertreatment system  100 , for example, during a scheduled maintenance of the aftertreatment system  100 , so as to decrease the backpressure. In some embodiments, the second filter  142  may be removed if a second pressure drop across the second filter  142  is greater than a predetermined pressure drop threshold which may correspond to a high backpressure. 
     In some embodiments, the aftertreatment system  100  may also comprise a controller  170  communicatively coupled to the first filter  140  and/or the second filter  142 . In various embodiments, the controller  170  may be included in a control circuitry, for example, the control circuitry  371  described in further detail herein. The controller  170  is configured to determine the first filtration efficiency of the first filter  140  during operation of the aftertreatment system  100 . For example, the first filter pressure sensor  138  (e.g., a differential pressure sensor or a delta pressure sensor) may be operatively coupled to the first filter  140  and configured to determine a pressure drop across the first filter  140 . The controller  170  may be configured to interpret a pressure signal from the first filter pressure sensor  138  to determine a first pressure drop across the first filter  140 . The controller  170  may also be configured to determine a flow rate of the exhaust gas (e.g., from a signal received from an exhaust flow sensor or based on operating condition of the engine). The controller  170  may determine the first filtration efficiency based on the first pressure drop and the flow rate of the exhaust gas (e.g., a ratio of the first pressure drop to the flow rate). 
     In response to the pressure drop being greater than a predetermined pressure drop threshold, the controller  170  generates a fault code instructing a user to remove the second filter  142  from the aftertreatment system  100 . The fault code may be stored in a memory of a central controller of a vehicle or any other assembly including the aftertreatment system  100 , which may be retrieved during a maintenance interval of the vehicle. In other embodiments, the controller  170  may also activate an indicator lamp (e.g., an indicator on a dash display), thereby informing the user that the second filter  142  should be removed. 
     In some embodiments, the controller  170  may also be configured to determine a pressure drop across the second filter  142 . For example, a second filter pressure sensor  148  may be operably coupled to the second filter  142  and configured to determine a pressure drop thereacross. The controller  170  may be configured to interpret a pressure signal from the second filter pressure sensor  148  to determine a pressure drop across the second filter  142 . In response to the pressure drop being greater than a predetermined pressure threshold (e.g., corresponding to second filter  142  being substantially clogged or a high back pressure exerted on the exhaust gas), the controller  170  generates the fault code. 
     In particular embodiments, the aftertreatment system  100  may also include a hydrocarbon (HC) insertion assembly  122  configured to insert hydrocarbons into the exhaust gas flow path on, or upstream of the oxidation catalyst  130 . The inserted hydrocarbons are oxidized on the oxidation catalyst  130  and serve to increase the temperature of the exhaust gas to a temperature sufficient to oxidize PM trapped in the first and/or second filters  140  and  142  so as to regenerate the first and/or second filters  140  and  142 . 
     For example, the filters  140  and/or  142  may become increasingly clogged with PM over time. This may increase filtration efficiency of the first and/or second filters  140  and  142  by reducing a porosity of the filters  140  and  142  as previously described herein, but also cause an increase in backpressure on the exhaust gas which reduces fuel efficiency. If not regenerated, the filters  140  and  142  may eventually become completely blocked with PM or the backpressure can become sufficiently high so as to crack the first and/or second filter  140  and  142 . In some embodiments, the hydrocarbon insertion assembly  122  may be activated to insert hydrocarbons into the exhaust gas, for example, into or upstream of the oxidation catalyst  130 , in response to a backpressure of the exhaust gas increasing beyond a predetermined pressure threshold which may correspond to an amount of clogging of the first and/or second filter  140  and  142 . For example, the controller  170  may activate the hydrocarbon insertion assembly  122  in response to the pressure drop across the second filter  142  being greater than a predetermined pressure threshold. The hydrocarbons may combust in the exhaust gas, thereby increasing a temperature of the exhaust gas above a temperature threshold sufficient to oxidize PM trapped in the first and/or second filters  140  and  142  so as to regenerate the filters  140  and/or  142 . For example, the second filter  142  may be regenerated before removal from the aftertreatment system  100 . 
       FIG. 2  is a schematic flow diagram of a method  200  for controlling filtration efficiency of an aftertreatment system (e.g., the aftertreatment system  100 ) as fuel economy of an engine producing an exhaust gas flowing through the aftertreatment system, according to an embodiment. The aftertreatment system includes an SCR system (e.g., the SCR system  150 ) a first filter (e.g., the first filter  140 ) positioned upstream of the SCR system and a second filter (e.g., the second filter  142 ) positioned downstream of the first filter, for example, between the first filter and the SCR system or downstream of the SCR system. The second filter may have a smaller pore size than the first filter, as previously described herein with respect to the aftertreatment system  100 . 
     The method  200  comprises determining a filtration efficiency of the first filter during operation of the aftertreatment system, at  202 . For example, the filtration efficiency of the first filter  140  is determined by the controller  170 . In some embodiments, the method  200  may also include determining a first pressure drop across the first filter, and a flow rate of the exhaust gas downstream of the first filter (e.g., by the controller  170 ). The filtration efficiency may be based on the first pressure drop and the flow rate of the exhaust gas, for example, a ratio of the pressure drop to the flow rate. 
     At  204 , it is determined if the first filtration efficiency is equal to or greater than a first filtration efficiency threshold. In response to the first filtration efficiency of the first filter being equal to or greater the first filtration efficiency threshold ( 204 :YES), the method  200  includes instructing a user to remove the second filter from the aftertreatment system, at  206 . For example, as exhaust gas flows through the first filter  140 , PM accumulates in the first filter  140  reducing its porosity and increasing its filtration efficiency. Once the first filtration efficiency of the first filter  140  reaches the first filtration efficiency threshold, corresponding to a desired filtration efficiency from the first filter  140 , the first filter  140  may be sufficient to provide a desired filtration efficiency from the aftertreatment system  100  for meeting PM emission standards without the second filter  142 . The user may be instructed via an audio signal (e.g., an alarm), a video signal (e.g., lighting an indicator lamp on a dashboard) or via a fault code (e.g., second filter remove code) generated by the controller  170 , the fault code being available to the user on demand. 
     In some embodiments, the method  200  may also include determining a second pressure drop across the second filter in response to the first filtration efficiency being less than the filtration efficiency threshold, at  208 . If the pressure drop across the second filter is less than a predetermined pressure drop threshold at  210 , the method  200  returns to operation  202 . In response to the second pressure drop being greater than a predetermined pressure drop threshold, in some embodiments, a regeneration of at least the second filter may be initiated, at  212 . For example, the second filter  142  and optionally, also the first filter  140  may be heated above a regeneration temperature (e.g., via a heater coupled to the second filter  142  and/or the first filter  140  or flowing exhaust gas at a temperature greater than the regeneration through the aftertreatment system  100 ) to oxidize the accumulated PM (e.g., soot) in the second filter  142  and, in some embodiments, also the first filter  140 . The method then returns to operation  210 . If it is determined that the second pressure drop is still greater than the predetermined pressure drop, the user is instructed to remove the second filter, at  214 . For example, the second pressure drop being above the predetermined pressure drop threshold may correspond to high back pressure exerted on the exhaust gas which may reduce a fuel economy of the engine producing the exhaust gas below a desirable level or damage the second filter  142 . 
