WO2019209162A1

WO2019209162A1 - Method and system for determination of and for reduction of a risk for formation of solid deposits

Info

Publication number: WO2019209162A1
Application number: PCT/SE2019/050365
Authority: WO
Inventors: David TEMPELMANN; Henrik BIRGERSSON
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2018-04-24
Filing date: 2019-04-18
Publication date: 2019-10-31
Anticipated expiration: 2020-10-24
Also published as: SE541802C2; SE1850484A1

Abstract

A method and a system for determination of a formation of solid deposits of a reducing agent on an inner wall of an evaporation unit are presented. The method includes - determining a representation of a model temperature Tmodel- i for a position Pi, on an inner wall of the evaporation unit, based on a temperature model for the evaporation unit, the temperature model assuming that the evaporation unit is free of solid deposits of the reducing agent; - determining a representation of a measured temperature Tmeasure-i for the position Pi; - determining one or more representations of differences ΔΤ; between one or more of the representation of the model temperature Tmodel- i and one or more of the representation of the measured temperature Tmeasure-i, respectively; and - determining a formation of a solid deposit of the reducing agent if at least one of the representations of differences ΔΤ; exceeds a detection thresholds ΔTi-det-th;ΔTi > ΔTi-det-th; respectively.

Description

METHOD AND SYSTEM FOR DETERMINATION OF AND FOR REDUCTION OF A RISK FOR FORMATION OF SOLID DEPOSITS

Technical field

The present invention relates to a method for determination of a formation of solid deposits, according to the preamble of claim 1. The present invention relates to a method for

reduction of a risk for formation of solid deposits. The present invention also relates to a system arranged for determination of a formation of solid deposits, according to the preamble of claim 14. The present invention also relates to a control system arranged for reduction of a risk for formation of solid deposits. The invention also relates to a computer program and a computer-readable medium, 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 comprise requirements defining acceptable limits of exhaust emissions from combustion engines in for example vehicles. For example, emission levels of nitrogen oxides NOx, hydrocarbons C_xH_y, carbon monoxide CO, particle mass PM and/or particle number concentration PN 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. 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 the 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 includes 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 at least one catalyst, wherein an additive/reducing agent 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.

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

Brief description of the invention

The additive/reducing agent being injected into the exhaust stream is thus very important for the reduction of the

nitrogen oxides NOx in the exhausts. However, it is sometimes difficult to know exactly how much reducing agent to inject, e.g. for transient conditions, in order to properly reduce nitrogen oxides NOx and not to cause

residues/precipitates/crystallisations. Therefore, the control of the injected amount may be inexact/unreliable, which may be problematic. Especially, if too much additive/reducing agent is injected into the exhaust stream, there is a risk that residues/precipitates/crystallisations of additive/reducing agent are formed downstream of the dosage device injecting the additive/reducing agent into the exhaust stream, e.g. in an evaporation unit/chamber . Such additive/reducing agent

residues/precipitates/crystallisations (hereafter commonly denoted residues and/or deposits) of additive/reducing agent being formed in the exhaust treatment system potentially increase the back pressure of the exhaust treatment system, and therefore potentially also increase the fuel consumption of the engine. The fuel consumption may also be increased when fuel is used for eliminating residues and/or deposits having been formed. Further, such additive/reducing agent residues in the exhaust treatment system may have a negative effect on the general purification performance of the exhaust treatment system, since the additive/reducing agent residues in the evaporation chamber reduces the evaporation efficiency, which may result in that too little evaporated additive/reducing agent reaches the SCR catalyst.

The increased back pressure and/or the less efficient exhaust purification of the exhaust treatment system may also result in a number of control system related problems. One or more control systems arranged for controlling the exhaust treatment system may be unaware of these problems, and may thus keep on controlling the system based on the assumption that the back pressure is not increased and/or that an efficient reduction of nitrogen oxides NOx is achieved by the system.

Also, if too little additive/reducing agent is injected into the exhaust stream, the reduction of the nitrogen oxides NOx in the exhausts may become deficient/unacceptable, and may result in that requirements in emission standards are not fulfilled .

An object of the present invention is at least partly solve at least some of the above mentioned problems/disadvantages.

The object is achieved through the above mentioned method for determination of a formation of solid deposits of a reducing agent on at least one inner wall of an evaporation unit of an exhaust treatment system arranged for treating an exhaust stream from an engine, in accordance with the characterising portion of claim 1. The method includes

- determining at least one representation of a model

temperature T_modeij for at least one position Pi on at least one inner wall of the evaporation unit, wherein the determination of the at least one representation of the model temperature Tmodei i is based on a temperature model for the evaporation unit, the temperature model assuming that the evaporation unit is free of solid deposits of the reducing agent;

- determining, by use of at least one temperature sensor, at least one representation of a measured temperature T_measure for the at least one position P_j on at least one inner wall of the evaporation unit;

- determining one or more representations of differences D7^ between one or more of the at least one representation of the model temperature T_{modei t} and one or more of the at least one representation of the measured temperature T_measure ,

respectively;

- determining a formation of at least one solid deposit of the reducing agent if at least one of the one or more

representations of differences

exceeds one or more

detection thresholds DT[ d_et_thr‘ DG^ > DG;j_et_jhr' respectively.

Hereby, it is possible to determine/detect and/or eliminate solid residues in the evaporation unit. Especially, a reliable and early determination/detection of a formation of solid deposits is made possible.

The present invention utilizes the insulating properties of the solid deposits, i.e. the fact that the solid

deposits/residues insulate the inner wall of the evaporation unit from the spray impacts of the relatively cool reducing agent. Due to this insulation, the at least one representation of a measured temperature T_measure increases when they are formed. The at least one representation of a model temperature Tmodeij does, however, not increase when the solid deposits are formed, since the temperature model is based on the assumption that there are no solid deposits. Therefore, the one or more representations of differences D7^ are greater than zero when the solid deposits are formed, which is utilized by the present invention as an indication of formation of deposits, by comparing them to a suitable threshold value DG; ^_et th·

The determination of formation of deposits provided by the present invention does not affect the tail pipe emissions, since the determination is performed during normal operation of the exhaust treatment system. Thus, the determination according to the present invention does not rely on an

interruption of the injection of reducing agent in order to work, which over time reduces the emission of NO_x.

Preferably, the solid deposits should be determined/detected already when they are formed, i.e. including a first stage of formation, a precursor stage, up to final stage in which deposits are fully formed/created. By an early determination of the formation of deposits, as is possible when the herein described embodiments are used, the above mentioned drawbacks are minimized. Also, an early elimination of deposits is easier and quicker, due to their initially smaller size, than a later elimination of a fully developed solid deposit is. Thus, the herein described embodiments facilitates early determination of deposits and also facilitates easy and quick elimination of deposits.

Thus, the determination of formation of solid deposits described in this document includes both

determination/detection of precursors of deposits/residues, i.e. the stadium before the solid deposits/residues actually form, and determination/detection of formed, i.e. existing, solid deposits/residues.

By the use of the present invention, the performance of the evaporation chamber is improved regarding an amount of

reducing agent being possible to evaporate. This is possible, since the present invention offers a reliable determination of formation of solid deposits/residues, which makes it possible to, at low risk for formation of deposits, increase the amount of injected reducing agent.

Thus, the amount of reducing agent to be injected may be increased in some situations, whereby the efficiency of the reduction of the nitrogen oxides NOx in the one or more reduction catalyst devices using reducing agents for their reduction may be considerably increased, without risking that reducing agent residues are formed. Since the risk for

creating reducing agent residues is considerably reduced when the present invention is utilised, the risk for having to perform fuel consuming residue eliminating actions is also considerably reduced, which reduces the fuel consumption over time .

An exhaust treatment system implementing the present invention therefore has potential to meet the emission requirements in the Euro VI emission standard. Additionally, the exhaust treatment system according to the present invention has potential to meet the emission requirements in several other existing and/or future emission standards. The invention may also be generally used for improving the control of a dosage device and/or an engine, resulting in e.g. improved fuel efficiency and/or reduced fuel consumption.

