Hydrocarbon adsorber regeneration system

A regeneration system includes a first module, a mode selection module and an adsorber regeneration control (ARC) module. The first module monitors at least one of (i) a temperature of a first catalyst of a catalyst assembly in an exhaust system of an engine and (ii) an active catalyst volume of the first catalyst. The mode selection module is configured to select an adsorber regeneration mode and generates a mode signal based on the at least one of the temperature and the active catalyst volume. The ARC module at least one of activates an air pump and cranks the engine to regenerate an adsorber of the catalyst assembly while the engine is deactivated based on the mode signal.

FIELD

The present disclosure relates to hydrocarbon adsorbers of an exhaust system.

BACKGROUND

Catalytic converters are used in an exhaust system of an internal combustion engine (ICE) to reduce emissions. For example, a thee-way catalyst converter (TWC) reduces nitrogen oxide, carbon monoxide and hydrocarbons within an exhaust system. The three-way catalyst converter: converts nitrogen oxide to nitrogen and oxygen; converts carbon monoxide to carbon dioxide; and oxidizes unburnt hydrocarbons (HC) to produce carbon dioxide and water.

An average catalyst light-off temperature at which a catalytic converter typically begins to function is approximately 200-350° C. As a result, a catalytic converter does not function or provides minimal emission reduction during a warm up period that occurs upon a cold start up of an engine. Exhaust system temperatures are less than the catalyst light-off temperature during an engine cold start. During the warm up period, HC emissions may not be effectively processed by the catalytic converter.

A hydrocarbon adsorber may be used to trap HC during the warm up period. Hydrocarbon adsorbers typically trap HC when at a temperature approximately less than 200° C. and release trapped hydrocarbons at temperatures greater than or equal to approximately 200° C.

During certain driving cycles, such as start/stop applications (short engine operation periods) and short trips, hydrocarbon adsorber regeneration time may be limited. For this reason, regeneration of a hydrocarbon adsorber may not be completed, which can cause low temperature fouling of the hydrocarbon adsorber. This degrades emission performance during, for example, an engine cold start.

SUMMARY

A regeneration system is provided and includes a first module, a mode selection module and an adsorber regeneration control (ARC) module. The first module monitors at least one of (i) a temperature of a first catalyst of a catalyst assembly in an exhaust system of an engine and (ii) an active catalyst volume of the first catalyst. The mode selection module is configured to select an adsorber regeneration mode and generates a mode signal based on the at least one of the temperature and the active catalyst volume. The ARC module at least one of activates an air pump and cranks the engine to regenerate an adsorber of the catalyst assembly while the engine is deactivated based on the mode signal.

In other features, a method of operating a regeneration system includes monitoring at least one of (i) a temperature of a catalyst of a catalyst assembly in an exhaust system of an engine and (ii) an active catalyst volume of the catalyst. An adsorber regeneration mode is selected and a mode signal is generated based on the at least one of the temperature and the active catalyst volume. An air pump is activated and/or the engine is cranked to regenerate an adsorber of the catalyst assembly while the engine is deactivated based on the mode signal.

In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a tangible computer readable medium such as but not limited to memory, nonvolatile data storage, and/or other suitable tangible storage mediums.

DETAILED DESCRIPTION

As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, and/or a combinational logic circuit.

InFIG. 1, an exemplary engine system10that includes an adsorber regeneration system12is shown. The engine system10includes an engine14with an exhaust system16. The exhaust system16includes a close coupled catalyst or catalytic converter (CC)18and an adsorber (e.g., HC adsorber) and catalyst (underfloor) assembly19. The adsorber regeneration system12regenerates an adsorber of the underfloor assembly19. Example adsorbers are shown inFIGS. 2-5. Although the engine system10is shown as a spark ignition engine, the engine system10is provided as an example. The adsorber regeneration system12may be implemented on various other engine systems, such as gasoline engine systems and diesel engine systems. The gasoline engine systems may be alcohol-based, such as methanol, ethanol, and E85 based engine systems.

The engine system10includes the engine14that combusts an air and fuel mixture to produce drive torque. Air enters the engine14by passing through an air filter20. Air passes through the air filter20and may be drawn into a turbocharger22. The turbocharger22when included compresses the fresh air. The greater the compression, the greater the output of the engine14. The compressed air passes through an air cooler24when included before entering an intake manifold26.

Air within the intake manifold26is distributed into cylinders28. Fuel is injected into the cylinders28by fuel injectors30. Spark plugs32ignite air/fuel mixtures in the cylinders28. Combustion of the air/fuel mixtures creates exhaust. The exhaust exits the cylinders28into the exhaust system16.

