SE1450417A1 - Exhaust after-treatment arrangement and a motor vehicle comprising such an exhaust after-treatment arrangement - Google Patents

Abstract

SUMMARY Exhaust after-treatment arrangement comprising: - an inlet (11) for receiving exhaust gases from an internal combustion engine, - a particulate filter (14) arranged downstream of the inlet, - a mixing channel (15) arranged downstream of the particulate filter, which is delimited in a radially delimited manner. of a tubular wall (18), - a SCR catalyst (16) arranged downstream of the mixing channel, - an injection means (17) for injecting the reducing agent into the mixing channel, and - a heat transfer channel (13) arranged between the inlet and the particle filter extending along with the outside of the tributary tubular wall to allow the transfer of heat from the exhaust gases flowing through the heat transfer channel to the tubular wall. The heat transfer duct is separated from the particulate filter so that exhaust gases flowing into the exhaust after-treatment arrangement via the inlet are prevented from emitting heat to the particulate filter before passing through the heat transfer duct. The invention also relates to a motor vehicle provided with such an exhaust after-treatment. (Fi9 1)

Description

satorn. During the injection of urea into the exhaust gases, ammonia is formed and it is this ammonia that constitutes the reducing substance that contributes to the catalytic conversion in the SCR catalyst. The ammonia is accumulated in the catalyst by being adsorbed on active sites in the catalyst and NOX present in the exhaust gases is converted to nitrogen gas and water when it is brought into contact with the accumulated ammonia on the active sites in the catalyst in the catalyst.

When urea is used as a reducing agent, it is injected into the exhaust gases in the form of a liquid urea solution by means of an injection means. the injection takes place in a duct flowing through the exhaust gases which is located upstream of the SCR catalyst. In the following description text and in the following patent claims, the term “mixing channel” is used as a term for this channel where the reducing agent is injected and mixed with the exhaust gases. The injection means comprises a nozzle via which the urea solution is injected under pressure into the mixing channel in finely divided form as a spray. During large parts of a diesel engine's operating condition, the exhaust gases have a sufficiently high temperature to be able to evaporate the urea solution so that ammonia is formed. However, it is difficult to avoid that part of the added urea solution comes into contact with and sticks to the inner wall surface of the mixing channel in an undisturbed state. If the temperature of the wall surface is lower than about 190 ° C, a film of ureal solution can be formed on the wall surface struck by the urea solution which is then drawn along by the exhaust gas flow. After this film has been moved a certain distance in the exhaust line, the water in the urea solution will boil away under the influence of the hot exhaust gases. Solid urea remains, which is slowly evaporated by the heat in the exhaust line. If the supply of solid urea is greater than the evaporation, a solid urea accumulates in the exhaust line. If the layer of urea becomes sufficiently thick, the urea and its decomposition products will react with each other to form primitive polymers on urea base, so-called urea lumps. Such lumps of urea can eventually block an exhaust line. For this reason, during cold start it is inappropriate to start the injection of urea before the wall surfaces of the mixing channel have had time to be heated by the passing exhaust gases to a temperature of 190 ° C, which means that the NOX-reducing activity of the SCR catalyst is delayed at cold start. In the case of a truck, for example, in cold start it normally takes about 300-500 seconds before the wall surfaces of the mixing duct are heated to the required temperature of about 190 ° C in the case where these wall surfaces are only heated by the exhaust gases flowing through the mixing duct. In order to achieve an improved exhaust gas purification, it is desirable to achieve a faster heating of the wall surfaces of the mixing channel during cold start, in order to reduce the delay of the SCR catalyst's NOX-reducing activity. WO 2012/050509 A1 US 2010/0212301 A1 is the former known to direct the exhaust gases on the outside of the wall of the mixing duct before the exhaust gases are led into the tea. Through, for example, and the mixing duct, whereby the heating of the wall surfaces of the mixing duct is accelerated during cold start.

A motor vehicle which is equipped with an SCR catalyst has a particle filter in the exhaust line upstream of the particle filter in the re-SCR catalyst and often also an oxidation catalyst in the exhaust duct. The oxidation catalyst converts hydrocarbons (HC) and carbon monoxide (CO) to carbon dioxide (CO2). When the particulate filter needs to be regenerated, i.e. freed from particles deposited therein, unburned fuel is entrained to accompany the exhaust gases into the oxidation catalyst, where the fuel is oxidized while generating such a temperature increase of the exhaust gases that a combustion of the particles deposited in the particulate filter occurs.

