EP1588032B1 - Method for the post-injection of hydrocarbon-, alcohol- and/or reducing-agent-type regeneration solution (e.g. diesel fuel and/or urea and/or ammoniacal solution) for the regeneration of diesel engine exhaust gas filtration systems - Google Patents

Abstract

The process involves injecting diesel oil, up stream of an oxidation catalyst, from an electro-magnetic injector (9) for pulverizing the oil by compressed air. The temperature of an exhaust gas is increased to accelerate the speed of oxidation of the carbon particles for regenerating a filtration device of exhaust gas products. The temperature is increased when the start of binding of the particles is detected. An independent claim is also included for a device for post injection of diesel oil.

Description

The present invention generally relates to the field of particulate filters and, more particularly, to a method of post-injection of regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg gas oil and / or urea and / or solution ammonia) upstream of a diesel engine exhaust filter device to regenerate this filter.

In addition, the present invention also aims at the management of this injection device which aims to inject a homogeneous mixture of air and regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg diesel and / or urea and / or ammoniacal solution) on the oxidation catalyst located upstream of the filtration system so as to increase the temperature of the exhaust gases as for a combustion. A high temperature level is necessary to oxidize and burn the carbonaceous particles produced by the engine and retained on this filtration system, in order to prevent their accumulation, this last phase constituting regeneration, object of the method according to the invention.

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 90%. 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 more than 90% the total mass of particles emitted by diesel engines.

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 cordierite body, quartz or silicon carbide, generally of honeycomb structure to have a maximum filtration area.

The major difficulty of operation of such particulate filters lies in controlling the oxidation and combustion phase of the 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 the oxidation of nitrogen monoxide (NO) contained in the exhaust gas in nitrogen dioxide (NO ₂ ), the latter having the property of catalyzing combustion. 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.

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 370 ° 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 device for introducing the complementary additive.

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 filter 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 large flow of exhaust gas. 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.

On recent common-rail diesel engines, a diesel injection after-injection technique has been used to increase the temperature of the exhaust gases and thus be able to significantly oxidize and burn the carbon particles retained on the filter, this technique of direct injection that uses electromagnetic injectors effectively allows for a new fuel injection into the combustion chamber at the moment when the exhaust valve opens and thus obtain a homogeneous mixture with the exhaust gas and complete oxidation of this gas oil on the oxidation catalyst located between the engine outlet and the particulate filter.

Processes for post-injection of regeneration liquid of the diesel and / or alcohol type are also known for the regeneration of filtration means arranged downstream of combustion catalysts in diesel engine exhaust systems. These processes are described in particular in the following patent applications or patents: US-4,372,111 , US-B-5,207,990 , EP-A-1 158 143 , US-B-6,023,930 , JP-A-07 119444 and US-B-5,522,218 .

These known processes have in common, on the one hand, not to allow optimal, safe and economical regeneration of the filtration means, and, on the other hand, to provide no satisfactory solution to the technical problem of thermal degradation and coking the regeneration liquid, especially when it comes to diesel, and especially at the nozzles of the injectors belonging to the post-injection means. The post-injectors are thus quickly damaged by the heat of the exhaust manifold and are therefore neither reliable nor effective.

In such a technical context, the objective of the present invention is to provide a method of post-injection of hydrocarbon-type regeneration liquid, alcohol and / or reducing agent (eg gas oil and / or urea and / or ammoniacal solution) adaptable to all diesel engines allowing regeneration of a filtration device, which overcomes the disadvantages of the various existing techniques of treating the carbonaceous particles and of soot emitted by the diesel engines by increasing, when necessary, the temperature of the exhaust gas to obtain the correct oxidation temperature.

Another object of the invention is to provide a method of post-injection of regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg gas oil and / or urea and / or ammoniacal solution), thus avoiding any risk of accumulation of particles in the filter device and therefore any risk of uncontrolled regeneration.

Yet another object of the invention is to provide a method of post-injection of regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg gas oil and / or urea and / or ammoniacal solution), which is not not subject to the technical problem of thermal degradation and coking of the regeneration liquid, especially when it comes to diesel, and in particular at the nozzles of the injectors belonging to the post-injection means.

