FR2927118A1 - Particle filter for exhaust pipe of supercharged internal combustion engine, has exhaust gas input channels situated close to central axis of monolithic hub and having circulation part whose length is shorter than that of output channels - Google Patents

Abstract

The filter (12) has a monolithic hub (120) with exhaust gas input and output channels (124, 125) separated by porous walls, extending longitudinally between a concave input surface (130) and concave output surface (131) of the hub. Each of the channels has an exhaust gas circulation part and a closed part. The closed parts of the channels are situated on a side of the surfaces (130, 1231) of the hub, respectively. The input channels are situated close to a central axis (Z) of the hub, and the circulation part of the channels (124) has a length shorter than that of the channels (125).

Description

TECHNICAL FIELD RELATING TO THE INVENTION The present invention relates to a particulate filter of an exhaust pipe of an internal combustion engine having a matrix with adjacent channels separated by porous walls, extending longitudinally along a central axis of the matrix between an inlet face and an outlet face of the exhaust gas, and having an exhaust gas circulation part and a closed part, channels of which said channels are Input have their closed portion located on the side of the output face of the matrix and so-called output channels have their closed portion located on the side of the input face of the matrix. It also relates to an exhaust pipe of an internal combustion engine comprising such a particulate filter and an internal combustion engine comprising such an exhaust pipe. BACKGROUND OF THE INVENTION Internal combustion engines emit unburned hydrocarbons, soot particles and pollutant nitrogen oxide molecules in their exhaust gases. In order to limit these pollutant emissions, exhaust gas treatment devices are located on the exhaust line downstream of the combustion chamber.

These treatment devices comprise in particular a particulate filter placed downstream of an oxidation catalyst in the direction of flow of the exhaust gas. This particulate filter operates in two alternating operating phases: in a first phase, called normal operation, it traps the soot particles. In a second phase, known as active regeneration of the particulate filter, the particles trapped inside the filter are burned and the non-polluting gases from their combustion are conveyed to the outside of the engine in the exhaust gas. A particulate filter is conventionally formed of a monolithic porous ceramic matrix that comprises a multitude of channels. These channels are alternately open on an input or output face of the matrix. The exhaust gases enter the open channels on the inlet face of the particle filter matrix, pass through the porous sidewalls of these channels and exit the particle filter through the open channels on the outlet face of the filter. The particles present in the exhaust gas do not pass through the porous sidewalls of the channels, and remain trapped in the open channels on the inlet face of the particle filter matrix. The temperature at the inlet of the particulate filter during the active regeneration phase reaches a value between 550 and 650 ° C., approximately equal to 620 ° C. When the exhaust gases pass through the particulate filter during the active regeneration thereof, they become heated in contact with the burning particles. Their temperature is therefore greater downstream of the filter than upstream. These exhaust gases evacuate the heat generated by the combustion of the particles towards the outside of the particulate filter. Under certain conditions, this evacuation of the heat can become insufficient. For example, in the case of the engine idling during the regeneration of the filter, the flow of exhaust gas in the filter decreases sharply and no longer allows to evacuate the heat generated by the combustion of the particles. The combustion reaction accelerates because the oxygen content increases and the temperature in the particulate filter increases rapidly: it is called runaway combustion. The runaway of combustion may also be due to the presence of an excessive amount of particles trapped in the particulate filter. This runaway can cause degradation of the particulate filter, or even its destruction because the monolith can crack. It is therefore sought to minimize the risk of runaway combustion of particles in the particulate filter. For this, it is known, for example, to place absorption zones with high thermal capacities in the filter which absorb and dissipate the heat generated by the combustion of the particles. OBJECT OF THE INVENTION The object of the present invention is to provide a simple particulate filter to be made and which limits the risks of runaway of the combustion reaction of the particles trapped in a particulate filter during its regeneration.

For this purpose, it is proposed according to the invention a particulate filter as defined in the introduction, wherein at least the inlet channels located near the central axis of the matrix have a circulation portion of shorter length than that of the other channels. The exhaust gas passing through the particulate filter is hotter at the center of the exhaust pipe than at the periphery of the pipe because it is not in contact with the outer walls of the filter and dissipates less energy. The runaway of the combustion is favored by the heating of the exhaust gases flowing in the center of the particulate filter in contact with the particles in combustion. According to the invention, the length of the circulation part of the inlet channels through which the exhaust gases enter the particle filter is smaller when these input channels are close to the axis of the matrix than when they are located on the periphery of the matrix. The exhaust gases passing through the central inlet channels of the particulate filter are thus less in contact with the particles in combustion.