     In some embodiments, the second filter  142  may be rotatably mounted within the housing  101  and configured to rotate between a first configuration in which the second filter  142  is positioned within the exhaust gas flow path and a second configuration in which the second filter  142  rotated within the housing  101  to provide a flow path for the exhaust gas to bypass the second filter  142 . For example, a biasing member (e.g., a spring) may be coupled to the second filter  142  and configured to bias the second filter  142  into the first configuration to cause the exhaust gas to flow through the second filter  142 . As the second filter  142  gets increasing clogged, a pressure of the exhaust gas on the second filter  142  increases due to the decreasing porosity of the second filter  142 . Once the pressure of the exhaust gas is equal to or greater than a predetermined pressure threshold which may occur after the first filter  140  has reached its filtration efficiency threshold, the pressure may be sufficient to overcome the biasing force of the biasing member to move the second filter  142  into the second configuration. This allows the exhaust gas to bypass the second filter  142 , therefore reducing the backpressure on the exhaust gas and increasing fuel economy. This may obviate removing of the second filter  142  from the housing  101 . 
     In other embodiments, the aftertreatment system  100  may also include a bypass conduit (not shown) such as the bypass conduit  345  described with respect to  FIG. 3A , fluidly coupling an exhaust gas flow path of the exhaust gas downstream of the first filter  140  and upstream of the second filter  142  to an exhaust gas flow path downstream of the second filter  142 . A pressure activated valve may be disposed in the bypass conduit and may be configured to open in response to a pressure of the exhaust gas exceeding a predetermined pressure threshold, for example, due to the porosity of the second filter  142  dropping too low, as previously described herein. The pressure activated valve may close again after the second filter is regenerated, and the cycle is repeated. 
       FIG. 3A  is a schematic illustration of an aftertreatment system  300 , according to yet another embodiment. The aftertreatment system  300  is configured to receive an exhaust gas from an engine (e.g., a diesel engine, a gasoline engine, a natural gas engine, a dual fuel engine, a biodiesel engine, an E-85 engine, or any other suitable engine) and reduce constituents of the exhaust gas such as, for example, NOx gases, CO, hydrocarbons, etc. The aftertreatment system  300  may comprise the reductant storage tank  110 , the reductant insertion assembly  120 , a housing  301 , the first filter  140 , the second filter  142  and the SCR system  150 , as previously described herein with respect to the aftertreatment system  100 . 
     The housing  301  defines an internal volume within which the components of the aftertreatment system  300 , i.e., the first filter  140 , the second filter  142  and the SCR system  150  are positioned, as previously described herein. An inlet conduit  302  is fluidly coupled to an inlet of the housing  101  and structured to receive exhaust gas from the engine and communicate the exhaust gas to an internal volume defined by the housing  301 . Furthermore, an outlet conduit  304  may be coupled to an outlet of the housing  301  and structured to expel treated exhaust gas into the environment (e.g., treated to remove PM such as soot and ash by the first and/or second filters  140  and  142  and/or reduce constituents of the exhaust gas such as NOx gases included in the exhaust gas). The first sensor  103  may be positioned in the inlet conduit  302  and the second sensor  105  may be positioned in the outlet conduit  304 , as previously described herein with respect to the aftertreatment system  100 . 
     In some embodiments, the aftertreatment system  300  may also include the oxidation catalyst  130  (e.g., a diesel oxidation catalyst) disposed upstream of the first filter  140 , for example, in the housing  301 . The hydrocarbon insertion assembly  122  may be configured to insert hydrocarbons (e.g., fuel such as diesel) into the exhaust gas upstream of or on the oxidation catalyst  130  to a raise a temperature of the exhaust gas, for example, for regenerating the first filter  140  and/or the second filter  142 . 
     The first filter  140  is disposed upstream of the SCR system  150  and the second filter  142  is disposed downstream of the first filter  140 , for example, downstream of the SCR system  150  as shown in  FIG. 3A . For example, insertion of the reductant into the SCR system  150  may result in significant amount of solid particles (e.g., reductant particles, soot, ash, etc.) being present in the exhaust gas downstream of the SCR system  150 , and positioning the second filter  142  downstream of the SCR system  150  may allow capture of such particles downstream of the SCR system  150 . In other embodiments, the second filter  142  may be disposed upstream of the SCR system  150 . A pressure sensor  346  (e.g., a differential or delta pressure sensor) is operatively coupled to the second filter  142  and is configured to determine a pressure drop across the second filter  142 . The pressure drop may indicate a degree of clogging of the second filter  142 . The first filter  140  and the second filter  142  have the same structure and function as described with respect to the aftertreatment system  100 . 
     The aftertreatment system  300  also comprises a bypass conduit  345  fluidly coupling an exhaust gas flow path of the exhaust gas downstream of the first filter  140  and upstream of the second filter  142  to an exhaust gas flow path downstream of the second filter  142 . For example, the bypass conduit  345  may fluidly a couple a volume of the housing  301  located between the SCR system  150  and the second filter  142  to a volume of the housing  301  downstream of the second filter  142 . The bypass conduit  345  therefore provides a bypass flow path for the exhaust gas to bypass the second filter  142 . 
     A valve  344  is operatively coupled to the bypass conduit  345 . The valve  344  may include a butterfly valve, a rotation valve, a diaphragm valve, a needle valve, a pinch valve, a check valve or any other suitable valve. The valve  344  is moveable between a closed position in which the exhaust gas flows through the second filter  142 , and an open position in which at least a portion of the exhaust gas flows through the bypass conduit  345  so as to bypass the second filter  142 . In various embodiments, a degree of opening of the valve  344  may be adjusted to control an amount of exhaust gas flowing through the second filter  142  and the amount of exhaust gas bypassing the second filter  142 . For example, the valve  344  may be initially closed when the first filter  140  is new or is recently regenerated to cause the exhaust gas to flow through the second filter  142  and provide high filtration efficiency. Over time, the first filter  140  gets increasingly clogged with PM and experiences an increase in its first filtration efficiency. Furthermore, the second filter  142  also gets increasingly clogged as previously described herein with respect to the aftertreatment system  100  causing an increasing in backpressure on the exhaust gas which may reduce fuel economy of the engine producing the exhaust gas. The valve  344  may therefore, be increasingly opened to cause at least a portion of the exhaust gas to bypass the second filter  142  through the bypass conduit  345  so as to reduce a back pressure on the exhaust gas. The valve  344  may be completely opened once a first filtration efficiency of the first filter  140  has reached a first filtration efficiency threshold corresponding to a desired filtration efficiency from the aftertreatment system  300  and/or a pressure drop across the second filter  142  is greater than a pressure drop threshold. 
