EP4602255A1

EP4602255A1 - Exhaust treatment system, method for treatment of an exhaust stream and control system therefore

Info

Publication number: EP4602255A1
Application number: EP23907946.0A
Authority: EP
Inventors: Magnus Nilsson; Henrik BIRGERSSON
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2022-12-19
Filing date: 2023-12-08
Publication date: 2025-08-20
Also published as: WO2024136720A1; SE2251493A1; CN120283103A; SE546382C2

Abstract

An exhaust treatment system (250, 350) arranged for treatment of an exhaust stream (203, 303) resulting from a combustion in a combustion engine (201, 301) is presented. The exhaust treatment system (250, 350) comprises at least one fiber structure (280a-d, 380a-d) arranged downstream of an evaporation arrangement to interact with particles in the exhaust stream (203, 303). These particles are created by one or more of the supply of the additive into the exhaust stream and a transformation of the additive when flowing through the exhaust treatment system. The at least one fiber structure (280a-d, 380a-d) has a fiber to volume ratio F/V in an interval of 40% to 90%, such that: -- the particles are caused to interact with the at least one fiber structure (280a-d, 380a-d), thereby being at least partly captured and removed from the exhaust stream (203, 303); and -- accumulation of soot and ash created by the combustion, which would affect the interaction of the at least one fiber structure (280a-d, 380a-d) and the particles, is at least partly avoided.

Description

EXHAUST TREATMENT SYSTEM, METHOD FOR TREATMENT OF AN EXHAUST STREAM AND CONTROL SYSTEM THEREFORE

Technical field

The present invention relates to an exhaust treatment system, a method for treatment of an exhaust stream, and a control system for controlling the exhaust treatment system to perform the method.

The invention also relates to a computer program and a computer program product, which implement the method according to the invention.

Background

The following background description constitutes a description of the background to the present invention, and thus need not necessarily constitute prior art.

In connection with increased government interests concerning pollution and air quality, primarily in urban areas, emission standards and regulations regarding emissions from combustion engines have been drafted in many jurisdictions.

Such emission standards often consist of requirements defining acceptable limits of exhaust emissions from combustion engines in for example vehicles. For example, emission levels of nitrogen oxides NOx, hydrocarbons CxH_y, carbon monoxide CO and particles PM are often regulated by such standards for most types of vehicles. Vehicles equipped with combustion engines typically give rise to such emissions in varying degrees. In this document, the invention will be described mainly for its application in vehicles, i.e. for internal combustion engines. However, the invention may be used in substantially all applications where combustion engines are used, for example in vessels such as ships or aeroplanes/helicopters, wherein regulations and standards for such applications limit emissions from the combustion engines.

In an effort to comply with these emission standards, the exhausts caused by the combustion of the combustion engine are treated (purified). A common way of treating exhausts from a combustion engine comprises a so-called catalytic purification process, which is why vehicles equipped with a combustion engine usually comprise at least one catalyst. There are different types of catalysts, where the different respective types may be suitable depending on for example the combustion concept, combustion strategies and/or fuel types which are used in the vehicles, and/or the types of compounds in the exhaust stream to be purified. In relation to at least nitrous gases (nitrogen monoxide, nitrogen dioxide), referred to below as nitrogen oxides NOx, vehicles often comprise a catalyst, wherein an additive is supplied to the exhaust stream resulting from the combustion in the combustion engine, in order to reduce nitrogen oxides NOx, primarily to nitrogen gas and aqueous vapour. This is described in more detail below.

SCR (Selective Catalytic Reduction) catalysts are a commonly used type of catalysts for this type of reduction, primarily for heavy goods vehicles. SCR catalysts usually use ammonia NH3, or a composition from which ammonia may be generated/formed, as an additive to reduce the amount of nitrogen oxides NOx in the exhausts. The additive, for example urea, is injected into the exhaust stream resulting from the combustion engine upstream of the catalyst. The additive added to the catalyst is adsorbed (stored) in the catalyst, in the form of ammonia NH3, so that a redoxreaction may occur between nitrogen oxides NOx in the exhausts and ammonia NH3 available via the additive.

Summary

When the additive is injected into the exhaust stream, i.e. when the additive is supplied into the exhaust treatment system, small particles may be created from the additive at the injection. Also, when the injected additive travels with the exhaust stream through the components of the exhaust treatment system, further small particles may be created from the additive due to the treatment of the exhaust stream performed by the components of the exhaust treatment system. Thus, these small additive based particles may be created from the additive at the injection and/or from various transformations of the additive when flowing through the exhaust treatment system. The particles may therefore comprise urea and/or polymeric biproducts based on urea, depending on where in the exhaust treatment system they are created.

These small additive based particles may for example have a diameter in the interval of 10 to 23 nm, and may flow with the exhaust stream through the entire exhaust treatment system and be emitted at the tailpipe. Thus, at least a portion of these additive based particles may, e.g. due to their small size, pass through each of the components of the exhaust treatment system, also through the SCR catalysts, and may be emitted into the environment as emissions. The additive based particles may also comprise combustion-based particles, i.e. particles created at the combustion in the combustion engine. Thus the small-sized particles may then, due to interaction and/or mixing with particles from the combustion, comprise a mixture of additive based particles and soot and/or ash. These small particles may, if being emitted, have health effects.

One objective of the present invention is to at least partly prevent these small additive based particles from being emitted into the environment.

The objective is achieved through the above mentioned exhaust treatment system arranged for treatment of an exhaust stream resulting from a combustion in a combustion engine, the exhaust treatment system comprising:

- a particulate filter arranged to catch soot and ash created by the combustion;

- a dosing arrangement arranged downstream of the particulate filter to supply an additive into the exhaust stream, the additive being mixed with the exhaust stream by an evaporation arrangement arranged at the dosing arrangement;

- a reduction catalyst arrangement arranged downstream of the dosing arrangement for reduction of nitrogen oxides NOx in the exhaust stream by utilization of the supplied additive; and

- at least one fiber structure arranged downstream of the evaporation arrangement to interact with particles in the exhaust stream, the particles being created by one or more of the supply of the additive into the exhaust stream and a transformation of the additive when flowing through the exhaust treatment system, wherein the at least one fiber structure has a fiber to volume ratio F/V in an interval of 40% to 90%, such that: -- the particles are caused to interact with the at least one fiber structure, thereby being at least partly captured and removed from the exhaust stream; and

-- accumulation of soot and ash created by the combustion, which would affect the interaction of the at least one fiber structure and the particles, is at least partly avoided.

Hereby, the small additive particles are at least partly removed from the exhaust stream before the exhaust stream is emitted from the tailpipe. Thus, these small particles, possibly having a diameter in the interval of 10 to 23 nm, are dissolved by the interaction with the at least one fiber structure, and are at least partly hindered from leaving the tailpipe. The material structure as such of the at least one fiber structure facilitates entrapment of the additive based particles. Soot and ash from the combustion may be accumulated only to a low degree, such that the interaction performance of the at least one fiber structure is not degraded.

