EP1662105B1 - System for treating NOx in the exhaust gas stream of an automotive internal combustion engine - Google Patents

System for treating NOx in the exhaust gas stream of an automotive internal combustion engine Download PDF

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Publication number
EP1662105B1
EP1662105B1 EP05292350A EP05292350A EP1662105B1 EP 1662105 B1 EP1662105 B1 EP 1662105B1 EP 05292350 A EP05292350 A EP 05292350A EP 05292350 A EP05292350 A EP 05292350A EP 1662105 B1 EP1662105 B1 EP 1662105B1
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EP
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Prior art keywords
plasma
temperature
catalyst
catalytic
temperatures
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EP05292350A
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German (de)
French (fr)
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EP1662105A1 (en
Inventor
François Baudin
Stéphanie Schneider
Yvane Lendresse
Sabine Calvo
Patrick Da Costa
Gérald DJEGA-MARIADASSOU
Cyril Thomas
Ahmed Khacef
Jean-Marie Cormier
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Universite Pierre et Marie Curie Paris 6
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Universite Pierre et Marie Curie Paris 6
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/24—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by constructional aspects of converting apparatus
    • F01N3/28—Construction of catalytic reactors
    • F01N3/2803—Construction of catalytic reactors characterised by structure, by material or by manufacturing of catalyst support
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F01N13/0097—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are arranged in a single housing
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0892—Electric or magnetic treatment, e.g. dissociation of noxious components
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/28—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being a plasma reactor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2370/00—Selection of materials for exhaust purification

