FR2830275A1 - EXHAUST GAS TREATMENT SYSTEM FOR A COMBUSTION ENGINE - Google Patents

Abstract

System for treatment of exhaust gas (G) from combustion motor comprises a treatment element in parallelepiped form in the exhaust line (16) and system for producing high voltage/low current discharge between cathodes (24) and anode (22) to form chemical species for regenerating treatment element .The anode extends within the element parallel to the opposite walls (42,44) of the element and parallel to the direction of flow of the gases. The cathodes are arranged on the opposite walls parallel to the anode. The anode and cathodes comprise networks of conductors (40).

Description

"Exhaust gas treatment system of a combustion engine"

  The invention relates to a gas treatment system.

  combustion engine exhaust.

  The invention relates more particularly to a system for treating the exhaust gases of a combustion engine, of the type which comprises a treatment element disposed in an exhaust line and a system for producing high voltage electrical discharges and low intensity, between at least to a cathode and an anode which are arranged in the exhaust line. Diesel and petrol engines emit polluting substances such as unburnt hydrocarbons, nitrogen oxides, carbon oxides and particles in the case of diesel engines. We know that one of the major concerns of equipment manufacturers and motor vehicle manufacturers is the reduction of pollution caused by

operation of these engines.

  Different technical solutions have therefore been considered

  o to try to reduce the pollution levels of these engines.

  The control of gaseous pollutant emissions can be obtained by introducing specific catalysts into the exhaust line, such as the three-way catalyst for petrol engines operating at stoichiometry OR nitrogen oxide panning for petrol direct injection engines. or diesel operating in a lean mixture (high oxypene content). In the case of the nitrogen oxide trap, the reducing agents are the unburnt hydrocarbons accessible in the exhaust gases, unlike the SCR catalysis o using an external reducing agent, as for example

example urea.

  The treatment of particles on current diesel engines is possible thanks to the introduction into the exhaust line of these engines of a particle filter as already proposed in the prior art. These are often adapted to trap particles or "soot" contained in the exhaust gases of these engines and burn them during a regeneration phase of the filter. Different regeneration strategies are available in the literature, referring for example to the post injection of fuel to reach the combustion temperature of the soot (600 C minimum) or for example to additional means

  heater placed upstream of the particulate filter.

  The present invention proposes the use of o technology of non-thermal plasma in a catalytic and / or filtering material in order to help the treatment of gaseous pollutants contained in a gasoline or diesel engine exhaust, among others the catalysis of reduction of oxides d nitrogen, and / or to induce the combustion of soot trapped in a filter

  s placed in a gasoline or diesel engine exhaust line.

  This technology consists in forming metastable species, radicals and highly reactive ions by collision between gas molecules and energetic electrons produced by electric discharges, without raising the

  o temperature of the reaction medium.

  The physical characteristics of electric shocks vary according to the intended application, the consumption and conversion levels required for engine applications, in particular

  motor vehicle (variable frequency, voltage, intensity).

  The metestable species, radicals and highly energetic electrons produced are promoters of chemical reduction, for example nitrogen oxides and soot particles, by direct interactions of these very long-lived species.

short with pollutants.

  The invention therefore proposes a system for treating the exhaust gases of a combustion engine, of the type which comprises a treatment element disposed in an exhaust line and a system for producing high voltage electrical discharges and low intensity, between at least one cathode and an anode arranged in the exhaust line, to form chemical species favorable to the regeneration of the treatment element, characterized in that the anode extends in the element treatment in a direction substantially parallel to the direction of flow of the exhaust gases in the exhaust line, and in that at least one cathode is arranged at least partially at the periphery of the treatment element

  in a direction substantially parallel to that of the anode.

