SE537980C2 - Exhaust after-treatment arrangement and a motor vehicle comprising such an exhaust after-treatment arrangement - Google Patents

Abstract

SUMMARY Exhaust gas 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. tubular cradle (18), - an SCR catalyst (16) arranged downstream of the mixing channel, - an injector (17) for injecting reducing agent into the mixing channel, and - a heat transfer channel (13) arranged between the inlet and the particle filter extending along the outside of said tubular cradle to allow the transfer of heat from the exhaust gases flowing through the heat transfer channel to the tubular cradle. The heat transfer duct is separated from the particulate filter so that the exhaust gases flowing into the exhaust after-treatment arrangement via the inlet are prevented from emitting heat to the particulate filter before they have passed through the heat transfer duct. The invention also relates to a motor vehicle provided with such an exhaust after-treatment arrangement.

Description

FIELD OF THE INVENTION AND PRIOR ART The present invention relates to an exhaust aftertreatment arrangement according to the preamble of claim 1. The invention also relates to a motor vehicle arrangement with a sadant handling device.

In order to meet current requirements for exhaust gas purification, today's motor vehicles are usually equipped with one or more catalysts in the exhaust line to achieve catalytic conversion of environmentally hazardous constituents in the exhaust gases into less environmentally hazardous substances.

One method used to achieve efficient catalytic conversion is based on the injection of reducing agents into the exhaust gases upstream of a catalyst. A reduction substance present in the reducing agent or formed by the reducing agent is forced by the exhaust gases into the catalyst where it is adsorbed on the active charge in the catalyst, which gives rise to the accumulation of the reducing agent in the catalyst. The accumulated reduction substance can then react with an exhaust substance to convert this exhaust substance into an area with less environmental impact. Such a reduction catalyst can, for example, be of the SCR type (SCR = Selective Catalytic Reduction). This type of catalyst is still referred to as the SCR catalyst. An SCR catalyst reduces nitrogen oxides (NO) in the exhaust gases. In an SCR catalyst, a urea reducing agent is usually injected into the exhaust gases upstream of the catalyst. 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 accumulates in the catalyst by being adsorbed on the active batches in the catalyst and in the exhaust gases NO is converted to nitrogen gas and water as it is brought into contact with the accumulated ammonia on the active batches in the catalyst.

When urea is used as a reducing agent, this is injected into the exhaust gases in the form of a liquid-shaped urea solution with the aid of an injection means. The injection takes place in a duct through which the exhaust gases flow, which is upstream of the SCR catalyst. In the following description text and in the appended claims, the term "mixing channel" is used as a designation 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 under pressure is injected 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 black to avoid that part of the supplied urea solution comes into contact with and sticks to the inner cradle surface of the mixing channel in an unoranged state. If the rock surface temperature is lower than about 190 ° C, a film of urea release can be formed on the rock surface hit by urea discharge, 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 action of the hot exhaust gases. What remains is solid urea which is slowly evaporated by the heat in the exhaust line. If the supply of solid 2 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 probing products will react with each other to form primitive polymers on urea base, so-called urea lumps. Such urea lumps can eventually block an exhaust line. For this reason, during cold start ° it is appropriate to start the injection of urea before the cradle surfaces of the mixing channel have been 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, during a cold start it normally takes about 300500 seconds before the rocking surfaces of the mixing channel are heated to the required temperature of about 190 ° C in the case where these rocking surfaces are only heated by the exhaust gases flowing through the mixing channel. In order to achieve an improved exhaust gas purification, it is unreasonable to achieve a faster heating of the cradle surfaces of the mixing channel during cold start in order to reduce the delay of the SCR catalyst's NOx-reducing activity. For example, WO 2012/050509 Aloch US 2010/0212301 Al edge to guide the exhaust gases on the outside of the cradle of the mixing channel before the exhaust gases are led into the mixing channel, whereby the heating of the cradle surfaces of the mixing channel is accelerated at cold start.

A motor vehicle equipped with an SCR catalyst usually has a particulate filter in the exhaust line upstream of the SCR catalyst and often also an oxidation catalyst in the exhaust line upstream of the particulate filter. The oxidation catalyst converts the hydrocarbons (HC) and carbon monoxide (CO) to carbon dioxide (CO2). When the particulate filter needs to be regenerated, i.e. released from the deposited 3 particles, the combustion fuel is caused 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.

The said fuel can, for example, be injected into the exhaust line upstream of the oxidation catalyst with the aid of an fuel injection device. Alternatively, the unburned fuel which is brought to accompany the exhaust gases may be injected into the internal combustion engine as post-injections into one or more of the cylinders of the internal combustion engine, which post-injections are carried out so late in each operation that no combustion occurs in the cylinder (s) of the industry injected through these mail injections.

