WO2012150395A1

WO2012150395A1 - Exhaust line and vehicle fitted with this line

Info

Publication number: WO2012150395A1
Application number: PCT/FR2012/050803
Authority: WO
Inventors: Julien Chapel; Nicolas Ferrand
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2011-05-02
Filing date: 2012-04-12
Publication date: 2012-11-08
Also published as: EP2705230A1

Abstract

The invention relates to a vehicle exhaust line (40) equipped with a selective catalytic reduction system for the selective catalytic reduction of nitrogen oxides, characterized in that the line (40) comprises: - an exhaust pipe (44) for discharging the exhaust gases into the atmosphere, - a tube (46) supplying the pipe (44) with reducing agent from a reservoir, the tube (46) being fixed by one of its ends to the exhaust pipe (44) and supporting a connection member (52), - a non-return valve preventing particles from travelling back towards the reservoir, a length of the tube (46) between its ends extending along the pipe (44). The invention also relates to a vehicle fitted with this line. The invention allows the selective catalytic reduction technique to be employed with a lower risk of fouling.

Description

AN EXHAUST LINE AND VEHICLE PROVIDED WITH THIS LINE

The present invention claims the priorities of the French applications 1 153729 filed May 2, 201 1 and 1 153730 filed May 2, 201 1 whose contents (texts, drawings and claims) are here incorporated by reference.

[Ooo2] The invention relates to a vehicle exhaust system equipped with a selective catalytic reduction system of nitrogen oxides (often referred to by the English acronym "SCR") and to the vehicle equipped with this line. 'exhaust. [ooo3] The combustion of fossil fuel such as oil or coal in a combustion system, particularly diesel fuel in a diesel engine, can result in the production of significant amounts of pollutants that can be discharged by the engine. escape into the environment and cause damage. Among these pollutants, the emission of nitrogen oxides called NO _x is a problem since these gases are suspected to be one of the factors contributing to the formation of acid rain and deforestation.

[ooo4] The legislation on emissions from vehicles and heavy vehicles provides for a reduction in the emission of pollutants into the atmosphere. This concerns inter alia releases of NO _x nitrogen oxides. To achieve this goal, a judicious alternation of combustion and hybridization modes or post-treatments in the exhaust line can be developed. In the context of post-treatment techniques, the document WO-A2-2007104779 mentions the selective catalytic reduction (Selective Catalytic Reduction) process which allows the reduction of nitrogen oxides by injection of a reducing agent or agent. reducer (these two terms being equivalent) in the exhaust line. This reducing agent is generally ammonia. This ammonia can come from the decomposition by thermolysis of a solution of an ammonia precursor whose concentration can be that of the eutectic. Such an ammonia precursor is generally a urea solution. [ooo5] With the selective catalytic reduction process, the high NO _x emissions produced in the combustion chamber during a Optimized efficiency combustion is treated at the outlet of the combustion chamber in a specific catalyst. This treatment requires the use of the reducing agent at a precise concentration level and in an extreme quality. The solution is thus precisely metered and injected by a nozzle into the exhaust stream. The solution is then hydrolysed before converting nitrogen oxide (ΝΟχ) to nitrogen (N ₂ ) and water (H ₂ 0) which are harmless to the environment.

[0oo6] The systems implementing the selective catalytic reduction process whether with precursor or without precursor may comprise a non-return valve as is the case of the system described later in Figure 1. These systems can become contaminated as explained in US-B-6 387 336 and US-A-201 0/0242439 in the case of liquid urea.

[ooo7] There is therefore a need for an exhaust line implementing the selective catalytic reduction technique with a reduced risk of fouling. [0oo8] For this the invention provides a vehicle exhaust line equipped with a selective catalytic reduction system of nitrogen oxides. The line comprises an exhaust pipe for the discharge of exhaust gases into the atmosphere and a tube supplying a reducing agent piping from a tank, the tube being fixed by one of its ends to the exhaust pipe and supporting a connection member. The line further comprises a check valve preventing the rise of particles to the tank. A section of the tube between its ends extends along the pipe.

[Ooo9] Alternatively, the exhaust pipe is provided with an insulation fiber, a section of the tube between its ends extending into the fiber. [ooi o] Alternatively, the tube has a bend.

[Ooi i] Alternatively, the tube has two elbows.

Alternatively, the line further comprises a pipe connected to the tube by the snap-in element, a bend to facilitate the snapping of the snap-on element. Alternatively, the line further comprises a pipe connected to the tube by the connecting member, a bend to facilitate the connection of the connecting member.

