DE102013008534A1 - Method for reducing e.g. hydrocarbon emissions from diesel engine of light duty vehicle during low exhaust gas temperature operation, involves treating released emissions with oxidation catalyst and nitrogen oxide reduction catalyst - Google Patents

Abstract

The method involves storing hydrocarbon and nitrogen oxide emissions from an internal combustion engine (20) during a low exhaust gas temperature operation in an exhaust gas flowpath (18) upstream of a nitrogen oxide reduction catalyst (16). The stored hydrocarbon and nitrogen oxide emissions are released into the exhaust gas flowpath when the exhaust temperature increases toward effective operating temperature, which is equal to 200 degree Celsius. The released hydrocarbon and nitrogen emissions are treated with an oxidation catalyst and the nitrogen oxide reduction catalyst. The oxidation catalyst is a hydrocarbon storage device catalyst. The nitrogen oxide reduction catalyst is a selective catalytic reduction catalyst. An independent claim is also included for a system for reducing nitrogen oxide and hydrocarbon emissions from an internal combustion engine during a low exhaust gas temperature operation.

Description

Cross-reference to related applications

The present application claims the effect of the filing date of provisional patent application No. 61/650722 filed on May 23, 2012, which is incorporated herein by reference.

background

The control of SCR (Selective Catalytic Reduction) catalysts is becoming increasingly important to meet modern combustion engine emission standards. The performance of a typical SCR catalyst in the removal of nitrogen oxide (NO _x) emissions is dependent on the exhaust gas temperature at the inlet of the SCR catalyst. Copper-exchanged zeolite-based SCR catalysts are formulated to operate satisfactorily over a fairly wide temperature range. However, current Cu zeolite compositions operate with maximum efficiency when exposed to exhaust gas temperatures of 200-400 ° C. For the certification of certain diesel engines, the emission behavior of the engine during the cold part of the certification cycle is weighted almost equally as the emission behavior of the engine during the hot part of the certification cycle. For this reason, improvements are desired which prevent slippage of hydrocarbon (HC) and NO _x emissions produced by the engine through the aftertreatment system at low exhaust temperature operating conditions, e.g. At temperatures less than 200 ° C.

Typical diesel exhaust aftertreatment systems include a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF) in addition to the SCR catalyst. The DOC is responsible for the oxidation of hydrocarbons (HC), carbon monoxide (CO) and nitrogen monoxide (NO). Similar to the SCR catalyst, the DOC is unable to effectively and efficiently oxidize these molecules at cold exhaust gas temperatures. In order to meet the NO _x and HC emission levels (eg, 0.02 and 0.01 g / mile, respectively, for Tier 2 Bin 2 federal certification) at low temperature conditions, improvements in the aftertreatment configuration are required to prevent slippage of these test contaminants through the exhaust gas flow path during low temperature operation. Therefore, further technical developments are desired in this field.

Brief description of the invention

One embodiment is a specific method and system for managing low temperature NO _x and HC emissions to improve NO _x conversion efficiency of diesel aftertreatment systems at low exhaust gas temperature conditions. In one embodiment, a multi-component treatment system is provided which passively operated HC and NO _x -Speichereinrichtungen for improved reduction of NO _x - comprising and HC emissions at low temperatures to achieve desired emissions for light duty vehicles, although applications with other vehicles not excluded are. The systems and methods reduce the need for external equipment designed to artificially increase the exhaust temperature during cold start cycles, which is advantageous because such external equipment tends to increase fuel economy and greenhouse gas emissions, although the use of such external equipment is not excluded. The systems and methods presented herein provide cost and fuel consumption reductions as compared to conventional thermal management strategies for reducing low temperature NO _x and HC emissions. Other embodiments, aspects, objects, features, advantages, aspects, and benefits will become apparent from the following description and drawings.

Brief description of the drawings

1 shows an exemplary system for reducing HC and NO _x emissions of an internal combustion engine at low exhaust temperature operating conditions;

2 shows a schematic view of a controller, which is part of the system 1 represents; and

3 FIG. 12 is a graph showing an estimated influence of hydrocarbon storage on HC slip as a function of time at low exhaust temperature operating conditions. FIG.

