FR2925577A3 - Exhaust gas depolluting device for exhaust line of internal combustion engine i.e. oil engine, has thermal stabilizer stabilizing temperature of exhaust gas and arranged in upstream of temperature sensor in exhaust line - Google Patents

Abstract

The device has a depollution unit burning pollutants such as carbon monoxide and nitrogen oxide, by introducing a reducing agent in an exhaust line (7), where the unit is constituted of a catalytic oxidation device (8) and a particle filter (9). A temperature sensor (12) evaluates temperature of exhaust gas in upstream of the filter. A thermal stabilizer (21) stabilizes the temperature of the exhaust gas and is arranged in upstream of the sensor in the exhaust line, where the stabilizer is made of sic or cordierite. The stabilizer has a section that is same as a section of the line.

Description

EXHAUST GAS DEPOLLUTION DEVICE OF AN IMPROVED INTERNAL COMBUSTION ENGINE

The invention relates to the field of exhaust gas depollution and more particularly relates to a device for cleaning up the exhaust gas of an internal combustion engine. Pollution control standards are becoming more and more restrictive, in particular by substantially lowering the thresholds for discharging particles into the atmosphere as well as pollutants such as nitrogen oxides and carbon monoxide. In order to reduce their quantity, post-treatment means, in particular hot oxidation devices such as catalysts, and particulate filters, take place in the exhaust line in order to retain and / or transform these pollutants before that they are released into the atmosphere. Particle filters operate alternately in two phases, a first phase during which particles are trapped in the filter and a second phase, usually called regeneration, during which the particles are removed to prevent the accumulation of particles from clogging up. the exhaust duct and cause backpressures to the engine exhaust, which would reduce its performance. The removal of the particles is generally done by increasing the internal temperature of the filters in order to burn the particles retained therein by the addition of a reducing agent upstream thereof and capable of causing an exothermic reaction. . One possibility described in the prior art, -2 is based on the use of a small amount of fuel as a reducing agent. More particularly, a small amount of the fuel is injected into the exhaust line upstream of a vaporization catalyst in contact with the hot exhaust gases. The fuel vapors thus formed oxidize in the catalyst according to an exothermic chemical reaction, the released heat allowing to raise the temperature in the filter to burn the particles. It is necessary to regulate very precisely the amount of fuel to be vaporized, in order to control the temperature of the particle filter as close as possible to a value for burning the particles, for example 550 ° C. Indeed, a temperature too low would not burn the particles, and too high a temperature would lead to deterioration of the particulate filter or the catalytic oxidation device. Generally, this regulation is carried out with respect to the measurement of the inlet temperature of the TeFAP particulate filter, a measurement which is very fluctuating, in particular because of the turbulence present in the exhaust line at this point, which leads to inaccuracy in the amount of reducing agent introduced into the exhaust line.

The invention aims to improve exhaust gas post-treatment devices and in particular to provide a post-processing device that overcomes the disadvantages of the prior art.

It is an object of the present invention to provide a device for the depollution of the exhaust gases of an internal combustion engine, suitable for being placed in an exhaust line connected to said engine, comprising at least one component pollution control device capable of burning pollutants for the introduction of a reducing agent into the exhaust line upstream thereof, a temperature sensor capable of evaluating the temperature of the TeFAP exhaust gas upstream of the organ depollution device, characterized in that a means of thermal stabilization of the temperature of the exhaust gas is disposed upstream of the temperature sensor in the exhaust line.

According to particular embodiments, the depollution device comprises one or more of the following characteristics: the thermal stabilization means may have a function of stabilizing the turbulence of the exhaust gases; the stabilizing means may comprise conduits; - the ducts may extend rectilinearly, substantially longitudinally relative to the walls of the exhaust duct in which it is arranged, and may have a substantially constant section between the inlet and the outlet, - the stabilizing means may be in sic or cordierite, - the temperature sensor may be disposed upstream of the pollution control member adapted to burn pollutants so as to measure the temperature of the exhaust gas entering therein the stabilizing means may be arranged between two depollution devices, preferably between a catalytic oxidation device and a particulate filter, -4- the reducing agent can be introduced into the exhaust line via a dedicated injector upstream of the depollution devices; the thermal stabilization means can be arranged in a main duct of the exhaust line and a bypass is made around it this means of thermal stabilization, the inlet being made upstream of the means and the outlet being made downstream of this means and upstream of the temperature sensor so that in the first moments of a regeneration phase, the exhaust gas can flow in this branch until the temperature measured by the sensor approaches a threshold temperature Ts or setpoint Tc, - the exhaust line may comprise a main duct and a bypass in which the thermal stabilization means is arranged and whose output opens into the main pipe upstream of the temperature sensor so that in the first insta In a regeneration phase, the exhaust gases can circulate in the main pipe until the temperature TeFAP measured by the sensor approaches a threshold temperature Ts or a set temperature Tc and that once this temperature Ts, Tc is approached, the exhaust gases can circulate in the bypass by the thermal stabilization means, - a valve preferably controlled by the electronic control unit at least as a function of a delay signal and / or a temperature signal measured by the temperature sensor, may allow exhaust gas to flow through the main conduit or bypass.

