FR3032226A1 - METHOD FOR OPERATING AN EXHAUST GAS TREATMENT DEVICE - Google Patents

Abstract

The invention relates to the operation of a treatment device (5) of. exhaust gas (3), the device (5) being housed inside an exhaust line (2) fitted to a motor (1), the device (5) comprising successively in a direction of circulation (7). ) of the exhaust gases (3) inside the exhaust line (2) from the engine (1) to an external environment (4): a first treatment unit (PNA) for, in particular, converting monoxide nitrogen and / or nitrogen oxides, a second treatment unit (LNT) for trapping nitrogen dioxide, a third treatment unit (MIX) for injecting a reducing agent, and a fourth processing member (SCRF) comprising a reduction catalyst (6) and a particulate filter (10). When an exhaust gas temperature (Tgaz) is between an initial temperature and a threshold temperature, the treatment unit (PNA) is active.

Description

METHOD FOR OPERATING AN EXHAUST GAS TREATMENT DEVICE The invention relates to a method of operating an exhaust gas treatment device, the treatment device being housed inside an exhaust line fitted to an internal combustion engine of which is provided with a motor vehicle, the treatment device comprising a first treatment member for oxidizing carbon monoxide, oxidizing unburned hydrocarbons, converting nitrogen monoxide into nitrogen dioxide and / or storing nitrogen oxides, second processing member for trapping nitrogen dioxide and treating the nitrogen oxides during operation of the rich-mode internal combustion engine, a third processing member for injecting a reducing agent, mixing the reducing agent and the exhaust gas and converting the reducing agent, and a fourth treatment member comprising a reduction catalyst for reducing nitrogen oxides and a particulate filter for retaining s particles. [0002] Document FR 2,970,298 describes an exhaust line that equips an internal combustion engine which is provided with a motor vehicle. The internal combustion engine produces exhaust gases that are exhausted from the internal combustion engine to an outside environment via the exhaust line. The exhaust gases contain pollutants, such as unburned hydrocarbons, soot particles, carbon monoxide and nitrogen oxides or the like, which are preferable not to be discharged into the external environment. To do this, the exhaust line houses an exhaust gas treatment device. [0003] The treatment device comprises an oxidation catalyst member which comprises an oxidation catalyst cake made from a nitrogen oxide adsorbing material. The oxidation catalyst is a three-way catalyst contributing to a decrease in the amount of three pollutants inside the exhaust gas, namely nitrogen oxides, carbon monoxide and unburned hydrocarbons. The treatment device also comprises a selective catalytic reduction member disposed downstream of the oxidation catalytic member in a flow direction of the exhaust gas inside the exhaust line. The selective catalytic reduction member is provided for reducing nitrogen oxides. The selective catalytic reduction member is associated with an injector which is capable of delivering, within the exhaust line, a reducing agent, such as urea or the like, to improve a reduction of the nitrogen oxides by the selective catalytic reduction member. The treatment device finally comprises a particle filter for retaining particles. The exhaust gas treatment device deserves to be improved to be effective over an exhaust gas temperature range that is the widest possible, this to clean up the exhaust from cold temperatures to engine start up to motorway runs with higher temperatures. An object of the present invention is to provide a method of operation of an exhaust gas treatment device which is housed inside an exhaust line inside which the gases circulate. exhaust systems produced by an internal combustion engine, the operating method for conversion and / or retention of pollutants contained within the exhaust gas, irrespective of the temperature of the exhaust gas, particularly including between 20 ° C and 600 ° C. [0008] A method of the present invention is a method of operating an exhaust gas treatment device. The treatment device is housed inside an exhaust line fitted to an internal combustion engine which is provided with a motor vehicle. The treatment device comprises a first treatment member for oxidizing carbon monoxide, oxidizing unburned hydrocarbons, converting nitric oxide to nitrogen dioxide and / or storing nitrogen oxides, a second treatment member for trapping the nitrogen dioxide and treat the nitrogen oxides 20 during operation of the rich-mode internal combustion engine, a third treatment member for injecting a reducing agent, mixing the reducing agent and the exhaust gas and converting the reducing agent, and a fourth processing member comprising a reduction catalyst for reducing nitrogen oxides and a particulate filter for retaining particles. [0009] According to the present invention, the operating