EP1421267B1 - Method for regenerating an exhaust gas filtering device for diesel engine and device therefor - 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

The present invention generally relates to the field of particulate filters and more particularly to a method of regenerating a diesel engine exhaust filtration device.

In addition, the present invention also relates to a filter device for retaining the carbonaceous particles and soot, produced by the engine and burn them regularly to prevent their accumulation, the latter phase constituting regeneration, the object of the method 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 automobile fleet are at the origin of a significant rejection of pollutants in the atmosphere which causes its modification. This change is twofold. First of all, there is a chemical modification. The latter is mainly reflected by a continuous increase in the content of carbon compounds in the air. These compounds are especially carbon monoxide (CO) and some unburned hydrocarbons, resulting from incomplete combustion. The presence of these compounds in the atmosphere constitutes a much greater direct risk to health. Thus, CO is a very powerful respiratory toxin. Polycyclic aromatic hydrocarbons (PAHs), such as benzopyrene, benzanthracene or even fluoranthrene, which are particularly important in fumes, soot or engine exhaust gases, are recognized carcinogens.

The atmosphere is also modified by the release of solid particles. These particles are classified according to their size. Thus, the smallest so-called particles that can not be sedimented, because they are incapable of being deposited on the ground under the effect of gravitation, are the most dangerous for human health because they are likely to penetrate 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 report, the public authorities, both at national and international level, are trying to put anti-pollution standards in place. These standards mainly affect the automotive industry. In this way, car brands have to make regular modifications to their vehicles in order to bring them into compliance with these standards.

In addition to the development of new engines with ever lower fuel consumption, a special effort has been made to develop new exhaust systems designed to reduce the emission of unburnt pollutants and solid particles. For example, automobile manufacturers have developed catalytic converters or catalysts, usually consisting of a stainless steel casing, a thermal insulator and a honeycomb support impregnated with precious metals such as platinum or aluminum. rhodium. These catalysts make it possible to reduce, above all, the emissions of polycyclic hydrocarbons and CO, and this in a proportion of the order of 50%. However, they have no effect on solid particle emissions. Thus, especially in diesel engines that produce many solid particles, these catalysts do not provide significant improvement in air quality.

Other techniques have been developed to limit the emission of polluting particles by vehicles. This is the case of the particulate filter. This filter makes it possible to reduce by 90% the total mass of particles emitted by diesel engines. It is even more effective at retaining very fine particles, since the retention rate can be up to 99%.

The particulate filter, however, requires regeneration to burn the particles that have been trapped. The particles are generally trapped by a filter cartridge forming part of the particulate 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 have a maximum filtration surface.

A major disadvantage of such particulate filters is the incomplete combustion of particles retained by the filter cartridge. Indeed, for urban use conditions, the temperature of the exhaust gas 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 fuel in diesel engines only start 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 arranging upstream of the filter, a catalyst for oxidation of nitric oxide (NO) contained in the gases nitrogen dioxide (NO ₂ ) exhaust system, the latter having the property of catalyzing the combustion of carbonaceous particles from 250 ° C. However, this method requires the use of a diesel fuel whose sulfur content is less than 50 ppm (parts per million), to keep a conversion efficiency of NO to NO ₂ sufficient.

This technique, called "Continuous Regenerating Trap " (CRT), combines the effects of the particulate filter and the NO oxidation catalyst. This system requires regular regeneration to ensure proper operation of the filters, which limits the pressure drop of the filter by eliminating the risk of uncontrolled and exothermic regeneration.

Such operation is obtained only when the exhaust gas or the combustion chamber have a temperature greater than 300 ° C for at least 30% of the operating time of the vehicle.

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

Other techniques involve the use of organometallic additives added to the gas oil such as cerium, iron, strontium, calcium or others. 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 in the region of 300 ° C.

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

Another major disadvantage lies in the fact that it is necessary to provide a complementary additivation device.

Yet another disadvantage of these techniques is that they have an even greater tendency to clog the filter and therefore the resulting reactions, if the temperatures reached in operation are not sufficiently high, the additives present in the carbonaceous materials contributing to foul the filtering media even more quickly

Other techniques have consisted in experimenting with devices based on complementary heating means such as burners, electrical 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 gas flow large exhaust. Such a device therefore requires a significant heating power to simultaneously bring to the right temperature the exhaust gas and the mass of the filter cartridge.