  According to other characteristics of the invention: o - the treatment element is cylindrical with a longitudinal axis parallel to the direction of the flow of gases in the exhaust line, the anode is a conducting wire which extends along D the longitudinal axis, and the cathode is tubular and envelops the treatment element; The processing element is of parallelopipedic shape, two opposite faces of which are parallel to the direction of the anode, and it comprises two cathodes which are arranged on said opposite faces so that electrical discharges occur simultaneously between the anode and the two cathodes; o - the anode and / or at least one cathode is a plate of conductive material; The anode and / or at least one cathode is a network of conductive wires which extends in a plane parallel to the direction of flow of the gases in the exhaust line; - the conducting wires are parallel to the direction of flow of the exhaust gases; - the conducting wires are perpendicular to the direction of flow of the exhaust gases; The processing element consists of two blocks which are arranged on either side of the anode so that a block is interposed between the anode and each cathode; - The treatment system consists of a stack of treatment elements, and the two adjacent treatment elements comprise a common cathode; The processing element comprises a particle filter; - the treatment system includes a catalyst,

  in particular a catalyst for the reduction of nitrogen oxides.

  Other characteristics and advantages of the invention

  will appear on reading the following detailed description for the

  understanding of which reference will be made to the appended drawings in which: FIG. 1 schematically represents an exhaust line of a combustion engine equipped with an o treatment system for exhaust gases; - Figure 2 shows a sectional view along line 2-2 of Figure 1 of the exhaust gas treatment system according to a first embodiment of the invention; - Figure 3 shows schematically in perspective an exhaust gas treatment system according to a second embodiment of the invention; and FIG. 4 diagrammatically shows in cross section the exhaust gas treatment system according to a variant of the second embodiment of

The invention.

  The description which follows is given, without limitation, in

  reference to a treatment system 10 which includes a particle filter. Without departing from the scope of the invention, the particle filter can be replaced by a catalyst such as a

: 5 reduction of nitrogen oxides.

  FIG. 1 shows an exhaust gas treatment system G of a combustion engine 12. The engine 12 can in particular be a diesel engine or a petrol engine operating in lean mixture such as a

gasoline with direct injection.

  An exhaust line 14 allows the evacuation of gases G from the engine to the atmosphere. The processing system 10 intended

  to purify the exhaust gases G is interposed in line 14.

  It mainly consists of a processing element 16

arranged in a room 18.

  The processing system 10 also includes a system 20

  for producing electric shocks.

  Electric discharges are produced by an impulse generator 26 between an anode 22 and a cathode 24

  arranged in the exhaust line 14.

  The technology used is that of non-thermal plasmas. o Consequently, the electrical discharges are produced at a frequency which can range from a single shot to several tens of kHz for a high applied voltage (up to several tens b of kV) between the anode (s) and the cathode (s) and consist of high current impulses (up to several

kA) and short service life.

  Electric discharges are produced so that they propagate in the exhaust gases G to process nitrogen oxides and produce oxidizing activated species

  promoting the combustion of particles.

  According to the invention, the anode 22 extends in the treatment element 16 in a direction substantially parallel to the direction of flow of the exhaust gases G in the exhaust line 14. In addition, at least a cathode 24 is arranged at the periphery of the treatment element 16 according to

  a direction substantially parallel to that of the anode.

  For security reasons, in particular to limit the risk of short circuits, the pulse generator 26 supplies the anode 22, located inside the treatment element 16, under high voltage, and the cathode 24, arranged at the periphery of the processing element 16, being connected to the electrical ground of the system. Figure 2 shows in section a first mode of

realization of the invention.

  Chamber 18 is here substantially cylindrical, the longitudinal axis of which corresponds to the general direction of flow

  exhaust gases G in line 14.

  The processing element 16, which here is a filter element also called a particle trap, consists of longitudinal inlet and outlet channels 17B which are alternately plugged and open at the inlet and which are inversely open and plugged at the outlet respectively . The walls of these are porous. to Thus, the exhaust gases G re-enter the channels which are open at the entrance and pass through the porous walls

  so as to come out through the channels 17B which are open at the outlet.

  As they pass through the walls, the particles are trapped so that the exhaust gases coming out of the element

  s treatment 16 are free of particles.

  The anode 22 extends in the treatment element 16 in a direction substantially parallel to the direction of flow of the exhaust gases G. The anode 22 here consists of a conductive wire which extends

  o longitudinally to the processing element 16.

  Cathode 24 which is tubular in shape

the processing element 16.

  Thus, the system formed by the processing element 16,

  The anode 22 and the cathode 24 is symmetrical.

  When the treatment element 16 is saturated, that is to say that the quantity of particles stored is greater than a threshold

  predetermined, its regeneration is initiated.

