FR3107727A1 - Exhaust line - Google Patents

Abstract

Exhaust line The invention relates to an exhaust line (1) capable of transporting exhaust gases from an inlet (2) connectable to an internal combustion engine to an outlet (3) opening into the open air. , comprising at least one first purification member (4) arranged close to the inlet (2), a first silencer (7) placed downstream of said at least one first purification member (5) and at least one second purification (5) equipped with a heating element (6), arranged further downstream. Figure for abstract: Figure 1

Description

Exhaust line

The invention relates to the field of exhaust lines for internal combustion engines and more particularly their equipment used to filter/depollute exhaust gases.

It is known, in order to reduce the concentrations of nitrogen oxides NOx in the exhaust gases, to equip the exhaust line with a purification device, for example a catalyst. Such a catalyst converts NOx into harmless compounds: N ₂ , CO ₂ , which can be released into the atmosphere. To operate correctly, such a catalyst must have a high temperature, at least equal to an operating temperature preferably greater than 350°C. To reach this temperature, heating can be provided by the exhaust gases themselves. Also to make the most of this heating, the catalytic converter is placed as close as possible to the engine at the entrance to the exhaust line. However, on starting, the exhaust gases are hot only after an initial engine warm-up phase. It is known to associate the catalyst with a heating element making it possible to heat the catalyst and/or the exhaust gases. However, such an arrangement requires waiting for the catalyst to be hot before starting the engine and also requires a particular heating element: a static induction heating element or a blower. The heating time, typically 10 seconds, delays the starting of the engine by the same amount, and thus contributes to degrading the user experience.

Also, a means of reducing this heating time is sought.

In order to solve this problem, the idea of the invention is to take advantage of the volume of the exhaust line to save time and correspondingly reduce the delay in starting the engine.

For this, the subject of the invention is an exhaust line capable of transporting exhaust gases from an inlet, connectable to an internal combustion engine, to an outlet opening into the open air, comprising at least a first purification device placed near the inlet, a first silencer placed downstream of said at least one first purification device and at least one second purification device equipped with a heating element, placed further downstream, preferably near the exit

Particular features or embodiments, usable alone or in combination, are:
- the second purification member is a catalyst, preferably a three-way catalyst,
- the heating element is of the type capable of heating the exhaust gases and is arranged immediately upstream of the second purification member,
- the heating element comprises a foam or a grid,
- the second purification member and the heating element are integrated with the first silencer in the same first casing arranged near the outlet,
- the second purification member and the heating element are integrated separately from a first silencer arranged near the outlet, preferably downstream of the first silencer,
- the second purification unit is thermally insulated,
- the first purification device is integrated with a second silencer in the same second envelope,
- the first purification unit is integrated with or is replaced by a first particle filter in the same second envelope,
- the line also includes a third silencer in a third casing arranged in an intermediate position between the inlet and the outlet,
- the line also includes a third purification device and/or a second particle filter, integrated in the third casing,
- the first purification member and/or the third purification member is/are a catalyst, preferably a three-way catalyst and the first particulate filter and/or the second particulate filter is/are a gasoline particulate filter.

In a second aspect of the invention, a vehicle includes such an exhaust line.

The invention will be better understood on reading the following description, given solely by way of example, and with reference to the appended figures in which:

shows a block diagram of a first embodiment of the invention,

to [Fig.7] show block diagrams of other embodiments of the invention.

Referring to Figure 1, an exhaust line 1 is capable of transporting exhaust gases. For this it includes a pipe connecting an inlet 2, connectable to an internal combustion engine on its exhaust outlet, to an outlet 3 leading to the open air. Such an exhaust line 1 comprises a first purification member 4, such as a catalyst. This first purification member 4 is preferably arranged as close as possible to the inlet 2, in order to be as close as possible to the engine and thus take advantage of its heat to reach or exceed its operating temperature as quickly as possible, i.e. typically 350° C. .