Description of the illustrative embodiments

For a better understanding of the principles of the invention, reference will now be made to the embodiments shown in the figures and technical terms will be used to describe the same. It is understood, however, that this is not a limitation of the scope of the invention, but that all changes and other modifications of the illustrated embodiments and any other Applications of the principles of the invention presented herein, which would normally occur to a person skilled in the art of the invention, are conceivable.

There are provided systems and methods for an internal combustion engine for reducing HC and NO _x emissions at low exhaust temperature operating conditions. The systems and methods reduce test pollutants at least at low exhaust gas temperature conditions. The described systems and methods are configured so that vehicles equipped therewith are operable to meet emissions standards at low exhaust temperature operating conditions without the need for external aftertreatment heating systems that increase vehicle fuel economy and greenhouse gas emissions, although the use of such external systems is not excluded. In one embodiment, the systems and methods are applicable to Light Duty Certified Chassis Vehicles, although applications for other types of vehicles are not excluded.

The systems and methods include an aftertreatment system architecture that is configured to cache HC emissions and NO _x emissions during low exhaust temperature operating periods, and then passively release the stored NO _x and HC emissions for aftertreatment as the exhaust gas temperature increases. The systems and methods are configured so that at temperatures at which HC and NO _x emissions are released, the Diesel Oxidation Catalyst (DOC) and SCR catalysts are effective to increase the HC and NO _x emissions released from the storage devices reduce before they exit the exhaust tailpipe.

In one embodiment the aftertreatment system to a direct-coupled HC-storage means (SDHC), which is located immediately downstream of the turbocharger, wherein a direct-coupled NO _x storing means (NSD) is arranged immediately downstream of the HC trap. At low exhaust gas temperatures, the HC storage device readily adsorbs and stores hydrocarbons (HC). In a specific embodiment, the HC storage device comprises a catalyst, such as a zeolite-based catalyst, for storing and adsorbing HC. As the exhaust gas temperature increases, the HC storage device effectively oxidizes gas phase hydrocarbons (HC) stored on the surface of the HC storage device to form H ₂ O and CO ₂ . The N-storage means is any suitable component, such as a NO _x adsorbent, which is capable of storing NO _x at low exhaust temperatures passively and then release the stored NO _x with increasing exhaust gas temperature. The N-type storage device may also have an oxidation function primarily for NO oxidation to NO ₂ , but under normal operating conditions will not be able to effectively reduce NO _x to N ₂ and H ₂ O. The N-type memory device relies on a downstream SCR (selective catalytic reduction) catalyst or other NO _x reduction catalyst to chemically reduce NO _x to N ₂ and H ₂ O.

In another embodiment, systems and methods for reducing the HC and NO _x emissions of lean burn internal combustion engines at low exhaust temperature operating conditions are disclosed. As in 1 includes an exemplary aftertreatment system 10 a directly coupled HC memory device (HCSD) 12 and an N-memory device (NSD) 14 with a downstream standard SCR or NAC NO _x reduction catalyst 16 for receiving by an internal combustion engine 20 generated exhaust gas in the exhaust gas flow path 18 , The HC memory device 12 and the N memory device 14 are passive devices that require little or no active control strategies, although the use of active tax strategies is not excluded.

At low exhaust gas temperatures that result in low catalyst temperatures, the HC storage device adsorbs and stores 12 willingly HC on the surface of a catalyst until the HC storage device 12 reaches a surface temperature at which it can effectively oxidize the stored HC to form CO ₂ and H ₂ O. The N memory device 14 It will readily adsorb and store NO _x on the surface of its catalyst under low exhaust gas temperature conditions and then begin to desorb this NO _x as the exhaust gas temperature, and hence the NSD catalyst temperature, increases. The N memory device 14 is configured to release the stored NO _x at an exhaust gas temperature at which the reduction catalyst 16 is highly effective to reduce NO _x to N ₂ and H ₂ O. After the aftertreatment system 10 has reached its operating temperature, the catalyst of the HC memory device 12 and / or the catalyst of the N-memory device 14 work as a DOC catalyst and are then jointly responsible for the oxidation of HC, CO and NO.

