FR3123382A1 - Device and method for injecting a fluid into an exhaust duct, associated exhaust line and vehicle - Google Patents

Abstract

Device and method for injecting a fluid into an associated exhaust duct, exhaust line and vehicle The device (20) comprises: - a reservoir (21) of fluid, the fluid being an aqueous solution of urea; - an enclosure (22) delimiting a heating chamber (32) for the fluid; - at least one heating element (26) configured to heat the fluid; wherein the heating chamber (32) contains at least one solid catalyst (78), catalyzing the conversion of urea to ammonia. Figure for abstract: 2

Description

Device and method for injecting a fluid into an exhaust duct, associated exhaust line and vehicle

The present invention relates to a device for injecting a fluid into an exhaust duct of a vehicle, the fluid being an aqueous solution of urea.

In such an injection device, the fluid is heated before being introduced into the exhaust duct.

The fluid is injected inside a heating chamber, one end of which communicates with the exhaust duct. Said end is closed by a valve. During heating, the pressure inside the chamber increases. Beyond a certain pressure, the opening of the valve then causes a powerful jet of fine droplets of fluid from inside the chamber towards the exhaust duct.

The heating also aims to convert at least a part of the urea into ammonia.

The exhaust line typically comprises a selective catalytic reduction (SCR) purification element, arranged downstream of the injection device. In the SCR purification element, the NOx contained in the exhaust gas reacts with ammonia and is converted into nitrogen gas N₂ and in water.

Hard deposits are sometimes observed inside the heating chambers of existing injection devices.

When said hard deposits are in large quantities, they can prevent the correct operation of the injection device, for example by clogging the orifice through which the fluid is injected into the exhaust duct, or by interfering with the valve closing said orifice. .

One of the aims of the invention is to remedy these drawbacks.

To this end, the invention relates to a device for injecting a fluid into an exhaust duct, comprising:

- A fluid reservoir, the fluid being an aqueous solution of urea;

- an enclosure defining a heating chamber for the fluid;

- a first injection system configured to inject the fluid from the reservoir into the heating chamber;

- at least one heating element configured to heat the fluid; and

- a second injection system configured to inject the heated fluid from the heating chamber into the exhaust duct;

wherein the heating chamber contains at least one solid catalyst, catalyzing the conversion of urea to ammonia.

Thanks to the invention, the conversion of the urea contained in the fluid into ammonia is facilitated. The at least one catalyst accelerates the chemical reactions transforming urea into ammonia.

Urea is first subjected to a thermolysis reaction:

CO (NH ₂ ) ₂ NH ₃ + HNCO (1)

Isocyanic acid HNCO is then hydrolyzed:

HNCO ₊ H2O NH3 ₊ CO2 ( ₂ )

Isocyanic acid HNCO is very reactive and can create deposits by reacting with other components. Adding a catalyst accelerates the conversion to ammonia and therefore minimizes the risk of creating deposits.

The fact that the catalyst is in solid form, and is located in the heating chamber, makes the invention easy to implement.

Additionally, the heat provided by the heating element is used both to pressurize the fluid and to increase the efficiency of the catalyst.

According to other characteristics of the invention, taken in isolation or according to any technically possible combination:

- a solid catalyst catalyzes the conversion of isocyanic acid into ammonia;

- a catalyst is chosen from the following list: zirconium oxide ZrO ₂ ; titanium oxide TiO ₂ ; aluminum oxide Al ₂ O ₃ ; silicon oxide SiO ₂ ; Socony Mobil-5 H-ZSM-5 zeolite;

- a catalyst is included in a coating deposited on a surface of a part of the heating chamber, said surface being in contact with the fluid;

- a catalyst is included in a material constituting part of the heating chamber, said part being in contact with the fluid;

- said part is the enclosure;

- the heating chamber comprises a heat transfer element, in thermal contact with the at least one heating element and in direct contact with the fluid filling the heating chamber, said part being the heat transfer element.

The invention further relates to a method for injecting a fluid into an exhaust duct, the fluid being an aqueous solution of urea , the method comprising the following steps:

- injection of the fluid into a heating chamber;

- heating of the fluid inside the heating chamber; and

- injection of the heated fluid from the heating chamber into the exhaust duct;
wherein the heating chamber contains at least one solid catalyst, catalyzing the conversion of urea to ammonia.

The invention further relates to an exhaust line comprising an exhaust pipe and an injection device having the above characteristics, for injecting a fluid into the exhaust pipe, the fluid being an aqueous solution of urea , the exhaust line comprising a member for purification by selective catalytic reduction, arranged along the exhaust duct downstream of the injection device.