In order to be able to start the engine, even when the first purification member 4 is not yet hot, while ensuring the treatment of NOx in a zero emission perspective, it is, according to the invention, as illustrated in Figure 1, added a second purification member 5. This second purification member 5, not being hot at start-up, is equipped with a heating element 6.

According to one embodiment, the heating element 6 is made of an electrically conductive material which is permeable to the exhaust gas. The heating element 6 can be substantially flat and not very thick. Advantageously, the heating element 6 can have the shape of a plate. By “slightly thick”, we mean that the thickness is between 0.3 mm and 30 mm.

According to a first embodiment, the heating element 6 comprises a grid. Its thickness is between 0.3 mm and 10 mm, and preferably between 0.5 and 2 mm.

According to a second embodiment, the heating element 6 comprises a foam or a honeycomb. Its thickness is between 5 mm and 30 mm, and preferably between 10 mm and 20 mm.

The heating element 6 typically extends in a plane substantially perpendicular to the pipe forming the exhaust line 1.

The heating element 6 typically heats up by the Joule effect.

It comprises a network of passages for the exhaust gases, producing a turbulent flow of the exhaust gases through the heating element 6.

The material constituting the heating element 6 is typically a metal, such as stainless steel, a metal alloy or a ceramic. For example, this material is an alloy of iron, such as FeCrAl. According to a variant, this material is a nickel or copper alloy, such as NiCr. According to another variant, this material is a silicon carbide SiC ceramic.

The heating element 6 typically comprises a foam, with randomly or regularly arranged open pores.

According to an alternative, the heating element 6 comprises a mesh of metal wires or a grid, or a honeycomb material.

The pore density is typically between 5 and 40 ppi (in English “pore per inch”, ie pores per inch), ie a density substantially between 2 and 16 pores per cm. The material typically has a developed surface comprised between 500 and 5000 m2/m3, preferentially comprised between 1000 and 3000 m2/m3, and still preferentially comprised between 1500 and 2500 m2/m3.

Advantageously, the heating element 6 is coated with at least one catalytic function coating making it possible to contribute to the purification of the exhaust gases. This coating is intended for the oxidation and/or reduction of the polluting compounds of the exhaust gases. It may for example be of the same type as those used in TWC (Three-way Catalyst), DOC (Diesel Oxidation Catalysis), PNA (Passive NOx Absorber), LNT (Lean NOx Trap), SCR (Selective Catalytic Reduction) or even for the hydrolysis of a reducing agent used for the reduction of nitrogen oxides. Alternatively or additionally, this coating is designed to increase the roughness of the surface of the material, in order to promote turbulence and increase heat exchange.

Due to its porosity, the heating element 6 also performs a particle filter function. The heating element 6 is regenerated each time it is heated, the trapped soot particles being eliminated by combustion.

Advantageously, the heating element 6 is made of material: it is in one piece, in the same material.

Typically, the heating element 6 is obtained by cutting a plate from a single piece of electrically conductive material.

Alternatively, the heating element 6 is obtained by foundry, extrusion, sintering, additive manufacturing (3D printing), etc.

The heating element 6 has a thickness comprised between 2 and 50 mm, preferentially comprised between 5 and 30 mm, and still preferentially comprised between 10 and 20 mm.

In other words, the heating element 6 is in the form of a slice of electrically conductive material, cut directly to the desired shape.

It should be noted that the exhaust gases present at start-up in the exhaust line 1 downstream of the first purification unit 4 are "clean" in that they have been treated by the first purification unit 4 before the previous one. engine shutdown.

Also, the volume of exhaust gas between the downstream of the first purification member 4 and the upstream of the second purification member 5, which should be called buffer volume, is used to give the second member of purification 5 the time to reach its operating temperature. Thus, the expulsion time, taken by the motor to expel the buffer volume beyond the second purification member 5 is deducted from the heating time necessary for the second purification member 5 to reach its operating temperature. The delay in starting the motor thus becomes equal to the heating time subtracted from the expulsion time.

For an engine with a displacement of one liter, assuming a typical buffer volume of 30 liters, the expulsion of the buffer volume is carried out in 60 engine cycles, i.e. at the average starting speed, in an expulsion time of 5 seconds .