The system 10 can in addition to the in 1 components shown a control unit 100 and other aftertreatment components. For example, the system assigns 10 typically a reductant dosing device 17 on, which at a point upstream of the reduction catalyst 16 connected to the exhaust pipe. That in the exhaust gas flow path 18 Injected reducing agent is any reducing agent used in a NO _x reduction system. For example, the reducing agent may contain at least ammonia (gaseous or aqueous) and urea. The system 10 may also include a diesel particulate filter (DPF) connected to the HC storage device 12 and the N memory device 14 at engine operating conditions where the exhaust temperatures for a NO _x reduction by the reduction catalyst 16 are effective, upstream of the reduction catalyst 16 arranged DOC / DPF system forms. The system 10 may be downstream of the reduction catalyst 16 arranged ammonia oxidation catalyst (AMOX) have. In certain embodiments, the AMOX catalyst may not be present or the AMOX catalyst may be present with the reduction catalyst 16 (or with the last SCR catalyst, if multiple SCR catalysts are present) combined, for example, a washcoat coating on the rear portion of the reduction catalyst 16 is applied, which serves to at least partially oxidize ammonia. In other embodiments, any of these components may be present or absent, catalysed or non-catalysed, and arranged in a different order. In addition, certain components or all components may be arranged in the same or in separate housings.

In the system 10 with the control unit 100 can the controller 100 comprise a plurality of modules configured to functionally perform operations for controlling the SCR system. In certain embodiments, the controller forms a portion of a processing subsystem that includes one or more computing devices including storage, processing, and communication hardware. The control unit 100 may be a single device or a distributed device, and the functions of the controller may be performed by hardware or software. The control unit 100 can communicate with any sensor, actuator, network, and / or any data connection of the system.

In certain embodiments, such as in 2 illustrated, includes the controller 100 a NO _x determination module 102 , a temperature determination module 104 and a dosage control module 106 , The present description with modules highlights the structural independence of the aspects of the controller 100 and provides a grouping of processes and responsibilities of the controller 100 Within the scope of the present application, other groupings are possible that perform similar overall operations. Modules may be implemented as hardware and / or software on a computer-readable storage medium, and modules may be distributed over various hardware and software components. More detailed descriptions of certain embodiments of the controller's operations are included in the section that is incorporated herein by reference 2 Refers.

The exemplary system 10 also has various sensors. In the 1 The sensors shown include one upstream of the HC storage device 12 arranged first NO _x sensor 22 and a downstream of the reduction catalyst 16 arranged second NO _x sensor 24 , Alternatively or additionally, a NO _x sensor 38 at the outlet of the N memory device 14 or between the inlet to the reduction catalyst 16 and the outlet of the N memory device 14 be arranged. The system 10 also has a first temperature sensor 26 at the inlet of the HC storage device 12 , a second temperature sensor 28 between the HC memory device 12 and the N memory device 14 , a third temperature sensor 30 at the outlet of the N memory device 14 and a fourth temperature sensor 32 at the outlet of the reduction catalyst 16 on. Other sensors for measuring or determining the mass flow through the exhaust system, the temperature of any components of the aftertreatment system, in the reduction catalyst 16 stored or outputted amount of ammonia, etc. may be provided.

The illustrated sensors are merely exemplary and may be rearranged, removed, or replaced, and other sensors may be provided that are incorporated in FIG 1 are not shown. In addition, certain sensors may instead be virtual sensors coming from others in the system 10 instead, values displayed by sensors may instead be supplied via a data connection or network communication to a memory location of a computer-readable memory or to the system 10 be provided in another way if the sensor providing the sensed parameter is not part of the defined system 10 is.

The exemplary controller 100 in the 1 and 2 is configured to perform operations for providing a reductant dosing command for effectively removing NO _x emissions by means of the reduction catalyst 16 perform. The controller operations of the controller 100 in 2 include nominal value control operations for a NO _x post-treatment system using a reductant. Nominal value controls for a NO _x after-treatment system, such as an SCR aftertreatment system are well known in the art and will not be described further herein. Any nominal value controls for NO _x post-treatment may be made by the system described herein 10 be used.

