EP1581727B1 - Aid system for regeneration of a particle filter in an exhaust line of a diesel engine - Google Patents

Abstract

A system for assisting regeneration of a particle filter in an exhaust line (3) of a motor vehicle diesel engine (1) associated with: air admission means (2); exhaust gas recycling means (4); a turbocompressor (5); a particle filter (7); a common system (8) for feeding fuel to the engine; means (16) for adding to the fuel an additive adapted to be deposited on the particle filter (7) to reduce the combustion temperature of particles trapped therein; means (20, 21, 22) for acquiring information relating to operation of the engine; and monitoring means (17) adapted to trigger a phase of regeneration of the particle filter by combustion of the particles trapped therein by triggering a phase of multiple injection of fuel. The filter (7) is impregnated with a catalyst for oxidizing hydrocarbons and CO present in the exhaust gases.

Description

The invention relates to the automotive industry and, more particularly, the depollution of internal combustion engines, in particular diesel engines.

Diesel motor vehicles of recent design are equipped on their exhaust systems, different devices for the treatment of pollutants produced by the combustion of fuel in the engine.

A first of these devices ensures the oxidation of the exhaust gas through the passage of these gases on an oxidation catalyst.

A second of these devices, generally disposed immediately downstream of the previous one, is a particulate filter (FAP) on which the particles (soot) produced by the combustion are deposited. Periodically, these soot must be burned, especially with the help of an increase in the temperature of the FAP or the exhaust gases, to prevent the filter from clogging and make it regain its original performance (operation called "Regeneration").

To assist this combustion of soot can be added to the fuel, using a suitable device, an additive such as ceria and / or iron oxide that mixes with soot and lowers their combustion temperature. On the other hand, every 80 000km or 120 000km, for example, a cleaning of the FAP is necessary to remove the additive and unburnt residues.

The performance of these oxidation and filtration functions in separate devices leads to the design of very cumbersome exhaust lines, or the need for thorough cleaning of the FAP that can be judged too frequent.

The object of the invention is to give the possibility to the manufacturer to reduce the size of the exhaust lines of diesel engines of motor vehicles and / or reduce the periodicity of thorough cleaning of the FAP necessary for the proper operation of the line of exhaust.

For this purpose, the subject of the invention is a motor vehicle comprising a diesel engine equipped with an exhaust line in which is integrated a particulate filter, air intake means in the engine, recycling means engine exhaust gas at its inlet, a turbocharger, a common fuel supply system for the engine cylinders, comprising electrically driven injectors, associated with these cylinders, means for adding an additive to the fuel intended to be deposited on the particulate filter, to lower the combustion temperature particles trapped therein, means for acquiring information relating to different operating parameters of the engine and associated members thereof, and means for controlling the operation of the admission means, recycling means , the turbocharger and / or the supply system for controlling the operation of the engine, these means being further adapted to trigger a regeneration phase of the particulate filter by combustion of the particles trapped therein by engaging an injection phase multiple fuel in the cylinders of the engine during their expansion phase, the particulate filter being impregnated with a catalyst for oxidation of hydrocarbons and CO present in the exhaust gas flowing through said particulate filter, and having a zone stronger impregnation by the oxidation catalyst

According to the invention, the zone of highest impregnation is located in the center of the cross section of the particle filter, over part of its length from the inlet face of the particulate filter, the surface of said zone of more high impregnation representing 20 to 70% of the cross section of said particulate filter and this zone of stronger impregnation being present on 10 to 60% of the length of the particulate filter from its inlet face, the end portion of the filter with particles being free from impregnation by the oxidation catalyst.

It is known from the document WO 01/12320 an exhaust line equipped with a particulate filter whose regeneration is operated continuously, at low temperature (that is to say below 400 ° C). The upstream portion of the filter is covered with a catalytic coating, licked by the exhaust gas in their progression towards the downstream part of the filter, this catalytic coating promoting the oxidation of the soluble organic fraction of the exhaust gas. The catalyst may be a metal or a mixture of metals.