     While  FIG. 3A  shows the bypass conduit and the small pore size second filter  142  positioned downstream of the larger pore size first filter  140 , in other embodiments, a bypass conduit may be positioned across the upstream, filter alternatively, or additionally to the bypass conduit positioned around the downstream filter. For example,  FIG. 3B  is a schematic block diagram of an aftertreatment system  300   b,  according to another embodiment. The aftertreatment system  300   b  is similar to the aftertreatment system  300  with the following differences. 
     The aftertreatment system  300   b  includes a first filter  140   b  and a second filter  142   b  positioned downstream of the first filter  140   b.  A first bypass conduit  345   b  fluidly couples an exhaust gas flow path upstream of the first filter  140   b  to an exhaust gas flow path between the first filter  140   b  and the second filter  142   b.  A first bypass conduit  345   b  is operably coupled to the first bypass valve  344   b.  Furthermore, a second bypass conduit  365   b  fluidly couples an exhaust gas flow path between the first filter  140   b  and the second filter  142   b,  to an exhaust gas flow path downstream of the second filter  142   b.  The first valve  344   b  and the second valve  364   b  may be selectively opened or closed to cause a larger portion of the exhaust gas to flow through the first filter  140   b  (first valve  344   b  closed and second valve  364   b  open), a larger portion of the exhaust gas to flow through the second filter  142   b  (first valve  344   b  open and second valve  364   b  closed) or the exhaust gas to flow through each of the filters  140   b  and  142   b  (both valve  344   b  and  364   b  closed). 
     In some embodiments, the first filter  140   b  may have a smaller pore size and therefore, a higher filtration efficiency than the second filter  142   b.  In such embodiments, the second bypass conduit  365   b  may be excluded such that a degree of opening of the first valve  344   b  may be controlled to provide high fuel economy or high filtration efficiency, as described herein. Furthermore, the first filter  140   b  may have a smaller diameter than the second filter  142   b.  In other embodiments, the second filter  142   b  may have a higher filtration efficiency than the first filter  140   b  to provide high filtration efficiency or fuel economy, as previously described with respect to  FIG. 3A . 
     Referring again to  FIG. 3A , a controller  370  may be operatively coupled to the valve  344  and configured to move the valve  344  into an open position, a closed position or control a degree of opening of the valve  344  so as to a control a ratio of the exhaust gas flowing through the second filter  142  or the bypass conduit  345 . In some embodiments, the controller  370  may also be communicatively coupled to the first sensor  103 , the second sensor  105  and/or the pressure sensor  346 . In some embodiments, the controller  370  may also be communicatively coupled to the engine and configured to determine one or more engine operating parameters (e.g., engine speed, engine torque, exhaust gas flow rate, fuel insertion rate, intake air flow rate, etc.) associated with the engine. The controller  370  may be operatively coupled to these components using any type and any number of wired or wireless connections. For example, a wired connection may include a serial cable, a fiber optic cable, a CAT5 cable, or any other form of wired connection. Wireless connections may include the Internet, Wi-Fi, cellular, radio, Bluetooth, ZigBee, etc. In one embodiment, a controller area network (CAN) bus provides the exchange of signals, information, and/or data. The CAN bus includes any number of wired and wireless connections. 
     In some embodiments, the controller  370  may be configured to determine an operating condition of the engine. For example, the controller  370  may be configured to receive an engine signal from the engine, a first sensor signal from the first sensor  103  and/or a second sensor signal from the second sensor  105  to determine an operating condition of the engine, for example, is the engine operating under a high PM operating condition in which a higher amount of PM is included in the exhaust gas emitted by the engine (e.g., during high engine load conditions) or a low PM operating condition in which a lower PM is included in the exhaust gas relative to the high PM operating condition (e.g., operating under steady state or low load conditions). 
     The controller  370  is configured to control the valve  344  such that the valve  344  is more closed during the high particulate matter operating condition of the engine than during the low particulate matter operating condition of the engine, such that a larger portion of the exhaust gas flows through the second filter  142  during the high particulate matter operating condition of the engine than during the low particulate matter operating condition of the engine. For example, in response to the engine operating under a high PM operating condition, the controller  370  may be configured to cause the valve  344  to open a first predetermined amount such that the valve  344  is more closed than open so as to cause a larger portion of the exhaust gas to flow through the second filter  142  than the bypass conduit  345  and provide high filtration efficiency. When the engine is operating under the high PM operating condition, the controller  370  may completely close the valve  344  or open the valve  344  a small degree to cause a larger portion of the exhaust gas to flow through the second filter  142  than the bypass conduit  345 . The second filter  142  increases the filtration efficiency, as previously described herein. In some embodiments, the high PM operating condition corresponds to a larger amount of reductant being inserted into the SCR system  150  relative to the low PM operating condition. 
     In contrast, in response to the engine operating under a low PM operating condition, the controller  370  may be configured to cause the valve  344  to open a second predetermined amount such that the valve  344  is more open than closed so as to cause a larger portion of the exhaust gas to flow through the bypass conduit  345  and provide high fuel economy. For example, when the engine is operating under the low PM operating condition, the controller  370  may be configured to open the valve  344  a larger degree or completely open the valve  344  so as to cause a larger portion or substantially all of the exhaust gas to bypass the second filter  142  via the bypass conduit  345 . As previously described herein, as the second filter  142  becomes increasingly clogged, a backpressure on the exhaust gas increases which reduces fuel economy. If the filtration efficiency desired from the aftertreatment system  300  is being met (e.g., due to the first filter  140  reaching the first filtration efficiency threshold), then allowing a larger portion of the exhaust gas to bypass the second filter  142  reduces the backpressure on the exhaust gas and increases fuel economy. The valve  345  is controlled that the exhaust gas expelled into the environment from the aftertreatment system  300  has a PM count which is lower than a predetermined threshold, for example, to meet an emission standard. Thus, regardless of the high PM or low PM operating condition, the controller  370  is configured to ensure that the exhaust gas emitted from the aftertreatment system  300  meets a desired emission standard. 
     In some embodiments, the controller  370  may be configured to determine an operating condition of the aftertreatment system  300  (e.g., a pressure drop across the first filter  140 , a filtration efficiency of the first filter  140 , a pressure drop across the second filter  142 , a flow rate and/or temperature of the exhaust gas) and open or close the valve  344  based on the operating condition of the aftertreatment system  300 . 
     The controller  370  may be configured to determine whether a first filtration efficiency of the first filter  140  is less than or equal to a first filtration efficiency threshold or greater than the first filtration efficiency threshold. The controller  370  is configured to control the valve  344  such that the valve  344  is more closed when the first filtration efficiency is less than or equal to the first filtration efficiency threshold than when the first filtration efficiency is greater than the first filtration efficiency threshold, such that a larger portion of the exhaust gas flows through the second filter  142  when the first filtration efficiency is less than the first filtration efficiency threshold. For example, the valve  344  may be initially in the closed position when the first filtration efficiency is less than or equal to the first filtration efficiency threshold such that substantially all of the exhaust gas flows through the second filter  142 . In response to the first filtration efficiency being greater than a first filtration efficiency threshold, the controller  370  increasingly opens the valve  344  so that the valve is less closed relative to when the first filtration efficiency is less than or equal to the first filtration efficiency threshold and more of the exhaust gas flows through the bypass conduit  345  than the second filter  142 . 