WO-A-00/34632 describes all the features of the preambles of the independent claims 1 and 3.

Furthermore, US-A-4,462,812 discloses a particle separator for use in the exhaust system of a diesel engine, which comprises a filter retained in a chamber of this separator, so that the exhaust gas arriving can circulate freely around the free portion of this filter, to heat its external surface, and thus reduce the thermal stresses that are generated in this filter during its operation and its regeneration.

Finally, US-B-6,273,120 relates to a device for introducing a liquid reductant into an exhaust gas purification system, comprising a mixing chamber of this reducer with a gas, in communication with a transport pipe of this type. gearbox as well as with a pipe for transporting this gas, while a device for controlling the pressure in the line of the gearbox is provided, depending on the pressure of the gas in the gas line.

In such a technical context, the objective of the present invention is to provide a method of regeneration of a filtration device, which overcomes the disadvantages of the various existing techniques of 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 object of the invention is to provide a regeneration process that does not lead to significant overconsumption of fuel and, more generally, does not entail additional financial cost for the user.

Yet another object of the invention is to provide a regeneration process that does not affect the performance of the engine, in particular by pressure losses, due to the counterpressure exerted by the exhaust gases on the engine, due to clogging of the filter device.

Finally, a final objective of the invention is to provide a filtration device for implementing the regeneration method according to the invention.

These objects, among others, are achieved by the present invention which firstly relates to a regeneration method according to the appended claim 1.

Another object of the invention relates to a filtration device for carrying out the regeneration method according to the invention. This device is in accordance with the appended claim 3.

• La figure 1 représente une vue générale schématique du système comprenant le dispositif de filtration et permettant la mise en oeuvre du procédé de régénération.
• La figure 2 représente une vue en coupe longitudinale du dispositif de filtration selon un premier mode de réalisation.
• La figure 3 représente une vue en coupe transversale, selon l'axe II-II, du dispositif de filtration représenté en coupe longitudinale sur la figure 3.
• La figure 4 représente une variante de ce premier mode réalisation, vue en coupe longitudinale du dispositif de filtration.
• La figure 5 représente une vue en coupe longitudinale du dispositif de filtration selon un second mode de réalisation.

The present invention will be better understood on reading the description which follows, made with reference to the drawings which show, in no way limiting, an embodiment of the filtration device according to the invention and in which:

• FIG. 1 represents a schematic overall view of the system comprising the filtration device and allowing the implementation of the regeneration method.
• Figure 2 shows a longitudinal sectional view of the filter device according to a first embodiment.
• FIG. 3 represents a cross-sectional view along axis II-II of the filtration device shown in longitudinal section in FIG.
• FIG. 4 represents a variant of this first embodiment, seen in longitudinal section of the filtration device.
• FIG. 5 represents a longitudinal sectional view of the filtration device according to a second embodiment.

The system that allows the implementation of the regeneration method according to the invention is shown schematically in Figure 1, according to a preferred embodiment. In this system, collaborate various mechanical elements of the vehicle, which are or are not part of the filter 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 feed system 14, produces exhaust gas in operation. These gases are recovered through a manifold (not shown) at the engine outlet and are evacuated via an exhaust duct 16. This duct joins an enclosure 18 containing a catalyst production means. 20 and a filtering means 22. A temperature probe 24 and a pressure sensor 26 are also placed at the chamber 18. These probes have the function of measuring the temperature and the pressure in the vicinity of the production means. of combustion catalyst. 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 ducts 30 and 32 and triggers their opening. The conduit 30 connects a secondary reservoir 34 to the injection chamber 36. This secondary reservoir 34 supplies the injection chamber 36 with diesel fuel. Itself is fed by the main tank 12 through a piping system 38.

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

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

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

The combustion catalyst production means 20 and the filtration means 22 are grouped together in the chamber. The combustion catalyst production means 20 consists of 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 thermal inertia possible. According to a preferred embodiment, these cartridges are preferably based on platinum and are the seat of a conversion of the nitrogen monoxide (NO) contained in the exhaust gases to nitrogen dioxide (NO ₂ ), which constitutes the combustion catalyst. NO ₂ diffuses to the filtration medium 22.

