EP1573181A2

EP1573181A2 - Methods and device for filtration of exhaust gases for a diesel engine with a filtration surface which is variable by means of controlled obstruction

Info

Publication number: EP1573181A2
Application number: EP03756052A
Authority: EP
Inventors: Jean Claude Fayard
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-06-04
Filing date: 2003-06-03
Publication date: 2005-09-14
Also published as: WO2003102389A2; US20050257518A1; WO2003102389A9; US7314501B2; FR2840354A1; MXPA04012166A; CA2487942A1; CN101405486A; JP2006515395A; AU2003253083A1

Abstract

The invention relates to particle filters for the exhaust gases of diesel engines. The aim of the invention is to optimise the process of filtration, particularly in terms of the regeneration of the filtration means, such as to provide a satisfactory solution to the problem of clogging of said filtration means by carbon particles. According to the invention, said aim is achieved with a method whereby all or some of the particles contained in the exhaust gases are retained on the filtration means and burnt due to the action of a combustion catalyst, characterised in obstructing at least a part of the filtration means when the temperature θg of the exhaust gases for filtration is equal to or less than a threshold temperature θs, such as to limit or avoid the cooling of the obstructed part of the filtration means and to maintain the same at a temperature θo greater than or equal to θs up until the time when θg becomes greater than θs again and thus permits an accelerated regeneration of the obstructed part of the filtration means. The invention further relates to an exhaust gas filtration device which permits the carrying out of said method for filtration with continuous and regular regeneration of the filtration means.

Description

METHOD AND APPARATUS FOR FILTERING EXHAUST <φZ FOR A DIESEL ENGINE WITH VARIABLE FILTRATION SURFACE BY

ORDER OBSTRUCTION

The present invention relates generally to the field of particle filters and more particularly to an exhaust gas filtration device for a diesel engine.

More particularly, the present invention relates to a device for filtering exhaust gases for a diesel engine further comprising a means for filtering said gases with variable capacity, in which is arranged a means of catalysis associated or not with a post injection of diesel and an exhaust gas recirculation system.

The reduction of polluting emissions produced by internal combustion engines and in particular diesel engines, is the objective that the public authorities have set themselves. To this end, the introduction of ever more stringent standards requires car manufacturers to develop engines with increasingly reduced pollutant emissions, in order to limit the release of unburnt particles. As the modification of engine combustion is no longer sufficient to reach these low levels, the additional use of exhaust gas filtration devices will be essential to retain these particles and meet standards.

Thus, in order to reduce the emission of unburnt polluting gases and solid particles, automobile manufacturers have developed and have generalized the use of catalytic converters or catalysts, generally consisting of a stainless steel casing, of an insulator. and a honeycomb support impregnated with precious metals such as platinum or rhodium.

These catalytic converters now also have a particle filter which has the function of retaining the carbon particles, constituting the unburnt particles emitted by the engine. However, an additional difficulty has arisen when using such filters, which consists in finding solutions so that these carbon particles trapped on the filter can burn or oxidize as they are deposited in order to '' avoid clogging of the latter.

All diesel particulate filter techniques, used today or in development, all face the major problem of incomplete combustion of particles retained on the filter media. In fact, for urban conditions of use, the temperature of the exhaust gases reached is insufficient to cause this combustion and to limit the clogging of the induced filter.

Without chemical assistance, the carbon particles resulting from the combustion of diesel fuel only begin to oxidize significantly above 500 ° C, these temperatures soia ^'Amais conditionsΛs reached in urban driving, the bus engines, so it is necessary to use necessarily in a chemical process to reduce this oxidation temperature.

In the absence of chemical assistance, it follows a clogging of the filter which, in addition to the fact that it causes a pressure drop at the level of the engine and therefore a malfunction of the latter, will cause violent reactions linked to combustion. instantaneous excessive concentration of these carbon particles in the filter, when the disruption of the engine will cause this combustion to start violently. The rapid combustion of a large mass of particles in fact generates a temperature above 1000 ° C. and generally leads to destruction of the filter by thermal shock, the temperatures obtained being too high locally.

To obtain the oxidation of these particles continuously, several systems are already used.

Thus, some systems propose to have upstream of the particulate filter, an oxidation catalysis means allowing the transformation of nitrogen monoxide NO, contained in the exhaust gases, into nitrogen dioxide N0 ₂ from 250 ° C. This technique, called "Continuous Regenerating Trap" (CRT), combines the effects of the particle filter and the NO oxidation catalyst.