The fiber to volume ratio F/V being in the interval of 40% to 90% provides for the above mentioned small additive based particles being captured and removed although accumulation of soot and ash is at least partly avoided. Thus, the fiber to volume ratio F/V in the interval of 40% to 90% defines the at least one fiber structure such that it, although providing a poor filtering in the traditional sense of catching large soot and ash particles, surprisingly efficiently catches and removes the small additive based particles.

The at least one fiber structure is possible to implement essentially anywhere in the exhaust treatment system, which makes the implementation flexible, and it does not affect the functions of the other components in the exhaust treatment system. Especially, since the at least one fiber structure is separated from the evaporation arrangement by its position downstream of the evaporation arrangement, it does not affect the function of the evaporation arrangement.

The exhaust treatment system according to the present invention has potential to meet the emission requirements in current and/or future emission standards.

According to an embodiment, the at least one fiber structure is arranged at least 0.1 meter downstream of the dosing arrangement. Hereby, the at least one fiber structure is separated from the dosing arrangement, and thus also from the evaporation arrangement, such that it does not affect the injection of additive into the exhaust stream. Thus, the at least fiber structure is by this placement arranged to interact with, and remove, the small additive based particles. However, the injected additive intended to be used by the catalysts in the system reaches the catalysts such that efficient reduction of nitrogen oxides NOx is provided.

According to an embodiment, the at least one fiber structure is comprised in the reduction catalyst arrangement.

By this position of the at least one fiber structure as integrated in the reduction catalyst arrangement, an efficient removal of the particles is provided by a compact component solution.

According to an embodiment, the at least one fiber structure is arranged downstream of the reduction catalyst arrangement.

Hereby, the at least one fiber structure does not affect the performance of the reduction catalyst arrangement.

According to an embodiment, the exhaust treatment system further comprises a slip catalyst arrangement arranged downstream of the reduction catalyst arrangement for oxidation of a residue of additive in the exhaust stream, and the at least one fiber structure is arranged downstream of the reduction catalyst arrangement and upstream of the slip catalyst arrangement.

At this position, an efficient function of the at least one fiber structure may be provided.

According to an embodiment, the exhaust treatment system further comprises a slip catalyst arrangement arranged downstream of the reduction catalyst arrangement for oxidation of a residue of additive in the exhaust stream, and the at least one fiber structure is comprised in the slip catalyst arrangement.

By this position of the at least one fiber structure as integrated in the slip catalyst, a removal of the additive based particles is provided by a compact component solution. According to an embodiment, the exhaust treatment system further comprises a slip catalyst arrangement arranged downstream of the reduction catalyst arrangement for oxidation of a residue of additive in the exhaust stream, and the at least one fiber structure is arranged downstream of the slip catalyst arrangement.

At this position, an efficient function, i.e. an efficient capture and removal of the additive based particles, for the at least one fiber structure may be provided.

According to an embodiment, the reduction catalyst arrangement comprises one or more in the group of:

- at least one selective catalytic reduction catalyst;

- at least one slip catalyst.

Hereby, an efficient removal of nitrogen oxides NOx may be provided.

According to an embodiment

- the at least one fiber structure comprises at least one section arranged to be heated to an interaction temperature Ti by the exhaust stream flowing through it, the interaction temperature Ti exceeding a particle temperature Tp at which the particles thermally dissolve; Ti>Tp; and

- the at least one fiber structure is arranged to interact with the particles such that the particles at least partly come in physical contact with the heated at least one section.

Thus, the additive based particles are efficiently dissolved by the at least one fiber structure which is at least partly heated by the exhaust stream.

According to an embodiment, the interaction temperature Ti is at least 150 °C.

When the interaction temperature Ti reaches and/or exceeds 150 °C, the additive based particles are efficiently dissolved and thus removed from the exhaust stream. Thus, if the interaction temperature Ti initially is lower than 150 °C, some particles may at first be accumulated in the at least one fiber structure. Then, when the interaction temperature Ti reaches 150 °C, these accumulated particles are dissolved.

According to an embodiment, the at least one fiber structure at least partially comprises an inert material. Thus, the additive based particles are here efficiently thermally dissolved by heat. Also, the material structure of the at least one fiber structure as such facilitates entrapment of the additive based particles.

According to an embodiment, the inert material is one or more in the group of:

- a metallic material; and

- a non-metallic material.

Thus, a number of materials and/or mixes of materials may be utilized in the at least one fiber structure for removing the additive based particles. Hereby, an implementation flexibility is provided. In different implementations, materials such as cordierite, silicon carbide, aluminum titanate and/or polymer composites may be used.

According to an embodiment, the at least one fiber structure at least partially comprises an active catalytic material.

Hereby, the additive based particles may be dissolved by use of an active catalytic material, such as for example precious metals, Vanadium, Iron (Fe), Copper, Titanium, Tungsten and/or Aluminium, which may possibly also have other functions in the exhaust treatment system. Hereby, an efficient solution which takes up no, or very little, extra space is provided.

According to an embodiment, the material is coated on the at least one fiber structure.

Thus, the material being used for removing the additive based particles, which may be an inert or a catalytically active material, may be coated on the at least one fiber structure. The coating of the material may improve the efficiency for the at least one fiber structure regarding capturing and dissolving of entrapped additive based particles.

According to an embodiment, the at least one fiber structure comprises a porous structure/formation/construction/constitution/composition/fabric/web/texture arranged to let the exhaust stream flow through it.

Hereby, i.e. by the porous structure/formation/construction/constitution/composition/fabric/web/texture, the additive based particles are effectively caused to interact with the at least one fiber structure such that they are dissolved.

According to an embodiment,

- the at least one fiber structure has a cross section area A in inches² and a length L in inches; and

- an area to length ratio A/L in inches for the at least one fiber structure has a value of at least 17 inches and at most 150 inches; 17<A/L<150 inches.

Within this interval for the area to length ratio A/L, a very small-sized and efficient fiber structure is provided.

According to an embodiment, the additive comprises one or more in the group of:

- ammonia, and

- a substance from which ammonia may be extracted and/or released.

Hereby, an efficient reduction of nitrogen oxides NOx in the exhaust stream may be provided by the exhaust treatment system.

According to an embodiment, the particles comprise one or more in the group of:

- urea; and

- polymeric biproducts based on urea.

Thus, the additive based particles are relatively instable and may be dissolved by the least one fiber structure. The particles may alternatively be captured by the at least one fiber structure.

According to an embodiment, the fiber to volume ratio F/V of the at least one fiber structure is in the interval of 40% to 70%.

Hereby, the interaction between the at least one fiber structure and the additive based particles is provided, which efficiently dissolves the particles.

According to an embodiment, the exhaust treatment system comprises:

- an upstream dosing device arranged to supply an additive into the exhaust stream;

- an upstream reduction catalyst device arranged downstream of the upstream dosing device for reduction of nitrogen oxides NOx in the exhaust stream by utilizing the supplied additive; - the particulate filter arranged downstream of the upstream reduction catalyst device to catch soot and ash created by the combustion;

- the dosing arrangement arranged as a downstream dosing device downstream of the particulate filter to supply an additive into the exhaust stream, the additive being mixed with the exhaust stream by an evaporation arrangement arranged at the downstream dosing device as a downstream evaporation arrangement;

- the reduction catalyst arrangement arranged as a downstream reduction catalyst device downstream of the downstream dosing device to reduce nitrogen oxides NOx in the exhaust stream by utilizing the supplied additive; and

- the at least one fiber structure arranged downstream of the downstream evaporation arrangement.

