Systems and methods for reducing NOx and HC emissions

Abstract

System, with: an internal combustion engine (22); an exhaust line which is in fluid communication with the internal combustion engine (22); at least one device installed close to the engine, which is in fluid communication with the exhaust line and is configured to provide a storage point for hydrocarbons and nitrogen oxides in an exhaust gas generated by the internal combustion engine (22) under low-temperature operating conditions, wherein the at least one device installed close to the engine further comprises an oxidation catalyst downstream of the hydrocarbon storage location and nitrogen oxides, a particulate filter and a selective catalytic reduction (SCR) section downstream of the oxidation catalyst, which is in fluid communication with the exhaust pipe, a second SCR element (20) which is in fluid communication with the exhaust gas line downstream of the SCR part; a first reducing agent injection nozzle (28) located upstream of the SCR section, which is configured to selectively supply a reducing agent to the exhaust gas flow path in response to a first reducing agent injection nozzle command; and a second reducing agent injection nozzle (30) located downstream of the SCR part and upstream of the second SCR element (20), which is configured to selectively supply the reducing agent to the exhaust gas flow path in response to a second reducing agent injection nozzle command.

Description

GENERAL STATE OF THE ART

[0001] There is increasing interest in controlling catalysts with selective catalytic reduction (SCR) to meet modern emission limits applicable to internal combustion engines. An example of an internal combustion engine catalyst with SCR is disclosed in US 2013 / 0 305 695 A1. The effectiveness of a typical SCR catalyst in removing nitrogen oxide (NOx) emissions depends strongly on the exhaust gas temperature at the inlet of the SCR catalyst. Current catalyst formulations typically operate at maximum efficiency when exposed to exhaust gas temperatures of 200-400°C. For the certification of certain diesel engines, the engine's emissions performance in the cold part of the certification cycle is weighted almost equally to the engine's emissions performance in the hot part of the certification cycle.For this reason, improvements are desired that prevent hydrocarbon (HC) and NOx emissions produced by the engine from slipping through the aftertreatment system under low-temperature exhaust conditions, such as temperatures below approximately 200°C, as well as under high-temperature conditions, such as temperatures above 400°C. An example of this is disclosed in document DE 10 2013 008 534 A1.

[0002] In addition to the SCR catalyst, typical diesel aftertreatment systems include a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF). 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 oxidize these molecules at cold exhaust temperatures. Furthermore, regeneration of the aftertreatment components and the associated high temperatures increase reductant consumption. Improvements to aftertreatment concepts are necessary to mitigate the slip of these test pollutants through the exhaust flow path during low- and high-temperature operating conditions and to reduce reductant consumption. Accordingly, technological advancements in this area are desirable. SUMMARY OF THE INVENTION

[0003] Disclosed are particular methods and systems for managing low-temperature NOx and low-temperature HC emissions to improve the NOx and HC conversion efficiency of diesel aftertreatment systems under low- and high-temperature conditions. In some embodiments, a multi-component aftertreatment system is provided that includes passively operated HC and NOx storage devices, an oxidizer, and a particulate filter having a selective catalytic reduction (SCR) section for enhanced mitigation of NOx and / or HC emissions under low- and high-temperature conditions to achieve desired emission levels for light-duty vehicles, although applications to other vehicles are not precluded. In certain embodiments, the particulate filter is a close-coupled diesel particulate filter.In other embodiments, a diesel particulate filter SCR part is provided close to the engine, either with a separate SCR catalyst adjacent to the particulate filter or as an SCR washcoat applied to the particulate filter.

[0004] Embodiments of the systems and methods further include a second SCR element downstream of a close-coupled particulate filter-SCR (DPF-SCR) portion, and reductant injectors upstream and downstream of the DPF-SCR portion for injecting a reductant at one or both of the reductant injection locations in response to certain operating conditions. Further embodiments include connecting the SCR portion of the DPF-SCR portion to the second SCR element at a separate distance that allows operation of the second SCR element at a different temperature regime than the SCR portion under certain operating conditions to improve the NOx reduction efficiency of the second SCR element.Still further embodiments comprise a mixer upstream of the DPF-SCR element and / or a mixer downstream of the DPF-SCR element and upstream of the second SCR element for improving reducing agent mixing and the flow distribution of the reducing agent over any cross-section upstream of the corresponding SCR section or SCR element.

[0005] The systems and methods reduce the need for external devices designed to artificially increase exhaust gas temperature for cold-start cycles, which is advantageous because such external devices tend to increase fuel consumption and greenhouse gas emissions, although the use of such external devices is not precluded. The systems and methods disclosed herein result in a reduction in cost, fuel consumption, and / or reductant consumption over current thermal management strategies for mitigating low-temperature NOx and low-temperature HC emissions. Close-coupled may mean being as close as possible to a location downstream of a turbine portion of a turbocharger or exhaust manifold, being within a specified distance downstream of the turbine or exhaust manifold (such as within 12 inches), and / or being within a specified heat transfer regime.area that is different from the second SCR element downstream of the DPF-SCR element.

[0006] This summary is intended to introduce a selection of concepts that are further described below in the illustrative embodiments. This summary is not intended to identify the most important or essential features of the claimed subject matter, nor is it intended to limit the object of the claimed subject matter. Other embodiments, forms, objects, features, advantages, aspects, and benefits will become more clearly apparent from the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 shows a block diagram of an exemplary system for reducing HC and NOx emissions from an internal combustion engine under low exhaust temperature operating conditions. Fig. 2 shows a block diagram of various embodiments of the system of Fig. 1 . Fig. 3 shows a schematic diagram of a control system that includes part of the system Fig. 1 includes. Fig. 4 is a flowchart of an operation of the system of Fig. 1 . DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0007] For a better understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and technical terms will be used to describe them. Nevertheless, it is to be understood that this is not intended to limit the scope of the invention, but that modifications and further variations of the illustrated embodiments and further applications of the inventive principles presented herein are possible, as would normally occur to one skilled in the art to which the invention relates.

[0008] Disclosed are systems and methods for reducing HC and NOx emissions at low exhaust temperature operating conditions for an internal combustion engine. The systems and methods reduce test pollutants at least at low exhaust temperature conditions. The disclosed systems and methods are configured such that vehicles equipped therewith are operable to meet emission limits at low exhaust temperature operating conditions without requiring external aftertreatment heating systems that increase the vehicle's fuel consumption and greenhouse gas emissions, although the use of such external systems is not precluded. In one embodiment, the systems and methods are applicable to certified light-duty vehicles, although applications for other vehicle types are not precluded.