The adsorber regeneration system12includes the exhaust system16and an engine control module (ECM)40. The exhaust system16includes the CC18, the underfloor assembly19, the ECM40, the exhaust manifold42, and may include an air pump46. As an example, the CC18may include a three-way catalyst (TWC). The CC18may reduce nitrogen oxides NOx, oxidizes carbon monoxide (CO) and oxidizes unburnt hydrocarbons (HC) and volatile organic compounds. The CC18oxidizes the exhaust based on a post combustion air/fuel ratio. The amount of oxidation increases the temperature of the exhaust. The ECM40includes an adsorber regeneration control (ARC) module48, which controls regeneration of the adsorber.

Optionally, an EGR valve (not shown) re-circulates a portion of the exhaust back into the intake manifold26. The remainder of the exhaust is directed into the turbocharger22to drive a turbine. The turbine facilitates the compression of the fresh air received from the air filter20. Exhaust flows from the turbocharger22to the CC18.

The adsorber regeneration system12may operate in an active adsorber regeneration mode, a passive adsorber regeneration mode, or a non-adsorber regeneration mode. The active adsorber regeneration mode refers to regeneration of the adsorber when the engine14is deactivated or OFF. During active adsorber regeneration mode, the temperature of the adsorber is increased to be greater than or equal to a regeneration temperature (e.g., 200° C.). This allows trapped HC to be released from the adsorber. The engine may be OFF when, for example, the engine speed is equal to 0 meters per second (m/s), fuel to the engine is disabled, and/or spark is disabled. During the active adsorber regeneration mode the adsorber may be regenerated by operating in an air pumping mode. The air pumping mode may include activation of the air pump46and/or cranking of the engine14. The engine14may be used as an air pump to inject air into the exhaust system16when, for example, fuel and spark of the engine14is disabled.

The passive adsorber regeneration mode refers to regeneration of the adsorber when the engine14is activated or ON. The passive adsorber regeneration mode may be performed, for example, after a cold start period. The adsorber regeneration system12operates in a non-adsorber regeneration mode (i.e. the adsorber is not being regenerated) during the cold start period. The cold start period refers to a period upon activation of the engine14when temperature of the engine14is less than a predetermined temperature. During the cold start period temperatures of the catalyst(s) of the exhaust system16, such as catalysts of the CC18and/or the underfloor assembly19, are increased to at least a light-off temperature. During the cold start period, the adsorber is trapping HC. During the passive adsorber regeneration mode, temperature of the adsorber is greater than or equal to the regeneration temperature.

The engine system10may be a hybrid electric vehicle system and include a hybrid control module (HCM)60and one or more electric motor(s)62. The HCM60may be part of the ECM40or may be a stand alone control module, as shown. The HCM60controls operation of the electric motor(s)62. The electric motor(s)62may supplement and/or replace power output of the engine14. The electric motor(s)62may be used to adjust speed of the engine14(i.e. rotating speed of a crankshaft66of the engine14).

The ECM40and/or HCM60may control operation of the electric motor(s)62to maintain a current engine speed during an engine speed maintaining mode or to increase speed of the engine14during the air pumping mode. The electric motor(s)62may be connected to the engine14via a belt/pulley system, via a transmission, one or more clutches, and/or via other mechanical connecting devices. In one embodiment, the ECM40and/or HCM60activates (powers) the electric motor(s)62to prevent the crankshaft66from rotating during the engine speed maintaining mode (engine speed maintained at 0 revolutions per minute (RPM)). This may occur when vehicle speed is greater than 0 meters (m)/second (s). The ECM40and/or HCM60may control operation of the electric motor(s)62and/or starter64to rotate the crankshaft66during the air pumping mode. The ECM40and/or HCM60may deactivate or adjust operation of the electric motor(s)62to allow the crankshaft66to rotate when vehicle speed is greater than 0 m/s.

During the air pumping mode, air is pumped into the exhaust system16to heat the adsorber. The air pump46and/or the engine14may be used to pump air into the exhaust system16. The engine14is deactivated, but intake and exhaust valves of the engine14may be permitted to open and close. This allows air to be drawn into and pumped out of cylinders28. The air pump46pumps air into the exhaust system16upstream from the CC18. The air pump46may pump ambient air into the exhaust system16. The ambient air may be directed to the exhaust manifold42and/or exhaust valves of the engine14. Heated air that is upstream from the underfloor assembly19is directed through the underfloor assembly. This is performed to maintain the temperature of the absorber at a temperature greater than the regeneration temperature and/or to increase the temperature of the adsorber to be greater than or equal to the regeneration temperature.

