FR2877692A1 - Particle filter for exhaust line of diesel engine of motor vehicle, has gas outlet end associated to magnetic field generation units attracting residues in gas and sensitive to field, where filter has honey-comb structure with porous walls - Google Patents

Abstract

The filter (31) has a gas inlet end (32), and a gas outlet end (33) associated to magnetic field generation units (34) that attract residues contained in the gas and those sensitive to a magnetic field. The generation units have an electromagnet whose electrical energy supply is controlled by control units. The filter has a honey-comb structure with a succession of porous walls that are made of porous material.

Description

The present invention relates to a particulate filter for line

  exhaust system of a motor vehicle diesel engine.

  Pollutant emissions from engines, including diesel engines, must be controlled at the source and / or removed prior to discharge to the atmosphere to comply with existing regulations.

  In general, at least three functions must be fulfilled in the treatment of exhaust gases: - an oxidation function which acts on hydrocarbons and CO to convert them to water vapor and CO2; a function of filtration and combustion of soot particles; a function for reducing the concentration of NOx nitrogen oxides.

  The oxidation function of the hydrocarbons and CO is generally ensured by a catalytic bread consisting of a porous medium on which is placed an oxidation catalyst, often a metal such as platinum.

  This catalytic bread is placed in the exhaust line upstream of a ceramic particulate filter which performs the function of filtering soot and where, periodically, is carried out the combustion of soot accumulated therein. This filter may comprise an impregnation with a compound assisting the regeneration of the particulate filter.

  As for the reduction of NOX, it is obtained essentially by a motor design adapted for this purpose, but it can be reinforced by the use of an additional catalytic medium trapping the NOX, and treating them with assistance of the engine control.

  To reduce the size of the exhaust line, several or all of these functions can be grouped together in the same filter medium whose surfaces are coated or impregnated by the various catalysts adapted to the desired functions.

  This filtering medium is most often constituted by a porous honeycomb structure having a gas inlet end having exhaust gas inlet channels and a gas outlet end having gas outlet channels. exhaust, separated by porous partitions. The inlet channels are closed at their end facing downstream of the exhaust line, and the outlet channels are closed at their end facing upstream of the exhaust line, so that the gases are forced to cross the porous walls which then retain the soot.

  Periodically, in order to remedy the progressive clogging of the filter, a regeneration operation is carried out. This consists in temporarily increasing the temperature of the exhaust gases for example by means of a post-injection of fuel in the exhaust line upstream of the filter, to raise it above the combustion temperature of the soot . In addition, an additive such as ceria may be added to the engine feed fuel to mix with the particles and deposit on the particulate filter to lower the soot combustion temperature.

  This regeneration of the filter is however never perfect, and it still remains inside the filter a number of solid mineral residues, namely the residues of the regeneration aid additive and other fuel additives , ash from the combustion of the lubricant, various chemical species resulting from engine wear or the external environment. These residues must be periodically removed (eg every 80,000km or 120,000km) removed from the particulate filter during thorough cleaning.

  The presence of incombustible residues in the filter is a hindrance to the completion of catalysis. The filter therefore gradually loses its effectiveness for the treatment of gaseous emissions until a thorough cleaning operation has been carried out. Indeed, these different residues gradually foul the filter as the life of the vehicle and reduce the useful volume of it.

  The object of the invention is therefore to solve these problems.

  For this purpose, the subject of the invention is a particulate filter for a diesel engine exhaust line of a motor vehicle, of the type comprising a gas inlet end and an outlet end of the gases, characterized in that the end of the gas outlet is associated with means for generating a magnetic field attraction residues contained in the gas and sensitive to this field.

  According to other features of the invention: the means for generating the magnetic field comprise a permanent magnet; the means for generating the magnetic field comprise an electromagnet whose power supply is controlled by control means when triggering a regeneration phase of the filter; the residues comprise residues of an additive to aid the regeneration of the particulate filter; the additive is mixed with the engine feed fuel to be deposited with the particles to which it is mixed, on the particulate filter; the particulate filter is associated with catalyst means; the particle filter is associated with means forming a NOx trap; the particle filter is associated with means containing an OSC function; and said filter is a honeycomb filter having porous walls defining, in cooperation with nonporous sealing elements, inlet channels and exhaust gas outlet channels.