This means consists of a catalytic support on which is fixed the catalyst, which is generally a precious metal such as platinum or rhodium. The NO ₂ produced by the action of the latter has the property of oxidizing the carbon particles from 250 ° C. However, the proper functioning of the filter depends on the average temperature reached and the ratio of particles emitted relative to the NO formed. To ensure proper functioning of the filters, this CRT system requires regular regeneration, which limits the pressure drop of the filter by eliminating the risk of uncontrolled and exothermic regeneration.

Such operation is only obtained when the exhaust gases or the combustion chamber have a temperature above 250 ° C for at least 30% of the vehicle operating time.

Otherwise, violent reactions develop due to the excessive concentration of carbonaceous particles clogging the filter. These reactions consist in the too rapid combustion of a large mass of particles, which generally leads to destruction of the filter by thermal shock, the temperatures obtained being very high locally.

There is a similar means constituting a variant of the latter, in which the catalyst is deposited directly on the particle filter. However, only certain materials constituting the particle filter are capable of fixing the metal catalysts. This is particularly the case for cordierite. However, materials of this type are known to be pa-Particularly sensitive to the increase in temperature and thermal shock. It then appears that sudden increases in temperature which can occur in the particulate filter when it is clogged, are liable to cause irreversible deterioration of the latter. It is then necessary to replace the particulate filter and more generally the exhaust device, which represents an absolutely prohibitive cost.

Other regeneration techniques call for the use of organometallic additives added to diesel fuel such as cerium, iron, strontium, calcium or the like so as to coat the carbon particles to form metal oxide of the catalyst and thus obtain an oxidation thereof at a lower temperature.

These techniques make it possible to obtain an effect similar to that obtained with NO ₂ by catalyzing the combustion of carbonaceous materials at temperatures close to 300, 350 ° C.

A first drawback of these techniques is the prohibitive cost of the additives used associated with the fact that it is necessary to provide a complementary additivation device.

The other drawback of these techniques is that they exhibit an even greater tendency to clogging of the filter and therefore to the reactions which result therefrom, if the temperatures reached in operation are not sufficiently high, the additives present in the carbonaceous materials contribute to foul the filter media even faster,

Other techniques have consisted in experimenting with devices based on complementary heating means such as burners, electric resistors or others. These additional heating means are implemented only when the cartridge has a start of clogging, resulting in an increase in the pressure drop. Such a regeneration device is implemented with the engine running, that is to say in the presence of a large flow of exhaust gas. Such a device therefore requires significant heating power to simultaneously bring the exhaust gases and the mass of the filter cartridge to the correct temperature.

In such a technical context, the objective of the present invention is to provide a method of filtering exhaust gases (in particular from diesel engines) which will remedy the drawbacks of the various existing techniques, by optimizing the filtration of exhaust gases. , for example diesel engines, in particular in terms of regeneration of the filtration means, so as to provide a satisfactory solution to the problem of clogging of the filtration means with carbon particles.

Another objective of the invention is to provide an exhaust gas filtration process incorporating regular, efficient and continuous regeneration, so that this avoids all Ae of accumulation of particles in the filtration means and therefore any risk of uncontrolled regeneration.

Yet another objective of the invention is to provide a method of filtering exhaust gases in which the integrated regeneration does not result in significant overconsumption of fuel and more generally, does not entail any additional financial cost for the user.

Yet another objective of the invention is to provide a method of filtering exhaust gases in which the integrated regeneration does not affect the performance of the engine, in particular by pressure losses, due to the back pressure exerted by the exhaust gas on the engine, due to clogging of the filtration device.

Finally, another objective of the invention is to provide a filtration device making it possible to implement the filtration process according to the invention.

These objectives, among others, are achieved by the present invention which firstly relates to a method of filtering exhaust gases e.g. emitted by a diesel engine. This exhaust gas filtration process, in which all or part of the particles contained in said exhaust gases, are retained on filtration means and are burned by the action of a combustion catalyst. This process essentially consists in obstructing at least part of the filtration means as soon as the temperature θg of the exhaust gases to be filtered becomes less than or equal to a threshold temperature θs, so as to limit, or even avoid, the cooling of the part. obstructed and to maintain it at a temperature θo greater than or equal to θs until the moment when θg becomes again greater than θs, and then allow an accelerated regeneration of this obstructed part of the filtration means, due to the temperature conditions which are better than those which would have reigned if this part of the filtration means had not been obstructed.