[0009] The systems and methods include an aftertreatment system architecture configured to temporarily store HC and NOx emissions during low exhaust temperature operating periods and then passively release the stored NOx and HC emissions for aftertreatment as the exhaust temperature increases. The systems and methods are configured such that, at temperatures where HC and NOx emissions are released, the diesel oxidation catalyst (DOC) and SCR catalysts are effective to mitigate the released HC and NOx emissions from the storage devices before they exit the exhaust tailpipe.

[0010] In one embodiment, the aftertreatment system includes a close-coupled HC storage device (HCSD) located directly downstream of a turbocharger with a close-coupled NOx storage device (NSD) located immediately downstream of the HCSD. In another embodiment, the NSD is located upstream of the HCSD. At low exhaust temperatures, the HCSD readily adsorbs and stores HC. In a particular embodiment, the HCSD includes a catalyst, such as a zeolite-based catalyst, for storing and adsorbing HC, which could be any suitable storage medium for a hydrocarbon storage device.As exhaust temperature increases, the HCSD releases stored HC stored by the HCSD, which is then effectively oxidized by a downstream, close-coupled oxidation catalyst, such as a diesel oxidation catalyst (DOC), to form H2O and CO2. The NSD is any suitable component, such as a NOx adsorber, capable of passively storing NOx at low exhaust temperatures and then releasing the stored NOx as exhaust temperature increases. As exhaust temperature increases, the NSD releases NOx, and the NO portion of the NOx is partially oxidized to form NO2 before being converted to N2 and H2O by a DPF-SCR portion downstream of the DOC. In one embodiment, the HCSD, NSD, and DOC are separate devices.In other embodiments, the HSCD, NSD, and DOC are integrated into a single catalyst component that performs all of the previously described functions. In yet another embodiment, the DPF-SCR portion is a close-coupled device within the exhaust manifold, although embodiments without a close-coupled DPF-SCR portion are conceivable.

[0011] In a further embodiment, a reductant system upstream of the DPF-SCR section is provided for injecting a reductant to facilitate NOx conversion via the DPF-SCR section at low-temperature operating conditions, although operation for NOx conversion at other temperature operating conditions is not precluded. In one embodiment, the reductant is supplied to the exhaust stream as a gaseous reductant to avoid the disadvantages of a liquid reductant at low-temperature operating conditions. In one embodiment, the gaseous reductant is stored using a solid storage medium, although other gaseous reductant storage / conversion devices are also conceivable. In another embodiment, the reductant is stored in a liquid medium and supplied to the exhaust stream as a liquid for hydrolysis in the exhaust stream.In another embodiment, a second SCR element is present downstream of the DPF-SCR portion, and a second reductant location is provided upstream of and downstream of the second SCR element. The second reductant location may use gaseous reductant from the gaseous reductant source or liquid reductant from a second liquid reductant source to facilitate NOx conversion via the second SCR element. In a further embodiment, the downstream SCR element is connected to the DPF-SCR portion by an exhaust conduit providing a cooling separation distance to permit use of the second SCR element with reductant injection at the second location for NOx reduction during a regeneration event associated with the upstream components.The second SCR element is also usable for NOx conversion under regular, non-high-temperature operating conditions. In still further embodiments, reductant is provided at the second location in response to the ammonia storage conditions of the DPF-SCR portion and / or the ability of the DPF-SCR portion to effectively treat the current NOx content in the exhaust stream.

[0012] Systems and methods for reducing HC and NOx emissions from lean-burn combustion engines for operating conditions with low exhaust gas temperatures are also described in Fig. 1. As in Fig. 1, an exemplary aftertreatment system 10 includes a close-coupled HCSD 12 and NSD 14, followed by a close-coupled DOC 16 and a close-coupled DPF-SCR device 18. The aftertreatment system 10 further includes a second or downstream SCR element 20, which may be a standard SCR or NAC-type NOx reduction catalyst. The elements 12, 14, 16, 18, and 20 are configured to receive exhaust gases in an exhaust stream produced by an internal combustion engine 22 in the exhaust flow path 24. The HCSD 12 and NSD 14 are passively operated storage devices that require little or no active control strategies, although the use of active control strategies is not precluded.The DPF-SCR device 18 includes a particulate filter and an SCR portion, either as a separate SCR element or as a washcoat applied to the particulate filter, which is connected to and spaced apart from the second SCR element 20 by an exhaust cooling gap, such as an exhaust cooling line 26. As further explained below, the exhaust cooling gap allows the exhaust gas to cool before reaching the second SCR element in response to, for example, a regeneration event or other high-temperature condition of the upstream elements 12, 14, 16, and 18, such that the second SCR element 20 operates in a different temperature range than the DPF-SCR device 18 under certain operating conditions.

[0013] In other embodiments of Fig. 1, such as in Fig. 2, a low-pressure exhaust gas recirculation (LPEGR) system 100 may be present to recirculate exhaust gas from the exhaust system 104 to the intake system 102 at a location downstream of a turbine 108 of a turbocharger 106. The turbocharger 106 may include a compressor 110 in the intake system 102 driven by the turbine 108. The LPEGR system 100 has an LPEGR conduit 112 connecting the exhaust system 104 to the intake system 102 through an EGR flow control valve 114 controllable by the controller 40 to control EGR flow. The LPEGR conduit 112 may branch from one of a number of locations of the exhaust system. For example, the LPEGR line 112 may be downstream of the DPF-SCR device 18 and upstream of the second SCR element 20.In another embodiment, such as shown by LPEGR conduit 112', the EGR flow branches off at a location located between two portions 20a and 20b of the second SCR element 20. Alternatively, as shown by LPEGR conduit 112", the EGR flow may branch off at a location downstream of the second SCR element 20. The LPEGR system 100 may or may not affect HC and NOx emissions during low-temperature operating conditions, and the controller 40 (discussed below) may be configured to consider LPEGR operating modes when determining the reductant injection strategy.

