FR3082556A1 - COMBUSTION GAS PURIFICATION DEVICE HAVING A THERMALLY DECOMPOSABLE SPACER - Google Patents

Abstract

The invention relates to a device for purifying combustion gases comprising at least two depollution substrates (2,3) mounted in a casing (1). When mounting the device, it is necessary to maintain a space between the two substrates (2,3) and to avoid premature damage caused by a spacer likely to enter into vibration. To solve this problem, the purification device according to the invention comprises a spacer (4) separating the substrates (2,3) and the device is remarkable in that the spacer (4) consists of a thermally decomposable material under the action of the temperature of the flow of combustion gases intended to flow through the substrates (2, 3). The invention applies to the automobile industry as well as to any combustion appliance capable of being equipped with a combustion gas exhaust line.

Description

The field of the invention relates to devices for purifying combustion gases, in particular the devices for purification arranged in an exhaust line of a vehicle heat engine. automobile.

In the automotive industry, increasingly demanding pollution control standards have prompted manufacturers to equip vehicle exhaust systems with sophisticated purification devices in order to chemically and mechanically treat polluting particles. Conventionally, the purification devices comprise a tubular envelope (commonly called by the English term "canning") in which the flow of combustion gases circulates grouping together several depollution substrates, in particular catalysts, mounted in series in the direction of flow flow gases so that the latter pass successively through the substrates. Between two depollution substrates it is generally necessary to maintain a spacing space to allow for example the introduction of a probe or to avoid contact between the two substrates.

We know from the prior art the document US20040105792A1 describing a purification device comprising two catalysts mounted in series in a metal casing, which are separated by spacers, T-shaped or arcs, arranged at the periphery of the envelope to permanently maintain a space between the two catalysts. According to this technology, the spacers are made of metallic fabric, a material sufficiently resistant to the temperatures of thermal resistance of the substrates, up to peaks of approximately 1000 ° C.

Other purification technologies provide for the installation next to each other of a catalyst and a particle filter. However, the substrate of a particulate filter is made of a honeycomb structure which is particularly vulnerable to vibrations or to contact with elements mounted nearby. When mounting in the envelope, it is then necessary to provide a space between the two substrates to avoid contact between them. Unlike catalysts which have passage conduits open at inlet and outlet to allow the flow of gas flow from one end to the other of the conduit, the conduits of a particle filter are alternately obstructed at the inlet or at the outlet to create a filtration path by forcing the gases to pass through the porous walls of the conduits. The slightest crack or perforation in the walls would therefore prevent the filtering action of the particle filter.

In addition, in a driving situation, the presence of a metal spacer near the substrate of a particulate filter can cause erosion of the substrate due to the vibrations of the vehicle and of the own exhaust line under the action of the exhaust flow. It is therefore not advisable to permanently install such a spacer near the particle filter.

There is therefore a need to find a solution to ensure a spacing between the two substrates during assembly in the envelope while avoiding exposing the particle filter to a risk of damage during the running of the vehicle. .

More specifically, the invention relates to a device for purifying combustion gases comprising a tubular casing intended for the circulation of a flow of combustion gases, first and second depollution substrates mounted in series next to each other on the other inside the envelope in the direction of circulation of the flow of combustion gases and a spacer separating the first and second substrates to maintain a spacing space during their mounting in the envelope. According to the invention, the spacer consists of a thermally decomposable material under the action of the temperature of the flow of combustion gases intended to circulate through the first and second substrates.

Alternatively, the spacer has the shape of a ring and is disposed on the periphery of the first and second substrates.

Alternatively, the spacer further comprises means for holding in abutment against an internal surface of the envelope.

Alternatively, the purification device is remarkable in that the material of the spacer is flammable and in that the self-ignition point of said material is less than 700 ° C.

Alternatively, the point of self-ignition of the material of the spacer is greater than 300 ° C, and preferably greater than 450 ° C.

[012] According to a variant, the spacer comprises a combustion retarder.

Alternatively, the melting point of the material of the spacer is greater than 500 ° C.

