SE1251469A1 - Process and system for reducing a coating in a finishing system - Google Patents

Abstract

The present invention relates to a method for reduction of a first coating in a post-treatment system (200), which system is intended to treat an exhaust flow arising from combustion in a combustion engine (101), said first coating being formed by an additive supplied to said post-treatment system (200) by being supplied to a first catalyst (201) for reduction of at least one first compound (NOx) in said exhaust flow. The method, during the reduction of said first coating, comprises - determining a first content (Hi) of said first compound (NOx) at a location downstream of said first catalyst (201), and - taking a first remedial measure to reduce the content of said first compound (NOx) when said first content (H1) is greater than a second content (H2). The invention relates also to a system and a vehicle.

Description

10 l5 where an additive is supplied to the exhaust gas stream resulting from the combustion engine combustion to reduce nitrogen oxides NOK mainly to nitrogen gas and water vapor.

A common type of catalyst for this type of reduction, especially for heavy vehicles, are SCR (Selective Catalyst Reduction) catalysts. SCR catalysts typically use ammonia (NH3), or a composition from which ammonia can be generated / formed, as an additive to reduce the amount of nitrogen oxides NOX. The additive is injected into the exhaust gas stream resulting from the internal combustion engine upstream of the catalyst. The additive fed to the catalyst is adsorbed (stored) in the catalyst, whereby nitrogen oxides in the exhaust gases react with the additive stored in the catalyst.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of reducing at least one coating in a finishing system. This object is achieved by a method according to the characterizing part of claim 1.

The present invention relates to a method for reducing a first coating in a finishing system, said finishing system being arranged for treating an exhaust stream resulting from a combustion at an internal combustion engine, and wherein said first coating is formed by an additive supplied to said finishing system, wherein said additive is fed to a first catalyst for reducing at least one first compound in said exhaust stream. The method comprises, at the beginning of the reduction of said first coating: - controlling a content of said first compound (NOX) emitted by said internal combustion engine (101) to a relatively high content (NÛLHIGH) f and at the ongoing reduction of said first coating: - at a position downstream of said first catalyst, determining a first content of said first compound, and - taking a first action to reduce the content of said first compound when said first content exceeds a second content.

The present invention is thus applicable to after-treatment systems where an additive is supplied to the exhaust gas stream. As above, an example of such a system is the SCR system. These types of systems are associated with certain disadvantages. A problem with e.g. SCR systems, and injection of its additives, such as e.g. urea or AdBlue, is that the addition of additives can cause a coating structure, such as a crystal structure, such as e.g. urea, can occur in the after-treatment system, such as in pipes / catalysts / mufflers at or downstream of the injection site. The coating can e.g. consists of a urea build-up or a build-up of a composition from / with which urea can be formed.

These structures can grow so large that the performance of the internal combustion engine is affected by the exhaust flow in the exhaust system being affected (throttled), and with a large build-up of build-up, continued engine operation can in the worst case be completely prevented. The coating can also damage components in the finishing system if e.g. crystal formations, e.g. in the form of lumps, release from the place where they have formed and then carried with the exhaust stream to e.g. a subsequent SCR catalyst. l0 l5 The structure of the coating can e.g. occur when e.g. a vehicle, and thus its internal combustion engine, is driven under static conditions. This can e.g. happen if e.g. a vehicle is driven for a long time in such a way that the temperature of the resulting exhaust stream is kept relatively low.

By raising the temperature of the exhaust stream at the same time as the supply of additives is switched off, occurring coatings can be reduced by combustion, and problems with e.g. crystal build-up is reduced / eliminated. During ongoing reduction, however, the content of the compound (s) the additive is intended to reduce rises to undesirable / impermissible levels.

According to the present invention, this is avoided by determining a first content of at least one compound which is normally reduced by using the additive, this content being determined for a position downstream of said first catalyst. By then comparing this determined first content with a second content, where this second content may consist of a predetermined content and set to some applicable value as below, a further action is taken in the further reduction of said coating when said first content exceeds said second content. .