[0014] At low exhaust temperatures, which result in low catalyst temperatures, the HCSD 12, in one embodiment, is configured to readily adsorb and store HC until the HCSD 12 reaches a temperature at which it effectively releases the hydrocarbons to the DOC 16, which oxidizes the stored HC to form CO2 and H2O. Furthermore, the NSD 14 may be configured to readily adsorb and store NOx with its catalyst at low exhaust temperature conditions and then begin to desorb this NOx as the exhaust temperature, and thus the NSD catalyst temperature, increases. The NSD 14 is configured to release the stored NOx at an exhaust temperature at which the released NO portion of the NOx is oxidized and converted to NOx at the DOC 16, and at which NOx is further treated at the DPF-SCR device 18 to reduce NOx to N2 and H2O.Once the aftertreatment system 10 reaches operating temperature, the DOC 16 is responsible for the oxidation of HC, CO, and NO in the exhaust gas. The DPF-SCR device 18 can be combined as a single element as shown, for example, by applying an SCR washcoat section to a particulate filter substrate, or as separate DPF and SCR components in a common housing or in separate housings.

[0015] In one embodiment, exhaust aftertreatment system 10 includes a DOC 16 operable to catalyze an oxidation of one or more compounds in the exhaust gas flowing through exhaust flowpath 24, for example, an oxidation of unburned hydrocarbons or an oxidation of NO to NO2. The oxidation catalyst 16 may be any of a variety of flow-through oxidation catalysts. Generally, the oxidation catalyst 16 includes a substrate having an active catalyst layer configured to oxidize at least some particulate matter (e.g., the soluble organic fraction of soot) in the exhaust gases and to reduce unburned hydrocarbons and CO in the exhaust gases to less environmentally harmful compounds. For example, in some implementations, the oxidation catalyst 16 may sufficiently reduce hydrocarbon and CO concentrations to meet required emission limits.

[0016] The exhaust aftertreatment system 10 may also include a DPF-SCR device 18 with a particulate filter configured to reduce the particulate content in the exhaust gases flowing through the exhaust flow path 24. In one embodiment, the particulate filter portion is a catalytic soot filter. The DPF-SCR device 18 may be any of various prior art particulate filters configured to reduce concentrations of particulate matter, such as soot and ash, in the exhaust gas to meet required emission limits. The DPF-SCR device 18 includes a filter substrate that captures soot and other particulate matter generated by the engine 22. In one embodiment, the system 10 is configured to periodically regenerate the DPF-SCR device 18 to remove particulate matter that has accumulated on the particulate filter portion over time.For example, the DPF-SCR device 18 may be regenerated by raising the temperature of the exhaust gases above a threshold temperature corresponding to the combustion of the particulate matter. The temperature threshold may be associated with a high-temperature operating condition. In one embodiment, the temperature threshold is 400°C. In other embodiments, other temperature thresholds are contemplated, ranging from 350°C to 500°C.

[0017] The SCR catalyst washcoat or SCR catalyst of the DPF-SCR device 18 and / or the second SCR element 20 may be configured to receive reductant gas or liquid injected into the exhaust flowpath 24 and to catalyze the reduction of NOx in the exhaust gas. The SCR catalyst washcoat and / or SCR catalyst elements may be any of various catalysts known in the art. For example, in some implementations, the SCR catalyst and / or washcoat is a zeolite-based catalyst, such as a Cu zeolite or Fe zeolite catalyst, or a vanadium-based catalyst. The formulation of the SCR portion of the DPF-SCR device 18 and the SCR element 20 may be the same or different.

[0018] The system 10 also includes a first reductant injector 28 upstream of the DPF-SCR device 18 and a second reductant injector 30 downstream of the DPF-SCR device 18 and upstream of the second SCR element 20. The reductant injectors 28, 30 are connected to a reductant source 32. In one embodiment, the reductant source 32 stores an amount of a dry NOx reductant, such as ammonia (NH3), in a solid storage medium, although any storage suitable for a gaseous reductant is contemplated. In other embodiments, the reductant source 32 is a source of a liquid reductant. In one embodiment, the solid storage medium may be any material comprising adsorption or absorption of molecular ammonia in a solid state, or a solid chemical compound that can be processed to produce gaseous ammonia.In a particular embodiment, the solid storage medium comprises metal ammonia salts. The NOx reductant stored in the solid storage medium housed in the reductant source 32 may be ammonia or any other known reductant capable of storage and selective release from a solid storage medium. The reductant source 32 may be a cartridge or housing providing one or more storage units having one or more compartments for storing ammonia in the solid storage medium.

[0019] The reducing agent source 32 is connected to one or both of the reducing agent injectors 28, 30 by a reducing agent supply system 34, 35 configured to deliver a gaseous reducing agent released from the solid storage medium in the reducing agent source 32 and supply the gaseous reducing agent to the exhaust gas flow path 24 through the corresponding reducing agent injector 28, 30. The gaseous reducing agent passes through a reducing agent supply channel from the reducing agent source 32 to a metering device 36, 37 and from the metering device 36, 37 to the injector 28, 30 for mixing with the exhaust gas in the exhaust gas flow path 24.The respective supply systems 34, 35 include sensors, control valves, heating sources, coolant channels and other devices useful for releasing gaseous reductant from the solid storage medium and for delivering the gaseous reductant into the exhaust flow path 24 in the desired amount, rate and time.

[0020] In one embodiment, the gaseous reductant source 32 is operatively coupled to at least one engine coolant feed passage and one engine coolant return passage (not shown) that provide a heating source that heats the solid storage medium stored in the reductant source 32 to release the stored reductant in the form of a gas. In other embodiments, other means for heating the solid storage medium in the reductant source 32 are provided, including, for example, an electrical heating element connected to a power source such as a battery or generator. The heating source may be embedded in the solid storage medium or extend around the outside of the solid storage medium, or comprise a combination of these arrangements.In one embodiment, upon heating the solid storage material, gaseous NH3 is released from the solid storage medium into the corresponding supply channel by thermal desorption. The consumption rate of the released NH3 gas is measured by the metering device 36, 37 as it is mixed into the exhaust flow path 24. A pressure / temperature controller of the reductant source 32 may be provided to control the release of the reductant gas.

[0021] In an alternative embodiment, the system 10 further includes a liquid reductant source (not shown) that stores an amount of liquid NOx reductant, such as ammonia (NH3), in a liquid storage medium. In one embodiment, the liquid storage medium is diesel emissions fluid stored in a tank. Other liquid reductant storage media, such as urea, are also contemplated. The liquid reductant source is connected to the first reductant injector 28 and / or second reductant injector 30. Alternatively, both a gaseous and a liquid reductant source are connected and selectively operable to provide reductant to both reductant injectors 28, 30 in response to certain operating conditions.