Definitions

  • the present invention relates to a system for treating the nitrogen oxides of the exhaust gas of a motor vehicle engine, comprising, in an exhaust line thereof, means for producing non-thermal plasma at from the exhaust gases they receive at the inlet and the nitrogen oxide reduction catalyst forming means arranged at the outlet of the plasma production means.
  • the combustion of an air / fuel mixture in a motor vehicle engine produces oxides of nitrogen (nitrogen monoxide NO and nitrogen dioxide NO 2 ).
  • a technology for the treatment of NOx present in the exhaust gas uses a catalyst arranged in the exhaust line of the engine.
  • a catalyst has a permanent catalytic activity during the operation of the engine.
  • Such a catalyst uses unburnt hydrocarbons from the exhaust gases to reduce NOx at catalytic sites provided for this purpose.
  • the thermal window of catalytic activity of such a catalyst i.e., the temperature range where the catalyst is effective in reducing NOx, is relatively low.
  • its use is incompatible with the operation of a vehicle engine for particular whose exhaust temperature can vary widely.
  • the document WO 00/43469 A discloses a device and method for removing at least a portion of at least one pollutant in an exhaust gas stream containing an exhaust gas formed from the combustion of fuel in a lean-burn engine.
  • the document BE 1006164A discloses a catalyst device for the reduction of nitrogen oxides in an exhaust gas which occurs in a wide range of temperatures.
  • the object of the present invention is to solve the aforementioned problem by proposing a NOx treatment system emitted by a motor vehicle engine having a thermal window of significant catalytic activity and compatible with a substantially permanent operation of the engine lean mixture, so that such a system can be implanted in motor vehicles for particular for effective treatment of NOx.
  • a motor vehicle engine 10 is associated with means 12 for supplying fuel to its cylinders and means 14 for admitting air at its inlet.
  • the engine 10 is also associated with an exhaust line 16 of its exhaust gas comprising a reactor 18 for producing non-thermal plasma.
  • the reactor 18 comprises a cylindrical body comprising at least a first peripheral electrode connected to the ground of high voltage electrical supply means and a second central electrode, in the form of a wire, connected to a terminal of setpoint voltage of the high voltage supply means.
  • the power supply means 20 are controllable and connected to the vehicle battery, for example. They comprise a waveform generator suitable for forming electric discharges in the exhaust gas passing through the reactor 18 to thereby produce a non-thermal plasma.
  • the means 20 are adapted to deliver predetermined voltage pulses to the reactor electrodes or a sinusoidal voltage.
  • the catalyst 22 comprises a plurality of successive separate catalytic elements 22a, 22b, 22c arranged in series.
  • Each of these catalytic elements has a catalytic activity (NOx conversion rate) in a variable thermal window depending on the nature of the gases they treat, that is to say depending in particular on the composition of the gases. unburned hydrocarbon exhaust and plasma exhaust gas characteristics, as will be explained in more detail later.
  • the thermal windows of the elements 22a, 22b, 22c of the catalyst 22 are complementary, a first window being in low temperatures, a second in intermediate temperatures and a third in high temperatures.
  • the total thermal window of catalytic activity of the catalyst 22 is important, as will be explained in more detail later.
  • the operation of the motor 10 and of the components which have just been described is controlled by a unit 24 implementing a NOx treatment control strategy which maximizes the catalytic activity of the catalyst 22 for the exhaust gas temperature, while by minimizing the fuel consumption induced by the reactor 18 power supply.
  • a first temperature sensor 26 is arranged upstream of the catalyst 22 to acquire the temperature of the exhaust gas at the inlet thereof and delivers the upstream temperature acquired to the unit 24.
  • a second temperature sensor 28 is also provided downstream of the catalyst 22 to acquire the temperature of the exhaust gas leaving the latter, and delivers the downstream temperature acquired to the unit 24.
  • Means 30 for acquiring the operating point of the motor 10, for example the rotational speed thereof, the motor torque required by the driver and / or the air flow at the input of the motor 10, are also provided and deliver the operating point acquired to the unit 24.
  • These means 30 comprise for example a speed sensor for the acquisition of the rotational speed of the motor 10, a position sensor of the accelerator pedal for the acquisition of the requested torque and a flowmeter arranged at the inlet of the intake means 14 for acquiring the air flow admitted into the engine 10.
  • a second embodiment of the reactor and the catalyst is schematically presented on the figure 2 .
  • identical or similar elements are referenced by the same number.
  • the reactor 18 and the catalyst 22 are structurally similar to those of the figure 1 but are incorporated in the same body 32, that is to say that the reactor 18 is arranged inside the catalyst 22.
  • the non-thermal plasma is directly produced from the gases present in the catalyst.
  • the reaction medium bathing the catalytic elements of the catalyst comprises a concentration of reactive elements, such as free radicals for example, greater because of the time of transport thereof to the catalytic elements with respect to to this one of the embodiment of the figure 1 .
  • the catalytic element 22a upstream of the catalyst has a catalytic activity in a high temperature window, that is to say having a main catalytic activity between about 300 ° C and about 500 ° C without plasma in the treated gases, and between about 200 ° C and about 400 ° C with plasma in the treated gases.
  • the upstream catalytic element is Al 2 O 3 alumina.
  • Table 1 presents the main characteristics of alumina Al 2 O 3 illustrated in FIGS. 3A, 3B, 4A and 4B .
  • the nature of the exhaust gas treated with alumina depends on their unburned hydrocarbon composition at the engine outlet.
  • the unburned hydrocarbons present at the outlet of the engine in the exhaust gas are substantially propene.
  • the unburned hydrocarbons present at the engine outlet are a mixture of propene, propane, toluene and decane in the standard proportions of exhaust gas of a heat engine.
  • the nature of the treated exhaust gas also depends on the presence or absence of non-thermal plasma in the alumina-treated gases.
  • a first main column “Propene” of Table 1 refers to the catalytic properties of Al 2 O 3 alumina in the presence of propene as a major reducer in the exhaust gas at the engine outlet.
  • a second main column “Hydrocarbon mixture” refers to these same properties in the presence of the mixture of unburned hydrocarbons in the exhaust gas leaving the engine.
  • a first main line of Table 1 “Plasma-free” refers to the catalytic properties of alumina Al 2 O 3 in the absence of plasma in the treated exhaust gas and a second main line “With plasma” refers these same properties in the presence of plasma.
  • Each of the first and second main columns of Table 1 is divided between a first column "Window (° C)", which lists thermal windows of catalytic activities of alumina Al 2 O 3 , and a column “AC (%) which lists the minimal catalytic activities of alumina Al 2 O 3 corresponding to these thermal windows.
  • Table 1 Catalytic activity of alumina Al ⁇ sub> 2 ⁇ / sub> O ⁇ sub> 3 ⁇ / sub> depending on the temperature and the nature of the treated gases.
  • the intermediate catalytic element 22b of the catalyst 22, downstream of the upstream catalytic element 22a, has a thermal window of intermediate catalytic activity, lower than that of the first upstream catalytic element, that is to say having a catalytic activity main between about 200 ° C and about 300 ° C with or without plasma in the treated gases.
  • This intermediate catalytic element 22b is for example formed of a transition metal deposit on cerium and zirconium oxides.
  • the intermediate catalytic element 22b is of the Rh / Ce0 2 -Zr0 2 and / or Pd / Ce0 2 -Zr0 2 type .
  • Table 2 organized identically in Table 1, shows the main catalytic characteristics, as illustrated in FIGS. 5A, 5B, 6A and 6B of an element of the type Pd-Rh / Ce0 2 -Zr0 2 as a function of the temperature and the nature of the gases described previously.
  • Table 2 Catalytic activity of Pd-Rh / Ce0 ⁇ sub> 2 ⁇ / sub> -Zr0 ⁇ sub> 2 ⁇ / sub> as a function of the temperature and the nature of the gases treated.
  • the catalytic element 22c downstream of the catalyst 22, downstream of the intermediate catalytic element 22b, has a thermal window of low catalytic activity, lower than that of the intermediate catalytic element 22b, that is to say having a main catalytic activity between about 150 ° C and about 300 ° C with or without plasma in the treated gases.
  • This downstream element 22c is for example formed of a deposit of precious metal on cerium and zirconium oxides.
  • the catalytic element 22c downstream is Ag / Ce0 2 -Zr0 2 type .
  • Table 3 organized identically in Table 1, shows the main catalytic characteristics, as illustrated in FIGS. 7A, 7B, 8A and 8B of an element of the Ag / Ce0 2 -Zr0 2 type as a function of the temperature and the nature of the gases described previously.
  • Table 3 Catalytic activity of Ag / Ce0 ⁇ sub> 2 ⁇ / sub> -Zr0 ⁇ sub> 2 ⁇ / sub> as a function of the temperature and the nature of the gases treated.
  • propene Hydrocarbon mixture Window (° C) AC (%) Window (° C) AC (%) Without plasma 200-250 10 200-250 10 300-400 300-400 250-300 18 250-300 18 With plasma 150-400 20
  • thermal windows of catalytic activity of the various elements 22a, 22b, 22c are complementary and decrease in the direction of the flow of the exhaust gases in the exhaust line 16.
  • each of the elements 22a, 22b, 22c of the catalyst 22 exhibits a total catalytic activity as a function of the temperature and the nature of the treated exhaust gases as illustrated in FIGS. FIGS. 9A, 9B, 10A and 10B .
  • Table 4 organized in a manner identical to Table 1, summarizes the main characteristics of the catalyst 22.
  • Table 4 total catalytic activity of the catalyst, formed successively, in the gas flow direction, of Al ⁇ sub> 2 ⁇ / sub> O ⁇ sub> 3 ⁇ / sub>, of Pd-Rh / Ce0 ⁇ sub > 2 ⁇ / sub> -Zr0 ⁇ sub> 2 ⁇ / sub> and Ag / Ce0 ⁇ sub> 2 ⁇ / sub> -Zr0 ⁇ sub> 2 ⁇ / sub> depending on the temperature and nature of the gases treaties.
  • the catalyst 22 thus has a catalytic activity in a thermal window at least equal to [200-500] ° C., which makes it possible to obtain NOx treatment in a wide operating range of a particular vehicle engine.
  • the three catalytic elements Al 2 O 3 , Ph-Rh / CeO 2 -ZrO 2 and Ag / CeO 2 -ZrO 2 are deposited on a single support, such as cordielite, mullite, carborundum (SiC ), metal, or any type of substrate suitable for use as a catalyst support.
  • the unit 24 comprises means 40 for storing a first and a second threshold temperature T1, T2.
  • the storage means 40 are connected to first and second comparison means 42, 44 of the threshold temperatures T1, T2 at the upstream temperatures Td and downstream Td respectively acquired.
  • T1, T2 threshold temperatures are for example determined experimentally and depend in particular on the composition of catalytic elements, their precious metal charge and the catalyst volume, as well as the adjustment of the engine.
  • T1 is for example equal to 200 ° C and T2 is for example equal to 350 ° C.
  • the activation / deactivation means 46 activate the high voltage power supply of the plasma production reactor if this activation has the effect of a significant catalytic activity increase of the catalyst, for example greater than 10%.
  • the activation / deactivation means 46 does not energize the plasma generating reactor, an activation condition of this reactor being that at least one type of catalyst element present in the catalyst 22 is in a primed state.
  • the NOx are then not treated by the non-primed catalytic elements and thus pass through the catalyst without reduction in nitrogen. Indeed, the activation of the reactor would have substantially no effect on the catalytic activity of the catalyst. This phase corresponds to the cold start of the vehicle.
  • the catalytic elements are ignited and the means 46 activate the reactor for the production of plasma.
  • the three catalytic elements including alumina whose thermal window is located in the high temperatures in the absence of plasma with an evolution thereof to lower temperatures in the presence of plasma discharges in the exhaust gas, participate in the reduction of NOx exhaust gas.
  • the activation of the reactor thus results in a significant gain in the total catalytic activity of the catalyst greater than 10%, thus justifying the overconsumption of fuel induced by the activity of the reactor.
  • the means 46 control the means 20 for supplying the reactor steadily.
  • the supply means 20 are controlled by the activation / deactivation means 46 so that they deliver to the electrodes of the reactor a power of between 250 and 300 W, for example.
  • the means 46 control the supply means 20 according to the amount of NOx present in the exhaust gas and / or the temperature thereof.
  • the means 46 receive the operating point Pf of the engine and determine, for example by means of a predetermined map and stored therein, the amount of NOx emitted by the engine for the operating point. The means 46 then control the feed means 20 of the reactor so that they deliver a modulated power according to the amount of NOx determined, for example increasing in function of an increasing amount of NOx emitted by the engine.
  • the means 46 deactivate the plasma production reactor. Indeed, for temperatures greater than T2, only the high temperature catalytic element, that is to say alumina, has a catalytic activity. However, for these temperatures, the thermal window of catalytic activity of alumina is significantly greater without plasma than with plasma in the presence of the hydrocarbon mixture in the exhaust gases, as is illustrated in FIGS. Figures 4A and 4B . Since the activity gain by activation of the reactor is zero, the reactor is not activated for temperatures greater than T2. This makes it possible to reduce the fuel consumption of the engine for the production of energy necessary for the operation of the reactor supply means.
  • the means 46 are also adapted to control the operation of the motor supply means and / or the air inlet intake means of the engine in order to modify the unburned hydrocarbon composition of the exhaust gases and thus modulate the catalytic activity of the catalyst as a function of the composition of the exhaust gas in propene or in a mixture of hydrocarbons.
  • the means 46 is capable of modifying the fuel injection strategy in the engine cylinders by controlling a late injection of fuel therein, or post-injection.
  • the post-injection of fuel into the engine cylinders has the effect of significantly increasing the amount of unburned hydrocarbons in the exhaust gas, which leads to a temporary increase in the HC / NOx ratio of the amount of unburned hydrocarbons the amount of NOx in the exhaust gas, and therefore to an improvement in the conversion of NOx into nitrogen.
  • This unit implements in a simple manner a control strategy which maximizes, as a function of temperature, the catalytic activity of a catalyst comprising three complementary catalytic elements, in a broad thermal window of approximately [200, 500] ° C. while minimizing fuel over-consumption induced by the use of a plasma generating reactor.
  • system according to the invention may comprise a single sensor placed upstream of the catalyst, and the control unit is adapted to compare this acquired temperature with the aforementioned threshold temperatures for a control of the reactor supply means similar to that described previously.
  • the acquired downstream temperature being substantially that of the last catalytic element of the catalyst, which allows a control closer to the temperature thereof.
  • the catalyst may comprise 2 or more portions of catalytic element types.
  • Another variant consists in replacing the catalytic elements of Ag / CeO 2 -ZrO 2 and Pd-Rh / CeO 2 -ZrO 2 type with a material containing no precious metals, namely two elements of CeO 2 -ZrO 2 , so that the cost of the system is significantly reduced due to the absence of precious metals.
  • the catalyst comprises an alumina Al 2 O3 portion upstream of a portion of CeO 2 -ZrO 2.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Combustion & Propulsion (AREA)
  • Toxicology (AREA)
  • Health & Medical Sciences (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
  • Treating Waste Gases (AREA)
  • Control Of Eletrric Generators (AREA)
  • Hybrid Electric Vehicles (AREA)
  • Catalysts (AREA)

Abstract

The system has an exhaust pipe (16) with a reactor (18) producing non-thermal plasma from exhaust gas received in its inlet. A catalyst (22) arranged in a downstream of the reactor reduces nitrogen oxide. The catalyst has different catalytic units (22a, 22b, 22c) including thermal windows for different catalytic activities. The windows are complementary and are operated in high, medium and low temperatures, respectively.

Description

La présente invention concerne un système de traitement des oxydes d'azote de gaz d'échappement d'un moteur thermique de véhicule automobile, comprenant, dans une ligne d'échappement de celui-ci, des moyens de production de plasma non-thermique à partir des gaz d'échappement qu'ils reçoivent en entrée et des moyens formant catalyseur de réduction d'oxydes d'azote agencés en sortie des moyens de production de plasma.The present invention relates to a system for treating the nitrogen oxides of the exhaust gas of a motor vehicle engine, comprising, in an exhaust line thereof, means for producing non-thermal plasma at from the exhaust gases they receive at the inlet and the nitrogen oxide reduction catalyst forming means arranged at the outlet of the plasma production means.

