FR2829180A1 - METHOD FOR REGENERATING AN EXHAUST GAS FILTERING DEVICE FOR A DIESEL ENGINE AND IMPLEMENTING DEVICE - Google Patents

Abstract

The invention concerns a method for regenerating a device filtering exhaust gases produced by a diesel engine, said method being of the type wherein particles, retained on a filtering means (22) of the filtering device, are burnt by the action of a combustion catalyst system. Said method consists essentially in retaining the hot exhaust gases around the filtering means (22) so as to feed to the particles, at least part of the heat energy required for their combustion and in burning said particles to regenerate the filtering device. The invention also concerns a device for implementing the method, comprising a means for producing a combustion catalyst (20), a filtering means (22) of exhaust gases and a diesel oil injecting means, the means for producing a combustion catalyst and filtering means being contained in a reaction chamber (18).

Description

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METHOD FOR REGENERATING A GAS FILTERING DEVICE
EXHAUST SYSTEM FOR A DIESEL ENGINE AND IMPLEMENTATION DEVICE
The present invention relates generally to the field of particle filters and more particularly to a method of regenerating an exhaust gas filtration device for a diesel engine.

 In addition, the present invention also relates to a filtration device intended to retain the carbonaceous and soot particles produced by the engine and to burn them regularly in order to avoid their accumulation, this last phase constituting the regeneration, object of the process according to the invention.

 The development of the industrial era has had serious consequences for the environment. Indeed, the polluting industries but also the development of the car fleet are at the origin of a significant release of pollutants into the atmosphere which leads to its modification. This change is twofold. First of all, we note a chemical modification. The latter is mainly reflected by a continuous growth in the content of air in compounds, derived from carbon. These compounds include carbon monoxide (CO) and certain unburnt hydrocarbons, resulting from incomplete combustion. The presence of these compounds in the atmosphere poses a much greater direct health risk. CO is therefore a very powerful respiratory toxicant. Polycyclic aromatic hydrocarbons (PAHs), such as benzopyrene, benzanthracene or even fluoranthrene, which are particularly important in engine smoke, soot or exhaust gases are recognized carcinogens.

 The atmosphere is also changed by the release of solid particles. These particles are classified according to their size. Thus, the smallest so-called inedible particles, because they are unable to settle on the ground under the effect of gravitation, are the most dangerous for human health, because they are capable of entering the pulmonary alveoli. In addition, they contaminate the highest layers of the atmosphere and are therefore responsible for global pollution.

 Also, in light of this alarming observation, the public authorities, both at national and international level, are trying to set up anti-pollution standards. These standards mainly affect the automotive industry. Thus, automobile brands must regularly make modifications to their vehicles in order to bring them into compliance with these standards.

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 In addition to the development of new engines with ever lower fuel consumption, a special effort has been made on the development of new exhaust systems, intended to reduce the emission of unburnt pollutants and solid particles. Thus, car manufacturers have developed catalytic converters or catalysts, generally consisting of a stainless steel casing, a thermal insulator and a honeycomb support impregnated with precious metals such as platinum or rhodium. These catalysts make it possible, above all, to reduce the emissions of polycyclic hydrocarbons and CO, and this in a proportion of the order of 50%. However, they have no effect on the emission of solid particles. Thus, in particular in the case of diesel engines which produce numerous solid particles, these catalysts do not bring any significant improvement in the quality of the air.

 Other techniques have been developed to limit the emission of polluting particles from vehicles. This is the case with the particle filter. This filter allows the total mass of particles emitted by diesel engines to be reduced by 90%. It is even more effective for the retention of very fine particles, since the retention rate can go up to 99%.

 The particle filter however requires regeneration to burn the particles that have been trapped. The particles are generally trapped by a filter cartridge that is part of the particle filter. This cartridge, to withstand the high temperatures encountered, may consist of a porous body of cordierite, quartz or silicon carbide, generally of honeycomb structure to present a maximum filtration surface.

