FR2956698A1 - Exhaust element for exhaust line utilized to circulate exhaust gas produced by engine of motor vehicle for treating pollutants, has opening by which stream of gaseous reducing agent is introduced during rotation of vanes - Google Patents

Abstract

The element has a main duct (2) extending along longitudinal axis (XX) and bringing exhaust gas produced by an internal combustion engine toward a nitrogen oxide selective catalytic reduction (SCR) catalyst (4). A mixer (9) includes a rotation axle (11) parallel to the longitudinal axis. A pair of vanes (10, 10') is symmetrical around the rotation axle and is arranged in such manner that circulation of exhaust gas in the main duct drives the vanes in rotation. A stream of gaseous reducing agent is introduced through an opening (7) during rotation of the vanes.

Description

Exhaust line element and exhaust line comprising such an exhaust element

TECHNICAL FIELD OF THE INVENTION The present invention relates to an exhaust line element comprising a gas mixer and more particularly relates to the field of the treatment of pollutants by catalysis using a reducing agent.

BACKGROUND For many years, automotive engine manufacturers have made great efforts to reduce the emission into the atmosphere of environmentally harmful chemical compounds produced by combustion engines during fuel combustion. .

Among these compounds, nitrogen oxides, mainly NO monoxide and NO2 dioxide nitrogen, together referred to under the abbreviation NO.

To limit the emission of nitrogen oxides in the atmosphere, a solution currently used is to place on the exhaust system of the vehicle a system of treatment of NO, called SCR system ("Selective Catalytic Reduction") having function of chemically reducing the nitrogen oxides into di-nitrogen molecules and water vapor by means of a reducing agent. In practice, the reducing agent is injected into the exhaust line upstream of a specific catalyst SCR in which the reduction reaction occurs.

There are two SCR channels, one with an ammonia precursor reducing agent such as an aqueous solution of urea and the other with ammonia reducing agent, NH3, gaseous.

SCR with urea has been previously favored for reasons of vehicle implantation. The aqueous solution of urea requiring a reservoir, the liquid supply circuit is relatively simple. This path has the disadvantage of requiring a set of sequential physico-chemical processes: the injection of the aqueous solution of urea, the atomization of the urea spray droplets and droplets, evaporation and decomposition chemical droplets in NH3 and finally the mixture of NH3 with the exhaust gas. Moreover, given the space available in the exhaust line for the injection / mixing phenomena, the SCR solution with the aqueous urea solution greatly complicates the homogenization of the reducing agent with the oxidant.

The other route explored is SCR with ammonia, gaseous NH3. In this case, the ammonia is injected as a gas directly into the exhaust gas where it must then mix.

It is known to leave an adequate distance between the reducing agent injector and the SCR catalyst to allow obtaining a homogeneous mixture as complete as possible between the exhaust gas and the reducing agent.

In order to improve the homogeneity of this mixture and to shorten the distance required for homogenization, it is known to use a so-called static mixer, that is to say without moving parts, positioned inside. of the exhaust duct, between the point of injection of reducing agent in the exhaust gas and the entry of the catalyst SCR.

Document FR2921415 is particularly known an exhaust line comprising a static mixer, intended to be disposed within said exhaust line. The mixer in question comprises a solid central zone and has a plurality of wings around the central zone and extending around the solid central zone. The exhaust line further comprises means for spraying a liquid containing a reducing chemical species, the projected liquid droplets forming a cone flaring towards the mixer.

However, such a device requires on the one hand a sophisticated injection means because comprising a spray nozzle of the liquid in the form of droplets and on the other hand is not sufficient to actually allow the effective preparation and obtaining a homogeneous mixture of exhaust gases and ammonia over a short axial distance from the injection point.