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

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

The enclosure 18 has in its lower part a retention chamber to increase their residence time in the enclosure, purified exhaust gas through the filtration means (filter units or particulate filters).

This increase in the residence time of the exhaust gas allows the latter to come to heat the filter units or particulate filters and therefore the particles themselves. This remarkable feature keeps them at a temperature well above the usual temperature. This temperature can reach the temperature allowing their combustion in the presence of combustion catalyst. In this case, the regeneration takes place without injection of diesel fuel.

A variant of this embodiment is shown in FIG. 4. According to this variant, the particulate filters 22a, 22b and 22c are arranged in opposite directions. The device then comprises a particular zone of retention of the exhaust gases, not yet 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 in the particle filters, which goes from one on the other hand, to promote the exchange of heat between the gases and the filters and, on the other hand, to limit the loss of heat by exchange with the outside.

According to a second embodiment of the device according to the invention, the filter units 44 are independent of one another. Thus, each filter unit is separated from 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 significantly reduce the thermal expansion stresses, especially in the event of sudden combustion of retained particles, which greatly limits the risk of the filter units deteriorating; on the other hand, the available surface area for the heat transfer by the gases is considerably increased, which further increases this heat transfer.

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

According to an exemplary embodiment, each filter unit is a square-based cylinder having a width and a depth of 35 mm, and a length ranging from 150 to 300 mm.

In the case where the temperature is not sufficient to trigger the combustion of the particles, the regeneration occurs through the injection of diesel fuel.

In order to do this, the temperature in the vicinity of the catalyst production means is measured by means of the probe 24. The measured temperature value θ _m is collected by the control electronics unit. The housing will compare this value θ _m to a reference value θ _r , corresponding to the temperature at which the combustion of diesel in the presence of catalyst is complete.

If the measured temperature θ _m is greater than or equal to the reference value θ _r , the electronic control unit triggers the opening of the 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 fuel mixes with the compressed air and the mixture thus formed is pulverized in the nebulized form. in the gas evacuation duct 16. This spraying is done through an orifice formed in the wall of the chamber 36, facing which there is a nozzle, fixed to the chamber, to obtain a jet nebulized under pressure. According to an exemplary embodiment, the chamber 36 is of the compressed air paint gun type.

When the quantity of diesel fuel required, predetermined by the electronic control unit, has been injected, the supply of diesel fuel is cut off by closing solenoid valve 33. Only the supply of compressed air persists so that the latter is sprayed. in the conduit 16 instead of the mixture. This prolonged supply of compressed air is intended to remove 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 fuel required for the regeneration. Thus, over-consumption of diesel can not occur. In addition, thanks to this embodiment, the frequency of the regeneration cycles is limited by the time required to fill the secondary tank 34, which also avoids excessive consumption of fuel.

The fuel injected into the exhaust duct 16 enters the enclosure and undergoes complete combustion at the catalyst producing means. This combustion induces a significant increase in temperature up to a temperature θ _c at which the combustion of the particles which clog the filtration means will proceed. The NO ₂ molecules produced will catalyze this combustion reaction. Thus, this reaction occurs at a temperature below normal temperature. During this combustion, the solid particles are transformed into gases which are evacuated.

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

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

According to a variant of this embodiment, an additional temperature sensor is disposed 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, thanks to the temperature probe 24 and to the pressure probe 26. The measured pressure value P _m reflects the degree of obstruction filtration means by the particles. Indeed, if the filtering means is clogged, the exhaust gases pass more difficultly and then exert a back pressure. Thus, the measurement of the pressure P _m corresponds to the best means of controlling the clogging of the filtration means. The electronic control unit compares the measured value P _m with a reference value P _r , corresponding to the maximum acceptable degree of obstruction of the filtration means. If P _m is greater than or equal to P _r , the electronic control unit compares θ _m with θ _r . If θ _m is greater than or equal to θ _r , the housing then triggers the diesel injection post-injection 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 certain degree of clogging, which allows to greatly limit overconsumption of fuel.

EXAMPLE

By way of non-limiting example, is presented below a filtration device used with an industrial vehicle engine, the engine Renault VI 620-45 supercharged, 10 liters of displacement and a power of 190 kW. This engine equips urban buses.