Alternatively, the connecting member is a snap-in element. Alternatively, the line further comprises a pipe connected to the tube by the connecting member, the tube being more rigid than the pipe.

Alternatively, the line further comprises a pipe connected to the tube by the snap-in element, the tube being more rigid than the pipe.

In a variant, the pipework forms a ceramic sheath of the selective catalytic reduction system.

Alternatively, the pipe section is supported by the pipe by one or more thermal bridges.

In a variant, the supports are regularly spaced apart.

Alternatively, the reducing agent is gaseous ammonia. It is also proposed a vehicle having one of the previously described lines.

Other features and advantages of the invention will appear on reading the following detailed description of the embodiments of the invention, given by way of example only and with reference to the drawings which show: FIG. 1 a block diagram of an example of a selective catalytic reduction system;

• Figure 2, a diagram of an example of an exhaust line;

• Figure 3, a diagram of another example of an exhaust line;

• Figure 4, an enlarged view of a portion of the exhaust line of Figure 3;

FIG. 5, a line example view; FIG. 6, a perspective view of another example of a line;

FIG. 7, a perspective view of another example of a line;

• Figure 8, a perspective view of another example of line.

The implementation of the selective catalytic reduction technique of nitrogen oxides requires complex interfacing with the various elements of the vehicle and the environment. This complexity is well evidenced by the block diagram of Figure 1. This has been simplified by only representing the external elements interacting directly with the system implementing the selective catalytic reduction technique. Thus, the pedestrians, the occupants of the vehicle are not represented in this synoptic diagram.

In this example, one or more reservoirs (sometimes called vectors) storing a reducing agent can be used. Such reservoirs may in particular be in the form of a solid storage cartridge of the strontium chloride type. In Figure 1, two tanks 10 are used. The two tanks may have the same size or not. The desorption of the reductant contained in the tanks 10 is usually obtained by implementing an internal or external heating. This heating is represented diagrammatically by the heating elements 12. In addition, each of the tanks 10 are insulated by a main sheath 14 ("canning main" according to the English expression) and an insulator 16 placed in contact with the tank 10. This allows in particular to isolate the tanks 10 relative to the outside air represented by the bubble 18. The set of elements 10, 12, 14 and 16 corresponding exchange a heat flow. In addition, the assembly is connected to the rest of the vehicle (bubble 20) by a device 22 for holding and protecting the elements. In order not to weigh down Figure 1, the interaction between all the elements 10, 12, 14 and 16 and the device 22 is not shown schematically.

At the outlet of the tanks 10, the gaseous stream of reducing agent can be filtered by filters 24 for storage in the solid state when the temperature of the heating element 12 decreases. Ideally, each filter 24 has a particle size smaller than the smallest of the grains of salt contained in the reservoir 10 when it is at ambient temperature. Thus, the filter 24 is typically a metal filter with gas passage orifices whose characteristic size is of the order of one micron. The presence of the filters 24 can be avoided for economic reasons.

From the tanks 1 0, 26 hoses allow the transport of the gear in the gaseous state. The hoses 26 may be provided with nonreturn valves 28. According to the embodiments no, one or more of the hoses 26 are provided with the valves 28.

The hoses 26 meet at a branch 30. This branch 30 may in particular have the shape of a T. According to some embodiments, the branch 30 may be part of a housing 32. The housing 32 may include a pressure sensor 34 and a sonic neck 35. The housing 32 may also include one or more solenoid valves 36. The housing 32 shown schematically in Figure 1 comprises two solenoid valves 36. The position of the second solenoid valve 36 may be upstream or downstream of the first solenoid valve 36 which can be dedicated to the pressure sensor 34. In such a configuration, the purge of the selective catalytic reduction system can also be achieved by opening the first solenoid valve 36 during restart. The housing 32 may also include temperature sensors. In the case of the figure

1, the housing 32 does not have one.

Such a housing 32 is connected to a gear reducer injection system 38 in the exhaust line 40, which system will be described more precisely in the figures.

2, 3 and 4.

All of the actuators can be controlled by an EE box 42. For this, the housing 42 will exchange information with a computer 44 concerning the state of the system. Thus, the housing 42 can extract data from the heating elements 1 2, the pressure sensor 34 or the state of the solenoid valves 36. The computer 43 issues binary commands based on the information received. The role of the box 42 is also to convert these binary orders into electrical order for the various actuators of the system.