La combustion de mélange air/carburant dans un moteur thermique de véhicule automobile produit des oxydes d'azotes (monoxyde d'azote NO et dioxyde d'azote NO2).The combustion of an air / fuel mixture in a motor vehicle engine produces oxides of nitrogen (nitrogen monoxide NO and nitrogen dioxide NO 2 ).

Une technologie pour le traitement des NOx présents dans les gaz d'échappement, connue sous le nom de DeNOx permanente, utilise un catalyseur agencé dans la ligne d'échappement du moteur. Un tel catalyseur présente une activité catalytique permanente pendant le fonctionnement du moteur. Un tel catalyseur utilise les hydrocarbures imbrûlés des gaz d'échappement pour réduire les NOx sur des sites catalytiques prévus à cet effet. Toutefois, la fenêtre thermique d'activité catalytique d'un tel catalyseur, c'est-à-dire la plage de températures où le catalyseur est efficace pour réduire les NOx, est relativement faible. Aussi, son utilisation est peu compatible avec le fonctionnement d'un moteur de véhicule pour particulier dont la température des gaz d'échappement peut varier dans de larges mesures.A technology for the treatment of NOx present in the exhaust gas, known as the permanent DeNOx, uses a catalyst arranged in the exhaust line of the engine. Such a catalyst has a permanent catalytic activity during the operation of the engine. Such a catalyst uses unburnt hydrocarbons from the exhaust gases to reduce NOx at catalytic sites provided for this purpose. However, the thermal window of catalytic activity of such a catalyst, i.e., the temperature range where the catalyst is effective in reducing NOx, is relatively low. Also, its use is incompatible with the operation of a vehicle engine for particular whose exhaust temperature can vary widely.

Il est également connu de disposer un générateur de plasma en amont du catalyseur. Un tel générateur produit du plasma à partir des gaz d'échappement afin d'augmenter l'efficacité catalytique du catalyseur. Toutefois, la fenêtre thermique d'activité catalytique de cet agencement reste relativement faible, de sorte que son utilisation est également peu compatible avec le fonctionnement d'un moteur de véhicule pour particulier.It is also known to have a plasma generator upstream of the catalyst. Such a generator produces plasma from the exhaust gases to increase the catalytic efficiency of the catalyst. However, the thermal window of catalytic activity of this arrangement remains relatively small, so that its use is also incompatible with the operation of a particular vehicle engine.

Le document WO 00/43469 A décrit un dispositif et un procédé pouf enlever au moins une partie d'au moins un polluant dans un flux de gaz d'échappement contenant un gaz d'échappement formé à partir de la combustion de carburant dans un moteur en mélange pauvre.The document WO 00/43469 A discloses a device and method for removing at least a portion of at least one pollutant in an exhaust gas stream containing an exhaust gas formed from the combustion of fuel in a lean-burn engine.

Le document BE 1006164A décrit un dispositif de catalyseur pour la réduction des oxydes d'azote dans un gaz d'échappement qui se présente dans une large gamme de températures.The document BE 1006164A discloses a catalyst device for the reduction of nitrogen oxides in an exhaust gas which occurs in a wide range of temperatures.

Le but de la présente invention est de résoudre le problème susmentionné en proposant un système de traitement des NOx émis par un moteur thermique de véhicule automobile présentant une fenêtre thermique d'activité catalytique importante et compatible avec un fonctionnement sensiblement permanent du moteur en mélange pauvre, de sorte qu'un tel système peut être implanté dans des véhicules automobiles pour particulier pour un traitement efficace des NOx.The object of the present invention is to solve the aforementioned problem by proposing a NOx treatment system emitted by a motor vehicle engine having a thermal window of significant catalytic activity and compatible with a substantially permanent operation of the engine lean mixture, so that such a system can be implanted in motor vehicles for particular for effective treatment of NOx.

A cet effet, l'invention a pour objet un système de traitement des NOx de gaz d'échappement d'un moteur thermique de véhicule automobile, comprenant, dans une ligne d'échappement de celui-ci, des moyens de production de plasma non-thermique à partir des gaz d'échappement qu'ils reçoivent en entrée et des moyens formant catalyseur DeNOx agencés en sortie des moyens de production de plasma, caractérisé en ce que les moyens formant catalyseur comprennent des éléments catalytiques de types différents présentant des fenêtres thermiques d'activités catalytiques complémentaires et variables en fonction de la nature des gaz qu'ils traitent, ledit système comprenant en outre :

  • des premiers moyens d'acquisition de la température des gaz d'échappement en amont des moyens formant catalyseur ; et
  • des moyens de commande des moyens de production de plasma en fonction de la température acquise pour optimiser la réduction des NOx à cette température,
lesdits moyens de commande activant lesdits moyens de production de plasma si, pour la température amont acquise, le gain d'activité catalytique totale d'une telle activation est supérieur à un seuil prédéterminé.For this purpose, the subject of the invention is an exhaust gas NOx treatment system for a motor vehicle engine, comprising, in an exhaust line thereof, non-conventional plasma production means. -thermal from the exhaust gases they receive at the inlet and DeNOx catalyst means arranged at the output of the plasma production means, characterized in that the catalyst means comprise catalytic elements of different types having thermal windows complementary and variable catalytic activities depending on the nature of the gases they treat, said system further comprising:
  • first means for acquiring the temperature of the exhaust gas upstream of the catalyst means; and
  • means for controlling the plasma production means as a function of the temperature acquired to optimize the reduction of NOx at this temperature,
said control means activating said plasma generating means if, for the acquired upstream temperature, the total catalytic activity gain of such an activation is greater than a predetermined threshold.

Selon d'autres caractéristiques :

  • les types d'éléments catalytiques sont sélectionnés pour que la fenêtre thermique totale d'activité catalytique des moyens formant catalyseur comprennent la fenêtre de 200°C à 500°C ;
  • les éléments catalytiques sont choisis dans le groupe consistant en du Al2O3, et du CeO2-ZrO2 imprégné d'un élément métallique de transition ou précieux ;
  • les éléments catalytiques sont successivement, dans le sens de l'écoulement des gaz d'échappement, de l'Al2O3, du Rh-Pd/CeO2-ZrO2 et du Ag/CeO2-ZrO2 ;
  • les éléments catalytiques sont déposés sur un support unique ;
  • le support unique est choisi dans le groupe consistant en de la cordierite, de la mullite, du SiC et du métal ;
  • les éléments catalytiques sont choisis dans le groupe consistant en du Al2O3 et du CeO2-ZrO2 ;
  • les moyens de production de plasma non-thermique sont agencés à l'intérieur des moyens formant catalyseur ;
  • il comprend des seconds moyens d'acquisition de la température en aval des moyens formant catalyseur, et les moyens de commande comprennent des moyens de détermination de l'état d'amorçage des types d'éléments catalytiques en fonction de ces températures acquises, et une condition d'activation des moyens de production de plasma est qu'au moins un type d'éléments catalytiques soit amorcé ;
  • les moyens de commande comprennent des moyens de comparaison des températures amont et aval acquises à des première et seconde températures de seuil prédéterminées respectivement, et :
    • lorsque les températures amont et aval sont inférieures à leurs températures de seuil respectives, les moyens de production de plasma sont inactifs ;
    • lorsque la température amont est supérieure à la première température de seuil et la température aval inférieure à la seconde température de seuil, les moyens de production de plasma sont actifs ; et
    • lorsque les températures amont et aval sont supérieures à leurs températures de seuil respectives, les moyens de production de plasma sont inactifs ;
  • les première et seconde températures de seuil sont respectivement d'environ 200°C et 350°C ; et
  • les moyens de commande sont en outre adaptés pour commander l'alimentation de carburant dans les cylindres du moteur et/ou le débit d'air admis dans le moteur pour modifier la composition en hydrocarbure des gaz d'échappement en sortie de celui-ci.
According to other characteristics:
  • the types of catalytic elements are selected so that the total thermal window of catalytic activity of the catalyst means comprises the window of 200 ° C to 500 ° C;
  • the catalytic elements are selected from the group consisting of Al 2 O 3 , and CeO 2 -ZrO 2 impregnated with a transition or precious metal element;
  • the catalytic elements are successively, in the direction of the flow of the exhaust gas, Al 2 O 3 , Rh-Pd / CeO 2 -ZrO 2 and Ag / CeO 2 -ZrO 2 ;
  • the catalytic elements are deposited on a single support;
  • the single support is selected from the group consisting of cordierite, mullite, SiC and metal;
  • the catalytic elements are selected from the group consisting of Al 2 O 3 and CeO 2 -ZrO 2 ;
  • the non-thermal plasma production means are arranged inside the catalyst means;
  • it comprises second means for acquiring the temperature downstream of the catalyst means, and the control means comprise means for determining the starting state of the types of catalytic elements as a function of these temperatures acquired, and a the activation condition of the plasma generating means is that at least one type of catalytic element is initiated;
  • the control means comprise means for comparing the upstream and downstream temperatures acquired at first and second predetermined threshold temperatures respectively, and:
    • when the upstream and downstream temperatures are below their respective threshold temperatures, the plasma generating means are inactive;
    • when the upstream temperature is higher than the first threshold temperature and the downstream temperature lower than the second threshold temperature, the plasma generating means are active; and
    • when the upstream and downstream temperatures are above their respective threshold temperatures, the plasma generating means are inactive;
  • the first and second threshold temperatures are respectively about 200 ° C and 350 ° C; and
  • the control means are further adapted to control the supply of fuel to the engine cylinders and / or the flow rate of air admitted into the engine to modify the hydrocarbon composition of the exhaust gases leaving the engine.