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

SUMMARY OF THE INVENTION According to the present invention, said object is achieved with the aid of an exhaust gas aftertreatment arrangement having the features defined in claim 1. The exhaust gas aftertreatment 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 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 cradle to allow transfer of heat from those flowing through the heat transfer channel the exhaust gases to the rudder-shaped cradle and to the exhaust gases flowing through the mixing channel.

The heat transfer duct is separated from the particulate 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 cradle of the mixing duct, the inside of which forms an internal cradle surface of the mixing duct. In this way, a heating of this inner rock surface of the mixing channel is effected 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 heat up 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 large 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. long period of time. By heating the tubular cradle of the mixing channel with the aid of exhaust gases which have not yet come into heat-transferring contact with the particle filter, a faster heating of this tubular cradle and also a faster heating of the downstream mixing channel arranged with the SCR catalyst, a case where the tubular rock of the mixing channel is heated with the aid of exhaust gases which have already come into heat-transferring contact with and lost some of their heat energy to the particle 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 particulate filter, the heat transfer duct being separated from the oxidation catalyst so that the exhaust gases flowing into the exhaust aftertreatment arrangement are heated through the pre-oxidation inlet. 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. Thus, during a cold start, the exhaust gases will be cooled as they pass through the oxidation catalyst. An oxidation catalyst has large ceramic surfaces and has a relatively large thermal inertia, which means that the oxidation catalyst heats up relatively slowly during a cold start and will therefore exert a cooling effect on the exhaust gases for a relatively long period of time. By heating the tubular cradle of the mixing channel 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 cradle is thus achieved at cold start and also a faster heating of the downstream mixing channel arranged with the SCR catalyst. when the tubular rock 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 by 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 introduced into the oxidation catalyst, since the exhaust gases passing through the mixing duct in this case of the heat evolution in the oxidation catalyst, will have a higher temperature than the exhaust gases passing through the heat transfer duct. This enables a reduction of 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, making it possible to use a higher regeneration temperature without affecting the function of SCR. catalyst. An increase in the regeneration temperature in turn enables a faster regeneration 7 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 description below.

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

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

It is shown in: Fig. 1 a principle sketch of an internal combustion engine with associated exhaust system, where the exhaust system comprises an exhaust aftertreatment 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, along the line II-II in Fig. 1, and Fig. 3 a schematic diagram of an internal combustion engine with associated exhaust system, where the exhaust system comprises an exhaust after-treatment arrangement according to a second embodiment of the invention. 8 537 980 DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION The invention will be described in the following when applying 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 device and a particulate filter are contained 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. through the exhaust line 4 and pass through the exhaust aftertreatment 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, - a SCR catalyst 16 arranged downstream of the mixing channel 15, and 9 - an injection means 17 in the form of an injection nozzle or the like injecting reducing agent into the mixing channel 15.

The heat transfer duct 13, the particulate filter 14, the mixing duct 15 and the SCR catalyst 16 are arranged in series with each other in order to be flowed in turn by the exhaust gases from the internal 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 rock 18, preferably of metal, which extends between the upstream and downstream of the mixing chamber. The heat transfer channel 13 extends along the outside of the tubular cradle 18 of the mixing channel to allow heat transfer from the exhaust gases flowing through the heat transfer channel 13 to the tubular cradle 18 and to the exhaust gases flowing through the mixing channel 15. The heat transfer channel 13 may be arranged to extend along the outside of the entire cradle 18 having the mixing channel or along the outside of a certain part of this cradle.

In the illustrated embodiments, the heat transfer channel 13 is arranged to surround the tubular cradle 18 of the mixing channel 18. The heat transfer channel 13 in this case has an annular cross-section, as illustrated in Fig. 2. The mixing channel 15 and the heat transfer channel 13 are advantageously concentric, as illustrated in Fig. 2.