[0022] As previously explained, the SCR element 20, at least under certain operating conditions, operates in a different temperature range than the SCR portion of the DPF-SCR device 18 and is disposed in a significantly different thermal environment than the DPF-SCR device 18. An exemplary significantly different thermal environment is a thermal environment that varies according to a temperature observed over time, for example, after an engine start event, in which the downstream SCR element 20 warms up more slowly and / or warms up to a different final temperature than the upstream SCR portion of the DPF-SCR device 18.Another exemplary significantly different thermal environment is an environment having a differential heat transfer environment, either a static heat transfer environment and / or a dynamic heat transfer environment (e.g., when a vehicle including system 10 is moving). Another exemplary significantly different thermal environment is an environment where, in a first engine operating condition range, the upstream SCR portion of DPF-SCR device 18 is within a desired temperature operating range (e.g., cold start operation, warm-up operation, and / or operations between 200°C and 400°C) and, in a second engine operating condition range, the downstream SCR element 20 is within a desired temperature operating range.The desired temperature operating range for the SCR portion of the DPF-SCR device 18 and the SCR element 20 may be the same temperature range or a different temperature range and depends on one or more factors known in the art, including, but not limited to, catalyst formulations, space velocity and / or catalyst volume considerations, currently stored amounts of reductant on each SCR component, and / or the currently available NO:NO2 process ratio at each component.

[0023] Conditions defining a range of "engine operating conditions" should be understood broadly and may include information related to engine speed / load, but may alternatively or additionally include, without limitation, vehicle load (such as weight, road grade, etc.), ambient temperature, ambient pressure, ambient wind speed and direction, vehicle speed, transient or steady-state operating condition, timing and other engine fueling characteristics (e.g., post and / or pilot injection events), availability and use of hydrocarbon dosing in the aftertreatment system, turbocharger operating characteristics (such as wastegate values, VTG supercharger position, etc.), LPEGR operating characteristics, and / or the positions or use of cooler bypass devices (such as EGR coolers or intercooler bypasses - not shown).When there is an overlap of the first and second ranges of engine operating conditions—for example, when both the SCR portion of the DPF-SCR device 18 and the SCR element 20 are within the desired operating ranges at a particular engine operating condition—the controller 40 may treat NOx emissions with the SCR portion of the DPF-SCR device 18 and / or the SCR element 20 according to any desired operating principle, including, but not limited to, principles described herein. Example operating principles include favoring the SCR portion of the DPF-SCR device 18 and / or the SCR element 20 within the common engine operating ranges (e.g.,Continuous use of the upstream SCR portion of the DPF-SCR device 18 within a specific common engine operating range; remaining with a currently used one of the SCR portion of the DPF-SCR device 18 and the SCR element 20 until a switch is dictated by entering an engine operating range in which only the other of the SCR portion of the DPF-SCR device 18 and the SCR element 20 is preferred and subsequent switch; and / or by applying a hysteresis value to any switch. The hysteresis value may be in any units known in the art, for example, a time-based hysteresis, a temperature-based hysteresis, an engine load-based hysteresis, etc.

[0024] In certain embodiments, the size of each of the SCR portion of the DPF-SCR device 18 and the SCR element 20 is sized to fully treat NOx emissions of the engine 12, at least for those engine operating conditions in which the corresponding one of the SCR portions of the DPF-SCR device 18 and the SCR element 20 is dominant or active. In certain embodiments, the size of the SCR portion of the DPF-SCR device 18 is sized to fully treat the entire exhaust stream at normal operating temperatures. In yet another embodiment, the size of the SCR element 20 is sized to fully treat the entire exhaust stream at normal operating temperatures, or at a second operating condition, such as high operating temperatures.Normal operating temperatures include operating temperatures that are not high operating temperatures, such as operating temperatures during periods when an aftertreatment component is not undergoing heat-based regeneration, operating temperatures that are not cold-run or warm-up operating temperatures, and / or operating temperatures that are not fully loaded engine operating temperatures.

[0025] The system 10 may include a controller 40 and other aftertreatment components in addition to those described in Fig. 1. For example, the system 10 may include an ammonia oxidation catalyst (AMOX) downstream of the second SCR element 20. In certain embodiments, the AMOX may be absent, or the AMOX may be incorporated with the SCR element 20 (or with the last SCR catalyst if multiple SCR catalysts are present), for example, as a washcoat applied to the rear portion of the SCR element 20 that is susceptible to at least partially oxidizing ammonia. In other embodiments, any of these components may be present or absent, catalyzed or uncatalyzed, and may be arranged in alternating order. Furthermore, certain components or all of the components may be provided in the same housing or in separate housings.

[0026] For system 10 including controller 40, controller 40 may include a number of modules structured to functionally perform operations to control the SCR system. In certain embodiments, the controller forms part of a processing subsystem, including one or more computing devices having memory, processing, and communication hardware. Controller 40 may be a single device or a distributed device, and the functions of the controller may be performed by hardware or software-configured hardware. Controller 40 may be in communication with a sensor, an actuator, a data link, and / or a network within the system.

[0027] The exemplary system 10 further includes various sensors. The sensors shown in Fig. 1 include a first NOx sensor 42 located upstream of the HCSD 12 and a second NOx sensor 44 located downstream of the second SCR element 20. Alternatively or additionally, NOx sensors (not shown) may be present at the outlet of the NSD 14, at the outlet of the DPF-SCR device 18, and / or between the inlet to the second SCR element 20 and the outlet of the DPF-SCR device 18. The system 10 also includes a first temperature sensor 46, for example, at the inlet of the HCSD 12, a second temperature sensor 48 between the HCSD 12 and the NSD 14, a third temperature sensor 50 at the outlet of the NSD 14, a fourth temperature sensor 52 at the DPF-SCR device 18, and a fifth temperature sensor 54 at the second SCR element 20. Other embodiments provide NOx, temperature and / or NH3 sensors at the outlet of the DOC 16 and / or at the inlet to the DPF-SCR device 18.Additional sensors may be provided to measure or determine the mass flow through the exhaust system, the temperature of any components of the aftertreatment system, the amount of ammonia stored in one or both of the SCR catalysts 18, 20 or outlet thereof, etc.

[0028] The sensors shown are examples only and can be repositioned, removed and replaced and there may be other sensors that are not included in Fig. 1. Furthermore, certain sensors may instead be virtual sensors calculated from other parameters available to the system 10, or values ​​that could be displayed by sensors could, however, be delivered to a computer-readable storage location via a data connection or network communication or otherwise made available to the system 10 if the sensor providing the displayed parameter is not part of the defined system 10.