The invention further relates to a vehicle, with a heat engine and an exhaust line having the above characteristics, the exhaust line receiving the exhaust gases emitted by the heat engine.

Other aspects and advantages of the invention will appear on reading the following description, given by way of example and made with reference to the appended drawings, among which:

[Fig 1] The is a simplified schematic representation of a vehicle with an exhaust line according to the invention;

The is a perspective view of a section of part of a fluid injection device of the exhaust line of the ;

The is a simplified schematic representation showing a coating containing the at least one catalyst; and

The is a simplified schematic representation showing a part made of a material containing the at least one catalyst.

In the following, the terms "upstream" and "downstream" are defined with respect to the general direction of flow of a fluid, which may be diesel exhaust fluid, or exhaust gases. The term "general meaning" is understood here as meaning that, at the scale of the injection device, the fluid is intended to flow from upstream to downstream.

A vehicle 2 is schematized on the .

The vehicle 2 is typically a land vehicle, such as an automobile, a truck, a bus, a van or any other vehicle traveling on a road.

Alternatively, the vehicle is a train or a boat.

The vehicle 2 comprises a heat engine 4 and an exhaust line 10, the exhaust line 10 receiving the exhaust gases emitted by the heat engine 4.

The heat engine is typically a diesel engine.

The exhaust gases are purified in the exhaust line 10 and the purified exhaust gases are then discharged into the environment.

The exhaust line 10 comprises an exhaust duct 12, in which the exhaust gases circulate, and an injection device 20 arranged to inject a fluid into the exhaust duct 12 .

Exhaust duct 12 has an upstream end connected to a manifold (not shown) collecting the exhaust gases produced by heat engine 4.

The exhaust line 10 comprises a selective catalytic reduction (SCR) purification unit 11, arranged along the exhaust duct 12 downstream of the injection device 20.

The exhaust line 10 typically includes other elements, which are not shown on the : a catalytic oxidation device, a particulate filter, the turbine of a turbocharger, one or more silencers, etc.

The fluid is an aqueous urea solution, such as AUS 32 (for " Aqueous urea solution ", or aqueous urea solution in French), also commonly called Adblue®. It is sometimes called Diesel Exhaust Fluid (DEF).

Adblue® is an aqueous solution of urea composed of 32.5% urea and 67.5% demineralised water by mass.

Alternatively, another aqueous urea solution is used, for example with a different urea concentration of 32.5% by mass.

At least part of the urea is converted into gaseous ammonia NH ₃ in the injection device 20. If all the urea is not converted into gaseous ammonia NH ₃ in the injection device 20, another part is converted to ammonia NH ₃ in the exhaust duct 12.

As explained above, in the SCR purification device 11, the NOx contained in the exhaust gases react with the ammonia and are converted into gaseous nitrogen N ₂ and into water.

As shown in , the injection device 20 is fixed to the conduit 12 (not shown in the ) by means, for example, of a fixing flange 14.

The injection device 20 is for example configured to nebulize the fluid into fluid droplets before it is injected into the conduit 12.

According to a variant, the injection device 20 is configured to vaporize the fluid before its injection into the conduit 12. Thus, the fluid has passed into the gaseous state before its injection into the conduit 12.

The injection device 20 comprises a fluid reservoir 21, an enclosure 22, a first injection system 24, at least one heating element 26 and a second injection system 28 .

The enclosure 22 defines a heating chamber 32 in which the fluid is heated.

The enclosure 22 is for example closed.

As will be described later, however, it includes ports allowing fluid to enter heating chamber 32 and exit heating chamber 32.

For example, enclosure 22 comprises a tubular outer wall 34 extending around an extension axis A-A' between an upstream end 35 and a downstream end 36.

The tubular wall 34 delimits the heating chamber 32 radially outwards. The heating chamber 32 then has a cylindrical shape along the axis of extension A-A'.

First injection system 24 is configured to inject fluid from reservoir 21 into heating chamber 32.

For example, the first injection system 24 is configured to inject the fluid into the heating chamber 32 at the upstream end 35 of the enclosure 22.

The first injection system 24 is for example a solenoid valve. It comprises a channel 37 putting the reservoir 21 in fluid communication with the heating chamber 32, divided into an upstream channel 37U and a downstream channel 37D by a partition 38. The partition 38 comprises an injection orifice 40.