method comprises a first operating phase, when an exhaust gas temperature is between an initial temperature and a first threshold temperature, during which the first treatment is active. The operating method advantageously comprises a second operating phase 30, when the temperature of the exhaust gas is between the first threshold temperature and a second threshold temperature, during which the second treatment member is active. and stores the nitrogen dioxide, and converts the nitrogen dioxide to the nitrogen when operating the internal combustion engine in rich mode. The operating method advantageously comprises a reducing agent injection step inside the exhaust line, which is performed when the temperature of the exhaust gas is lower than the second threshold temperature. The operating method advantageously comprises a third operating phase when the temperature of the exhaust gas is greater than the second threshold temperature during which the injector and the mixer are active and during operation. of the internal combustion engine in lean mode. A processing device for carrying out such a method of operation is characterized in that the first treatment member is of a length taken along a direction of flow of the exhaust gases inside the line. exhaust which is between 2.5 centimeters and 12 centimeters. Preferably, the first processing member, the second processing member, the third processing member and the fourth processing member are arranged successively inside the exhaust line in the direction of circulation of the gases. exhaust inside the exhaust line. An exhaust line of the present invention is equipped with such a treatment device. An internal combustion engine of the present invention is equipped with such an exhaust line. [0017] A motor vehicle of the present invention is equipped with such an internal combustion engine. Other features and advantages of the present invention will appear on reading the description which will be made of embodiments, in connection with the figures of the attached plates, in which: FIG. a schematic view of an exhaust line of the present invention. Figure 2 is a schematic view of a method of operating the exhaust line illustrated in Figure 1. In Figure 1, a motor vehicle is equipped with an internal combustion engine 1 to provide for his movement. The internal combustion engine 1 is preferably a diesel engine. The internal combustion engine is equipped with an exhaust line 2 which is designed to channel an exhaust gas flow 3 from the internal combustion engine 1 to an outside environment 4. The exhaust gases 3 contain pollutants , such as unburned hydrocarbons, soot particles, carbon monoxide and nitrogen oxides NO, which it is preferable not to reject in the external environment 4. The exhaust line 2 houses an exhaust gas treatment device 3 for retaining the pollutants prior to evacuation of the exhaust gas 3 to the outside environment 4. The treatment device 5 comprises a plurality of PNA, LNT, MIX treatment devices and SCRF which are successively distributed inside the exhaust line 2 in a direction of circulation 7 of the exhaust gas 3 inside the exhaust line 2, including a first PNA processing member, a second LNT processor, a third MIX processor and a fourth SCRF processor. The exhaust gas 3 circulates inside the exhaust line 2 by being brought to a temperature of the gas Tg 'which is measured directly upstream of the first treatment member PNA via a temperature sensor S. [0024] The first PNA processing member is a passive adsorption device according to the acronym of "Passive NOx Adsorber" which is capable of retaining the nitrogen oxides at low temperature, especially when the temperature of the gases Tg 'is an ambient temperature of the order of 25 ° C to +/- 10 ° C, and to desorb the nitrogen oxides when the gas temperature Tg' is of the order of 250 ° C to +/- 10 ° C. The first PNA treatment member is also capable of oxidizing carbon monoxide and hydrocarbons and to produce a NO2 / NO ratio close to 0.5 from a gas temperature Tg 'of the order of 150.degree. +/- 10 ° C near. More particularly, the first PNA treatment member is preferably of small size and has a length E of between 2.5 centimeters and 12 centimeters. The short length of the first PNA treatment member and the thermal properties of the material which constitutes it (Cordierite, aluminum titanate, etc.) allow rapid priming of the first PNA treatment member, that is to say a passage of a temperature of the first processing member Tgata above 150 ° C to +/- 30 ° C. It follows that the temperature of the first treatment member '' ta is faster than a priming temperature beyond which the The first PNA treatment unit oxidizes carbon monoxide to carbon dioxide, oxidation of unburned hydrocarbons and conversion of nitric oxide to nitrogen dioxide. More particularly, the first PNA processing member is an oxidation catalyst based on platinum-type precious metals, palladium, with or without Rhodium.