The upstream and downstream reduction catalyst devices may be optimised individually, and with consideration of the entire exhaust treatment system’s function, which may result in an overall very efficient purification of the exhausts. This individual optimisation may also be used to reduce one or several of the volumes taken up by the upstream and downstream reduction catalyst devices, so that a compact exhaust treatment system is obtained.

Also, the two additive dosing devices in the system makes it possible to adjust the amount of additive being injected by the upstream and downstream dosing devices, respectively. Thus, by an active control of the upstream and downstream dosing, respectively, the amount of additive and/or of the additive based particles at the downstream reduction catalyst arrangement may be controlled to be suitable for efficient reduction of nitrogen oxides NOx and/or for keeping the additive based particles at a reasonable level, in relation to allowed emission levels.

According to an embodiment, the upstream reduction catalyst device comprises one or more in the group of:

- an upstream selective catalytic reduction catalyst; and

- an upstream slip catalyst.

Hereby, a flexible exhaust treatment system is provided, which efficiently reduces the nitrogen oxides NOx in the exhaust stream. The above-mentioned objective is achieved also through the above-mentioned method for treatment of an exhaust stream resulting from a combustion in a combustion engine. The method comprises:

- catching soot and ash created by the combustion by utilization of a particulate filter;

- controlling a supply of an additive into the exhaust stream by utilization of a dosing arrangement arranged downstream of the particulate filter, the additive being mixed with the exhaust stream by an evaporation arrangement arranged at the dosing arrangement;

- reduction of nitrogen oxides NOx in the exhaust stream by utilization of the supplied additive and a reduction catalyst arrangement arranged downstream of the dosing arrangement; and

- interaction of particles in the exhaust stream and at least one fiber structure arranged downstream of the evaporation arrangement, the particles being created by one or more of the supply of the additive into the exhaust stream and a transformation of the additive when flowing through the exhaust treatment system, wherein the at least one fiber structure has a fiber to volume ratio F/V in an interval of 40% to 90%, such that:

-- the particles are caused to interact with the at least one fiber structure, thereby being at least partly captured and removed by the at least one fiber structure; and -- accumulation of soot and ash created by the combustion, which would affect the interaction of the at least one fiber structure and the particles, is at least partly avoided.

The method has corresponding advantages as stated above for the exhaust treatment system.

The above-mentioned objective is also achieved through the above-mentioned control system arranged for treatment of an exhaust stream resulting from a combustion in a combustion engine. The treatment comprises:

- controlling a supply of an additive into the exhaust stream by utilization of a dosing arrangement arranged downstream of the particulate filter, the additive being mixed with the exhaust stream by an evaporation arrangement arranged at the dosing arrangement; - reduction of nitrogen oxides NOx in the exhaust stream by utilization of the supplied additive and a reduction catalyst arrangement arranged downstream of the dosing arrangement; and

The control system has corresponding advantages as stated above for the exhaust treatment system.

The above-mentioned objective is also achieved through the above-mentioned computer program and computer program product.

The computer program and computer program product, respectively, has corresponding advantages as stated above for the exhaust treatment system.

Brief list of figures

The invention will be illustrated in more detail below, along with the enclosed drawings, where similar references are used for similar parts, and where:

Figure 1 shows an example vehicle which may comprise an exhaust treatment system according to various embodiments of the present invention,

Figure 2a shows an example of an exhaust treatment system in which aspects and embodiments of the present invention may be implemented,

Figure 2b shows various embodiments of the implementation of the present invention in an exhaust treatment system, Figure 3a shows an example of an exhaust treatment system in which aspects and embodiments of the present invention may be implemented,

Figure 3b shows various embodiments of the implementation of the present invention in an exhaust treatment system,

Figure 4 shows a flow chart for the method for exhaust treatment according to the invention, and

Figure 5 shows a control device according to the present invention.

Description of preferred embodiments

Figure 1 schematically shows an example vehicle 100 comprising an exhaust treatment system 250, 350, which may be an exhaust treatment system 250, 350 according to an aspect or embodiment of the present invention. The powertrain comprises a combustion engine 101 , which in a customary manner, via an output shaft 102 of the combustion engine 101 is connected to a gearbox 103 via a clutch 106. An output shaft 107 from the gearbox 103 may drive the wheels 113, 114 e.g. via a final drive 108, such as e.g. a customary differential, and the drive shafts 104, 105 connected to the said final drive 108.

The combustion engine 101 , e.g. an internal combustion engine, may be controlled by the engine’s control system via a control device 115. Likewise, the clutch 106 and the gearbox 103 may be controlled by the vehicle’s control system, with the help of one or more applicable control devices (not shown). Naturally, the vehicle’s powertrain may also be of another type, such as a type with a conventional automatic gearbox, or a type with a hybrid driveline, etc.

The vehicle 100 also comprises an exhaust treatment/purification system 250, 350 for treatment/purification of exhaust emissions resulting from combustion in the combustion chamber of the combustion engine 101 .

Figure 2a shows an exhaust treatment system 250, which may illustrate a so-called Euro Vl-system. The exhaust treatment system 250 is connected to a combustion engine 201 , e.g. an internal combustion engine, e.g. via an exhaust conduit 202, wherein the exhausts generated at the combustion, that is to say the exhaust stream 203, is indicated with arrows. The exhaust stream 203 is led to a coated diesel particulate filter (cDPF) 210, which is coated with a catalytically oxidising coating, for example comprising at least one precious metal. Alternatively, a diesel oxidation catalyst (DOC) followed downstream by an uncoated diesel particulate filter (DPF) or a coated diesel particulate filter (cDPF) may be arranged in the exhaust treatment system 250 instead of the coated diesel particulate filter (cDPF). Thus, either of a coated diesel particulate filter (cDPF) 210 and a diesel oxidation catalyst (DOC) followed by a diesel particulate filter (DPF/cDPF) is arranged downstream of the combustion engine 201 in the exhaust treatment system 250.

During the combustion in the combustion engine 201 , soot and ash are created, and the coated diesel particulate filter (cDPF) 210, or alternatively the diesel particulate filter (DPF), is used to catch the soot and ash. The exhaust stream 203 is here led through a filter structure, wherein soot and ash from the exhaust stream 203 are caught when passing through, and are stored in the particulate filter 210.

The catalytic coating in the coated diesel particulate filter (cDPF) 210, or alternatively in the oxidation catalyst (DOC), has several functions and is normally used primarily to oxidise, during the exhaust treatment, remaining hydrocarbons CxH_y (also referred to as HC) and carbon monoxide CO in the exhaust stream 203 into carbon dioxide CO2 and water H2O. Also, a large fraction of the nitrogen monoxides NO occurring in the exhaust stream may be oxidised into nitrogen dioxide NO2. The oxidation of nitrogen monoxide NO into nitrogen dioxide NO2 is important to the nitrogen dioxidebased soot and ash oxidation in the filter, and is also advantageous at a potential subsequent reduction of nitrogen oxides NOx.