The first injection system 24 further comprises a shutter 42, an elastic member 44 and an actuator 46.

Shutter 42 is configured to be moved between a closed position in which orifice 40 is closed by shutter 42, and an open position in which orifice 40 is unobstructed and allows fluid to flow.

The elastic member 44 is configured to urge the shutter 42 into the closed position. The elastic member 44 is for example a spring capable of exerting a return force on the shutter 42 to drive it towards its closed position.

The actuator 46 is configured to move the shutter 42 from the closed position to the open position against the restoring force exerted by the elastic member 44.

The enclosure 22 further comprises an upper bottom 48 and a lower bottom 50, respectively closing the upstream end 35 and the downstream end 36 of the outer wall 34 tubular.

The downstream channel 37D is delimited by the upper bottom 48.

The partition 40 is part of the upper bottom 48.

The downstream channel 37D is in fluid communication with the heating chamber by several passages 52, arranged through the upper bottom 48.

The at least one heating element 26 is arranged around the tubular outer wall 34, on a radially outer side of the wall, opposite the heating chamber 32.

The at least one heating element 26 heats the fluid injected into the heating chamber by conduction through the tubular outer wall 34.

The at least one heating element 26 is of any type suitable for heating the fluid through the tubular outer wall 34. For example, it is an electrical resistance.

The injection device 20 includes a heating element 26 or more heating elements.

The tubular outer wall 34 is made of a material having good thermal conduction properties, for example austenitic steel.

For example, the at least one heating element 26 is intended to heat the fluid to a temperature above 20° C., for example between 20° C. and 500° C., preferably between 70° C. and 300° C., more preferably between 140°C and 200°C .

The at least one heating element 26 further comprises at least one connection element 54 connected to a source of electric current of the vehicle by strips 56 made of an electrically conductive material. The electric current source supplies electric current to the at least one heating element 26.

The injection device 20 further comprises a layer of thermal insulation material 58, arranged around the at least one heating element 26, radially outwards.

The injection device 20 further comprises a lower cover 60 arranged around the layer of insulating material. The lower cover 60 is integral with the flange 14.

The second injection system 28 is configured to inject the heated fluid from the heating chamber 32 into the exhaust duct 12.

The second injection system 28 is for example a solenoid valve similar to the first injection system 24. The second injection system 28 therefore comprises an injection orifice 62, a shutter 64, an elastic member 66 and an actuator 68.

The injection orifice 62 is provided through the lower bottom 50. The fluid is injected into the exhaust conduit 12 through the injection orifice 62 .

Shutter 64 is configured to be moved between a closed position in which port 62 is closed by shutter 64 and an open position in which port 62 is open and heated fluid can flow through the port 62 .

The elastic member 66 is configured to urge the shutter 64 into the closed position. The elastic member 66 is for example a spring capable of exerting a return force on the shutter 64 to drive it towards its closed position.

The actuator 68 is configured to move the shutter 64 from the closed position to the open position against the restoring force exerted by the elastic member 66.

In the example shown in , the elastic member 66 is arranged in the downstream channel 37D, the actuator 68 being arranged around the downstream channel 37D.

Advantageously, the enclosure 22 further comprises a central thermal insulation sleeve 70 extending inside the heating chamber 32, for example, along the axis of extension A-A'.

According to the example shown in , the second injection system 28 further comprises a control rod 72 integral with the elastic member 66 and the shutter 64. The elastic member 66 and the actuator 68 are configured to move the shutter 64 between the closed position and the open position by urging the control rod 72. The control rod 72 extends for example inside the central sleeve 70 and through the upper bottom 48, between the elastic member 66 and the shutter 64 .

Advantageously, the heating chamber 32 comprises a heat transfer element 77, in thermal contact with the at least one heating element 26 and in direct contact with the fluid filling the heating chamber 32.

The heat transfer element 77 is made of a material having good heat conduction properties. It is in direct contact with the tubular wall 34 so that heat is transferred by conduction from the tubular wall 34 to the heat transfer element 77, and by convection from the heat transfer element 77 to the fluid.

In the example above, the heat transfer element 77 has the shape of a helix, arranged around the axis A-A'.

It extends from the upstream end to the downstream end of the heating chamber 32.

The heat transfer element 77 defines a helical fluid passage from the upstream end 35 to the downstream end 36 of the heating chamber 32.

For example, the thermal transfer element 77 consists of a ribbon arranged in a helix, one edge of the ribbon being in direct contact with the tubular wall 34, and the opposite edge of the ribbon being in direct contact with the central sleeve 70.