In the case of an SCR catalyst, nitrogen oxides NOX are normally reduced, i.e. mainly nitrogen monoxide and nitrogen dioxide, respectively. In the reduction of the crystal build-up, the additive stored in the crystals will react with the passing exhaust stream so that a reduction of said first compound still takes place to a certain extent. As the crystals burn, however, the content of said first compound will rise and eventually reach undesirable and perhaps even, in cases where emissions of said first compound are regulated, impermissible levels. According to the invention, this is avoided by monitoring the content of said first compound in the discharged exhaust gas stream, and wherein an action is taken to reduce the content of the first compound when the emission becomes undesirably large. The operation is performed so that the content of said first compound downstream of said first catalyst is reduced. The measure can e.g. consists of controlling a content of said first compound emitted by said internal combustion engine. In the case of nitrogen oxides, the internal combustion engine can be controlled so that a lower content is emitted. Control of the content emitted by the internal combustion engine can be performed in various ways such as e.g. by regulating one or more of the injection angle / time and fuel / air mixture.

Alternatively or in combination, an amount of additive may be added to reduce said first content, the amount added being less than the amount normally required to reduce the content of said first compound when no contribution to the reduction is obtained from combustion of the coating.

Additional features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments and the accompanying drawings.

Brief Description of the Drawings Fig. 1A schematically shows a vehicle in which the present invention can be used.

Fig. 1B shows a control unit in the control system of the vehicle shown in Fig. 1.

Fig. 2 shows the finishing system in more detail for the vehicle shown in Fig. 1.

Fig. 3 shows an example of a dosing system for supplying additives to the exhaust gas stream.

Fig. 4 shows a method according to an exemplary embodiment of the present invention.

Fig. 5 shows an example of a time course for the amount / content of reducing agent released according to an embodiment of the present invention.

Fig. 6 shows an example of a time course for the content of the nitrogen oxides NOX generated during the combustion of the internal combustion engine according to an embodiment of the present invention.

Detailed Description of Embodiments Fig. 1A schematically shows a driveline in a vehicle 100 according to an embodiment of the present invention. The vehicle 100 schematically shown in Fig. 1 comprises only one axle with drive wheels 113, 114, but the invention is also applicable to vehicles where more than one axle is provided with drive wheels, as well as to vehicles with one or more additional axles, such as one or more several support axles. The driveline comprises an internal combustion engine 101, which is connected in a conventional manner, via a shaft outgoing on the internal combustion engine 101, usually via a flywheel 102, to a gearbox 103 via a clutch 106.

The internal combustion engine 101 is controlled by the control system of the vehicle via a control unit 115. Likewise, the clutch 106, which e.g. may be an automatically controlled clutch, and the gearbox 103 of the vehicle control system by means of one or more applicable control units (not shown). Of course, the driveline of the vehicle can also be of another type such as of a type with conventional automatic transmission etc.

A shaft 107 emanating from the gearbox 103 drives the drive wheels 113, 114 via an end gear 108, such as e.g. a conventional differential, and drive shafts 104, 105 connected to said final gear 108.

The vehicle 100 further includes an after-treatment system (exhaust purification system) 200 for treating (purifying) exhaust emissions resulting from combustion in the combustion engine 101 combustion chamber (eg, cylinders).

The after-treatment system is shown in more detail in Fig. 2. The figure shows the internal combustion engine 101 of the vehicle 100, where the exhaust gases generated during combustion are led via a turbocharger 220. In turbocharged engines, the exhaust gas resulting from combustion often drives a turbocharger which in turn compresses the incoming the air for the combustion of the cylinders. Alternatively, the turbocharger can e.g. be of compound type. The function for different types of turbochargers is well known, and is therefore not described in more detail here. The exhaust stream is then led via a pipe 204 (indicated by arrows) to a diesel particulate filter (DPF) 202 via a diesel oxidation catalyst (DOC) 205. During combustion in the internal combustion engine, soot particles are formed, and the particulate filter 202 is used to these soot particles. The exhaust stream is led through a filter structure where soot particles are captured from the passing exhaust stream and stored in the particulate filter.

