EP1581728A1

EP1581728A1 - Aid system for regeneration of a particle filter for an exhaust line

Info

Publication number: EP1581728A1
Application number: EP04700263A
Authority: EP
Inventors: Christine Rigaudeau; Yvan Agliany; Marion Wermester
Original assignee: Peugeot Citroen Automobiles SA
Current assignee: PSA Automobiles SA
Priority date: 2003-01-07
Filing date: 2004-01-06
Publication date: 2005-10-05
Anticipated expiration: 2024-01-06
Also published as: US20060201140A1; DE602004002557T2; US7328573B2; ATE340920T1; DE602004002557D1; ES2273201T3; EP1581728B1; WO2004070178A1

Abstract

A system for assisting regeneration of a particle filter of an exhaust line ( 3 ) of a diesel engine associated with, in particular: a particle filter ( 7 ); an oxidation catalytic converter ( 6 ); a common system ( 8 ) for feeding fuel to the cylinders of the engine; means ( 16 ) for adding to the fuel an additive adapted to reduce the combustion temperature of the trapped particles and propagate their combustion; and monitoring means ( 17 ) for triggering a phase of regeneration of the particle filter by combustion of the particles trapped therein during a phase of multiple injections of fuel; characterized in that the particle filter ( 7 ) is impregnated with a catalyst for oxidizing the hydrocarbons and CO present in the exhaust gases flowing through said particle filter.

Description

Aid system for the regeneration of a particulate filter for exhaust line.

The invention relates to the automotive industry. More specifically, it relates to the regeneration of particulate filters used in particular on the exhaust lines of diesel engines of vehicles of recent design. Diesel vehicles of recent design are fitted with particulate filters (DPFs) on their exhaust lines used to reduce their emissions of solid pollutants. These FAP collect soot on their walls which must be removed regularly to prevent the FAP from clogging, and restore it to its nominal efficiency. In addition, the clogging of the FAP gradually creates a negative pressure which is detrimental to the proper functioning of the engine. This elimination, called “regeneration of the FAP”, can be carried out by bringing the filter to a temperature higher than the combustion temperature of the soot (this normally being about 550 ° C.), by means of the exhaust gases which there circulating. To this end, a technical solution consists in: - adding to the fuel, for example when filling the tank, an additive for regeneration aid whose function is to lower the combustion temperature of the soot to around 450 ° C. and to provide available oxygen to propagate this combustion; in fact, this additive mixes with the soot during its formation in the combustion chamber, and is found within the soot bed which is deposited in the filter;

- And periodically carry out a post-injection or multiple injections of fuel upstream of the DPF, in particular in the engine cylinders during their expansion phase.

Post-injection or multiple injections have the effect of increasing the temperature of the exhaust gases and the amount of available hydrocarbons they contain. These hydrocarbons are converted on an oxidation catalyst placed upstream of the FAP according to an exothermic reaction which brings the exhaust gases to a temperature above 450 ° C. They then arrive on the soot bed, and the combustion of the soot occurs thanks to the high temperature of the exhaust gases and to the catalytic activity of the additive particles. It is propagated by the oxygen made available to the environment by the additive.

The regeneration aid additive is, for example, based on cerine CeO ₂ and / or ferric oxide Fe ₂ O ₃ , or on any metal oxide capable of giving off oxygen. The dosage of this additive is generally between a few ppm and 50 ppm of active material (cerium and / or iron). A drawback of this way of proceeding is that the periodic regeneration of the FAP allows the incombustible impurities constituted by mineral species to remain inside the filtering medium. These impurities are, to a large extent, residues of the regeneration aid additive. They gradually reduce the effectiveness of the FAP by fouling, which requires regular thorough cleaning of the FAP, for example every 80,000 km or every 120,000 km.

In order to further space out these thorough cleanings, it would be necessary to manage to reduce the amount of regeneration aid additive introduced into the fuel.