     Expanding further, in some embodiments, the controller  370  is configured to determine a first filtration efficiency of the first filter  140 . If the first filtration efficiency is less than a first filtration efficiency threshold, the controller  370  closes the valve  344  to cause the exhaust gas to flow through the second filter  142  so as to provide high filtration efficiency. In response to the first filtration efficiency being equal to or greater than the first filtration efficiency threshold, the controller  370  may increase opening of the valve  344  (e.g., completely open the valve  344 ) such that at least a portion of the exhaust gas bypasses the second filter  142  via the bypass conduit  345 . As previously described herein, the valve  345  is controlled that the exhaust gas expelled into the environment from the aftertreatment system  300  has a PM count which is lower than a predetermined threshold, for example, to meet the emission standard. 
     In some embodiments, the controller  370  may be configured to determine a first pressure drop across the first filter  140 . For example, a first pressure sensor  348  may be operatively coupled to the first filter  140  and configured to determine a pressure drop across the first filter  140 . The controller  370  may be operatively coupled to the first pressure sensor  348  and configured to determine a first pressure drop thereacross. The controller  370  may also be configured to determine a flow rate of the exhaust gas. The controller  370  may be configured to determine a first filtration efficiency of the first filter  140  based on the first pressure drop and the flow rate of the exhaust gas, for example, a ratio between the pressure drop (e.g., differential pressure) and the flow rate. 
     For example,  FIG. 5  shows a plot of filtration efficiency of a first filter vs. a flow restriction (i.e., a ratio of pressure drop across the first filter and a flow rate of the exhaust gas) across the first filter, according to a specific embodiment. As exhaust gas continues to flow through the first filter  140 , a PM load, for example, a soot load or an ash load on the first filter  140  continues to increase causing a corresponding increase in the filtration efficiency of the first filter (e.g., the first filter  140 ) until the first filtration efficiency reaches a first filtration efficiency threshold (e.g., greater than 95% filtration efficiency). In some embodiments, the first filtration efficiency threshold corresponds to a ash load of 0.1-10 g/L on the first filter  140  for a mileage of the engine producing the exhaust of less than 5,000 miles. For example, as shown in  FIG. 5 , for a particular first filter, the first filtration efficiency threshold corresponds to a 0.25 g/L soot load or equivalent 2 g/L ash load on the first filter, at which the first filtration efficiency is close to 100%. It should be appreciated that in other embodiments, the first filtration efficiency threshold may be different depending on the particular first filter used in the aftertreatment system  300 . 
     In some embodiments, the controller  370  may also be configured to determine a pressure drop across the second filter  142 . For example, the controller  370  may receive a pressure signal from the pressure sensor  346  and determine the pressure drop across the second filter  142  therefrom. In response to the pressure drop being greater than a predetermined pressure drop threshold, the controller  370  may be configured to open the valve  344  so as to allow at least a portion of the exhaust gas to bypass the second filter  142  via the bypass conduit  345 . For example, the pressure drop across the second filter  142  being greater than a predetermined pressure drop threshold may correspond to a high backpressure on the exhaust gas which reduces fuel economy below a fuel economy threshold. Thus, the controller  370  opens the valve  344  so as to allow at least a portion of the exhaust gas to bypass the second filter  142  and reduce back pressure on the exhaust gas. In some embodiments, the controller  370  may be configured to open the valve  344  if the second filter  142  is difficult to regenerate or a temperature of the exhaust gas reaching the second filter  142  is below a predetermined temperature threshold which may correspond to the pressure drop across the second filter  142  being greater than the predetermined pressure drop threshold. 
     In some embodiments, the controller  370  may also be configured to determine a temperature of the exhaust gas proximate to an inlet of the second filter  142 . For example, the controller  370  may be communicatively coupled to a temperature sensor  341  positioned upstream of the second filter  142  and receive a temperature signal therefrom corresponding to a temperature of the exhaust gas at the inlet of the second filter  142 . In response to the temperature of the exhaust gas being above the predetermined temperature threshold, the controller  370  may be configured to close the valve  344  so as to force hot exhaust gas to flow through the second filter  142  for regenerating the second filter  142 . In some embodiments, the controller  370  may also be communicatively coupled to the hydrocarbon insertion assembly  122  and configured to instruct the hydrocarbon insertion assembly  122  to insert hydrocarbons into the oxidation catalyst  130  for raising the temperature of the exhaust gas above the predetermined temperature threshold, for example, for regenerating the first filter  140  and/or the second filter  142 . 
     In particular embodiments, the controller  370  may be included in a control circuitry. For example,  FIG. 4  is a schematic block diagram of a control circuitry  371  that comprises the controller  370 , according to an embodiment. The controller  370  comprises a processor  372 , a memory  374 , or any other computer readable medium, and a communication interface  376 . Furthermore, the controller  370  includes an engine operating condition determination circuitry  374   a,  a pressure and flow rate determination circuitry  374   b,  a temperature determination circuitry  374   c  and a valve control circuitry  374   d.  It should be understood that the controller  370  shows only one embodiment of the controller  370  and any other controller capable of performing the operations described herein can be used. 
     The processor  372  can comprise a microprocessor, programmable logic controller (PLC) chip, an ASIC chip, or any other suitable processor. The processor  372  is in communication with the memory  374  and configured to execute instructions, algorithms, commands, or otherwise programs stored in the memory  374 . 
     The memory  374  comprises any of the memory and/or storage components discussed herein. For example, memory  374  may comprise a RAM and/or cache of processor  372 . The memory  374  may also comprise one or more storage devices (e.g., hard drives, flash drives, computer readable media, etc.) either local or remote to controller  370 . The memory  374  is configured to store look up tables, algorithms, or instructions. 
     In one configuration, the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  are embodied as machine or computer-readable media (e.g., stored in the memory  374 ) that is executable by a processor, such as the processor  372 . As described herein and amongst other uses, the machine-readable media (e.g., the memory  374 ) facilitates performance of certain operations to enable reception and transmission of data. For example, the machine-readable media may provide an instruction (e.g., command, etc.) to, e.g., acquire data. In this regard, the machine-readable media may include programmable logic that defines the frequency of acquisition of the data (or, transmission of the data). Thus, the computer readable media may include code, which may be written in any programming language including, but not limited to, Java or the like and any conventional procedural programming languages, such as the “C” programming language or similar programming languages. The computer readable program code may be executed on one processor or multiple remote processors. In the latter scenario, the remote processors may be connected to each other through any type of network (e.g., CAN bus, etc.). 