The object of the invention is to overcome the drawback of the prior art by proposing a new exhaust element enabling efficient preparation and obtaining a homogeneous mixture between the exhaust gases and a gaseous agent such as ammonia over a short axial distance from the injection site. The invention thus relates to an exhaust line element for an internal combustion engine comprising a main pipe extending along a longitudinal axis 35 and bringing the exhaust gases produced by the internal combustion engine to a catalyst for selective reduction of nitrogen oxides, at least one conduit for introducing a gaseous agent for selective catalytic reduction of the nitrogen oxides projecting into the main conduit via at least one introduction orifice, said introduction conduit being disposed , relative to the direction of flow of the exhaust gas, upstream of the catalyst, a mixer disposed between the introduction pipe and the catalyst, characterized in that the mixer comprises an axis of rotation parallel to the longitudinal axis, the minus a pair of symmetrical vanes around the axis of rotation, rotatably mounted and arranged so that the circulation of the exhaust gases in the duct incipal drives the blades in rotation and that the two blades of said pair pass, during their rotation, successively in a stream of gaseous reducing agent introduced by an introduction orifice.

Moreover, the invention may include one or more of the following features: Preferably, the insertion orifices are off-center with respect to the longitudinal axis.

For reasons of simplicity of embodiment, preferably each blade is a rectangular flat plate.

In a variant, each of the blades is carried by an arm mounted free to rotate about the axis of rotation.

Preferably, the axis of rotation is coincident with the longitudinal axis, so the mixer 25 is centered in the main conduit.

Preferably, the axis of rotation is fixed on the introduction conduit.

In another variant, the axis of rotation is maintained by at least one fastening rod 30 connecting the axis of rotation to the main duct.

In a variant, the mixer comprises a peripheral convergent, to allow an acceleration of the exhaust gas and increase the speed of rotation of the mixer.

Furthermore, the invention also relates to an exhaust line in which exhaust gases produced by an internal combustion engine circulates, said line comprising a selective reduction catalyst of nitrogen oxides, characterized in that it comprises an exhaust element of the invention arranged upstream of the selective reduction catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS Other particularities and advantages will appear on reading the following description of a particular embodiment, not limiting of the invention, with reference to the figures in which: - Figure 1 schematically shows a first embodiment of the invention. - Figure 2 schematically shows a second embodiment of the invention. - Figure 3 shows a front view of a third embodiment of the invention. - Figure 4 shows a fourth embodiment of the invention.

DETAILED DESCRIPTION FIG. 1 shows an exhaust line portion 1 of burnt gases produced by an internal combustion engine, not shown here. The exhaust line 1 comprises a main duct 2, extending along a longitudinal and central axis XX, in which circulates a stream 3 of burnt gas or exhaust gas and connected to a selective reduction catalyst 4 (or SCR). , for the reduction of NOx nitrogen oxides present in the exhaust gas, by selective catalytic reaction between NOx and a reducing agent. By reducing agent is meant an agent that can react chemically with pollutants to transform them into less polluting products. The catalyst 4 is provided with an inlet face 8, most often perpendicular to the flow direction of the exhaust gases.

Prior to the catalyst 4 SCR, relative to the direction of flow of the exhaust gas, means for injecting the reducing agent comprising a conduit 5 for introducing a stream 6 of reducing agent are arranged. The introduction duct 5 passes through the main duct 1 to protrude into the latter and allow the injection of reducing agent through an insertion orifice 7.

Preferably, the reducing agent is a gaseous reducing agent. More preferably the gaseous reducing agent is ammonia, the chemical species directly involved in the catalytic reduction of nitrogen oxides.

In this first embodiment shown in FIG. 1, and in accordance with the invention, provision is made in the exhaust line 1 between the catalyst 4 SCR and the ammonia introduction conduit 5 for a mixer 9 rotary.

The rotary mixer 9 comprises a set of blades, also called blades. The blading is mounted idle, that is to say in free rotation about an axis 11 rotational support. The axis 11 of rotation may be a metal rod on which the blade is mounted freely in rotation.

In this first embodiment, the blading of the mixer 9 is formed of a pair of blades 10, 10 'symmetrical with respect to the axis 11 of rotation and mounted free to rotate around the latter. For reasons of simplicity of embodiment, the blades 10, 10 'are preferably in the form of a rectangular flat plate. The blades may, however, have more complex shapes, such as curved or concave surfaces evoking receptacles, as long as they provide the operation described below.