Said metal may be a Group VIII metal such as platinum, palladium or rhodium, or a mixture of such metals.

As will have been understood, the essential feature of the invention is the carrying out of the oxidation of the exhaust gas and the filtration of the particles within the same reactor. This is achieved by impregnating the material constituting the FAP with an oxidation catalyst such as a metal, for example platinum.

• la figure 1 qui représente de façon schématique un moteur Diesel de véhicule et les différents organes associés à celui-ci ;
• la figure 2 qui représente schématiquement un exemple de FAP selon l'invention à imprégnation homogène ;
• les figures 3 à 6 qui montrent schématiquement d'autres exemples de FAP selon l'invention à imprégnation inhomogène.

The invention will be better understood on reading the description which follows, given with reference to the appended figures:

• the figure 1 which schematically represents a vehicle diesel engine and the various members associated therewith;
• the figure 2 which schematically represents an example of FAP according to the invention with homogeneous impregnation;
• the Figures 3 to 6 which schematically show other examples of FAP according to the invention with inhomogeneous impregnation.

We have shown on the figure 1 , a motor vehicle diesel engine which is designated by the general reference 1.

This diesel engine is associated with input air intake means thereof, which are designated by the general reference 2.

At the output, this engine is associated with an exhaust line which is designated by the general reference 3.

Means for recycling engine exhaust gas at the inlet thereof are also provided and are designated by the general reference 4.

These means are then interposed for example between the output of the engine and the air intake means 2 therein.

The exhaust line may also be associated with a turbocharger designated by the general reference 5 and more particularly to the turbine portion thereof, in a conventional manner.

Finally, the exhaust line comprises, according to the invention, a housing 6 enclosing a particulate filter designated by the general reference 7, the particulate filter being impregnated with an oxidation catalyst. The "oxidation" and "filtration" functions are therefore performed in the same medium, unlike the prior art where the gases successively pass through an oxidation medium and a filtration medium each dedicated to one of these functions and not to the other.

The engine is also associated with a common fuel system of the cylinders. This system is designated by the general reference 8 in this figure and comprises, for example, electrically operated injectors associated with these cylinders.

In the exemplary embodiment shown, the engine is a four-cylinder engine and therefore comprises four electrically operated injectors, respectively 9, 10, 11 and 12.

These different injectors are associated with a common fuel feed ramp designated by the general reference 13 and connected to fuel supply means designated by the general reference 14, comprising for example a high pressure pump.

These supply means are connected to a fuel tank designated by the general reference 15 and means for adding to this fuel an additive intended to be deposited on the particle filter to lower the combustion temperature of the trapped particles. In this one.

In fact, this additive may, for example, be contained in an auxiliary tank designated by the general reference 16 associated with the fuel tank 15 to allow the injection of a certain amount of this additive into the fuel.

Finally, this motor and the various components that have just been described are also associated with means for controlling their operation designated by the general reference 17 in this figure, comprising, for example, any appropriate calculator 18 associated with storage means. information 19, and input to different means for acquiring information relating to different operating parameters of the engine and these bodies, the computer being then adapted to control the operation of the admission means, recycling means, turbocharger and / or the power system, so as to control the operation of the engine and in particular the torque generated by it according to the driving conditions of the vehicle in a conventional manner.

For example, this calculator is connected to a differential pressure sensor 20 at the terminals of the particulate filter 7 and to temperature sensors 21, 22 respectively upstream of the particulate filter and downstream of this particulate filter. in the exhaust line.

The computer may also receive oxygen content information of the exhaust gas from a Lambda λ probe designated by the general reference 23 in this figure, integrated into the exhaust line.

At output, this computer is adapted to control the air intake means, the exhaust gas recycling means, the turbocharger, the means for adding fuel to the additive, the fuel supply means of the common rail and the various injectors associated with the engine cylinders.