In this respect, the exhaust treatment system 250 further comprises a reduction catalyst arrangement 220 arranged downstream of the coated diesel particulate filter (cDPF) 210. The reduction catalyst arrangement 220 may comprise at least one selective catalytic reduction (SCR) catalyst and/or at least one slip catalyst. The reduction catalyst arrangement 220 uses ammonia NH3, or a composition from which ammonia may be generated/formed, e.g. urea, as an additive for the reduction of nitrogen oxides NOx in the exhaust stream 203. After passing through the components of the exhaust treatment system, the exhaust stream is emitted into the environment at the tailpipe.

The reaction rate of this reduction is impacted, however, by the ratio between nitrogen monoxide NO and nitrogen dioxide NO2 in the exhaust stream, so that the reductive reaction is impacted in a positive direction by the previous oxidation of NO into NO2 in the coated diesel particulate filter (cDPF), or alternatively in the oxidation catalyst DOC.

The reduction catalyst arrangement 220 requires additives to reduce the concentration of a compound, such as for example nitrogen oxides NOx, in the exhaust stream 203. Such additive is injected into the exhaust stream downstream of the particulate filter 210 and upstream of the reduction catalyst arrangement 220, shown in figure 2a as a dosing arrangement 270. Such additive is often ammonia and/or urea based, or consists of a substance from which ammonia may be extracted or released, and may for example consist of AdBlue, which basically consists of urea mixed with water. Urea forms ammonia at heating (thermolysis) and at heterogeneous catalysis on an oxidizing surface (hydrolysis), which surface may, for example, consist of titanium dioxide TiO2, within the reduction catalyst arrangement 220. The exhaust treatment system may also comprise a separate hydrolysis catalyst.

An evaporation arrangement (not shown), e.g. a hydrolysis catalyst, which may consist of substantially any suitable hydrolysis coating, and/or a first mixer, is arranged at the dosing arrangement 270. The hydrolysis catalyst, and/or the first mixer, are then used to increase the speed of the decomposition of urea into ammonia, and/or to mix the additive with the emissions, and/or to vaporise the additive.

The additive may be provided from a container/tank 275, and the dosing of the additive may be controlled by a control unit/system 290.

The exhaust treatment system 250 may also be equipped with a slip-catalyst (SC) 240, which is arranged downstream of the reduction catalyst arrangement 220 to oxidise an excess of ammonia that may remain after the reduction catalyst arrangement 220, an/or to assist the reduction catalyst arrangement 220 with further reduction of NOx. Accordingly, the slip-catalyst SC 240 may provide a potential for improving the system’s total conversion/reduction of NOx.

The exhaust treatment system 250 may also be equipped with one or several sensors, such as one or several NOx and/or temperature sensors for the determination of nitrogen oxides and/or temperatures in the exhaust treatment system.

Figure 3a schematically shows another exhaust treatment system 350, which is connected via an exhaust pipe 302 to a combustion engine 301 , e.g. an internal combustion engine. Exhausts are generated at combustion in the engine 301 and the exhaust stream 303 (indicated with arrows) are led to an upstream dosage device 371 , arranged to add an additive into the exhaust stream 303. An upstream reduction catalyst device 330 is arranged downstream of the upstream dosage device 371 . The upstream reduction catalyst device 330 is arranged to reduce nitrogen oxides NOx in the exhaust stream 303, through the use of the additive added to the exhaust stream by the upstream dosage device 371. In more detail, the upstream reduction catalyst device 330 uses the additive, for example ammonia NHs, or a substance from which ammonia may be generated/formed/released, for the reduction of nitrogen oxides NOx in the exhaust stream 303. This additive may for example consist of the above mentioned AdBlue, and may be provided from a container/tank 375. The injection of the additive may be controlled by a control unit/system 390.

The upstream reduction catalyst device 330 may, according to various embodiments, comprise an upstream selective catalytic reduction (SCR) catalyst and/or an upstream slip catalyst. The upstream slip catalyst may be a conventional ammonia slip catalyst (ASC) or may be a multifunctional slip catalyst (SC), which is arranged primarily for reduction of nitrogen oxides NOx, and secondarily for oxidising the additive in the exhaust stream 303.

The multifunctional slip catalyst (SC) includes a nitrogen oxides NOx reducing coating being in direct contact with the exhaust stream 303. The multifunctional slip catalyst (SC) also includes one or several substances comprised in platinum group metals, and/or one or several other substances that provide similar characteristics as for the platinum group metals.

Thus, according to various embodiments, the upstream reduction catalyst device 330 may e.g. comprise one of:

- an upstream selective catalytic reduction catalyst SCRi followed downstream by an integrated or separate upstream slip-catalyst SCi, wherein the upstream slip-catalyst SCi is arranged primarily for reduction of nitrogen oxides NOx, and secondarily for oxidation of a residue of additive in the exhaust stream 303;

- an upstream slip-catalyst SCi, followed downstream by an integrated or separate upstream selective catalytic reduction catalyst SCRi, wherein the upstream slipcatalyst SCi is arranged primarily for reduction of nitrogen oxides NOx, and secondarily for oxidation of additive in the exhaust stream 303;

- an upstream slip-catalyst SCi, followed downstream by an integrated or separate upstream selective catalytic reduction catalyst SCRi, followed downstream by an integrated or separate additional upstream slip-catalyst SC , wherein the upstream slip-catalyst SCi, and/or the additional upstream slip-catalyst SC , are arranged primarily for reduction of nitrogen oxides NOx, and secondarily for oxidation of additive in the exhaust stream 303;

- an upstream slip-catalyst SCi, which is primarily arranged for reduction of nitrogen oxides NOx, and secondarily for oxidation of a residue of additive in the exhaust stream 303.

Downstream of the upstream reduction catalyst device 330, the exhaust treatment system 350 further comprises a coated diesel particulate filter (cDPF) 310, which is coated with a catalytically oxidising coating, for example comprising at least one precious metal for catching and oxidising soot and ash. Alternatively, a diesel oxidation catalyst (DOC) followed downstream by a diesel particulate filter (DPF/CDPF) may be arranged in the exhaust treatment system 350 instead of the coated diesel particulate filter (cDPF). Thus, either of a coated diesel particulate filter (cDPF) 310 and a diesel oxidation catalyst (DOC) followed by a diesel particulate filter (DPF/cDPF) is arranged downstream of the upstream reduction catalyst device 330 in the exhaust treatment system 350. Downstream of the particulate filter 310, the exhaust treatment system 350 comprises a downstream dosage device 372, which is arranged to supply additive to the exhaust stream 303, where such second additive comprises ammonia NHs, or a substance, for example AdBlue, from which ammonia may be generated/formed/released, as described above. The downstream additive may here be the same additive as the above mentioned additive injected by the upstream dosage device 371 , and may possibly also come from the same container/tank 375. Alternatively, the additives injected by the upstream 371 and downstream 372 dosage devices, respectively, may also be of different types and may come from different tanks. The injection by the downstream dosage device 372 may be controlled by a control unit/system 390.