The selective catalytic reduction technique of nitrogen oxides may in particular be applied in a vehicle exhaust line comprising exhaust gas piping for the discharge of exhaust gases into the atmosphere. Such a line 40 is shown in Figure 2. This line 40 comprises a pipe 44 in which the exhaust gas from the engine are released into the atmosphere after treatment. The flow direction of the exhaust gas in the pipe 44 from left to right is indicated by the arrows 45. The line 40 can equip any type of engine, including diesel engines.

The line 40 further comprises a tube 46 supplying reducing agent tubing 44. The tube 46 is generally metallic. When the tube 46 injects ammonia in the gaseous state, the selective catalytic reduction technique used is a decontamination technique qualified as a solid. The tube 46 is usually connected to the line 40 by welding or by means of a screw connection system. According to the example of FIG. 2, the tube 46 is welded as symbolically indicated by the reference number 48. [0032] According to the example of FIG. 3, the line 40 also comprises a pipe 50. The pipe 46 is generally more rigid than the pipe 50. Indeed, a flexible pipe 50 on the reducing agent storage tank side and vehicle underbody allows the existence of deflections between the exhaust line 40 and the vehicle. The pipe 50 is connected to the tube 46 by a connecting member 52. The connecting member 52 may in particular be a snap-on element 52.

Line 40 is further provided with a valve 54 anti-return. The valve 54 serves to pass the reducing agent from the tank 1 0 to the exhaust line 40 while preventing the particles and other compounds present in the exhaust line 40 back to the tank 1 0. The flapper 54 may advantageously be a spring ball type system with stop.

The non-return valve 54 may be in the pipe 50 or in the pipe 46. It is also possible for the valve 54 to be integrated in the connection member 52. An example of arrangement of the non-return valve 54 in the element 52 at the junction of the pipe 50 and the tube 46 so as to prevent the exhaust gases from to go up in the tube 46 is illustrated by the enlarged view of FIG. 4. This makes it possible to prevent the fouling of the tube 46 by soot or other sub-compounds during the pressure fluctuations in the line 40 and the stopping the engine. The rise of the exhaust in the tube 46 may occur during an engine stop or during a cutoff of the injection of reducing agent. Such a risk also exists during a transient phase of strong acceleration. As long as the pressure equilibrium is not achieved, a significant increase in the exhaust pressure is then observed so that the pressure can become greater than that in the tube 46. The clogging of the particulate filter, if the exhaust line is equipped with it, can also generate a point pressure increase favoring the rise of chemical elements from the exhaust line to the pipe.

Among the compounds that can foul the walls of the tube 46 and the valve 54, the mixture between the exhaust gas and a reducing agent such as ammonia can generate in particular ammonium bicarbonate (NH ₄ HC0 ₃ ) which the melting temperature is between 35 and 60 ° C, ammonium nitrate (NH ₄ N0 ₃ ) whose melting point is 170 ° C, various soot resulting from the imperfect combustion of the fuel (hydrocarbons and sub-compounds ), particles, other sub-compounds resulting from the reaction of the reducing agent with the exhaust gases (H ₂ 0, CO ₂ , CO, NO _x , etc.) and various additives present in the gases exhaust.

The integration of the valve 54 in the element 52 is justified by the removal of an interface. Indeed, an additional interface can not only be expensive and increase the risk of leakage.

However, the insertion of the check valve 54 in the element 52 has the disadvantage of increasing the positioning of the valve 54 relative to the line 40 stresses. Indeed, the good conservation of the joints of sealing imposes a maximum temperature generally of the order of 1 10 ° C (it may be higher depending on the material considered) for the valve 54. A severe maximum temperature of the environment is thus imposed because the heat conduction during the contact of the joints around the tube 46. Compliance with this constraint requires that a sufficient distance between the interface of the tube 46 on the hot exhaust and the snap-in element exists. This implies positioning at a distance greater than 20 cm from the tube 46.

Such positioning of the valve 54 has several consequences. Some are positive. Thus, the risk of clogging of the valve 54 decreases because the length of the tube 46 increases and therefore, the occurrence that the exhaust gas reaches the valve 54 decreases. Others are unfavorable. For example, the risk of fouling the tube 46 on the exhaust side increases. Indeed, the volume traveled by the gas in the tube 46 increases. As the thermal gradually decreases, the risk of fouling the walls of the tube 46 is increased. In addition, it becomes difficult to ensure that the non-return valve 54 is subjected episodically to an environment of a temperature of 80 ° C for cleaning the valve 54. In addition, the impact of the outside temperature, in the case where it is weak or the presence of an aulic flow generates dimensional constraints. Finally, the length of the tube causes a heat exchange with the outside resulting in a heat loss of the tube and therefore increases the risk of fouling.