The ECM40and/or HCM60control the engine14, the adsorber regeneration system12, the air pump46, the electric motor(s)62, and the starter64based on sensor information. The sensor information may be obtained directly via sensors and/or indirectly via algorithms and tables stored in memory70. Some example sensors80for determining exhaust flow levels, exhaust temperature levels, exhaust pressure levels, catalyst temperatures, oxygen levels, intake air flow rates, intake air pressure, intake air temperature, vehicle speed, engine speed, EGR, etc are shown. Exhaust flow sensors82, exhaust temperature sensors83, exhaust pressure sensors85, catalyst temperature sensors86, oxygen sensors88, an EGR sensor90, an intake air flow sensor92, an intake air pressure sensor94, an intake air temperature sensor96, vehicle speed sensor98and an engine speed sensor99are shown. The ARC module48may control operation of the adsorber regeneration system12, the engine14, the air pump46, the electric motor(s)62, and the starter64based on the information from the sensors80.

The oxygen sensors88may include a pre-converter O2sensor100and post-converter O2sensor102. The pre-converter O2sensor100may be connected to a first exhaust conduit103and upstream from the CC18. The post-converter O2sensor102may be connected to a second exhaust conduit105and downstream from the CC18. The pre-converter O2sensor100communicates with the ECM40and measures the O2content of the exhaust stream entering the CC18. The post-converter O2sensor102communicates with the ECM40and measures the O2content of the exhaust stream exiting the CC18. The primary and secondary O2signals are indicative of O2levels in the exhaust system16before and after the CC18. The O2sensors100,102generate respective primary and secondary O2signals that are feedback to the ECM40for closed loop control of air/fuel ratio(s).

As an example, the primary and secondary O2signals are weighted and a commanded air/fuel ratio is generated based, for example, 80% on the primary O2signal and 20% on the secondary O2signal. In another embodiment, the secondary O2signal is used to adjust a commanded air/fuel ratio that is generated based on the primary O2signal. The primary O2signal may be used for rough adjustment of an air/fuel ratio and the secondary O2signal may be used for fine adjustment of the air/fuel ratio. The ECM40adjusts fuel flow, throttle positioning, and spark timing based on the primary and secondary O2signals to regulate air/fuel ratio(s) in cylinders of the engine14.

The ARC module48may monitor signals from the oxygen sensors88. The ARC module48may, for example, adjust operation of the air pump46, the electric motor(s)62, and/or the starter64during the air pumping mode based on the signals from the oxygen sensors88.

Referring now also toFIG. 2, a functional block diagram of another engine system10′ is shown. The engine system10′ may be part of the engine system10. The engine system10′ includes the engine14, an adsorber regeneration system12′, an exhaust system16′, and an ECM40′. In the example shown, the exhaust system16′ includes in the following order: an exhaust manifold42′, a first exhaust conduit126, the CC18, a second exhaust conduit128, and an underfloor assembly130.

The adsorber regeneration system12′ includes the engine14, the CC18, an underfloor assembly19′, the air pump46, the ARC module48, and/or the starter64. The catalyst heating system12′ may also include exhaust flow, pressure and/or temperature sensors104,106,108,110. The first exhaust flow, pressure and/or temperature sensor104may be connected to a first exhaust conduit126and upstream from the CC18. The second exhaust flow, pressure and/or temperature sensor108may be connected to the CC18. The third exhaust flow, pressure and/or temperature sensor106may be connected to a second exhaust conduit128that is downstream from the CC18. The fourth exhaust flow, pressure and/or temperature sensor110may be connected to a third exhaust conduit130that is downstream from the underfloor assembly19′.

The underfloor assembly19′ may include an adsorber132, a catalyst134, such as a three-way catalyst, and a bypass valve136. The adsorber132may be a HC adsorber and include, for example, zeolite material. The catalyst134oxides CO remaining in the exhaust received from the CC18and the adsorber132to generate CO2. The catalyst134may also reduce nitrogen oxides NOx and oxidize unburnt HC and volatile organic compounds.

The ECM40′ and/or ARC module48controls position of the bypass valve136based on the mode of operation. For example, the bypass valve136may be in a partially or fully open position during the passive adsorber regeneration mode. As another example, the bypass valve136may be in a fully closed or nearly fully closed position (e.g., 95% closed) during the active adsorber regeneration mode. The bypass valve136may also be in the fully closed or nearly fully closed position (e.g., 95% closed) during the cold start period.