[0029] In certain embodiments, such as in Fig. 2, the controller 40 includes a NOx / NH3 determination module 60, a temperature determination module 62, a reductant injector selection module 64, and a reductant control module 66. The description provided herein, comprising modules, emphasizes the structural independence of the aspects of the controller 40 and represents an operational grouping and responsibilities of the controller 40. Other groupings that perform a similar overall operation are within the scope of the present patent application. More detailed descriptions of specific embodiments of controller operations are provided in the section relating to Fig. 3 refers to.

[0030] The exemplary control 40 in the Fig. 1 and Fig. 3 is configured to perform operations to provide a reductant injector command 68 for effective removal of NOx emissions with the DPF-SCR device 18 and / or the SCR element 20. The control method of the controller 40 in Fig. 2 includes steps that adjust nominal control steps for a NOx aftertreatment system that utilizes a reductant. Nominal control steps for a NOx aftertreatment system that includes an SCR aftertreatment system are known in the art and will not be described further here. Any nominal NOx aftertreatment control steps may be used by the system 10 disclosed herein.

[0031] The controller 40 includes the NOx / NH3 determination module 60, which receives NOx parameters 70 from NOx sensors, e.g., sensors 42, 44, and determines an amount of NOx emitted by the engine 22 and the DPF-SCR device 18 and / or the second SCR element 20. The controller 40 may also be configured to receive inputs from sensors and determine or calculate an amount of NOx at the outlet of the DPF-SCR device 18 or at other locations in the system 10. The NOx / NH3 determination module 60 may also receive NH3 parameters 72 from NH3 sensors or by calculation from other operating parameters and determine an amount of stored NH3, an NH3 storage capacity, and / or NH3 slip from the DPF-SCR device 18 and / or the second SCR element 20.

[0032] The controller 40 also includes a temperature determination module 62 that receives temperature parameters 74 from, for example, temperature sensors 46, 48, 50, 52, 54 to determine a temperature of the exhaust gas in the flowpath 24 and / or the various catalysts of the aftertreatment components in the flowpath 24. In one embodiment, the temperature determination module is configured to determine a low exhaust temperature operating condition 78 and an exhaust aftertreatment component regeneration condition 80. Other temperature conditions or operating modes could also be determined and are not precluded.

[0033] The controller 40 also includes the reductant injector selection module 64 configured to select one or both reductant injectors 28, 30 from which to deliver reductant in response to the operating conditions of the aftertreatment system 10, such as SCR operating parameters 76 and the temperature conditions determined by the temperature determination module 62. For example, the reductant injector selection module 64 may be configured to select operation of the reductant injector 28 with the "Injector #1" selection 82, select operation of the reductant injector 30 with the "Injector #2" selection 84, or select both injectors 28, 30 with the "Both Injectors" selection 86.The controller 40 further includes a reductant control module 66 that determines an appropriate reductant injector command 68 for the amount of reductant to be injected into the flow path 24 to provide a desired NOx emission level at the outlet of the DPF-SCR device 18 and / or the second SCR element 20.

[0034] During low-temperature operating conditions for the engine 22 and for exhaust and / or aftertreatment components in the flowpath 24, the second SCR element 20 is ineffective in treating NOx emissions to achieve desired emission targets. Furthermore, traditional oxidation catalysts upstream of the SCR element 20 are ineffective in removing HC to meet test emission levels during low-temperature operating conditions. Therefore, the HCSD 12 is configured to store HC and the NSD 14 is configured to store NOx during low exhaust temperature operating conditions until the aftertreatment components of the system 10 are brought to a temperature effective for removing the test pollutants from the emissions of the engine 22.

[0035] Furthermore, during low-temperature operating conditions 78, the reductant injector selection module 64 may select the reductant injector 28 to provide a gaseous reductant to the exhaust stream to enhance or enable low-temperature NOx reduction properties. Providing gaseous reductant when the temperature condition is less than the liquid reductant temperature threshold enables the treatment of NOx emissions during low-temperature operating conditions while avoiding or minimizing the formation of reductant deposits typically formed by dosing liquid reductant during low-temperature conditions. Accordingly, the HC and NOx storage times and required storage amounts by the HCSD 12 and NSD 14 may be reduced compared to a system using only a liquid reductant.In still further embodiments, a liquid reductant is provided with the reductant injection nozzle 28.

[0036] The amount of NOx accumulation by the NSD 14 during low exhaust temperature operating conditions may be determined based on the difference between the amount of NOx detected by the upstream NOx sensor 42 and the corresponding amount detected by the downstream NOx sensor 44 and converted by the oxidation catalyst 16 during low temperature operation. In one embodiment, the reductant control module 66 is configured to determine a reductant injector command 68 that provides reductant from the reductant injector 28 only during low temperature operating conditions.

[0037] During other operating conditions, reductant injection may be provided by the upstream reductant injector 28 when NH3 storage conditions exist in the DPF-SCR device 18. When the DPF-SCR device 18 lacks NH3 storage capacity, the reductant injector selection module 64 may select the downstream reductant injector 30 to provide the amount of reductant requested by the reductant injection command. Reductant injector 30 may also be selected during high-temperature operating conditions to provide a larger portion of the reductant to prevent high-temperature ammonia oxidation in the DPF-SCR device 18, thereby reducing reductant consumption.In yet another embodiment, in response to detecting a regeneration condition 80, the reductant injector selection module 64 selects the downstream reductant injector 30 to provide all or a portion of the reductant to a cooling second SCR catalyst element 20 separated from the DPF-SCR device 18 by the exhaust cooling conduit 26, while simultaneously deactivating the upstream reductant injector 28. At high regeneration temperatures, such as those above 550°C, the DPF-SCR device 18 may be less effective at converting NOx, so NOx conversion occurs in the downstream SCR element 20.In still further embodiments relating to low temperature and / or high temperature operating conditions, reductant may be provided simultaneously by the reductant injectors 28, 30 in a proportion and amount determined by the controller 40, and operation of the DPF-SCR device 18 and / or the second SCR element 20 may occur to convert NOx in the exhaust gases to the desired levels.