Yet another object of the invention is to provide a process for post-injection of regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg gas oil and / or urea and / or ammoniacal solution) not involving significant overconsumption of fuel and more generally, not entailing additional financial cost, for the user.

Yet another object of the invention is to provide a method of post-injection of regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg gas oil and / or urea and / or ammoniacal solution) that does not impair performance. 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, a final objective of the invention is to provide a filtration device for carrying out the method according to the invention of post-injection of regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg diesel and / or urea and / or ammonia solution).

These objectives, among others, are achieved by the present invention which concerns, first of all, a method of post-injection of a regeneration liquid according to claim 1.

The process according to the invention makes it possible to obtain a quality aerosol, which guarantees a very good regeneration of the particulate filter of the exhaust.

In this method of post-injection of diesel fuel, use is made of a device disposed at the outlet of the exhaust gases of a diesel engine and upstream of an oxidation catalyst, downstream of which are located the filtration means of the diesel engines. coal particles emitted by a diesel engine. In this process, the particles retained on a filtering means, are burned by the action of residual oxygen and nitrogen oxides contained in the exhaust gas.

According to a preferred arrangement of the invention, the post-injection flow of the regeneration liquid and the post-injection flow of the gaseous fluid, preferably compressed air, emanate from substantially concentric openings.

According to an even more preferred embodiment of the invention, a part of the gaseous fluid, preferably compressed air, borrows, until the post-injection opening, the same nozzle as the regeneration liquid.

To further improve the quality of the post-injection aerosol, it is provided according to the invention, that a portion of the gaseous fluid is mixed with the regeneration liquid before the post-injection.

One of the advantageous features of the invention to limit the risks of clogging, consists in maintaining the circulation of the gaseous fluid, preferably the compressed air, in the post-injection nozzle, after the interruption of the post-injection regeneration liquid through this nozzle, and for a period necessary for rinsing said nozzle.

In order to minimize the problem of coking and thermal degradation, it is ensured that the temperature of at least part of the post-injection means remains less than or equal to 120 ° C., preferably 100 ° C., during engine operation. .

To do this, at least a portion of the post-injection means is advantageously removed from the (or) conduit (s) in which (s) circulate the exhaust gas.

• * dans le groupe des hydrocarbures comprenant les produits de raffinage du pétrole (de préférence les essences et le gazole),
• * dans le groupe des alcools (de préférence le méthanol),
• * dans le groupe des agents réducteurs (de préférence l'urée et les solutions ammoniacales),
• * et leurs mélanges.

Preferably, the regeneration liquid is chosen:

• * in the group of hydrocarbons including petroleum refining products (preferably gasoline and diesel),
• in the group of alcohols (preferably methanol),
• in the group of reducing agents (preferably urea and ammoniacal solutions),
• * and mixtures thereof

• mesurer une température θ_m en amont du catalyseur d'oxydation,
• comparer θ_m à une température θ_r correspondant à la température à laquelle la combustion du liquide de régénération, en présence du catalyseur de combustion, est complète,
• si θ_m est supérieure ou égale à θ_r, déclencher une post-injection de liquide de régénération.

According to a preferred embodiment of the invention, the method comprises the following essential steps:

• measure a temperature θ _m upstream of the oxidation catalyst,
• comparing θ _m with a temperature θ _r corresponding to the temperature at which the combustion of the regeneration liquid, in the presence of the combustion catalyst, is complete,
• if θ _m is greater than or equal to θ _r , trigger a post-injection of regeneration liquid.

• mesurer une pression P_m en amont du système de filtration par une sonde 3, ladite pression P_m reflétant le degré d'obstruction du moyen de filtration 5 par les particules,
• comparer ladite pression P_m à une pression P_r de référence correspondant au degré d'obstruction maximal acceptable,
• si P_m est supérieure ou égale à la pression P_r et si θ_m est supérieure ou égale à θ_r, déclencher la post-injection de liquide de régénération.

According to an interesting variant of this preferred mode, it is provided:

• measuring a pressure P _m upstream of the filtration system by a probe 3, said pressure P _m reflecting the degree of obstruction of the filtration means 5 by the particles,
• comparing said pressure P _m with 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 and if θ _m is greater than or equal to θ _r , trigger the post-injection of regeneration liquid.