The ECM40′ may include an ARC module48. The ARC module48controls operation of the adsorber regeneration system12′ based on information from the sensors104-110and/or sensors80.

Referring now also toFIGS. 3-5, an example of the underfloor assembly19(engine exhaust gas treatment device) is shown. The underfloor assembly19may include a housing144, an adsorber146(e.g., a HC adsorber), an adsorber bypass conduit148, a catalyst member150, and a bypass valve assembly152. The housing144may define an exhaust gas inlet154and an exhaust gas outlet156and may include a nozzle158at the exhaust gas inlet154. The adsorber146may be located within the housing144between the exhaust gas inlet154and an exhaust gas outlet156forming a first flow path between the exhaust gas inlet154and the exhaust gas outlet156. As an example, the adsorber146may be formed from a zeolite material. The zeolite material may be used for treatment of alcohol-based fuel emissions, such as methanol emissions, ethanol emissions, E85 emissions, etc. The catalyst member150may include a three-way catalyst.

The adsorber bypass conduit148may extend through the adsorber146and define an adsorber bypass passage160. The adsorber bypass passage160defines a second flow path between the exhaust gas inlet154and the exhaust gas outlet156parallel to the first flow path defined through the adsorber146.

The catalyst member150may be located between the hydrocarbon adsorber146and the adsorber bypass conduit148and the exhaust gas outlet156. The catalyst member150may receive exhaust gas exiting the adsorber146and/or the adsorber bypass conduit48depending on the position of the bypass valve assembly152as discussed below.

The bypass valve assembly152may include a bypass valve162located in the adsorber bypass passage160and an electric actuation mechanism164engaged with the bypass valve162to displace the bypass valve162between a closed position (shown inFIG. 3) and an open position (shown inFIG. 2). The bypass valve162enables passage of exhaust through the absorber bypass passage160between the exhaust gas inlet154and the exhaust gas outlet156. The bypass valve162enables this passage when in the open position and inhibits (or prevents) communication between the exhaust gas inlet154and the exhaust gas outlet156when in the closed position. The bypass valve assembly152may also include a bypass valve sensor that detects position of the bypass valve162. This information may be feedback to the ECM40and/or the ARC module48for position control of the bypass valve162.

The nozzle158may form a converging nozzle including a nozzle outlet166defining a first inner diameter (D1). The nozzle outlet166may be located adjacent to an inlet168of the adsorber bypass passage160defined at an end170of the adsorber bypass conduit148. The nozzle outlet166may be concentrically aligned with the inlet68of the adsorber bypass passage160.

The inlet168of the adsorber bypass passage160may define a second inner diameter (D2). The first inner diameter (D1) may be less than the second inner diameter (D2). As an example, the first inner diameter (D1) may be eighty percent to ninety-nine percent of the second inner diameter (D2). The nozzle outlet166may also be axially spaced a distance (L) from the inlet168of the adsorber bypass passage160. In the example shown, the nozzle outlet166is axially spaced less than 10 millimeters from the inlet168of the adsorber bypass passage60. The difference between the first and second inner diameters (D1, D2) and/or distance (L) may define a spacing between the nozzle outlet166and the inlet168of the adsorber bypass passage160.

The end170of the adsorber bypass conduit148defining the inlet168may extend axially outward from the adsorber146in a direction from the exhaust gas outlet156toward the exhaust gas inlet154. The housing144may define an annular chamber172surrounding the adsorber bypass conduit148at a location axially between the inlet168of the adsorber bypass passage160and the hydrocarbon adsorber146. The annular chamber172may be in communication with the exhaust gas inlet154through the spacing defined between the nozzle outlet166and the inlet168of the adsorber bypass passage160.

The exhaust gas from the engine14may flow through the adsorber146in a first direction (A1) from the exhaust gas inlet154to the exhaust gas outlet156when the bypass valve62is in the closed position. The exhaust gas may flow from the exhaust gas inlet154through the adsorber46to the catalyst member150and out the exhaust gas outlet156. The housing144may include a diffuser174between the hydrocarbon adsorber146and the catalyst member150and define openings176. The openings176may be used to control exhaust flow rate through the adsorber146.

The exhaust gas may bypass the adsorber146when the adsorber bypass passage160is open and proceed to the catalyst member150. For example only, approximately 5-10% of the exhaust may flow through the adsorber when the adsorber bypass passage160is open (i.e. the bypass valve162is in the open position). A portion of the exhaust gas provided by the engine14may flow through the adsorber146in a reverse direction (discussed below) to purge HC stored within the adsorber146when the adsorber bypass passage160is open.