Regarding the oxidation catalyst DOC 205, this has several functions, and is normally used primarily to oxidize residual hydrocarbons and carbon monoxide in the exhaust stream to carbon dioxide and water during the post-treatment. During the oxidation of hydrocarbons (ie oxidation of fuel) heat is also formed, which can be used to raise the temperature of the particle filter at the emptying normally required at particle filters at intervals, so-called regeneration. The oxidation catalyst 205 can also oxidize a large proportion of the nitrogen monoxides (NO) present in the exhaust stream to nitrogen dioxide (NO2). The oxidation of nitrogen monoxide NO to nitrogen dioxide NO2 is further advantageous in the subsequent reduction of nitrogen oxides NOX. In this regard, the post-treatment system further comprises a SCR (Selective Catalytic Reduction) catalyst 201 arranged downstream of the particulate filter 202. SCR catalysts use ammonia (NH3), or a composition from which ammonia can be generated / formed, such as e.g. urea, as an additive to reduce the amount of nitrogen oxides NO2 in the exhaust gas stream.

However, the efficiency of this reduction is affected by the ratio of NO to NO 2 in the exhaust gas stream, so the reaction of the reduction is affected in a positive direction by the previous oxidation of NO to NO 2.

Regarding the present invention, the finishing system can generally be of different types, and needs e.g. do not include particle filter 202 or oxidation catalyst 205 as long as the after-treatment system is of a type where the addition of additives takes place to a catalytic exhaust gas purification process, as in said SCR catalyst 201. The after-treatment system may also include additional components not shown, such as e.g. and ASC (Ammonia Slip) catalyst.

Furthermore, the components DOC 205, DPF 202 and SCR catalyst 201 can be integrated in one and the same exhaust gas purification unit or alternatively consist of separate units.

As mentioned above, the SCR catalyst requires additives to reduce the concentration of a first compound such as e.g. nitrogen oxides in the exhaust gases from the internal combustion engine. This additive is often urea-based, and can e.g. consist of AdBlue, which in principle constitutes urea mixed with water. Urea forms ammonia when heated.

An example of an additive supply system is shown in more detail in Fig. 3, where of the above components only particle filter 202 and SCR catalyst 201 are shown, and where the system in addition to said catalyst 201 comprises a urea tank 302, which is connected to a urea dosing system (UDS) 303.

The UDS system 303 includes, or is controlled by, a UDS controller 304, which generates control signals for controlling the supply of additives so that the desired amount is injected into the exhaust stream from the urea tank 302 resulting from the combustion in the cylinders of the internal combustion engine 101 by means of an injection nozzle 305. about the SCR catalyst 201. Fig. 3 also shows a NOX sensor 308 arranged downstream of the SCR catalyst 201.

The more specific function of the UDS systems is well described in the prior art, and the exact procedure for injecting additives is therefore not described in more detail here. In general, however, the temperature at the injection point / SCR catalyst 201 should be at least 200-250 ° C, preferably above 300 ° C in order to obtain the desired reaction rates, and thus the desired reduction of said first compound, such as one or more types of nitrogen oxides. .

According to the above, however, such systems are associated with certain disadvantages. If e.g. the temperature at the position in the after-treatment system where the supply of additives takes place is too low, there is a risk that urea injected by means of the injection nozzle 305 instead of being directly evaporated by the passing exhaust stream hits relatively low-tempered pipe walls, whereby additives get stuck and start to build up crystals. As long as the vehicle is driven with varying and periodically higher loads with associated increases in the temperature in the finishing system, this crystal structure will not have time to grow undesirably large before the crystals are burned away by the passing exhaust stream. If, on the other hand, the vehicle is driven for a time under relatively static conditions with relatively light load, with low temperatures in the exhaust system as a result, this crystal build-up can continue until the vehicle's performance is adversely affected by the increased flow resistance. The crystal build-up can also mean that the SCR system's ability to convert NOX is affected if the supply of urea (such as spray image, amount) is disturbed due to that a coating in the form of lump formation occurs.