L'invention sera mieux comprise à la lecture de la description qui va suivre, donnée uniquement à titre d'exemple et faite en relation avec les dessins annexés, dans lesquels :

  • la figure 1 est une vue schématique d'un système conforme à l'invention associé à une unité de propulsion à moteur thermique d'un véhicule automobile ;
  • la figure 2 est une vue schématique d'un second mode de réalisation de la ligne d'échappement du système de la figure 1 ;
  • les figures 3A et 3B sont des graphiques illustrant l'activité catalytique de l'Al2O3 en fonction de la température, en présence de propène en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement ;
  • les figures 4A et 4B sont des graphiques illustrant l'activité catalytique de l'Al2O3 en fonction de la température, en présence d'un mélange d'hydrocarbures en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement;
  • les figures 5A et 5B sont des graphiques illustrant l'activité catalytique du Rh-Pd/CeO2-ZrO2 en fonction de la température, en présence de propène en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement;
  • les figures 6A et 6B sont des graphiques illustrant l'activité catalytique du Rh-Pd/CeO2-ZrO2 en fonction de la température, en présence du mélange d'hydrocarbures en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement;
  • les figures 7A et 7B sont des graphiques illustrant l'activité catalytique du Ag/CeO2-ZrO2 en fonction de la température, en présence de propène en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement;
  • les figures 8A et 8B sont des graphiques illustrant l'activité catalytique du Ag/CeO2-ZrO2 en fonction de la température, en présence du mélange d'hydrocarbures en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement;
  • les figures 9A et 9B sont des graphiques illustrant l'activité catalytique totale d'un catalyseur entrant dans la constitution de la figure 1 ou la figure 2 en fonction de la température, en présence de propène en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement;
  • les figures 10A et 10B sont des graphiques illustrant l'activité catalytique totale d'un catalyseur entrant dans la constitution de la figure 1 ou de la figure 2 en fonction de la température, en présence du mélange d'hydrocarbures en tant que réducteur de NOx, sans et avec traitement plasmatique des gaz d'échappement respectivement; et
  • la figure 11 est une vue schématique d'une unité de contrôle entrant dans la constitution du système de la figure 1.
The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the accompanying drawings, in which:
  • the figure 1 is a schematic view of a system according to the invention associated with a thermal engine propulsion unit of a motor vehicle;
  • the figure 2 is a schematic view of a second embodiment of the system exhaust line of the figure 1 ;
  • the Figures 3A and 3B are graphs illustrating the catalytic activity of Al 2 O 3 as a function of temperature, in the presence of propene as a NOx reducing agent, with and without plasma treatment of the exhaust gases respectively;
  • the Figures 4A and 4B are graphs illustrating the catalytic activity of Al 2 O 3 as a function of temperature, in the presence of a mixture of hydrocarbons as a NOx reducing agent, with and without plasma treatment of the exhaust gases respectively;
  • the Figures 5A and 5B are graphs illustrating the catalytic activity of Rh-Pd / CeO 2 -ZrO 2 as a function of temperature, in the presence of propene as a NOx reductant, with and with plasma treatment of the exhaust gases respectively;
  • the Figures 6A and 6B are graphs illustrating the catalytic activity of Rh-Pd / CeO 2 -ZrO 2 as a function of temperature, in the presence of the mixture of hydrocarbons as NOx reducing agent, with and with plasma treatment of the exhaust gases respectively;
  • the Figures 7A and 7B are graphs illustrating the catalytic activity of Ag / CeO 2 -ZrO 2 as a function of temperature, in the presence of propene as a NOx reducing agent, with and without plasma treatment of the exhaust gases respectively;
  • the Figures 8A and 8B are graphs illustrating the catalytic activity of Ag / CeO 2 -ZrO 2 as a function of temperature, in the presence of the mixture of hydrocarbons as a NOx reducing agent, with and with plasma treatment of the exhaust gases respectively;
  • the Figures 9A and 9B are graphs illustrating the total catalytic activity of a catalyst involved in the constitution of the figure 1 or the figure 2 depending on the temperature, in the presence of propene as NOx reductant, with and without plasma treatment of the exhaust gases respectively;
  • the Figures 10A and 10B are graphs illustrating the total catalytic activity of a catalyst involved in the constitution of the figure 1 or from figure 2 depending on the temperature, in the presence of the hydrocarbon mixture as a NOx reducing agent, with and without plasma treatment of the exhaust gases respectively; and
  • the figure 11 is a schematic view of a control unit entering the constitution of the system of the figure 1 .

Sur la figure 1, un moteur thermique 10 de véhicule automobile est associé à des moyens 12 d'alimentation en carburant de ses cylindres et des moyens 14 d'admission d'air en entrée de celui-ci.On the figure 1 a motor vehicle engine 10 is associated with means 12 for supplying fuel to its cylinders and means 14 for admitting air at its inlet.

Le moteur 10 est également associé à une ligne d'échappement 16 de ses gaz d'échappement comprenant un réacteur 18 de production de plasma non-thermique.The engine 10 is also associated with an exhaust line 16 of its exhaust gas comprising a reactor 18 for producing non-thermal plasma.

Le réacteur 18 est par exemple constitué d'un corps cylindrique comprenant au moins une première électrode périphérique connectée à la masse de moyens 20 d'alimentation électrique haute tension et d'une seconde électrode centrale, en forme de fil, connectée à une borne de tension de consigne des moyens 20 d'alimentation haute tension.For example, the reactor 18 comprises a cylindrical body comprising at least a first peripheral electrode connected to the ground of high voltage electrical supply means and a second central electrode, in the form of a wire, connected to a terminal of setpoint voltage of the high voltage supply means.

Les moyens 20 d'alimentation sont commandables et connectés à la batterie du véhicule par exemple. Ils comprennent un générateur de formes d'onde appropriées pour la formation de décharges électriques dans les gaz d'échappement traversant le réacteur 18 pour ainsi produire un plasma non-thermique.The power supply means 20 are controllable and connected to the vehicle battery, for example. They comprise a waveform generator suitable for forming electric discharges in the exhaust gas passing through the reactor 18 to thereby produce a non-thermal plasma.

Par exemple, les moyens 20 sont adaptés pour délivrer des impulsions de tension prédéterminées aux électrodes du réacteur ou une tension sinusoïdale.For example, the means 20 are adapted to deliver predetermined voltage pulses to the reactor electrodes or a sinusoidal voltage.

Un catalyseur 22 de réduction des NOx, agencé en aval du réacteur 18 dans la ligne d'échappement 16, reçoit les gaz d'échappement en sortie du réacteur 18, c'est-à-dire directement les gaz d'échappement du moteur ou le plasma non-thermique produit par le réacteur 18 selon que celui-ci est actif ou non.A NOx reduction catalyst 22, arranged downstream of the reactor 18 in the exhaust line 16, receives the exhaust gas at the outlet of the reactor 18, that is to say directly the exhaust gas from the engine or the non-thermal plasma produced by the reactor 18 according to whether it is active or not.

Le catalyseur 22 comprend une pluralité d'éléments catalytiques 22a, 22b, 22c distincts successifs agencés en série.The catalyst 22 comprises a plurality of successive separate catalytic elements 22a, 22b, 22c arranged in series.

Chacun de ces éléments catalytiques présente une activité catalytique (taux de conversion des NOx) dans une fenêtre thermique variable en fonction de la nature des gaz qu'ils traitent, c'est-à-dire en fonction notamment de la composition des gaz d'échappement en hydrocarbures imbrûlés et des caractéristiques plasmatiques des gaz d'échappement, comme cela sera expliqué plus en détail par la suite.Each of these catalytic elements has a catalytic activity (NOx conversion rate) in a variable thermal window depending on the nature of the gases they treat, that is to say depending in particular on the composition of the gases. unburned hydrocarbon exhaust and plasma exhaust gas characteristics, as will be explained in more detail later.

De manière avantageuse, les fenêtres thermiques des éléments 22a, 22b, 22c du catalyseur 22 sont complémentaires, une première fenêtre étant comprise dans des températures basses, une seconde dans des températures intermédiaires et une troisième dans les hautes températures. Ainsi, la fenêtre thermique totale d'activité catalytique du catalyseur 22 est importante, comme cela sera également expliqué plus en détail par la suite.Advantageously, the thermal windows of the elements 22a, 22b, 22c of the catalyst 22 are complementary, a first window being in low temperatures, a second in intermediate temperatures and a third in high temperatures. Thus, the total thermal window of catalytic activity of the catalyst 22 is important, as will be explained in more detail later.