     In another configuration, the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  are embodied as hardware units, such as electronic control units. As such, the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  may be embodied as one or more circuitry components including, but not limited to, processing circuitry, network interfaces, peripheral devices, input devices, output devices, sensors, etc. 
     In some embodiments, the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  may take the form of one or more analog circuits, electronic circuits (e.g., integrated circuits (IC), discrete circuits, system on a chip (SOCs) circuits, microcontrollers, etc.), telecommunication circuits, hybrid circuits, and any other type of “circuit.” In this regard, the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  may include any type of component for accomplishing or facilitating achievement of the operations described herein. For example, a circuit as described herein may include one or more transistors, logic gates (e.g., NAND, AND, NOR, OR, XOR, NOT, XNOR, etc.), resistors, multiplexers, registers, capacitors, inductors, diodes, wiring, and so on. 
     Thus, the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  may also include programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. In this regard, the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  may include one or more memory devices for storing instructions that are executable by the processor(s) of the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d.  The one or more memory devices and processor(s) may have the same definition as provided below with respect to the memory  374  and the processor  372 . 
     In the example shown, the controller  370  includes the processor  372  and the memory  374 . The processor  372  and the memory  374  may be structured or configured to execute or implement the instructions, commands, and/or control processes described herein with respect the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d.  Thus, the depicted configuration represents the aforementioned arrangement where the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  are embodied as machine or computer-readable media. However, as mentioned above, this illustration is not meant to be limiting as the present disclosure contemplates other embodiments such as the aforementioned embodiment where the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d,  or at least one circuit of the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d  are configured as a hardware unit. All such combinations and variations are intended to fall within the scope of the present disclosure. 
     The processor  372  may be implemented as one or more general-purpose processors, an application specific integrated circuit (ASIC), one or more field programmable gate arrays (FPGAs), a digital signal processor (DSP), a group of processing components, or other suitable electronic processing components. In some embodiments, the one or more processors may be shared by multiple circuits (e.g., the engine operating condition determination circuitry  374   a,  the pressure and flow rate determination circuitry  374   b,  the temperature determination circuitry  374   c  and the valve control circuitry  374   d ) may comprise or otherwise share the same processor which, in some example embodiments, may execute instructions stored, or otherwise accessed, via different areas of memory). Alternatively or additionally, the one or more processors may be structured to perform or otherwise execute certain operations independent of one or more co-processors. In other example embodiments, two or more processors may be coupled via a bus to enable independent, parallel, pipelined, or multi-threaded instruction execution. All such variations are intended to fall within the scope of the present disclosure. The memory  374  (e.g., RAM, ROM, Flash Memory, hard disk storage, etc.) may store data and/or computer code for facilitating the various processes described herein. The memory  374  may be communicably connected to the processor  372  to provide computer code or instructions to the processor  372  for executing at least some of the processes described herein. Moreover, the memory  374  may be or include tangible, non-transient volatile memory or non-volatile memory. Accordingly, the memory  374  may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described herein. 
     The communication interface  376  may include wireless interfaces (e.g., jacks, antennas, transmitters, receivers, communication interfaces, wire terminals, etc.) for conducting data communications with various systems, devices, or networks. For example, the communication interface  376  may include an Ethernet card and port for sending and receiving data via an Ethernet-based communications network and/or a Wi-Fi communication interface for communicating with, for example, the first sensor  103 , the second sensor  105 , the engine, the valve  344 , the pressure sensor  346 , the first pressure sensor  348 , the hydrocarbon insertion assembly  122  and/or any other component of the aftertreatment system  300 . The communication interface  376  may be structured to communicate via local area networks or wide area networks (e.g., the Internet, etc.) and may use a variety of communications protocols (e.g., IP, LON, Bluetooth, ZigBee, radio, cellular, near field communication, etc.). 
     The engine operating condition determination circuitry  374   a  may be configured to receive an engine operating condition signal, for example, from the engine, the first and/or second sensors  103  and  105  or any other sensor and determine if the engine is operating under a high PM operating condition or a low PM operating condition. Furthermore, the engine operating condition determination circuitry  374   a  may also be configured to determine an aftertreatment operating condition signal, for example, from the pressure sensors  346  and/or  348 , from the temperature sensor  341 , the first sensor  103  and/or the second sensor  105 . 
     The valve control circuitry  374   d  is configured to generate a valve signal configured to open the valve  344 , close the valve  344  or adjust a degree of opening of the valve  344 , as previously described herein. In response to the engine operating under the high PM operating condition, the valve control circuitry  374   d  may be configured to cause the valve  344  to open the first predetermined amount such that the valve  344  is more closed than open or completely close the valve  344  to increase a filtration efficiency of the aftertreatment system  300 , as previously described herein. Furthermore, in response to the engine operating under the low PM operating condition, the valve control circuitry  374   d  may be configured to cause the valve  344  to open the second predetermined amount such that the valve  344  is more open than closed or completely open the valve  344  to increase a fuel economy of the engine, as previously described herein. 
     The pressure and flow rate determination circuitry  374   b  is configured to determine a first pressure drop across the first filter  140  (e.g., from a pressure signal received from the first pressure sensor  348 ) and determine a flow rate of the exhaust gas (e.g., from a flow rate signal received from a flow rate sensor or based on one or more engine operating conditions). The pressure and flow rate determination circuitry  374   b  may determine a first filtration efficiency of the first filter  140  based on the first pressure drop and the exhaust gas flow rate (e.g., a ratio of the pressure drop to the exhaust gas flow rate). In response to the first filtration efficiency being equal to or greater than the first filtration efficiency threshold, the valve control circuitry  374   d  may increase opening of the valve  344  or otherwise completely open the valve  344 . 
     In some embodiments, the pressure and flow rate determination circuitry  374   b  may also be configured to determine a pressure drop across the second filter  142  (e.g., from a pressure signal received from the pressure sensor  346 ). In response to the pressure drop across the second filter  142  being greater than a predetermined pressure drop threshold, the valve control circuitry  374   d  may be configured to open the valve  344  so as to allow at least a portion of the exhaust gas to bypass the second filter  142 , as previously described herein. 
     The temperature determination circuitry  374   c  may be configured to determine a temperature of the exhaust gas proximate to the inlet of the second filter  142  (e.g., from a temperature signal received from the temperature sensor  341 ). In response, to the temperature of the exhaust gas being above the predetermined temperature threshold, the valve control circuitry  374   d  may be configured to close the valve  344  (e.g., by the second predetermined amount or completely close the valve  344 ) so as to force hot exhaust gas to flow through the second filter  142  for regenerating the second filter  142 , as previously described herein. In some embodiments, the temperature determination circuitry  374   c  may also be configured to instruct the hydrocarbon insertion assembly  122  to insert hydrocarbons into the oxidation catalyst  130  or the exhaust gas to raise a temperature of the exhaust gas to the predetermined temperature threshold for regenerating the first and/or second filters  140  and  142 . 