In such situations, therefore, measures must be taken to avoid problems with far-reaching crystal build-up. This can be done by raising the temperature of the exhaust stream at the same time as the supply of additives is interrupted, whereby the crystal build-up can be reduced. However, in this reduction of crystals, elevated and undesirable emissions of said first compound such as NOX may occur. The present invention provides a method of preventing such undesirable emissions from occurring. An exemplary method 400 according to the invention is shown in Fig. 4. The invention may be implemented in any applicable control unit, such as e.g. the control unit 208 shown in Fig. 2. In general, control systems in modern vehicles consist of a communication bus system consisting of one or more communication buses for interconnecting a number of electronic control units (ECUs) such as the control units, or controllers, ll5, 208, 304 and various other means. vehicle located components. Such a control system may comprise a large number of control units, and the responsibility for a specific function may be divided into more than one control unit. For the sake of simplicity, however, only the said control units are shown in the figures.

The present invention is thus in the embodiment shown implemented in the control unit 208, which in the embodiment shown is also responsible for other functions in the finishing system. For example. the control unit can be responsible for so-called regeneration, i.e. emptying the particle filter 202.

The control unit 208 can also be responsible for urea injection, ie. the function performed by the control unit 304 as above.

The invention can also be implemented in a control unit dedicated to the present invention, or in whole or in part in one or more other control units already existing in the vehicle, such as e.g. engine control unit ll5.

The operation of the control unit 208 (or the control unit (s) to which the present invention is implemented) according to the present invention may depend on sensor signals from one or more NOX sensors 210, 308, as well as on one or more temperature sensors 211-2122 for determining temperatures. in the finishing system. Likewise, the function of the control unit will probably be e.g. depend on information such as received from the control unit (s) controlling motor functions, ie in the present example the control unit 115.

Control units of the type shown are normally arranged to receive sensor signals from different parts of the vehicle. The control unit 208 can e.g. receive sensor signals as above, as well as from controllers other than controller 115. Furthermore, such control units are usually arranged to emit control signals to various vehicle parts and components. For example. the control unit 208 can emit signals to e.g. engine control unit ll5. l0 l5 l2 The control is often controlled by programmed instructions. These programmed instructions typically consist of a computer program, which when executed in a computer or controller causes the computer / controller to perform the desired control, such as method steps of the present invention.

The computer program is usually part of a computer program product, the computer program product comprising an applicable storage medium l11 (see Fig. 1B) with the computer program 109 stored on said storage medium l1l.

Said storage medium l1l can e.g. consists of someone from the group: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk drive, etc., and be arranged in or in connection with the control unit, the computer program being executed by the control unit. By changing the instructions of the computer program, the behavior of the vehicle in a specific situation can thus be adapted.

An exemplary control unit (control unit 208) is shown schematically in Fig. 1B, wherein the control unit may in turn comprise a calculation unit 120, which may consist of e.g. any suitable type of processor or microcomputer, e.g. a Digital Signal Processor (DSP), or an Application Specific Integrated Circuit (ASIC). The computing unit 132 is connected to a memory unit 112, which provides the computing unit 132 e.g. the stored program code 109 and / or the stored data calculation unit 120 need to be able to perform calculations. The calculation unit 120 is also arranged to store partial or final results of calculations in the memory unit 112.

Furthermore, the control unit is provided with devices 122, 123, 112, 125 for receiving and transmitting input and output signals, respectively. These input and output signals may contain waveforms, pulses, or other attributes, which of the input 122 devices 125, 125 may be detected as information for processing the computing unit 120. The output signals 123, 124 for transmitting output signals are arranged to convert calculation results from the computing unit. 120 to output signals for transmission to other parts of the vehicle control system and / or the component (s) for which the signals are intended. Each of the connections to the devices for receiving and transmitting input and output signals, respectively, may consist of one or more of a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Oriented Systems Transport), or any other bus configuration; or by a wireless connection. Referring again to Fig. 4, the exemplary method 400 shown begins in step 401, where it is determined whether a reduction in occupancy, i.e. in this example reduction of said crystal build-up is to be started. This determination does not in itself be the subject of the present invention, but can be performed in any applicable manner. For example. an estimation of the crystal structure can be performed. By e.g. determine or estimate a temperature for the point / area where the additive is injected, or other applicable place, it is possible, based on this temperature, to estimate an expected crystal structure, where this expected crystal structure can be determined by means of e.g. table lookup or applicable calculation.