Le fonctionnement du moteur 10 et des organes qui viennent d'être décrits est commandé par une unité 24 mettant en oeuvre une stratégie de contrôle du traitement des NOx qui maximise l'activité catalytique du catalyseur 22 pour la température des gaz d'échappement, tout en minimisant la consommation de carburant induite par l'alimentation en énergie du réacteur 18.The operation of the motor 10 and of the components which have just been described is controlled by a unit 24 implementing a NOx treatment control strategy which maximizes the catalytic activity of the catalyst 22 for the exhaust gas temperature, while by minimizing the fuel consumption induced by the reactor 18 power supply.

Un premier capteur de température 26 est agencé en amont du catalyseur 22 pour acquérir la température des gaz d'échappement en entrée de celui-ci et délivre la température amont acquise à l'unité 24.A first temperature sensor 26 is arranged upstream of the catalyst 22 to acquire the temperature of the exhaust gas at the inlet thereof and delivers the upstream temperature acquired to the unit 24.

Dans le mode de réalisation préféré de l'invention, un second capteur de température 28 est également prévu en aval du catalyseur 22 pour acquérir la température des gaz d'échappement en sortie de celui-ci, et délivre la température aval acquise à l'unité 24.In the preferred embodiment of the invention, a second temperature sensor 28 is also provided downstream of the catalyst 22 to acquire the temperature of the exhaust gas leaving the latter, and delivers the downstream temperature acquired to the unit 24.

Des moyens 30 d'acquisition du point de fonctionnement du moteur 10, par exemple le régime de rotation de celui-ci, le couple moteur demandé par le conducteur et/ou le débit d'air en entrée du moteur 10, sont également prévus et délivrent le point de fonctionnement acquis à l'unité 24.Means 30 for acquiring the operating point of the motor 10, for example the rotational speed thereof, the motor torque required by the driver and / or the air flow at the input of the motor 10, are also provided and deliver the operating point acquired to the unit 24.

Ces moyens 30 comprennent par exemple un capteur de régime pour l'acquisition du régime de rotation du moteur 10, un capteur de la position de la pédale d'accélérateur pour l'acquisition du couple demandé et un débitmètre agencée en entrée des moyens 14 d'admission pour l'acquisition du débit d'air admis dans le moteur 10.These means 30 comprise for example a speed sensor for the acquisition of the rotational speed of the motor 10, a position sensor of the accelerator pedal for the acquisition of the requested torque and a flowmeter arranged at the inlet of the intake means 14 for acquiring the air flow admitted into the engine 10.

Un second mode de réalisation du réacteur et du catalyseur est présenté de manière schématique sur la figure 2. Sur les figures 1 et 2, les éléments identiques ou analogues sont référencés par le même numéro.A second embodiment of the reactor and the catalyst is schematically presented on the figure 2 . On the Figures 1 and 2 identical or similar elements are referenced by the same number.

Dans ce mode de réalisation, le réacteur 18 et le catalyseur 22 sont structurellement analogues à ceux de la figure 1, mais sont incorporés dans un même corps 32, c'est-à-dire que le réacteur 18 est agencé à l'intérieur du catalyseur 22.In this embodiment, the reactor 18 and the catalyst 22 are structurally similar to those of the figure 1 but are incorporated in the same body 32, that is to say that the reactor 18 is arranged inside the catalyst 22.

Ainsi, le plasma non-thermique est directement produit à partir des gaz présents dans le catalyseur. Ceci présente l'avantage que le milieu réactionnel baignant les éléments catalytiques du catalyseur comporte une concentration d'éléments réactifs, tels que des radicaux libres par exemple, plus importante du fait du temps de transport de ceux-ci vers les éléments catalytiques minimal par rapport à celui-ci du mode de réalisation de la figure 1.Thus, the non-thermal plasma is directly produced from the gases present in the catalyst. This has the advantage that the reaction medium bathing the catalytic elements of the catalyst comprises a concentration of reactive elements, such as free radicals for example, greater because of the time of transport thereof to the catalytic elements with respect to to this one of the embodiment of the figure 1 .

Il va maintenant être expliqué plus en détail la constitution du catalyseur 22 de la figure 1 ou de la figure 2 en relation avec les figures 3 à 10 qui illustrent l'activité catalytique de différents types d'éléments catalytiques en fonction de la température et de la nature des gaz traités par ceux-ci.It will now be explained in more detail the constitution of the catalyst 22 of the figure 1 or from figure 2 in relation to Figures 3 to 10 which illustrate the catalytic activity of different types of catalytic elements as a function of the temperature and the nature of the gases treated therewith.

L'élément catalytique 22a amont du catalyseur présente une activité catalytique dans une fenêtre de températures hautes, c'est-à-dire présentant une activité catalytique principale entre environ 300°C et environ 500°C sans plasma dans les gaz traités, et entre environ 200°C et environ 400°C avec plasma dans les gaz traités.The catalytic element 22a upstream of the catalyst has a catalytic activity in a high temperature window, that is to say having a main catalytic activity between about 300 ° C and about 500 ° C without plasma in the treated gases, and between about 200 ° C and about 400 ° C with plasma in the treated gases.

Par exemple, l'élément catalytique amont est de l'alumine Al2O3.For example, the upstream catalytic element is Al 2 O 3 alumina.

Le tableau 1 présente les principales caractéristiques de l'alumine Al2O3 illustrées sur les figures 3A, 3B, 4A et 4B.Table 1 presents the main characteristics of alumina Al 2 O 3 illustrated in FIGS. 3A, 3B, 4A and 4B .

La nature des gaz d'échappement traités par l'alumine dépend de leur composition en hydrocarbures imbrûlés en sortie de moteur.The nature of the exhaust gas treated with alumina depends on their unburned hydrocarbon composition at the engine outlet.

Dans une première variante, les hydrocarbures imbrûlés présents en sortie du moteur dans les gaz d'échappement sont sensiblement du propène.In a first variant, the unburned hydrocarbons present at the outlet of the engine in the exhaust gas are substantially propene.

Dans une seconde variante, les hydrocarbures imbrûlés présents en sortie du moteur sont un mélange de propène, de propane, de toluène et de décane dans les proportions classiques de gaz d'échappement d'un moteur thermique.In a second variant, the unburned hydrocarbons present at the engine outlet are a mixture of propene, propane, toluene and decane in the standard proportions of exhaust gas of a heat engine.

La nature des gaz d'échappement traités dépend également de la présence ou l'absence de plasma non-thermique dans les gaz traités par l'alumine.The nature of the treated exhaust gas also depends on the presence or absence of non-thermal plasma in the alumina-treated gases.

Une première colonne principale « Propène » du tableau 1 référence les propriétés catalytiques de l'alumine Al2O3 en présence de propène en tant que réducteur majoritaire dans les gaz d'échappement en sortie du moteur. Une seconde colonne principale « Mélange d'hydrocarbures » référence ces mêmes propriétés en présence du mélange d'hydrocarbures imbrûlés dans les gaz d'échappement en sortie du moteur.A first main column "Propene" of Table 1 refers to the catalytic properties of Al 2 O 3 alumina in the presence of propene as a major reducer in the exhaust gas at the engine outlet. A second main column "Hydrocarbon mixture" refers to these same properties in the presence of the mixture of unburned hydrocarbons in the exhaust gas leaving the engine.

Une première ligne principale du tableau 1 « Sans plasma » référence les propriétés catalytiques de l'alumine Al2O3 en absence de plasma dans les gaz d'échappement traités et une seconde ligne principale « Avec plasma » référence ces mêmes propriétés en présence de plasma.A first main line of Table 1 "Plasma-free" refers to the catalytic properties of alumina Al 2 O 3 in the absence of plasma in the treated exhaust gas and a second main line "With plasma" refers these same properties in the presence of plasma.

Chacune des première et seconde colonnes principales du tableau 1 est partagée entre une première colonne « Fenêtre (°C) », qui répertorie des fenêtres thermiques d'activités catalytiques de l'alumine Al2O3, et une colonne « AC (%) », qui répertorie les activités catalytiques minimales de l'alumine Al2O3 correspondants à ces fenêtres thermiques. Tableau 1 : activité catalytique de l'alumine Al2O3 en fonction de la température et de la nature des gaz traités. Propène Mélange d'hydrocarbures Fenêtre (°C) AC (%) Fenêtre (°C) AC (%) Sans plasma 400-500 10 300-340 10 480-500 340-355 30 440-480 355-440 40 Avec plasma 200-250 20 200-250 20 345-375 350-500 250-295 30 250-275 30 305-345 325-350 295-305 40 275-325 40 Each of the first and second main columns of Table 1 is divided between a first column "Window (° C)", which lists thermal windows of catalytic activities of alumina Al 2 O 3 , and a column "AC (%) Which lists the minimal catalytic activities of alumina Al 2 O 3 corresponding to these thermal windows. Table 1: Catalytic activity of alumina Al <sub> 2 </ sub> O <sub> 3 </ sub> depending on the temperature and the nature of the treated gases. propene Hydrocarbon mixture Window (° C) AC (%) Window (° C) AC (%) Without plasma 400-500 10 300-340 10 480-500 340-355 30 440-480 355-440 40 With plasma 200-250 20 200-250 20 345-375 350-500 250-295 30 250-275 30 305-345 325-350 295-305 40 275-325 40

L'élément catalytique 22b intermédiaire du catalyseur 22, en aval de l'élément catalytique 22a amont, présente une fenêtre thermique d'activité catalytique intermédiaire, inférieure à celle du premier élément catalytique amont, c'est-à-dire présentant une activité catalytique principale entre environ 200°C et environ 300°C avec ou sans plasma dans les gaz traités.The intermediate catalytic element 22b of the catalyst 22, downstream of the upstream catalytic element 22a, has a thermal window of intermediate catalytic activity, lower than that of the first upstream catalytic element, that is to say having a catalytic activity main between about 200 ° C and about 300 ° C with or without plasma in the treated gases.