If the heating time is short enough or if the expulsion time is long enough, the starting delay can advantageously cancel out, allowing immediate starting, as soon as the driver requests it.

In order to maximize the buffer volume and therefore the expulsion time, so as to minimize the start-up delay, the second purification member 5 is advantageously placed downstream of the first purification member 4 and preferably as far as possible from the first purification unit 4, or close to outlet 3.

The heating element 6 is preferably arranged as close as possible to the second purification member 5 in order to optimize the heating and limit the heat losses.

According to another feature, the second purification member 5 is a catalyst, preferably a three-way catalyst, or in English a “three-way catalyst”, conventionally abbreviated TWC.

The heating element 6 can be of any type. It can act by directly heating the second purification member 5, by any heating means. It can also act by heating the exhaust gases before their introduction into the second purification member 5. In this case the heating element is advantageously placed upstream of the second purification member 5. In order to limit heat losses, this upstream is preferably immediate. The heating element 6 can be an electrically heated catalyst, or in English an “electrically heated catalyst”, conventionally abbreviated EHC.

On starting, in a first phase, the exhaust gases newly produced by the engine push the old "clean" exhaust gases contained in the buffer volume. The heating by the heating element 6 of the second purification member 5 is started in such a way that the second purification member 5 reaches its operating temperature at the latest at the end of the expulsion of the old exhaust gases from the buffer volume. In a second phase, beginning when the second purification member 5 reaches its operating temperature, the second purification member 5 processes the new exhaust gases which follow the buffer volume.

At this moment, the first purification member 4 has probably not reached its operating temperature. The second purification member 5 is thus the first operational purification member for treating the exhaust gases. During the first two phases, the new exhaust gases heat the first purification member 4. A third phase begins when the first purification member 4 reaches its operating temperature and then mainly handles the treatment of the exhaust gases. The role of the second purification member 5 then becomes secondary, in that it receives already treated exhaust gases. The second purification member 5 remains advantageous in that it makes it possible to treat excess exhaust gases with respect to the processing capacity of the first purification member 4. This can occur in the event of very high engine load.

The processing capacity of the second purification unit 5 can be used as a backup, in the event of failure or surplus at the level of the first purification unit 4. Alternatively this capacity can be used to reduce the capacity and therefore the dimensions of the first organ of purification 4.

An exhaust line 1 is typically terminated by a first silencer 7, placed in a first casing 8, this first casing 8 being placed close to the outlet 3. Also, according to another characteristic, more particularly illustrated in FIG. 2, this advantageous location can be reused by integrating the second purification member 5 and the heating element 6 with this first silencer 7, and this advantageously within the same first envelope 8.

Such integration may be impossible or difficult due to integration constraints. Also, according to another feature, more particularly illustrated in Figure 3, the second purification member 5 and the heating element 6 can be integrated separately from the first silencer 7 and on the contrary be connected to the first silencer 7 by a pipe. The arrangement of the second purification member 5 and heating element 6 assembly relative to the first silencer 7 can be arbitrary. However, in order to maximize the buffer volume, the second purification unit 5 and heating element 6 assembly is preferably placed downstream of the first silencer 7.

According to another characteristic, in order to always remain ready to process the exhaust gases, the second purification member 5 is advantageously thermally insulated.

For acoustic reasons, it is advantageous for an exhaust line 1 to comprise a silencer divided into at least two separate parts, a part advantageously close to the outlet 3 and a part preferably in an intermediate position, substantially median, between the input 2 and output 3.

Also, according to another characteristic, more particularly illustrated in Figures 4-7, a second silencer 9 and/or a third silencer 12 is/are advantageously added to the exhaust line 1.

According to a first embodiment, more particularly illustrated in FIG. 4, the second silencer 9 is advantageously associated with the first purification member 4 and therefore arranged close to the inlet 2. Advantageously, the second silencer 9 is integrated with the first purification unit 4 in the same second envelope 10.