[0038] Referring to Fig.4, a flowchart of one embodiment of a process for treating exhaust emissions is shown. The process 200 includes a step 202 for operating the internal combustion engine. During operation of the internal combustion engine, an exhaust gas or exhaust stream is produced, which is fed to an aftertreatment system connected to the internal combustion engine. The process 200 further includes a step 204 for storing at least a portion of the hydrocarbons and nitrogen oxides in the exhaust gases at a storage location close to the engine during low-temperature operating conditions, for example, when the aftertreatment components are ineffective or less effective at treating these constituents. In one embodiment, the low-temperature operating condition is a cold-start operation or a warm-up operation of an engine. In other embodiments, the low-temperature operating conditions are lower than an effective operating temperature of 180°C to 220°C.In other embodiments, an effective operating temperature is approximately 200°C. However, it should be understood that low-temperature operating temperature ranges, actual operating temperature thresholds, and high-temperature operating temperature ranges may vary based on the design and materials of the aftertreatment system components and / or the designed emission reduction control requirements.

[0039] Process 200 continues in step 206 to release the stored hydrocarbons and nitrogen oxides from the storage location in response to an increase in the operating temperature of the exhaust system from the low-temperature operating condition. The release of the hydrocarbons and / or nitrogen oxides may be a passive release that occurs as the operating temperature increases or in response to the operating temperature of one or more components of the aftertreatment system reaching a threshold temperature or temperature range. In one embodiment, hydrocarbons are stored with a hydrocarbon storage device and NOx emissions are stored with a NOx storage device, such as a NOx adsorber.In further embodiments, the aftertreatment system comprises an oxidation catalyst downstream of storage devices, a particulate filter and SCR portion downstream of the oxidation catalyst, and a second SCR element downstream of the SCR portion and located in a significantly different thermal environment.

[0040] Process 200 continues in step 208 with the selection of one of an upstream reductant injector and a downstream reductant injector, such as reductant injectors 28, 30 discussed herein. For example, the first reductant injector may be selected to inject reductant into the exhaust stream only at a first location upstream of the SCR portion in response to a low-temperature operating condition, and the second reductant injector may be selected to inject reductant into the exhaust stream only at a second location downstream of the SCR portion and upstream of the SCR element during a high-temperature operating condition, such as particulate filter regeneration. Process 200 continues in step 210 with the injection of reductant from the selected reductant injector.As previously explained, under certain operating conditions, simultaneous reductant injection from both reductant injectors may be performed. Under other operating conditions, simultaneous injection of reductant at the first and second locations is prevented, such as during low-temperature operating conditions and particulate filter regeneration.

[0041] Process 200 continues in step 212 with treating the released hydrocarbons with an oxidation catalyst downstream of the hydrocarbon storage location. Process 200 also includes a step 214 for treating the released nitrogen oxides with the SCR element and / or the downstream SCR portion and the reductant injected by the selected associated reductant injector. The amount of reductant injected into the exhaust flow path is determined as an amount sufficient for the SCR portion and / or the second SCR element to convert a desired amount of NOx emissions from the internal combustion engine.As previously explained, the reductant may be a liquid reductant from both injectors, a gaseous reductant from both injectors, or a gaseous reductant from the upstream reductant injector and a liquid reductant from the downstream reductant injector.

[0042] As can be seen from the figures and explanations presented above, many aspects of the present disclosure are conceivable.

[0043] One aspect includes an exemplary set of embodiments relating to a method comprising: storing, at a location in an exhaust flow path, hydrocarbon and NOx emissions of an internal combustion engine during low exhaust temperature operation; releasing the stored hydrocarbon and NOx emissions into the exhaust flow path as the exhaust temperature increases to an effective operating temperature; and treating the released hydrocarbon and NOx emissions downstream of the storage location with an oxidation catalyst, a particulate filter, and an SCR portion, and a second SCR element downstream of the SCR portion of the particulate filter.

[0044] In certain embodiments, the method comprises storing hydrocarbon emissions with a hydrocarbon storage device. In other embodiments, the method comprises storing NOx emissions with a NOx storage device. In other embodiments, the NOx storage device is a NOx adsorber. In certain embodiments, the effective operating temperature is approximately 200°C. In other embodiments, the method further comprises selecting a reductant injector location upstream of the SCR portion of the particulate filter and / or downstream of the SCR portion of the particulate filter in response to an operating temperature of the exhaust gas such that an amount of reductant injected into the exhaust flowpath is sufficient for the SCR portion and / or the second SCR element to convert a desired amount of NOx emissions from the internal combustion engine.In one embodiment, the reducing agent is a gaseous reducing agent that is supplied to the first and second reducing agent injection nozzles. In another embodiment, the gaseous reducing agent is supplied to the first reducing agent injection nozzle and the liquid reducing agent is supplied to the second reducing agent injection nozzle.

[0045] Another aspect includes an exemplary set of embodiments relating to a method comprising: operating an internal combustion engine to produce an exhaust stream; storing hydrocarbons and nitrogen oxides in the exhaust stream at low-temperature operating conditions with at least one close-coupled storage device receiving the exhaust stream, and further comprising an oxidation catalyst downstream of the at least one storage device, a particulate filter, and an SCR portion downstream of the oxidation catalyst, and a second SCR element downstream of the SCR portion; releasing the stored hydrocarbons and nitrogen oxides in response to an increase in operating temperatures from the low-temperature operating conditions;Treating the released hydrocarbons and nitrogen oxides with the oxidation catalyst, the particulate filter, and the SCR portion, wherein the treating comprises delivering reductant to a first location upstream of the SCR portion or a second location downstream of the SCR portion and upstream of the second SCR element, wherein the second SCR element is positioned in a significantly different thermal environment than the SCR portion when the internal combustion engine produces the exhaust stream;

[0046] In one embodiment, the method comprises injecting reductant into the exhaust stream only at a first location in response to a low-temperature operating condition and injecting reductant into the exhaust stream only at the second location during regeneration of the particulate filter. In a refinement of this embodiment, the low-temperature operating condition is a cold-start operation or a warm-up operation of an engine. In another refinement, the method comprises preventing simultaneous injection of reductant at the first and second locations during the low-temperature operating condition and during regeneration of the particulate filter.

[0047] Another aspect and exemplary set of embodiments relates to a system having an internal combustion engine and an exhaust conduit in fluid communication with the internal combustion engine. The system includes at least one close-coupled device in fluid communication with the exhaust conduit and configured to provide a storage location for hydrocarbons and nitrogen oxides in an exhaust gas produced by the internal combustion engine during low-temperature operating conditions. The at least one close-coupled device includes an oxidation catalyst downstream of the hydrocarbon and nitrogen oxide storage location, a close-coupled particulate filter, and an SCR portion downstream of the oxidation catalyst and in fluid communication with the exhaust conduit. A second SCR element is in fluid communication with the exhaust conduit downstream of the SCR portion.The system includes a first reductant injector upstream of the SCR portion and configured to selectively provide a reductant to the exhaust flow path in response to a first reductant injector command, and a second reductant injector downstream of the SCR portion and upstream of the second SCR element and configured to selectively provide the reductant to the exhaust flow path in response to a second reductant injector command.