In this first embodiment, and as illustrated in FIG. 1, each of the blades 10, 10 'is integral with an individually referenced carrying arm 12, 12' respectively. In addition, the blades 10, 10 'are arranged in the extension of their respective carrier arm. The blade may be attached to its support arm by a fastening means known to those skilled in the art such as a weld spot, a rivet, etc. The support arms may advantageously be metal rods of small cross sections so as to generate only a small pressure drop in the exhaust gas.

The end of the support arm opposite to that carrying the blade is secured to rotation guide means 13 known to those skilled in the art such as, for example a bearing or a ball bearing. These guide means 13 allow the free rotation of the blade around the axis 11 of rotation.

Preferably, the support arms 12, 12 'are arranged in opposition relative to the axis 11 of rotation and aligned along an axis YY perpendicular to the central axis XX.

In this first preferred embodiment, the axis 11 of rotation is fixed on the introduction conduit 5. Thus the introduction conduit 5 ensures the maintenance of the rotary mixer 9 in the main conduit 2. More preferably, the axis 11 of rotation of the mixer 9 is fixed to the introduction conduit 5, coinciding with the central axis XX.

The blades 10, 10 'are positioned on their respective carrying arm 12, 12' so that during their circumferential movement they pass successively opposite the opening 7 of ammonia introduction.

To do this, the position of the opening 7 of ammonia introduction is off-center with respect to the central axis XX.

The operation is then as follows: On the one hand, the flow 6 of exhaust gas from the operation of the combustion engine comes during its passage through the blades 10, 10 'exert a thrust on the latter, which by appropriate inclination of the blades 10, 10 'with respect to the flow of exhaust gas, drives the assembly in a rotational movement as illustrated by the arrows 14.

On the other hand, the stream 6 of ammonia is introduced into the exhaust gas 3 via the introduction orifice 7.

The blades 10, 10 ', during their displacement, pass successively at the level of the injection orifice 7 and deviate in their stroke the flow of ammonia introduced through the orifice of its original path to disperse and brew in the exhaust gases. The exhaust gas 3 thus mixed with ammonia will water the catalyst 4 SCR on the entire input surface 8.

The invention is not limiting of this first embodiment.

Figure 2 shows a second embodiment of the invention. This second embodiment differs from the first embodiment in that the introduction conduit 5 comprises a second ammonia introduction orifice 7 'and the mixer 9 comprises a second pair of blades 15, 15' arranged on the same pair of carrier shafts 12, 12 'between the axis 11 of rotation and the first pair of blades 10, 10'. Each of the blades 15, 15 'of the second pair of vanes is integral with their respective carrier shaft 12, 12'. The second pair of blades is arranged so that during their circumferential movement around the axis 11 of rotation, each blade 15, 15 'passes successively opposite the second orifice 7' ammonia introduction. The orifices 7, 7 'of introduction are off-center with respect to the longitudinal axis.

Figure 3 now shows a front view of a third embodiment of the invention. This third embodiment differs from the first embodiment in that the mixer 9 comprises a second pair of blades 16, 16 'carried on a second pair of support arms respectively referenced 17, 17'. In this embodiment, the vanes 16, 16 'are arranged in the extension of their respective carrier arm, the end of the support arm opposite to that carrying the blade being secured to the means 13 for rotating guidance. The blades may be of different surfaces to modulate the distribution of ammonia in the main conduit 2.

The support arms 17, 17 'are arranged in opposition relative to the axis 11 of rotation and aligned along an axis ZZ perpendicular to the axis YY and the central axis XX, not visible in FIG. 3 because perpendicular to the plane of Figure 3.

Figure 4 shows a fourth embodiment. In this embodiment, the mixer 9 comprises a peripheral convergent 18. The convergent 18 ensures the acceleration of the exhaust gas therethrough, which allows the exercise of a greater thrust on the blades 10, 10 ', therefore a greater speed of rotation of the blade and therefore a greater mixing of the ammonia flow emerging from the introduction port with the exhaust gas.

In fifth embodiment not shown, the axis 11 of rotation can be maintained by at least one fixing rod connecting the axis 11 of rotation to the main conduit 2.

The five embodiments mentioned above are not limiting of the invention. The essence of the invention is that the blades cooperate with the introduction ports so that the different streams of gaseous reducing agent introduced into the main conduit through the orifices are deflected by the passage of the blades in said flows .