Said fuel can, for example, be injected into the exhaust line upstream of the oxidation catalyst by means of a fuel injection device. As an alternative, the unburned fuel brought along with the exhaust gases can be injected into the internal combustion engine as post-injection in one or more of the internal combustion engine cylinders, which post-injection is performed so late during the respective working operations that no combustion takes place in the cylinder (s) of the fuel injected through these post-injections.

OBJECT OF THE INVENTION The object of the present invention is to provide a further development of the technique previously known from the above-mentioned documents to provide a solution which enables a faster heating of the wall surfaces of the mixing channel at cold start and thereby an earlier start of reducing agent. the injection.

SUMMARY OF THE INVENTION According to the present invention, said object is achieved by means of an exhaust gas after-treatment arrangement having the features defined in claim 1.

The exhaust after-treatment arrangement according to the invention comprises: - an inlet for receiving exhaust gases from an internal combustion engine, - a particulate filter arranged downstream of the inlet, - a mixing channel arranged downstream of the particulate filter, which is delimited in the radial direction of a tubular wall. catalyst, - an injection means for injecting reducing agent into the mixing channel, and - a heat transfer channel arranged between said inlet and the particle filter extending along the outside of at least a part of said tubular wall to allow heat transfer from the the exhaust gases flowing through the heat transfer channel to the tubular wall and to the exhaust gases flowing through the mixing channel.

The heat transfer duct is separated from the particle filter so that the exhaust gases flowing into the exhaust after-treatment arrangement via said inlet are prevented from emitting heat to the particulate filter before they have passed through the heat transfer duct. The exhaust gases flowing through the heat transfer duct will emit heat to the tubular wall of the mixing duct, the inside of which forms an inner wall surface of the mixing duct. This results in a heating of this internal wall surface of the mixing channel and also a heating of the exhaust gases flowing through the mixing channel. At cold start, the particulate filter arranged upstream of the SCR catalyst is cold, which means that the particulate filter will gradually be heated by absorbing heat from the passing exhaust gases. Thus, during a cold start, the exhaust gases will be cooled as they pass through the particulate filter.

The type of particulate filter commonly used in an exhaust system of an internal combustion engine has surfaces of alumina ceramic with a large area and has a relatively high thermal inertia, which means that the particulate filter heats up relatively slowly during a cold start and will therefore have a cooling effect on the exhaust gases. a relatively long period of time. By heating the tubular wall of the mixing channel by means of exhaust gases which have not yet come into heat-transferring contact with the particle filter, a faster heating of this tubular wall and also a faster heating of the SCR catalyst arranged downstream of the mixing channel is thus achieved during cold start. compared with a case where the tubular wall of the mixing channel is heated by means of exhaust gases which have already come into heat-transferring contact with and lost some of their heat energy to the particulate filter.

According to an embodiment of the invention, the exhaust gas aftertreatment arrangement comprises an oxidation catalyst arranged between the heat transfer duct and the particle filter, the heat transfer duct being separated from the oxidation catalyst so that the exhaust gases flowing into the exhaust aftertreatment arrangement through the preheated oxidation array the heat transfer duct.

At cold start, the oxidation catalyst arranged upstream of the SCR catalyst is cold, which means that the oxidation catalyst will gradually be heated by absorbing heat from the passing exhaust gases. At cold start, the exhaust gases will thus be cooled during their passage through the oxidation catalyst. An oxidation catalyst has surfaces of ceramic with a large area and has a relatively large thermal inertia, which means that the oxidation catalyst heats up relatively slowly during a cold start and will therefore have a cooling effect on the exhaust gases for a relatively long period of time. By heating the tubular wall of the mixing duct with the aid of exhaust gases which have not yet come into heat-transferring contact with the oxidation catalyst, a faster heating of this tubular wall and thus a faster heating of the SCR catalyst arranged downstream of the mixing duct is thus achieved during cold start. when the tubular wall of the mixing channel is heated by means of exhaust gases which have already come into heat-transferring contact with and lost some of their heat energy to the oxidation catalyst.