The amount of particles trapped in the central input channels is also smaller than in the peripheral input channels and the exhaust gases passing through these central input channels are in contact with a smaller amount of burning particles. The heating of the exhaust gases flowing in the center of the matrix of the particulate filter is therefore limited. The risks of runaway combustion are then reduced. The temperature in the particulate filter is more homogeneous, and the distribution of particles trapped in the particulate filter is more uniform. According to a first advantageous characteristic of the particulate filter according to the invention, the inlet and outlet channels located near the central axis of the matrix have a circulation portion of shorter length than that of the other channels. Such a particle filter can easily be obtained directly by molding the matrix, or by machining a conventional cylindrical matrix.

Advantageously then, said input and output faces of the matrix are concave. Thus, the total length of the channels of the matrix decreases regularly from the periphery of the matrix to its center. The closed areas preferably having identical lengths, the length of the channel circulation parts decreases regularly from the periphery of the matrix to its center. Alternatively, said input face of the matrix is plane and said output face is concave or said input face of the matrix is concave and said output face is flat.

Likewise, the length of the channel circulation portions then regularly decreases from the periphery of the die to its center. According to another advantageous characteristic of the particle filter according to the invention, the input channels located near the central axis of the matrix have a closed portion of greater length than that of the other channels. Thus, the length of the circulation portions of the input channels located near the axis of the matrix is smaller than that of the other channels. Advantageously then, said input and output faces of the matrix are plane. It is then possible to use a conventional cylindrical matrix, with planar input and output faces.

It is also proposed according to the invention an exhaust pipe of an internal combustion engine comprising a particulate filter as described above. The invention finally relates to an internal combustion engine comprising such an exhaust pipe.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description, with reference to the appended drawings, given by way of non-limiting example, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: FIG. 1 is a diagrammatic view of various components of an internal combustion engine comprising a particle filter according to the invention, FIG. 2 is a longitudinal sectional view along a plane P shown in FIG. 2 is a front view of the particle filter matrix of FIG. 2; in longitudinal section of a matrix of a particle filter according to a second embodiment of the invention; FIG. 5 is a longitudinal sectional view of a matrix of a particle filter according to a variant of the second Embodiment of the Invention - Figure 6 is a longitudinal sectional view of a matrix of a particulate filter according to a third embodiment of the invention. For the sake of simplification of the figures, the references designating similar elements of the particle filter in FIGS. 2 to 6 have been preserved from one figure to another. FIG. 1 shows a supercharged internal combustion engine comprising a combustion chamber 23 supplied with fresh air through an intake line 300 and opening downstream on an exhaust line 400. The intake line 300 comprises an intake pipe 4 in which fresh air circulates. The fresh air flow rate is measured at the inlet of the intake duct 4 by an air flow meter 1. The engine comprises a turbocharger 14 comprising two turbines 2, 9. The driving turbine 9 is placed in a duct. exhaust 70 and drives the driven turbine 2 placed in the intake pipe 4 to compress the fresh air circulating there.

As this compression has the effect of heating up the air, an air cooler 3 is provided on the path of the intake duct 3 which cools the air leaving the turbocharger 14. The intake duct 4 opens into a manifold 6. It comprises upstream of this manifold 6 an intake flap 5. The orientation of the intake flap 5 relative to the axis of the intake duct 4 controls the flow of fresh air entering the manifold 6. The manifold 6 is connected to an intake valve 21 of a cylinder 20 of the engine. The compressed air enters via this intake valve 21 into a combustion chamber 23 of the cylinder 20 and an injector 8 is provided which injects the fuel into this chamber. After the combustion, the residual exhaust gases are expelled from the combustion chamber 23 through an exhaust valve 22 in the exhaust line 70 of the exhaust line 400. Part of this exhaust gas is taken by a recirculation circuit 17 which brings them, after passing through an air cooler 15, to the collector 6 where they mix with the fresh air arriving from the intake pipe 4. The exhaust gas supply in the manifold 6 is regulated by a valve 13 called EGR (Exhaust Gas Recirculation). The exhaust gases that are not directed in the recirculation line 17 flow in the exhaust pipe 70 to arrive at the driving turbine 9 of the turbocharger 14. They then pass through an oxidation catalyst 11 and a particulate filter 12 of the exhaust line 400 before being released into the atmosphere. The engine advantageously comprises an electronic control unit (ECU) 30 which controls the actuation of the intake flap 5 and the EGR valve 13 to regulate the flow of air into the manifold 6 and therefore the amount of air introduced into the combustion chamber. The electronic control unit 30 also controls the amount of fuel injected by the injector 8 into the combustion chamber as well as the moment of this injection. When the quantity of particles trapped in the particle filter 12 reaches a threshold value, the active regeneration of the particle filter 12 is triggered. The quantity of particles trapped in the particulate filter 12 is estimated by the electronic control unit 30 from, for example, information given to it by two probes 18, 19 of pressures placed in the exhaust pipe 70 on the other hand. other of the particulate filter 12.