• Deux cartouches de catalyseurs à base de platine permettant la transformation du NO en NO₂. Ces cartouches, de 7,5 pouces diamètre et de 3 pouces de long, montées en parallèle sur un support métallique, tel que représenté sur la figure 2. Le volume de catalyseur a été déterminé de sorte que le taux de conversion de NO en NO₂ soit supérieur à 85 %.
• Trois filtres à particules IBIDEN, de type nid d'abeille en carbure silicium, montés en parallèle. Ces filtres ont une section de 162 cm² (diamètre 143,8 mm) et une longueur de 254 mm.
• Un système d'injection de gazole comportant une chambre d'injection tel que décrit précédemment et un réservoir secondaire d'une capacité de 50 cm³. Le débit de système d'injection est de 50 cm³ par minute. Ce débit a été déterminé de sorte que l'augmentation de température des gaz d'échappement, engendrée par la post-injection soit comprise entre 170 et 250°C, selon les conditions d'utilisation.
• Un boîtier électronique commandant la post-injection de gazole. Une temporisation limite la durée de la post-injection à 1 minute et une programmation spécifique du boîtier permet d'obtenir au plus une post-injection toutes les 5 minutes.

The filtration device is composed of:

• Two platinum-based catalyst cartridges for transforming NO to NO ₂ . These cartridges, 7.5 inch diameter and 3 inches long, mounted in parallel on a metal support, as shown in Figure 2. The catalyst volume was determined so that the NO to NO conversion rate ₂ is greater than 85%.
• Three IBIDEN particle filters of silicon carbide honeycomb type, mounted in parallel. These filters have a section of 162 cm ² (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 cm ³ . The Injection system flow rate is 50 cm ³ per minute. This flow rate has been determined so that the increase in temperature of the exhaust gas generated by the post-injection is between 170 and 250 ° C, depending on the conditions of use.
• An electronic box controlling the post-injection of diesel. A delay limits the duration of the post-injection to 1 minute and 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 control unit has been set up so that the 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 the regeneration to be done correctly, it is necessary that the time during which the temperature of the exhaust gas is greater than 300 ° C., is 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 that is constantly higher than 300 ° C., regardless of the initial temperature of the exhaust gas.

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

The regeneration process according to the invention and the associated filtration device are therefore particularly suitable for the treatment of the exhaust gases of urban public transport vehicles. Indeed, the gases produced by these vehicles are generally at a temperature below that required to allow the regeneration of conventional filtration devices, resulting in clogging of these devices and therefore their rapid deterioration by sudden combustion reactions. Now, 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 that can reach more than 500 ° C. The problem of filter regeneration is therefore less crucial. However, existing systems typically use organometallic additives to catalyze the combustion of particulates, resulting in a cost of operation important. The device according to the invention, associated with its regeneration process, overcomes this problem of cost.

Thus, if the filtration device according to the invention does not comprise any new technical elements, the inventors have the merit of having been able to combine and adapt various existing techniques in order to potentiate their effects and to obtain a device having a very high degree of efficiency. high efficiency, to fight against the emission of polluting particles produced by diesel engines and, secondly, 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 (14)

1. Method of regenerating a device for filtering the exhaust gases produced by a diesel engine, this method being of the type in which particles, held on a filtration means (22) of the filtration device, are combusted by the action of a combustion catalyst (20), the filtration means (22) for exhaust gases being provided downstream of a production means of the combustion catalyst (20), characterised in that the method consists essentially of retaining the hot exhaust gases around the filtering means (22) in order to supply to the particles at least some of the calorific energy necessary to their combustion and in burning the particles so as to regenerate the filtering device and also consists in:

   - implementing a means of producing combustion catalyst (20) in the filtration device,

   - measuring a temperature θ_m in the vicinity of the means of producing combustion catalyst (20),

   - comparing θ_m to a temperature θ_r corresponding to the temperature at which the combustion of the diesel oil is complete in the presence of the combustion catalyst,

   - if θ_m is greater than or equal to θ_r, triggering post-injection of diesel oil via an injection means into the filtration device for a specified duration in order to bring about an increase in temperature of the particles in order to permit their combustion.
2. Method according to the preceding claim, characterised in that it also consists in:

   - measuring a pressure P_m in the vicinity of the means of producing combustion catalyst (20), the pressure P_m reflecting the degree of obstruction of the filtration means (22) by the particles,

   - comparing the pressure P_m to a reference pressure P_r corresponding to the maximum acceptable degree of obstruction,

   - if P_m is greater than or equal to the pressure P_r, comparing θ_m to θ_r,

   - if θ_m is greater than or equal to θ_r, triggering post-injection of diesel oil.
3. Device permitting the implementation of the regeneration method according to claim 1 or 2, comprising a means of producing combustion catalyst (20), a filtration means (22) of the exhaust gases downstream of the means of producing combustion catalyst, a means of injecting diesel oil upstream of the means of producing combustion catalyst, the same means of producing combustion catalyst and filtration means being contained in a reaction enclosure (18) in the path of the flux of exhaust gases produced by an engine (10), as well as an electronic control housing (28) and at least one temperature sensor (24) located inside the said enclosure (18) and being used to measure the temperature θ_m within the same, characterised in that the means of injecting diesel oil communicates with an evacuation pipe (16) for the exhaust gases and in that the electronic control housing (28) is connected to the temperature sensor (24), compares the value θ_m measured with the reference value θ_r, and triggers the injection of diesel oil into the evacuation pipe (16) via the injection system when the measure θ_m is greater than or equal to the reference value θ_r.
4. Device according to claim 3, permitting the implementation of the regeneration method according to claim 2, characterised in that it comprises at least one pressure sensor (26), located inside the enclosure (18) and being used to measure the pressure P_m within the same, and in that the electronic control housing (28) is connected to the pressure sensor (26), compares the value P_m measured with the reference value P_r, and triggers the injection of diesel oil into the evacuation pipe (16) via the injection system when the measurement P_m is greater than or equal to the reference value P_r.
5. Device according to claim 3 or 4, characterised in that the filtration means, formed by an assembly of filtering units (44), is immersed in a chamber for receiving the exhaust gases, the exhaust gases being used to heat the filtering units.
6. Device according to claim 5, characterised in that the filtration means is formed by at least two particle filters (22a, 22b) comprising a body (40) formed by the filtering units (44) which are connected by a joint (46), and a metal casing (42).
7. Device according to one of claims 3 to 6, characterised in that the injection means comprises a diesel oil reservoir (34) and an injection chamber (36) of the diesel oil contained in the reservoir, located in the evacuation pipe (16).
8. Device according to the preceding claim, characterised in that the chamber (36) is supplied on the one hand with diesel oil via a first pipe (30) connecting the same to the reservoir (34), and on the other hand with compressed air via a second pipe (32) connecting the same to the engine (10), the chamber comprising an aperture via which the diesel oil is injected into the filtration device.
9. Device according to either of claims 7 or 8, characterised in that the pipes (30 and 32) supplying the chamber (36) of the injection system with diesel oil and compressed air each comprise a solenoid valve (31 and 33) controlled by the electronic control housing, the opening of these solenoid valves bringing about the input of diesel oil and compressed air into the chamber (36) and hence the injection of diesel oil into the pipe for evacuating the exhaust gases.
10. Device according to either of claims 8 or 9, characterised in that the chamber (36) of the injection system is equipped with a nozzle opposite the aperture for injecting the diesel oil in a vaporised form into the evacuation pipe for the gases (16).
11. Device according to one of claims 5 to 10, characterised in that the filtering units (44) are formed preferably of silicon carbide or any other equivalent material which has a honeycomb structure.
12. Device according to one of claims 3 to 11, characterised in that the means of producing combustion catalyst is formed by at least one cartridge with a platinum base or a base of any other equivalent material which catalyses the conversion of nitrogen monoxide (NO) contained in the exhaust gases into nitrogen dioxide (NO₂), the NO₂ produced catalysing the combustion reaction of the particles clogging the filter.
13. Device according to one of claims 7 to 12, characterised in that the capacity of the secondary reservoir (34) is preferably equivalent to the maximum volume of diesel oil injected during post-injection.
14. Device according to one of claims 6 to 13, characterised in that the particle filters (22a and 22b) are located in parallel in the enclosure (18).

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