In order to effectively deflect the ammonia flow, the blades pass at a distance D (see Figure 1) of the introduction conduit 5, near the introduction ports 7 between a minimum distance Dmin and a maximum distance Dmax . On the one hand, the distance, Dmin, of the introduction conduit must be sufficient to at least leave sufficient clearance to avoid the risk of contact between the blade and the introduction conduit. In practice, the distance Dmin can be between 0.1 and 1 mm. On the other hand, the distance, Dmax, of the introduction conduit must be sufficient for the dawn to effectively stir the ammonia. In practice, the distance Dmax can be between 20 and 30 mm.

Furthermore, a blade has a surface S (see Figure 1) between a minimum surface, Smin, and a maximum area, Smax, to ensure the mixing of ammonia. On the one hand, the minimum surface, S min, corresponds substantially to the flow surface of the insertion orifice 7. As an indication, the flow area of an ammonia introduction port may be of the order of 20 mm 2. In addition, the maximum area, Smax, is equal to 1 / 2n of the section of the main duct taken orthogonally to the longitudinal axis XX at the mixer 9, n being the total number of blades of the mixer 9.

According to another variant, the flow of reducing agent can be introduced into the main duct by several introduction ducts. The introduction ducts can lead into the main duct by several introduction ports. The mixer may comprise several pairs of carrying arms and each pair of carrying arms may carry several pairs of blades arranged at different heights and suitably so that each of the different flow of reducing agent introduced through the orifices is swept by at least one pair of blades. In addition, the position of the blade relative to the axis of rotation and the surface of the blade can modulate their circumferential speed and the distribution of ammonia.

The invention has many advantages: it does not require a drive motor blades which are molted by the kinetic energy of the exhaust gas, the invention is a simple and economical solution for actively stirring the gases . In addition, the invention is compact and generates a small pressure drop inside the main conduit.

Claims (9)

Revendications1. An exhaust line element for an internal combustion engine comprising a main duct (2) extending along a longitudinal axis (XX) and conveying the exhaust gases produced by the internal combustion engine to a catalyst (4) of selective reduction of the nitrogen oxides, at least one conduit (5) for introducing a gaseous agent for the selective catalytic reduction of the nitrogen oxides projecting into the main conduit (2) through at least one orifice (7). ), said inlet duct (5) being arranged, in relation to the direction of flow of the exhaust gas, upstream of the catalyst (4), a mixer (9) arranged between the duct (5) of introduction and the catalyst (4), characterized in that the mixer (9) comprises an axis (11) of rotation parallel to the longitudinal axis (XX), at least one pair of symmetrical blades (10, 10 ') around of the axis (11) of rotation, mounted free to rotate and arranged so that the circulation exhaust gas in the main duct (2) drives the blades (10, 10 ') in rotation and that the two blades (10, 10') of said pair pass, during their rotation, successively in a flow of gaseous reducing agent introduced through an orifice (7) of introduction. 2. Exhaust line element according to claim 1, characterized in that the orifices (7) of introduction are off-center with respect to the longitudinal axis (XX). 3. Exhaust line element according to claim 1 or claim 2, characterized in that each blade (10, 10 ') is a rectangular flat plate. 4. Exhaust line element according to any one of the preceding claims, characterized in that each of the blades (10, 10 ') is carried by an arm (12, 12') mounted free to rotate about the axis ( 11) rotation. 5. Exhaust line element according to any one of the preceding claims, characterized in that the axis (11) of rotation coincides with the longitudinal axis (XX). 6. Exhaust line element according to any one of the preceding claims, characterized in that the axis (11) of rotation is fixed on the conduit (5) of introduction. 7. Exhaust line element according to any one of claims 1 to 5, characterized in that the axis (11) of rotation is held by at least one fastening rod connecting the axis (11) of rotation to led (2) main. 8. exhaust line element according to any one of the preceding claims, characterized in that the mixer (9) comprises a convergent (18) device. 9. Exhaust line in which exhaust gases produced by an internal combustion engine circulates, said line comprising a catalyst (4) for selective reduction of nitrogen oxides, characterized in that it comprises an element of Exhaust according to any preceding claim disposed upstream of the catalyst (4) selective reduction.