In cases where the said expected value is calculated, this can e.g. performed using an applicable calculation model, where e.g. different calculation models can be used to represent different operating conditions to enable as good a representation as possible. In addition to temperature, the calculation model can e.g. take into account the flow of the exhaust gas, the amount / mass flow of added additives, etc.

The calculation model can e.g. be drawn up based on practical tests or otherwise produced. The temperature for e.g. the place where the additive hits surrounding pipes or the like can be determined by means of a temperature sensor if the grain is available, alternatively the temperature can be determined by means of a temperature model based on e.g. the temperature sensors normally present in the after-treatment system, preferably together with saving exhaust gas mass flow. The calculation model can be refined by e.g. also take into account additional circumstances such as e.g. outside temperature and vehicle speed.

According to one embodiment, it is alternatively or additionally determined whether a predetermined operating condition of said vehicle is fulfilled, said operating condition relating to a condition where there is an increased risk of occupancy in the exhaust system, and if said operating condition is met, at least one restraining measure is taken to counteract the build-up. Said operating condition can e.g. based on parameters as above, alternatively it can e.g. determine whether the vehicle has been driven "statically" for a certain period of time. Such a determination of the need for reduction of occurring coating is described in the international application WO2011 / 087445.

If it is then determined in step 401 that the amount of additive which has crystallized and formed a coating, e.g. a certain mass, exceeds any applicable quantity / mass, such as e.g. a certain number of grams, the process proceeds to step 402, in which step a reduction / combustion of the resulting coating is started.

When coating reduction is to be performed in step 402, the temperature in the finishing system is raised. At the same time, the supply of additives is interrupted. Alternatively, the supply of the additive is not interrupted until a first temperature in the finishing system has been reached, where this first temperature is set to any applicable temperature, such as e.g. an applicable temperature in the range 250 ° C-400 ° C, e.g. in the range 300 ° C-350 ° C. The crystal reduction is accelerated according to the process according to the invention by the internal combustion engine being set to emit relatively high levels of nitrogen oxides (NOÄBKE) in order to thereby accelerate the reaction between the crystal structure and passing nitrogen oxides. For example. In step 402, in one embodiment, the internal combustion engine can be set to emit a relatively high NOX level (NOÄBKE), such as e.g. l000-2000 ppm or an applicable content / level exceeding 2000 ppm (generally the ratio of emissions of nitrogen oxides NOK from an internal combustion engine is such that increased NOX usually results in a better efficiency, where the efficiency can be affected in the desired way by affecting t. eg injection angle / time and fuel / air mixture).

The process then proceeds to step 403.

The temperature increase as above can e.g. is achieved by supplying unburned fuel to the exhaust gas stream, where the unburned fuel is then at least partially oxidized with associated heat evolution. This oxidation can e.g. occur in the oxidation catalyst 205 or the particulate filter 202 or in any other appropriate manner. Before unburned fuel is supplied to the exhaust gas stream, it can be ensured that e.g. the oxidation catalyst temperature exceeds a minimum temperature so that oxidation takes place safely. If not, the internal combustion engine 101 can first be controlled to a low efficiency mode of operation, and associated higher emitted exhaust temperatures, in order to raise the temperature of the aftertreatment system to a temperature which causes the supplied fuel to be oxidized.

The amount of fuel supplied can e.g. depend on parameters of the temperature of the oxidation catalyst 205, current flow in the exhaust gas stream, internal combustion engine load, current vehicle speed, etc., and / or controlled so that the desired temperature in the aftertreatment system is achieved.