It is particularly advantageous according to the invention to control the injections of regeneration liquid, using at least one computer, taking into account the temperature information θ _m and possibly pressure P _m , to obtain the temperature increase. sought for optimal regeneration of the filtration device.

According to another of its objects, the invention also provides a device according to claim 11.

• le capillaire (ou buse) et la canalisation sont concentriques et coaxiales, de même que leurs ouvertures respectives, qui débouchent dans le (ou les) conduit(s) d'échappement,
• et le capillaire (ou buse) est contenu dans la canalisation.

According to remarkable characteristics of the device according to the invention:

• the capillary (or nozzle) and the pipe are concentric and coaxial, as are their respective openings, which open into the exhaust duct (s),
• and the capillary (or nozzle) is contained in the pipeline.

• géographiquement à un endroit éloigné (par exemple à 200 mm) du conduit d'échappement, pour ne pas être soumis à des températures élevées,
• et en amont du catalyseur d'oxydation.

Les moyens de filtration des gaz d'échappement sont quant à eux en aval du catalyseur de d'oxydation (ou combustion). Le catalyseur et les moyens de filtration sont, en pratique, contenus dans une enceinte, qui se situe dans la trajectoire du flux des gaz d'échappement produit par un moteur.Advantageously, at least a part of the post-injection means, preferably at least the injector, is designed so that it is preferably arranged at a sufficient distance from the exhaust duct (s) so that not undergo thermal deterioration, ie remain during operation of the engine at a temperature less than or equal to 120 ° C, preferably at 100 ° C,
The post-injection of the regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg gas oil and / or urea and / or ammoniacal solution) is assisted by a gaseous fluid under pressure (for example compressed air). Thanks to the structure of the capillary assembly (or nozzle) / channel, the injector and its support are located:

• geographically at a remote location (eg 200 mm) from the exhaust duct, so as not to be subjected to high temperatures,
• and upstream of the oxidation catalyst.

The means for filtering the exhaust gases are in turn downstream of the oxidation catalyst (or combustion). The catalyst and the filtration means are, in practice, contained in an enclosure, which is in the path of the flow of exhaust gas produced by a motor.

According to a preferred embodiment of the device according to the invention, the means for supplying gaseous fluid under pressure, preferably in compressed air, are designed to allow the admission of gaseous fluid at the outlet of the injector, capillary head or nozzle, so that gaseous fluid under pressure, preferably compressed air, can flow with the post-injected regeneration liquid, in the capillary or nozzle.

According to an advantageous variant of this preferred embodiment, the means for supplying gaseous fluid under pressure, preferably in compressed air, comprise a solenoid valve controlling the admission of the gaseous fluid under pressure, preferably compressed air to the outlet of the injector, at the top of the capillary or nozzle, to allow said fluid to flow with the regeneration liquid, and, incidentally, to be able to rinse the capillary or nozzle, after the end of the post-injection, while maintaining for a time a flow of gaseous fluid under pressure, preferably compressed air, in the capillary or nozzle.

According to another variant of this preferred embodiment, the means for supplying pressurized gaseous fluid, preferably compressed air, as well as the post-injection means, preferably the injector holder, are designed in such a way that at least one calibrated orifice is provided for continuously feeding a flow of gaseous fluid pressurized, preferably compressed air mixed with the regeneration liquid, at the inlet of the capillary or nozzle, so as to achieve an emulsion and to ensure in addition and preferably the rinsing function, maintaining some time after closure, a flow rate in gaseous fluid, in the capillary or nozzle.

Advantageously, the regeneration liquid supply means are connected to the supply duct of at least one mechanical injection pump of the engine.

• * dans le groupe des hydrocarbures comprenant les produits de raffinage du pétrole (de préférence les essences et le gazole),
• * dans le groupe des alcools (de préférence le méthanol),
• * dans le groupe des agents réducteurs (de préférence l'urée et les solutions ammoniacales),
• * et leurs mélanges.