For some situations, for example a larger dosage amount (a more ample dosage) may be allowed to be injected by the reducing agent dosage device when the present invention is used, than has been allowed in known solutions. This more ample dosage of reducing agent may be viewed as a more

aggressive dosage, providing dosage amounts closer to, or even above, a dosage threshold value at which a risk for creating residues of reducing agent arises. Therefore, the control of the dosage of reducing agent and/or of the engine may be performed in a much more optimized way when the present invention is used, allowing also a control much closer to the limits where residues may be formed. This is possible since the control according to the present

invention is much more accurate and reliable than the control of the known methods. The present invention therefore for example makes it possible to, in some situations, in a

controlled fashion inject more reducing agent, i.e. to inject reducing agent more aggressively, into the exhaust stream than was possible in known methods, whereby a more efficient reduction of nitrogen oxides NOx is possible for the exhaust treatment system. The present invention therefore also makes it possible to, in some situations, run the engine such that the temperature T_exh ^of the exhaust stream is lower and/or run the engine more fuel efficient than was possible to safely do when the known methods were used.

Through the use of the present invention, a better fuel consumption optimisation may be obtained for the vehicle, since there is potential to control the engine in a more fuel efficient manner, due to a possibly more efficient reduction of nitrogen oxides NOx. Thus, a higher output of nitrogen oxides NOx from the engine may be allowed, since nitrogen oxides NOx may be efficiently reduced by the exhaust treatment system, whereby a higher efficiency for the engine is

obtained .

According to an embodiment of the present invention, the temperature model for the evaporation unit utilizes at least one in the group of :

- an exhaust temperature T_exh for the exhaust stream;

- an exhaust mass flow M_exh for the exhaust stream; - a reducing agent mass M_ag_ent; and

- a reducing agent mass flow M_ag_ent being injected into the exhaust stream as input parameters.

Hereby, the at least one representation of the model

temperature T_modeij may be accurately and reliably determined.

According to an embodiment of the present invention,

- the temperature model is determined by simulations and/or physical experiments resulting in a wall temperature profile Tprof for the at least one position P_j of the at least one inner wall, respectively; and

- the at least one representation of the model temperature Tmodei_j for the at least one position P_j of the evaporation unit corresponds to at least one temperature P_profj of the

temperature profile T_pr0f for at least one corresponding model position P_modelj· respectively.

By the experiments and/or simulations, the determination of the at least one representation of the model temperature T_modei i for the at least one position P_j can be made accurate and reliable .

According to an embodiment of the present invention, the at least one temperature sensor is located in the at least one position P_j at the internal wall of the evaporation unit, respectively, which has an increased risk for formation of the solid deposits, e.g. due to injection of a reducing agent into the exhaust stream, the reducing agent ending up at the at least one position P_j .

Thus, the at least one temperature sensor is placed in the interesting at least one position P_j having an increased risk for formation of deposits/residues. Therefore, the method is especially adapted for determining such formations in the positions Pi where they are most likely to occur.

According to an embodiment of the present invention, the at least one position P_j at the internal wall of the evaporation unit is determined based on at least one in the group of:

- one or more simulations;

- one or more models; and

- one or more physical tests.

Since the at least one position P_j may be determined in a number of ways, it is possible to find a reliable and accurate determination of the at least one position P_j for essentially any available evaporation unit.

According to an embodiment of the present invention, one or more of the at least one representation of a model temperature Tmodel_i r the at least one representation of the measured temperature Jmeasure and the one or more representations of differences ATt include statistically determined values.

To use statistically determined values is a great advantage regarding complexity when processing transient values, such as e.g. transient temperature values.

According to an embodiment of the present invention, the statistically determined values comprise one or more in the group of :

- mean values;

- moving average values;

- median values;

- filtered values; and

- statistic values. Hereby, the influence of noisy signals is mitigated, e.g. by usage of low pass filtered and/or mean values, such that reliable and low complexity determinations may be performed.

According to an embodiment of the present invention, the one or more detection thresholds DG; ^et th ^are determined based on at least one in the group of :

- one or more features of the evaporation unit; and

- an accuracy of the temperature model for the evaporation unit .

Hereby, the determination of formation of solid residues can be tailored for the used evaporation unit, which results in an accurate and reliable determination.

According to an embodiment of the present invention, the one or more detection thresholds DG; ^ _th are determined based on at least one in the group of :

- one or more simulations;

- one or more models;

- one or more empirical experiments; and

- one or more physical tests.

Since the one or more detection thresholds DG; ^et th may be determined in a number of ways, it is possible to find a reliable and accurate determination one or more detection thresholds DG; ^et th for essentially each available evaporation unit .

The above mentioned object is also achieved through the above mentioned method for reduction of a risk for formation of solid deposits of a reducing agent on at least one inner wall of an evaporation unit of an exhaust treatment system arranged for treating an exhaust stream from an engine, the method including :

- determination of a formation of solid deposits of a reducing agent using the method according to the above mentioned method for determination of a formation of solid deposits; and

- performing, if at least one formation of a solid deposit is determined, at least one action for reducing the at least one solid deposit.

Hereby, the robustness of the evaporation chamber, and of the control of the injection of the reducing agent, is increased. Also, the exhaust back pressure may be reduced in the exhaust treatment system, due to the reduced risk for residues of reducing agent forming in the system. This reduced back pressure also reduces the fuel consumption for the engine.

According to an embodiment of the present invention, the at least one action includes one or more in the group of:

- controlling an engine producing the exhaust stream to reduce a concentration of nitrogen oxides AfO_x in the exhaust stream;

- controlling an engine producing the exhaust stream to increase a temperature T_exh of the exhaust stream;

- controlling an engine producing the exhaust stream to increase an exhaust mass flow M_exh for the exhaust stream; and

- controlling a dosage device injecting the reducing agent into the evaporation unit to reduce an reducing agent mass agent and/or a reducing agent mass flow M_agent being injected into the exhaust stream.

By controlling the engine and/or the dosage device, the formation of solid deposits can be efficiently mitigated and/or eliminated.

The object is also achieved through the above mentioned computer program and computer-readable medium.

The object is achieved also through the above-mentioned system arranged for determination of a formation of solid deposits of a reducing agent, in accordance with the characterising portion of claim 14, including

- first means arranged for determining at least one

representation of a model temperature T_modei for at least one position P_j on at least one inner wall of the evaporation unit, wherein the determination of the at least one representation of the model temperature T_{modei t} is based on a temperature model for the evaporation unit, the temperature model assuming that the evaporation unit is free of solid deposits of the reducing agent ;

- second means arranged for determining, by use of at least one temperature sensor, at least one representation of a measured temperature T_measure for the at least one position P_j on at least one inner wall of the evaporation unit;

- third means arranged for determining one or more

representations of differences

between one or more of the at least one representation of the model temperature T_modeij and one or more of the at least one representation of the measured temperature T_{measure ir} respectively;

- fourth means arranged for determination a formation of at least one solid deposit of the reducing agent if at least one of the one or more representations of differences

exceeds one or more detection threshold NT_{[ det th}; Ti > T_{[ det th};

respectively .

According to an embodiment of the present invention, the first determination means is arranged for utilizing at least one in the group of :

- an exhaust temperature T_exh for the exhaust stream;

- an exhaust mass flow M_exh for the exhaust stream;

- a reducing agent mass M_ag_ent; and

- a reducing agent mass flow M_ag_ent being injected into the exhaust stream as input parameters for the temperature model for the evaporation unit. According to an embodiment of the present invention, the first determination means is arranged such that:

- the temperature model is determined by simulations and/or physical experiments resulting in a wall temperature profile prof for the at least one position P_j of the at least one inner wall, respectively; and

- the at least one representation of the model temperature T_modeij for the at least one position P_j of the evaporation unit corresponds to at least one temperature P_profj of the

temperature profile T_pr0f for at least one corresponding model position P_model_j· respectively.

According to an embodiment of the present invention, the second determination means is arranged for determining the at least one position P_j at the internal wall of the evaporation unit based on at least one in the group of :

- one or more simulations;

- one or more models; and

- one or more physical tests.

According to an embodiment of the present invention, the first, second and/or third determination units are arranged for providing the one or more of the at least one

representation of a model temperature T_modeij, the at least one representation of the measured temperature T_{measure t} and the one or more representations of differences

statistically determined values.

- mean values;

- moving average values;

- median values;

- filtered values; and

- statistic values.

According to an embodiment of the present invention, the third determination means is arranged for determining the one or more detection thresholds DG; ^ _th based on at least one in the group of :

- one or more features of the evaporation unit; and

- an accuracy of the temperature model for the evaporation unit .

According to an embodiment of the present invention, the third determination means is arranged for determining the one or more detection thresholds T^_{et th} based on at least one in the group of :

- one or more simulations;

- one or more models; and

- one or more physical tests.

The object is achieved also through the above-mentioned control system arranged for reduction of a risk for formation of solid deposits of a reducing agent, the system including:

- a herein described system arranged for determination of a formation of solid deposits of a reducing agent; and

- means arranged for performing, if at least one formation of a solid deposit of a reducing agent is determined, at least one action for reducing the at least one solid deposit.