The control unit 100 contains a NO _x determination module 102 , the NO _x parameter 108 of NO _x sensors 22 . 24 . 38 receives and one from the engine 20 or from the reduction catalyst 16 emitted NO _x amount determined. The control unit 100 may also be configured to control the amount of NO _x at the outlet of the N memory device 14 to determine or calculate. The control unit 100 further comprises a temperature determination module 104 , the temperature signals from temperature sensors 26 . 28 . 30 . 32 receives a temperature of the exhaust gas in the flow path 18 and / or the various catalysts of the after-treatment components in the flow path 18 to determine. The control unit 100 also has a dosage control module 106 put on a suitable dosing order for that in the flow path 18 to be injected reducing agent to desired NO _x emission levels at the outlet of the reduction catalyst 16 and finally get on the tailpipe.

During low temperature operating conditions for the engine 20 and for the exhaust gas and / or for the aftertreatment components in the flow path 18 is the reduction catalyst 16 for the treatment of NO _x emissions to achieve desired emission setpoints ineffective. In addition, conventional oxidation catalysts are upstream of the reduction catalyst 16 for removal of HC to achieve test emissions under low temperature operating conditions. Therefore, the HC memory device 12 configured to store HC at low exhaust temperature operating conditions, and the N memory device 14 configured to store NO _x at low exhaust temperature operating conditions until the temperature of the aftertreatment components of the system 10 has risen to a temperature that is suitable, the test pollutants from the emissions of the engine 20 to remove.

The low exhaust temperature operating conditions in the N-memory device 14 accumulated NO _x amount may be due to the difference between the through the upstream NO _x sensor 22 detected NO _x amount and by the downstream NO _x sensor 24 detected, corresponding and by the oxidation catalyst 16 amount converted during a low-temperature operation. The dosage control module 106 is configured to determine a dosing command that delays the reductant dosing at low temperature operating conditions because the NO _x sensor 24 NO _x values recorded due to NO _x storage by the N memory device 14 decreased or less than those by the NO _x sensor 22 certain values. As the exhaust gas temperature rises to an effective temperature or beyond, the dosing control module is 106 configured to increase the reductant dosing to that of the N-memory device 14 to treat released NO _x emissions by the NO _x sensor 38 and / or the NO _x sensor 24 or by a calculated or detected NO _x amount at the outlet of the N memory device 14 were determined. In addition, the dosing control module 106 be configured in certain embodiments, a future NO _x load and the timing of the release of the stored NO _x emissions by monitoring temperature parameters 110 predetermine. The reductant dosage amount may be increased prior to the release of NO _x emissions to obtain a sufficient amount of reductant on the reduction catalyst 16 which corresponds to the expected increased NO _x emissions.

The dosage control module 106 provides the reducing agent metering device 17 in response to a threshold deviation value 116 a reductant dosing command 114 , The threshold deviation value 116 includes a determination that NO _x emissions on the NO _x sensor 24 reach or meet a threshold deviation from an emission setpoint that requires it, the reduction catalyst 16 to supply a reducing agent. The one from the dosage control module 106 delivered reductant dosing command 114 may be a reduction catalyst 16 Include reductant amount to be supplied. The dosage control module 106 provides the reductant dosing command 114 in response to the threshold deviation value 116 indicating that the NO _x emission actual value deviates more from a NO _x emission target value than a threshold value. The reductant dosing command 114 may be provided according to any control method known in the art and / or according to specific control methods described herein. The reductant dosing command 114 may include an actuator command value, a voltage or other electrical signal, and / or a command received over a data link or network. In certain embodiments, a reductant dosing device in one communicates with the controller 100 system to the reductant dosing command 114 to an exhaust stream at the location of the reducing agent metering device 17 upstream of the reductant catalyst 16 Feed reducing agent.

The dosage control module 106 may be further configured to include a reductant dosing command 114 which can be retarded to those at low exhaust temperature operating conditions by the N-memory device 14 stored NO _x amount to be considered. The reductant dosing command in connection with the present invention includes decreasing the rate at which the reductant is injected and / or restricting the range of engine operating conditions where the reductant catalyst is 16 is used for the treatment of NO _x emissions, including such conditions that would otherwise result in treatment of NO _x emissions from the engine 20 by supplying reducing agent to the reduction catalyst 16 without a NO _x storage by the upstream of the catalyst 16 arranged N-memory device 14 would have led. However, the injection of reducing agent is for storage on the reduction catalyst 16 during a low temperature operation is not excluded.