  The loading of the particulate filter 16 can be determined by a differential pressure measurement sensor, not shown, which provides the value of the pressure drop produced by the particulate filter 16 between the inlet and the outlet of the chamber 18 When the value of the pressure drop is greater than a predetermined value, this means that the filter 16 is saturated, its

regeneration is then initiated.

  During the regeneration phase, the pulse generator 26 produces electric discharges which are distributed homogeneously in the treatment element 16. The homogeneous distribution of discharges in the treatment element s 16 is mainly due to the symmetry of the system formed by the treatment element 16, the anode 22 and the cathode 24. This makes it possible to cause the formation of activated oxidizing species in the immediate vicinity of the walls of the channels of the treatment element 16 which are charged with particles. This proximity and the homogeneous distribution of the oxidized species make it possible to promote the combustion of the stored particles.

in the processing element.

  Thus, the regeneration of the treatment system 10 is optimized. In order to overcome mechanical stresses which may be linked to vibrations or to the expansion of the materials constituting the treatment system 10, a strip of thermal wool 25 can be placed between the inner wall of the

chamber 18 and cathode 24.

  o The thermal wool strip 25 allows mechanical decoupling between the wall of the chamber 18 and the treatment element 16. In addition, it provides thermal insulation of the treatment element 16 so as to limit the temperature of the external face of the wall of the chamber 18, and to promote the rise in temperature inside the treatment element, which further facilitates the regeneration of the treatment system. Figures 3 and 4 show a second mode of

  preferred embodiment of the invention.

  o In the following description, we will not use

  limiting, a higher, lower orientation in accordance with

  the orientation from top to bottom of the figures.

  In accordance with FIG. 3, the chamber 18 of the treatment system receives a reactor 30 consisting of two upper and lower shells 32, 34 in which is arranged

  the processing element 16 of generally parallel shape

  lépipédique. The casing 18 makes it possible to connect the reactor 30 in a sealed manner to the exhaust line 14. The treatment element 16 consists of two upper and lower blocks 36, 38 which are symmetrical with respect to a

  median horizontal plane P of the reactor 30.

  The anode 22 is here constituted by a network of wires or conductors 40 parallel to each other which can be made of stainless steel. The network of conductive wires 40 extends between the two blocks 36 and 38 in the median horizontal plane P which is parallel to the direction of flow of the exhaust gases G in the

s line 14.

  The conductive wires are interconnected by two

  bars 41 of conductive material which extend along

  nally on both sides on side faces of the treatment element 16. The bars 41 allow on the one hand to stretch o the wires 40 between the upper and lower blocks 36, 38 and on the other hand to form two power elements common to all

son 40.

  The conducting wires 40 may be perpendicular to the direction of the flow of the exhaust gases G. confor

s also in Figure 3.

  According to a variant, they can also be oriented differently, in particular in a direction parallel to the direction of flow of the exhaust gases G. According to another variant, the anode 22 can be formed

  o by a plate of conductive material.

  According to the invention, a first cathode 24 is interposed between the upper wall 42 of the upper block 36 and the

  inner wall of the upper shell 32.

  Similarly, a second cathode 24 is interposed between the lower wall 44 of the lower block 38 and the wall

  inside of the lower shell 34.

  The cathodes 24 consist of a plate of conductive material which can be made of stainless steel. Thus, the first and second cathodes 24 each extend in a plane parallel to that of the plane of the wires

conductors 40 forming the anode 22.

  Each upper 36 and lower 38 block is interposed

  o between anode 22 and the first and second cathode 24.

  The system formed by the cathodes 24 and the blocks 36, 38 of the treatment element 16 are symmetrical with respect to the

  median horizontal plane P containing the anode 22.

  Thus, the electric discharges caused by the pulse generator 26 occur simultaneously between

  the anode 22 and each of the first and second cathodes 24.

  Consequently, the electric discharges are distributed homogeneously in the processing element 16, which

  promotes the combustion of stored particles.

  o The casing 18, which allows the reactor 30 to be connected in a leaktight manner to the exhaust line 14, also makes it possible to maintain the two upper 36 and lower 38 blocks of the reactor 30. The casing 18 must allow the conductors to pass electrics to connect the anode 22 and the cathodes 24 to the

impulse generator 26.