According to the invention, the heating chamber 32 contains at least one solid catalyst 78, catalyzing the conversion of urea into ammonia.

Catalyst 78 is in solid form. It is placed inside the heating chamber 32, and remains permanently inside the heating chamber 32.

As explained above, urea is converted into ammonia NH ₃ by two successive reactions.

Urea is first subjected to a thermolysis reaction:

CO (NH ₂ ) ₂ NH ₃ + HNCO (1)

Isocyanic acid HNCO is then subjected to a hydrolysis reaction:

HNCO ₊ H2O NH3 ₊ CO2 ( ₂ )

The overall reaction is:

CO (NH ₂ ) ₂ + H ₂ O 2 NH ₃ + CO ₂

The at least one solid catalyst 78 advantageously catalyzes the conversion of isocyanic acid into ammonia, that is to say the hydrolysis reaction.

The at least one catalyst 78 is chosen from the following list: zirconium oxide ZrO ₂ ; titanium oxide TiO ₂ ; aluminum oxide Al ₂ O ₃ ; silicon oxide SiO ₂ ; Socony Mobil-5 H-ZSM-5 zeolite.

According to one embodiment, a single catalyst is used. Said catalyst is selected from the above list.

According to another embodiment, several catalysts are used together. Advantageously, each catalyst is chosen from the above list.

According to an embodiment shown in the , the at least one catalyst 78 is included in a coating 80 deposited on a surface of part of the heating chamber, said surface being in contact with the fluid.

Preferably, said part is enclosure 22.

In this case, the coating containing the catalyst is deposited on one or more of the following elements of the enclosure: the tubular wall 34, the upper bottom 48, the lower bottom 50, the central sleeve 70 .

Alternatively, said part is the heat transfer element 77. In other words, the coating containing the catalyst is applied to the heat transfer element 77.

Advantageously, the part(s) on which the coating 80 is deposited is made of stainless steel.

According to another embodiment shown in the , the at least one catalyst 78 is included in a material constituting part of the heating chamber.

Again, said part is preferably enclosure 22.

In this case, the catalyst is included in the material constituting one or more of the following elements of the enclosure: the tubular wall 34, the upper bottom 48, the lower bottom 50, the central sleeve 70.

Alternatively, said part is the heat transfer element 77.

The operation of the injection device 20 is described below.

The first injection system 24 injects fluid from the reservoir 21 into the heating chamber 32.

The fluid is injected into the heating chamber 32 at the upstream end 35 of the enclosure 22.

The fluid is then heated by the at least one heating element 26.

The fluid circulates between the upstream end 35 and the downstream end 36.

It follows the helical passage defined by the heat transfer element 77.

When the fluid has reached a predefined temperature, the second injection system 28 injects the heated fluid from the heating chamber 32 into the exhaust duct 12, for example from the downstream end 36 of the enclosure 22.

During the heating of the fluid in the heating chamber 32, at least part of the urea contained in the fluid is converted into gaseous ammonia NH ₃ . If all the urea is not converted into gaseous ammonia NH ₃ in the heating chamber, another part is converted into ammonia NH ₃ in the exhaust pipe 12.

Urea undergoes a thermolysis reaction and generates isocyanic acid and ammonia. The isocyanic acid is then subjected to a hydrolysis reaction.

The at least one catalyst 78 accelerates the conversion of urea into gaseous ammonia NH ₃ , in particular the hydrolysis reaction.

According to a second aspect, the invention relates to a method for injecting a fluid into an exhaust duct 12, the fluid being an aqueous urea solution.

The method is specially adapted to be implemented with the injection device described above. Conversely, the injection device described above is specially designed to implement the injection method.

The process includes the following steps:

- Injection of the fluid into a heating chamber 32;

- heating of the fluid inside the heating chamber 32; and

- injection of the heated fluid from the heating chamber 32 into the exhaust duct 12.

According to the invention, the heating chamber 32 contains at least one solid catalyst 78, catalyzing the conversion of urea into ammonia.

The fluid is as defined above.

Heating chamber 32 is as defined above.

The fluid is injected into the heating chamber 32 by means of the first injection system 24 defined above.

The fluid inside the heating chamber 32 is heated by the at least one heating element 26 defined above.

The heated fluid is injected from the heating chamber 32 into the exhaust conduit 12 by the second injection system 28 defined above.

The at least one solid catalyst 78 is as defined above.