In addition, with the solution according to the invention, the temperature increase obtained of the exhaust gases during their passage through the oxidation catalyst in connection with a regeneration of the particulate filter can be used to preheat the exhaust gases which are led into the oxidation catalyst, since the exhaust gases passing through the mixing channel therein cases, due to the heat evolution in the oxidation catalyst, will have a higher temperature than the exhaust gases passing through the heat transfer duct. This makes it possible to reduce the amount of fuel that needs to be introduced into the oxidation catalyst in connection with a regeneration of the particulate filter and a reduction of the amount of noble metal required in the oxidation catalyst in order to obtain the desired regeneration performance. Because the exhaust gases passing through the mixing duct in connection with a regeneration of the particulate filter emit heat to the exhaust gases passing through the heat transfer duct, the heat increase of the SCR catalyst during regeneration is also reduced, whereby it becomes possible to use a higher regeneration temperature without affect the function of the SCR catalyst. An increase in the regeneration temperature in turn enables faster regeneration and a reduction in the amount of fuel that needs to be introduced into the oxidation catalyst in connection with the regeneration.

Other advantageous features of the exhaust after-treatment arrangement according to the invention appear from the dependent claims and the following description.

The invention also relates to a motor vehicle having the features defined in claim 7.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail below with the aid of exemplary embodiments, with reference to the accompanying drawing.

It is shown in: Fig. 1 a schematic diagram of an internal combustion engine with associated exhaust system, the exhaust system comprising an exhaust after-treatment arrangement according to a first embodiment of the present invention, Fig. 2 a section through the mixing and heat transfer ducts illustrated in Fig. 1, according to line II -II in Fig. 1, and Fig. 3 is a principle sketch of an internal combustion engine with associated exhaust system, the exhaust system comprising an exhaust after-treatment arrangement according to a second embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The invention will be described in the following in the application of a motor vehicle. However, the invention is not limited to this application but can be used in all contexts where an SCR catalyst with associated reducing agent injector and a particulate filter is included in an exhaust system of an internal combustion engine.

Figs. 1 and 3 schematically show an internal combustion engine 1 of a motor vehicle 2. The exhaust gases leaving the internal combustion engine are received by an exhaust system 3, which comprises an exhaust line 4 connected to the internal combustion engine 1 and an exhaust after-treatment arrangement 10 arranged in the exhaust line. 1 flow through the exhaust line 4 and pass through the exhaust after-treatment arrangement 10 before exiting the environment via an exhaust outlet 5.

The exhaust after-treatment arrangement 10 comprises: - an inlet 11 connected to the exhaust line 4 for receiving exhaust gases from the internal combustion engine 1, - an outlet 12 for discharging the exhaust gases after their passage through the exhaust after-treatment arrangement 10, - a heat transfer duct 13 arranged downstream of the inlet 11, particulate filter 14, - a mixing channel 15 arranged downstream of the particulate filter 14, - an SCR catalyst 16 arranged downstream of the mixing channel 15, and - an injection means 17 in the form of an injection nozzle or the like for injecting reducing agent into the mixing channel 15.

The heat transfer duct 13, the particle filter 14, the duct 15 and the SCR catalyst 16 are arranged in series with the mixing ducts in order to be in turn flowed through by the exhaust gases from the combustion engine 1.

The particulate filter 14 may, for example, be of the type having interior surfaces of alumina ceramic.

The mixing channel 15 is delimited in the radial direction by a tubular wall 18, preferably of metal, which extends between the upstream end and the downstream end of the mixing chamber.

The heat transfer duct 13 extends along the outside of the tubular wall 18 of the mixing duct to allow the transfer of heat from the exhaust gases flowing through the heat transfer duct 13 to the tubular wall 18 and to the exhaust gases flowing through the mixing duct 15. The heat transfer channel 13 may be arranged to extend along the outside of the entire wall 18 of the mixing channel or along the outside of a certain part of this wall.

In the illustrated embodiments, the heat transfer duct 13 is arranged to surround the tubular wall 18 of the mixing duct. The heat transfer duct 13 in this case has an annular cross-section, as illustrated in Fig. 2. The mixing duct 15 and the heat transfer duct 13 are advantageously concentrated, as illustrated in Figs. In the illustrated embodiments, the injector 17 is arranged to inject under pressure a liquid reducing agent in the form of urea as a spray 21 into the mixing duct 15, the injector 17 being so arranged relative to the heat transfer duct 13 that the heat transfer duct extends on the the outside of the part of the tubular wall 18 of the mixing channel which is hit by the spray 21 of urea. A storage container 22 for reducing agent is connected to the injector 17. The supply of reducing agent to the injector 17 is controlled by means of a control valve 23 arranged between the storage container 22 and the injector 17. The control valve 23 is controlled by an electronic control device (not shown). which determines the amount of reducing agent currently to be injected into the exhaust gases. The control device controls by means of the control valve 23 how much reducing agent is injected into the exhaust gases. In the supply line 24 between the storage container 22 and the control valve 23, a pump 25 is arranged for supplying reducing agent from the storage container to the control valve while maintaining a given pressure of the reducing agent which is supplied to the control valve.