 A major drawback of such particle filters consists in the incomplete combustion of the particles retained by the filter cartridge. In fact, for urban use conditions, the temperature of the exhaust gases reached is insufficient to cause their combustion and significantly limit clogging of the filter and therefore its regeneration. Without chemical assistance, the carbonaceous particles resulting from the combustion of diesel in diesel engines do not begin to oxidize significantly above 500 C. These temperatures are almost never reached in urban driving conditions.

 It then appears necessary to use a chemical process to remove these particles. Different techniques are used to obtain their combustion.

 A first technique consists in placing upstream of the filter, a catalyst for the oxidation of nitrogen monoxide (NO) contained in the gases.

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 nitrogen dioxide (N02) exhaust, the latter having the property of catalyzing the combustion of carbonaceous particles from 250 C. However, this process requires the use of diesel fuel with a sulfur content of less than 50 ppm (parts per million), to keep sufficient conversion efficiency from NO to N02.

 This technique, called "Continuous Regenerating Trap" (C. R. T.), combines the effects of the particulate filter and the NO oxidation catalyst. To ensure proper functioning of the filters, this 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 300 C for at least 30% of the vehicle's 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.

 Other techniques call for the use of organometallic additives added to diesel fuel such as cerium, iron, strontium, calcium or others. These techniques make it possible to obtain an effect similar to that obtained with NO2 by catalyzing the combustion of carbonaceous materials at temperatures in the region of 300 C.

 A first drawback of these techniques is the prohibitive cost of the additives used.

 Another major drawback lies in the fact that it is necessary to provide an additional additivation device.

 Yet another drawback of these techniques is that they have 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 contributing to foul the filter media even faster.

 Other techniques have consisted in experimenting with devices based on additional heating means such as burners, electrical resistors or others. These additional heating means are used 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 gas flow

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 important exhaust. 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 process for regenerating a filtration device, which overcomes the drawbacks of the various existing techniques consisting in treating the carbonaceous particles and soot emitted by diesel engines.

 Another object of the invention is to provide a regeneration process, thus avoiding any risk of accumulation of particles in the filtration device and therefore any risk of uncontrolled regeneration.

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

 Finally, a final objective of the invention is to provide a filtration device making it possible to implement the regeneration method according to the invention.

 These objectives, among others, are achieved by the present invention which firstly relates to a method of regenerating a device for filtering the exhaust gases emitted by a diesel engine, this method being of the type in which particles, retained on a filtration means of said filtration device, are burned by the action of a combustion catalyst. This process essentially consists in retaining the hot exhaust gases around the filtration means in order to supply the particles with at least part of the heat energy necessary for their combustion and in burning said particles so as to regenerate the filtration device.

 According to a variant, this method also consists in: - implementing a means of producing combustion catalyst in the filtration device, - measuring a temperature 8m in the vicinity of the means of producing combustion catalyst, - comparing 8m to a temperature Gold corresponding to the temperature at which the combustion of diesel fuel, in the presence of the combustion catalyst, is complete,

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 - if 8m is greater than or equal to 8r, initiate a post-injection of diesel, via an injection means, into the filtration device, for a determined period, in order to cause an increase in temperature of the particles to allow their combustion.

 According to yet another variant, this method also consists in: - measuring a pressure Pm in the vicinity of the combustion catalyst production means, said pressure Pm reflecting the degree of obstruction of the filtration means by the particles, - measuring the temperature 8m, - compare said pressure Pm to a reference pressure Pr corresponding to the maximum acceptable degree of obstruction, - if Pm is greater than or equal to the pressure Pr, compare 8m to Gold, - if 8m is greater than or equal to Gold, trigger post-injection of diesel.

 Another object of the invention relates to a filtration device allowing the implementation of the regeneration process according to the invention. This device comprises a means for producing combustion catalyst, a means for filtering the exhaust gases downstream from the means for producing combustion catalyst, and a means for injecting diesel fuel upstream from the means for producing combustion catalyst. , the means for producing combustion and filtration catalyst being contained in an enclosure, which is located in the path of the flow of exhaust gases produced by an engine.