[0048] In one embodiment, the system includes the SCR portion connected to the second SCR element by a separation distance from the SCR portion to the second SCR element, providing exhaust cooling. In another embodiment, a source of liquid reductant is connected to each of the first and second reductant injectors. In yet another embodiment, a source of gaseous reductant is connected to at least the first reductant injector. In a refinement of this embodiment, the source of gaseous reductant is connected to the first and second reductant injectors.In a further refinement, during at least low temperature operating conditions of the second SCR element, the first reductant injector command provides a gaseous reductant to the exhaust gas only from the first reductant injector, and the second reductant injector command provides a gaseous reductant to the exhaust gas only from the second reductant injector during at least one high temperature operating condition associated with regeneration of the particulate filter.

[0049] In another embodiment, the SCR component is applied as a washcoat to the particulate filter. In yet another embodiment, the at least one storage device comprises separate devices for hydrocarbon storage, nitrogen oxide storage, and the oxidation catalyst. In another embodiment, the at least one storage device comprises a combined device for hydrocarbon storage, nitrogen oxide storage, and the oxidation catalyst.

[0050] In another embodiment, the system comprises: a controller having a NOx determination module structured to determine a NOx amount at an outlet of the SCR portion of the particulate filter and / or the second SCR element; a temperature determination module structured to determine a current operating temperature of the exhaust gas in the exhaust flow path; an injector selection module structured to select a first reductant injector and / or a second reductant injector for reductant injection in response to the current operating temperature;and a reductant control module structured to determine a corresponding one of the first and second reductant injector commands for the selected one of the first and second reductant injectors in response to the amount of NOx to achieve a desired NOx conversion by the SCR portion and / or the SCR element. In a refinement of this embodiment, the injector selection module is structured to select the first reductant injector in response to the current operating temperature indicative of low exhaust temperature operating conditions. In another refinement, the injector selection module is structured to select the second reductant injector in response to the current operating temperature indicative of particulate filter regeneration.

[0051] Yet another aspect and exemplary set of embodiments includes a system having an internal combustion engine capable of generating an exhaust stream and an aftertreatment system operably connected to receive the exhaust stream generated by the internal combustion engine. The aftertreatment system includes at least one close-coupled device configured to provide a storage location for hydrocarbons and nitrogen oxides in the exhaust stream during low-temperature operating conditions. The at least one close-coupled device further includes an oxidation catalyst downstream of the hydrocarbon and nitrogen oxide storage location, a close-coupled particulate filter and an SCR portion downstream of the oxidation catalyst, and a second SCR element downstream of the particulate filter and SCR portion.The second SCR element is disposed in a significantly different thermal environment than the SCR portion when the internal combustion engine generates the exhaust stream. The system further includes a reductant source in fluid communication with a first reductant injector upstream of the SCR portion and a second reductant injector downstream of the SCR portion. The first and second reductant injectors are configured to selectively provide a reductant to the exhaust stream.

[0052] In one embodiment, the reductant in the reductant source is a liquid reductant. In another embodiment, the reductant in the reductant source is a gaseous reductant. In a refinement of this embodiment, the gaseous reductant is supplied to the exhaust stream only from the first reductant injector during at least low-temperature operating conditions of the second SCR element. In a further refinement, reductant is supplied to the exhaust stream only from the second reductant injector during at least one high-temperature operating condition associated with regeneration of the particulate filter. In another embodiment, the SCR portion is included as a washcoat on the particulate filter.In yet another embodiment, the at least one storage device comprises a separate device for each of hydrocarbon storage, nitrogen oxide storage, and the oxidation catalyst. In yet another embodiment, the at least one storage device comprises a combined device for hydrocarbon storage, nitrogen oxide storage, and the oxidation catalyst.

[0053] While the invention has been described in detail in the drawings and the foregoing description, it is to be considered as illustrative and not restrictive in nature, it being understood that only certain embodiments have been shown and described, and that all changes and modifications which come within the spirit of the invention are intended to be protected. In reading the claims, it is to be understood that the use of words such as "a", "an", "at least one", or "at least a part" is not intended to limit the claim to only one element unless expressly stated to the contrary in the claim. When the phrase "at least a part" and / or "a part" is used, the element may include part and / or all of the element unless expressly stated to the contrary.