The present descriptions are illustrative embodiments for carrying out procedures for controlling an aftertreatment system at low temperature operating conditions. The operations illustrated are intended to be exemplary only, and operations may be combined or shared, added or removed, and rearranged in whole or in part, unless otherwise specifically stated is specified. Certain illustrated operations may be performed by a computer executing a computer program product on a computer readable storage medium, the computer program product including instructions that cause the computer to perform one or more of the operations or issue instructions to other devices to perform one or more of the operations ,

An Exemplary HC Storage Device (HCSD) 12 is operable to store HC over a range of operating temperatures below an effective operating temperature. For example, the HC memory device stores 12 at temperatures below 200 ° C, HC emissions that typically occur when operating a diesel engine. When the exhaust gas temperatures reach and exceed 200 ° C, the HC storage device jumps 12 to oxidize the stored HC emissions and form CO ₂ and H ₂ O. In one embodiment, the catalyst is the HC storage device 12 a zeolite catalyst having an oxidation catalyst disposed thereon, as in the diagram 300 of the 3 is shown, shows a curve 302 at the inlet of the HC storage device 12 Cumulative HC emissions received over time at the beginning of a low-temperature operation. curves 304 and 306 show the from the HC memory device 12 minimum HC output over time during low temperature operation. As the operating temperature increases over time, as if through a curve 308 shown, the hydrocarbons (HC) stored until a sufficiently high catalyst temperature of the HC storage device is reached to oxidize the hydrocarbons.

As apparent from the figures and the foregoing description, various embodiments of the present invention are conceivable.

An exemplary set of embodiments is a method comprising the steps of storing hydrocarbons and NO _x emissions from an internal combustion engine during operation with low exhaust gas temperature in an exhaust gas flow path upstream of a NO _x reduction catalyst, the release of the stored hydrocarbon and NO _x - Emissions into the exhaust gas flow path as the exhaust gas temperature increases toward an effective operating temperature and treating the released hydrocarbon and NO _x emissions through the NO _x reduction catalyst.

In certain embodiments, the method of the _NOx reduction catalyst is a selective catalytic reduction catalyst. In other embodiments, the method includes storing hydrocarbon emissions on the surface of a catalyst of a hydrocarbon storage device. In other embodiments, the method includes storing NO _x emissions on the surface of a catalyst of an NO _x storage device. In other embodiments, the NO _x storage device is a NO _x adsorber. In certain embodiments, the effective operating temperature is about 200 ° C. In other embodiments, the method further comprises delaying reductant dosing during low exhaust gas temperature operation such that an amount of reductant metered into the exhaust gas flow path during low exhaust temperature operation is insufficient for the NO _x reduction catalyst to control the NO _x emissions from the internal combustion engine treated.

Another set of exemplary embodiments is a method comprising the steps of operating an internal combustion engine for generating hydrocarbon and _NOx emissions in an exhaust gas flow path during operation with low exhaust gas temperature, the storage of HC and NO _x emissions from the combustion engine during the Operating with lower Exhaust gas temperature upstream of a NO _x reduction catalyst, and supplying a Reduktionsmitteldosierungsbefehls, according to which the NO _x emissions are treated by the NO _x reduction catalyst when the exhaust gas temperature reaches an effective operating temperature at which the stored HC and NO _x emissions released become.

In still other embodiments, the method further comprises delaying reductant dosing during low exhaust temperature operation such that an amount of reductant metered into the flow path during low exhaust temperature operation is insufficient for a NO _x reduction catalyst to exclude NO _x emissions treated the internal combustion engine. In another embodiment, storing hydrocarbon emissions comprises storing hydrocarbon emissions on the surface of a catalyst of a hydrocarbon storage device, and releasing the stored hydrocarbons comprises oxidizing the hydrocarbons as the exhaust gas temperature increases toward the effective operating temperature. In a refinement of this embodiment, storing NO _x emissions includes storing NO _x emissions on the surface of a catalyst of a NO _x storage device. In yet another refinement, the NO _x storage device is a NO _x adsorber. In other embodiments, the effective operating temperature is about 200 ° C. In other embodiments, the NO _x reduction catalyst is a selective catalytic reduction catalyst.