 The filtration means, consisting of a set of filter units, is immersed in an exhaust gas receiving chamber, said exhaust gases heating the filter units.

 Preferably, the filtration means is constituted by at least two particle filters comprising a body, formed by the filtering units secured by a seal, and a metal casing.

 Advantageously, the diesel injection means communicates with an exhaust gas discharge pipe.

 According to another characteristic, this injection means comprises a secondary diesel tank and an injection chamber for the diesel contained in the tank, in the exhaust gas evacuation pipe.

 Thus, the chamber injection chamber is supplied, on the one hand, with diesel fuel via a first conduit connecting it to the secondary tank, and on the other hand, with compressed air via a second duct connecting it to the engine, the

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 chamber comprising an orifice through which the diesel fuel is injected into the filtration device.

 Advantageously, the device comprises an electronic control unit.

 The device also includes at least one temperature probe, placed inside the enclosure, making it possible to measure the temperature 8m within it.

 According to a remarkable variant, it also includes at least one pressure probe, inside said enclosure, making it possible to measure the pressure Pm within it.

 Remarkably, the electronic control unit is connected to the temperature and pressure probes, compares the values 8m and possibly Pm measured, respectively with the reference values 8r and possibly Pr, and triggers the injection of diesel fuel into the pipe d 'evacuation, via the injection system, when the measurements 8m and possibly Pm are greater than or equal to the reference values 8r and possibly Pr.

 Advantageously, the conduits supplying the chamber of the injection system with diesel and compressed air each comprise a solenoid valve controlled by the electronic control unit, the opening of these solenoid valves causing the entry of diesel and compressed air into the chamber and therefore the post-injection of diesel fuel into the exhaust gas evacuation pipe.

 Advantageously, the chamber of the injection system is provided with a nozzle, opposite the orifice making it possible to inject the diesel fuel in nebulized form, into the gas evacuation pipe.

 Preferably, the filter units are advantageously made of silicon carbide or any equivalent material, the structure of which is of the honeycomb type.

 According to another remarkable characteristic of the invention, the means for producing a combustion catalyst consists of at least one cartridge based on platinum or any equivalent material, catalyzing the transformation of nitrogen monooxide (NO), contained in the gases. nitrogen dioxide (NO2) exhaust.

 According to another remarkable characteristic, the capacity of the secondary tank is preferably equivalent to the maximum volume of diesel injected during post-injection.

 Advantageously, the particle filters are placed in parallel in the filtration device.

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The present invention will be better understood on reading the description which follows, made 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:
FIG. 1 represents a general schematic view of the system comprising the filtration device and allowing the implementation of the regeneration process.

 FIG. 2 represents a view in longitudinal section of the filtration device according to a first embodiment.

 FIG. 3 represents a cross-sectional view, along the axis i-i), of the filtration device shown in longitudinal section in FIG. 3.

 FIG. 4 represents a variant of this first embodiment, seen in longitudinal section of the filtration device.

 FIG. 5 represents a view in longitudinal section of the filtration device according to a second embodiment.

 The system which allows the implementation of the regeneration method according to the invention is shown schematically in Figure 1, according to a preferred mode. 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 the regeneration of this device.

 Thus, a diesel engine 10, supplied with fuel by a main tank 12 via a supply system 14, produces in operation exhaust gases. These gases are recovered via a manifold (not shown) at the outlet of the engine and are evacuated via an exhaust duct 16.

This conduit joins an enclosure 18 containing a means for producing combustion catalyst 20 and a filtration means 22. Are also placed at the enclosure 18, a temperature probe 24 and a pressure probe 26. These probes have for function of measuring the temperature and pressure in the vicinity of the combustion catalyst production means. The data relating to these measurements are transmitted to an electronic control unit 28 and are analyzed by the latter.