According to a variant of the device in which at least one of the first and second substrates comprises a thermally expandable retaining ply from an expansion temperature threshold so as to freeze said substrate in a mounting position in the envelope under the action of the flow of combustion gases, the self-ignition point of the material of the spacer is greater than the expansion temperature threshold of the retaining ply.

[015] According to a variant, the first substrate is a catalyst and the second substrate is a particle filter.

The invention also relates to a combustion gas exhaust line for an internal combustion engine of a motor vehicle comprising a purification device according to any one of the preceding embodiments.

[017] The invention also relates to a motor vehicle comprising an internal combustion engine, in which the engine is connected to an exhaust line comprising a purification device according to any one of the preceding embodiments.

The invention makes it possible to facilitate the mounting of the purification device when the substrates are placed in the envelope. The use of a spacer which can be thermally decomposed under the action of the flow of combustion gases makes it possible to reduce the risk of premature damage to a particulate filter when the vehicle is running.

[019] Other characteristics and advantages of the present invention will appear more clearly on reading the detailed description which follows, comprising embodiments of the invention given by way of non-limiting examples and illustrated by the appended drawings, in which :

FIG. 1 schematically represents a device for purifying combustion gases according to the invention;

FIG. 2 represents a section of the purification device according to the invention and a first geometrical arrangement of the spacer;

FIG. 3 represents a section of the purification device according to the invention and a second geometrical arrangement of the spacer;

Figure 4 shows a section of the purification device according to the invention and a third geometrical arrangement of the spacer.

The invention relates to devices for purifying combustion gases comprising at least two depollution substrates mounted one next to the other, in particular those emitted by a heat engine of a motor vehicle. The invention applies to the automotive industry as well as to any type of combustion gas purification installation.

[021] Figure 1 shows a combustion gas purification device according to the invention intended to equip an exhaust line of a motor vehicle. The purification device comprises a tubular casing 1 in which are successively disposed in the direction of circulation FP of the flow of combustion gas first of all a catalyst 2 then a particle filter 3. The casing 1 has a cross section of substantially cylindrical and is made of metallic material. Catalyst 2, of known technology, for example of the selective catalytic reduction type (SCR), consists of a substrate in honeycomb structure forming open conduits at inlet and outlet s 'extending parallel to the direction of circulation FP of the flow of combustion gases. The walls of the conduits of the catalyst 2 contain a catalytic impregnation based on precious metal which transforms the polluting gases into harmless gases. The particulate filter 3, of known technology, for example of the selective catalytic reduction filter type (SCRF, “Selective Catalytic Reduction Filter” in English), consists of a honeycomb substrate forming conduits alternately obstructed at the inlet or at the outlet extending parallel to the direction of circulation FP of the flow of combustion gases to create a soot filtration path by forcing the gases to pass through the porous walls of the conduits.

[022] Furthermore, during the manufacture of the purification device, a spacer 4 is mounted between the catalyst 2 and the particle filter 3 to ensure a spacing space between the two substrates 2, 3 during the operation of mounting in the casing 1. To avoid premature damage to the particulate filter 3 during the operation of the purification device, damage which may be caused by impacts with the spacer, the latter is designed so as to decompose under the action thermal flow of combustion gases when the vehicle is running, preferably during the first kilometers, or even from the factory. To this end, according to the invention the spacer 4 is made of a material which can be thermally decomposed under the action of the temperature of the flow of combustion gases intended to circulate in the envelope during the running of the vehicle. The material is chosen to achieve total thermal decomposition and preferably so as to be flammable within the expected temperature range of the flue gas stream.

[023] More specifically, the spacer 4 is made of a flammable material and is judiciously chosen so that the physical properties of the material have a self-ignition point of less than 700 ° C to guarantee its decomposition or combustion during 'a rolling cycle. In addition, the volume of the spacer is dimensioned to allow its combustion under the action of the flow of combustion gases. The self-ignition point of the material is defined and known for example from the specifications communicated in the technical sheet.