The heat transfer duct 13 is separated from the particulate filter 14 so that the exhaust gases flowing into the exhaust after-treatment arrangement 10 via the inlet 11 are prevented from emitting heat to the particulate filter 14 before passing through the heat transfer duct 13. The heat transfer duct 13 is thus arranged in such a manner to the particle filter 14 that the walls of the heat transfer channel are not in heat transfer contact with the particle filter 14 or the housing 26 surrounding the particle filter. A heat insulating medium, for example air, or a heat insulating material is arranged in the space 27 between the outer wall 28 of the heat transfer duct and the housing 26 of the particulate filter to keep the heat transfer duct 13 thermally insulated from the particulate filter 14. At cold start, i.e. when the internal combustion engine 1 is started in cold state, the various components of the exhaust aftertreatment arrangement 10 are initially cold and when the hot exhaust gases from the internal combustion engine after cold start flow through the heat transfer duct 13 they will give off heat to the mixing 18 and to the flowing exhaust gases, which gives a relatively fast when the wall 18 has reached a temperature of about 190 ° C, the injection of reducing agent into the mixing channel 15 can begin, whereby the SCR catalyst 16 can start to operate at full power. During an initial period of time after cold start, before the particulate filter 14 has been properly heated by the exhaust gases passing through the particulate filter, the exhaust gases will, when passing through the particulate filter 14, lose a significant part of their heat energy to the particulate filter. During this initial period of time, the exhaust gases flowing into the mixing duct 15 will thus have a markedly lower temperature than the exhaust gases flowing into the heat transfer duct 13.

In the embodiment illustrated in Fig. 3, in addition to the above-mentioned components, the exhaust after-treatment arrangement 10 also comprises an oxidation catalyst 29, which is arranged in series with and between the heat transfer duct 13 and the particle filter 14. The heat transfer duct 13 is separated both from the particle filter 14 and from the oxidation catalyst 29 so that the exhaust gases flowing into the exhaust aftertreatment arrangement 13 via the inlet 11 are also prevented from dissipating heat to the oxidation catalyst 29 before passing through the heat transfer channel 13. The heat transfer channel 13 is thus arranged in such a manner relative to oxidation 29 that the walls of the heat transfer duct are not in heat transfer contact with the oxidation catalyst 29 or the housing 30 surrounding the oxidation catalyst. A heat insulating medium, for example air, or a heat insulating material is provided in the space 31 between the outer wall 28 of the heat transfer duct and the housing 30 of the oxidation catalyst to keep the heat transfer duct 13 thermally insulated from the oxidation catalyst 29. At cold start, the oxidation catalyst 14 and the particulate catalyst are cold. During an initial period of time after cold start, before the oxidation catalyst 29 and the particulate filter 14 have been properly heated by the exhaust gases passing through the oxidation catalyst and the particulate filter, the exhaust gases will pass a significant part of their passage through the oxidation catalyst 29 and the particulate filter 14. heat energy to these. During this initial period of time, the exhaust gases flowing into the mixing duct 15 will thus have a markedly lower temperature than the exhaust gases flowing into the heat transfer duct 13.