The supply of the unburned fuel to the exhaust gas stream can be carried out in several different ways. For example. the after-treatment system may comprise an injector in the exhaust system upstream of the oxidation catalyst, whereby fuel can be injected into the exhaust stream by means of the injector. Alternatively, fuel can be supplied to the exhaust gas stream by injection into the combustion engine combustion chamber late in the combustion cycle so that no or only portions of the regeneration fuel are burned in the cylinders, with unburned fuel accompanying the exhaust stream to the aftertreatment system.

By raising the temperature in the after-treatment system, and thus the area (s) where crystal build-up has occurred, the crystals will be burned by the passing exhaust stream and the build-up will thus be reduced. During the combustion of the resulting crystals, ammonia / urea will be released, and nitrogen oxides NOX will thus still be reduced as above even if the supply of additional additives is switched off. However, as this reduction continues and the coating of crystals becomes smaller and smaller, an ever smaller proportion of the nitrogen oxides NOX will be reduced, whereby the content of nitrogen oxides NOX in the exhaust gas stream leaving the vehicle will rise to ever higher levels. How the amount / content of reducing agent released during the combustion of the crystals formed varies over time is illustrated in Figure 5. At time T0 the increase of the temperature in the finishing system begins. At time TO, the amount / content of combustion-reducing reducing agent R0 is substantially equal to zero. At time T1, the temperature in the after-treatment system has been raised to such a high temperature that the amount / content of reducing agent released during combustion begins to increase relatively sharply. At time T2, the amount / content of combustion-released reducing agent has reached a maximum value of RMAX. After time T2, the amount / content of combustion-reducing reducing agent decreases until time T4, where the amount / content of combustion-reducing reducing agent R4 is substantially equal to zero.

In step 403, a first content is determined for a first compound, i.e. in this case a NOX content H1 downstream of the SCR catalyst 201 by means of the NOX sensor 308. This determined NOX content is then compared in step 404 with a second, predetermined NOX content H2, where the content H2 is set to some applicable value. For example. said second NOK content can be Hz set to any applicable value in the range of 200-500 ppm. As long as the NOX content H1 determined in step 403 is less than said second NOK content H2, the procedure remains in step 404. On the other hand, when the determined NOX content H1 exceeds said second NOX content H2, which, with reference to Fig. 5, e.g. may occur at time T3, the process proceeds to step 405 to take at least one step of lowering said first NOX content H1 to a level below said second content H2.

Figure 6 illustrates how the combustion of the internal combustion engine, according to an embodiment of the invention, is controlled in such a way that the proportion of the nitrogen oxides NOX generated during the combustion results in an improved process. l0 l5 l8 The times T0-T4 in figure 6 correspond to the times T0-T4 in figure 5.

Up to the time T1 in Figure 6, the combustion engine combustion is controlled in such a way that the proportion of the nitrogen oxides generated during combustion is an arbitrarily applicable NOX1 content. From time T2, the combustion of the internal combustion engine is controlled in such a way that the proportion of the nitrogen oxides generated during the combustion is a relatively high content of NOXHIGH. The crystal reduction is hereby accelerated according to the method according to the invention by the internal combustion engine being set to emit relatively high levels of nitrogen oxides NOXHIGH in order thereby thereby accelerating the reaction between the crystal structure and passing nitrogen oxides.

According to one embodiment, the combustion of the internal combustion engine is controlled in such a way that the proportion of the nitrogen oxides generated during the combustion increases gradually or gradually / continuously from time T1, in order to then at time T2 reach the relatively high content of NOXHIGH.

According to one embodiment, the combustion engine combustion is controlled in such a way that the proportion of the nitrogen oxides generated during the combustion increases gradually or gradually / continuously already from time T0, in order to then at time T2 reach the relatively high NOXHIGH content.

The content of nitrogen oxides in the exhaust gas emitted from the after-treatment system should not be too high. If e.g. The NO2 content in the exhaust gas stream amounts to or exceeds concentrations in the order of 300-500 ppm, released nitrogen dioxide NO2 will generate a yellow-brown-red smoke, which is not only perceived as very disgusting, but which also contributes negatively to the environment by forming unwanted compounds in reactions with the surroundings. There may also be statutory emission levels that may not be exceeded. According to the present invention l0 l5 l9, therefore, measures are taken to regulate the emissions of nitrogen oxides NOX even during ongoing crystal reduction. For example. For example, the combustion engine combustion can be controlled in such a way that the proportion of the nitrogen oxides NOX generated during combustion is reduced, as illustrated in Figure 6 at time T3. As mentioned above in connection with step 402, the combustion engine can be set to emit high levels of nitrogen oxides to reduce the crystal build-up, thereby accelerating the reduction.

