FR3040193B1 - SELECTIVE CATALYTIC REDUCTION SYSTEM - Google Patents

Abstract

The invention relates mainly to a mixing box (10) for selective catalytic reduction system intended to be installed in an exhaust line of a heat engine, characterized in that said mixing box comprises: a first compartment ( 110) configured to guide and accelerate exhaust gas, - a second compartment (210) comprising an injection zone of a reducing agent and a straight passage in which a mixture can be made between said reducing agent and said exhaust gas from said first compartment (110), and - a third compartment (310) configured to homogenize said mixture from said second compartment (210).

Description

SELECTIVE CATALYTIC REDUCTION SYSTEM

The present invention relates to a selective catalytic reduction system and the corresponding exhaust line. The invention finds a particularly advantageous application with thermal engines, especially motor vehicles, and more particularly equipped with a turbocharger.

In a context of pollution of the exhaust gas of an engine including diesel type, the selective catalytic reduction systems (or SCR for "Selective Catalyst Reduction" in English) are intended to reduce nitrogen oxides (NOX) contained in the exhaust gas. The SCR system uses a chemical reaction between these same NOX and a reducing agent. Conventionally, the reducing agent takes the form of ammonia injected into the exhaust line. The injection of ammonia is usually carried out by means of another chemical species, such as urea, which decomposes into ammonia and carbon dioxide under the effect of heat.

SCR systems described for example in WO201512829 comprise a housing with internal walls spiral winding to increase the distance traveled by the exhaust gas and facilitate mixing with the reducing agent. Such an installation requires the presence of an impactor located near the injector to ensure the formation of droplets of reducing agent during its injection. However, the presence of the impactor increases the overall size of the assembly, which does not allow a satisfactory freedom of installation, in particular for an installation of the SCR system at the outlet of the turbocharger.

Furthermore, SCR systems based on different shapes are also known and disclosed in WO2013156856, such as bends or baffles upstream of the injector forcing the exhaust gases to swirl during injection. However, these vortices do not offer an optimal quality of the mixture between the reducing agent and the exhaust gas during the injection.

The invention aims to effectively overcome these disadvantages by providing a mixing box for selective catalytic reduction system for an exhaust line of a heat engine, including a motor vehicle (or other mode of motorized locomotion), such as said mixing box comprises: a first compartment configured to guide and accelerate exhaust gases; a second compartment comprising an injection zone for a reducing agent and a straight corridor in which a mixture can be made; between said reducing agent and said exhaust gases from said first compartment, and - a third compartment configured to homogenize said mixture from said second compartment.

The invention thus makes it possible, by the presence of the rectilinear corridor, to increase the travel distance of the mixture between the reducing agent and the exhaust gases that promotes the vaporization of the reducing agent when the gases are not present. still hot which eliminates a large impactor. The invention also makes it possible to take into account diesel depollution system architectures that aim to bring a catalyst closer to the turbocharger. The latter, being for example a diesel oxidation catalyst, is placed horizontally for balancing the turbine, the SCR system catalyst could thus be placed at the end of the turbocharger. The invention also makes it possible to install the urea injection mixing box between a horizontal catalyst and the rest of the vertically installed pollution control system. This improves the integration of the pollution control system insofar as the mixing box can be masked in a connecting cone between the diesel oxidation catalyst and the SCR system catalyst, unlike other systems mentioned above. .

In one embodiment, said first compartment has a spiral shape.

In one embodiment, said third compartment has a shape of spiral, helix, elbow, fins, or baffles.

According to one embodiment, said third compartment extends transversely relative to said second compartment so that the assembly has a bent shape. Thus the system is generally L-shaped, this particular form offers a compact installation freedom.

In one embodiment, an injector is located at an end of said rectilinear corridor.

In one embodiment, said first compartment incorporates a concentrator.

In one embodiment, said injection zone of a reducing agent is positioned in the second compartment downstream of the concentrator.

In one embodiment, said third compartment incorporates a diffuser so as to ensure a uniform watering of a catalytic reduction system catalyst.

The invention also relates to a vehicle engine exhaust line characterized in that it comprises: - a turbocharger exhaust turbine, - a first directly connected exhaust gas treatment device to the turbocharger exhaust turbine, - a mixing box as defined above.

In one embodiment, said first exhaust gas treatment device is an oxidation catalyst, especially for diesel type engines.

The invention will be better understood on reading the description which follows and the examination of the figures that accompany it. These figures are given for illustrative but not limiting of the invention.

Figures 1a and 1b are schematic representations of a mixing box according to the invention installed in an exhaust line; Figure 2 is a perspective view illustrating a flow direction of the exhaust gas inside a mixing box according to the present invention; Figures 3a and 3b are views respectively in perspective and in section of the first compartment of the mixing box according to the present invention; Figures 4a and 4b are views respectively in perspective and in section of the second compartment of the mixing box according to the present invention; Figures 5a and 5b are views respectively in perspective and in section of the third compartment of the mixing box according to the present invention; Figure 6 is a schematic representation illustrating the direction of flow of the exhaust gas inside the compartments of the mixing box according to the present invention.

Identical elements, similar, or the like retain the same reference from one figure to another.

In the following description, the relative terms "upstream" and "downstream" are understood in relation to the normal flow direction of the exhaust gases inside the exhaust line of the engine indicated by the arrows on the figures. In addition, it is considered that a communication between two elements is "direct" when no other device is interposed between these two elements.

Figures 1a and 1b schematically show an exhaust line 100 of a heat engine 1 equipped with a turbocharger 2. A first exhaust gas treatment device 3 is intended to be directly connected to the output of the Turbocharger exhaust turbine 2.