The regeneration liquid is preferably chosen:

• * in the group of hydrocarbons including petroleum refining products (preferably gasoline and diesel),
• in the group of alcohols (preferably methanol),
• in the group of reducing agents (preferably urea and ammoniacal solutions),
• * and mixtures thereof

Remarkably, the device according to the invention comprises a temperature probe and a pressure probe. In addition, the computer (or electronic control unit), which is connected to the temperature probe and the pressure sensor, is used to compare the values θ _m and possibly P _m respectively measured with the reference values θ _r and possibly P _r , and triggers the post-injection of regeneration liquid into the exhaust pipe, via the means for supplying regeneration liquid, means for supplying gaseous fluid under pressure, preferably compressed air. , and post-injection means, when the measurements θ _m and possibly P _m are greater than or equal to the reference values θ _r and possibly P _r .

Advantageously, the temperature probe and the possible pressure sensor are located substantially at the same level on the exhaust duct

In practice and for example, the post-injection is performed by a conventional electromagnetic injector of the same type as that used on gasoline engines, this injector being disposed on an injector door remote from the exhaust duct. The regeneration liquid of the hydrocarbon, alcohol and / or reducing agent type (eg gas oil and / or urea and / or ammoniacal solution) originating from this injector is fed through a capillary contained in a pipe constituted eg by a metal tube to the duct exhaust hot. This tube is fed with compressed air so as to arrive concentrically around the capillary to open into the duct exhaust and cause a good spray of regeneration liquid hydrocarbon type, alcohol and / or reducing agent (eg gas oil and / or ethanol and / or urea and / or ammonia solution). The injection of regeneration liquid and the supply of compressed air are controlled by the electronic control unit, which governs the opening / closing of solenoid valves allowing the post-injection of regeneration liquid into the gas evacuation duct. exhaust.

Advantageously, in the injector holder, a calibrated orifice in connection with the air inlet and facing the injector nose is arranged so as to generate an air / liquid regeneration emulsion at the inlet of the capillary and allow to inject this regeneration liquid in perfectly nebulized form at the outlet into the gas evacuation duct.

• La figure 1 représente une vue générale schématique du système comprenant le dispositif de filtration avec son catalyseur d'oxydation et en amont de cet ensemble le système de post-injection permettant la mise en oeuvre du procédé de régénération.
• La figure 2 représente une vue détaillée du dispositif de post-injection selon un premier mode de réalisation.
• La figure 3 représente une vue détaillée d'une variante du dispositif de post-injection selon un deuxième mode de réalisation.
• La figure 4 représente une vue générale du système de post-injection intégré dans un ensemble moteur filtre à particules.

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 post-injection device integrated in a filtration system according to the invention and in which :

• The figure 1 represents a schematic overview of the system comprising the filtration device with its oxidation catalyst and upstream of this set the post-injection system for the implementation of the regeneration process.
• The figure 2 represents a detailed view of the post-injection device according to a first embodiment.
• The figure 3 represents a detailed view of a variant of the post-injection device according to a second embodiment.
• The figure 4 represents a general view of the post-injection system integrated into a particulate filter engine assembly.

The system that allows the implementation of the regeneration process according to the invention is schematically represented in FIG. figure 1 in a preferred mode. In this system, collaborate various mechanical elements of a particulate filter which are or are not part of the filtration device and which contribute to controlling the regeneration of the filtration system.

Thus, the exhaust gas at the outlet of the diesel engine on the duct 1, are controlled by the temperature of the probe 2 and pressure by the probe 3 to be then directed to the oxidation catalyst 4, then to the filter cartridges 5, the assembly being contained in a metal casing 6 and insulated by ceramic elements 7.

A computer 8 will control when necessary the diesel fuel injections from the electromagnetic injector 9 mounted on an injector block 10, it will be fed from a diesel engine bypass duct 11, the diesel fuel being directed to the exhaust duct by the capillary 12.

This capillary 12 opens at the center of the pipe 13 in the exhaust pipe 14 upstream of the oxidation catalyst 4, so as to obtain a good air spray which will arrive concentrically and which will be admitted from the solenoid valve 15, powered by a pressure regulator, not shown.

A second solenoid valve 16 will purge the capillary to prevent diesel stagnant inside thereof and can coke and cause its obstruction near the exhaust pipe which is very hot.