In step 405, a measure can thus be constituted by the nitrogen oxide content H1 emitted by the internal combustion engine being reduced to a level which means that the content determined by the NOX sensor 308 does not exceed said second content H2. The reduction can e.g. is carried out by continuous control so as to ensure at all times that the desired levels emitted from the vehicle 100 are not exceeded. According to one embodiment, the combustion of the internal combustion engine can be controlled in such a way that the proportion of the nitrogen oxides NOX generated during the combustion is gradually reduced, as illustrated in Figure 6 at times T3, T3 ', T3 "and T3"'. According to one embodiment, the combustion of the internal combustion engine can be controlled in such a way that the proportion of the nitrogen oxides NOX generated during the combustion is reduced substantially continuously, or at least in arbitrarily small steps.

According to one embodiment, the combustion of the internal combustion engine can be controlled in such a way that the proportion of the nitrogen oxides NOX generated during the combustion at time T3 is substantially directly, in one step, reduced to a relatively low content of NOXLOW.

Said relatively low content of NOXLOW may be lower than 400 ppm.

Said relatively low content of NOXLOW can be included in the range 100-300 ppm. Said relatively low content of NOXLOW may be lower than 300 ppm. Said relatively low content of NOXLOW may be lower than l00 l0 l5 ppm. Said relatively low content of NOXLOW may be dependent on the present legal requirements regarding emissions, and can be determined / determined at least in part based on said legal requirements.

Alternatively, or in combination, additives may be added to an extent which causes the combined reduction of nitrogen oxides produced by crystal combustion and the addition of the additive to ensure that said second content of H 2 is not exceeded.

According to one embodiment, the engine is controlled to emit a high NOX level NOXHIGH, such as e.g. 1000-2000 ppm or an applicable content exceeding 2000 ppm, wherein then dosing of additives is controlled so that the emitted NOX content downstream of the SCR catalyst 201 is less than said second content. The supply required can be very limited, at least initially, since reduction of NOX will be largely accomplished by the crystal buildup.

The process then proceeds to step 406 to determine whether the reduction of the crystal build-up has been performed to the desired extent and thus can be interrupted. As long as this is not the case, the procedure returns to step 403 for re-determining said first content H1. If the reduction is complete, the process is terminated in step 407.

Whether the reduction of the coating has been carried out to a sufficient extent can be determined in any applicable way. For example. the reduction can be considered completed when it has been going on for a first time at the same time as the temperature in the finishing system has reached some applicable value. Said first time can e.g. constitute a function of said determined temperature.

Alternatively, to ensure that the crystals have been reduced to the desired extent, the amount of additive injected 105 l5 2l can be compared with the measured NOX conversion. In this determination, the NOK sensor 308 can be used together with a content H3 determined from a second, upstream SCR catalyst 201 determined NOK sensor 210. As long as the sensor values indicate that a higher NOK conversion is obtained compared to what the added amount of additives can achieve, at least a part of the crystal structure remains.

According to one embodiment, the NOX content emitted by the internal combustion engine is lowered at the same time as the dosing of additives is interrupted, whereby signals from NOX sensors before and after the SCR catalyst 201 are compared to see if they show equal value. Both of these solutions require NOX sensors both upstream and downstream of the SCR catalyst. The NOX sensor arranged upstream of the SCR catalyst can alternatively be replaced by a model of the NOX levels generated by the internal combustion engine at different operating points to determine said level H3.

Furthermore, the present invention has been exemplified above in connection with vehicles. However, the invention is also applicable to arbitrary vessels / processes where finishing systems as above are applicable, such as e.g. water or aircraft with combustion processes as above.