It is therefore a question, according to the invention, of filtering the exhaust gases on a filtration means consisting for example of at least two cartridges arranged in an envelope, one of the two cartridges being switched off each time the engine is running without load or at idle to maintain in the insulated and flowless cartridge a temperature sufficient to cause a significant continuous regeneration speed each time the engine is again operated with hot exhaust gases. Each cartridge is preferably in turn switched off so that it regenerates continuously.

In the filter units thus isolated and maintained at high temperature in the absence of cold gas, the regeneration process will continue to continue slowly thanks to the very slight flow which will be maintained, but above all these filter units will be at a temperature maintained at an optimum until the engine is operated again and hot exhaust gases are admitted again. The regeneration process in these cartridges thus isolated Apurra thus taking place permanently eliminating any risk of clogging.

Preferably, the different parts of the filtration means are each successively subjected to the obstruction / regeneration sequence for each variation of θg between a value vl greater than or equal to θs, a value v2 less than or equal to θs and again a value v3 greater or equal to θs, vl = or ≠ v3, so as to allow regular and continuous regeneration of the filtration means.

According to a remarkable method of the invention, the obstruction of part of the filtration means consists in preventing the circulation of the exhaust gases in at least 30%, preferably in at least 50% and more prefer! Still in 50 to 75% of the filtration means, this percentage expressing a percentage by volume.

Preferably, θs = 250 ° C or 300 ° C.

Advantageously, the exhaust gases come from a supercharged diesel engine and the reference parameters, namely the temperature θg of the exhaust gases and the threshold temperature θs, are given indirectly by the boost pressure and / or the speed of the engine and / or by the back pressure upstream of the filtration means, the threshold boost pressure being preferably = 2.5% of the maximum engine boost pressure.

According to a preferred embodiment, the filtration means consist of at least two - preferably at least three - filter cartridges, each equipped with a shutter, two of the three cartridges which preferably comprise the filtration means the obstinate part of the filtration means when θg <θs.

According to another of these aspects, the invention relates to an exhaust gas filtration device comprising at least one means of catalysis, means for filtering said exhaust gases, arranged in a reaction enclosure in the path of the flow. exhaust gases produced by an engine, said device being characterized in that the filtration means is constituted by at least two assemblies each comprising a catalyst support attached to a filter cartridge fitted with a flow obstruction means.

Advantageously, the device comprises a means for recirculating the exhaust gases at the intake of the engine, the operation of which is associated with cutting off. of the flow in one or more cartridges each time the engine is not accelerated, so that the increase in back pressure generated automatically opens a valve which allows this recirculation of the exhaust gases.

According to a preferred characteristic of the device of the invention, each of the filter cartridges has a flow obstruction means, arranged upstream or downstream, controlled by an electronic computer which will take into account all the engine operating conditions, so as to isolate at least one cartridge each time the accelerator position is at zero (not accelerated).

In an advantageous embodiment of the device according to the invention, the filtration means consists of at least three cartridges with a means of obstructing the flow rate on each of them, controlled by an electronic computer which will take into account all the engine operating conditions, so as to isolate in turn at least two cartridges when the engine is not accelerated, and to isolate the cartridge which filters the gases in the non-accelerated position, each time the engine is accelerated.

Advantageously, the flow obstruction means arranged on each filter cartridge include a calibrated orifice of small size to maintain a very low flow.

According to an advantageous variant, the device comprises a system for post-injection of diesel into the exhaust gases, by means of a sprayer, preferably upstream of the filtration device and of the catalysts, controlled by an electronic computer which will take into account account for all engine operating conditions, this diesel post-injection system being possibly associated with an exhaust gas recirculation system.

In this variant, it may be appropriate for the injected diesel to contain an organometallic as a combustion catalyst supplied or not supplied from a specific tank.

Finally, in the context of the invention, the device may use the use of known organometallic additives which will be injected by the post injection system in place of diesel.

In the preferred embodiment, the filtration means consists of a set of at least two filtering units each equipped with an obstruction means controlled by a computer which will take into account the engine operating conditions. When the device according to the invention has more than two filtering units, each of said filtering units will include an obstruction means so that they can be switched off in turn.

The obstruction means for each of the cartridges used will be disposed downstream of the filtration unit.