 The electronic control unit is connected to two conduits 30 and 32 and triggers their opening. The conduit 30 connects a secondary tank 34 to the injection chamber 36. This secondary tank 34 supplies the injection chamber 36 with diesel. Itself is supplied by the main tank 12 through a piping system 38.

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 The conduit 32 connects, in turn, the engine 10 to the injection chamber 36. It allows the engine 10 to supply the injection chamber 36 with compressed air.

 The conduits 30 and 32 are opened by two solenoid valves 31 and 33, electrically controlled by the electronic control unit.

 A detailed view in longitudinal section of the enclosure 18 is shown in FIG. 2.

 In the enclosure are grouped the combustion catalyst production means 20 and the filtration means 22. The combustion catalyst production means 20 is constituted by two cartridges 20a and 20b for the production of combustion catalysts.

 These cartridges are preferably on a metal support so as to obtain the lowest possible thermal inertia. According to a preferred embodiment, these cartridges are preferably based on platinum and are the site of a transformation of the nitric oxide (NO) contained in the exhaust gases into nitrogen dioxide (NO2), which constitutes the combustion catalyst.

The N02 product diffuses up to filtration means 22.

 The filtration means 22 is constituted by a set of three-dimensional filter units. Advantageously, these filter units are of the silicon carbide honeycomb type.

 According to a first embodiment shown in FIG. 2, these filter units are assembled so as to form the body of a particle filter. Thus, the filtration means is constituted by three particle filters 22a, 22b and 22c. These particle filters thus arranged, are shown seen from above in FIG. 3. The filters consist of a body 40, and of a metal casing 42. The body 40 consists of the assembly of several filtering units 44, separated by a seal 46, which has the function of compensating for their expansion.

 The enclosure 18 comprises in its lower part a retention chamber making it possible to increase their residence time in the enclosure, exhaust gases purified by passage through the filtration means (filter units or particulate filters).

 This increase in the residence time of the exhaust gases allows the latter to come to heat the filter units or the particle filters and therefore the particles themselves. This remarkable characteristic makes it possible to maintain the latter at a temperature much higher than the usual temperature. This temperature can reach the temperature allowing their combustion in the presence of

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 combustion catalyst. In this case, the regeneration takes place without injection of diesel.

 A variant of this embodiment is shown in FIG. 4.

According to this variant, the particle filters 22a, 22b and 22c are arranged in the opposite direction. The device then includes a special area for retaining exhaust gases, which have not yet been filtered. Indeed, these are contained between the catalyst cartridges and the lower support 48 of the filters, which allows a longer residence time of the exhaust gases, before their passage through the particulate filters, which ranges from a on the one hand, favor the heat exchange between the gases and the filters and on the other hand, limit the heat loss by exchange with the outside.

 According to a second embodiment of the device according to the invention, the filtering units 44 are independent of each other. Thus, each filter unit is separated from the adjacent ones by a space sufficient to allow their expansion. This arrangement is particularly advantageous because, on the one hand, it makes it possible to very considerably reduce the stresses of thermal expansion, in particular in the event of sudden combustion of retained particles, which greatly limits the risk of seeing the filtering units deteriorate; on the other hand, the area available for heat transmission by gases is increased considerably, which further accentuates this heat transmission.

 A variant of this second embodiment, shown in FIG. 5, consists in placing the filter units 44 in the opposite direction in the filtration device, with a support positioned in the lower part, like the variant of the first embodiment. of embodiment, shown in FIG. 4. The advantages of this arrangement are identical to those mentioned above in the description of FIG. 4.

 According to an exemplary embodiment, each filtering unit is a cylinder with a square base having a width and a depth of 35 mm, and a length varying from 150 to 300 mm.

 In the event that the temperature is not sufficient to trigger the combustion of the particles, the regeneration occurs by means of the injection of diesel fuel.