In particular, this computer is adapted to trigger a regeneration phase of the particulate filter by combustion of the particles trapped therein by engaging a phase of multiple injections of fuel in the cylinders of the engine during their expansion phase.

The particles emitted by the engine during its operation are indeed trapped in the particulate filter. It is then necessary to regenerate it regularly by combustion of these particles.

In conventional systems where the oxidation and filtration functions are separated, the engine, during its normal operating phases, emits exhaust gases containing mainly hydrocarbons, CO, CO ₂ , water vapor , NO _x , oxygen and particles at a temperature of 180-200 ° C. Passage into the reactor containing the oxidation catalyst (generally a metal such as platinum) converts about 90% or more of CO, hydrocarbons with oxygen to CO ₂ and water vapor. The combustible fraction of the soot (so-called "soluble organic fraction", abbreviated to SOF), in the form of condensed hydrocarbons on the particles, is also treated by the oxidation catalyst. At the outlet of the oxidation catalyst, the exhaust gas therefore contains only significantly more residual oxygen, CO ₂ , water vapor (these two compounds in greater quantities than at the inlet of the catalyst). oxidation), NO _x and particles. These discharges then enter the FAP, where they are purified of the particles which are deposited on the walls of the filter. Releases to the atmosphere then significantly contain only oxygen, CO ₂ , water vapor and NO _x . However, these NO _x can be processed in an NO _x treatment device, such as a NO _x trap, and thus not be released to the atmosphere.

In the system according to the invention, the reactor containing the oxidation catalyst is removed as such. Its function is transferred to the particle filter 7 which consists of a material traditionally used for this purpose (Such as a ceramic, for example silicon carbide), but which is impregnated with an oxidation catalyst such as platinum and / or palladium. This catalyst is carried by a "washcoat" of oxide (Al ₂ O ₃ for example), which can also contain compounds having a function OSC (storage of oxygen): for example materials of the cerium oxide group and / or mixed oxide of cerium and zirconium. This impregnation may concern only the surface of the pores, or the entire material. Optionally, this material can be adapted, from the point of view of its porosity and the distribution of the pore diameter, so that the catalyzed oxidation reaction occurs there with optimal efficiency, comparable to that which is observed in the conventional separate oxidation reactors, without producing too much back pressure which would hinder the flow of gases. The pore size is centered on about 9 μm in a conventional particle filter. In an impregnated particle filter according to the invention, this pore size can be centered on sizes of 11 μm up to 20-30 μm. These values are given only as examples.

If an exhaust line comprising a modified FAP 7 according to the invention is compared with an exhaust line comprising a conventional FAP located immediately downstream of an oxidation catalyst, it can be said that at the inlet modified FAP 7 according to the invention, there are emissions of gases and particles identical to those which usually enter the oxidation reactor. At the outlet of the FAP 7 modified according to the invention, there are gas emissions identical to those coming out of the FAP of the prior art.

A notable advantage of the invention is that SOF soot is not treated before the soot passes on the FAP 7. It is thus available to make soot combustion easier during regeneration phases thanks to the heat released locally by burning SOF.

As has been said, periodically the FAP 7 undergoes a regeneration phase, during which soot which partially clog it is burned. The timing of this regeneration can be chosen in different ways. Regeneration can be systematically decided after the vehicle has traveled a given distance since the last regeneration date. It can also be triggered when the differential pressure sensor 20 finds a significant pressure differential between the incoming gases and the outgoing gases, sign of a start of clogging of the FAP 7. The trigger can also be decided by an estimate of the amounts of accumulated soot in FAP 7 after consulting a map based on the type of taxiing performed.

For this regeneration, a regeneration aid additive, such as ceria, can be added to the fuel which lowers the soot combustion temperature to about 450 ° C and provides available oxygen for this combustion. And at the moment of regeneration, it is possible to carry out an additional injection of fuel upstream of the FAP 7, for example by switching on a multiple injections phase in the cylinders of the engine 1 during the expansion phase. This additional injection is intended to increase the temperature of the exhaust gas and their hydrocarbon and CO contents, compared to the normal operating phases of the engine 1.