By way of nonlimiting example, the material of the spacer can be chosen from the following materials: Polyethylene (PE), Polystyrene (PS), Polypropylene (PP), any synthetic polymer whose physical properties allow its total thermal decomposition under the action of the flow of exhaust gases for temperatures below 700 ° C, as well as paper, cardboard, wood or wood-based material.

[025] The dimensions of the spacer are chosen so as to allow a space between the substrates of about 2mm to 20mm. For this purpose, the thickness of the cross-section of the spacer is between 2mm and 20mm.

For information, in the case of an automotive application, it is recalled that in an urban driving cycle the temperature of the combustion gases circulating in the casing 1 can be between 200 ° C and 300 ° C with a gradient temperature between the center of the envelope 1 and its periphery can be from 50 ° C to 150 ° C depending on whether the rolling cycle has significant dynamics or has reached a stabilized speed. In a loaded driving cycle, of the highway driving type, the temperature of the combustion gases circulating in the envelope 1 can be between approximately 300 ° C. and 550 ° C. with a temperature gradient between the center of the envelope 1. and its periphery can be from 50 ° C to 100 ° C.

In an alternative embodiment, the spacer 4 is made of material of the paper, cardboard or wood derivative type, the physical properties of which have a self-ignition point of less than 300 ° C. to allow the combustion of the spacer from the first running cycle of the vehicle. The spacer can be positioned in the central zone of the casing 1 or at the periphery of the casing.

In another alternative embodiment of the purification device, the catalyst 2 comprises a retaining ply (not shown in FIG. 1) thermally expandable from an expansion temperature threshold so as to freeze the substrate in its mounting position in the enclosure under the action of the flow of combustion gases. Following the expansion of the sheet, the substrate remains stationary in the envelope so as to avoid any contact with the other substrate. Conventionally, the expansion temperature threshold is within a range of 300 ° C to 500 ° C. It is therefore necessary that the spacer ensures the spacing at least until the expansion of the retaining plies. To this end, the self-ignition point of the material of the spacer 4 is greater than 300 ° C. and preferably, the self-ignition point is greater than the expansion temperature threshold of the retaining ply. . As an example, the material can be Polyethylene (PE), Polystyrene (PS), Polypropylene (PP).

In another variant, the material of the spacer has a flash point greater than 450 ° C and less than 700 ° C. Thus, the combustion of the spacer is caused only during a regeneration phase of the conventional particle filter controlled during the running of the vehicle to burn the soot depositing in the particle filter. A regeneration phase of the particulate filter provides the conditions (in time and temperature) for combustion of the spacer without material residues interfering with the particulate filter. For this purpose, the spacer preferably comprises a combustion retarder so that the spacer degrades after the expansion of the retaining plies. For example, the material can be a thermoplastic polymer, of the polyvinyl chloride type or of the polyethylene type, and which material comprises a flame retardant additive. Any other means to delay combustion of the spacer may be used.

[030] Furthermore, according to a variant, the material of the spacer is chosen so that the melting point is greater than 500 ° C. Thus, in urban cycle driving conditions, the spacer is not affected thermally by the flow of combustion gases. Thermal decomposition, in particular the start of softening of the material, will only be triggered during a piloted regeneration phase of the particle filter or during a stabilized charged phase (motorway cycle) so as to avoid an unstabilized thermal situation which could cause a flow of material during rolling. This situation is likely to cause the deposit of residues which can degrade the substrate of the particle filter.

[031] Preferably, the spacer 4 has the shape of a ring and is arranged at the periphery of the substrates 2, 3 of the catalyst and of the particle filter. At the peripheral zone of the casing 1, the temperatures of the flow of combustion gases reach values high enough to allow thermal decomposition of the spacer once the running cycle is stabilized, whether in the urban cycle, in the loaded cycle or only during a regeneration phase of the particulate filter. Thus, the complete combustion of the spacer is then ensured because the gas temperatures will be kept stabilized for a sufficient time to ensure complete combustion without leaving partially softened residues which can damage the substrate of the particle filter 3. In fact, the central zone of the casing 1 is liable to be subject to greater temperature differences which may cause an undesirable change in the state of the material of the spacer without reaching complete ignition. The positioning of the spacer on the periphery avoids this risky situation for the particle filter. In addition, in the event of softening of the material of the spacer, due to the positioning at the periphery, the material residues penetrate the centric zone, which is hotter than the peripheral zone, thus ensuring their total combustion.