According to various embodiment of the invention, an evaporation arrangement may be arranged at the upstream 371 and/or downstream 372 dosing arrangements, respectively, to increase the speed of the decomposition of urea into ammonia, and/or to mix the additive with the emissions, and/or to vaporise the additive.

The exhaust treatment system 350 also comprises a downstream reduction catalyst device 320, which is arranged downstream of the downstream dosage device 372. The downstream reduction catalyst device 320 is arranged to reduce nitrogen oxides NOx in the exhaust stream 303 through use of the additive injected by the downstream dosage device 372, and possibly also additive remaining in the exhaust stream 303 which was injected by the upstream dosage device 371 .

The downstream reduction catalyst device 320 may comprises at least one selective catalytic reduction catalyst and/or at least one slip catalyst.

Thus, according to various embodiments, the downstream reduction catalyst device 320 may comprise one of:

- a downstream selective catalytic reduction catalyst SCR2; and

- a downstream selective catalytic reduction catalyst SCR2, downstream followed by an integrated or separate downstream slip-catalyst SC2, wherein the downstream slip-catalyst SC2 is arranged to oxidise a residue of additive and/or to assist SCR2 with an additional reduction of nitrogen oxides NOx in the exhaust stream 303. After passing through the components of the exhaust treatment system, the exhaust stream is emitted into the environment at the tailpipe of the exhaust treatment system.

The exhaust treatment system 350 may also be equipped with one or several sensors (not shown), such as one or several NOx sensors and/or one or several temperature sensors, which are arranged for the determination of NOx-concentrations and temperatures in the exhaust treatment system 350, respectively.

Through the use of the exhaust treatment system 350 shown in Figure 3a, both the upstream reduction catalyst device 330 and the downstream reduction catalyst device 320 may be optimised with respect to a selection of catalyst characteristics for the reduction of nitrogen oxides NOx, and/or with respect to volumes for the upstream 330 and downstream 320 reduction catalyst devices, respectively.

The particulate filter 310 may hereby be used to improve the efficiency, by taking into account how its thermal mass, i.e. its thermal inertia, impacts the temperature of the downstream reduction catalyst 320. By taking into account the thermal inertia of the particulate filter 310, the upstream reduction catalyst device 330 and the downstream reduction catalyst device 320, respectively, may be optimised with respect to the specific temperature function each will experience.

The exhaust treatment system 350 reduces the amount of nitrogen oxides NOx in the exhaust stream in substantially all driving modes, comprising especially cold starts and throttle, that is to say increased requested torque.

The above mentioned slip-catalyst SC may, according to various embodiments, be a catalyst, which is arranged to oxidise additive in the exhaust stream 303, and/or which is arranged so that it is able to reduce residual nitrogen oxides NOx in the exhaust stream 303.

In more detail, such a slip-catalyst SC may e.g. according to various embodiments be arranged primarily to reduce nitrogen oxides NOx, and secondarily to oxidise additive. In other words, the slip-catalyst SC may take care of slip-residues of both additive and nitrogen oxides NOx. This may also be described as the slip-catalyst SC being an extended ammonia slip-catalyst ASC, which is set up to reduce nitrogen oxides NOx in the exhaust stream 303, so that a general/multifunctional slip-catalyst SC is obtained, which takes care of several types of slip, meaning that it takes care of residues of both additive and nitrogen oxides NOx. At least the following reactions may for example be carried out in a multifunctional slip-catalyst SC, which both reduces nitrogen oxides NOx and oxidises additive: (Equation 1 ) and

NOx + NH3 -> N2 + H2O. (Equation 2)

Here, the reaction according to equation 1 results in an oxidation of residue of additive, comprising ammonia. The reaction according to equation 2 results in a reduction of nitrogen oxides NOx.

Accordingly, the additive may here be oxidised, as well as residues of ammonia NH3, isocyanic acid HNCO, urea or similar may be oxidised. These residues of additive, that is to say ammonia NH3, HNCO, urea or similar, may here also be used to oxidise nitrogen oxides NOx.

In order to obtain these characteristics, that is to say to obtain a multifunctional slipcatalyst, the slip-catalyst may according to one embodiment comprise one or several substances comprised in platinum metals (PGM; Platinum Group Metals), that is to say one or several of indium, osmium, palladium, platinum, rhodium and ruthenium. The slip-catalyst may also comprise one or several other substances, which give the slip-catalyst similar characteristics as platinum group metals. The slip-catalyst may also comprise an NOx-reducing coating, where the coating may for example comprise Cu- or Fe-Zeolite or vanadium. Zeolite may here be activated with an active metal, such as for example copper (Cu) or iron (Fe).

For both the upstream 330 and downstream 320 reduction catalyst devices, its catalytic characteristics may be selected based on the environment to which it is exposed, or will be exposed to. Additionally, the catalytic characteristics for the upstream 330 and downstream 320 reduction catalyst devices may be adapted so that they may be allowed to operate in symbiosis with each other. The upstream 330 and downstream 320 reduction catalyst devices may also comprise one or several materials, providing the catalytic characteristic. For example, transition metals such as vanadium and/or tungsten may be used, for example in a catalyst comprising V2Os/WO3/TiO2. Metals such as iron and/or copper may also be comprised in the upstream 330 and/or downstream 320 reduction catalyst devices, for example in a Zeolite-based catalyst.

According to the present invention at least one fiber structure 280a-d, 380a-d is arranged downstream of the evaporation arrangement to interact with certain smallsized additive based particles in the exhaust stream 203, 303. The evaporation arrangement is here arranged at the dosing arrangement 270, 372, as mentioned above. These particles may be created by the supply of the additive into the exhaust stream 203, 303 and/or by a transformation of the additive when the additive is flowing through the exhaust treatment system 250, 350, as mentioned above. The particles may comprise urea and/or polymeric biproducts based on urea. The injected additive comprises ammonia and/or a substance from which ammonia may be extracted and/or released.

Thus, the exhaust treatment system 250 shown in figure 2b comprises an evaporation arrangement arranged at the dosing arrangement 270, and the exhaust treatment system 350 shown in figure 3b comprises an evaporation arrangement arranged at the downstream dosing device 372, respectively. The at least one fiber structure 280a-d, 380a-d is arranged downstream of that evaporation arrangement, as illustrated in figures 2b and 3b, respectively.

The at least one fiber structure 280a-d, 380a-d has a fiber to volume ratio F/V chosen such that the additive based particles are caused to interact with the at least one fiber structure 280a-d, 380a-d, whereby the particles are at least partly captured and removed from the exhaust stream 203, 303. The fiber to volume ratio F/V is also chosen in an interval of 40% to 90%, such that accumulation of soot and ash created by the combustion is at least partly avoided. Hereby, the interaction of the at least one fiber structure 280a-d, 380a-d and the particles is not affected. The fiber to volume ratio F/V is a ratio between the solid fiber volume F and the total available volume V, which should be understood as the volume fraction containing solid material in the fiber structure in relation to the total volume of the fiber structure. This may also be explained as the fiber volume fraction F/V.