Cet élément catalytique 22b intermédiaire est par exemple formé d'un dépôt de métal de transition sur des oxydes de cérium et de zirconium.This intermediate catalytic element 22b is for example formed of a transition metal deposit on cerium and zirconium oxides.

De manière préférentielle, l'élément catalytique 22b intermédiaire est du type Rh/Ce02-Zr02 et/ou Pd/Ce02-Zr02.Preferably, the intermediate catalytic element 22b is of the Rh / Ce0 2 -Zr0 2 and / or Pd / Ce0 2 -Zr0 2 type .

Le tableau 2, organisé de manière identique au tableau 1, présente les principales caractéristiques catalytiques, telles qu'illustrées sur les figures 5A, 5B, 6A et 6B, d'un élément du type Pd-Rh/Ce02-Zr02 en fonction de la température et de la nature des gaz décrite précédemment. Tableau 2 : activité catalytique du Pd-Rh/Ce02-Zr02 en fonction de la température et de la nature des gaz traités. Propène Mélange d'hydrocarbures Fenêtre (°C) AC (%) Fenêtre (°C) AC (%) Sans plasma 210-300 10 225-250 10 300-350 250 15 250-270 20 280-300 270-280 23 Avec plasma 200-245 20 150-230 10 255-280 355-450 245-255 30 230-270 20 280-355 270-280 23 Table 2, organized identically in Table 1, shows the main catalytic characteristics, as illustrated in FIGS. 5A, 5B, 6A and 6B of an element of the type Pd-Rh / Ce0 2 -Zr0 2 as a function of the temperature and the nature of the gases described previously. Table 2: Catalytic activity of Pd-Rh / Ce0 <sub> 2 </ sub> -Zr0 <sub> 2 </ sub> as a function of the temperature and the nature of the gases treated. propene Hydrocarbon mixture Window (° C) AC (%) Window (° C) AC (%) Without plasma 210-300 10 225-250 10 300-350 250 15 250-270 20 280-300 270-280 23 With plasma 200-245 20 150-230 10 255-280 355-450 245-255 30 230-270 20 280-355 270-280 23

L'élément catalytique 22c aval du catalyseur 22, en aval de l'élément catalytique 22b intermédiaire, présente une fenêtre thermique d'activité catalytique basse, inférieure à celle de l'élément catalytique 22b intermédiaire, c'est-à-dire présentant une activité catalytique principale entre environ 150°C et environ 300°C avec ou sans plasma dans les gaz traités.The catalytic element 22c downstream of the catalyst 22, downstream of the intermediate catalytic element 22b, has a thermal window of low catalytic activity, lower than that of the intermediate catalytic element 22b, that is to say having a main catalytic activity between about 150 ° C and about 300 ° C with or without plasma in the treated gases.

Cet élément 22c aval est par exemple formé d'un dépôt de métal précieux sur des oxydes de cérium et de zirconium.This downstream element 22c is for example formed of a deposit of precious metal on cerium and zirconium oxides.

De manière préférentielle, l'élément catalytique 22c aval est du type Ag/Ce02-Zr02.Preferably, the catalytic element 22c downstream is Ag / Ce0 2 -Zr0 2 type .

Le tableau 3, organisé de manière identique au tableau 1, présente les principales caractéristiques catalytiques, telles qu'illustrées sur les figures 7A, 7B, 8A et 8B, d'un élément du type Ag/Ce02-Zr02 en fonction de la température et de la nature des gaz décrite précédemment. Tableau 3 : activité catalytique du Ag/Ce02-Zr02 en fonction de la température et de la nature des gaz traités. Propène Mélange d'hydrocarbures Fenêtre (°C) AC (%) Fenêtre (°C) AC (%) Sans plasma 200-250 10 200-250 10 300-400 300-400 250-300 18 250-300 18 Avec plasma 150-400 20 150-400 20 Table 3, organized identically in Table 1, shows the main catalytic characteristics, as illustrated in FIGS. 7A, 7B, 8A and 8B of an element of the Ag / Ce0 2 -Zr0 2 type as a function of the temperature and the nature of the gases described previously. Table 3: Catalytic activity of Ag / Ce0 <sub> 2 </ sub> -Zr0 <sub> 2 </ sub> as a function of the temperature and the nature of the gases treated. propene Hydrocarbon mixture Window (° C) AC (%) Window (° C) AC (%) Without plasma 200-250 10 200-250 10 300-400 300-400 250-300 18 250-300 18 With plasma 150-400 20 150-400 20

Ainsi, les fenêtres thermiques d'activité catalytique des différents éléments 22a, 22b, 22c sont complémentaires et décroissent dans le sens de l'écoulement des gaz d'échappement dans la ligne d'échappement 16.Thus, the thermal windows of catalytic activity of the various elements 22a, 22b, 22c are complementary and decrease in the direction of the flow of the exhaust gases in the exhaust line 16.

Ainsi, en combinant l'activité catalytique de chacun des éléments 22a, 22b, 22c du catalyseur 22, ce dernier présente une activité catalytique totale en fonction de la température et de la nature des gaz d'échappement traités telles qu'illustrées sur les figures 9A, 9B, 10A et 10B.Thus, by combining the catalytic activity of each of the elements 22a, 22b, 22c of the catalyst 22, the latter exhibits a total catalytic activity as a function of the temperature and the nature of the treated exhaust gases as illustrated in FIGS. FIGS. 9A, 9B, 10A and 10B .

Le tableau 4, organisé d'une manière identique au tableau 1, récapitule les principales caractéristiques du catalyseur 22. Tableau 4 : activité catalytique totale du catalyseur, formé successivement, dans le sens d'écoulement des gaz, d'Al2O3, de Pd-Rh/Ce02-Zr02 et de Ag/Ce02-Zr02 en fonction de la température et de la nature des gaz traités. Propène Mélange d'hydrocarbures Fenêtre (°C) AC (%) Fenêtre (°C) AC (%) Sans plasma 200-240 10 220-225 20 290-500 310-450 240-255 20 225-260 30 265-290 270-310 255-265 25 260-270 40 Avec plasma 150-180 10 200-220 20 340-400 300-450 180-255 20 220-250 40 265-340 290-300 255-265 55 250-255 50 265-290 255-265 55 Table 4, organized in a manner identical to Table 1, summarizes the main characteristics of the catalyst 22. Table 4: total catalytic activity of the catalyst, formed successively, in the gas flow direction, of Al <sub> 2 </ sub> O <sub> 3 </ sub>, of Pd-Rh / Ce0 <sub > 2 </ sub> -Zr0 <sub> 2 </ sub> and Ag / Ce0 <sub> 2 </ sub> -Zr0 <sub> 2 </ sub> depending on the temperature and nature of the gases treaties. propene Hydrocarbon mixture Window (° C) AC (%) Window (° C) AC (%) Without plasma 200-240 10 220-225 20 290-500 310-450 240-255 20 225-260 30 265-290 270-310 255-265 25 260-270 40 With plasma 150-180 10 200-220 20 340-400 300-450 180-255 20 220-250 40 265-340 290-300 255-265 55 250-255 50 265-290 255-265 55

Le catalyseur 22 présente ainsi une activité catalytique dans une fenêtre thermique au moins égale à [200 - 500]°C, ce qui permet d'obtenir un traitement des NOx dans une large gamme de fonctionnement d'un moteur thermique de véhicule pour particulier.The catalyst 22 thus has a catalytic activity in a thermal window at least equal to [200-500] ° C., which makes it possible to obtain NOx treatment in a wide operating range of a particular vehicle engine.

De manière avantageuse, les trois éléments catalytiques Al2O3, Ph-Rh/Ce02-Zr02 et Ag/Ce02-Zr02 sont déposés sur un support unique, comme de la cordielite, de la mullite, du carborundum (SiC), du métal, ou tout type de substrat propre à servir comme support de catalyseur.Advantageously, the three catalytic elements Al 2 O 3 , Ph-Rh / CeO 2 -ZrO 2 and Ag / CeO 2 -ZrO 2 are deposited on a single support, such as cordielite, mullite, carborundum (SiC ), metal, or any type of substrate suitable for use as a catalyst support.

Il va maintenant être décrit avec la figure 11, l'agencement et le fonctionnement de l'unité 24 de contrôle du traitement des NOx des gaz d'échappement émis par le moteur 10.It will now be described with the figure 11 , the arrangement and the operation of the unit 24 for controlling the NOx treatment of the exhaust gases emitted by the engine 10.