To overcome the aforementioned drawbacks, it may be noted that all the dissolution reactions of the compounds formed or soot separation are endothermic (heat must be provided for these reactions to take place).

Thus, for the case of ammonium nitrate, it is an odorless crystalline substance having hydroscopic properties and tending to agglomerate into lumps. Its dissolution in water, whose solubility varies with temperature, is an endothermic process. The corresponding chemical reaction is written:

NH ₄ N0 ₃ (s) → NH ₄ ⁺ _(aq) + N0 ₃ ^" (aq)

The abbreviation "s" means solid while the abbreviation "aq" means aqueous. Ammonium nitrate is decomposed by heat to water and nitrous oxide in the gaseous state (formula N ₂ 0). Thus, the following three reactions take place:

NH ₄ N0 ₃ → 2H ₂ 0 + N ₂ + ½ 0 ₂ (1)

NH ₄ N0 ₃ → 2H ₂ O ₍ i> + N ₂ O _(g) (2) [0046] NH ₄ N0 ₃ → 2H ₂ O _(g) + N ₂ O _(g) (3)

The abbreviation "I" means liquid while the abbreviation "g" means gaseous.

The three reactions (1), (2) and (3) are endothermic and the enthalpy values associated with these reactions, respectively: · ΔΗι = - 1 18.04 kJ. mol ^"1 for the reaction (1) of decomposition of ammonium nitrate;

• ΔΗ ₂ = - 126 kJ.mol ^"1 for reaction (2) decomposition of ammonium nitrate with formation of nitrous oxide;

• ΔΗ ₃ = - 43 kJ mol ^-1 for the reaction (3) of decomposition of ammonium nitrate with formation of nitrous oxide;

Due to the existence of such endothermic reactions, it is favorable to provide heat to potentially detach the soot present in the valve 54 and also sublimate the ammonium bicarbonate deposits.

Such heat input reduces the risk of fouling. Such a reduction in the risks makes it possible to prevent an insufficient injection of reducing agent, which would result in an efficiency of the post-treatment system in terms of insufficient depollution.

To obtain such a heat input, according to the example of Figure 5, it is therefore proposed a line 40 as described in Figure 2 for which the tube 46 is arranged with respect to the pipe 44 so that the skin temperature of the tube 46 is less than a predetermined skin temperature. In addition, the distance between the tube 46 and the pipe 44 may be sufficiently small so that the amount of heat exchanged between the tube 46 and the pipe 44 is greater than a threshold value when the exhaust line 10 is in operation. In addition, the length of the tube 46 may be chosen to be sufficient so that the amount of soot deposited on the tube 46 is less than a threshold value when the exhaust line 40 is in operation. A particular example of arrangement of the tube 46 to obtain the above effects is illustrated in Figure 5. According to this example, the tube 46 comprises a section 56. The section 56 of the tube 46 is then along the Piping 44. The section 56 can then be at a relatively small distance from the tube 46 to eliminate fouling of the tube 46. It is thus proposed to run a portion of the tube 46 along the exhaust the time that the skin temperature of the tube due to conduction has sufficiently decreased and thus allows the integration of the snap-in element 22 and the holding of its joints. The scrubbing heat is ensured by the fact that the path remains in a sufficiently hot thermal environment. This thus reduces the risk of failure of the tube 46 due to the strong limitation of the risk of clogging of the tube 46 and the valve 54. The risk of failure of the tube 46 due to the shift of the element 22 and maintaining a relatively high temperature is also decreased. This also avoids the use of electric heating systems as is the case in systems using Adblue (trademark) liquid while allowing to deport the valve 54 to minimize its fouling by the exhaust gas.

In addition, according to the example of Figure 5, the tube 46 may include a bend 58. This allows to extend the length of the tube 46 while making its integration into the vehicle possible. Without elbow 58, the length of the tube 46 is limited by the fact that a tube 46 perpendicular to the pipe 44 is bulky and hardly fits under the vehicle. In particular, the length of the tube 46 may then be sufficient so that the amount of soot deposited on the tube 46 is less than a threshold value when the exhaust line 40 is in operation. FIG. 6 is a perspective view showing a configuration with two elbows 58, the second elbow 58 facilitating the insertion of the pipe 50 into the tube 46.