The invention also relates to an internal combustion engine comprising such a depollution device arranged in its exhaust line. Such a depollution device comprises a thermal stabilization means which makes it possible to reduce thermal fluctuations. The temperature at the inlet of the pollution control device downstream of the thermal stabilization means is more stable over time and the thermal regulation is less dispersed during different runs (return to idle and recovery).

Other characteristics and advantages of the invention will become clear from reading the following description of non-limiting embodiments thereof, in conjunction with the appended figures in which: FIG. 1 schematically shows an internal combustion engine and its exhaust line provided with a thermal stabilization means; FIGS. 2a and 2b are respectively a three-quarter perspective view and a front view of a thermal stabilization means according to a preferred embodiment of the invention; FIGS. 3a and 3b show simulation results of the temperature before the particulate filter as a function of time respectively in an exhaust line that is devoid and provided with thermal stabilization means; Figure 4 schematically shows an internal combustion engine and its exhaust line provided with thermal stabilization means and a bypass around this means.

As illustrated in FIG. 1, an internal combustion engine 1, of the Diesel type, is supplied with fresh air, according to arrow 2, by an intake manifold 3 which brings air into combustion chambers of the cylinders. of the engine 1. Injectors 4 controlled by an injection control system 5 inject fuel into the same combustion chambers for the purpose of mixing it with the air admitted to it and reducing it by combustion. The exhaust gases comprising the combustion residues are collected by an exhaust manifold 6 connected to the combustion chambers of the combustion engine 1. The gases are then conveyed by the exhaust line 7 which comprises at least one depollution device , and in the illustrated example, a catalytic oxidation device 8, and downstream of the latter, a particulate filter 9. The exhaust gas, after having passed through the catalytic oxidation device 8, then the filter particles 9, are released into the atmosphere according to the arrow 10. The exhaust line 7 may comprise other devices, and in particular a silencer or at least one other catalytic oxidation device placed upstream of the oxidation device catalytic converter 8 and downstream of the exhaust manifold 6. An electronic control unit 11 receives signals from different sensors. In particular, a temperature sensor 12 is placed in the exhaust line downstream of the catalytic oxidation device 8 and upstream of the particle filter 9. The temperature sensor 12 is connected via the connection 13 to the electronic control unit 11. Two pressure sensors 14 and 15 are capable of measuring the pressure respectively upstream and downstream of the particulate filter 9. The pressure sensors 14 and 15 are connected by the connections 16 and 17 to the electronic control unit 11 and allow it to determine a pressure differential between the inlet and the outlet of the particulate filter 9, indicative of the level of particles trapped therein. The electronic control unit 11 comprises software and memory means. In particular, memory means 18 for storing the nominal quantities of fuel, and more generally of a reducing agent, to be injected for the regeneration of the particulate filter 9 as a function of the measured temperatures and the operating conditions of the engine. internal combustion. The memory means 18 may also contain maps of the various parameters necessary for the regeneration of the particle filter 9. The module 19, shown diagrammatically in FIG. 1, located inside the electronic control unit 1 1, is capable of deciding whether to regenerate the particle filter 9 as a function of the pressure measurements made by the pressure sensors 14 and 15. The module 19 is also capable of managing the duration of the injection of the fuel for maintaining the high temperature, for example of the order of 550 ° C, for the regeneration of the particulate filter 9, depending on the temperature measurement before the TeFAP particle filter detected by the temperature sensor 12. -8 The introduction of the reducing agent into the exhaust line 7 may in particular be carried out according to two different solutions. A first solution is to modify the injection patterns to generate late fuel injections into the combustion chamber so that a portion of fuel passes directly into the exhaust line without being reduced by combustion. A second solution is based on the use of a dedicated additional injector arranged in the exhaust line so that it injects fuel directly into the exhaust line upstream of the depollution devices and more particularly upstream of the exhaust system. catalytic oxidation device. In the remainder of the description, we will describe a motor 1 whose exhaust line 7 receives a reducing agent by means of late injections into the combustion chamber. An output signal from the electronic control unit 11 is fed through the connection 20 to the fuel injection control system 5. One or more late fuel injections, or otherwise late compared to the normal engine cycle , makes it possible to increase the temperature of the particulate filter 9 to the temperature necessary for the regeneration. The regeneration phase is controlled in the following manner. When the electronic control unit 11 has determined that it is necessary to initiate a regeneration phase according to the pressure measurement, upstream and downstream of the particle filter 9, a signal is emitted towards the control system injection 5 taking into account the TeFAP temperature measured by the temperature sensor 12.