According to an embodiment, the at least one fiber structure 280a-d, 380a-d is arranged at least 0.1 meter downstream of the dosing arrangement, i.e. downstream of the evaporation arrangement at the dosing arrangement 270 shown in figure 2b or downstream of the downstream evaporation arrangement at the downstream dosing device 372 shown in figure 3b, respectively. For example, the at least one fiber structure 280a-d, 380a-d may be arranged at least 0.5 meter downstream of the dosing arrangement, or any other suitable distance downstream of the dosing arrangement, such that it does not interfere with the injection of the additive.

According to various embodiment, where the at least one fiber structure 280d, 380d is arranged downstream of the reduction catalyst arrangement 220, the downstream reduction catalyst device 320 and/or the slip catalyst 240, 340, the at least one fiber structure 280d, 380d may be arranged at least 1 .5 meter downstream of the dosing arrangement 270 shown in figure 2b or at least 1 .5 meter downstream of the downstream dosing device 372 shown in figure 3b, respectively. For e.g. exhaust treatment systems having a vertical tailpipe, the at least one fiber structure 280d, 380d may be arranged at least 3 meters downstream of the dosing arrangement 270 shown in figure 2b or at least 3 meters downstream of the downstream dosing device 372 shown in figure 3b, respectively.

According to an embodiment, the at least one fiber structure 280a is comprised in the reduction catalyst arrangement 220, as shown in figure 2b.

According to an embodiment, the at least one fiber structure 380a is comprised in the downstream reduction catalyst device 320, as shown in figure 3b.

According to an embodiment, the at least one fiber structure 280b-d is arranged 225, 240, 245 downstream of the reduction catalyst arrangement 220, as shown in figure 2b. According to an embodiment, the at least one fiber structure 380b-d is arranged 325, 340, 345 downstream of the downstream reduction catalyst device 320, as shown in figure 3b.

According to an embodiment, the at least one fiber structure 280b is arranged 225 downstream of the reduction catalyst arrangement 220 and upstream of the slip catalyst arrangement 240, as shown in figure 2b.

According to an embodiment, the at least one fiber structure 380b is arranged 325 downstream of the downstream reduction catalyst device 320 and upstream of the slip catalyst arrangement 340, as shown in figure 3b.

According to an embodiment, the at least one fiber structure 280c is comprised in the slip catalyst arrangement 240, as shown in figure 2b.

According to an embodiment, the at least one fiber structure 380c is comprised in the slip catalyst arrangement 340, as shown in figure 3b.

According to an embodiment, the at least one fiber structure 280d is arranged 245 downstream of the slip catalyst arrangement 240, as shown in figure 2b.

According to an embodiment, the at least one fiber structure 380d is arranged 345 downstream of the slip catalyst arrangement 340, as shown in figure 3b.

According to an embodiment, the reduction catalyst arrangement 220, 320 comprises at least one selective catalytic reduction catalyst and/or at least one slip catalyst.

According to an embodiment, the at least one fiber structure 280a-d, 380a-d comprises at least one section arranged to be heated by the exhaust stream 203, 303 to an interaction temperature Ti when the exhaust stream flows through the at least one fiber structure 280a-d, 380a-d. The interaction temperature Ti exceeds a particle temperature Tp at which the particles thermally dissolve; Ti>Tp. Also, the at least one fiber structure 280a-d, 380a-d is arranged, by its fiber to volume ratio F/V, to interact with the exhaust stream 203, 303, and thus also with the particles, such that at least a portion of the particles come in physical contact with the heated at least one section. Hereby, the particles hitting the at least one heated section are thermally dissolved and removed from the exhaust stream. The interaction temperature Ti may, according to an embodiment, be at least 150 °C.

At a cold start, i.e. before the at least one section has been heated to the interaction temperature Ti, then some particles may initially be accumulated in the at least one fiber structure 280a-d, 380a-d. However, when the at least one section has been heated to the interaction temperature Ti, the accumulated particles are thermally dissolved and removed from the exhaust stream 203, 303.

According to an embodiment, the at least one fiber structure 280a-d, 380a-d at least partially comprises an inert material, i.e. comprises a chemically inactive material, which is not prone to be involved in chemical reactions. The at least one fiber structure 280a-d, 380a-d may be made of the inert material, or the inert material may be coated on the at least one fiber structure 280a-d, 380a-d. The inert material may be a metallic and/or a non-metallic material, for example cordierite, silicon carbide, aluminum titanate and/or polymer composites.

According to an embodiment, the at least the at least one fiber structure 280a-d, 380a-d at least partially comprises an active catalytic material. The at least one fiber structure 280a-d, 380a-d may be made of the active catalytic material, or the active catalytic material may be coated on the at least one fiber structure 280a-d, 380a-d. The active catalytic material may be for example precious metals, Vanadium, Iron (Fe), Copper, Titanium, Tungsten and/or Aluminium.

According to an embodiment, the at least one fiber structure 280a-d, 380a-d comprises a porous structure/formation/construction/constitution/composition/fabric/web/texture arranged to let the exhaust stream 203, 303 flow through it. The porous constitution has the above mentioned fiber to volume ratio F/V, which causes the particles to interact with the at least one fiber structure 280a-d, 380a-d, i.e. with the porous constitution, whereby the particles are dissolved and removed from the exhaust stream 203, 303.

According to an embodiment, the at least one fiber structure 280a-d, 380a-d has a cross section area A in inches² and a length L in inches such that the area to length ratio A/L in inches for the at least one fiber structure 280a-d, 380a-d has a value of at least 17 inches and at most 150 inches; 17<A/L<150 inches. This interval for the area to length ratio A/L may e.g. be used for effectively providing sufficient interaction of the at least one fiber structure and the additive based particles. It should be noted that the at least one fiber structure may have a very short length L in relation to its cross section area A due to its simple constitution.

The above mentioned interval corresponds to an area to length ratio A/L interval of 425<A/L<3810 mm, if the area A is measured in mm² and the length L is measured in mm.

The important thing is the ratio between the area A of the cross section and the length L of the at least one fiber structure. The at least one fiber structure may e.g. have a shorter length L in relation to the area A than filter structures of conventional particulate filters have.

The at least one fiber structure 280a-d, 380a-d may have a number of different shapes. According to various embodiments, the at least one fiber structure 280a-d, 380a-d has a circular cross-section, has an oval cross-section, has a rectangular cross-section, or has another suitable form. The cross section of the at least one fiber structure may have essentially any shape being suitable for connecting the at least one fiber structure to upstream and/or downstream components in the exhaust treatment system 250, 350.

According to ab embodiment, the fiber to volume ratio F/V of the at least one fiber structure 280a-d, 380a-d is in the interval of 40% to 70%.

Hereby, the interaction between the particles and the at least one fiber structure 280a-d, 380a-d is provided, such that the additive based particles are removed from the exhaust stream 203, 303.

According to an aspect of the present invention, a method 400 for treatment of an exhaust stream 203, 303 resulting from a combustion in a combustion engine 201 , 301 is provided.