According to a variant of the invention, the obstruction means can also be incorporated upstream of the filtration unit and of the associated catalyst.

According to a remarkable characteristic of the invention, said filtering units will each integrate upstream a catalyst wafer preferably on a metal support.

The catalyst is a conventional oxidation catalyst based on platinum so as to obtain total oxidation of the hydrocarbons and of the CO.

According to another variant of the invention, the filtration device comprises a system allowing the recycling of the exhaust gases each time the filtration capacity will be reduced, thus taking advantage of the increase in the back pressure caused by this restriction for direct a portion of the unfiltered exhaust gas into the intake duct through a non-return valve.

According to a variant of the invention, the filtration device comprises more than three cartridges and a sufficient number so that for full load operating conditions one of the cartridges is isolated, this cartridge being reserved for the filtration of gases at partial load or in slow motion. The objective being to maintain at high temperature, the filtering medium and the catalyst of each of the cartridges used at full load. The cartridge used at idle will be swapped with one of the others when a start of clogging is detected.

The present invention will be better understood on reading the description which follows, given with reference to the drawings which represent, in a nonlimiting manner, an exemplary embodiment of the filtration device according to the invention and in which:

Figure 1, according to a preferred embodiment of the invention, shows a general view of the system comprising the filtration device with two cartridges, each having upstream an oxidation catalyst on a metal support and downstream a valve controlled to obstruct completely when necessary the flow of gases to be filtered. The filtration device being associated with an exhaust gas recycling system with its non-return valve.

FIG. 2 represents a general view of the filtration device comprising a catalyst independent of the filtering units associated with an obstruction system arranged upstream.

FIG. 3 represents a general view of the filtration device which incorporates a diesel injection system. Figure 4 shows a variant of the filtering device incorporating three filter cartridges.

FIG. 5 represents a general schematic view of the filtration device with all the variants incorporated in the engine environment.

The system which allows the implementation of the filtration device according to the invention is shown in detail in Figure 1, according to a preferred embodiment. In this system, various mechanical elements of the vehicle collaborate, which may or may not be part of the filtration device and which contribute to regeneration.

Thus, the exhaust gases at the outlet of the engine are introduced into the device through the pipe 1, then are directed towards each catalyst wafer on a metallic support 2, to be filtered on the two filter cartridges 3, these cartridges will preferably be made of silicon carbide, but may also consist of a leaving filter media in cordierite or other ceramic materials. They will be placed inside an enclosure 4 and isolated from the latter by means of an insulator 6, so as not to be cooled by the ambient air.

Valves 5 will be arranged at the outlet of these filter cartridges so as to be able to completely isolate each cartridge and completely obstruct the outlet channel. These valves will be controlled by pneumatic cylinders 7, the exhaust gases then being directed towards the outlet 8.

The device will operate as follows, each time the accelerator position returns to the zero position (not accelerated), a position detector not described will send the information to a computer, which will alternately control each cylinder to obstruct completely one of the two cartridges and use only one for these particular operating conditions. The filter media of the cartridge obstructed by the valve will thus maintain the high temperature it had reached during the last acceleration, the valve will not be erased to restart it until the engine is again used, so again at high exhaust gas temperatures. To allow each of them to be able to regenerate in good conditions, it will be the same cartridge which will be obstructed for a time between 5 and 10 minutes and alternatively, another possibility will be to measure the back pressure at idle on the cartridge used and control the rotation each time a predetermined level is reached.

In this figure 1 is also shown the possibility of associating an exhaust gas recycling system which is implemented automatically, by the conduit 16, in the direction of the intake manifold 20, each time one of the valves 5 is obstructed, and that the increase in induced back pressure results in establishing a flow rate through the valve 17, these conditions correspond to a zero accelerator position, therefore a low exhaust gas temperature. The recyJfcge will reduce the deΛiz exhaust flow filtered through the cartridge which will remain in action under these conditions and therefore reduce its cooling. Similarly, the introduction of hot exhaust gases mixed with the intake air into the manifold at 20, after the turbo compressor 18, through the engine 21, will lead to a significant increase in temperature exhaust gases evacuated through the pipe 22, which can bring it to idle from the usual 90 to 100 ° C to more than 160 ° C at the inlet of the device 23.

The valve 17 is of the non-return valve type having a large passage section or better of the type with blades allowing a flow for a few millibars of overpressure. The dimensioning of the valve 17 and of the conduit going to the intake manifold 20 is such that this assembly allows recycling of the exhaust gases comprised between 30 to 60% of the flow rate for idling operating conditions.