The reliability and accuracy of the temperature measurement upstream of the particulate filter 9 depends on the amount of fuel to be injected and, finally, the efficiency and endurance of the depollution devices 8, 9. Thermal stabilization means 21 or thermal stabilizer is disposed upstream of the particle filter 9 and more particularly upstream of the temperature sensor 12 and can reduce or completely cancel the fluctuations in the temperature of the TeFAP exhaust gas before the filter. particles 9. The thermal stabilization means 21 is disposed between the output of the oxidation device 8 and the inlet of the particulate filter 9. The thermal stabilization means 21 makes it possible to linearize the flow of the exhaust gases, which is that is, forcing the exhaust gases to flow substantially along a generatrix of the exhaust duct, thus avoiding swirling movements around the temperature sensor. 12. The flow of the exhaust gas passing through the exhaust line 7 is thus stabilized in its flow, in the vicinity of the temperature sensor 12.

For this purpose, represented in FIG. 2, the thermal stabilization means 21 comprises a plurality of through ducts, preferably extending in a rectilinear manner, substantially longitudinally with respect to the walls of the exhaust duct in which it is arranged, and whose section is substantially constant between the inlet and the outlet. It will be ensured to use a thermal stabilizer 21 whose geometry disturbs little or not the permeability of the exhaust line 7. The thermal stabilization means 21 consists of a molding of several conduits of reference section substantially equal to 1 mm2 (square millimeter). The number of ducts depends on the diameter of the exhaust duct. It will be possible to make use of a heat stabilizer 21 made of a material suitable for use as a constituent of a particulate filter 9, for example in sic or cordierite.

More particularly, it will be possible to use a particle filter section 9 devoid of particle capture devices, so as not to reduce the permeability of the exhaust line 7. In particular, it will be possible to make sure to use sections or drops of remaining materials during the manufacture of a particulate filter 9, which allows to advantageously valorize a portion of the manufacturing waste. This thermal stabilization means 21 has a section substantially equal to the section of the exhaust line, which advantageously allows easy assembly, without modification of the exhaust line and without introducing a pressure drop. FIGS. 3a and 3b respectively show simulation results of the TeFAP temperature before the particle filter 9 as a function of time, respectively in an exhaust line 7 which is devoid of noise, and provided with thermal stabilization means 21. The comparison of these graphs show that in the absence of thermal stabilization means 21, the regulation of this temperature TeFAP oscillates in significant proportions of the order of plus or minus 40 ° C around a set value Tc while in presents such a means, the oscillations are erased. The suppression of temperature oscillations TeFAP before particulate filter 9 makes it possible to regulate the quantity of fuel introduced into the exhaust line 7 more finely, and in particular makes it possible to reduce the quantity necessary for the regeneration of the filter 9. .