Alternatively, in the case of severe applications with a high risk of fouling, it may be advisable to use the calories present in the exhaust line. Examples of such applications are the cases of long length between the non-return valve 54 and the pipe 44, of a vehicle operating under low temperature conditions, of tube 46 traveling in low temperature zones or deposition of compounds which are difficult to decompose. low temperature (such as ammonium nitrate). Thus, following the implementation of the line 40, it may be that the temperature of the thermal environment to limit the risk of fouling is insufficient (not enough radiation, too much air renewal for example). To solve this problem, it may be chosen to add supports between the exhaust line and the pipe.

FIG. 7 illustrates an example of an exhaust line 40 in which the calories present in the piping 44 are advantageously recovered. Figure 7 thus provides a line 40 as described in Figure 5. The line 14 has further comprises at least one support 60 serving as a thermal bridge. The support 60 brings the calories to the pipe to limit its fouling under normal operating conditions and regenerates the deposits during the phases of temperature rise (for example during a regeneration of the particulate filter where the gases have temperatures 550 to 600 ° C at the injection site). Such a support may in particular be a particulate filter pressure tube support as usually used. The additional cost associated with the addition of the thermal bridge (or paw recovery) is thus reduced. For a slightly increased risk of damaging the line 40 during assembly or transport operations, the use of a support 60 makes it possible to promote the regeneration of the deposits while ensuring the mechanical retention of the tube 46. Better mechanical support ensures a reduction of the vibrations and a possible deflection. The addition of thermal bridges can be modulated on production vehicles according to the climate of the local country. Such regeneration effect deposits while improving the mechanical maintenance of the tube 46 is increased if the supports are evenly spaced. For this, thermal bridges 60 may be made at regular intervals between the exhaust and the tube 46. [0060] Alternatively, it may be proposed to provide the pipe 44 with an insulation fiber 62. The fiber 62 may have an annular shape around the pipe 44 as shown in the schematic section of FIG. 8. This fiber has the property of conserving heat for the elements placed within it. In addition, it can have complex shapes to adapt to all forms of piping 44.

This increases the effects obtained previously with the line according to Figure 5. In addition, if the tube 46 is integrated with the fibrous insulation of the pipe 44 exhaust, the risk of being damaged during the Mounting manipulations are limited. According to Figure 8, this effect is further increased because a thermal bridge 60 as described with reference to Figure 7 is present.

The variant of Figure 8 allows, in addition to contributing to the slag, to limit the risk of fouling by limiting the sensitivity to external conditions. This variant thus combines preventive and curative aspects. Each of the previously presented variants allows to take advantage of the thermal exhaust to obtain a slagging of the tube and the pipe (curative aspect).

Claims

A vehicle exhaust line (40) equipped with a selective catalytic reduction system for nitrogen oxides characterized in that the line (40) comprises:

an exhaust pipe (44) for the discharge of the exhaust gases into the atmosphere,

- a tube (46) supplying a reducing agent to the pipe (44) from a reservoir, the tube (46) being fixed at one end to the exhaust pipe (44) and supporting a connection member (52)

- A check valve (54) preventing the return of particles to the tank, a section (56) of the tube (46) between its ends extending along the pipe (44).

2. The line of claim 1, characterized in that the exhaust pipe is provided with an insulating fiber (62), a section of the tube (46) between its ends being in the fiber (62).

3. The line according to one of claims 1 or 2, characterized in that the tube (46) comprises a bend (58) or two bends (58).

4. The line according to one of claims 1 to 3, characterized in that the line (40) further comprises a pipe (50) connected to the tube (46) by the connecting member (52), an elbow ( 58) for facilitating the connection of the connecting member (52).

5. The line according to one of claims 1 to 4, characterized in that the member (52) connection is a member (52) snap.

6. The line according to one of claims 1 to 5, characterized in that the pipe (44) forms a ceramic coating of the selective catalytic reduction system.

7. The line according to one of claims 1 to 6, characterized in that the section (56) of the tube (46) is supported by the pipe (44) by one or more thermal bridges (60).

8. The line of claim 7, characterized in that the bridges (60) are evenly spaced.

9. The line according to one of claims 1 to 8, characterized in that the reducing agent is ammonia gas.

10. A vehicle characterized in that the vehicle comprises the line (40) according to one of claims 1 to 9.