According to an embodiment of the present invention, the at least one means arranged for performing the at least one action is arranged for performing one or more in the group of:

- controlling an engine producing the exhaust stream to reduce a concentration of nitrogen oxides NO_x in the exhaust stream;

The systems and system embodiments herein described have the same advantages as their corresponding methods and method embodiments .

Brief list of figures

The embodiments of 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 schematically shows an example vehicle, in which the embodiments of the present invention may be implemented,

Figure 2 schematically shows a traditional exhaust treatment system, in which the embodiments of the present invention may be implemented, Figure 3 schematically shows some parts of an exhaust

treatment system, in which the embodiments of the present invention may be implemented,

Figure 4 shows a flow chart for a method according to an embodiment of the present invention,

Figure 5 shows a flow chart for a method according to an embodiment of the present invention,

Figure 6 shows a control device, in which the embodiments of the present invention may be implemented,

Figure 7 shows a non-limiting principle illustration of an embodiment of the present invention.

Description of preferred embodiments

Figure 1 schematically shows an example vehicle 100 comprising an exhaust treatment system 250. The powertrain comprises a combustion engine 101, which in a customary manner, via an output shaft 102 on the combustion engine 101, usually via a flywheel, is connected to a gearbox 103 via a clutch 106.

The combustion engine 101 is controlled by the engine's control system via a control device 215. 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, of a type with a hybrid powertrain, etc. A Hybrid powertrain may include the

combustion engine and at least one electrical machine, such that the power/torque provided to the clutch/gearbox may be provided by the combustion engine and/or the electric machine. An output shaft 107 from the gearbox 103 drives the wheels 113, 114 via a final drive 108, such as e.g. a customary differential, and the drive shafts 104, 105 connected to the final drive 108.

As mentioned above, the vehicle 100 also comprises an exhaust treatment system/exhaust purification system 250 for

treatment/purification of exhaust emissions resulting from combustion in the combustion chamber (s) of the combustion engine 101, which may comprise cylinders. The exhaust

treatment system 250 may be controlled by a control unit 260

Figure 2 schematically shows an exhaust treatment system 250, in which the present invention may be implemented. The system 250 may illustrate a system fulfilling e.g. the Euro VI

emission standard, and which is connected to a combustion engine 101 via an exhaust conduit 202, wherein the exhausts generated at combustion, that is to say the exhaust stream 203, is indicated with arrows. The exhaust stream 203 is led to a diesel particulate filter (DPF) 220, via a diesel

oxidation catalyst (DOC) 210. During the combustion in the combustion engine, soot particles are formed, and the

particulate filter 220 is used to catch these soot particles. The exhaust stream 203 is here led through a filter structure, wherein soot particles from the exhaust stream 203 are caught passing through, and are stored in the particulate filter 220.

The oxidation catalyst DOC 210 has several functions and is normally used primarily to oxidise, during the exhaust

treatment, remaining hydrocarbons C_xH_y (also referred to as HC) and carbon monoxide CO in the exhaust stream 203 into carbon dioxide C0₂ and water H₂0. The oxidation catalyst DOC 210 may also oxidise a large fraction of the nitrogen monoxides NO occurring in the exhaust stream into nitrogen dioxide N0₂. The oxidation of nitrogen monoxide NO into nitrogen dioxide N0₂ is important for the nitrogen dioxide based soot 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 device 230, possibly including an SCR (Selective Catalytic Reduction) catalyst, downstream of the particulate filter DPF 220. SCR catalysts use ammonia NH₃ , or a composition from which ammonia may be generated/formed, e.g. urea, as a

reducing agent for the reduction of nitrogen oxides NOx in the exhaust stream. The reaction rate of this reduction is

impacted, however, by the ratio between nitrogen monoxide NO and nitrogen dioxide N0₂ in the exhaust stream, so that the reductive reaction is impacted in a positive direction by the previous oxidation of NO into N0₂ in the oxidation catalyst DOC. This applies up to a value representing approximately 50% of the molar ratio N0₂ / NOx .

As mentioned above, the reduction catalyst device 230,

including e.g. the SCR-catalyst , requires reducing agent to reduce the concentration of a compound, such as for example nitrogen oxides NOx, in the exhaust stream 203. Such reducing agent is injected into the exhaust stream upstream of the reduction catalyst device 230 by a dosage device 271 being provided with reducing agent by an reducing agent providing system 270. Such reducing agent often comprises ammonia and/or is urea based, or comprises a substance from which ammonia may be extracted or released, and may for example comprise AdBlue, which basically comprises urea mixed with water. Urea forms ammonia at heating (thermolysis) and at heterogeneous

catalysis on an oxidizing surface (hydrolysis), which surface may, for example, comprise titanium dioxide Ti0_{2 r} within the SCR-catalyst. The reducing agent is evaporated in an evaporation chamber 280. The exhaust treatment system may also comprise a separate hydrolysis catalyst.

The exhaust treatment system 250 may also be equipped with an ammonia slip-catalyst (ASC) 240, which is arranged to oxidise a surplus of ammonia that may remain after the reduction catalyst device 230. Accordingly, the ammonia slip-catalyst ASC 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 -, temperature and/or mass flow sensors, for example arranged in the tailpipe 264 downstream of the components 210, 220, 230, 240 or

arranged upstream, within and/or between these components 210, 220, 230, 240, for the determination of measured values for nitrogen oxides, temperatures and/or mass flow in the exhaust treatment system.

A control device/system/means 290 may be arranged/configured for performing some embodiments of the present invention. The control device/system/means 290 is in figure 2 illustrated as including separately illustrated units 291, 292, 293 arranged for performing the embodiments of the present invention, as is described below. Also, control device/system/means 390 may be arranged/configured for performing some embodiments of the present invention. The control device/system/means 290 is in figure 2 illustrated as including separately illustrated units 391, 392, 393, 394 arranged for performing the present

invention, as is described below.

Also, as described herein, an engine control

device/system/means 215 may be arranged for controlling the engine 201, a control system/means 290, 390 may be arranged for controlling the reducing agent providing system 270 and/or the dosage device 271, possibly via an exhaust treatment system control unit 260, and to send control signals to the engine control device/system/means 215, and a control

device/means 600 may be implemented for performing embodiments of the invention. These means/units/devices systems 290, 291, 292, 293, 390, 391, 392, 393, 394, 215, 260, 600 may, however be at least to some extent logically separated but physically implemented in at least two different physical units/devices. These means/units/devices 290, 291, 292, 293, 390, 391, 392,

393, 394, 215, 260, 600 may also be at least to some extent logically separated and implemented in at least two different physical means/units/devices. Further, these

means/units/devices 290, 291, 292, 293, 390, 391, 392, 393,

394, 215, 260, 600 may be both logically and physically arranged together, i.e. be part of a single logic unit which is implemented in a single physical means/unit/device . These means/units/devices 290, 291, 292, 293, 390, 391, 392, 393,

394, 215, 260, 600 may for example correspond to groups of instructions, which may be in the form of programming code, that are input into, and are utilized by at least one

processor when the units are active and/or are utilized for performing its method step, respectively. It should be noted that the control system/means 290, 390 may be implemented at least partly within the vehicle 100 and/or at least partly outside of the vehicle 100, e.g. in a server, computer, processor or the like located separately from the vehicle 100.

As mentioned above, the units 291, 292, 293, 391, 392, 393,

394 described above correspond to the claimed means 291, 292, 293 391, 392, 393, 394 arranged for performing the embodiments of the present invention, and the present invention as such.

In the exhaust treatment system 250, there is, as mentioned above, a risk that the relatively cold reductant/additive/reducing agent cools down components, especially the evaporation chamber 280, of the exhaust

treatment system, and may thereby give rise to

deposits/residues/precipitates/crystallisations (herein commonly denoted residues and/or deposits) in these

components. This risk of solid deposits/residuals downstream of the injection device 271 increases if the injected amount of reductant is large.

The temperature of the exhaust treatment system itself, e.g. the temperature in the evaporation chamber 280 and/or in the reduction catalyst device 230, may depend on a number of factors, such as how the driver drives the vehicle. For example, the temperature may depend on the torque requested by a driver and/or by a cruise control, on the

appearance/features of the road section in which the vehicle is located, and/or the driving style of the driver.

The function and efficiency for catalysts in general, and for reduction catalyst devices in particular, is normally strongly dependent on the temperature over the reduction catalyst device. The term temperature of the exhaust treatment

system/component as used herein, means the temperature

in/at/for the exhaust stream flowing through the components of the exhaust treatment system. The components, e.g. the

catalyst substrates, will also assume this temperature due to their heat exchanging ability.