As soon as the engine is run, the pressure in the intake manifold will exceed the back pressure at the inlet of the filter, blocking the valve 17 and automatically interrupting the exhaust gas recycling rate.

In FIG. 2, the variant of the device shown is differentiated by the use of a common catalyst 14 for the two cartridges 3 and by the use of butterflies 15, arranged upstream of the cartridges to obstruct the filters in place of the valves 5 , used in the preferred embodiment of Figure 1.

Figures 3 and 5 show the possibility of having in addition a diesel injection system upstream of the filtration device, controlled from the information collected on the pressure 9 and temperature 10 sensors, disposed upstream of the filters, the computer will be able to adapt the best strategy to keep each of the filters in perfect state of cleanliness, even going so far as to cause additional injection of diesel fuel through the sprayer 11, supplying air 12 and diesel fuel 13. These injections are intended to increase the temperature of the exhaust gases when the engine is at full power, so as to raise the filter medium to higher temperature to accelerate the regeneration speed. These injections will only be implemented if a start of clogging of the filter is detected.

Figure 4 is a variant which uses three filter cartridges instead of two and which allows better conservation of the temperature in the filter medium.

Indeed, with a device comprising three cartridges, it is possible to introduce an additional variant in the isolation control of each of the cartridges using the information against pressure and temperature given to the computer by the probes according to a strategy set out below. .

For example, each time the accelerator position returns to zero, two of the three cartridges will be obstructed and the gas flow in this position will not will only go through a Jktouche. The re-delivery of these d cartridges will only be done during the next acceleration gradually, the information against pressure will be taken into account to determine the appropriate time to restart these cartridges. For example, the computer will trigger the opening of the valve of a first cartridge as soon as a back pressure level of 100 mbar is detected, the opening of the valve of the second cartridge taking place if this level of back pressure of 100 mbar persists.

Depending on the type of engine used, this level of back pressure could be different from the value of 100 mbar that we took as an example.

A variant of the strategy described above could be to use the temperature information in addition, for example each time the temperature θs will be less than 250 ° C or 300 ° C, decide to close one or more cartridges for a level of back pressure and independently of other conditions of use.

As we have seen, the objective of each of the valves fitted to each cartridge is to be able to isolate them to maintain the high temperature level obtained during the full load of the previous engine and to prevent them from cooling on partial load or the idling which follows, this high temperature favoring the combustion reactions there will be a major advantage in keeping the valve closed a low flow of exhaust gas to maintain these combustion reactions which are very exotheπniques and which will contribute to raising even these temperatures. This operation will be possible by producing valves provided with a calibrated hole of small diameter 24, of less than 1 to a few millimeters, the dimension of which will depend on the engine displacement to allow the necessary flow to pass.

It should be known that the possibility of maintaining the filtering medium at a higher temperature on at least one of the two cartridges, will make it possible to obtain on it a much greater reduction efficiency of nitrogen oxides thanks to the reaction of oxides of nitrogen on the carbon which will take place at higher temperature. With this device, reductions of more than 30% of nitrogen oxides have been observed according to official measurement procedures.

In the same way, a higher efficiency of reduction of hydrocarbons on the official pollution cycles was observed thanks to the maintenance in temperature of at least one of the catalyst wafers for the devices where each cartridge is equipped with its catalyst.

A variant of this control for a system comprising at least three cartridges, and the dimensioning of each of which will be provided so that the filtration of the exhaust gases for full load conditions can be carried out on only two of it will consist in specializing two of the cartridges for full load operation and one reserved for idle operation and partial loads so as to maintain the filter medium and the catalyst at high temperature. cartridges used under full load conditions, and o tβjr a maximum reduction of all pollutants. To allow each of them to be able to regenerate in good conditions, the computer will change the cartridge used exclusively at idle and replace it with a used full load, as soon as a level of back pressure is detected.

The proper functioning of the device associated with the catalytic and assistance means described above necessarily requires the use of diesel fuel with a sulfur content limited to 50 ppm, a level which will be generalized from 2005.

However, for gas oils having sulfur contents greater than this value of 50 ppm, it may be advantageous to use a device such as that described in FIG. 3 in which the gas oil sprayer 11 will be used to inject an organometallic additive solution into diesel from a specific additional tank containing this mixture.