 To do this, the temperature in the vicinity of the catalyst production means is measured, using the probe 24. The measured temperature value 8m is collected by the electronic control unit. The box will compare this 8m value with a gold reference value, corresponding to the temperature at which the combustion of diesel fuel, in the presence of catalyst, takes place completely.

 If the measured temperature 8m is greater than or equal to the reference value Or, the electronic control unit triggers the opening of the

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 solenoid valves 31 and 33. This opening causes the entry of diesel and compressed air into the chamber 36. In the chamber 36, the diesel mixes with the compressed air and the mixture, thus formed, is sprayed, in nebulized form in the gas evacuation duct 16. This spraying takes place through an orifice provided in the wall of the chamber 36, opposite which is a nozzle, fixed to the chamber, making it possible to obtain a spray nebulized under pressure. According to an exemplary embodiment, the chamber 36 is of the compressed air paint spray gun type.

 When the required quantity of diesel fuel, predetermined by the electronic control unit, has been injected, the diesel fuel supply is cut off by closing the solenoid valve 33. Only the compressed air supply persists so that the latter is sprayed in the conduit 16 in place of the mixture.

The purpose of this prolonged supply of compressed air is to eliminate any remaining diesel fuel in the injection chamber 36 and the conduit 16.

 The capacity of the secondary tank 34 is determined so that it corresponds to the maximum volume of diesel necessary for regeneration.

Thus, there can be no overconsumption of diesel. In addition, thanks to this embodiment, the frequency of the regeneration cycles is limited by the time necessary to fill the secondary tank 34, which also makes it possible to avoid consequent overconsumption of fuel.

 The fuel injected into the discharge pipe 16 enters the enclosure and undergoes complete combustion at the level of the catalyst production means.

This combustion induces a significant increase in temperature up to a temperature Oc at which the combustion of the particles which clog the filtration means will take place. The NO2 molecules produced will catalyze this combustion reaction. Thus, this reaction occurs at a temperature below the normal temperature. During this combustion, the solid particles are transformed into gases which are evacuated.

 The filtration means is then found free of deposits and recovers its full filtration capacity.

 According to a particular embodiment, the measurement of Om can be used by the electronic unit in order to evaluate the temperature of the particles at the level of the filtration means. Indeed, if 6m is close to the temperature at which the combustion of particles can be done without post-injection of diesel, the computer can decide not to trigger this post-injection, which allows a substantial saving of fuel.

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 According to a variant of this embodiment, an additional temperature probe is arranged near the filtration means so as to obtain the exact temperature of the particles.

 A third operational mode consists in simultaneously measuring the temperature and the pressure at the level of the catalyst production means, using the temperature probe 24 and the pressure probe 26. The pressure value Pm measured reflects the degree of obstruction of the means of filtration by particles. In fact, if the filtration means is clogged, the exhaust gases pass more difficultly and then exert a back pressure. Thus, the measurement of the pressure Pm corresponds to the best means of controlling the clogging of the filtration means. The electronic control unit compares the measured value Pm with a reference value Pr, corresponding to the maximum acceptable degree of obstruction of the filtration means. If Pm is greater than or equal to Pr, the electronic control unit compares 8m to Or. If 8m is greater than or equal to 8r, the unit then triggers the post-injection of diesel which leads to the regeneration of the filtration means. This operational mode has the advantage of triggering post-injection only when the filtration means has reached a determined degree of clogging, which makes it possible to greatly limit the overconsumption of fuel.

EXAMPLE
By way of nonlimiting example, below is a filtration device used with an industrial vehicle engine, the Renault VI 620-45 supercharged engine, with 10 liters of displacement and an output of 190 Kw. This engine is fitted to city buses.

 The filtration system is composed of: - Two cartridges of platinum-based catalysts allowing the transformation of NO into N02. These cartridges, 7.5 inches in diameter and 3 inches long, mounted in parallel on a metal support, as shown in FIG. 2. The volume of catalyst was determined so that the rate of conversion of NO to N02 is greater than 85%.