The first PNA processor also includes materials that have the ability to store NO oxides. These materials are of the cerium and / or barium type. These materials store NOx nitrogen oxides up to a gas temperature Tg 'which is less than 250 ° C, and then NOx azoboxides are thermally destocked. The first PNA processor after its priming temperature is converted converts carbon monoxide and unburnt hydrocarbons into water and carbon dioxide. The first PNA processor also converts nitrogen monoxide from the engine into nitrogen dioxide. The second LNT processing member is disposed downstream of the first processing member PNA according to the flow direction 7 of the exhaust gas 3 inside the exhaust line 2. The second LNT processing member is a trapping member which is intended to retain nitrogen dioxide at low and medium temperatures, that is to say typically at temperatures below about 350 ° C to +/- 20 ° C. When the gas temperature Tg 'is greater than a first threshold temperature Tiseuil, which is for example of the order of 200 ° C to +/- 20 ° C, the internal combustion engine 1 operates in rich mode intermittently. Operating phases of the internal combustion engine 1 with a richness of close to 1 to +/- 10% allow destocking NOx nitrogen oxides present on the second LNT processing member and also convert them into dinitrogen. More particularly, the second LNT processing member is a type of LNT oxidation catalyst according to the acronym "Lean NOx Trap". The second LNT processing member is also composed of platinum, palladium and / or rhodium precious metals. The second LNT processing member also comprises cerium and / or barium storage materials. The chemical status of Cerium and Barium allows a stronger bond with NO2. Destocking NOx nitrogen oxides and their conversion to nitrogen and oxygen are carried out during transient phase in rich mode or close to a richness equal to 1 to +/- 10% near the internal combustion engine 1. The second The LNT treatment unit mainly captures the nitrogen dioxide present in the exhaust gas 3. The nitrogen dioxide is obtained during the passage of the NOx through the first treatment element PNA. The fourth processing unit SCRF is preceded by a third processing member MIX which is a system for injecting, mixing and transforming a reducing agent. The third treatment unit MIX comprises an injector 8 of the reducing agent, such as urea or the like, inside the exhaust line 2. The third treatment unit MIX also comprises a mixer 9 for mixing the exhaust gas reducing agent 3. The third treatment unit MIX is arranged downstream of the second LNT treatment unit in the direction of circulation 7 of the exhaust gases 3 inside the exhaust line 2 The injector 8 delivers the reducing agent when the temperature of the exhaust gas Tg 'exceeds an injection temperature T ,,, which is lower than 10 ° C to 20 ° C at a second threshold temperature T2e threshold. The second threshold temperature T2seuil is in particular equal to 250 ° C to +/- 20 ° C. This is the field in which the injection temperature of the reducing agent is set. After an injection authorization of the reducing agent, a setpoint is sent to the internal combustion engine 1 via a motor control to stop the passages in rich. These passages in richness greater than or close to 1 to +/- 10% allow to purge the LNT. The fourth processing unit SCRF comprises a reduction catalyst 6 which is able to reduce the nitrogen oxides with the reducing agent in dinitrogen and water. The fourth processing unit SCRF is activated when the temperature of the exhaust gas Tg 'at the inlet of the fourth processing unit SCRF exceeds 150 ° C. The effectiveness of the fourth SCRF treatment unit is conditioned by the availability of the reducing agent. The fourth processing unit SCRF is active after authorization of injection of the reducing agent. The fourth processing unit SCRF also comprises a particulate filter 10 which is able to retain particles prior to evacuation of the exhaust gas 3 from the exhaust line 2 to the outside environment 4. [0032] In FIG. 2, an operating method 100 comprises a first operating phase 101 which is implemented when the temperature of the exhaust gas Tg 'is lower than the first threshold temperature Tisew, which is of the order of 200 ° C to +/- 20 ° C, during which the first PNA processing member and the second LNT processing member store the nitrogen oxides. The first operating phase 101 is implemented as soon as the temperature of the exhaust gas Tg 'is greater than an initial temperature T ,,, t, which is of the order of 150 ° C to +/- 20 ° C near. The operating method 100 comprises a second operating phase 102 which is implemented when the temperature of the exhaust gas Tg 'is between the first threshold temperature Tiseuil and the second threshold temperature T2seuil, during wherein the second LNT processing member is active and stores the nitrogen dioxide, when operating the internal combustion engine 1 in rich mode, NOx nitrogen oxides are destocked and processed. The second threshold temperature T2se ,,, which is of the order of 250 ° C to +/- 20 ° C, corresponds to a mixer temperature 9 which is of the order of 220 ° C to +/- 20 ° C near. The second phase of operation 102 comprises an injection step 104 during which the reducing agent is delivered inside the exhaust line 2. The injection step 104 is carried out before stopping the passages. rich mode of a fuel supply of the internal combustion engine 1. The operating method 100 comprises a third operating phase 103 which is implemented when the temperature of the exhaust gas Tg 'is greater than the second threshold temperature T2seuil, during which the injector 8 is active and delivers the reducing agent inside the exhaust line 2 so that the nitrogen oxides are reduced by the reduction catalyst 6. During the third operating phase 103, the internal combustion engine 1 is in lean mode. When the internal combustion engine 1 operates in lean mode, that is to say with a fuel deficit, the second LNT processing member is no longer purged by a transition to rich mode of the internal combustion engine 1. 0035] All of these provisions is such that the operating method 100 of the treatment device 5 has a maximum efficiency whatever the temperature of the exhaust gas Tg '.