The first device 3 for treating the exhaust gas comprises for example a diesel oxidation catalyst for the oxidation of hydrocarbon and nitric oxide to nitrogen dioxide and water. In an alternative embodiment, the first device 3 is a passive absorber of nitrogen oxide (or "passive NOX absorber" in English) or a nitrogen oxide trap (or "lean NOX trap" in English) . An output of the device 3 is in direct communication with a selective catalytic reduction system, called SCR system for "Selective Catalyst Reduction" in English.

As is apparent from Figure 2, the SCR system comprises a mixing box 10 having three compartments 110, 210, 310. The first compartment 110 shown in detail in Figure 3a and 3b directly communicates with the first device 3 of exhaust gas treatment. The compartment 110 advantageously has a spiral shape capable of guiding the gases 111 coming from the first device 3 to the second compartment 210. This form of spiral makes it possible to accelerate the gases 111 before the injection of the reducing agent.

In addition, the first compartment 110 incorporates a concentrator. This concentrator may for example be in the form of a grid or a cone converging reducing the diameter of the gas passage, which allows to concentrate and accelerate the flow of the exhaust gas at the inlet of the mixing box 10 .

Furthermore, the second compartment 210, visible in FIGS. 4a and 4b, comprises a rectilinear corridor and a reducing agent injection zone 51. For this purpose, a reducing agent injector 5 is positioned at the one end of the corridor, preferably at an upstream end, such that the reducing agent, for example taking the form of a solution of urea solubilized in water, is injected in the axis of the flow of the exhaust 111 from the first compartment 110. This injection in the corridor ensures a homogeneous mixture 211 between the reducing agent and the exhaust gas 111 in acceleration whose flow is substantially straight in the corridor. In addition, the rectilinear corridor increases the travel length of the mixture 211, which promotes the vaporization of the reducing agent when the gases 111 are not yet hot. Such a configuration thus allows an implantation of the injector 5 in a direction which is not necessarily perpendicular to the flow of the exhaust gas 111. There is thus a freedom of installation of the mixing box 10 at the output of the turbocharger 2.

The third compartment 310, shown in detail in Figures 5a and 5b, is configured to homogenize the mixture 211 from the second compartment 210. More specifically, the shape of the compartment 310 allows to finalize the brewing, accelerate the mixture 211, and to prepare the inlet of the mixture 211 in a second device 4 for treating the exhaust gas. The device 4 is preferably constituted by an SCR system catalyst communicating directly with the outlet of the third compartment 310. The third compartment 310 may take a spiral shape, but may also take the form of a helix, elbow, d fins or baffles, to standardize the watering of the device 4 and thus maximize its processing potential.

The third compartment 310 also incorporates a diffuser for uniform watering of the catalytic reduction system catalyst 4 located downstream of the third compartment 310. The diffuser, for example in the form of a cone, increases the gas flow diameter 211. which makes it possible to standardize the watering of the SCR catalyst 4.

In the exemplary embodiment shown in FIG. 2, the third compartment 310 extends in a transverse plane P3 with respect to the plane P2 in which the second compartment 210 extends. In other words, the assembly has a shape The angle α between the two planes P2, P3 is preferably between 80 and 100 degrees, and is about 90 degrees. This compact form of the assembly thus offers freedom of installation at the outlet of the turbocharger 2.

The mixing box 10 thus allows both to promote the mixture 211 between the reducing agent and the exhaust gas, to promote the vaporization of the reducing agent before reaching the catalyst SCR 4 and to maximize the pollution control potential of the catalyst SCR 4. In addition, the mixing box 10 allows a guiding of the exhaust gases 111, 211 along their path. Indeed, the exhaust gases 111, 211 move in all the compartments 110, 210, 310 parallel to the guide walls, unlike the devices forming swirls (or "swirl" in English) commonly used and in which the gases turn around an axis of the direction of advancement of gases.

Claims (9)

Claims: 1. Mixing box (10) for a selective catalytic reduction system intended to be installed in an exhaust line (100) of a heat engine, particularly a motor vehicle, said mixing box comprising: a first compartment (110); ) configured to guide and accelerate exhaust gases (111), - a second compartment (210) comprising an injection zone (51) of a reducing agent and a rectilinear corridor in which a mixture can be formed ( 211) between said reducing agent and said exhaust gas (111) issuing from said first compartment (110), and - a third compartment (310) configured to homogenize said mixture (211) issuing from said second compartment (210), characterized in that said third compartment (310) extends transversely of said second compartment (210) so that the assembly has a bent shape. 2. Mixing box according to claim 1, characterized in that said first compartment (110) has a spiral shape. 3. Mixing box according to claim 1 or 2, characterized in that said third compartment (310) has a shape of spiral, helix, elbow, fins, or baffles. 4. Mixing box according to any one of claims 1 to 3, characterized in that an injector (5) is located at an end of said rectilinear corridor. 5. Mixing box according to any one of claims 1 to 4, characterized in that said first compartment (110) incorporates a concentrator. 6. Mixing box according to claim 5, characterized in that said injection zone (51) of a reducing agent is positioned in the second compartment (210) downstream of the concentrator, 7. A mixing box according to any one of claims 1 to 6, characterized in that said third compartment (310) incorporates a diffuser so as to ensure a uniform watering of a catalytic reduction system catalyst (4). 8. Exhaust line (100) of a combustion engine (1) characterized in that it comprises - a turbocharger exhaust turbine (2), - a first device (3) for treating exhaust gases. directly connected to the turbocharger exhaust turbine (2), - a mixing box (10) as defined in any one of the preceding claims, 9. Exhaust line according to claim 8, characterized in that said first device (3) for treating the exhaust gas is an oxidation catalyst.