A detailed view of the post-injection device, in particular of the injector holder according to a first embodiment, is shown in FIG. figure 2 .

The computer 8 from the temperature and pressure information collected by the probes 2 and 3 and according to the strategy that will have been set will control an injection of diesel fuel from the electromagnetic injector 9 fed diesel fuel by the engine circuit 11 At the outlet of this electromagnetic injector, the injected diesel fuel volume will be directed by the capillary 12 towards the exhaust duct 1 where it will be sprayed at 14 by means of the air that will arrive concentrically through the pipe 13. The air flow rate Spraying will be controlled by the solenoid valve 15 supplied by a not shown pressure regulator, its opening will be simultaneous with that of the injector 11, so as to obtain a good spray from the start, against its closure will be delayed a few seconds so as to be able to perform the rinsing operation of the capillary with air, which will be fed from the solenoid valve 16 from there In the injector, a non-return valve 17 will prevent any accumulation of diesel in the conduit of the injector holder 10 so as to allow an effective rinsing.

A variant of this embodiment is shown on the figure 3 . According to this variant, to improve the diesel fuel spraying quality and simplify the production of this assembly, the injector holder 10 and supplied with air by a single solenoid valve whose opening will be simultaneous with the diesel injector 9, but whose closing will be delayed a few seconds, as for the previous embodiment, so that the operation of rinsing the capillary is done automatically through the air flow controlled by the calibrated air nozzle 18. This air flow will also allow , as soon as the solenoid valve 15 opens, to form an emulsion with the diesel fuel-gas from the injector 9 in the chamber 19 and then to be directed by the capillary 12 to the outlet in the exhaust pipe at 14 This emulsion will lead to the center of the tube 13 where it will meet the air flow conveyed by this tube, to be finely pulverized and to obtain a much higher quality of nebulization, thanks to the emulsion already formed. e in the capillary. When closing the injector, maintaining the air flow for a few additional seconds, allows the capillary 12 to be completely rinsed.

In this embodiment, good results have been obtained with an air supply pressure, for example 3 bars, supplied by the solenoid valve 15 by a 4/6 mm rilsan tube, for example, and by a restriction. at the inlet of the injector holder 2 mm, eg, in diameter and by an air nozzle of 0.45 mm, eg, to supply the chamber 19 to the inlet of the capillary 12. This stainless steel capillary, eg, of 1 / 1.6 mm was 50 cm long and was contained in a 4/6 mm stainless steel tube, eg, the quality of diesel fog obtained made it possible to make injections up to temperatures of catalyst entry of 270 ° C, eg, without observing hydrocarbon emissions.

On the figure 4 is shown the post-injection device associated with a particle filtration system, the assembly being mounted on a diesel engine 20 powered by an air compressor 21, and escaping through a turbine 22 to evacuate the exhaust gas by a pipe 23, to the system in 1 where are arranged the temperature sensors 2 and pressure 3 before spraying at 14 the diesel fuel with the air from the pipe 13. The injector 9 being fed by a line 11 mounted bypassing the diesel fuel supply of the injection pump 24 of the engine.

In the regeneration process of the particle filters with the post-injection device, if the temperature is not sufficient to trigger the combustion of the particles, the regeneration occurs through the injection of diesel fuel.

For this purpose, the temperature in the vicinity of the inlet of the catalyst is measured, thanks to the probe 2, eg of the thermocouple or thermistor type arranged at the inlet of the system. The measured temperature value θ _m is collected by the computer 8. The computer will compare this value θ _m with a reference value θ _r , corresponding to the temperature at which the combustion of the diesel fuel on the catalyst with the excess air , is done completely. Those skilled in the art are perfectly able to determine θ _r . In practice, for diesel engines, θ _r is, for example, ≥ 300 ° C.

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 injector 9 and of the solenoid valve 15. This opening causes the entry of diesel into the capillary and compressed air in the tube 13. At the outlet of the tube 13 at 14, the diesel fuel mixes with the compressed air and the mixture, thus constituted, is sprayed, in the nebulized form in the exhaust gas duct. exhaust 1.