  To do this, electrically insulated orifices (not shown) are made in its wall so that con conductive elements connect the anode 22 and the cathodes 24 to the

  o pulse generator 26 respectively.

  The conductive elements can be strips in

  copper 50 and 52, as shown in Figure 3.

  The envelope 18 makes it possible to form a Faraday cage so as to limit the electromagnetic disturbances produced by

the processing system 10.

  Similarly to the first embodiment, in order to overcome the mechanical stresses which can be linked to vibrations or to the expansion of the materials constituting the treatment system 10, strips of thermal wool 25 can be placed between the cathodes 24 and upper blocks 36 and

  lower 38 of the processing element 16.

  o The material constituting the upper 32 and lower 34 shells must have a very low electrical conductivity due to the presence of the electrodes 22, 24 so as to reduce as much as possible the risk of short-circuits. In addition, this material must be able to withstand high temperatures. Consequently, the upper 32 and lower 34 shells can be made in

  ceramic or with a ceramic coating.

  According to a variant of the second embodiment, the invention proposes in accordance with FIG. 4 that the processing system 10 consists of a stack of elements

  o processing 16. Here, two processing elements 16 are stacked.

  In order to minimize the size of the system 10, the

  two elements have a common cathode 54.

  Such an embodiment makes it possible to adapt the processing capacity of the system 10 as a function of the vehicle on which it is mounted and of the quantity of polluting substances to be treated, from

  of a single model of processing element 16.

  This optimizes the production costs of

treatment systems 10.

Claims (10)

  1. Exhaust gas treatment system (10) (G) of a combustion engine (12), of the type which comprises a treatment element (16) arranged in an exhaust line (14) and a system (20) for producing electric discharges of high voltage and low intensity, between at least one cathode (24) and an anode (22) arranged in the exhaust line (14), to form chemical species favorable to regeneration of the treatment element (16), 10 characterized in that the anode (22) extends in the treatment element (16) in a direction substantially parallel to the direction of flow of the exhaust gases ( G) in the exhaust line (14), and in that at least one cathode (24) is arranged at least partially at the periphery of the treatment element (16) in a direction substantially parallel to that anode (22).   2. Treatment system (10) for exhaust gases according to the preceding claim, characterized in that the treatment element (16) is cylindrical with a longitudinal axis o parallel to the direction of gas flow in the line exhaust (14), in that the anode (22) is a conductive wire which extends along the longitudinal axis, and in that the cathode (24)   is guardian and envelops the treatment element (16).   3. exhaust gas treatment system (10) according to claim 1, characterized in that the treatment element (16) is of rectangular shape, two opposite walls (42,44) of which are parallel to the direction of the anode (22), and in that it comprises two cathodes (24) which are arranged on the opposite walls (42, 44) so that electrical discharges or occur simultaneously between the anode (22) and the two cathodes (24).   4. gas treatment system (10) according to the preceding claim, characterized in that the anode (22) and / or at least one cathode (24) is a plate made of material driver.   S. Gas treatment system (10) according to claim 3, characterized in that the anode (22) and / or at least one cathode (24) is a network of conductive wires (40) which extends in a plane parallel to the direction of gas flow in the exhaust line (14).   6. Processing system (10) according to the preceding claim, characterized in that the conducting wires (40) are   to parallel to the direction of flow of the exhaust gases (G).   7. Treatment system (10) according to claim 5,   characterized in that the conductive wires (40) are perpendicular   the direction of the exhaust gas flow direction (G).   8. Processing system (10) according to any one of   s claims 3 to 7, characterized in that the   treatment (16) consists of two blocks (36, 38) which are arranged on either side of the anode (22) so that a block   (36, 38) is interposed between the anode (22) and each cathode (24).   9. Processing system (10) according to any one of   o Claims 3 to 8, characterized in that it consists of a   stack of treatment elements (16), and in that two adjacent treatment elements (16) have a cathode common (54).   10. Processing system (10) according to any one of   previous claims, characterized in that the element of   treatment (16) comprises a particle filter.   11. Processing system (10) according to any one of   previous claims, characterized in that it comprises a   catalyst, in particular an oxide reduction catalyst