The electronic control unit 30 also receives here other information transmitted by different sensors of the engine, including for example the flow meter 1 which measures the flow of fresh air at the inlet of the intake pipe 4, a sensor of temperature 7 and a oxygen sensor 10 located upstream of the turbine 9 of the turbocharger 14 and a temperature sensor 16 located upstream of the particle filter 12, just before its inlet. This information makes it possible in particular to regulate the temperature of the exhaust gases passing through the particulate filter 12 with a view to its active regeneration. An additional injection nozzle 100 passes through the wall 50 of the exhaust pipe 70 upstream of the oxidation catalyst 11 and the particulate filter 12. This injection nozzle 100 is here placed downstream of the turbocharger 14. injection of fuel directly into the exhaust pipe 70 through the injection nozzle 100 is also controlled by the electronic central unit 30.

The particulate filter 12 comprises a monolithic matrix 120 made of refractory ceramic, for example cordierite. This matrix 120 is made by molding or extrusion. This matrix 120 is for example of cylindrical shape of revolution about an axis of symmetry. When the particulate filter 12 is in place in the exhaust pipe 70, this axis of symmetry is parallel to or coincident with the axis of the exhaust pipe. The die 120 has a lateral surface 121, an inlet face 130 through which the exhaust gases enter and an outlet face 131 through which the exhaust gases exit when the particulate filter 12 is positioned in the fuel line. exhaust 70 on the exhaust path. Alternatively, the matrix may have a volume delimited by an ovoid surface truncated at its two longitudinal ends along an axis 7 parallel to the axis of the pipe. The die 120 has a number of adjacent channels 124, 125 separated by porous walls, extending longitudinally between the input face 130 and the output face 131 of said die 120.

These channels 124, 125 have for example a square section, as shown in Figure 3. Alternatively, they may have a circular, oval, octagonal or rectangular section. The section of these channels 124, 125 is preferably constant over their entire length. Alternatively, it is possible to envisage channels whose section varies regularly along the matrix, for example channels having a frustoconical shape. Typically, the diameter D of the matrix 120 is between 15 and 30 cm (variable depending on the need), and its length L is between 20 and 50 cm (variable depending on the need). The section of the channels 124, 125 has a side of length S between 1 and 5 mm. Each channel 124, 125 includes a hollow exhaust gas circulation portion in which the exhaust gas is free to circulate, and a closed closed portion through which the exhaust gas does not flow. This closed portion is for example closed by a plug 122, 123. This plug 122, 123 is located at one end of the channel 124, 125, either on the side of the input face 130 of the die, or on the side of the face 131 of the die 120 of the die 120. The plugs 122 located on the side of the input face 130 of the die are called plugs 122 before, while the plugs 123 located on the side of the exit face 131 of the die are called plugs 123 back.

Thus, the channels 124, 125 can be divided into two groups: the inlet gas channels 124 are closed off by a rear plug 123 and the exhaust gas exit channels 125 are closed by a plug 122 before . As can be seen in FIG. 3, where the input channels 124 are shown in white and the output channels 125 are shaded, the input and output channels 124 are preferably alternately distributed in the matrix 120. 8 The plugs 122 and 123 forwards are made for example in the same material as the matrix 120 of the particulate filter 12. Alternatively, they may be made of another refractory ceramic material.

According to a particularly advantageous characteristic of the invention, at least the inlet channels 124 located near the central Z axis of the matrix 120 have a circulation portion of shorter length than that of the other channels 124, 125. a first embodiment shown in Figures 2 and 3, the input faces 130 and 131 output of the matrix 120 are concave. This shape of the input and exit faces 130 and 131 is obtained either directly during the molding of the die 120, or by machining the die 120. The plugs 123 rear and 122 before which seal the channels 124 input and 125 output are preferably here the same length.