In the illustrated embodiments, the injection means 17 is arranged to inject under pressure a liquid reducing agent in the form of urea as a spray 21 into the mixing channel 15, the injection means 17 being arranged in relation to the heat transfer channel 13 that the heat transfer channel extends from the outside of the channel. tubular rock 18 struck 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). the amount of reducing agent that is accidentally to be injected into the exhaust gases. With the aid of the control valve 23, the control device regulates the amount of reducing agent 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 partially arranged on a so-called 14 that the cradles of the heat transfer channel are not in heat transfer contact with the particle filter 14 or the cavity 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 cradle 28 of the heat transfer duct and the particle filter housing 26 to keep the heat transfer duct 13 thermally insulated from the particle filter 14. At cold start, i.e. when the internal combustion engine 1 is started in cold to stand, the various components of the exhaust aftertreatment arrangement 10 are initially cold and when the hot exhaust gases from the combustion engine after cold start flow through the heat transfer duct 13 they will emit heat to the cradle 18 of the mixing duct and to the exhaust gases flowing through the mixing duct 15, giving a relatively fast heating the said cradle 18. When the cradle 18 at night has a temperature of about 190 ° C, the injection of reducing agent into the mixing channel 15 can be started, whereby the SCR catalyst 16 can start to operate at full power. During an initial period of time after a cold start, before the particle filter 14 has had time to be properly heated by the exhaust gases passing through the particle filter, the exhaust gases will, when passing through the particle filter 14, lose a significant part of their heat energy to the particle filter. During this initial time period, the exhaust gases flowing into the mixing duct 15 will thus have a significantly lower temperature than the exhaust gases flowing into the heat transfer duct 13.

In the embodiment illustrated in Fig. 3, the exhaust aftertreatment arrangement 10 comprises, in addition to the above components, 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 from the particle filter 14 and from oxidation. the exhaust gases flowing into the exhaust aftertreatment arrangement 12 via the inlet 11 are also prevented from dissipating heat to the oxidation catalyst 29 before passing through the heat transfer duct 13. The heat transfer duct 13 is thus arranged in such a manner as to heat the oxidation catalyst 29 to not heat in heat transfer contact with the oxidation catalyst 29 or the casing 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 cradle 28 of the heat transfer channel and the oxidation catalyst housing 30 to keep the heat transfer channel 13 thermally insulated from the oxidation catalyst 29. At cold start, the oxidation catalyst 29 and the particulate filter are cold. During an initial period of time after cold start, before the oxidation catalyst 29 and the particle filter 14 have been properly heated by the exhaust gases passing through the oxidation catalyst and the particle filter, the exhaust gases will pass a significant part of their heat energy through the oxidation catalyst 29 and the particle filter 14. During this initial period of time, the exhaust gases flowing into the mixing duct 15 will thus have a significantly lower temperature than the exhaust gases flowing into the heat transfer duct 13.

When the particulate filter 14 of the exhaust aftertreatment arrangement 10 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 a temperature increase of the exhaust gases that combustion of the particles deposited in the particulate filter 14 occurs. In the embodiment illustrated in Fig. 3, said unburned fuel is caused to accompany the exhaust gases by being injected into the internal combustion engine 1 as mail injections into one or more of the cylinders of the internal combustion engine, which post injections are carried out so late during each work stroke that it does not occur. any combustion in the cylinder (s) of the industry 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 stall between the internal combustion engine 1 and the oxidation catalyst 29 in connection 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 substantially 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 during 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 leads in in turn to a reduction in the amount of fuel that needs to be introduced into the exhaust gases in order to achieve the desired regeneration effect.

The exhaust aftertreatment 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 not limited in any way 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 deviating from the basic idea of the invention as defined in the appended claims.

Claims (7)

PATE NTKRAV 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 of a tubular rock (18), - a SCR catalyst (16) arranged downstream of the mixing channel (15), and - an injector (17) for injecting reducing agent into the mixing channel (15), characterized in that the exhaust gas aftertreatment arrangement (10 ) comprises a heat transfer channel (13) arranged between said inlet (11) and the particle filter 14. which extends along the outside of at least a part of said tubular cradle (18) to allow transfer of heat from the exhaust gases flowing through the heat transfer channel (13). to the tubular cradle (18) and to the exhaust gases flowing through the mixing duct 15., the heat transfer duct (13) being separated from the particulate 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 channel (13) surrounds said tubular cradle (18) or at least a part thereof. 16 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) exhaust gases flowing into the exhaust aftertreatment arrangement (10) via said inlet (11) are prevented from delivering heat to the oxidation catalyst (29) before passing through the heat transfer duct (13). Exhaust after-treatment arrangement according to any one of claims 1-3, 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 any one of claims 1-4, 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) 17 according to any one of claims 1-6. 18 86 ° T1,4 co cs) c, 2 5 £ A / ir 8r) 81 1ino —7) 91— 1 -ho 411- _Z he 11-4-1 11 4- Ar EZ ° f!, 1 -, \ S 9 N 4- / .7- .. ---- 1 ....) _ Eta / Z1) i AZ / A (aaO55a) g ne 'z ° A' \ k ir t