 - Three IBIDEN particle filters, of the silicon carbide honeycomb type, mounted in parallel. These filters have a section of 162 cm2 (diameter 143.8 mm) and a length of 254 mm.

 - A diesel injection system comprising an injection chamber as described above and a secondary tank with a capacity of 50 cm3. The

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 injection system flow rate is 50 cm3 per minute. This flow rate was determined so that the increase in temperature of the exhaust gases, generated by the post-injection is between 170 and 250 C, depending on the conditions of use.

 - An electronic unit controlling the post-injection of diesel. A delay limits the duration of the post-injection to 1 minute and a specific programming of the housing allows to obtain at most one post-injection every 5 minutes.

 The test was carried out on a bench, under conditions corresponding to urban driving conditions.

 The electronic unit has been adjusted so that post-injection is triggered as soon as the back pressure reaches 120 mb and the gas temperature is above 300 C.

 It is known that, for regeneration to take place correctly, it is necessary that the time during which the temperature of the exhaust gases is greater than 300 ° C., be greater than 30% of the time of use of the vehicle.

 The device described in this example makes it possible to obtain an exhaust gas temperature constantly greater than 300 ° C., whatever the initial temperature of the exhaust gases.

 Thus, the back pressure value measured after each regeneration process of the filtration device is 50 mb, which corresponds to the back pressure value measured on a new filtration device. The regeneration of the device is therefore complete.

 The regeneration method according to the invention and the associated filtration device are therefore particularly suitable for the treatment of exhaust gases from urban public transport vehicles. In fact, the gases produced by these vehicles are generally at a temperature lower than that necessary to allow the regeneration of conventional filtration devices, which leads to clogging of these devices and therefore their rapid deterioration by brutal combustion reactions. However, the results obtained with the present technique make it possible to envisage a minimum service life of the filtration device of 100,000 km, on vehicles of this type.

 Such a technique could also be used on passenger vehicles. Indeed, the latter operating at higher speeds, the exhaust gases produced have much higher temperatures which can reach more than 500 C. The problem of filter regeneration is therefore less crucial. However, existing systems generally use organometallic additives to catalyze the combustion of particles, which generates an operating cost.

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 important. The device according to the invention, associated with its regeneration method, overcomes this cost problem.

 Thus, if the filtration device according to the invention does not include new technical elements, the inventors have the merit of having been able to combine and adapt different existing techniques in order to potentiate their effects and to obtain a device having a very high efficiency, to fight against the emission of polluting particles produced by diesel engines and, on the other hand, to obtain excellent results in terms of filter regeneration, even in the case of vehicles whose engine speeds do not allow to obtain exhaust gases having a high temperature.

Claims (19)