The object of the invention is to propose a technical solution making it possible to reduce this quantity, without however affecting the efficiency of the reduction of the pollutant emissions emitted with the exhaust gases. To this end, the subject of the invention is a system for assisting the regeneration of a particulate filter integrated in an exhaust line of a diesel engine of a motor vehicle, in which the engine is associated with different members, among which :

means for admitting air into the engine, means for recycling the exhaust gases from the engine at the inlet thereof,

- a turbocharger,

a particle filter of the type comprising a filtering medium intended to trap particles of soot present in the exhaust gases of said engine,

- an oxidation catalyst placed upstream of the particulate filter in the exhaust line or merged with it,

- a common fuel supply system for the engine cylinders, comprising electrically controlled injectors, associated with these cylinders,

means for adding to the fuel an additive intended to be deposited in the bed of soot particles, in order to lower the combustion temperature of the particles trapped in the filter and to propagate their combustion, means for acquiring information relating to different operating parameters of the engine and of the members associated with it, and

means for controlling the operation of the intake means, recycling means, the turbocharger and / or the fuel system for controlling the operation of the engine, these means being further adapted to trigger a regeneration phase of the filter particles by combustion of the particles trapped therein by initiating a phase of multiple injections of fuel into the engine cylinders during their expansion phase, characterized in that said filter medium of said particle filter is coated and / or impregnated with a material capable of constituting an oxygen reserve capable of propagating the combustion of soot during a regeneration operation of the particulate filter.

Said material can be cerium oxide. Said material can be a mixed oxide of cerium and zirconium.

The particulate filter can also be coated and / or impregnated with at least one catalyst promoting the initiation of reactions tending to reduce the polluting emissions of the engine.

The particle filter can also be coated and / or impregnated with at least one catalyst which promotes the initiation of the combustion of soot. Said catalyst can be a group VIII metal, such as platinum, palladium or rhodium or a mixture of such metals.

The distribution of the different materials may not be uniform in the filter. The material capable of constituting a reserve of oxygen can be preferably placed in the downstream area of the inlet channels of the filter. The catalyst favoring the initiation of the combustion of the soot can be preferably placed in the upstream zone of the inlet channels of the filter. The end part of the downstream zone of the filter can be devoid of material constituting a reserve of oxygen and catalyst.

The material constituting an oxygen reserve can be arranged in a preferred manner in the peripheral zone of the cross section of the filter. The catalyst favoring the initiation of the combustion of the soot can be preferably placed in the central zone of the cross section of the filter.

As will be understood, the invention consists in providing a coating and / or impregnation of the filtering medium of the FAP with a compound which acts as an oxygen reservoir allowing the propagation of the combustion reaction of soot during of the regeneration operation. This compound can also play a catalytic role in the initiation of the combustion of soot, but it should be understood that it is the propagation function of this combustion which constitutes the essential aspect of the invention.

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

- Figure 1 which shows schematically a vehicle diesel engine and the various members associated therewith; - Figures 2 to 4 which schematically, seen in longitudinal section, different examples of particle filters used in the context of the invention and highlight different possibilities of distribution of the compounds they contain;

- Figures 5 and 6 which schematically, seen in cross section, two examples of radial distribution of the compounds contained by a particle filter used in the context of the invention.

FIG. 1 shows a diesel engine of a motor vehicle which is designated by the general reference 1.

This diesel engine is associated with air intake means at the inlet 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 the exhaust gas from the engine at the inlet thereof are also provided and are designated by the general reference 4.

These means are then interposed for example between the outlet of the engine and the means 2 for admitting air into it.

The exhaust line can also be associated with a turbocharger designated by the general reference 5 and more particularly with the turbine portion thereof, in a conventional manner. Finally, the exhaust line comprises an oxidation catalyst designated by the general reference 6, disposed upstream of a particle filter designated by the general reference 7, disposed in the exhaust line.

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

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

These different injectors are associated with a common fuel supply manifold 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 to means for adding to this fuel an additive, for example based on cerine and / or ferric oxide (or any metal oxide capable of giving off oxygen), intended to be deposited on the particulate filter to lower the combustion temperature of the particles trapped in it.

In fact, this additive can 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 engine and the various members which 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 suitable computer 18 associated with storage means for information 19, and connected as input to different means for acquiring information relating to different operating parameters of this engine 1 and of these members, this computer 18 then being adapted to control the operation of the intake means 2, means recycling 4, the turbocharger 5 and / or the supply system 14 to control the operation of the engine 1 and in particular the torque generated by it as a function of the running conditions of the vehicle in a conventional manner.