According to another feature, the first purification unit 4 may include a first particle filter 11, as shown in Figure 5.

According to another characteristic, the first purification unit 4 can also comprise a catalyst.

According to another characteristic, in the two preceding cases, the first purification unit 4, optionally comprising the first particle filter 11, and the second silencer 9 are advantageously integrated into the same second casing 10.

According to another embodiment, alternative or complementary, more respecting the condition of presence of a silencer in the intermediate position, the exhaust line 1 further comprises a third silencer 12, arranged in an intermediate position, substantially median, between the inlet 2 and output 3, as shown in Figure 6.

According to another characteristic, the third silencer 12 is advantageously arranged in a third casing 13.

According to another characteristic, more particularly illustrated in FIG. 7, the exhaust line 1 further comprises a third purification member 14 and/or a second particulate filter 15, arranged in an intermediate position. Advantageously, this or these component(s) is/are integrated into the third casing 13.

According to another characteristic, the first purification member 4 and/or the third purification member 14 is/are a catalyst, preferably a three-way catalyst or in English a “three-way catalyst”, conventionally abbreviated TWC.

According to another characteristic, the first particulate filter 11 and/or the second particulate filter 14 is/are a gasoline particulate filter or in English a “gasoline particle filter” conventionally abbreviated GPF.

The invention also relates to a vehicle comprising such an exhaust line 1 according to any one of the embodiments previously described.

The invention has been illustrated and described in detail in the drawings and the foregoing description. This must be considered as illustrative and given by way of example and not as limiting the invention to this description alone. Many variant embodiments are possible.

1: exhaust line,
2: input,
3: output,
4: first organ of purification,
5: second organ of purification,
6: heating element,
7: first silencer,
8: first envelope,
9: second silencer,
10: second envelope,
11: first particulate filter,
12: third silencer,
13: third envelope,
14: third organ of purification,
15: second particulate filter

Claims (13)

Exhaust line (1) suitable for transporting exhaust gases from an inlet (2), connectable to an internal combustion engine, up to an outlet (3) opening out into the open air, comprising at least one first purification unit (4) disposed close to the inlet (2), characterized in that it further comprises a first silencer (7) placed downstream of said at least one first purification member (4) and at least one second member purification (5) equipped with a heating element (6), arranged further downstream, preferably close to the outlet (3). Line (1) according to the preceding claim, wherein the second purification member (5) is a catalyst, preferably a three-way catalyst. Line (1) according to any one of the preceding claims, in which the heating element (6) is of the type suitable for heating the exhaust gas and is arranged immediately upstream of the second purification member (5). Line (1) according to any of the preceding claims, wherein the heating element comprises a foam or a grid. Line (1) according to any one of the preceding claims, in which the second purification member (5) and the heating element (6) are integrated with the first silencer (7), in the same first casing (8) arranged at near the exit (3). Line (1) according to any one of Claims 1 to 4, in which the second purification member (5) and the heating element (6) are integrated separately from a first silencer (7) arranged close to the outlet ( 3), preferably downstream of the first silencer (7). Line (1) according to any one of the preceding claims, in which the second purification member (5) is thermally insulated. Line (1) according to any one of the preceding claims, in which the first purification member (4) is integrated with a second silencer (9) in the same second casing (10). Line (1) according to any one of the preceding claims, in which the first purification member (4) is integrated with or is replaced by a first particle filter (11) in the same second casing (10), the first filter particles (11) preferably being a gasoline particulate filter. Line (1) according to any one of the preceding claims, further comprising a third silencer (12) in a third casing (13) arranged in an intermediate position between the inlet (2) and the outlet (3). Line (1) according to the preceding claim, further comprising a third purification device (14) and/or a second particle filter (15), integrated in the third casing (13). Line (1) according to claim 11, wherein the first purification member (4) and/or the third purification member (14) is/are a catalyst, preferably a three-way catalyst, and the second particle filter (15) is a gasoline particulate filter. Vehicle characterized in that it comprises an exhaust line (1) according to any one of the preceding claims.