Figure 3 schematically illustrates some parts/components of the exhaust treatment system 250 through which the exhaust stream 203 passes. Figure 3 mainly illustrates the evaporation chamber 280, the dosage device 271, the reducing agent

providing system 270 and a control device 290/390 according to some embodiments of the present invention. As is understood by a skilled person, figure 3 illustrates only one possible example of the evaporation chamber, and the evaporation chamber 280 may be designed in a large number of ways. The evaporation chamber may for example include only one pipe/tube through which the exhaust stream is passed/guided, or may include two or more pipes/tubes, which may be arranged

coaxially, through which the exhaust stream passes. The evaporation chamber may also include at least one

atomizer/evaporator/vaporizer in one or more of the at least one pipe/tube. The embodiments of the present invention are generally applicable for all of these large number of designs for the evaporation chamber 280.

As is schematically illustrated in figure 3, the reducing agent is sprayed/in ected into the exhaust stream 203 by the dosage device 271. The reducing agent may hit the inner walls 281 of the evaporation chamber in some positions P_j and may in the at least one position start to form solid

deposits/residues 285 of the reducing agent, due to the reducing agent cooling down the inner wall in that at least one position. In this document, the notation "inner walls" refers to one or more wall parts which comes in contact with the exhaust stream 203, and which may possibly also come in contact with the reducing agent. In other words, the inner walls define/form/provide/delimit a path for the exhaust stream through the evaporation chamber/unit 280. Since the reducing agent is injected into the exhaust stream, the reducing agent may possibly also hit the inner walls

delimiting the path. The inner walls may thus be located on a side of the above mentioned one or more pipes/tubes, which define/form/provide/delimit a path for the exhaust stream through the evaporation chamber/unit 280. The control devices 290/390 illustrated in figure 3 include at least the herein described units/means 291, 292, 293/391, 392, 393, 394 and are arranged for performing the herein described embodiments of the present invention. The control devices 290/390 are coupled/connected to the reducing agent providing system 270 and/or the dosage device 271, possibly via the exhaust treatment system control unit 260. The control devices 290/390 are also coupled/connected to an engine control device 215 arranged for controlling the engine 201. The control devices 290/390 are also coupled/connected to at least one temperature sensor 265i of the evaporation chamber. As

described below, the at least one temperature sensor 265i may be located in/at the internal wall of the evaporation unit 280 at a position which has an increased risk for formation of the solid deposits 285 due to spraying of reducing agent.

Figure 3 will be used for explaining the embodiments of the present invention. Figure 3 is for that reason simplified, and only illustrates the parts needed for understanding the embodiments of the present invention.

Figure 4 shows a flow chart diagram illustrating a method 400 according to an embodiment of the present invention.

The method 400 determines/detects a formation of solid

deposits 285 of a reducing agent on at least one inner wall 281 of an evaporation unit 280 of an exhaust treatment system 250 arranged for treating an exhaust stream 203 from an engine 101. As explained above, the engine 201 produces an exhaust stream 203 being treated by an exhaust treatment system 250 by use of at least one reducing agent being injected into the exhaust stream 203 by the dosage device 271. The determination of solid deposits described in this document includes both determination/detection of precursors of deposits/residues, i.e. the stadium before the solid deposits/residues actually form, and determination/detection of formed, i.e. existing, solid deposits/residues.

The reducing agent is injected into an evaporation chamber 280 when being injected into the exhaust stream 203, and the reducing agent is there evaporated. Hereby, the reducing agent is provided to the reduction catalyst device 230 in gaseous form downstream of the dosage device 271 and evaporation chamber 280, which makes the function of the reduction

catalyst device 230 efficient. The injection of the reducing agent into the evaporation chamber 280 is in figure 3

schematically illustrated as dotted lines. The reducing agent may reach/end up at an inner/internal wall 281 inside of the evaporation chamber 280. The internal wall 281 of the

evaporation chamber 280 may be divided into sections/positions P_j along the length of the evaporation chamber 280, i.e. in the flow direction of the exhaust stream 203 flowing through the evaporation chamber 280.

In a first step 410 of the method, at least one representation of a model temperature T_modeij for at least one position P_j on at least one inner wall 281 of the evaporation unit 280 is determined. The determination 410 of the at least one

representation of the model temperature T_modei is based on a temperature model for the evaporation unit 280, which assumes that the evaporation unit is free of solid deposits of the reducing agent. Thus, at least one representation of a model temperature T_{modei i} is determined as if there were no solid deposits/residues, even if there are, or may be, one or more solid deposits/residues on the inner walls.

In a second step 420, at least one representation of a

measured temperature T_measure for the at least one position P_j on at least one inner wall 281 of the evaporation unit 280 is determined by use of at least one temperature sensor 265i. The at least one representation of a measured temperature T_measure may thus be determined by use of at least one internal

temperature sensor 265 (shown in figure 3) arranged at the at least one position P_j at the internal wall 281 of the

evaporation chamber 280. Hereby, a very reliable value for at least one representation of a measured temperature T_{measure t} is provided. According to an embodiment, the at least one

internal temperature sensor 265 has the same temperature as the inner wall, and may e.g. be attached to the inner wall, or may be embedded in the internal wall 281, i.e. is embedded within the material/castings of the internal wall 281.

In a third step 430, one or more representations of

differences

between one or more of the at least one

representation of the model temperature T_{modei i} and one or more of the at least one representation of the measured temperature Tmeasure _f respectively, are determined. Thus, one or more representations of differences

between measured T_{measure t} and modelled T_{modei t} temperature representations are hereby

determined .

In a fourth step 440, a formation of at least one solid deposit /residue 285 of the reducing agent is determined if at least one of the one or more representations of differences D7^ exceeds one or more detection thresholds

Ti > T_{[ det th} ; respectively .

The present invention utilizes the insulating properties of the solid deposits/residues. As is schematically illustrated in figure 7, the at least one representation of a model temperature T_m0dei and the at least one representation of a measured temperature T_measure for the at least one position P_j are essentially equal, i.e. essentially coincide, when there are no solid deposits formed in the evaporation unit.

Therefore, the one or more representations of differences

are very small, essentially equal to zero, when there are no solid deposits.

However, when a formation of solid deposits starts, the solid deposits/residues insulate the inner wall of the evaporation unit from the cooling effects of the reducing agent, wherefore the at least one representation of a measured temperature Tmeasure i increases (due to the formed solid deposits as a result of this insulation) .

Since the temperature model is based on the assumption that there are no solid deposits, the at least one representation of a model temperature T_{moiei i} does not increase when the solid deposits are formed, which results in the one or more

representations of differences

having values being greater than zero when the solid deposits have formed. The one or more representations of differences

may therefore be used as an indicator for formed solid deposits, by being compared to a suitable threshold value T ^ _th;

> T ^_{et tfl}.

The present invention provides for an accurate and reliable determination/detection of deposits provided, without

affecting the tail pipe emissions, since the determination may be performed without interrupting the injection of reducing agent. Hereby, the present invention over time reduces the emission of NO_x.

The early determination of the formation of deposits, as is possible when the herein described embodiments are used, facilitates easy and quick elimination of deposits. By the use of the embodiments of the present invention, the performance of the evaporation chamber is improved, since the present invention offers a reliable determination of formation of solid deposits/residues, which makes it possible to, at low risk for formation of deposits, increase the amount of

injected reducing agent. Thus, the amount of reducing agent to be injected may be increased in some situations, whereby the efficiency of the reduction of the nitrogen oxides NOx in the one or more reduction catalyst devices may be considerably increased .

Therefore, when the embodiments of the present invention are used, a better fuel consumption optimisation may be obtained for the vehicle, because a higher output of nitrogen oxides NOx from the engine may be allowed, since nitrogen oxides NOx may be efficiently reduced by the exhaust treatment system, whereby a higher efficiency for the engine is obtained.