Thus, for example, this computer 18 is connected to a differential pressure sensor 20 at the terminals of the assembly formed by the catalyst 6 and the particle filter 7, to temperature sensors 21, 22 and 23, respectively upstream of the catalyst 6, between this catalyst 6 and the particle filter 7 and downstream of this particle filter 7 in the exhaust line 3. The computer 18 can also receive information on the oxygen content of the exhaust gases from a Lambda λ probe designated by the general reference 24 in this figure, integrated in the exhaust line 3.

At output, this computer 18 is suitable for controlling the air intake means 2, the exhaust gas recycling means 4, the turbocharger 5, the means 16 for adding the additive to the fuel, the means 14 supplying fuel to the common rail 8 and the various injectors 9-12 associated with the cylinders of the engine 1.

In particular, this computer 18 is adapted to trigger a regeneration phase of the particle filter 7 by combustion of the particles trapped in it by initiating a phase of multiple injections of fuel into the cylinders of the engine 1 during their expansion phase.

The particles emitted by the engine 1 during its operation are in fact trapped in the particle filter. It should then be regenerated regularly by combustion of these particles. An exhaust line 3 of an internal combustion engine 1 according to the invention therefore comprises, in known manner, a reactor 6 containing an oxidation catalyst (for example a metal such as platinum) ensuring, by an exothermic reaction, the conversion of the hydrocarbons and CO contained in the exhaust gases into CO ₂ and water vapor. Then, according to the invention, the exhaust line 3 comprises a FAP 7 which has the particularity of being coated and / or impregnated over all or part of its surface and / or its volume with a compound such as a material belonging for example to the group of cerium oxide and / or mixed oxide of cerium and zirconium. This compound must be capable of constituting an oxygen reserve capable of propagating the combustion of the soot initiated during an operation for regenerating the FAP 7. It is then said that this compound has an “OSC function” (for “oxygen storage capacity”). ).

At the same time, this compound helps to lower the combustion temperature of the soot, as does the regeneration aid additive usually introduced into the fuel. However, the introduction of this additive remains necessary even with the use of a FAP 7 according to the invention. Indeed, the compound having an OSC function deposited on the FAP 7 and / or the impregnating agent (this last term meaning that it is present on the surface of the pores located inside the filtering elements constituting the walls of the FAP) ensures only surface contact with the soot. This effect may not be sufficient to lower the combustion temperature of the soot by itself in the proportions ensuring a regeneration of the FAP 7 as fast as desired for the envisaged applications. From this point of view, the addition of cerine and / or iron oxide (for example) to the fuel makes it possible to incorporate the regeneration aid additive within the soot themselves, which gives it optimal efficiency. However, the use of a FAP 7 according to the invention combined with the use of a regeneration aid additive provides an additional lowering of the soot combustion temperature, which is obviously very favorable from the point of view energy. In practice, it is conceivable that the combustion temperature of the soot can be lowered to 400 ° C where, previously, with the same or even greater quantity of regeneration aid additive, a combustion temperature was obtained. 450 ° C.

It goes without saying that when the compound exhibiting an OSC function is not distributed uniformly over the whole of the filter medium, it must be present in a privileged manner in the parts of the filter medium where the soot is mainly captured. This is, for example, the case of the surface of the filtering medium which constitutes the inlet of the FAP 7, in particular the surfaces defining the inlet channels of the FAP 7 when the latter has a honeycomb structure as it is classically known.

The compound having an OSC function may not be the only compound coating and / or impregnating the FAP 7. It can be used in conjunction with one or more catalysts intended to promote the initiation of the combustion of soot and / or other reactions tending to reduce polluting emissions from the engine, for example a metal such as platinum to catalyze the oxidation of hydrocarbons and CO, a catalyst for the treatment of nitrogen oxides, etc. It can therefore be envisaged that the conversion of hydrocarbons and CO takes place in part or in whole within the FAP 7 and not necessarily in a separate medium 6 upstream of the FAP 7. In this case, FIG. 1 would be modified, in that zones 6 and 7 would be confused, and the temperature sensor 22 removed.

It is possible, for example, to combine the compound having an OSC function with a “washcoat” deposited on the FAP 7. The addition of a washcoat on the filter composed of Ce oxide or of mixed Ce / Zr oxide, capable of providing oxygen during combustion contributes to improving the oxidation of soot, by lowering the initiation temperature of combustion, as well as the propagation of combustion.