       FIG. 6  is a schematic illustration of an aftertreatment system  400 , according to another embodiment. The aftertreatment system  400  is configured to receive an exhaust gas from an engine (e.g., a diesel engine, a gasoline engine, a natural gas engine, a dual fuel engine, a biodiesel engine, an E-85 engine, or any other suitable engine) and reduce constituents of the exhaust gas such as, for example, NOx gases, CO, hydrocarbons, etc. The aftertreatment system  400  may comprise the reductant storage tank  110 , the reductant insertion assembly  120 , a housing  401 , the first filter  140 , a second filter  442  disposed downstream of the first filter  140 , the SCR system  150  disposed downstream of the second filter  442 , and the controller  370  as previously described herein with respect to the aftertreatment system  100 ,  300 . In other embodiments, the second filter  442  may be disposed downstream of the SCR system  150 . In some embodiments, the aftertreatment system  400  may also include the oxidation catalyst  130  disposed upstream of the first filter  140 , and the hydrocarbon insertion assembly  122  for selectively inserting hydrocarbons into the exhaust gas, as previously described herein. 
     The housing  401  includes an inlet conduit  402  having the first sensor  103  disposed therein, and an outlet conduit  404  having the second sensor  105  disposed therein. The second filter  442  may have a smaller diameter than the first filter  140  or otherwise a diameter of the housing  401  such that a bypass conduit  445  is defined around the second filter  442  between an outer radial surface of the second filter  442  and an inner radial surface of the housing  401 . The second filter  442  may have a smaller pore size and, thereby a higher filtration efficiency than the first filter  140 , and may be similar in function to the second filter  142 , as previously described herein. The pressure sensor  346  may be operatively coupled to the second filter  442  and configured to determine a pressure drop across the second filter  442 . Furthermore, the temperature sensor  341  may be positioned upstream of the second filter  442  and configured to determine a temperature of the exhaust gas entering the second filter  442 . 
     A valve  460  is disposed at an inlet of bypass conduit  445  between the inner surface of the housing  401  and an outer surface of the second filter  442 . The valve  460  is configured to be selectively opened to control an amount of exhaust gas flowing through the second filter  442  and/or around the second filter  442  through the bypass conduit  445 . For example, the controller  370  may be operatively coupled to the valve  460  and configured to open the valve  460 , close the valve  460  or open the valve  460  a predetermined amount, for example, to control an amount of the exhaust gas flowing through the second filter  442  and through the bypass conduit  445 , as previously described herein. 
     In some embodiments, the valve  460  may include a ring type valve. Referring also now to  FIGS. 7A-7B and 8A-8B , a portion of the housing  401  is shown that includes the first filter  140 , the second filter  442  and the valve  460  positioned therebetween. As shown in  FIG. 7B , the valve  460  includes a plurality of rings including a first ring  462  defining a plurality of first openings  464 , for example, a plurality of equally spaced slits defined through the first ring  462 . The first ring  462  defines a first diameter D 1  at a first end  463  thereof proximate to an outlet of the first filter  140  and a second diameter D 2  at a second end  465  thereof proximate to an inlet of the second filter  442  which is smaller than the first diameter D 1 . The second diameter D 2  may be approximately equal to an outer diameter of the second filter  442 . The first end  463  may be coupled to an inner surface of the housing  401  and/or an outer surface of the first filter  140 , for example, to prevent leakage of the exhaust gas therethrough between the housing  401  and the first end  463 . Furthermore, the second end  465  may be coupled to the inlet of the second filter  442 , for example, to prevent leakage of the exhaust gas between the second end  465  and the second filter  442 . In various embodiments, the first ring  462  may be immovably disposed in the housing  401 . 
     The valve  460  also comprises a second ring  466  defining a plurality of second openings  468 , for example, a plurality of equally spaced slits defined through the second ring  466 . The second ring  466  abuts the first ring  462  and is axially aligned therewith. The second ring  466  may be substantially similar to the first ring  462  in size and shape. Furthermore, a radial spacing between the plurality of first openings  464  and the plurality of second openings  468  may be approximately equal to each other. 
     The second ring  466  maybe rotatable relative to the first ring  462 , for example, in a scissor like motion, such that in a closed position of the valve  460  ( FIG. 8A ), the plurality of first openings  464  are misaligned with the plurality of second openings  468  such that the exhaust gas flows through the second filter  442 . In the open position shown in  FIG. 8B , the second ring  466  is rotated relative to the first ring  462  to move the valve  460  into the open position in which the plurality of first openings  464  are aligned with the plurality of second openings  468  such that a flow path is defined therethrough. More of the exhaust gas flows through the second filter  442  when the valve  460  is in the closed position than when the valve  460  is in the open position. In some embodiments, at least a portion of the exhaust gas flows through the plurality of first and second openings  464  and  468  and through the bypass conduit  445  around the second filter  442  in the open position of the valve  460 , thereby bypassing the second filter  442 . In various embodiments, an external rotational actuator with a cam may be used to provide six degrees of rotation to the second ring  466  relative to the first ring  462  for opening or closing of the valve  460 . The second ring  466  may be variably rotated relative to the first ring  462  to control the amount of exhaust gas flowing through the second filter  442  vs. the bypass conduit  445 . 
     While shown as including the first ring  462  and the second ring  466 , in other embodiments, the valve  460  may include more than two rings, for example, three rings or four rings each having predetermined space therebetween. With two rings, the valve  460  may have a 50% open frontal area. In a three ring arrangement, two of the rings may be rotatable relative to a third stationary and may be able to provide up to 66% open frontal area. Similarly, in a four ring arrangement, at least two of rings may be rotatable such that the valve may be able to provide up to 75% open frontal area. 
       FIG. 9  is a schematic illustration of an aftertreatment system  500 , according to an embodiment. The aftertreatment system  500  is configured to receive an exhaust gas from an engine (e.g., a diesel engine, a gasoline engine, a natural gas engine, a dual fuel engine, a biodiesel engine, an E-85 engine, or any other suitable engine) and reduce constituents of the exhaust gas such as, for example, NOx gases, CO, hydrocarbons, etc. The aftertreatment system  500  may comprise a housing  501 , the first filter  140 , the SCR system  150  disposed downstream of the first filter  140 , a second filter  542  disposed downstream of the SCR system  150 , and the controller  370 , as previously described herein with respect. In other embodiments, the second filter  442  may be disposed upstream of the SCR system  150  and downstream of the first filter  140 . In some embodiments, the aftertreatment system  500  may also include the oxidation catalyst  130  disposed upstream of the first filter  140 . Furthermore, an ammonia slip catalyst may be disposed downstream of the SCR system  150 . 
     The housing  501  includes an inlet conduit  502  having the first sensor  103  disposed therein, and an outlet conduit  504  having the second sensor  105  disposed therein. A reductant injector  582  may be disposed upstream of the SCR system  150  and configured to insert reductant into the exhaust gas. In some embodiments, the aftertreatment system  500  may also include a mixer  580  disposed upstream of the SCR system  150  and configured to facilitate mixing of the reductant with the exhaust gas. A plurality of temperature sensors T 1 , T 2 , T 3 , T 4  and T 5  may be disposed at various locations along the housing  501  and configured to measure the temperature of the exhaust gas at the respective locations. The first pressure sensor  348  may be operatively coupled to the first filter  140  and configured to determine a pressure drop thereacross, as previously described herein. 