The temperature model for the evaporation unit 280 may, according to an embodiment utilize an exhaust temperature T_exh for the exhaust stream 203, an exhaust mass flow M_exh for the exhaust stream 203, a reducing agent mass M_agent and/or a reducing agent mass flow M_agent being injected into the exhaust stream 203 as input parameters. Thus, the at least one

representation of the model temperature T_modei for the at least one position P_j on the at least one inner wall 281 of the evaporation unit 280 is determined based on one or more of the exhaust temperature Texhr the exhaust mass flow M_exhr the reducing agent mass M_agent and the reducing agent mass flow

Hereby, the at least one representation of the model temperature T_modeij may be accurately and reliably determined. The temperature model may be determined/calculated/defined in a number of ways. For example, the temperature model may be determined/calculated/defined based on simulations. The temperature model may also be determined/calculated/defined based on numerical/physical experiments. The simulations and/or experiments should here be performed such that they result in a wall temperature profile T_pr0f for the at least one position P_j of the at least one inner wall 281, respectively. The wall temperature profile T_pr0f may here have a temporal resolution, which may be used for determining the herein mentioned statistically determined values, which is explained more in detail below. It may be noted that the wall

temperature profile T_pr0 may be determined with or without usage of physical sensors in the evaporation unit, as

described below.

The at least one representation of the model temperature T_modeij for the at least one position P_j of the evaporation unit 280 corresponds to at least one temperature Ppro_fj of the

temperature profile T_pr0 for at least one corresponding model position P_model_j· respectively. Thus, for each interesting position P_j on the evaporation unit wall, a corresponding model position P_model i is included in the model. Therefore, a

representation of the model temperature T_modei for each such interesting position P_j is also available in the model as a corresponding temperature T_{proi t} of the temperature profile T_pr0f for the corresponding model position P_model_j · Here, the at least one interesting position P_j has an increased risk for a

formation of solid deposits 285, since the injected reducing agent is likely to hit/end up at the wall in the at least one position P_j . According to an embodiment of the present invention, the model temperature T_modeij for each such interesting position Pi is modelled as being attached to, or embedded in, the internal wall 281 of the evaporation chamber 280, e.g. as attached on the surface, for example on the back side surface of the internal wall, or as embedded within the material/castings of the evaporation chamber. As mentioned above, the temperature model here assumes that the evaporation unit is free of solid deposits of the reducing agent. Thus, the model temperature Tmodei i ^maY be modelled as corresponding to the actual

temperature at the internal wall 281 where the reducing agent may come in contact with the evaporation chamber, but where no solid residues have formed. When the model temperature T_modei i is then compared to an actually measured temperature T_measure for the same position P_j, a very exact determination of the risk e.g. for formation of reducing agent residues may be achieved .

Here, the temperature model is used in combination with at least one measurement of an exhaust temperature T_exh for the exhaust stream 203 in the exhaust treatment system 250, for example in combination with a measurement being performed by at least one temperature sensor arranged upstream of the evaporation chamber 280. Thus, one or more upstream

temperature measurements are then input into the temperature model, and the model temperature T_modei related to the at least one corresponding position P_j at the internal wall 281 is determined. Since the model temperature T_{modei i} is modelled as being attached to, or embedded within, the internal wall 281 of the evaporation chamber, the model temperature T_{modei i} may differ from the exhaust temperature T_exh of the exhaust stream 203. For example, for temperature transient behavior, e.g.

when sprayed reducing agent quickly changes the model temperature T_modei , the change of the model temperature T_moden is faster than the change of the exhaust temperature T_exh However, when for example the exhaust temperature T_exh changes rather quickly, such as e.g. in connection with a cold start demanding a higher engine load/torque after the engine and the exhaust treatment system initially having been cold, the change of the model temperature T_{modei i} is slower than the change of the exhaust temperature Texh due to the thermal inertia of the evaporation chamber 280.

The determination 440 of a formation of residues is according to the herein described embodiments based on the modelled and measured actual temperatures where reducing agent residues could be created.

According to an embodiment of the present invention, the at least one temperature model for the evaporation chamber 280 may also be used in combination with at least one prediction of an exhaust temperature T_exh for the exhaust stream 203 in order to determine at least one representation of a model temperature T_{modei i} . The prediction may e.g. be based on one or more of a number of factors, including for example the torque requested by a driver and/or by a cruise control, on the appearance/features of the road section in which the vehicle is located, and/or the driving style of the driver.

According to an embodiment of the present invention, at least one representation of a model temperature T_{modei i} is determined based on a combination of the exhaust temperature T_exh _r which may be measured and/or predicted, and the at least one

internal wall temperature, which may be measured, modelled and/or calculated. The temperature model being used for determining at least one representation of a model temperature T_modei may use the exhaust temperature T_exh for the exhaust stream 203, the exhaust mass flow M_exh, the reducing agent mass M_agent and/or the reducing agent mass flow M_agent as input parameters. Hereby, the determination of formation of residues takes into account the cooling effect on the internal wall 281 by the reducing agent being injected, and the cooling effect on the internal wall 281 from the exhausts themselves. Thus, the determination 440 of residues according to the herein presented embodiments are based on a rather complete information related to a risk for forming of residues on the internal wall 281.

The temperature model may for example be determined/defined based on simulations, such as numerical experiments, and/or physical experiments. These simulations and/or experiments may then result in a wall temperature profile T_pr0f, possibly having a temporal temperature resolution, as mentioned above.

As a non-limiting example, the temperature model may be

experimentally determined by injecting, by use of a dosage device 271, differing dosages of the reducing agent into a prototype/physical model of the evaporation chamber 280. The prototype/physical model may here at least in size and

geometry essentially corresponding at least partly to an actual evaporation chamber 280 being included in the exhaust treatment system, and may possibly also have an experimental mass flow corresponding to the exhaust mass flow M_exh flowing through the prototype/physical model. The prototype/physical model has at least one position defined as corresponding to the at least one position P_j at the evaporation chamber inner wall 281. Along the internal wall of the prototype/physical model, at least one experimental internal temperature related to at least one position P_j is then measured. Thus, at one or more prototype/physical model positions corresponding to the one or more positions P_j of the evaporation chamber 280 (shown in figure 3), the at least one experimental internal

temperature resulting from the actual injection of the

reducing agent is measured, respectively. Hereby, the wall temperature profile T_pr0f for the one or more positions P_j is determined. This may be performed for differing operation points of the engine 101.

According to an embodiment of the present invention, the at least one position P_j is chosen as a point having an increased risk for formation of the solid deposits 285 due to the injection of a reducing agent into the exhaust stream 203, because of the injected reducing agent ending up at the wall at the least one position P_j .

Thus, based on the temperature profile T_pr0f, it is determined where along the internal wall 281 the reducing agent ends up, and cools down the wall, which may be used as an indicator of where along the internal wall 281 there is a potential risk for formation of solid deposits. A hereby identified at least one cold position Pi cold is related to a position P_j in which, i.e. in and/or downstream of which, the risk for formation of deposits may be increased. Often, the deposits/residues are formed/created downstream adjacent to at least one cold position P_jCOid, where the temperature is slightly higher than in the at least one cold position Picoid· Thus, by analyzing the temperature profile T_pr0 , at least one cold position Picoid which is often colder than other positions along the internal wall of the prototype/physical model may be detected/found. Of course, it may be extra interesting and/or efficient to analyse areas around such identified one or more extra cold positions Pi cold when the risk for formation of deposits is to be determined, since it is likely that such a solid residue may occur adjacent to such cold positions Pi coid r and more precisely in a position P_j at and/or adjacent/directly

downstream of such a one or more extra cold positions Pi cold ·

The exhaust stream mass flow M_exh used as a parameter for the model may be determined in a number of ways. For example, the exhaust stream mass flow M_exh may be determined based on at least one mass flow model for the exhaust treatment system 250. This model may take into account e.g. the physical form and dimension of the exhaust treatment system and/or an operation mode for the engine 201 producing the exhaust stream 203. The exhaust stream mass flow M_exh may also be determined based an amount of fuel and an amount of air being input into the cylinders of the engine 201 producing the exhaust stream 203. The exhaust stream mass flow M_exh may also be determined based on at least one measurement of the exhaust mass flow M_exh for the exhaust stream 203. This measurement may e.g. be performed by at least one mass flow sensor arranged upstream the evaporation chamber 280 in the exhaust treatment system 250.

Generally, the herein mentioned at least one position _j at the internal wall 281 of the evaporation unit 280 is located where there is an increased risk for formation of the solid deposits 285 due to the injection of a reducing agent into the exhaust stream 203. Due to a number of parameters, such as e.g. an evaporation unit geometry, an exhaust mass flow M_exh for the exhaust stream, a reducing agent mass M_agent and/or a reducing agent mass flow M_agentr the reducing agent being injected into the exhaust stream 203 has a higher likelihood to hit the wall in some positions than in other positions. In other words, the injected reducing agent will more often end up in some

positions than in others along the inner wall. Such more likely hit positions are of course particularly interesting for the determination of formation of solid deposits,

wherefore the one or more positions Pi being interesting for the determination correspond, according to an embodiment, to such more likely hit positions.