The compound with an OSC function can be combined in addition with a catalyst formed by a metal from group VIII of the periodic table or a mixture of such metals, such as platinum and / or palladium and / or rhodium. Thus, it directly oxidizes soot (by availability of activated oxygen) or indirectly by exothermic reactions taking place on platinum, palladium or rhodium (by oxidation of hydrocarbons and CO). This reduces pollutant emissions and provides local temperature, which indirectly helps in the oxidation of soot.

Platinum and / or palladium and / or rhodium can be deposited only on a washcoat dΑI ₂ 0 ₃ or be mixed with the washcoat or the compound with OSC function.

The washcoat deposited on the FAP can be composed of alumina (large surface catalytic support) supplemented by Ce oxide (CeO ₂ ), and / or mixed oxide Ce _x Zr _y O ₂ , in variable proportion , these oxides can be intimately linked to alumina. The amount of washcoat can vary from a few grams / liter to a few tens of g / 1.

The quantity of precious metals must be sufficiently dispersed and stable, to remain accessible and effective in converting pollutants. The quantity of precious metals is dependent on the quantity of washcoat and can vary from a few tenths of grams to several grams on the entire particle filter, depending on the role to be given to these precious metals. To treat exhaust gases, several grams are usually required. FIGS. 2 to 5 schematically show various possible modes of distribution of the different compounds which have been mentioned over the length of the inlet channels 25 of the FAP 7. In the examples shown, the outlet channels 26 of the FAP 7 are devoid of impregnation , but it goes without saying that an impregnation could be practiced there if it is deemed useful in order to complete reactions which have been initiated in the input channels 25.

In the case of FIG. 2, there is an impregnation of the entire surface of the inlet channels 25 of the FAP 7 by a single layer 27 comprising at the same time the material with OSC function, a metallic catalyst and a washcoat. This layer 27 can be homogeneous in quantity and composition over the entire length of the channels 25. It is also possible to provide for these characteristics to be varied along the channels 25: - The quantity of metallic catalyst can be greater in the upstream area 28 than in the downstream area 29 of each channel 25, said upstream area representing 10 to 50% (for example) of the length of the channel 25; the aim is thus to achieve faster oxidation of hydrocarbons and CO; the catalyst content of the upstream zone 28 can be, for example, from 1.5 to 5 times that of the downstream zone 29;

- The amount of material with OSC function can be greater in the downstream area 29 than in the upstream area 28 of each downstream 25, said downstream area representing 10 to 50% (for example) of the length of the channel 25; the aim is thus to promote the initiation of the combustion of soot mainly in the downstream zone 29, that is to say where the soot tends to accumulate in a privileged manner.

In the case of FIG. 3, there is an impregnation of the upstream zone 28 of the channels 25 with a layer 30 comprising both the material with OSC function, the metal catalyst and the washcoat, and an impregnation of the downstream zone 29 with a layer 31 comprising only the OSC-functional material and the washcoat. Alternatively, the OSC material could be absent from the upstream area.

In the case of FIG. 4, there is an impregnation of the upstream zone 28 of the channels 25 with a layer 32 containing the OSC-functional material and the washcoat, said layer 32 itself being coated with a layer 33 containing the metal catalyst and the washcoat. As for the downstream zone 29 of the channels 25, it is only impregnated with the layer 32 of material with OSC function and of washcoat.

In all the configurations which have been exposed, it is also possible to choose not to provide a coating and / or impregnation of the downstream zone 29, or at least of its terminal part. It is indeed there that the impurities, ashes and various residues, remaining after the combustion of the soot tend to accumulate, and these impurities alter the functioning of the catalysts. Eliminating these catalysts in areas where they would, in any case, be less effective than in the rest of the FAP 7 makes it possible to save materials and limit the pressure losses of the gases inside the FAP 7.

Similarly, as can be seen in FIGS. 5 and 6, the distribution of the catalysts can be modulated according to the cross section of the FAP 7. FIG. 5 shows a FAP 7 seen in cross section. The lateral modules 34 are, for example, impregnated with a greater quantity of material with an OSC function than the most central modules 35. In this variant, the distribution of the material with an OSC function is substantially homogeneous inside each module. This may not always be the case, for example as shown in FIG. 6, where portions of the side modules 34 are also included in the zone of weakest impregnation so as to give the zone of weakest impregnation a cross section substantially circular.

Typically, the zone of strongest impregnation represents from 30 to 80% of the surface of the cross section of the FAP 7. In this zone, the amount of material with OSC function is typically of the order of 1.5 to 5 times that present in areas of weakest impregnation.