Method for operating (100) an exhaust gas treatment device (5) (3), the treatment device (5) being housed inside an exhaust line (2) equipping an internal combustion engine (1) provided with a motor vehicle, the treatment device (5) comprising a first treatment unit (PNA) for oxidizing carbon monoxide, oxidizing unburned hydrocarbons, converting nitric oxide into nitrogen dioxide and / or nitrogen oxide storage, a second treatment unit (LNT) for trapping nitrogen dioxide and treating nitrogen oxides during operation of the internal combustion engine (1) in rich mode, a third treatment unit (MIX) for injecting a reducing agent, mixing the reducing agent and the exhaust gases (3) and transforming the reducing agent, and a fourth treatment unit (SCRF) comprising a reduction catalyst (6) for reducing nitrogen oxides and a 15 particles (10) for retaining particles, characterized in that the operating method (100) comprises a first operating phase (101), when an exhaust gas temperature (Tgaz) is between a temperature initial (T) and a first threshold temperature (Tiseuii), during which the first treatment unit (PNA) -is active. 2. Operating method (100) according to the

Claims (1)

REVENDICATIONS1. characterized in that the operating method (100) comprises a second operating phase (102), when the exhaust gas temperature (Tg ') is between the first threshold temperature (Tiseuil) and a second threshold temperature ( T2seuii), during which the second treatment unit (LNT) is active and stores the nitrogen dioxide, and converts the nitrogen dioxide to the nitrogen during operation of the internal combustion engine (1). rich mode. 3. Operation method (100) according to claim 2, characterized in that the operating method (100) comprises a step of injecting (104) reducing agent into the exhaust line ( 2), which is performed when the temperature of the exhaust gas (Tg ') is less than the second-threshold temperature (T2 threshold) .4. Operating method (100) according to any one of claims 1 to 3, characterized in that the operating method (100) comprises a third operating phase (103) when the exhaust gas temperature (Tg ' ) is greater than the second threshold temperature (T2seuii) during which the injector (8) and the mixer (9) are active and when operating the internal combustion engine (1) in poor mode . 5. Treatment device (5) for carrying out a method of operation (100) according to any one of the preceding claims, characterized in that the first processing member (PNA) is of a length (E ) taken in a direction of circulation (7) of the exhaust gas (3) within the exhaust line (2) which is between 2.5 centimeters and 12 centimeters. Treatment device (5) according to claim 5, characterized in that the first treatment unit (PNA), the second treatment unit (LNT), the third treatment unit (MIX) and the fourth treatment unit ( SCRF) are arranged successively inside the exhaust line (2) in the direction of circulation (7) of the exhaust gas (3) inside the exhaust line (2). 7. Exhaust line (2) equipped with a treatment device (5) according to any one of claims 5 and 6. 8. Internal combustion engine (1) equipped with an exhaust line (2) according to claim 7. 9. A motor vehicle equipped with an internal combustion engine (1) according to claim 8.