Another exemplary set of embodiments is a system with an internal combustion engine, a fluid-conductively connected with the engine exhaust line, a fluid-conductively connected to the exhaust conduit hydrocarbon storage device, a fluid-conductively connected to the exhaust conduit NO _x adsorber, a downstream of the NO _x adsorber arranged NO _x Reduction catalyst and a downstream of the NO _x reduction catalyst and downstream of the NO _x adsorber to the exhaust line operatively connected Reduktionsmitteldosiereinrichtung.

In certain embodiments, the system includes the NO _x reduction catalyst downstream of the hydrocarbon storage device. In a refinement of this embodiment, the reductant dosing device is operatively connected to the exhaust gas line downstream of the hydrocarbon storage device and the NO _x adsorber. In another embodiment, the Reduktionsmitteldosiereinrichtung downstream of the hydrocarbon storage means and the NO _x adsorber operatively connected to the exhaust pipe.

In certain embodiments, the system includes a controller having an NO _x ratio determination module configured to determine a NO _x amount at an outlet of the NO _x reduction catalyst, a temperature determination module configured to an actual operating temperature to determine the exhaust gas in the exhaust gas flow path, and to set a dosage control module that is configured to a reducing agent dosing command in response to the amount _{of NOx} to achieve desired NO _x emissions from NO _x reduction catalyst.

In another exemplary embodiment of the system, the controller is configured to provide a delayed reductant dosing command at low exhaust temperature operating conditions. In another embodiment, the hydrocarbon storage device includes a catalyst configured to store hydrocarbon emissions at low exhaust temperature operating conditions and to oxidize the stored hydrocarbons when the exhaust temperature reaches an effective temperature. In a refinement of this embodiment, the NO _x adsorber is configured to adsorb NO _x emissions at low exhaust temperature operating conditions and to release and oxidize NO _x emissions when the exhaust gas temperature has reached an effective temperature. In another embodiment, the system comprises a first NO _x sensor at an inlet of the hydrocarbon storage means and a second _NOx sensor at an outlet of the nitrogen oxide reduction catalyst. In another embodiment, the system comprises an _x NO _x sensor at an outlet of the NO storing means.

Although the invention has been shown and described in detail in the figures and foregoing description, the same is to be regarded as illustrative and not restrictive, and it is understood that only certain exemplary embodiments have been shown and described, and that all changes and modifications that may occur in the The spirit of the inventions are to be protected. When reading the claims, when words such as "a", "an", "at least one" or "at least a portion" are used, it is not intended to limit the claim to a single element unless expressly stated otherwise in the claim is. If the phrase "at least one section" and / or "a section" is used, the article may include a part and / or the entire article, unless expressly stated otherwise.

Claims (26)