The purpose of such a distribution of the OSC function material is to carry out the oxygen supply in a privileged way at the place where it is more difficult to convert the soot, that is to say on the periphery of the FAP 7 where the conditions are the least favorable. The distribution of the other materials impregnating the FAP 7 can also be modulated over the cross section of the FAP 7, but not necessarily in the same direction as that of the material with OSC function. It is thus preferable to favor the most central modules 35 for impregnation with the metal catalyst, in order to convert the hydrocarbons and the CO preferably where the flow conditions and the thermal conditions are most favorable for this purpose. Again, typically, the areas with the highest impregnation can contain 1.5 to 5 times more metallic catalyst than the areas with the lowest impregnation.

In practice, it is advantageous to take advantage of the use of a FAP 7 according to the invention to reduce the quantity of regeneration aid additive used (of the order of 50% or more). This has the effect of reducing the amount of noncombustible residue that is deposited in the FAP 7, and therefore making its thorough cleaning less often necessary.

It should be understood that the application of a FAP 7 according to the invention to the exhaust lines of diesel engines is only a preferred application. A FAP 7 according to the invention could be used on the exhaust line of any type of internal combustion engine for which a FAP 7 would be useful.

Claims

1. A system for assisting the regeneration of a particulate filter integrated into an exhaust line (3) of a diesel engine of a motor vehicle, in which the engine (1) is associated with various members, among which: - means (2) for admitting air into the engine,

- means (4) for recycling the exhaust gas from the engine at the inlet thereof,

- a turbocharger (5),

- a particle filter (7) of the type comprising a filtering medium intended to trap soot particles present in the exhaust gases of said engine (1),

- an oxidation catalyst (6) placed upstream of the particulate filter (7) in the exhaust line (3) or merged with it,

- a system (8) for the common supply of fuel to the engine cylinders, comprising electrically controlled injectors (9, 10, 11, 12), associated with these cylinders,

- means (16) for adding to the fuel an additive intended to be deposited in the bed of soot particles, to lower the combustion temperature of the particles trapped in the filter (7) and propagate their combustion, - means (20, 21, 22) for acquiring information relating to different operating parameters of the engine and of the members associated with it, and

- Means (17) for controlling the operation of the intake means, recycling means, the turbocharger and / or the fuel system to control the operation of the engine, these means being further adapted to trigger a regeneration phase of the particle filter by combustion of particles trapped therein by initiating a phase of multiple injections of fuel into the engine cylinders during their expansion phase, characterized in that said filter medium of said particle filter (7) is coated and / or impregnated with a material capable of constituting an oxygen reserve capable of propagating the combustion of the soot during a regeneration operation of the particulate filter.

2. System according to claim 1, characterized in that said material is cerium oxide.

3. System according to claim 1, characterized in that said material is a mixed oxide of cerium and zirconium.

4. System according to one of claims 1 to 3, characterized in that the particle filter (7) is also coated and / or impregnated with at least one catalyst promoting the initiation of reactions tending to reduce the polluting emissions of the engine.

5. System according to claim 4, characterized in that the particle filter (7) is also coated and / or impregnated with at least one catalyst promoting the initiation of the combustion of soot.

6. System according to claim 4 or 5, characterized in that said catalyst is a group VIII metal, such as platinum, palladium or rhodium or a mixture of such metals.

7. System according to one of claims 1 to 6, characterized in that the distribution of the different materials is not uniform in the filter (7).

8. System according to claim 7, characterized in that the material capable of constituting an oxygen reserve and disposed in a privileged manner in the downstream zone (29) of the inlet channels (25) of the filter (7).

9. System according to claims 5 and 7 or 8, characterized in that the catalyst promoting the initiation of the combustion of soot is preferably placed in the upstream zone (28) of the inlet channels (25) of the filter (7 ).

10. System according to one of claims 7 to 9, characterized in that the end part of the downstream zone (29) of the filter (7) is devoid of material constituting a reserve of oxygen and catalyst.

11. System according to one of claims 7 to 10, characterized in that the material constituting an oxygen reserve is preferably arranged in the peripheral zone (34) of the cross section of the filter (7).

12. System according to claim 5 and one of claims 7 to

12, characterized in that the catalyst favoring the initiation of the combustion of the soot is preferably placed in the central zone (35) of the cross section of the filter (7).