The invention has many advantages.

Since the at least one solid catalyst catalyzes the conversion of isocyanic acid to ammonia, the isocyanic acid disappears quickly, as soon as it is formed by the thermolysis reaction. As a result, isocyanic acid is not available to react with other elements and create deposits.

A catalyst chosen from the following list is particularly suitable for the invention: zirconium oxide ZrO ₂ ; titanium oxide TiO ₂ ; aluminum oxide Al ₂ O ₃ ; silicon oxide SiO ₂ ; Socony Mobil-5 H-ZSM-5 zeolite. Such a catalyst is particularly effective in accelerating the conversion of urea into ammonia.

It is particularly convenient for the at least one catalyst to be included in a coating deposited on a part of the heating chamber. It allows good contact between the fluid and the at least one catalyst, since the coating is deposited on a surface of the part which is in contact with the fluid. The coating is a thin layer, thus providing access to most of the catalyst molecules. The production of parts with a coating is simple and economical. Since the at least one catalyst is embedded in a thin coating, it does not increase the total volume occupied by the heating chamber. The coating is designed with its support so that the device operates in good conditions (volume, exchange surface, weight, etc.).

It is also convenient for the at least one catalyst to be included in the material forming part of the heating chamber. The production of such parts is simple and economical. Since the at least one catalyst is included in the material constituting the part, this does not increase the total volume occupied by the heating chamber. This allows the device to operate in good conditions (volume, exchange surface, weight, etc.).

It is particularly advantageous for said part to be the enclosure, since it offers a large surface in contact with the fluid.

The same applies when said part is the heat transfer element.

Other embodiments can be considered.

For example, the at least one solid catalyst can be carried by a dedicated part, received in the heating chamber. The dedicated part has no other function than to carry the at least one solid catalyst.

The at least one heating element is not necessarily outside the heating chamber. In one embodiment, it is inside the heating chamber.

Claims (10)

Device (20) for injecting a fluid into an exhaust duct (12), comprising:
- a reservoir (21) of fluid, the fluid being an aqueous solution of urea
- an enclosure (22) defining a heating chamber (32) for the fluid;
- a first injection system (24) configured to inject fluid from the reservoir (21) into the heating chamber (32);
- at least one heating element (26) configured to heat the fluid; and
- a second injection system (28) configured to inject the heated fluid from the heating chamber (32) into the exhaust duct (12);
wherein the heating chamber (32) contains at least one solid catalyst (78), catalyzing the conversion of urea to ammonia. Apparatus according to claim 1, wherein the at least one solid catalyst (78) catalyzes the conversion of isocyanic acid to ammonia. Device according to Claim 1 or 2, in which the at least one catalyst (78) is chosen from the following list: zirconium oxide ZrO ₂ ; titanium oxide TiO ₂ ; aluminum oxide Al ₂ O ₃ ; silicon oxide SiO ₂ ; Socony Mobil-5 H-ZSM-5 zeolite. Device according to any one of claims 1 to 3, in which the at least one catalyst (78) is included in a coating (80) deposited on a surface of a part of the heating chamber (32), said surface being in contact with the fluid. Device according to any one of Claims 1 to 4, in which the at least one catalyst (78) is included in a material constituting a part of the heating chamber (32), said part being in contact with the fluid. Apparatus according to claim 4 or 5, wherein said part is the enclosure (22). Device according to Claim 4 or 5, in which the heating chamber (32) comprises a heat transfer element (77), in thermal contact with the at least one heating element (26) and in direct contact with the filling fluid. the heating chamber (32), said part being the heat transfer element (77). Method of injecting a fluid into an exhaust duct (12), the fluid being an aqueous solution of urea , the method comprising the following steps:
- injection of the fluid into a heating chamber (32);
- heating the fluid inside the heating chamber (32); and
- injection of the heated fluid from the heating chamber (32) into the exhaust duct (12);
wherein the heating chamber (32) contains at least one solid catalyst, catalyzing the conversion of urea to ammonia. Exhaust line (10) comprising an exhaust duct (12) and an injection device (20) according to any one of claims 1 to 7 for injecting a fluid into the exhaust duct (12), the fluid being an aqueous urea solution, the exhaust line (10) comprising a member for purification by selective catalytic reduction (11), arranged along the exhaust duct (12) downstream of the injection device (20 ). Vehicle (2), with a heat engine (4) and an exhaust line (10) according to claim 9, the exhaust line (10) receiving exhaust gases emitted by the heat engine (4).