In a first step 410, soot and ash created by the combustion are caught by utilization of a particulate filter 210, 310. In a second step 420, a supply of an additive into the exhaust stream by utilization of a dosing arrangement 270, 372 arranged downstream of the particulate filter 210, 310 is controlled. The additive is mixed with the exhaust stream by an evaporation arrangement arranged at the dosing arrangement 270, 372.

In a third step 430, nitrogen oxides NOx in the exhaust stream 203, 303 are reduced by utilization of the supplied additive and a reduction catalyst arrangement 220, 320 arranged downstream of the dosing arrangement 270, 372.

In a fourth step 440, particles in the exhaust stream 203, 303 are caused to interact with the at least one fiber structure 280a-d, 380a-d arranged downstream of the evaporation arrangement. These particles are, as described above, created by one or more of the supply of the additive into the exhaust stream 203, 303 and a transformation of the additive when flowing through the exhaust treatment system 250, 350. The at least one fiber structure 280a-d, 380a-d has a fiber to volume ratio F/V in an interval of 40% to 90%, such that:

-- the particles are caused to interact with the at least one fiber structure 280a-d, 380a-d, thereby being at least partly captured and removed by the at least one fiber structure 280a-d, 380a-d; and

-- accumulation of soot and ash created by the combustion, which would affect the interaction of the at least one fiber structure 280a-d, 380a-d and the particles, is at least partly avoided.

A person skilled in the art will realise that a method for treatment of an exhaust stream according to the present invention may also be implemented in a computer program, which when executed in a computer will cause the computer to execute the method. The computer program usually forms a part of a computer program product 503, wherein the computer program product comprises a suitable digital non-volatile I permanent I persistent I durable storage medium on which the computer program is stored. Said non-volatile/permanent/persistent/durable computer readable medium consists of a suitable memory, e.g.: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash, EEPROM (Electrically Erasable PROM), a hard disk device, etc. Figure 5 schematically shows a control device 500. The control device 500 comprises a calculation unit 501 , which may consist of essentially a suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP), or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC). The calculation unit 501 is connected to a memory unit 502, installed in the control device 500, providing the calculation device 501 with e.g. the stored program code and/or the stored data, which the calculation device 501 needs in order to be able to carry out calculations. The calculation unit 501 is also set up to store interim or final results of calculations in the memory unit 502.

Further, the control device 500 is equipped with devices 511 , 512, 513, 514 for receiving and sending of input and output signals, respectively. These input and output signals may contain wave shapes, pulses, or other attributes, which may be detected as information by the devices 511 , 513 for the receipt of input signals, and may be converted into signals that may be processed by the calculation unit 501 . These signals are then provided to the calculation unit 501. The devices 512, 514 for sending output signals are arranged to convert the calculation result from the calculation unit 501 into output signals for transfer to other parts of the vehicle’s control system, and/or the component(s) for which the signals are intended.

Each one of the connections to the devices for receiving and sending of input and output signals may consist of one or several of a cable; a data bus, such as a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport) bus, or any other bus configuration; or of a wireless connection.

A person skilled in the art will realise that the above-mentioned computer may consist of the calculation unit 501 , and that the above-mentioned memory may consist of the memory unit 502.

Generally, control systems in modern vehicles consist of a communications bus system, consisting of one or several communications buses to connect a number of electronic control devices (ECUs), or controllers, and different components localised on the vehicle. Such a control system may comprise a large number of control devices, and the responsibility for a specific function may be distributed among more than one control device. Vehicles of the type shown, thus often comprise significantly more control devices than what is shown in Figure 5, which is well known to a person skilled in the art within the technology area.

As a person skilled in the art will realise, the control device 500 in figure 5 may comprise one or several of the control devices 290 and 390 in figures 2a-b and 3a-b, respectively.

The present invention, in the embodiment shown, is implemented in the control device 500. The invention may, however, also be implemented wholly or partly in one or several other control devices, already existing in the vehicle, or in a control device dedicated to the present invention.

A person skilled in the art will also realise that the above exhaust treatment system may be modified according to the different embodiments of the method according to the invention. In addition, the invention relates to the motor vehicle 100, for example a car, a truck or a bus, or another unit comprising at least one exhaust treatment system according to the invention, such as for example a vessel or a voltage/current- generator.

The present invention is not limited to the embodiments of the invention described above, but relates to and comprises all embodiments within the scope of the enclosed independent claims.

Claims

1 . An exhaust treatment system (250, 350) arranged for treatment of an exhaust stream (203, 303) resulting from a combustion in a combustion engine (201 , 301 ), the exhaust treatment system comprising:

- a particulate filter (210, 310) arranged to catch soot and ash created by the combustion;

- a dosing arrangement (270, 372) arranged downstream of the particulate filter (210, 310) to supply an additive into the exhaust stream (203, 303), the additive being mixed with the exhaust stream (203, 303) by an evaporation arrangement arranged at the dosing arrangement (270, 372);

- a reduction catalyst arrangement (220, 320) arranged downstream of the dosing arrangement (270, 372) for reduction of nitrogen oxides NOx in the exhaust stream (203, 303) by utilization of the supplied additive; and

- at least one fiber structure (280a-d, 380a-d) arranged downstream of the evaporation arrangement to interact with particles in the exhaust stream (203, 303), the particles being created by one or more of the supply of the additive into the exhaust stream (203, 303) and a transformation of the additive when flowing through the exhaust treatment system (250, 350), wherein the at least one fiber structure (280a-d, 380a-d) has a fiber to volume ratio FA/ in an interval of 40% to 90%, such that:

-- the particles are caused to interact with the at least one fiber structure (280a-d, 380a-d), thereby being at least partly captured and removed by the at least one fiber structure (280a-d, 380a-d); and

-- accumulation of soot and ash created by the combustion, which would affect the interaction of the at least one fiber structure (280a-d, 380a-d) and the particles, is at least partly avoided.

2. The exhaust treatment system (250, 350) as claimed in claim 1 , wherein the at least one fiber structure (280a-d, 380a-d) is arranged at least 0.1 meter downstream of the dosing arrangement (270, 372).

3. The exhaust treatment system (250, 350) as claimed in any one of claims 1-2, wherein the at least one fiber structure (280a, 380a) is comprised in the reduction catalyst arrangement (220, 320).

4. The exhaust treatment system (250, 350) as claimed in any one of claims 1-2, wherein the at least one fiber structure (280b-d, 380b-d) is arranged downstream of the reduction catalyst arrangement (220, 320).

5. The exhaust treatment system (250, 350) as claimed in any one of claims 1-2, further comprising a slip catalyst arrangement (240, 340) arranged downstream of the reduction catalyst arrangement (220, 320) for oxidation of a residue of additive in the exhaust stream (203, 303), wherein the at least one fiber structure (280b, 380b) is arranged downstream of the reduction catalyst arrangement (220, 320) and upstream of the slip catalyst arrangement (240, 340)

6. The exhaust treatment system (250, 350) as claimed in any one of claims 1-2, further comprising a slip catalyst arrangement (340, 3,40) arranged downstream of the reduction catalyst arrangement (220, 320) for oxidation of a residue of additive in the exhaust stream (203, 303), wherein the at least one fiber structure (280c, 380c) is comprised in the slip catalyst arrangement (240, 340).