The at least one position P_j at the internal wall 281 of the evaporation unit 280 may be determined in various ways

according to some embodiments of the invention. For example, the at least one position P_j may be determined based on one or more simulations of injections into the evaporation unit, based on one or more injection and/or evaporation unit models, and/or based on one or more empirical experiments, e.g. one or more physical tests, related to injections into an evaporation unit .

According to an embodiment of the present invention, the at least one temperature sensor 265i is located at the at least one position P_j at the internal wall 281, respectively, which has such an increased risk for formation of the solid deposits

285.

Thus, for the at least one position P_j at the internal wall 281, the at least one temperature sensor 265i is located, based on which the at least one representation of a measured

temperature T_{measure t} is determined, and also the at least one representation of a model temperature T_modei is determined. Hereby, the at least one representation of a measured

temperature T_measure and the at least one representation of a model temperature T_modeij corresponding to the at least one position P_j, respectively, may be compared in order to determine the one or more representations of differences D7^ that are used for determining if solid deposits have been formed, are forming, or are beginning to form (precursors) in the at least one position Pi, respectively.

As mentioned above, the one or more representations of

differences D7^ are compared to one or more detection

thresholds

det thr' DG^ > DG; _det th> respectively. Here, the one or more detection thresholds DG; ^et th may have one common value for every one of the at least one position Pi, or may have at least partly differing values for two or more positions Pi .

The one or more detection thresholds DG; ^et th may, according to an embodiment, be determined based on one or more features of the evaporation unit 280 and/or on an accuracy of the

temperature model for the evaporation unit 280. The one or more detection thresholds DG; ^ _th may be determined based on one or more simulations, on one or more models and/or on one or more physical tests. The one or more detection thresholds ATi det th may for example have values being related to, e.g.

being a portion of, the model temperature T_modei . As a non limiting example, the one or more detection thresholds DG; ^et th may have values being less than half of the corresponding model temperatures T_modeli; AT_{idet th}<0.S_*T_moden; respectively.

The flow chart of figure 5 illustrates a method 500 for reduction of a risk for formation of solid deposits 285 of a reducing agent on at least one inner wall 281 of an

evaporation unit 280 of an exhaust treatment system 250 arranged for treating an exhaust stream 203 from an engine 101, according to an embodiment of the present invention.

In a first step 510 of the method, a formation of solid deposits of a reducing agent is determined by usage of the herein described method 400, i.e. according to the method described above in connection with figure 4, possibly

implementing any one of the herein described embodiments.

In a second step 520 of the method, at least one action 521, 522, 523, 524 for reducing the formation of the at least one solid deposit is performed if at least one formation of a solid deposit is determined.

Hereby, a risk for formation of solid deposits in the

evaporation unit is reduced, which also reduces the risk for increased exhaust back pressure. Hereby, the fuel consumption may be reduced over time, since the probability for a need for performing fuel consuming deposit eliminating actions is considerably reduced. Also, the control system regulating the injection of the reducing agent may more aggressively inject reducing agent, since a possible formation of solid deposits is determined at an early stage, when the deposits are still small (e.g. are only precursors), which also makes the

elimination of the deposits much easier and quicker. An aggressive injection may lead to a more efficient reduction of nitrogen oxides NO_x.

The at least one action which may be performed if formation of solid deposits is determined may include control 521 of the engine 101 producing the exhaust stream 203 such that the concentration of nitrogen oxides NO_x in the exhaust stream 203 is reduced. Hereby, less reducing agent may be injected into the exhaust stream in order to still fulfil emission standards and regulations. The decreased injection reduces the risk for further formation of residues, and facilitates elimination of already formed deposits.

The at least one action that may be performed if formation of solid deposits is determined may also include control 522 of the engine 101 producing the exhaust stream 203 such that the exhaust temperature T_exh is increased, whereby elimination of already formed deposits is facilitated, and further formation of residues is mitigated.

The at least one action that may be performed if formation of solid deposits is determined may also include control 523 of the engine 101 producing the exhaust stream 203 such that an exhaust mass flow M_exh of the exhaust stream 203 is increased. The control of the exhaust mass flow may be achieved by control of a device for exhaust recirculation (EGR) 211

(schematically illustrated in figure 2) . Combustion engines are supplied with air at an inlet, to achieve a gas mixture which is suitable for combustion, together with fuel that is also supplied to the engine. The combustion takes place in the engine's cylinders, wherein the gas mixture is burned. The combustion generates exhausts, which leave the engine at an outlet. The exhaust recirculation conduit 211 is arranged from the outlet of the engine to its inlet, and leads back a part of the exhausts from the outlet to the inlet. Thus, the suction losses at the air intake may be reduced, and the exhaust mass flow M_exh output from the engine 201 may be controlled/adjusted .

The exhaust mass flow M_exh influences where the reducing agent will hit the internal wall 281 of the evaporation chamber, or at least influences where and how the reducing agent will cause heat exchange with the internal wall. Thus, the heart exchange is dependent on the exhaust mass flow M_exh. For example, a lower exhaust mass flow M_exh may have the effect that the reducing agent hits the wall closer to the dosage device 271 than for a higher exhaust mass flow M_exh. A higher exhaust mass flow M_exh would correspondingly result in that the reducing agent hits the internal wall 281 farther away from the dosage device 271. Thus, if the exhaust mass flow M_exh is adjusted by the control, also the impact the exhaust mass flow M_exh has on the internal wall temperature

along the wall 281 is ad usted/controlled. Also, smaller deposits may also be blown away by higher exhaust mass flow M_exhr such that the deposits are eliminated.

An increased exhaust mass flow M_exhr an increased output of nitrogen oxides NO_x and/or an increased exhaust temperature T_exh may be achieved by decreasing the fraction of the exhaust stream which is recirculated through the EGR device 211. For example, an increased exhaust mass flow M_exh may be useful if a formation of reducing agent residues is determined/detected. Correspondingly, e.g. a decreased exhaust mass flow M_exh may be achieved by increasing the fraction of the exhaust stream, which is recirculated through EGR device 211.

Thus, by the control 521, 522, 523 of the engine 201, the exhaust temperature Texh ^of the exhaust stream 203 may be increased, the exhaust mass flow M_exh may be increased and/or the amount of outputted nitrogen oxides NO_x may be reduced if a formation of deposits is determined. Correspondingly, the temperature T_exh for the exhaust stream 203 may be decreased, the exhaust mass flow M_exh may be decreased and/or the amount of outputted nitrogen oxides NOx may be increased if it is determined that there are no deposits forming, whereby the engine may be run more efficiently regarding e.g. fuel

consumption. The temperature T_exh for the exhaust stream 203, the exhaust mass flow M_exh and/or the amount of outputted nitrogen oxides NO_x may be controlled e.g. by adaption of the engine load/torque and/or the revolutions per minute (RPM) for the engine 101.

According to an embodiment of the present invention, the control 521, 522, 523 of the engine 101 includes a control of at least one injection strategy for the engine 101.

According to one embodiment of the present invention, the timing of fuel injections into the respective cylinders in the engine may be controlled, so that at least the nitrogen oxides NO_x output from the engine 101 and/or the temperature T_exh ^of the exhaust stream 203 is controlled. Often, the output nitrogen oxides NO_x and/or the temperature T_exh of the exhaust stream 203 are relatively easily controlled.

According to one embodiment of the present invention, an injection pressure for an injection of fuel into cylinders of the engine 101 is controlled, whereby at least the nitrogen oxides NO_x and/or the exhaust temperature T_exh output from the engine 201 is controlled. For example, an increase of the exhaust temperature T_exh and/or a reduction of the nitrogen oxides NO_x may be performed by adjusting the injection

pressure if a formation of reducing agent residues is

determined .

The at least one action that may be performed if formation of solid deposits is determined may also include control 524 of a dosage device 271 injecting the reducing agent into the evaporation unit 280, such that a reducing agent mass M_ag_ent being injected and/or a reducing agent mass flow M_ag_ent being injected are reduced/decreased. The decreased injection then reduces the risk for further formation of residues. Thus, the amount of reducing agent being injected into the exhaust stream may for example be decreased if it is determined that a formation of residues is in progress, i.e. if solid residues/deposits are probable to grow, e.g. if precursors are determined/detected. Correspondingly, if forming residues are not detected, the amount of injected reducing agent may be increased, if necessary for achieving an efficient reduction of nitrogen oxides A fO_x in the downstream at least one

arranged reduction catalyst device 230. Basically, the more reducing agent being injected, the colder the internal wall 281 gets, since it is cooled down by the reducing agent.