The exhaust gas may flow through the adsorber146in a second direction (A2) opposite the first direction (A1) and from the exhaust gas outlet156to the exhaust gas inlet154when the bypass valve162is in the open position. The exhaust gas flows through the adsorber bypass passage160in the first direction (A1) to the catalyst member150and out the exhaust gas outlet156. The exhaust gas may flow through the adsorber146in the second direction (A2) may be generated by the arrangement between the nozzle outlet166and the inlet168of the adsorber bypass conduit148. More specifically, the spacing between the nozzle outlet166and the inlet168of the adsorber bypass conduit148may create a localized low pressure region within the annular chamber172.

As a result, a portion of the exhaust gas may flow from a high pressure region of the housing144between the adsorber146and the catalyst member150through the adsorber146in the second direction (A2). The exhaust gas may flow to the adsorber bypass conduit148through the spacing defined between the nozzle outlet166and the inlet168of the adsorber bypass conduit148.

Referring again toFIGS. 1 and 2and toFIG. 6, where an ECM40″ is shown. The ECM40″ may be used in the absorber regeneration systems12,12′ ofFIGS. 1 and 2. The ECM40″ includes the ARC module48and may further include a vehicle speed module180and an engine speed module182. The vehicle speed module180determines speed of a vehicle based on information from, for example, the vehicle speed sensor98. The engine speed module182determines speed of the engine14based on information from, for example, the engine speed sensor99.

The ARC module48includes an engine monitoring module184, an underfloor catalyst monitoring module186, a first comparison module188, a second comparison module190, a mode selection module192, a bypass valve control module194, an air pumping module196and a regeneration monitoring module198. The ARC module48operates in the adsorber regeneration and non-adsorber regeneration modes. The ARC module48may operate in more than one of the modes during the same period.

Referring now also toFIG. 7, a method of operating an absorber regeneration system is shown. Although the method is described with respect to the embodiments ofFIGS. 1-6, the method may be applied to other embodiments of the present disclosure. The method may begin at200. Below-described tasks202-216are iteratively performed and may be performed by one of the ECMs40,40′,40″ ofFIGS. 1, 2 and 6.

At202, sensor signals are generated. The sensor signals may include exhaust flow signals, exhaust temperature signals, exhaust pressure signals, catalyst temperature signals, an oxygen signal, an intake air flow signal, an intake air pressure signal, an intake air temperature signal, a vehicle speed signal, an engine speed signal, an EGR signal, etc., which may be generated by the above-described sensors80and104-110ofFIGS. 1 and 2.

At204, the ARC module48and/or the engine monitoring module184determines whether the engine14is OFF. The engine monitoring module may generate an engine monitoring signal Engine based on the engine speed signal SENG, a fuel supply signal FUEL and/or an ignition enable signal SPARK. The engine monitoring signal Engine indicates state of the engine. The ARC module48proceeds to206when the engine is OFF, otherwise the ARC module returns to202.

At206, the ARC module48determines whether temperature TUFCATand/or active volume PVACTIVEof an underfloor catalyst of an underfloor catalyst assembly, such as one of the catalyst134,150, is greater than a predetermined value(s). The underfloor catalyst monitoring module186may estimate the temperature TUFCATand/or the active volume PVACTIVEusing a first thermal model and based on engine parameters and/or exhaust temperatures, some of which are described below with respect to equations 1 and 2. The underfloor catalyst monitoring module186may directly determine the temperature of the underfloor catalyst via a temperature sensor of the underfloor catalyst. The first thermal model may include equations, such as equations 1 and 2.

FRateis exhaust flow rate through the CC18, which may be a function of mass air flow and fuel quantity supplied to the cylinders28. The mass air flow may be determined by a mass air flow sensor, such as the intake air flow sensor92. SENGis speed of the engine14(i.e. rotational speed of the crankshaft66). DC is duty cycle of the engine. CMassis mass of the underfloor catalyst. CIMPis resistance or impedance of the underfloor catalyst. ERunTimeis time that the engine14is activated (ON). ELoadis current load on the engine14. TEXHmay refer to a temperature of the exhaust system, and based on one or more of the temperature sensors104-110. Tambis ambient temperature. CAM is cam phasing of the engine14. SPK is spark timing. The temperature signals and the active catalyst volume signal PVACTIVEmay be based on one or more of the engine system parameters provided in equations 1 and 2 and/or other engine system parameters, such as mass of the underfloor catalyst CMass.