The entrance 130 and exit 131 faces of the matrix 120 being concave, they are curved towards the interior of the particle filter 12, so that the total length L1 of a channel 124, 125 of the matrix 120 is all the weaker as this channel 124, 125 is close to the axis Z of symmetry of the matrix 120.

Consequently, the length of the circulation portion of each channel 124, 125 is all the smaller as this channel 124, 125 is close to the axis Z of symmetry of the matrix 120. The length L2 of the circulation part an inlet channel 124 is measured between an inner face 127 of the front plug 122 facing the interior of the particle filter 12 and the exit face 131 of the die 120. The length of the circulation portion of a output channel 125 is measured between an inner face 126 of the rear plug 123 facing inwardly of the particle filter 12 and the input face 130 of the die 120. The length of the input channels 124 and 125 output of the matrix 120 decreases regularly from the length of the peripheral channels furthest from the Z axis of symmetry of the matrix 120, up to the length of the channel or channels extending along the axis Z of symmetry. The difference in length between the peripheral channels furthest from the Z axis and the channels closest to this Z axis is here preferably between 5 and 15 cm. For a matrix 120 of length L equal to 30 cm, this difference is for example equal to 10 cm. According to a second embodiment of the particle filter according to the invention, shown in FIG. 4, said input face 130 of the matrix 120 is plane and said outlet face 131 is concave. This form of the exit face 131 is obtained either directly during the molding of the die 120, or by machining the die 120. As in the first embodiment, the rear plugs 123 and 122 before which seal the input channels 124 and 125 output preferably have the same thickness here. Since the exit face 131 of the die 120 is concave, it is curved towards the inside of the particle filter 12, so that, as in the first embodiment, the total length of the inlet channels 124 and 125 The output channel is all the smaller as these input and output channels 124 are close to the symmetry Z axis of the matrix 120. These lengths decrease regularly here since the length of the peripheral channels farthest from the Z axis of symmetry of the matrix 120, up to the length of the channels extending along the Z axis of symmetry. The difference in length between the peripheral channels furthest from the Z axis and the channels closest to this Z axis is here preferably between 1 and 10 cm. For a matrix 120 of length L equal to 30 cm, this difference is for example equal to 5 cm. According to a variant of this second embodiment of the particle filter according to the invention, shown in Figure 5, said input face 130 of the die 120 is concave and said output face 131 is flat. This embodiment is similar in all respects to the second embodiment described above. According to a third embodiment of the particle filter 12 according to the invention, represented in FIG. 6, the input 130 and output 131 faces of the matrix 120 are planar. The rear plugs 123 closing the input channels 124 of the matrix 120 of the particle filter 12 have a length E which increases as the input channel 124 is close to the Z axis of said matrix 120. the length L3 of the circulation portion of an inlet channel 124, measured between said inlet face 130 of the die 120 and the inner face 126 of the rear plug 123, is all the smaller as this channel 124 The inlet plugs are close to the Z axis of symmetry of the die 120. Here, the plugs 122 before closing off the outlet channels 125 of the die 120 of the particle filter 12 have a constant length E2. The circulation parts of the output channels 125 thus have here all the same length L4. Whatever the embodiment of the particulate filter 12, when it is in place in the exhaust pipe 70, the exhaust gases enter the inlet channels 124 open on the inlet face 130 of the matrix 120. These input channels 124 being closed by a rear plug 123 on the side of the outlet face 131 of the die 120, the exhaust gas can pass through the particle filter 12 only through the d channels. entrance 124.

The exhaust gases are thus forced through the porous sidewalls of the inlet channels 124 to circulate in the outlet channels 125 in order to pass through the particulate filter 12 and to join the exhaust pipe 70. The porous walls of the inlet channels 124 have pores smaller than the average size of the particles present in the exhaust gas, so that these particles can not pass through the porous walls and pass through the channels 125 output. The particles are trapped inside the inlet channels 124. When the quantity of trapped particles exceeds a predetermined threshold value, an active regeneration phase is triggered: the temperature of the exhaust gases entering the particle filter 12 is increased by late fuel injections into the combustion chamber 23 by the injector 8 or directly in the exhaust pipe 70 through the injection nozzle 100. These hot exhaust gases trigger the combustion of the particles in the particulate filter 12. In the particulate filter 12 according to the invention the length of the flow portion of the central input channels 124 near the Z axis of the array is smaller than that of the peripheral input channels 124. During the regeneration of the particulate filter, the exhaust gases passing through the filter heat up in contact with the burning particles. Their temperature increases from the inlet face 130 to the outlet face 131 of the die 120. The exhaust gas is also hotter in the center of the exhaust pipe 70 than at its periphery, and the exhaust gas The exhaust 35 passing through the channels 124, 125 of the die 120 of the particle filter 12 near the Z axis of the die 120 is hotter than those passing through the peripheral channels 124, 125. The combustion runaway is generally triggered in an area of the particulate filter 12 where the exhaust gas reaches very high temperatures, i.e. in the central channels 124, 125 of the die 120, the side of the outlet face 131 of the matrix 120 of the particulate filter 12.