Correspondingly, the less reducing agent being injected, the less cooling effect will reach the internal wall. Thus, if a formation of residues is determined/detected, the amount of injected reducing agent may be reduced, by reducing/decreasing the injected reducing agent mass flow M_agent and/or reducing agent mass M_agent.

The amount of reducing agent to be injected into the exhaust stream may, by use of the herein described embodiments, be precisely controlled, such that the evaporation of the

injected reducing agent is improved/optimized.

Two or more of the above mentioned actions 521, 522, 523, 524 may be used in combination for reducing the risk for further formation of residues and/or for facilitating elimination of already formed deposits.

As a non-limiting example, if a formation of reducing agent residues is determined when the dosage device 271 currently injects 20 grams of reducing agent per minute, the deposits may be mitigated by some embodiments of the present invention by reducing the injection of reducing agent to 15 grams per minute, by increasing the exhaust mass flow M_exh by 500 kilos per hour, and/or by increasing the exhaust temperature T_exh with 50 °C. By performing one or more of these actions, the risk for continued forming/growing of reducing agent residues is considerably reduced, and reducing agent residues may be efficiently avoided and/or eliminated.

In this document, the at least one representation of a model temperature T_modeij, the at least one representation of the measured temperature T_measure , and the one or more

representations of differences D7^ that are used in various embodiments of the present invention may include suitable statistically determined values. Essentially any such suitable statistically determined value may be used in this respect, e.g. a statistically determined value including and/or being based on mean values, moving average values, median values, filtered values, and/or statistic values. Essentially, any measure/value representing an at least scalar value

corresponding to a time-dependent behavior of the model temperature T_modeij, the measured temperature T_measure , and/or the differences D7^ may be used as such a statistically determined value when implementing the embodiments of

described herein.

A person skilled in the art will realise that a method for determination of formation of solid residues and/or for reduction of a risk for formation of solid deposits 285 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 603, wherein the computer program product comprises a suitable digital non-volatile/permanent/persistent/durable storage medium on which the computer program is stored. The non volatile/permanent/persistent/durable computer readable medium includes 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 6 schematically shows a control device/means 600. The control device/means 600 comprises a calculation unit 601, which may include 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 601 is

connected to a memory unit 602, installed in the control device/means 600, providing the calculation device 601 with e.g. the stored program code and/or the stored data, which the calculation device 601 needs in order to be able to carry out calculations. The calculation unit 601 is also set up to store interim or final results of calculations in the memory unit 602.

Further, the control device/means 600 is equipped with devices 611, 612, 613, 614 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 611, 613 for the receipt of input signals, and may be converted into signals that may be processed by the calculation unit 601. These signals are then provided to the calculation unit 601. The devices 612, 614 for sending output signals are arranged to convert the calculation result from the calculation unit 601 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 include 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 comprise the calculation unit 601, and that the above-mentioned memory may comprise the memory unit 602.

Generally, control systems in modern vehicles include of a communications bus system, comprising 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 figures 1, 2, 3 and 6, 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/means 600 in figure 6 may comprise and/or illustrate one or several of the control devices/systems/means 215 and 260 in figure 1, the control devices/systems/means 215, 260, 270, 290, 390 in figure 2, or the control

devices/systems/means 215, 260, 270, 290, 390 in figure 3. The control device/means 290, 390 in figures 2 and 3 are arranged for performing the present invention. The units/means 291,

292, 293, 294, 391, 392, 393, 394 may for example correspond to groups of instructions, which can be in the form of

programming code, that are input into, and are utilized by a processor when the units are active and/or are utilized for performing its method step, respectively. The present invention, in the embodiment shown, may be

implemented in the control device/means 600. 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 .

According to an aspect of the present invention, a system 290 arranged for determination of a formation of solid deposits of a reducing agent on at least one inner wall 281 of an

evaporation unit 280 of an exhaust treatment system 250 arranged for treating an exhaust stream 203 from an engine 101 is disclosed. As described above, the exhaust stream 203 is produced by an engine 201, and is then treated by an exhaust treatment system 250 including e.g. a reduction catalyst device. At least one reducing agent is injected into the exhaust stream 203 by the dosage device 271, and is evaporated in an evaporation chamber 280 when being injected into the exhaust stream 203.

The system 290 includes a first means 291, e.g. a first determination unit 291, arranged for determining 410 at least one representation of a model temperature T_modei for at least one position P_j on at least one inner wall 281 of the

evaporation unit 280. The determination 410 of the at least one representation of the model temperature T_modei is, as described in detail above for the embodiments of the present invention, based on a temperature model for the evaporation unit 280, wherein the temperature model assumes that the evaporation unit 280 is free of solid deposits 285 of the reducing agent. The first determination means/unit 291 may be arranged for performing any above described embodiment related to the determination of the at least one representation of a model temperature T_{modei i} . The system 29 0 also includes second means 292 , e.g. a second determination unit 292 , arranged for determining 42 0 , by use of at least one temperature sensor 26 5 i , at least one

representation of a measured temperature T_measure for the at least one position P_j on at least one inner wall 2 8 1 of the evaporation unit 2 8 0 . The second determination means/unit 292 may be arranged for performing any above described embodiment related to the determination of the at least one

representation of a measured temperature T_measurei.

The system 290 further includes third means 293, e.g. a third determination unit 293, arranged for determining 430 one or more representations of differences

between one or more of the at least one representation of the model temperature T_modei i and one or more of the at least one representation of the measured temperature T_measure , respectively. Thus, one or more differences

between one or more modelled and measured temperature values for the at least one position P_ir

respectively, are here determined. The third determination means/unit 293 may be arranged for performing any above

described embodiment related to the determination of the one or more representations of differences D7^ .

The system 290 further includes fourth means 294, e.g. a fourth determination means 294, arranged for determining 440 a formation of at least one solid deposit 285 of the reducing agent if at least one of the one or more representations of differences D7^ exceeds one or more detection threshold APj e_{t tf}t/ ATi > AT_\ de_{t thr} respectively. The determination means/unit 294 may be arranged for performing any above described embodiment related to the determination of formations of deposits. The system 290 may thus be arranged/modified for performing any of the in this document described embodiments of the method according to the present invention.

According to an aspect of the present invention, a control system 390 arranged for reduction of a risk for formation of solid deposits is disclosed. The system 390 includes a system 290 arranged for determination of a formation of solid

deposits as described herein. The system 390 further includes means 391, 392, 393, 394, e.g. at least one action unit 391, 392, 393, 394, arranged for performing 520, if at least one formation of a solid deposit of a reducing agent is

determined/detected, at least one action 521, 522, 523, 534 for reducing the at least one solid deposit. These actions may, according to various embodiments of the present

invention, include controlling 521, 522, 523 the engine 101 and/or include controlling 524 the dosage device 271 injecting the reducing agent into the evaporation unit, as described in detail above.

The system 390 may be arranged/modified for performing any of the in this document described embodiments of the method according to the present invention.

The exhaust treatment system 250 shown in figures 2 and 3 includes only one dosage device 271, only one reduction catalyst device 230, and only one evaporation chamber 280 for pedagogic reasons. It should, however, be noted that the present invention is not restricted to such systems, and may instead be generally applicable in any exhaust treatment system including one or more dosage devices, one or more reduction catalyst devices, and one or more evaporation chambers. For example, the present invention is especially applicable on systems including a first dosage device, a first evaporation chamber, a first reduction catalyst device, a second dosage device, a second evaporation chamber and a second reduction catalyst device. Each one of the first and second reduction catalyst devices may include at least one SCR-catalyst , at least one ammonia slip catalyst ASC, and/or at least one multifunctional slip-catalyst SC. The

multifunctional slip catalyst SC may be arranged primarily for reduction of nitrogen oxides NOx, and secondarily for

oxidation of reducing agent in the exhaust stream. The

multifunctional slip catalyst SC may also be arranged for performing at least some of the functions normally performed by a DOC, e.g. oxidation of hydrocarbons C_xH_{y (}also referred to as HC) and carbon monoxide CO in the exhaust stream 203 into carbon dioxide C0₂ and water H₂0 and/or oxidation of nitrogen monoxides NO occurring in the exhaust stream into nitrogen dioxide N0₂.

The present invention is also related to a vehicle 100, such as e.g. a truck, a bus or a car, including the herein

described system 290, 390 for arranged for controlling a dosage device 271 and/or an engine 201.