     The second filter  542  is disposed downstream of the SCR system  150 . The second filter  542  may have a smaller pore size and, therefore a higher filtration efficiency than the first filter  140 , and may be similar in function to the second filter  142 ,  442 . The second filter  542  defines a bypass conduit  545  therethrough, for example, through a longitudinal axis thereof. A valve  544  (e.g., a butterfly valve) is disposed in the bypass conduit  545  and moveable between an open position and a closed position. For example, the controller  370  may be configured to instruct the valve  544  to move into a closed position in response a high PM operating condition of the engine, when the first filtration efficiency of the first filter  140  is below the first filtration efficiency threshold and/or if a pressure drop across the second filter  542  is below a predetermined pressure drop threshold. In response to a low PM engine operating condition, or a first filtration efficiency of the first filter  140  reaching the first filtration efficiency threshold, the controller  370  may be configured to open the valve  544  causing at least a portion of the exhaust gas to flow through the bypass conduit  545  defined through the second filter  542  so as to reduce back pressure on the exhaust gas and increase fuel economy, as previously described herein. 
       FIG. 10  is a plot of overall filtration efficiency vs. time of an aftertreatment system coupled to an engine operating at high engine load. The aftertreatment system includes a first filter having a first filtration efficiency and a second filter having a second filtration efficiency greater than the first filtration efficiency. The second filter is positioned downstream of the first filter. For example, the first filter may be a new filter or a recently regenerated filter and the first filtration efficiency may be lower than a first filtration efficiency threshold which does not provide sufficient filtration efficiency to meet a particle emissions standard desirable from the aftertreatment system. 
     The aftertreatment system also includes a bypass conduit (e.g., bypass conduit  345 ,  445 ,  545 ) having a valve (e.g., the valve  344 ,  460 ,  544 ) disposed thereon, and configured to allow at least a portion of the exhaust gas to bypass the second filter when the valve is open. As shown in  FIG. 10 , when the valve is open such that the exhaust gas or a large portion of the exhaust gas bypasses the second filter, the overall filtration efficiency of the aftertreatment system is about 50% corresponding to the first filtration efficiency, which may be below a desired filtration efficiency from the aftertreatment system. In contrast, when the valve is closed, a large portion or substantially all of the exhaust gas is forced to flow through the second filter. In this configuration, the overall filtration efficiency of the aftertreatment system is about 100% corresponding to the filtration efficiency of each of the first and second filters, as previously described herein. This shows that including the second filter in the aftertreatment system may selectively increase the filtration efficiency of the aftertreatment system by closing the valve, and may selectively increase a fuel economy of the engine by opening the valve to reduce a backpressure on the exhaust gas, as previously described herein. 
       FIGS. 11A-11B  are schematic flow diagrams of a method  600  for controlling filtration efficiency and fuel economy of an aftertreatment system, according to an embodiment. The aftertreatment system (e.g., the aftertreatment system  300 ,  400 ,  500 ) may include a first filter (e.g., the first filter), a second filter (e.g., the second filter  142 ,  442 ,  542 ) positioned downstream of the first filter, a bypass conduit (e.g., the bypass conduit  345 ,  445 ,  545 ) fluidly coupling an exhaust gas flow path downstream of the first filter and upstream of the second filter to an exhaust gas flow path downstream of the second filter and a valve (e.g., the valve  344 ,  460 ,  544 ) operatively coupled to the bypass conduit. In various embodiments, the aftertreatment system may also include a SCR system (e.g., the SCR system  150 ) positioned upstream or downstream of the second filter. 
     The method  600  includes determining an operating condition of the engine, at  602 . For example, the controller  370  may be configured to receive a signal from the engine, the first sensor  103 , the second sensor  105 , the pressure sensor  346  or the first pressure sensor  348  to determine the operating condition of the engine. At  604 , it is determined if the engine is operating under a high PM operating condition. In response, to the engine operating under the high PM operating condition ( 604 :YES) (or otherwise if a high filtration efficiency is desired), the valve is opened a first predetermined amount, at  606  such that the valve is more closed than open so as to cause a larger portion of the exhaust gas to flow through the second filter than the bypass conduit and provide high filtration efficiency. For example, the controller  370  may be configured to cause the valve  344 ,  460 ,  544  to slightly open or be substantially closed so as to cause a larger portion of the exhaust gas (e.g., substantially all of the exhaust gas) to flow through the second filter, therefore providing high filtration efficiency. 
     In response to the engine operating under a low PM operating condition ( 604 :NO) (or otherwise, if high fuel economy is desired), the valve is opened a second predetermined amount, at  608  such that the valve is more open than closed so as to cause a larger portion of the exhaust gas to flow through the bypass conduit and provide high fuel economy. For example, the controller  370  may cause the valve  344 ,  460 ,  544  to open a large degree, for example, completely open so as to allow a larger portion of the exhaust gas (e.g., substantially all of the exhaust gas) to bypass the second filter (e.g., the second filter  142 ,  442 ,  542 ) via the bypass conduit (e.g., the bypass conduit  345 ,  445 ,  545 ), therefore reducing backpressure on the exhaust gas and providing high fuel economy. 
     In some embodiments, the method  600  also includes determining a first filtration efficiency of the first filter, at  610 . For example, the controller  370  may determine a first pressure drop across the first filter  140 , determine a flow rate of the exhaust gas, and determines the first filtration efficiency of the first filter  140  based on a pressure drop across the first filter and an exhaust flow rate, as previously described herein. 
     At  612 , it is determined if the first filtration efficiency exceeds a predetermined filtration efficiency threshold, for example, determined by the controller  370 . If the first filtration efficiency is less than the predetermined filtration efficiency threshold ( 612 :NO), for example, corresponding to a desired filtration efficiency of the aftertreatment system, the method  600  returns to operation  610 . In response to the first filtration efficiency exceeding the predetermined filtration efficiency threshold, the valve is opened a predetermined amount, at  614 , for example, completely opened to allow at least a portion or substantially all of the exhaust gas to bypass the second filter via the bypass conduit. This reduces backpressure on the exhaust gas and increases fuel economy, while providing the desired filtration efficiency via the first filter. 
     In some embodiments, the method  600  also includes determining a pressure drop across the second filter, at  616 . For example, the controller  370  may interpret a signal from the pressure sensor  346  to determine a pressure drop across the second filter. At  618 , it is determined if the pressure drop exceeds a pressure drop threshold. The pressure drop may correlate to an amount of clogging corresponding to an amount of back pressure exerted on the exhaust gas. If the pressure drop is less than the pressure drop threshold ( 618 :NO), the method returns to operation  616 . In response to the pressure drop being greater than the predetermined threshold (e.g., corresponding to the exhaust gas back pressure being too high), the valve is opened (e.g. by the controller  370 ) to allow at least a portion of the exhaust gas to bypass the second filter via the bypass conduit so as to decrease a back pressure on the exhaust gas. 