7. The exhaust treatment system (250, 350) as claimed in any one of claims 1-2, further comprising a slip catalyst arrangement (240, 340) arranged downstream of the reduction catalyst arrangement (220, 320) for oxidation of a residue of additive in the exhaust stream (203, 303), wherein the at least fiber structure (280d, 380d) is arranged downstream of the slip catalyst arrangement (240, 340).

8. The exhaust treatment system (250, 350) as claimed in any one of claims 1-7, wherein the reduction catalyst arrangement (220, 320) comprises one or more in the group of:

- at least one selective catalytic reduction catalyst;

- at least one slip catalyst.

9. The exhaust treatment system (250, 350) as claimed in any one of claims 1-8, wherein

- the at least one fiber structure (280a-d, 380a-d) comprises at least one section arranged to be heated to an interaction temperature Ti by the exhaust stream (203, 303) flowing through it, the interaction temperature Ti exceeding a particle temperature Tp at which the particles thermally dissolve; Ti > Tp; and

- the at least one fiber structure (280a-d, 380a-d) is arranged to interact with the particles such that the particles at least partly come in physical contact with the heated at least one section.

10. The exhaust treatment system (250, 350) as claimed in claim 9, wherein the interaction temperature Ti is at least 150 °C.

11 . The exhaust treatment system (250, 350) as claimed in any one of claims 1-10, wherein the at least one fiber structure (280a-d, 380a-d) at least partially comprises an inert material.

12. The exhaust treatment system (250, 350) as claimed in claim 11 , wherein the inert material is one or more in the group of:

- a metallic material; and

- a non-metallic material.

13. The exhaust treatment system (250, 350) as claimed in any one of claims 1-12, wherein the at least one fiber structure (280a-d, 380a-d) at least partially comprises an active catalytic material.

14. The exhaust treatment system (250, 350) as claimed in any one of claims 11-13, wherein the material is coated on the at least one fiber structure (280a- d, 380a-d).

15. The exhaust treatment system (250, 350) as claimed in any one of claims 1-14, wherein the at least one fiber structure (280a-d, 380a-d) comprises a porous constitution arranged to let the exhaust stream (203, 303) flow through it.

16. The exhaust treatment system (250, 350) as claimed in any one of claims 1-15, wherein - the at least one fiber structure (280a-d, 380a-d) has a cross section area A in inches² and a length L in inches; and

- an area to length ratio A/L in inches for the at least one fiber structure (280a-d, 380a-d) has a value of at least 17 inches and at most 150 inches; 17<A/L<150 inches.

17. The exhaust treatment system (250, 350) as claimed in any one of claims 1 -16, wherein the additive comprises one or more in the group of:

- ammonia, and

- a substance from which ammonia may be extracted and/or released.

18. The exhaust treatment system (250, 350) as claimed in any one of claims 1 -1178, wherein the particles comprise one or more in the group of:

- urea; and

- polymeric biproducts based on urea.

19. The exhaust treatment system (250, 350) as claimed in any one of claims 1 -18, wherein the fiber to volume ratio F/V of the at least one fiber structure (280a-d, 380a-d) is in the interval of 40% to 70%.

20. The exhaust treatment system (250, 350) as claimed in any one of claims 1 -19, comprising:

- an upstream dosing device (371 ) arranged to supply an additive into the exhaust stream (303);

- an upstream reduction catalyst device (330) arranged downstream of the upstream dosing device (371 ) for reduction of nitrogen oxides NOx in the exhaust stream (303) by utilizing the supplied additive;

- the particulate filter (310) arranged downstream of the upstream reduction catalyst device (330) to catch soot and ash created by the combustion;

- the dosing arrangement arranged as a downstream dosing device (372) downstream of the particulate filter (310) to supply an additive into the exhaust stream (303), the additive being mixed with the exhaust stream (203, 303) by an evaporation arrangement arranged at the downstream dosing device (372) as a downstream evaporation arrangement; - the reduction catalyst arrangement arranged as a downstream reduction catalyst device (320) downstream of the downstream dosing device (372) to reduce nitrogen oxides NOx in the exhaust stream (303) by utilizing the supplied additive; and

- the at least one fiber structure (280a-d, 380a-d) arranged downstream of the downstream evaporation arrangement.

21 . The exhaust treatment system (250, 350) as claimed in claim 20, wherein the upstream reduction catalyst device (330) comprises one or more in the group of:

- an upstream selective catalytic reduction catalyst; and

- an upstream slip catalyst.

22. A method (400) for treatment of an exhaust stream (250, 350) resulting from a combustion in a combustion engine (201 , 301 ), the method comprising:

- catching (410) soot and ash created by the combustion by utilization of a particulate filter (210, 310);

- controlling (420) a supply of an additive into the exhaust stream (203, 303) by utilization of a dosing arrangement (270, 372) arranged downstream of the particulate filter (210, 310), the additive being mixed with the exhaust stream by an evaporation arrangement arranged at the dosing arrangement (270, 372);

- reduction (430) of nitrogen oxides NOx in the exhaust stream (203, 303) by utilization of the supplied additive and a reduction catalyst arrangement (220, 320) arranged downstream of the dosing arrangement (270, 372); and

- interaction (440) of particles in the exhaust stream (203, 303) and at least one fiber structure (280a-d, 380a-d) arranged downstream of the evaporation arrangement, the particles being created by one or more of the supply of the additive into the exhaust stream (203, 303) and a transformation of the additive when flowing through the exhaust treatment system (250, 350), wherein the at least one fiber structure (280a- d, 380a-d) has a fiber to volume ratio FA/ in an interval of 40% to 90%, such that:

-- the particles are caused to interact with the at least one fiber structure (280a-d, 380a-d), thereby being at least partly captured and removed by the at least one fiber structure (280a-d, 380a-d); and -- accumulation of soot and ash particles created by the combustion, which would affect the interaction of the at least one fiber structure (280a-d, 380a-d) and the particles, is at least partly avoided.

23. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to claim 22.

24. A computer-readable medium comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to claim 22.

25. A control system (500) arranged for controlling an exhaust treatment system (250, 350) for treatment of an exhaust stream (203, 303) resulting from a combustion in a combustion engine (201 , 301 ), the treatment comprising:

- controlling (420) a supply of an additive into the exhaust stream (203, 303) by utilization of a dosing arrangement (270, 372) arranged downstream of the particulate filter (210, 310), the additive being mixed with the exhaust stream (203, 303) by an evaporation arrangement arranged at the dosing arrangement (270, 372);

- reduction (430) of nitrogen oxides NOx in the exhaust stream (203, 303) by utilization of the supplied additive and a reduction catalyst arrangement (220, 320) arranged downstream of the dosing arrangement (270, 372);and

-- accumulation of soot and ash particles created by the combustion, which would affect the interaction of the at least one fiber structure (280a-d, 380a-d) and the particles, is at least partly avoided.