When the particulate filter 14 of the exhaust aftertreatment arrangement of Fig. 3 is to be regenerated, unburned fuel is brought to accompany the exhaust gases into the oxidation catalyst 29, where the fuel is oxidized while generating such an increase in the exhaust gases that a combustion of the particles deposited in the particulate filter 14 occurs. In the embodiment illustrated in Fig. 3, said unburned fuel is accompanied by the exhaust gases by being injected into the internal combustion engine 1 as post-injections in one or more of the cylinders of the internal combustion engine, which post-injections are performed so late during the respective working stroke that it does not occur. if there is any combustion in the cylinder (s) of the fuel injected through these post-injections. Alternatively, the exhaust aftertreatment arrangement 10 could be provided with a separate fuel injection device for injecting fuel into the exhaust gases at an injection site between the internal combustion engine 1 and the oxidation catalyst 29 in conjunction with a regeneration of the particulate filter 14. During the regeneration of the particulate filter 14 in the mixing duct 15, due to the heat evolution in the oxidation catalyst 29, to have a significantly higher temperature than the exhaust gases flowing into the heat transfer duct 13 and in this case the exhaust gases flowing towards the oxidation catalyst 29 and the particulate filter 14 will be preheated at their passage through the heat transfer duct 13 under the action of the exhaust gases flowing through the mixing duct 15, which leads to a reduction of the temperature increase which during the regeneration period needs to be effected in the exhaust gases during their passage through the oxidation catalyst 29. This led r in turn to a reduction in the amount of fuel that needs to be introduced into the exhaust gases to achieve the desired regeneration effect.

The exhaust after-treatment arrangement 10 may further comprise an abrasive catalyst 32 arranged downstream of the SCR catalyst 16 capable of oxidizing ammonia, as illustrated in Fig. 3.

In the illustrated embodiments, the various components 13, 14, 15, 16, 29, 32 of the exhaust aftertreatment arrangement are arranged in three separate units 33, 34, 35, which are connected to each other via pipelines 36, 37. The various components 13, 14, 15, 16, 29, 32 of the exhaust after-treatment arrangement 10 according to the invention could, however, alternatively be integrated in a common module and connected to each other via internal channels of this module.

The exhaust after-treatment arrangement according to the invention is particularly intended for use in a heavy motor vehicle, such as, for example, a bus, a towing vehicle or a truck.

The invention is of course in no way limited to the embodiments described above, but a number of possibilities for modifications thereof should be obvious to a person skilled in the art, without this for that reason deviating from the basic idea of the invention as defined in the appended claims. .

Claims (1)

16 PATENT REQUIREMENTS Exhaust after-treatment arrangement comprising: - an inlet (11) for receiving exhaust gases from an internal combustion engine, - a particulate filter (14) arranged downstream of the inlet (11), - a mixing channel (15) arranged downstream of the particulate filter (14) ), which is delimited in the radial direction by a tubular wall (18), - a SCR catalyst (16) arranged downstream of the mixing channel (15), and - an injection means (17) for injecting reducing agent into the mixing channel (15), characterized therefrom , that the exhaust after-treatment arrangement (10) comprises a heat transfer channel (13) arranged between said inlet (11) and the particle filter (14) extending along the outside of at least a part of said tubular wall (18) to allow heat transfer from the the heat transfer duct (13) flowing the exhaust gases to the tubular wall (18) and to the exhaust gases flowing through the mixing duct (15), the heat transfer duct (13) being separated from the particle the electric filter (14) so that the exhaust gases flowing into the exhaust after-treatment arrangement (10) via said inlet (11) are prevented from emitting heat to the particle filter (14) before they have passed through the heat transfer duct (13). . Exhaust after-treatment arrangement according to claim 1, characterized in that the heat transfer duct (13) surrounds said tubular wall (18) or at least a part thereof. 10 15 20 25 17. Exhaust after-treatment arrangement according to claim 1 or 2, characterized in that the exhaust after-treatment arrangement (10) comprises an oxidation catalyst (29) arranged between the heat transfer duct (13) and the particle filter (14), the heat transfer duct (13) being separated from the oxidation catalyst (29) that the exhaust gases flowing into the exhaust after-treatment arrangement (10) via said inlet (11) are prevented from emitting heat to the oxidation catalyst (29) before they have passed through the heat transfer channel (13). . Exhaust after-treatment arrangement according to one of Claims 1 to 3, characterized in that the exhaust after-treatment arrangement (10) comprises an abrasive catalyst (32) arranged downstream of the SCR catalyst (16) capable of oxidizing ammonia. . Exhaust after-treatment arrangement according to one of Claims 1 to 4, characterized in that the injector (17) is arranged to inject a liquid reducing agent in the form of urea as a spray (21) into the mixing channel (15). . Exhaust after-treatment arrangement according to one of Claims 1 to 5, characterized in that the mixing duct (15) and the heat transfer duct (13) are concentric. . Motor vehicle comprising an internal combustion engine (1) and an exhaust line (4) connected to the internal combustion engine, characterized in that the motor vehicle (2) comprises an exhaust after-treatment arrangement (10) arranged in the exhaust line (4) 18 according to any one of claims 1-6.