The fuel injected into the exhaust pipe 1 enters the enclosure 6 and undergoes complete combustion at the level of the catalyst 4. This combustion induces a significant increase in temperature up to a temperature θ _c at which the combustion of particles that clog the filter media. The NO ₂ molecules produced in association with the excess residual oxygen contained in the gases exhaust will catalyze this oxidation reaction. Thus, this reaction occurs at a temperature below the normal combustion temperature. During this oxidation, 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 .

Another operational mode consists in simultaneously measuring the temperature and the pressure at the level of the catalyst production means, thanks to the temperature probe 2 and to the pressure probe 3. 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 probe 3 is a conventional probe for measuring the absolute pressure. According to one variant, the pressure sensor 3 may be a differential pressure measuring probe, comprising a sensor located upstream of the filter and another downstream of said filter.

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. The determination of P _r indicating the clogging is made easily and arbitrarily by the skilled artisan. In practice and for example, the pressure P _r corresponds to the pressure measured with a new filter increased by 100 mbar.

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. With this information pressure the computer, always from values entered setpoint, can, depending on the level of against pressure, increase the injection time to reach a higher temperature.

EXAMPLE:

By way of non-limiting example, a filtration device used with an industrial vehicle engine, the supercharged Renault VI 620-45 engine, with a displacement of 10 liters and a power of 180 kW, is used. This engine equips urban buses.

• D'un catalyseur d'oxydation métallique à base de platine permettant l'oxydation totale du CO et des hydrocarbures à basse température ainsi que la transformation d'une partie du NO en NO₂, la teneur en platine était de 90 g par pied cubique.
• De filtres à particules IBIDEN, de type nid d'abeille en carbure silicium, montés en parallèle.
• Un système d'injection de gazole suivant le deuxième mode de réalisation représenté figure 3, le capillaire 12 utilisé était en inox de 1 mm de diamètre intérieur par 1,6 mm extérieur, quant au tube d'amené d'air 13, il était aussi en inox et avait pour dimension, 4 mm intérieur par 6 mm extérieur pour une longueur totale de 50 cm.
• Un boîtier électronique 8 commandant la post-injection de gazole. Une temporisation limite la durée de la post-injection à 20 s et correspond à une quantité injectée de 20 cm³ ensuite une programmation spécifique du boîtier permet d'obtenir au plus une post-injection toutes les 7 minutes.
• L'injecteur électromagnétique 9 était alimenté par la ligne 11 relié par un Té à la canalisation d'alimentation de la pompe à injection du moteur, permettant d'avoir une pression d'alimentation variant de 1 à 1,5 bars.

The filtration device is composed of:

• Of a platinum-based metal oxidation catalyst for the complete oxidation of CO and low temperature hydrocarbons as well as the conversion of a portion of the NO to NO ₂ , the platinum content was 90 g per cubic foot .
• IBIDEN particulate filters, silicon carbide honeycomb type, mounted in parallel.
• A diesel injection system according to the second embodiment shown figure 3 , the capillary 12 used was made of stainless steel 1 mm inside diameter by 1.6 mm outside, as for the air intake tube 13, it was also made of stainless steel and had the dimension, 4 mm inside by 6 mm outside for a total length of 50 cm.
• An electronic box 8 controlling the post-injection of diesel fuel. A delay limits the duration of the post-injection to 20 s and corresponds to an injected amount of 20 cm ^3, then a specific programming of the housing makes it possible to obtain at most one post-injection every 7 minutes.
• The electromagnetic injector 9 was fed by the line 11 connected by a tee to the supply line of the engine injection pump, allowing to have a supply pressure ranging from 1 to 1.5 bars.

The control unit has been set up so that the post-injection is triggered as soon as the back pressure reaches 150 mb and the gas temperature is above 300 ° C.

In these configurations, the bus has traveled more than 45,000 km without observing pressure drift, which shows that the post-injection system has done its job well by maintaining a constant temperature level sufficient for regeneration. filter is continuous despite the severe conditions of use.

A test was carried out after 15000 km of rolling on a pollution cycle representative of urban traffic conditions on the UTAC roller bank and gave the following remarkable results: TYPE L / 100 CO2 CO HC NOx particles Series 56.7 1420 4.06 1.06 23 0.43 Device 57.6 1452 0.20 0.03 21.5 0.03 Emissions in gram / kilometer.