Further embodiments of the method and system according to the invention are found in the appended claims. It should also be noted that the system may be modified according to various embodiments of the method according to the invention (and vice versa) and that the present invention is thus in no way limited to the above-described embodiments of the method according to the invention, but relates to and includes all embodiments within the appended independent the scope of protection of the requirements.

Claims (18)

l0 l5 20 25 30 22 Patent claim A method of reducing a first coating in a finishing system, said finishing system (200) being arranged to treat an exhaust stream resulting from a combustion at an internal combustion engine (101), and said first coating being formed by a to said finishing system. (200) added additive, wherein said additive is added to a first catalyst (201) for reduction of at least one first compound (NOX) in said exhaust gas stream, characterized in that the process comprises, upon initial reduction of said first coating: - controlling one of said first coatings. internal combustion engine (10l) emitted content of said first compound (NOX) to a relatively high content (NOXHIGH), and upon ongoing reduction of said first coating: - at a position downstream of said first catalyst (20l) determining a first content (H1) of said first compound (NOX), and - taking a first action to reduce the content of said first compound (NOX) when said first content t (H1) exceeds a second content (Hg. The process of claim 1, wherein said coating is formed at least partially upstream of said first catalyst (201). A method according to claim 1 or 2, wherein said first coating consists of a crystal structure formed by said additives supplied to said exhaust gas stream. A process according to any one of the preceding claims, wherein said first act of eating comprises reducing the content of said first compound (NOX) downstream of said first catalyst (201). A method according to any preceding claim, wherein said first actuation comprises controlling a content of said first compound (NOX) emitted by said internal combustion engine (101) - A method according to any one of the preceding claims, wherein said first measure comprises, in said reduction of said first coating, adding additives so that said first content (H1) is less than said second content (HQ). A process according to any one of the preceding claims, further comprising: - for a position upstream of said first catalyst (201), determining a third content (H3) of said first compound (NOX), and - determining whether said reduction of said coating has been carried out to a first extent based on said first and second contents. A method according to any one of the preceding claims, further comprising: - comparing said first content (H1) with a supply of additives, and - determining whether said reduction of said coating has been performed to a first extent based on said comparison. A method according to any one of the preceding claims, further comprising interrupting said reduction of said first coating when any of the following conditions are met: - said first coating has been reduced to a first extent, - a first time since the reduction of the coating began has elapsed. A method according to any one of the preceding claims, further comprising, before said determining said first content (H1) of said first compound (NOX): - estimating a magnitude of said first coating formed, and starting said reduction said first coating when the magnitude of said estimated coating exceeds a first value. The method of claim 10, further comprising performing said estimation using at least one representation of a temperature for said finishing system. A process according to any one of the preceding claims, wherein said first compound is a nitric oxide (NOK), and wherein said second content is a content in the range of 200-600 ppm. A method according to any one of the preceding claims, wherein said coating consists of urea or a composition from / with which urea can be formed. A computer program comprising program code, which when said program code is executed in a computer causes said computer to perform the method according to any one of claims 1-13. A computer program product comprising a computer readable medium and a computer program according to claim 14, wherein said computer program is included in said computer readable medium. A system for reducing a first coating in a finishing system, said finishing system (200) being arranged to treat an exhaust stream resulting from a combustion at an internal combustion engine (101), and wherein said first coating is formed by a to said finishing system (200). ) added additive, wherein said additive is supplied with a first catalyst (201) for reduction of at least one first compound (NOX) in said exhaust gas stream, characterized in that the system comprises means for, upon starting reduction of said first coating: - controlling one of said combustion engine (101) delivered content of said first compound (NOK) to a relatively high content (NOXHIGH), and in the event of ongoing reduction of said first coating: - at a position downstream of said first catalyst (201) determining a first content ( H1) of said first compound (NOX), and - take a first action to reduce the content of said first compound (NOX) when said first level (H1) exceeds a second level (HQ. Vehicle (100), characterized in that it comprises a system according to claim 16. Vehicle according to claim 17, characterized in that it comprises means for controlling the supply of said additive to said exhaust gas stream.