In conventional oxidation reactor and separate FAP systems, the additional injection is carried out before the oxidation reactor. It partially converts CO and additional hydrocarbons with oxygen consumption, increasing the temperature of the gases up to 450 ° C and more, thus allowing soot combustion in the FAP to be burned. The regeneration aid additive assists the propagation of combustion within soot.

In the system according to the invention, all the reactions just mentioned take place within FAP 7 directly on the filter media impregnated with the catalyst which constitutes it. In particular, the exothermic conversion reaction of hydrocarbons and CO emitted in large quantities takes place in the immediate vicinity of the soot bed, which makes it even more effective to increase the temperature of the soot, and thus initiate their combustion.

In addition, this exothermic reaction being more effective, it can reduce the amount of additive. At equal filtration volume, slower fouling is therefore observed by unburned residues.

In addition, instead of dealing with two reactors clearly separated or contiguous to each other, in the case of the invention there is no longer any more than a single reactor 6. This makes the assembly of the exhaust line 3 easier.

The figure 2 schematically represents in cross-section an example of FAP 7 of circular section divided into several modules 24. These modules 24 are impregnated with catalyst homogeneously on their section and on their length.

According to a preferred variant of the invention, the impregnation of the FAP 7 by the oxidation catalyst is not carried out homogeneously. The amount of catalyst is distributed favorably in FAP 7 zones the most favored thermally and where the gas flows are the most important, to increase the conversion of CO and hydrocarbons, and to prevent catalytic aging of the filter in the most heat-stressed areas.

The distribution of the catalyst may be inhomogeneous in the radial direction of FAP 7 and / or in the axial direction of FAP 7.

When the FAP 7 is implanted in the exhaust line, the trajectory of the gas flows from the combustion chamber leads to a flow gradient inside the FAP 7. The importance of this gradient depends on the operating conditions of the FAP 7. and the shape of the connecting cone between the main exhaust line and the FAP 7. The phenomenon results in higher gas velocities in the center of the FAP 7 while the gas flows are significantly reduced when one moves radially towards the periphery of the FAP 7. This phenomenon also has another consequence, namely that the temperatures in the center of the FAP 7 are higher than those at the periphery of the FAP 7. This phenomenon is accentuated by some particulate filters with high conductivity (those based on SiC for example) relative to a conventional catalyst. The temperature has a tendency to evacuate strongly towards the periphery and the length of the FAP 7.

To take account of this phenomenon, it is proposed to adopt distributions of the impregnation of FAP 7, such as those schematically Figures 3 to 6 .

The figure 3 shows a FAP 7 seen in cross section. The side modules 25 are impregnated with a smaller amount of catalyst than the more central modules 26.

In this variant, the distribution of the catalyst is substantially homogeneous within each module. This may not always be the case, for example as represented on the figure 4 , where portions of the lateral modules 25 are also included in the zone of highest impregnation, so as to give the zone of greater impregnation a substantially circular cross section.

Typically, the zone of highest impregnation represents from 20 to 70% of the surface area of the cross section of the FAP 7. In this zone, the amount of catalyst is typically of the order of 1.5 to 5 times that present in the areas of lower impregnation.

In addition to or in place of this particular radial distribution, it is possible to provide a non-homogeneous catalyst distribution in the longitudinal direction of the FAP 7.

In the example shown on the figure 5 , where the FAP 7 is shown schematically in longitudinal section, the zone of higher impregnation 27, besides not covering the entire cross section of FAP 7, is only present for part of the length of the FAP 7, typically 10 to 50%, or even 60% of this length from the inlet face 28 of the FAP 7. In the remainder of the FAP 7, the impregnation is carried out with a smaller and homogeneous amount of catalyst to form a zone 29 of lower impregnation.