These results demonstrate the effectiveness of this device, both regeneration material and pollution control on all pollutants.

The post injection method according to the invention associated with a filtration device using an oxidation catalyst is therefore particularly suitable for the treatment of the exhaust gases of public transit 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.

Thus, if the injection 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 different existing techniques in order to potentiate their effects and to obtain a device having a very high efficiency and robustness to allow a post injection of reliable diesel generating no parasitic hydrocarbon emission and to significantly increase the temperature of the exhaust gas to allow oxidation of the carbon particles retained on the filter and obtain excellent results in terms of filter regeneration, even in the case of vehicles whose engine speeds do not make it possible to obtain exhaust gases with a high temperature.

Claims (18)

1. A method for the post-injection of a regeneration liquid, particularly for the regeneration of a device for filtering exhaust gases produced by a diesel engine, this method being of the type wherein particulates, after being sent to an oxidation catalyst, are retained on a filtration means of said filtration device, in which:

   - the regeneration liquid comprises at least one hydrocarbon and/or at least one reducing agent,

   - the post-injection consists essentially in injecting, upstream of the catalyst, using post-injection means:

   * on the one hand, the regeneration liquid,

   * and on the other hand, at least one gaseous fluid, preferably compressed air,

   this regeneration liquid and this gaseous fluid together forming an aerosol suitable for spraying the regeneration liquid into the exhaust gases and for increasing their temperature, so as to accelerate the oxidation rate of said particulates and thereby contribute to the regeneration of the filtration device,
   characterized in that the regeneration liquid issuing from an injector is conveyed by a capillary contained in a line supplied with gaseous fluid, preferably compressed air; the capillary and the line are coaxial, and their respective openings are concentric and terminate in the exhaust pipe.
2. The method as claimed in claim 1, characterized in that a part of the gaseous fluid, preferably compressed air, passes through the same capillary as the regeneration liquid, up to the post-injection opening.
3. The method as claimed in claim 2, characterized in that a part of the gaseous fluid is mixed with the regeneration liquid before the post-injection.
4. The method as claimed in either of claims 2 and 3, characterized in that the flow of gaseous fluid, preferably compressed air, is maintained in the post-injection capillary, after the interruption of the post-injection of the regeneration liquid through this capillary, and during the time necessary for rinsing said capillary.
5. The method as claimed in any one of the preceding claims, characterized in that the temperature of at least a part of the post-injection means is kept lower than or equal to 120°C, preferably 100°C, while the engine is running.
6. The method as claimed in claim 5, characterized in that at least a part of the post-injection means is kept at a distance from the pipe in which the exhaust gases flow.
7. The method as claimed in any one of the preceding claims, characterized in that the regeneration liquid is selected:

   * from the group of hydrocarbons comprising oil refining products, preferably gasoline and diesel,

   * from the group of alcohols, preferably methanol,

   * from the group of reducing agents, preferably urea and ammoniacal solutions,

   * and mixtures thereof.
8. The method as claimed in any one of the preceding claims, characterized in that it further consists in:

   - measuring a temperature θ_m upstream of the oxidation catalyst,

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

   - if θ_m is equal to or greater than θ_r, initiating a post-injection of regeneration liquid.
9. The method as claimed in claim 8, characterized in that it further consists in:

   • measuring a pressure P_m upstream of the filtration system by a sensor (3), said pressure P_m reflecting the degree of obstruction of the filtration means (5) by the particulates,

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

   • if P_m is equal to or greater than the pressure P_r and if θ_m is equal to or greater than θ_r, initiating the post-injection of diesel.
10. The method as claimed in any one of the preceding claims, characterized in that the diesel injections are controlled, by means of at least one computer, taking account of the temperature θ_m data and possibly the pressure P_m data, to obtain the temperature increase desired for optimal regeneration of the filtration device.
11. A device for in particular putting into practice the post-injection method as claimed in any one of the preceding claims and comprising at least one exhaust pipe (1), at least one catalyst (4), and filtration means, further comprising:

    ■ regeneration liquid supply means (11),

    ■ means (15, 16, 17) for supplying pressurized gaseous fluid, preferably compressed air,