The temperature gain obtained thanks to the isolation of certain cartridges when the temperature conditions of the exhaust gases are too low, will make it possible to obtain, even with the use of such an additive, satisfactory operation in all cases.

In the same way, this device will apply to diesel engines of passenger vehicles, the management of the opening and closing of the valves on each cartridge being done directly from the computer which equips these common rail direct injection engines. This closure can, in the same way as that described above, be programmed at idle and at low loads. The temperatures reached on this type of engine will enable one of the two cartridges to be maintained almost permanently a regeneration reaction fast enough to keep it at a non-significant level of fouling.

Claims

1. A method of filtering exhaust gases, in which all or part of the particles contained in said exhaust gases are retained on filtration means and are burned by the action of a combustion catalyst, characterized in what it essentially consists in obstructing at least part of the filtration means as soon as the temperature θg of the exhaust gases to be filtered becomes less than or equal to a threshold temperature θs, so as to limit, or even avoid, the cooling of the obstructed part and to maintain it at a temperature θo greater than or equal to θ s until the moment when θg becomes again greater than θs, and then allow an accelerated regeneration of this obstructed part of the filtration means.

2. Method according to claim 1, characterized in that the different parts of the filtration means are successively each subjected to the regeneration obstruction sequence for each variation of θg between a value vl greater than or equal to θs, a value v2 less than or equal to θs and again a value v3 greater than or equal to θs, vl = or ≠ v3, so as to allow regular and continuous regeneration of the filtration means.

3. Method according to claim 1, characterized in that the obstruction of part of the filtration means consists in preventing the circulation of the exhaust gases in at least 30%, preferably in at least 50% and more preferably still in 50 to 75% of the filtration means, this percentage expressing a percentage by volume.

4. Method according to claim 1, characterized in that θs = 250 ° C or

300 ° C.

5. Method according to claim 1, characterized in that the exhaust gases comes from a supercharged diesel engine and in that the reference parameters, namely the temperature θg of the exhaust gases and the threshold temperature θs, are given indirectly by the boost pressure and / or engine speed and / or by the back pressure upstream of the filtration means, the threshold boost pressure is preferably = 2.5%) of the maximum boost pressure of the motor.

6. Method according to claim 1 characterized in that the filtration means consist of at least two - preferably at least three - cartridges filters, equipped "No shutter, two of the three cartridges that preferably count the filtration means constituting the obstmate part of the filtration means when θg <θs.

7. Exhaust gas filtration device comprising at least one catalysis means, filtration means (3) of said exhaust gases, arranged in a reaction enclosure (4) in the path of the flow of the exhaust gases produced by a motor (21), said device being characterized in that the filtration means (3) consists of at least two assemblies each comprising a catalyst support (2) attached to a filter cartridge fitted with an obstruction means flow (5).

8. Device according to claim 7, characterized by the establishment of an exhaust gas recirculation means (16) at the intake of the engine (20) whose operation is associated with the cutoff of the flow in one or several of the cartridges each time the engine is not accelerated, so that the increase in back pressure generated automatically opens a valve which allows this recirculation of the exhaust gases.

9. Device according to one of claims 7, 8, characterized in that each of the filter cartridges has a flow obstruction means (5), arranged upstream or downstream, controlled by an electronic computer which will take into account counts all the engine operating conditions, so as to isolate at least one cartridge each time the accelerator position is at zero (not accelerated).

10. Device according to one of claims 7 to 9, characterized in that the filtration means consists of at least three cartridges with a flow obstruction means (5) on each of them, controlled by a computer electronics which will take into account all the engine operating conditions, so as to isolate in turn, at least two cartridges when the engine is not accelerated, and to isolate the cartridge which filters the gases in the non-accelerated position, each time the engine will be accelerated.

11. Device according to one of claims 7 to 10, characterized in that the flow obstruction means arranged on each filter cartridge comprises a calibrated orifice of small dimension (24) to maintain a very low flow.

12. Device according to one of claims 7 to 11, characterized by the installation of a diesel post-injection system in the exhaust gases, by through a sprayer (11), upstream of the filtration device and the catalysts, controlled by an electronic computer which will take into account all engine operating conditions, this diesel post-injection system possibly being associated with an exhaust gas recirculation system (16), (17).

13. Device according to claim 12, characterized in that the injected diesel contains an organometallic as combustion catalyst supplied or not from a specific tank.