In the variant of the figure 6 , where the FAP 7 is shown diagrammatically in longitudinal section, the zone of lower impregnation 29 stops before the exit face 30 of the FAP 7, for example, as shown, at the end of the zone of stronger impregnation 27. In the end portion 31 of FAP7, there is therefore a non-catalyzed zone. In fact, in this end portion 31 where the ash of the additive of the tank 15 and the various other impurities tend to accumulate, the catalyst has a lower efficiency than in the area closer to the inlet of the FAP 7. It is therefore less useful to carry out an impregnation in this end portion 31, and completely eliminate it allows to save material, as well as to limit the pressure losses of the combustion gases. Of course, this absence of catalyst in the end portion 31 of the FAP 7 is also applicable in the case where the impregnation of FAP 7 by the catalyst is identical in all the areas where this impregnation exists.

Other elements than those described and represented can be added to the exhaust line 3 to give it additional features or to improve the existing functionalities, for example, as mentioned above, a NO _x trap .

It is possible to take advantage of the invention in two different ways.

One way is to keep the entire oxidation catalyst-FAP its usual volume. In doing so, the volume available for the deposition of the soot is increased since it can now be carried out in the whole of the assembly and not only in its part FAP. This makes it possible to delay the clogging of the FAP and to have to perform its regenerations and thorough cleanings only at a reduced frequency compared to to the prior art (the thorough cleaning may take place, for example, that every 160 000km or more, depending on the vehicles concerned, instead of every 80000km or 120 000km).

A second way is to reduce the size of the oxidation catalyst-FAP assembly, to a size providing a sufficient volume for soot deposition sufficient to impose a thorough cleaning frequency of the FAP comparable to that practiced with the exhaust lines of the prior art, in which the oxidation catalyst is distinct from the FAP. The advantage of the invention lies in the smaller size of the assembly.

The invention finds a preferred application to the exhaust lines of diesel engines, but it can be applied to the exhaust line of any type of internal combustion engine for which it would be necessary to use a particulate filter.

Claims (3)

1. Automobile vehicle comprising a diesel engine provided with an exhaust line in which a particle filter is integrated, with means (2) for the admission of air into the engine, with means (4) for recycling the exhaust gases of the engine at the inlet thereof, with a turbocompressor, with a system (8) for the common supply of fuel to the cylinders of the engine, comprising electrically operated injectors (9, 10, 11, 12) associated with these cylinders, with means (16) for the addition to the fuel of an additive intended to be deposited on the particle filter (7), to reduce the combustion temperature of the particles trapped therein, with means (20, 21, 22) for the acquisition of information relating to various parameters for the functioning of the engine and with organs associated therewith, and with means (17) for monitoring the functioning of the admission means, with recycling means, of the turbocompressor and/or of the supply system to monitor the functioning of the engine, these means being further adapted to trigger a regeneration phase of the particle filter (7) by combustion of the particles trapped therein by triggering a phase of multiple injections of fuel in the cylinders of the engine during their expansion phase, the particle filter (7) being impregnated with a catalyst for oxidation of the hydrocarbons and of the CO present in the exhaust gases circulating through the said particle filter, and having a zone of stronger impregnation (27) by the oxidation catalyst, characterized in that the said zone of stronger impregnation is situated in the centre of the cross-section of the particle filter (7), over a part of its length from the inlet face of the particle filter (7), the area of the said zone of stronger impregnation (27) representing 20 to 70% of the cross-section of the said particle filter (7) and this zone of stronger impregnation being present over 10 to 60% of the length of the particle filter (7) from its inlet face (28), the terminal part (31) of the particle filter (7) being without impregnation by the oxidation catalyst.
2. System according to Claim 1, characterized in that the said catalyst is a metal or a mixture of metals.
3. System according to Claim 2, characterized in that the said metal is a metal of the group Viii such as platinum, palladium or rhodium, or a mixture of such metals.

Images