     In some embodiments, the method  600  also comprises determining a temperature of the exhaust gas proximate to an inlet of the second filter, at  622 . For example, the controller  370  may be configured to receive a temperature signal from the temperature sensor  341  and interpret the temperature signal to determine the temperature of the exhaust gas at the inlet of the second filter. At  624 , it is determined if the temperature exceeds a predetermined temperature threshold. If the temperature is lower than the predetermined temperature threshold, the method  600  returns to operation  622 . In response to the temperature of the exhaust gas being above or greater than the predetermined temperature threshold, the valve is closed so as to force hot exhaust gas to flow through the second filter for regenerating the filter. For example, the controller  370  may be configured to close the valve  344 ,  460 ,  544  to force the exhaust gas through the second filter  142 ,  442 ,  542  so as to regenerate the second filter. In some embodiments, in which the aftertreatment system includes a hydrocarbon insertion assembly (e.g., the hydrocarbon insertion assembly  122 ) the method may also include inserting hydrocarbons into an oxidation catalyst (e.g., the oxidation catalyst  130 ) for raising the temperature of the exhaust gas above the predetermined temperature threshold. 
     In some embodiments, the controller  370 , the control circuitry  371 , or any of the controller or control circuitries described herein may comprise a system computer of an apparatus or system which comprises the aftertreatment system  300 ,  400 ,  500  (e.g., a vehicle, an engine or generator set, etc.). For example,  FIG. 12  is a block diagram of a computing device  730  in accordance with an illustrative implementation. The computing device  730  can be used to perform any of the methods or the processes described herein, for example, the method  200 , or  600 . In some embodiments, the controller  370  may comprise the computing device  730 . The computing device  730  comprises a bus  732  or other communication component for communicating information. The computing device  730  can also comprise one or more processors  734  or processing circuits coupled to the bus  732  for processing information. 
     The computing device  730  also comprises main memory  736 , such as a random access memory (RAM) or other dynamic storage device, coupled to the bus  732  for storing information and instructions to be executed by the processor  734 . Main memory  736  can also be used for storing position information, temporary variables, or other intermediate information during execution of instructions by the processor  734 . The computing device  730  may further comprise ROM  738  or other static storage device coupled to the bus  732  for storing static information and instructions for the processor  734 . A storage device  740 , such as a solid-state device, magnetic disk or optical disk, is coupled to the bus  732  for persistently storing information and instructions. For example, instructions corresponding operations of the method  200 ,  600  can be stored on the storage device  740 . The computing device  730  may be coupled via the bus  732  to a display  744 , such as a liquid crystal display or active matrix display, for displaying information to a user. An input device  742 , such as a keyboard or alphanumeric pad, may be coupled to the bus  732  for communicating information and command selections to the processor  734 . 
     According to various implementations, the methods described herein can be implemented by the computing device  730  in response to the processor  734  executing an arrangement of instructions contained in main memory  736  (e.g., the operations of the method  200 ). Such instructions can be read into main memory  736  from another non-transitory computer-readable medium, such as the storage device  740 . Execution of the arrangement of instructions contained in main memory  736  causes the computing device  730  to perform the illustrative processes described herein. One or more processors in a multi-processing arrangement may also be employed to execute the instructions contained in main memory  736 . In alternative implementations, hard-wired circuitry may be used in place of or in combination with software instructions to effect illustrative implementations. Thus, implementations are not limited to any specific combination of hardware and software. 
     Although an example computing device has been described in  FIG. 12 , implementations described in this specification can be implemented in other types of digital electronic, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. 
     Implementations described in this specification can be implemented in digital electronic, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. The implementations described in this specification can be implemented as one or more computer programs (i.e., one or more circuitries of computer program instructions) encoded on one or more computer storage media for execution by, or to control the operation of, data processing apparatus. A computer storage medium comprises a non-transitory computer readable medium and can be, or be included in, a computer-readable storage device, a computer-readable storage substrate, a random or serial access memory array or device, or a combination of one or more of them. Moreover, while a computer storage medium is not a propagated signal, a computer storage medium can be a source or destination of computer program instructions encoded in an artificially-generated propagated signal. The computer storage medium can also be, or be included in, one or more separate components or media (e.g., multiple disks, or other storage devices). Accordingly, the computer storage medium is both tangible and non-transitory. 
     The operations described in this specification can be performed by a data processing apparatus on data stored on one or more computer-readable storage devices or received from other sources. The term “data processing apparatus” or “computing device” encompasses all kinds of apparatus, devices, and machines for processing data, including, by way of example, a programmable processor, a computer, a system on a chip, or multiple ones, or combinations of the foregoing. The apparatus can comprise special purpose logic, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit). In addition to hardware, the apparatus can also comprise code that creates an execution environment for the computer program in question (e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, a cross-platform runtime environment, a virtual machine, or a combination of one or more of them). The apparatus and execution environment can realize various different computing model infrastructures, such as web services, distributed computing and grid computing infrastructures. 
     A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand-alone program or as a circuitry, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more circuitries, sub-programs, or portions of code). A computer program can be deployed to be executed on one computer, on multiple computers that are located at one site, or distributed across multiple sites and interconnected by a communication network. 
     Processors suitable for the execution of a computer program comprise, by way of example, both general and special purpose microprocessors and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for performing actions in accordance with instructions and one or more memory devices for storing instructions and data. Generally, a computer will also comprise, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data (e.g., magnetic, or flash drives). However, a computer need not have such devices. Devices suitable for storing computer program instructions and data comprise all forms of non-volatile memory, media and memory devices, including, by way of example, semiconductor memory devices (e.g., EPROM, EEPROM, and flash memory devices) or magnetic disks (e.g., internal hard disks or removable disks). The processor and the memory can be supplemented by, or incorporated in, special purpose logic. 
     It should be noted that the term “example” as used herein to describe various embodiments is intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such term is not intended to connote that such embodiments are necessarily extraordinary or superlative examples). 
     As utilized herein, the terms “substantially’ and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise arrangements and/or numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the inventions as recited in the appended claims. 
     As used herein, the term “approximately” generally mean plus or minus 10% of the stated value. For example, about 0.5 would include 0.45 and 0.55, about 10 would include 9 to 11, about 1000 would include 900 to 1100. 
     The term “coupled” and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another. 
     It is important to note that the construction and arrangement of the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements; values of parameters, mounting arrangements; use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. Additionally, it should be understood that features from one embodiment disclosed herein may be combined with features of other embodiments disclosed herein as one of ordinary skill in the art would understand. Other substitutions, modifications, changes, and omissions may also be made in the design, operating conditions, and arrangement of the various exemplary embodiments without departing from the scope of the present embodiments. 
     While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any embodiments or of what may be claimed, but rather as descriptions of features specific to particular implementations of particular embodiments. Certain features described in this specification in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various features described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.