Figure 7 schematically illustrates, in a non-limiting example, a principle utilized by the present invention. For pedagogic reasons, figure 7 schematically illustrates an essentially stationary operational point, for which the load, engine speed and exhaust temperature T_exh are essentially constant. However, the principle of the present invention may of course also be applied on other non-stationary operational points. As is illustrated in figure 7, the at least one representation of a model temperature T_modeij (solid line) for the at least one position P_j, which assumes that there are no solid deposits, and the at least one representation of a measured temperature T-measurej (dashed line) for the at least one position P_j

essentially coincide when there are no solid deposits formed in the evaporation unit. Thus, the one or more representations of differences

are small, close to zero, when there are no solid deposits.

But when a formation of solid deposits starts, the solid deposits/residues insulates the inner wall of the evaporation unit from the spray impacts of the reducing agent. Thus, the formed solid deposits prevent the relatively cold reducing agent from hitting the inner wall. Therefore, the measured temperature, i.e. the at least one representation of a

measured temperature T_measure increases due to the formed solid deposits as a result of this insulation. The model, however, is based on the assumption that there are no solid deposits, wherefore the at least one representation of a model

temperature T_modeii does not increase when the solid deposits are formed. Therefore, the one or more representations of differences

are greater than zero when the solid deposits have formed. These one or more representations of differences may then, according to the embodiments of the present invention be compared to a suitable threshold value T_{[ det th};

ATi > AT_{ det_jh r' in order to determine/detect formed solid

deposits, as described above.

The inventive method, and embodiments thereof, as described above, may at least in part be performed with/using/by at least one device. The inventive method, and embodiments thereof, as described above, may be performed at least in part with/using/by at least one device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof. A device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof may be one, or several, of a control unit, an electronic control unit (ECU), an electronic circuit, a computer, a computing unit and/or a processing unit .

With reference to the above, the inventive method, and

embodiments thereof, as described above, may be referred to as an, at least in part, computerized method. The method being, at least in part, computerized meaning that it is performed at least in part with/using/by the at least one device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof.

With reference to the above, the inventive method, and

embodiments thereof, as described above, may be referred to as an, at least in part, automated method. The method being, at least in part, automated meaning that it is performed

with/using/by the at least one device that is suitable and/or adapted for performing at least parts of the inventive method and/or embodiments thereof.

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. A method (400) for determination of a formation of solid deposits (285) of a reducing agent on at least one inner wall (281) of an evaporation unit (280) of an exhaust

treatment system (250) arranged for treating an exhaust stream (203) from an engine (101); characterized by:

- determining (410) at least one representation of a model temperature T_modeij for at least one position Pi on said at least one inner wall (281) of said evaporation unit (280), wherein said determining (410) of said at least one representation of said model temperature T_{modei t} is based on a temperature model for said evaporation unit (280), said temperature model assuming that said evaporation unit is free of solid deposits of said reducing agent;

- determining (420), by use of at least one temperature sensor (265i), at least one representation of a measured temperature Jmeasure for said at least one position Pi on said at least one inner wall (281) of said evaporation unit (280);

- determining (430) one or more representations of differences ATi between one or more of said at least one representation of said model temperature T_modeij and one or more of said at least one representation of said measured temperature T_{measure i r} respectively;

- determining (440) a formation of at least one solid deposit (285) of said reducing agent if at least one of said one or more representations of differences D7^ exceeds one or more detection thresholds NJi_det _th r N^i > N^i_de t_jh r' respectively.

2. The method (400) as claimed in claim 1, wherein said temperature model for said evaporation unit (280) utilizes at least one in the group of :

- an exhaust temperature T_exh for said exhaust stream (203); - an exhaust mass flow exh for said exhaust stream (203);

- a reducing agent mass agent r and

- a reducing agent mass flow M_ag_ent being injected into said exhaust stream (203) as input parameters.

3. The method (400) as claimed in any one of claims 1-2, wherein

- said temperature model is determined by simulations and/or physical experiments resulting in a wall temperature profile Tprof for said at least one position P_t of said at least one inner wall (281), respectively; and

- said at least one representation of said model temperature Tmodeij for said at least one position P_j of said evaporation unit (280) corresponds to at least one temperature Ppro_fj of said temperature profile T_pr0 for at least one corresponding model position P_model_j· respectively.

4. The method (400) as claimed in any one of claims 1-3, wherein said at least one temperature sensor (265i) is located in said at least one position P_j at said internal wall (281) of said evaporation unit (280), respectively, which has an increased risk for formation of said solid deposits (285) .

5. The method (400) as claimed in any one of claims 1-4, wherein said at least one position P_j at said internal wall (281) of said evaporation unit (280) is determined based on at least one in the group of :

- one or more simulations;

- one or more models; and

- one or more physical tests.

6. The method (400) as claimed in any one of claims 1-5, wherein one or more of said at least one representation of a model temperature T_modeij, said at least one representation of said measured temperature T_measure and said one or more

representations of differences D7^ include statistically determined values.

7. The method (400) as claimed claim 6, wherein said statistically determined values comprise one or more in the group of :

- mean values;

- moving average values;

- median values;

- filtered values; and

- statistic values.

8. The method (400) as claimed in any one of claims 1-7, wherein said one or more detection thresholds DG; ^e_t th ^are determined based on at least one in the group of :

- one or more features of said evaporation unit (280); and

- an accuracy of said temperature model for said evaporation unit (280) .

9. The method (400) as claimed in any one of claims 1-8, wherein said one or more detection thresholds DG; ^e_t th are determined based on at least one in the group of :

- one or more simulations;

- one or more models;

- one or more empirical experiments; and

- one or more physical tests.

10. A method (500) for reduction of a risk for formation of solid deposits (285) of a reducing agent on at least one inner wall (281) of an evaporation unit (280) of an exhaust treatment system (250) arranged for treating an exhaust stream (203) from an engine (101), characterized by:

- determination (510) of a formation of solid deposits of a reducing agent using said method (400) according to any one of claims 1-9; and

- performing (520), if at least one formation of a solid deposit is detected, at least one action (521, 522, 523, 524) for reducing said at least one solid deposit.

11. The method (500) as claimed in claim 10, wherein said at least one action (521, 522, 523, 524) includes one or more in the group of :

- controlling (521) said engine (101) producing said exhaust stream (203) to reduce a concentration of nitrogen oxides NO_x in said exhaust stream (203);

- controlling (522) said engine (101) producing said exhaust stream (203) to increase a temperature T_exh of said exhaust stream (203) ;

- controlling (523) said engine (101) producing said exhaust stream (203) to increase an exhaust mass flow M_exh for said exhaust stream (203); and

- controlling (524) a dosage device (271) injecting said reducing agent into said evaporation unit (280) to reduce an reducing agent mass M_agent and/or a reducing agent mass flow agent being injected into said exhaust stream (203) .

12. A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method according to any one of claims 1-11.

13. 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 any one of claims 1-11.

14. A system (290) arranged for determination of a formation of solid deposits of a reducing agent on at least one inner wall (281) of an evaporation unit (280) of an exhaust treatment system (250) arranged for treating an exhaust stream (203) from an engine (101); characterized by:

- first means (291) arranged for determining (410) at least one representation of a model temperature T_modei for at least one position P_j on said at least one inner wall (281) of said evaporation unit (280), wherein said determining (410) of said at least one representation of said model temperature T_{modei t} is based on a temperature model for said evaporation unit (280), said temperature model assuming that said evaporation unit (280) is free of solid deposits (285) of said reducing agent;

- second means (292) arranged for determining (420), by use of at least one temperature sensor (265i), at least one

representation of a measured temperature T_measure for said at least one position P_j on said at least one inner wall (281) of said evaporation unit (280);

- third means (293) arranged for determining (430) one or more representations of differences DR^ between one or more of said at least one representation of said model temperature T_{modei t} and one or more of said at least one representation of said measured temperature T_{measure ir} respectively;

- fourth means (294) arranged for determining (440) a

formation of at least one solid deposit (285) of said reducing agent if at least one of said one or more representations of differences DR^ exceeds one or more detection threshold AP_{j cjet} ATi > DT[ _de_tjhr' respectively.

15. A control system (390) arranged for reduction of a risk for formation of solid deposits of a reducing agent on at least one inner wall (281) of an evaporation unit (280) of an exhaust treatment system (250) arranged for treating an exhaust stream (203) from an engine (101), characterized by:

- a system (290) according to claim 14, arranged for

determination (510) of a formation of solid deposits of a reducing agent; and

- means (391, 392, 393, 394) arranged for performing (520), if at least one formation of a solid deposit of a reducing agent is determined, at least one action (521, 522, 523, 524) for reducing said at least one solid deposit.