    ■ post-injection means including:

    ✧ at least one injector (9), preferably electromagnetic,

    ✧ at least one injector-holder (10), on which said injector is arranged,

    ✧ at least one capillary (12) starting from the injector (9) and terminating in at least one exhaust pipe (1) via at least one opening (14), upstream of the catalyst (4),

    ✧ at least one line (13) connected to the means for supplying pressurized gaseous fluid, preferably compressed air, and terminating in the exhaust pipe (1), via at least one opening (14), characterized in that:

    ✧ the capillary (12) and the line (13) are coaxial, and their respective openings (14) are concentric and terminate in the exhaust pipe (1),

    ✧ the capillary (12) is contained in the line (13),

    the device further comprising:

    ■ possibly at least one temperature sensor (2) for measuring θ_m, arranged on the exhaust pipe(s) (1), upstream of the catalyst (4),

    ■ possibly at least one pressure sensor for measuring P_m in the exhaust pipe and arranged on said pipe(s) upstream of the catalyst (4),

    ■ at least one computer (8) for controlling the post-injection, to which are subjected the regeneration liquid supply means (11), the means (15, 16, 17) for supplying pressurized gaseous fluid, preferably compressed air, the post-injection means, and the temperature (2) or pressure (3) sensor(s), if any.
12. The device as claimed in claim 11, characterized in that at least a part of the post-injection means, preferably at least the injector (9), is designed so as to avoid suffering thermal damage, that is, to remain at a temperature lower than or equal to 120°C, preferably 100°C, while the engine is running, and with this aim, is preferably arranged at a sufficient distance from the exhaust pipe (1).
13. The device as claimed in any one of claims 11 and 12, characterized in that the means for supplying pressurized gaseous fluid, preferably compressed air, are designed to permit the intake of gaseous fluid at the outlet of the injector (9), at the head of the capillary (12), so that the pressurized gaseous fluid, preferably compressed air, can flow with the post-injected regeneration liquid in the capillary (12).
14. The device as claimed in claim 13, characterized in that the means for supplying pressurized gaseous fluid, preferably compressed air, comprise a solenoid valve (16) controlling the intake of pressurized gaseous fluid, preferably compressed air, at the outlet of the injector (9), at the head of the capillary (12), to permit said fluid to flow with the regeneration liquid and, secondarily, to rinse the capillary (12) after the end of the post-injection, by maintaining, for some time, a flow of pressurized gaseous fluid, preferably compressed air, in the capillary (12).
15. The device as claimed in any one of claims 11 to 14, characterized in that the means for supplying pressurized gaseous fluid, preferably compressed air, and the post-injection means, preferably the injector - holder (10), are designed so that at least one calibrated orifice (18) is provided for the continuous intake of a flow of pressurized gaseous fluid, preferably compressed air, mixed with the regeneration liquid, at the inlet of the capillary (12), in order to produce an emulsion and further and preferably to perform the rinsing function, by maintaining, for some time after the closure, a flow of said gaseous fluid in the capillary (12).
16. The device as claimed in any one of claims 11 to 15, characterized in that the regeneration liquid supply means (11) are connected to the feed line of at least one mechanical injection pump (24) of the engine.
17. The device as claimed in any one of claims 11 to 16, characterized in that the regeneration liquid is selected:

    * from the group of hydrocarbons comprising oil refining products, preferably gasoline and diesel,

    * from the group of alcohols, preferably methanol,

    * from the group of reducing agents, preferably urea and ammoniacal solutions,

    * and mixtures thereof.
18. The device as claimed in any one of claims 11 to 17, characterized in that it comprises a temperature sensor (2) and a pressure sensor (3) and in that the computer (8) which is connected to the temperature sensor (2) and to the pressure sensor (3), is used to compare the values θ_m and possibly P_m measured respectively with the reference values θr and possibly P_r, and initiates the post-injection of regeneration liquid into the exhaust pipe (1), via the regeneration liquid supply means (11), the means (15, 16, 17) for supplying pressurized gaseous fluid, preferably compressed air, and the post-injection means, when the measurements θ_m and possibly P_m are equal to or higher than the reference values θ_r and possibly P_r.

Images