As seen in Figure 2, the spacer ring 4 is of polygonal shape so that the sides thereof are all positioned in the peripheral zone of the envelope 1. The ring may have a plurality of sides having a number equal to or greater than three, preferably greater than eight.

[033] As can be seen in FIG. 3, in an alternative embodiment the spacer ring 4 is of annular shape judiciously positioned in the peripheral zone of the envelope 1.

[034] In Figure 4, the spacer 4 comprises in one embodiment of the holding means 5, for example lugs, for ensuring the maintenance of the spacer 4 in the mounting position at the periphery of the envelope 1.

The invention also relates to purification devices comprising two catalysts separated by a spacer or a particle filter mounted upstream of a catalyst. Referring to Figure 1, the first substrate 2 is a selective catalytic reduction type catalyst and the second substrate is a selective catalytic reduction filter. Alternatively, the first substrate 2 is for example a three-way catalyst and the second substrate 3 another three-way catalyst or a particle filter. In another variant, the first substrate 2 is an oxidation catalyst and the second substrate 3 is a particle filter. In another variant, the first substrate is a passive Nox (nitrogen oxide) absorber (PNA for “Passive Nox Absorber” in English) or a Nox trap (LNT “Lean Nox Trap” in English), and the second substrate is a particle filter.

The purification device according to the invention is advantageously mounted in an exhaust line of a motor vehicle, with diesel engine or petrol engine. However, it is conceivable to use a combustion gas purification device according to the invention for any type of pollution control installation having a combustion gas exhaust system, for example of the chimney type, or evacuation tube combustion appliances (e.g. boiler, radiators or stoves). The material of the spacer is adapted as a function of the temperature of the flow of combustion gases passing through the depollution substrates in order to be thermally decomposable under the action of said flow.

Claims (10)

1. A combustion gas purification device comprising a tubular casing (1) intended for the circulation of a flow of combustion gases, the first and second depollution substrates (2,3) mounted in series one next to the other inside the envelope in the direction of circulation (FP) of the flow of combustion gases and a spacer (4) separating the first and second substrates (2,3) to maintain a spacing space during of their mounting in the casing (1), characterized in that the spacer (4) consists of a material which is thermally decomposable under the action of the temperature of the flow of combustion gases intended to circulate through the first and second substrates (2, 3). 2. Device according to claim 1, characterized in that the spacer (4) has the shape of a ring and is arranged on the periphery of the first and second substrates. 3. Device according to claim 1 or 2, characterized in that the spacer further comprises holding means (5) bearing against an internal surface of the envelope (1). 4. Device according to any one of claims 1 to 3, characterized in that the material of the spacer (4) is flammable and in that the self-ignition point of said material is less than 700 ° C. 5. Device according to claim 4, characterized in that the self-ignition point of the material of the spacer (4) is greater than 300 ° C, and preferably greater than 450 ° C. 6. Device according to claim 5, characterized in that the spacer (4) comprises a combustion retarder. 7. Device according to claim 5 or 6, characterized in that the melting point of the material of the spacer (4) is greater than 500 ° C. 8. Device according to any one of claims 4 to 7, wherein at least one of the first and second substrates comprises a thermally expandable retaining ply from an expansion temperature threshold so as to freeze said substrate in a mounting position in the envelope under the action of the flow of combustion gases, characterized in that the self-ignition point of the material of the spacer (4) is greater than the expansion temperature threshold of the support ply. 9. Exhaust line for combustion gases for an internal combustion engine of a motor vehicle, characterized in that it comprises a purification device according to any one of claims 1 to 8. 10. Motor vehicle comprising an internal combustion engine, characterized in that 5 that the engine is connected to an exhaust line according to claim 9.