The first comparison module188may generate a first comparison signal COMP1based on the temperature TUFCATand a catalyst light-off temperature TCLO(e.g., 250° C.). The second comparison module190may generate a second comparison signal COMP2based on the active catalyst volume PVACTIVEand a predetermined active catalyst volume PVOXID. The predetermined active catalyst volume PVOXIDmay be, for example, 30-40% of the volume of the underfloor catalyst. The mode selection module192generates a mode signal MODE based on the first and second comparison signals COMP1, COMP2, the engine monitoring signal Engine, the regeneration complete signal REGCOMP, the speed of the vehicle SVEHand/or the engine speed SENG.

The ARC module48and/or the mode selection module192proceeds to208when one or both of the comparison signals COMP1, COMP2is, for example, HIGH. This indicates that temperature and/or active volume of the underfloor catalyst is at or greater than a predetermined level for oxidation of HC released from an absorber of the underfloor catalyst assembly. Otherwise, the ARC module48may return to202.

At208, the bypass valve control module194closes an adsorber bypass valve, such as one of the bypass valves136,162. This initiates the air pumping mode. The bypass valve may be fully closed. The bypass valve control module194generates a bypass control signal BVCONT and an air pump enable signal based on the mode signal MODE.

At210, the air pumping module196generates an air pumping signal AIRPUMP and/or an engine pump signal ENGPUMP based on the mode signal MODE and the pump enable signal PUMPENABLE. The air pumping signal AIRPUMP is generated to activate an air pump, such as the air pump46, to inject ambient air into the exhaust system. The engine pump signal ENGPUMP is generated to crank the engine to inject air from the engine into the exhaust system.

The pumping of air into the exhaust system leverages thermal energy in the engine, the close-coupled catalyst and/or other components of the exhaust system to regenerate the adsorber. The injected air is heated by the engine and exhaust system components and passed through the adsorber. This increases temperature of the adsorber to a temperature that is greater than a regeneration temperature. The adsorber than releases trapped HC, which is then oxidized by the underfloor catalyst. The temperature of the adsorber is maintained above, for example, 200° C. (regeneration temperature) during regeneration. During adsorber regeneration, temperature of the underfloor catalyst is greater than or equal to the light-off temperature due to previous engine operation. Task208may be performed while task210is performed.

At212, the ARC module48determines whether regeneration of the adsorber is complete. The ARC module48may determine if regeneration is complete based on a thermal energy model of the adsorber and/or the underfloor catalyst using, for example, equation 3.

AMassis mass of the adsorber. AIMPis resistance or impedance of the Adsorber. Rtimeis the amount of time that the ARC module48is in the adsorber regeneration mode (current regeneration period). This may be measured via a regeneration timer199. The thermal energy model refers to the thermal energy received by the adsorber and/or underfloor catalyst. The thermal energy model may include other engine characteristics, close-coupled catalyst and/or underfloor catalyst characteristics, such as sizes and volumes of the engine, the close-coupled catalyst, the adsorber, and the underfloor catalyst. Regeneration may be complete when the thermal energy Energy is greater than a predetermined thermal energy for a predetermined period and/or when the regeneration timer199exceeds a predetermined period.

At214, the ARC module48and the air pumping module cease operating in the air pumping mode. The mode selection module192may generate the mode signal MODE to indicate operating in a shutdown mode. The air pump may be deactivated and the engine is no longer cranked to inject air into the exhaust system. At216, the bypass valve control module194adjusts position of the adsorber bypass valve to a shut down position. The shut down position may be a partially or fully open position.

The above-described method may end during any of tasks202-216when, for example, when: the engine14is activated; the temperature of the underfloor catalyst is less than the catalyst light-off temperature TCLO; and/or the active volume of the underfloor catalyst is less than the predetermined active volume PVOXID. Activation of the engine14may include activating spark and fuel of the engine14and deactivating the air pump46. The air pump46may be used for exothermic assistance when the engine14is activated to adjust temperature of a catalyst with minimal associated fuel consumption. The above-described tasks performed at202-216are meant to be illustrative examples; the tasks may be performed sequentially, synchronously, simultaneously, continuously, during overlapping time periods or in a different order depending upon the application.

The above-described embodiments provide HC adsorber regeneration when an engine is OFF. This prevents low temperature fouling or choking of the HC adsorber and can improve performance of an exhaust system and increase operating life of an adsorber.