However, in the particle filter 12 according to the invention, the central input channels 124 being shorter, the quantity of particles trapped in these central input channels 124 is lower than in the peripheral input channels 124 and the exhaust gases passing through these central inlet channels 124 are in contact with a smaller amount of burning particles. In addition, the exhaust gas passes through the central channels 124, 125 of the particulate filter 12 more rapidly. The heating of the exhaust gases flowing in the center of the matrix 120 of the particulate filter 12 is therefore limited. A large amount of particles is burned in the peripheral channels of the particulate filter 12, but they benefit from greater heat exchange with the outside, which reduces the risk of runaway combustion. The risks of runaway combustion are reduced and the temperature in the particulate filter is more homogeneous.

The particulate filter according to the invention also allows a better uniformity of the distribution of particles in the filter. Indeed, the homogenization of the temperature in the particulate filter leads to a uniformization of the passive regeneration of said filter. This passive regeneration during which nitrogen dioxide molecules present in the exhaust gases oxidize the particles takes place throughout the operation of the engine in normal mode. Since this passive regeneration is favored in the areas of the particulate filter in which the temperature of the exhaust gas is highest, it creates inhomogeneities of particle distribution in the particulate filter with a preferential accumulation of particles in areas where the Exhaust gas temperature is the lowest, which makes the active regeneration of the particulate filter more difficult. The temperature of the particulate filter 12 is here more homogeneous, the passive regeneration is standardized and the particles are trapped uniformly: the active regeneration of the particulate filter 12 is facilitated, with less risk of runaway. For example, the regeneration temperature of the particulate filter is decreased. The performance of the particulate filter is thus improved. The present invention is not limited to the embodiments described and shown, but the skilled person will be able to make any variant within his mind.

It can for example be envisaged that the length of the channels decreases in steps from the periphery of the matrix to the center thereof. Whatever the embodiment of the invention, it can be envisaged to use front and rear plugs of greater length as the channels they are closing are closer to the axis of the matrix.

Claims (9)

A particulate filter (12) of an exhaust duct (70) of an internal combustion engine having a die (120) with adjacent channels (124,125) separated by porous walls extending longitudinally along a central axis (Z) of the die (120) between an inlet face (130) and an outlet face (131) of the exhaust gas, and having an exhaust gas circulation portion as well as a closed part, channels (124, 125) among which so-called input channels (124) have their closed part situated on the side of the exit face (131) of the matrix (120) and channels (125). ) have their closed part situated on the side of the input face (130) of the matrix (120), characterized in that at least the input channels (124) located close to the axis ( Z) of the matrix (120) have a circulation portion of shorter length than that of the other channels (124, 125). 2. Particulate filter (12) according to the preceding claim, wherein the inlet (124) and outlet (125) channels located near the central (Z) axis of the matrix (120) have a portion of circulation shorter in length than other channels (124, 125). 3. Particle filter (12) according to the preceding claim, wherein said input (130) and outlet (131) faces of the matrix (120) are concave. 4. Particle filter (12) according to one of claims 1 and 2, wherein said input face (130) of the matrix (120) is planar and said outlet face (131) is concave. 5. Particle filter (12) according to one of claims 1 and 2, wherein said input face (130) of the matrix (120) is concave and said output face (131) is flat. The particulate filter (12) of claim 1, wherein the inlet channels (124) near the central (Z) axis of the die (120) have a closed portion of greater length than the other channels (124, 125). 7. Particle filter according to the preceding claim, wherein said input (130) and output (131) faces of the matrix (120) are planar. 8. Exhaust pipe (70) of an internal combustion engine comprising a particulate filter (12) according to one of the preceding claims. 9. Internal combustion engine comprising an exhaust pipe (70) according to the preceding claim.