It is also noted by comparing these graphs that the time to reach a threshold temperature Ts close to the setpoint value Tc from which it can be considered that the regulation around the set temperature Tc can begin is reached after a longer time T2 > T1 when thermal stabilization means 21 are used. A second embodiment of the invention is shown in FIG. 4 in which a bypass 72 is made around the thermal stabilization means 21. The input of this bypass 72 is made upstream of the thermal stabilization means 21 and the outlet being made just upstream of the temperature sensor 12. A valve controlled by the electronic control unit 11 makes it possible to direct the exhaust gases in this branch 72 along the arrow 23 at the beginning of the regeneration phase before the a threshold temperature Ts has been reached. Once the threshold temperature Ts has been reached, the valve 22 is controlled so that the exhaust gases pass through the thermal stabilization means 21 located in the main duct according to arrow 24. It is thus possible to reduce the temperature rise time. of the particulate filter 9 and thus limit the amount of fuel to be introduced into the exhaust line 7 to regenerate the particulate filter 9. It can be ensured that outside the regeneration phase of the particulate filter 9, the Exhaust gas passes into the bypass 72 according to the arrow 23 to limit the pressure drop introduced into the main conduit by the thermal stabilization means 21 during the regeneration phase. Alternatively, according to an embodiment not shown, it can be ensured that the thermal stabilization means is housed in the bypass, so that it is used only when during the regeneration phases, the valve being adapted to allow the exhaust gases to pass through the bypass only during a regeneration phase, preferably once the threshold temperature Ts has been reached.

Such a depollution device makes it possible to improve the efficiency of the particulate filter 9 by a more precise management of the particulate filter inlet temperature 9.

Claims (10)

1) Device for the depollution of the exhaust gases of an internal combustion engine (1), suitable for being placed in an exhaust line (7) connected to said engine (1), comprising at least one pollution control device (8) , 9) capable of burning pollutants by introducing a reducing agent into the exhaust line (7) upstream thereof, a temperature sensor (12) able to evaluate the temperature of the TeFAP exhaust gas in upstream of the depollution device (9), characterized in that a thermal stabilization means (21) for the temperature of the exhaust gases is arranged upstream of the temperature sensor (12) in the exhaust line ( 7). 2) A pollution control device according to claim 1 characterized in that the thermal stabilization means (21) has a function of stabilizing the turbulence of the exhaust gas. 3) A pollution control device according to any one of the preceding claims characterized in that the stabilizing means (21) comprises through ducts. 4) A pollution control device according to claim 3 characterized in that the ducts extend in a rectilinear manner, substantially longitudinally with respect to the walls of the exhaust duct in which it is arranged, and 2925577 - 14 - have a substantially constant section between the entrance and the exit. 5) A pollution control device according to any one of the preceding claims characterized in that the stabilizing means (21) is sic or cordierite. 6) A pollution control device according to any preceding claim characterized in that the temperature sensor 10 (12) is disposed upstream of the pollution control member (9) capable of burning the pollutants so as to measure the temperature ( TeFAP) exhaust gases entering it. 7) A pollution control device according to one of the preceding claims characterized in that the stabilizing means (21) is disposed between two pollution control members (8,9), preferably between a catalytic oxidation device (8) and a particle filter (9). 20 8) A pollution control device according to any one of the preceding claims characterized in that the reducing agent is introduced into the exhaust line (7) by a dedicated injector upstream of the pollution control members (8,9). 9) depollution device according to any one of the preceding claims characterized in that the thermal stabilization means (21 is arranged in a main conduit of the exhaust line (7) and a bypass (72) is formed around this means for thermal stabilization (21), the inlet being made upstream of the means (21) and the outlet being produced downstream of this means (21) and upstream of the temperature sensor (12) so that that in the first instants of a regeneration phase, the exhaust gases can circulate in this branch (72) until the temperature measured by the sensor (12) approaches a threshold temperature Ts or setpoint Tc. 10) A pollution control device according to any one of claims 1 to 8 characterized in that the exhaust line (7) comprises a main conduit and a bypass (72) wherein the thermal stabilizing means (21) is arranged and whose outlet opens into the main pipe upstream of the temperature sensor (12) so that in the first instants of a regeneration phase, the exhaust gases can circulate in the main pipe until the TeFAP temperature measured by the sensor (12) approaches a threshold temperature Ts or a set temperature Tc and that once this temperature Ts, Tc approximated, the exhaust gases can circulate in the bypass (72). ) by the thermal stabilizing means (72). Il) depollution device according to any one of claims 9 or 10 characterized in that a valve (22) preferably controlled by the electronic control unit (II) at least according to a timing signal and / or of a temperature signal measured by the temperature sensor (12), circulates the exhaust gas in the main duct or in the bypass (72) .30- 16 - 12) Internal combustion engine (1) characterized in that it comprises a depollution device according to one of the preceding claims arranged in its exhaust line (7).