Claims

[1] System, with: an internal combustion engine (22); an exhaust line in fluid communication with the internal combustion engine (22); at least one device mounted close to the engine, which is in fluid communication with the exhaust line and is configured to provide a storage location for hydrocarbons and nitrogen oxides in an exhaust gas produced by the internal combustion engine (22) under low-temperature operating conditions, wherein the at least one device installed close to the engine further comprises an oxidation catalyst downstream of the storage location of the hydrocarbons and nitrogen oxides, a particulate filter and a selective catalytic reduction (SCR) part downstream of the oxidation catalyst and in fluid communication with the exhaust line, a second SCR element (20) in fluid communication with the exhaust line downstream of the SCR part; a first reductant injector (28) upstream of the SCR portion and configured to selectively provide a reductant to the exhaust flow path in response to a first reductant injector command; and a second reductant injector (30) downstream of the SCR portion and upstream of the second SCR element (20) and configured to selectively provide the reductant to the exhaust flow path in response to a second reductant injector command. [2] System according to claim 1, characterized by that the SCR part is connected to the second SCR element (20) by a separation distance between the SCR part and the second SCR element (20) providing exhaust gas cooling. [3] System according to claim 1, characterized by that a source (32) of a liquid reducing agent is connected to the first and second reducing agent injection nozzles (28, 30). [4] System according to claim 1, characterized by that a source (32) of a gaseous reducing agent is connected to at least the first reducing agent injection nozzle (28). [5] System according to claim 4, characterized by that the source (32) of gaseous reducing agent is connected to the first and second reducing agent injection nozzles (28, 30). [6] System according to claim 5, characterized by that the first reductant injector command provides a gaseous reductant to the exhaust gas only from the first reductant injector (28) at least during low temperature operating conditions of the second SCR element (20). [7] System according to claim 6, characterized by that the second reductant injector command provides a gaseous reductant to the exhaust gas only from the second reductant injector (30) during at least high temperature operating conditions associated with the regeneration of the particulate filter. [8] System according to claim 1, characterized by that the SCR part is contained in the particulate filter as a washcoat. [9] System according to claim 1, characterized by that the at least one storage device contains a separate device for each of the hydrocarbon storage, the nitrogen oxide storage and the oxidation catalyst. [10] System according to claim 1, characterized by that the at least one storage device comprises a combined device for hydrocarbon storage, nitrogen oxide storage and the oxidation catalyst. [11] The system of claim 1, further comprising a controller, the controller comprising: a NO x -Determination module used to determine a NO x -amount at an outlet of the at least one of the SCR part and the second SCR element (20) is structured; a temperature determination module (62) structured to determine a current operating temperature of the exhaust gas; an injector selection module structured to select the first reductant injector (28) and / or the second reductant injector (30) in response to the current operating temperature; a reductant control module (66) structured to provide the first and second reductant injector commands for the first and second reductant injectors (28, 30) in response to the NO x -quantity to be determined, to achieve a desired NO x -Conversion by the SCR part and / or the SCR element. [12] System according to claim 11, characterized byin that the injector selection module (64) is structured to select the first reductant injector (28) in response to a current operating temperature indicative of a low exhaust temperature operating condition. [13] System according to claim 11, characterized by in that the injector selection module (64) is structured to select the second reductant injector (30) in response to a current operating temperature indicative of regeneration of the particulate filter. [14] A system comprising: an internal combustion engine (22) capable of generating an exhaust gas stream; an aftertreatment system operatively connected to receive the exhaust gas stream generated by the internal combustion engine, the aftertreatment system comprising: at least one close-coupled device configured to provide a storage location for hydrocarbons and nitrogen oxides in the exhaust stream at low-temperature operating conditions, the at least one close-coupled device further comprising an oxidation catalyst downstream of the storage location for the hydrocarbons and nitrogen oxides; a particulate filter installed close to the engine downstream of the oxidation catalyst and a selective catalytic reduction (SCR) part; a second SCR element (20) downstream of the particulate filter and SCR part, wherein the second SCR element (20) is arranged in a significantly different thermal environment than the SCR part when the internal combustion engine generates the exhaust gas flow; and a reducing agent source (32) in fluid communication with a first reducing agent injection nozzle (28) upstream of the SCR part and with a second reducing agent injection nozzle (30) downstream of the SCR part, wherein the first and second reductant injection nozzles (28, 30) are configured to selectively supply a reductant to the exhaust gas stream. [15] System according to claim 14, characterized by that the reducing agent in the reducing agent source (32) is a liquid reducing agent. [16] System according to claim 14, characterized by that the reducing agent in the reducing agent source (32) is a gaseous reducing agent. [17] System according to claim 16, characterized by that the gaseous reducing agent is supplied to the exhaust gas stream only from the first reducing agent injection nozzle (28), at least during low-temperature operating conditions of the second SCR element (20). [18] System according to claim 17, characterized by that reducing agent is supplied to the exhaust gas stream only from the second reducing agent injection nozzle (30), at least under high-temperature operating conditions associated with the regeneration of the particulate filter. [19] System according to claim 14, characterized by that the SCR part is included as a washcoat on the particulate filter. [20] System according to claim 14, characterized by that the at least one storage device comprises a separate device for each of the hydrocarbon storage, the nitrogen oxide storage and the oxidation catalyst. [21] System according to claim 14, characterized by that the at least one storage device comprises a combined device for hydrocarbon storage, nitrogen oxide storage and the oxidation catalyst. [22] Method comprising: Operating an internal combustion engine to generate an exhaust gas stream; Storing hydrocarbons and nitrogen oxides in the exhaust gas stream at low-temperature operating conditions with at least one storage device installed close to the engine, which receives the exhaust gas stream, and further comprising an oxidation catalyst downstream of the at least one storage device, a particulate filter and a selective catalytic reduction (SCR) part downstream of the oxidation catalyst and a second SCR element (20) downstream of the SCR part; Releasing the stored hydrocarbons and nitrogen oxides in response to an increase in operating temperatures from the low-temperature operating conditions; Treating the released hydrocarbons and nitrogen oxides with the oxidation catalyst, the particulate filter and the SCR part, wherein the treating comprises supplying reducing agent to a first location upstream of the SCR part, or a second location downstream of the SCR portion and upstream of the second SCR element, wherein the second SCR element (20) is positioned in a significantly different thermal environment than the SCR portion when the internal combustion engine (22) generates the exhaust gas stream. [23] The method of claim 22, further comprising: Injecting reductant into the exhaust stream only at the first location in response to a low temperature operating condition; and injecting reducing agent into the exhaust gas stream only at the second point during regeneration of the particulate filter. [24] Method according to claim 23, characterized by that the low-temperature operating condition is a cold start operation or a warm-up operation of an engine. [25] The method of claim 23, further comprising preventing simultaneous injection of reductant at the first and second locations at the low temperature operating condition and during regeneration of the particulate filter. [26] Method comprising: Storing, at a location in an exhaust gas flow path, hydrocarbon and NO x -Emissions from an internal combustion engine during operation at low exhaust gas temperature; Release of stored hydrocarbons and NO x -Emissions into the exhaust gas flow path when the exhaust gas temperature increases to an effective operating temperature; and downstream treatment of the released hydrocarbons and NO x -Emissions with an oxidation catalyst, a particulate filter and an SCR part downstream of the oxidation catalyst and a second SCR element (20) downstream of the SCR part. [27] Method according to claim 26, characterized by that hydrocarbon emissions are stored with a hydrocarbon storage device and NO x -Emissions with a NO x -storage device. [28] Method according to claim 27, characterized by that the NO x -Storage device a NO x -adsorber. [29] Method according to claim 26, characterized by that the effective operating temperature is 200 °Celsius. [30] The method of claim 26, further comprising: Selecting a first reductant injector (28) upstream of the SCR portion or a second reductant injector (30) downstream of the SCR portion in response to the operating temperature; and injecting a reducing agent into the exhaust gas flow path in an amount sufficient for the SCR part and / or the second SCR element (20) to achieve a desired amount of NO x- to convert emissions from the combustion engine (22). [31] Method according to claim 30, characterized by that the reducing agent is a gaseous reducing agent which is supplied to the first and second reducing agent injection nozzles (28, 30). [32] Method according to claim 30, characterized by that the reducing agent comprises a gaseous reducing agent which is supplied to the first reducing agent injection nozzle (28) and a liquid reducing agent which is supplied to the second reducing agent injection nozzle (30).

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