  The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which: FIG. 1 represents a schematic sectional view of a portion an embodiment of a honeycomb-structured particulate filter comprising a catalytic medium and after it has been used for a period of time; FIG. 2 represents a schematic view illustrating a first embodiment of a particulate filter according to the invention; FIG. 3 represents a schematic view illustrating a second embodiment of a particle filter according to the invention; and FIG. 4 represents a schematic view illustrating a third embodiment of a particulate filter according to the invention.

  An example of a particle filter portion also known under the name FAP has indeed been illustrated in FIG.

  As is known, this particulate filter honeycomb structure consists of a succession of spaced walls 1, 2, 3, 4, 5 and 6 porous material forming a filter, such as a ceramic based on silicon carbide, cordierite, silicon nitride, mullite, etc.

  These porous walls 1 to 6 define, in cooperation with non-porous closure elements 7, 8, 9, 10, 11, a series of channels, namely: inlet channels 12, 13 at an inlet end filter gases, open towards the upstream side 14 of the particulate filter, and through which the exhaust gases to be treated enter the particulate filter, and - outlet channels 15, 16, 17 at an outlet end gases open towards the downstream side 18 of the particulate filter, and through which the treated exhaust flows out of this filter.

  The exhaust gases pass from the inlet channels 12, 13 to the outlet channels 15 to 17 through the porous walls 1 to 6 and by depositing therein the particles they contain.

  As is also known, the porous walls 1 to 6 are coated on their surfaces facing the inlet channels 12, 13 and the outlet channels 15 to 17 by a catalytic coating 19, 20, 21, 22, 23, 24, 25, 26, 27, and 28 for performing one or more of the following functions: - a function of oxidation of hydrocarbons and CO in water vapor and CO2, which can be ensured, for example, by a metal such as platinum; a function for treating NOx with a NOx storage material (such as barium oxide), and / or a metal for the oxidation of NOx to NO2 (such as platinum), and / or a catalyst for reduction (such as rhodium); - A function to assist the regeneration of the particulate filter, assistance or replacement of additives to lower the soot combustion temperature. This function can be provided by a material containing a function called OSC (oxygen storage capacity), that is to say a material capable of releasing oxygen that has previously been stored. Such materials may comprise, for example, cerium oxide or a mixed oxide of cerium and zirconium.

  The porosity and the pore size of the walls 1 to 6 defining the various channels 12 to 17 are, as is customary, adapted to ensure good catalytic efficiency, sufficient to comply with anti-pollution standards, without creating excessive pressure losses. at the terminals of the particulate filter.

  Similarly, the catalytic coatings 21, 22, 25 and 26 deposited on the surfaces of the walls 1 to 6 facing the inlet channels 12, 13 may not cover all of these surfaces, but may stop at a distance d shutter elements 10 and 11. Thus, at the end of each inlet channel 12, 13, a space 29, 30 of length equal to d whose walls which delimit it do not bear, for example, catalyst.

  This space 29, 30 represents, for example, between 1/10 and half of the length of the input channel 12, 13 corresponding to a length for example of 2.5 to 12.5 cm for a 25cm particle filter long.

  The catalytic coatings 19, 20, 23, 24, 27 and 28 deposited on the surfaces of the walls 1 to 6 facing the outlet channels 15 to 17 cover, in the illustrated example, all of these surfaces. It should be understood that these coatings are not necessarily indispensable, in particular if the only function assigned significantly to the catalyst is the aid for the regeneration of the particulate filter by action on the soot and which have already been trapped upstream of the corresponding surfaces. . It should also be understood that catalytic material may also be present on the pore surface within walls 1 to 6.