L'unité 24 comprend des moyens 40 de mémorisation d'une première et d'une seconde températures de seuil T1, T2.The unit 24 comprises means 40 for storing a first and a second threshold temperature T1, T2.

Les moyens 40 de mémorisation sont raccordés à des premiers et seconds moyens de comparaison 42, 44 des températures de seuil T1, T2 aux températures amont Tu et aval Td acquises respectivement.The storage means 40 are connected to first and second comparison means 42, 44 of the threshold temperatures T1, T2 at the upstream temperatures Td and downstream Td respectively acquired.

Les températures T1, T2 de seuil sont par exemple déterminées expérimentalement et dépendent notamment de la composition en éléments catalytiques, de leur charge en métaux précieux et du volume du catalyseur, ainsi que du réglage du moteur.The T1, T2 threshold temperatures are for example determined experimentally and depend in particular on the composition of catalytic elements, their precious metal charge and the catalyst volume, as well as the adjustment of the engine.

Dans le cas d'un catalyseur formé successivement, dans le sens d'écoulement des gaz, d'Al2O3, de Pd-Rh/Ce02-Zr02 et de Ag/Ce02-Zr02, T1 est par exemple égale à 200°C et T2 est par exemple égale à 350°C.In the case of a successively formed catalyst, in the gas flow direction, Al 2 O 3 , Pd-Rh / CeO 2 -ZrO 2 and Ag / CeO 2 -ZrO 2 , T1 is for example equal to 200 ° C and T2 is for example equal to 350 ° C.

Le résultat des comparaisons des moyens 42, 44 est délivré à des moyens 46 d'activation/désactivation du réacteur de production de plasma.The result of the comparisons of means 42, 44 is delivered to means 46 for activation / deactivation of the plasma production reactor.

Les moyens 46 d'activation/désactivation activent l'alimentation électrique haute tension du réacteur de production de plasma si cette activation a pour effet un gain d'activité catalytique du catalyseur important, par exemple supérieur à 10%.The activation / deactivation means 46 activate the high voltage power supply of the plasma production reactor if this activation has the effect of a significant catalytic activity increase of the catalyst, for example greater than 10%.

Si les températures amont et aval Tu, Td acquises sont inférieures à leurs températures de seuil T1, T2 respectives, aucune des portions du catalyseur n'est amorcée. Les moyens 46 d'activation/désactivation n'activent pas le réacteur de production de plasma, une condition d'activation de ce réacteur étant qu'au moins un type d'éléments catalytiques présent dans le catalyseur 22 soit dans un état amorcé.If the upstream and downstream temperatures Tu, Td acquired are lower than their respective threshold temperatures T1, T2, none of the catalyst portions are initiated. The activation / deactivation means 46 does not energize the plasma generating reactor, an activation condition of this reactor being that at least one type of catalyst element present in the catalyst 22 is in a primed state.

Les NOx ne sont alors pas traités par les éléments catalytiques non amorcés et traversent donc le catalyseur sans réduction en azote. En effet, l'activation du réacteur n'aurait sensiblement aucun effet sur l'activité catalytique du catalyseur. Cette phase correspond au démarrage à froid du véhicule.The NOx are then not treated by the non-primed catalytic elements and thus pass through the catalyst without reduction in nitrogen. Indeed, the activation of the reactor would have substantially no effect on the catalytic activity of the catalyst. This phase corresponds to the cold start of the vehicle.

Si la température amont Tu acquise est supérieure à la température T1 et que la température aval Td acquise est inférieure à la température T2, les éléments catalytiques sont amorcés et les moyens 46 activent le réacteur pour la production de plasma.If the upstream temperature T 1 acquired is greater than the temperature T 1 and the downstream temperature T d acquired is lower than the temperature T 2, the catalytic elements are ignited and the means 46 activate the reactor for the production of plasma.

En effet, dans la fenêtre thermique [200, 350]°C, les trois éléments catalytiques, y compris l'alumine dont la fenêtre thermique est située dans les hautes températures en absence de plasma avec une évolution de celle-ci vers les plus basses températures en présence de décharges plasma dans les gaz d'échappement, participent à la réduction des NOx des gaz d'échappement. L'activation du réacteur a ainsi pour effet un gain important de l'activité catalytique totale du catalyseur supérieur à 10%, justifiant ainsi de la surconsommation de carburant induite par l'activité du réacteur.Indeed, in the thermal window [200, 350] ° C, the three catalytic elements, including alumina whose thermal window is located in the high temperatures in the absence of plasma with an evolution thereof to lower temperatures in the presence of plasma discharges in the exhaust gas, participate in the reduction of NOx exhaust gas. The activation of the reactor thus results in a significant gain in the total catalytic activity of the catalyst greater than 10%, thus justifying the overconsumption of fuel induced by the activity of the reactor.

Dans un mode de réalisation de l'invention, les moyens 46 commandent les moyens 20 d'alimentation du réacteur de manière constante. Par exemple, les moyens 20 d'alimentation sont commandés par les moyens 46 d'activation/désactivation pour qu'ils délivrent aux électrodes du réacteur une puissance comprise entre 250 et 300W, par exemple.In one embodiment of the invention, the means 46 control the means 20 for supplying the reactor steadily. For example, the supply means 20 are controlled by the activation / deactivation means 46 so that they deliver to the electrodes of the reactor a power of between 250 and 300 W, for example.

Dans le mode de réalisation de la figure 11, les moyens 46 commandent les moyens 20 d'alimentation en fonction de la quantité de NOx présente dans les gaz d'échappement et/ou de la température de ceux-ci.In the embodiment of the figure 11 , the means 46 control the supply means 20 according to the amount of NOx present in the exhaust gas and / or the temperature thereof.

Les moyens 46 reçoivent le point de fonctionnement Pf du moteur et déterminent, par exemple à l'aide d'une cartographie prédéterminée et mémorisée dans ceux-ci, la quantité de NOx émise par le moteur pour le point de fonctionnement. Les moyens 46 commandent alors les moyens 20 d'alimentation du réacteur pour qu'ils leur délivrent une puissance modulée en fonction de la quantité de NOx déterminée, par exemple croissante en fonction d'une quantité croissante de NOx émise par le moteur.The means 46 receive the operating point Pf of the engine and determine, for example by means of a predetermined map and stored therein, the amount of NOx emitted by the engine for the operating point. The means 46 then control the feed means 20 of the reactor so that they deliver a modulated power according to the amount of NOx determined, for example increasing in function of an increasing amount of NOx emitted by the engine.

Si les températures amont et aval Tu, Td acquises sont supérieures à leurs températures seuil T1, T2 respectives, alors les moyens 46 désactivent le réacteur de production de plasma. En effet, pour des températures supérieures à T2, seul l'élément catalytique haute température, c'est-à-dire l'alumine, présente une activité catalytique. Or pour ces températures, la fenêtre thermique d'activité catalytique de l'alumine est significativement plus grande sans plasma qu'avec plasma en présence du mélange d'hydrocarbures dans les gaz d'échappement comme cela est illustré sur les figures 4A et 4B. Le gain d'activité par activation du réacteur étant nulle, le réacteur n'est donc pas activé pour des températures supérieures à T2. Ceci permet de réduire la consommation de carburant du moteur pour la production d'énergie nécessaire au fonctionnement des moyens 20 d'alimentation du réacteur.If the upstream and downstream temperatures Tu, Td acquired are greater than their respective threshold temperatures T1, T2, then the means 46 deactivate the plasma production reactor. Indeed, for temperatures greater than T2, only the high temperature catalytic element, that is to say alumina, has a catalytic activity. However, for these temperatures, the thermal window of catalytic activity of alumina is significantly greater without plasma than with plasma in the presence of the hydrocarbon mixture in the exhaust gases, as is illustrated in FIGS. Figures 4A and 4B . Since the activity gain by activation of the reactor is zero, the reactor is not activated for temperatures greater than T2. This makes it possible to reduce the fuel consumption of the engine for the production of energy necessary for the operation of the reactor supply means.

Les moyens 46 sont également adaptés pour commander le fonctionnement des moyens d'alimentation du moteur et/ou des moyens d'admission d'air en entrée du moteur afin de modifier la composition en hydrocarbures imbrûlés des gaz d'échappement et ainsi moduler l'activité catalytique du catalyseur en fonction de la composition des gaz d'échappement en propène ou en mélange d'hydrocarbures.The means 46 are also adapted to control the operation of the motor supply means and / or the air inlet intake means of the engine in order to modify the unburned hydrocarbon composition of the exhaust gases and thus modulate the catalytic activity of the catalyst as a function of the composition of the exhaust gas in propene or in a mixture of hydrocarbons.