A method, comprising the steps of: storing hydrocarbon (HC) and nitrogen oxide (NO _x ) emissions from an internal combustion engine in an exhaust flow path upstream of a NO _x reduction catalyst during low exhaust temperature operation; Releasing the stored HC and NO _x emissions into the exhaust flowpath as the exhaust gas temperature increases toward an effective operating temperature; and treating the stored HC and NO _x emissions by means of an oxidation catalyst and the NO _x reduction catalyst. The method of claim 1, wherein the NO _x reduction catalyst is a selective catalytic reduction catalyst. The method of claim 1, wherein the oxidation catalyst is a catalyst of a hydrocarbon storage device and storing HC emissions comprises storing HC emissions on the surface of the catalyst of the hydrocarbon storage device. The method of claim 3, further comprising oxidizing the stored hydrocarbons (HC) by means of the catalyst of the hydrocarbon storage device. The method of claim 1, wherein storing NO _x emissions comprises storing NO _x emissions on the surface of a catalyst of an NO _x storage device. The method of claim 5, wherein the NO _x storage device is a NO _x adsorber. The method of claim 1, wherein the effective operating temperature is about 200 ° C. The method of claim 1 further comprising delaying reductant dosing during low exhaust temperature operation such that an amount of reductant metered into the exhaust flow path during low exhaust temperature operation is insufficient for the NO _x reduction catalyst to control the NO _x emissions from the internal combustion engine treated. A method comprising the steps of: operating an internal combustion engine to produce hydrocarbon (HC) and nitrogen oxide (NO _x ) emissions into an exhaust gas flow path during low exhaust temperature operation; Storing HC and NO _x emissions from the internal combustion engine during low exhaust temperature operation upstream of a NO _x reduction catalyst; and providing a reductant dosing command according to which the NO _x emissions are treated by means of the NO _x reduction catalyst when the exhaust gas temperature reaches an effective operating temperature at which the stored HC and NO _x emissions are released. The method of claim 9, further comprising delaying the reductant metering during operation at a low exhaust gas temperature, so that a not sufficient to during operation at a low exhaust gas temperature in the exhaust gas flow path metered amount of reducing agent that the NO _x reduction catalyst, the _NOx emissions from the internal combustion engine treated. The method of claim 9, wherein storing HC emissions comprises storing HC emissions on the surface of a catalyst of a hydrocarbon storage device, and wherein releasing the stored HC emissions comprises oxidizing the hydrocarbons (HC) when the exhaust temperature is effective Operating temperature rises. The method of claim 11, wherein storing NO _x emissions comprises storing NO _x emissions on the surface of a catalyst of a NO _x storage device. The method of claim 12, wherein the NO _x storage device is a NO _x adsorber. The method of claim 9, wherein the effective operating temperature is about 200 ° C. The method of claim 9, wherein the NO _x reduction catalyst is a selective catalytic reduction catalyst. System comprising: an internal combustion engine; an exhaust pipe fluidly connected to the internal combustion engine; a hydrocarbon storage device fluidly connected to the exhaust conduit; a fluid-conductively connected to the exhaust pipe NO _x adsorber; a NO _x reduction catalyst disposed downstream of the NO _x adsorber; and a reducing agent metering device operably connected to the exhaust passage upstream of the NO _x reduction catalyst and downstream of the NO _x adsorber. The system of claim 16, wherein the NO _x reduction catalyst is disposed downstream of the hydrocarbon storage device. The system of claim 17, wherein the reductant dosing means is operably connected to the exhaust conduit downstream of the hydrocarbon storage means and the NO _x adsorber. The system of claim 16, wherein the reductant dosing means is operably connected to the exhaust conduit downstream of the hydrocarbon storage means and the NO _x adsorber. The system of claim 16, further comprising a controller comprising: an NO _x ratio determination module configured to determine a NO _x amount at an outlet of the NO _x reduction catalyst; a temperature determination module configured to determine an actual operating temperature of the exhaust gas in the exhaust gas flow path; and to set a dosage control module that is configured to a reducing agent dosing command in response to the amount _{of NOx} to achieve desired NO _x emissions from NO _x reduction catalyst. The system of claim 20, wherein the controller is configured to provide a delayed reductant dosing command at low exhaust temperature operating conditions. The system of claim 16, wherein the hydrocarbon storage device comprises a catalyst configured to store hydrocarbon (HC) emissions at operating conditions of low exhaust gas temperature and to oxidize the stored hydrocarbons (HC) when the exhaust gas temperature reaches an effective temperature. The system of claim 22, wherein the NO _x adsorber is configured to adsorb NO _x emissions at low exhaust temperature operating conditions and to release and oxidize NO _x emissions when the exhaust temperature is an effective temperature for NO _x conversion by the exhaust gas NO _x reduction device has reached. The system of claim 16, further comprising a first NO _x sensor at an inlet of the hydrocarbon storage means and a second _NOx sensor at an outlet of the NO _x reduction catalyst. The system of claim 16, further comprising a NO _x sensor between the NO _x adsorbent and the _NOx reduction catalyst. The system of claim 16, further comprising a _NOx sensor upstream of the NO _x reduction catalyst.

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