  As seen in this Figure 1, after prolonged use, the spaces 29, 30, free of catalyst on their periphery, have been preferred sites for the deposition of various particles and combustion residues.

  These combustion residues and in particular the residues of the regeneration aid additive are not normally destroyed by the catalytic reactions involved in the particulate filter.

  On the other hand, their presence on the surface of the walls 1 to 6 is a hindrance to the proper execution of the reactions, or even a real obstacle after a significant mileage which leads to the formation of a thick layer of residues.

  This produces a zone 29, 30 in any case catalytically little or not active at the end of each input channel 12, 13 of the filter.

  It has also been proposed not to provide catalytic coating in these areas.

  According to the invention, it is also planned to associate at this outlet end of the particles filter gases, means for generating a magnetic field of attraction of the residues contained in the gases and sensitive to this field.

  This then makes it possible to attract to the bottom of the particulate filter, all the residues, for example additives, based on metals, to reduce the volume occupied by these residues and consequently to increase the volume available for the storage of the particles. soot.

  Such additives are for example additives having compounds sensitive to the magnetic field, such as an additive based on a mixture of cerium / iron.

  This is for example illustrated in Figure 2, where the particulate filter is designated by the general reference 31 and has a gas inlet end designated by the general reference 32 and a gas outlet end designated by the general reference 33 .

  Means for generating a magnetic field are then associated with this output end 33, these field generation means being designated by the general reference 34.

  In FIG. 2, these means for generating the magnetic field are for example formed on a permanent magnet designated by the general reference 35.

  Of course, other arrangements may be envisaged, as illustrated for example in FIG. 3, on which the particle filter 31, its gas inlet end 32, its gas outlet end 33 and the means for generating the magnetic field 34.

  In this example of embodiment described in FIG. 3, these means comprise an electromagnet designated by the general reference 36, the electrical energy supply of which is provided by control means designated by the general reference 37, for example associated with the control computer. motor operation control, to activate the electromagnet during a regeneration phase of the particulate filter.

  FIG. 4 illustrates another embodiment in which the particle filter 31, its gas inlet 32, its gas outlet 33 and the magnetic field generating means 34 are recognized.

  In this example, the filter 31 has been removed from the vehicle during a maintenance operation. It can then be subjected to an intense magnetic field on its rear face, for example via an electromagnet.

  It is then conceivable that the association at the gas outlet end of the means for generating a magnetic field makes it possible to ensure an increase in the concentration of residues at this end of the particulate filter, in order to make it possible to increase the available volume for storage of soot and thus increase the life and efficiency of such a filter.

  Of course, still other arrangements can be envisaged.

Claims (9)

  Particle filter for a diesel engine exhaust line of a motor vehicle, of the type comprising a gas inlet end (32) and a gas outlet end (33), characterized in that the outlet end gases (33) is associated with means (34) for generating a magnetic field for attracting residues contained in the gases and sensitive to this field.   2. Particle filter according to claim 1, characterized in that the means for generating the magnetic field comprise a permanent magnet (35).   3. Particle filter according to claim 1, characterized in that the means for generating the magnetic field comprise an electromagnet (36) whose power is controlled by control means (37) when triggering a regeneration phase of the filter.   4. Particle filter according to any one of the preceding claims, characterized in that the residues comprise residues of an additive to aid the regeneration of the particulate filter.   5. Particle filter according to claim 4, characterized in that the additive is mixed with the engine feed fuel to be deposited with the particles to which it is mixed on the particulate filter.   6. Particle filter according to any one of the preceding claims, characterized in that the particulate filter is associated with catalyst means.   Particle filter according to one of the preceding claims, characterized in that the particulate filter is associated with NOx trap means.   8. Particle filter according to any one of the preceding claims, characterized in that the particulate filter is associated with means containing a function OSC.   9. Particle filter according to any one of the preceding claims, characterized in that said filter is a honeycomb filter, having porous walls (1 to 6) defining, in cooperation with closure elements (7). to 11) non-porous, inlet channels (12,13) and outlet channels (15,17) of the exhaust gas.