 CLAIMS 1. Method for regenerating a device for filtering the exhaust gases produced by a diesel engine, this method being of the type in which particles, retained on a filter means of said filter device, are burnt off by the action of a combustion catalyst, characterized in that it consists essentially in retaining the hot exhaust gases around the filtration means (22) in order to supply the particles with at least part of the heat energy required to their combustion and to burning said particles so as to regenerate the filtration device.  2. Method according to the preceding claim, characterized in that it also consists in: - implementing a means of producing combustion catalyst (20) in the filtration device, - measuring a temperature On in the vicinity of the means of production of combustion catalyst (20), - compare 6m at a temperature Or corresponding to the temperature at which the combustion of diesel fuel, in the presence of the combustion catalyst, is complete, - if 6m is greater than or equal to Qr, trigger a post- injection of diesel, by means of an injection, into the filtration device, for a determined period, in order to cause an increase in temperature of the particles to allow their combustion.  3. Method according to the preceding claim, characterized in that it also consists in: - measuring a pressure Pm in the vicinity of the means for producing combustion catalyst (20), said pressure Pm reflecting the degree of obstruction of the filtration means (22) by particles, - measure the temperature ûm, - compare said pressure Pm with a reference pressure Pr corresponding to the maximum acceptable degree of obstruction, - if Pm is greater than or equal to the pressure Pr, compare ûm with Or, - if On is greater than or equal to Gold, trigger the post-injection of diesel. <Desc / CRUD Page number 15>  4. Device allowing the implementation of the regeneration process according to one of the preceding claims, characterized in that it comprises a means for producing combustion catalyst (20), a means of filtration (22) of said gases. exhaust downstream of said combustion catalyst production means, and a diesel injection means upstream of said combustion catalyst production means, said combustion catalyst production and filtration means being contained in a reaction vessel (18 ), in the path of the flow of exhaust gases produced by an engine (10).  5. Device according to the preceding claim, characterized in that said filtration means, constituted by a set of filtering units (44), is bathed in an exhaust gas receiving chamber, said exhaust gases coming to heat said units filter.  6. Device according to claim 5, characterized in that said filtration means is constituted by at least two particle filters (22a, 22b) comprising a body (40), formed by the filtering units (44) secured by a seal ( 46), and a metal casing (42).  7. Device according to one of claims 4 to 6, characterized in that said diesel injection means communicates with a discharge pipe (16) of the exhaust gases.  8. Device according to one of claims 4 to 7, characterized in that said injection means comprises a diesel tank (34) and an injection chamber (36) of the diesel contained in said tank, in the conduit d 'evacuation (16).  9. Device according to the preceding claim, characterized in that said chamber (36) is supplied, on the one hand, with diesel fuel via a first conduit (30) connecting it to said tank (34), and on the other hand, in compressed air via a second conduit (32), connecting it to the engine (10), said chamber comprising an orifice through which the diesel fuel is injected into said filtration device.  10. Device according to one of claims 4 to 9, characterized in that it comprises an electronic control unit (28). <Desc / Clms Page number 16>  11. Device according to one of claims 4 to 10, characterized in that it comprises at least one temperature probe (24), placed inside said enclosure (18), used to measure the temperature 8m in sound breast.  12. Device according to one of claims 4 to 11, characterized in that it comprises at least one pressure probe (26), placed inside said enclosure (18), used to measure the pressure Pm in sound breast.  13. Device according to one of claims 11 or 12, characterized in that the electronic control unit (28) is connected to said temperature probe (24) and to said pressure probe (26), compares the Or values, and possibly Pm measured respectively with the reference values Or and possibly Pr, and triggers the injection of diesel fuel into the exhaust duct (16), via said injection system, when the measurements Or, and possibly Pm are greater than or equal to the reference values 8r and possibly Pr.  14. Device according to the preceding claim, characterized in that the conduits (30 and 32) supplying the chamber (36) of the injection system with diesel and compressed air each comprise a solenoid valve (31 and 33) controlled by the housing electronic control, the opening of these solenoid valves causing the entry of diesel and compressed air into the chamber (36) and therefore the injection of diesel in the exhaust gas discharge conduit.  15. Device according to one of claims 9 to 14, characterized in that the chamber (36) of the injection system is provided with a nozzle opposite the orifice for injecting the diesel in nebulized form, in the gas exhaust pipe.  16. Device according to one of claims 5 to 15, characterized in that the filtering units preferably consist of silicon carbide or any other equivalent material, the structure of which is of honeycomb type.  17. Device according to one of 4 to 16, characterized in that the means for producing the combustion catalyst consists of at least one cartridge based on platinum or any equivalent material, catalyzing the transformation of nitrogen monooxide (NO ), contained in the exhaust gas nitrogen dioxide <Desc / Clms Page number 17>  (NO2), the NO2 produced catalyzing the combustion reaction of particles clogging the filter.  18. Device according to one of claims 4 to 17, characterized in that the capacity of the secondary tank (34) is preferably equivalent to the maximum volume of diesel injected during post-injection.  19. Device according to one of claims 6 to 18, characterized in that the particle filters (22a and 22b) are placed in the enclosure (18), in parallel.