Par exemple, les moyens 46 sont propres à modifier la stratégie d'injection de carburant dans les cylindres du moteur, en commandant une injection tardive de carburant dans ceux-ci, ou post-injection. La post-injection de carburant dans les cylindres du moteur a pour effet d'augmenter significativement la quantité d'hydrocarbures imbrûlés dans les gaz d'échappement, ce qui conduit à une augmentation temporaire du rapport HC/NOx de la quantité d'hydrocarbures imbrûlés sur la quantité de NOx des gaz d'échappement, et donc à une amélioration de la conversion des NOx en azote.For example, the means 46 is capable of modifying the fuel injection strategy in the engine cylinders by controlling a late injection of fuel therein, or post-injection. The post-injection of fuel into the engine cylinders has the effect of significantly increasing the amount of unburned hydrocarbons in the exhaust gas, which leads to a temporary increase in the HC / NOx ratio of the amount of unburned hydrocarbons the amount of NOx in the exhaust gas, and therefore to an improvement in the conversion of NOx into nitrogen.

Il vient d'être décrit un mode de réalisation de l'unité de contrôle du traitement des NOx des gaz d'échappement d'un moteur thermique.It has just been described an embodiment of the NOx treatment control unit of the exhaust gas of a heat engine.

Cette unité met en oeuvre de manière simple une stratégie de contrôle qui maximise, en fonction de la température, l'activité catalytique d'un catalyseur comprenant trois éléments catalytiques complémentaires, dans une large fenêtre thermique d'environ [200, 500]°C, tout en minimisant la surconsommation de carburant induite par l'utilisation d'un réacteur de production de plasma.This unit implements in a simple manner a control strategy which maximizes, as a function of temperature, the catalytic activity of a catalyst comprising three complementary catalytic elements, in a broad thermal window of approximately [200, 500] ° C. while minimizing fuel over-consumption induced by the use of a plasma generating reactor.

En variante, le système conforme à l'invention peut comprendre un unique capteur placé en amont du catalyseur, et l'unité de contrôle est adaptée pour comparer cette température acquise aux températures seuil susmentionnées pour une commande des moyens d'alimentation du réacteur analogue à celle décrite précédemment.In a variant, the system according to the invention may comprise a single sensor placed upstream of the catalyst, and the control unit is adapted to compare this acquired temperature with the aforementioned threshold temperatures for a control of the reactor supply means similar to that described previously.

Prévoir deux capteurs en amont et en aval permet cependant une commande plus précise, la température aval acquise étant sensiblement celle du dernier élément catalytique du catalyseur, ce qui permet ainsi une commande au plus près de la température de celui-ci.Providing two sensors upstream and downstream, however, allows a more precise control, the acquired downstream temperature being substantially that of the last catalytic element of the catalyst, which allows a control closer to the temperature thereof.

En variante, le catalyseur peut comprendre 2 ou plus de portions de types d'éléments catalytiques.Alternatively, the catalyst may comprise 2 or more portions of catalytic element types.

Une autre variante consiste à remplacer les éléments catalytiques de type Ag/CeO2-ZrO2 et Pd-Rh/CeO2-ZrO2 par un matériau ne contenant pas de métaux précieux, à savoir deux éléments de CeO2-ZrO2, de sorte que le coût du système est significativement réduit du fait de l'absence de métaux précieux.Another variant consists in replacing the catalytic elements of Ag / CeO 2 -ZrO 2 and Pd-Rh / CeO 2 -ZrO 2 type with a material containing no precious metals, namely two elements of CeO 2 -ZrO 2 , so that the cost of the system is significantly reduced due to the absence of precious metals.

Par exemple, le catalyseur comprend une portion d'alumine Al2O3 en amont d'une portion de CeO2-ZrO2.For example, the catalyst comprises an alumina Al 2 O3 portion upstream of a portion of CeO 2 -ZrO 2.

Claims (12)

  1. System for treating nitrogen oxides, or NOx, in the exhaust gas of a passenger motor vehicle heat engine (10), comprising, in an exhaust line (16) thereof, means (18) for producing non-thermal plasma from the exhaust gases which they receive at the inlet and means (22) which form a NOx reduction catalyst arranged at the outlet of the plasma-producing means, characterised in that the means forming the catalyst comprise different types of catalytic elements having different thermal windows of catalytic activity, the catalytic elements being situated along the gas-flow direction in decreasing order of temperature of the thermal windows of catalytic activity, said system further comprising:
    - primary means (26) for acquiring the temperature of the exhaust gas upstream of the means forming the catalyst; and
    - control means (24) for the means (18) for producing plasma as a function of the temperature acquired to optimise NOx reduction at said temperature,
    said control means (24) actuating the plasma-producing means (18) when, for the acquired upstream temperature, the increase in overall catalytic activity of an actuation of this type is greater than a predetermined threshold.
  2. System according to claim 1, characterised in that the types of catalytic elements are selected in order that the overall thermal window of catalytic activity of means forming the catalyst comprise the window of from 200°C to 500 °C.
  3. System according to either claim 1 or claim 2, characterised in that the catalytic elements are chosen from the group consisting of Al2O3 and CeO2-ZrO2 impregnated with a transition-metal or precious-metal element.
  4. System according to claim 3, characterised in that the catalytic elements are successively, in the direction of the gas flow, Al2O3, Rh-Pd/CeO2-ZrO2 and Ag/ CeO2-ZrO2.
  5. System according to either claim 3 or claim 4, characterised in that the catalytic elements are placed on a single support.
  6. System according to claim 5, characterised in that the single support is chosen from the group consisting of cordierite, mullite, SiC and metal.
  7. System according to either claim 1 or claim 2, characterised in that the catalytic elements are chosen from the group consisting of Al2O3 and CeO2-ZrO2.
  8. System according to any one of claims 1 to 7, characterised in that the non-thermal plasma-producing means (18) are arranged inside the means (22) which form a catalyst.
  9. System according to any of the preceding claims, characterised in that it comprises secondary means (28) for acquiring the temperature downstream of the means (22) which form a catalyst, and in that the control means (24) comprise means (46) for determining the ignition state of the types of catalytic elements as a function of said acquired temperatures, and in that one actuation condition of the plasma-producing means (18) is that at least one type of catalytic element be activated.
  10. System according to claim 9 and any one of claims 4 to 6, considered collectively, characterised in that the control means comprise means (42, 44) for comparing upstream and downstream temperatures acquired at predetermined primary and secondary threshold temperatures respectively, and in that:
    - when the upstream and downstream temperatures are less than the respective threshold temperatures thereof, the plasma-producing means are inactive;
    - when the upstream temperature is greater than the primary threshold temperature and the downstream temperature is less than the secondary threshold temperature, the plasma-producing means are active; and
    - when the upstream and downstream temperatures are greater than the respective threshold temperatures thereof, the plasma-producing means are inactive.
  11. System according to claim 10, characterised in that the primary and secondary threshold temperatures are approximately 200°C and 350 °C respectively.
  12. System according to any of the preceding claims, characterised in that the control means (24) are further adapted to control fuel feed in the engine (10) cylinders and/or air flow introduced into the engine (10) to change the hydrocarbon composition of exhaust gas emitted from the engine.
EP05292350A 2004-11-08 2005-11-07 System for treating NOx in the exhaust gas stream of an automotive internal combustion engine Not-in-force EP1662105B1 (en)

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FR0411882A FR2877693B1 (en) 2004-11-08 2004-11-08 EXHAUST GAS NOx TREATMENT SYSTEM OF A MOTOR VEHICLE THERMAL MOTOR

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Publication number Priority date Publication date Assignee Title
US8438842B2 (en) 2008-04-08 2013-05-14 Mitsubishi Electric Corporation Exhaust gas purification device

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FR2912385B1 (en) 2007-02-13 2011-05-06 Gaz Transport & Technigaz CYLINDRICAL STRUCTURE COMPOSED OF RECTANGULAR ELEMENTS.

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DE4032085A1 (en) * 1990-10-10 1992-04-16 Didier Werke Ag Catalytic appts. for reducing nitrogen oxide(s) in I.C. engine exhaust - has catalyst bed of different materials active in different temp. ranges of exhaust gas
JP3922408B2 (en) * 1997-09-16 2007-05-30 株式会社デンソー Exhaust gas purification device for internal combustion engine
US6806225B1 (en) * 1998-06-30 2004-10-19 Toyota Jidosha Kabushiki Kaisha Catalyst for exhaust gas purification, process for producing the same, and method of purifying exhaust gas
EP1151183A4 (en) * 1999-01-21 2004-08-11 Litex Inc Combined plasma reactor catalyst systems for effective emission control over a range of operating conditions
JP3642032B2 (en) * 2001-03-02 2005-04-27 トヨタ自動車株式会社 Exhaust gas purification device for internal combustion engine
JP4222064B2 (en) * 2003-03-06 2009-02-12 マツダ株式会社 Exhaust gas purification catalyst
JP2004305841A (en) * 2003-04-03 2004-11-04 Honda Motor Co Ltd NOx REMOVAL SYSTEM

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Publication number Priority date Publication date Assignee Title
US8438842B2 (en) 2008-04-08 2013-05-14 Mitsubishi Electric Corporation Exhaust gas purification device

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DE602005006363T2 (en) 2009-06-10
DE602005006363D1 (en) 2008-06-12
ATE393872T1 (en) 2008-05-15
FR2877693B1 (en) 2007-04-13
EP1662105A1 (en) 2006-05-31

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