FR2939471A3 - Exhaust line for diesel engine of motor vehicle, has heating module provided between exhaust manifold and post-treatment system to heat exhaust gas supplied inside conduits whose walls are coated with zeolite to generate exothermicity - Google Patents

Abstract

The line (1) has a heating module (10) provided between an exhaust manifold and an exhaust gas post-treatment system (20) e.g. particle filter, for heating exhaust gas supplied inside rectilinear conduits (10). Walls of the conduits are coated with zeolite to generate exothermicity by the absorption of water. The module has a honey comb structure (12) defining the conduits (11) in which the zeolite forms an impregnation layer covering the walls of the conduits. The module and the system include respectively stainless steel outer enclosures (15, 25). An independent claim is also included for an internal combustion engine, comprising an engine-block with cylinders.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention generally relates to the treatment of exhaust gases discharged by internal combustion engines. It relates more particularly to an exhaust line of an internal combustion engine having, according to the flow direction of the exhaust gas, an exhaust manifold and an aftertreatment system of the exhaust gas. It also relates to an internal combustion engine comprising an engine block equipped with cylinders, a fresh air intake line in the cylinders of the engine block and such an exhaust gas exhaust line out of the block cylinders. -engine. TECHNOLOGICAL BACKGROUND Exhaust aftertreatment systems used to reduce pollutant emissions from engines operate optimally over a temperature range of 150 to 250 degrees Celsius. They therefore have greatly reduced performance at ambient temperature, just after the engine is started or during the cold phases of engine operation. As a result, most of the untreated pollutants are released from the engine within minutes of the start-up phase. One of the solutions to improve the efficiency of post-treatment systems is to increase the quantity of precious metals or to increase the volumes of these systems. Nevertheless, given the high price of precious materials used in post-treatment systems, for example that of precious metals, it is difficult to limit the phenomenon of cold pollutant discharges by this means. It is then known to raise artificially the temperature of the exhaust gas at the start of the engine in order to limit these emissions cold (case of heating strategies). Furthermore, for regeneration applications of the particulate filter in diesel engines, requiring a high temperature for the combustion of soot, it is also known to increase the temperature of the gases entering the particulate filter by generating a fuel injection either in the combustion chamber or directly in the exhaust line of the engine. This surplus fuel is oxidized in the oxidation catalyst placed upstream of the particulate filter, which then causes a very rapid rise in the temperature of the exhaust gas and thus allows to initiate the regeneration of soot. These methods, however, generate overconsumption of fuel and cause an increase in carbon dioxide emissions. Document US Pat. No. 5,398,747 also discloses a vehicle equipped with a heat exchanger comprising a fresh air inlet connected to the atmosphere and two heated air outlets respectively connected to the interior of the passenger compartment of the vehicle and to the exhaust line of the engine, upstream of its exhaust aftertreatment system. This heat exchanger is internally coated with zeolite and comprises a closed circuit for injecting water and ethanol into the zeolite. This zeolite is an alumino-silicated mineral whose crystal lattice has large cavities in which many water molecules can be housed. The adsorption of water by the zeolite is then accompanied by a release of heat to heat the fresh air taken from the atmosphere. A strong heat received by the zeolite then allows the desorption of this water. The water adsorption / desorption cycle can be renewed indefinitely. This property therefore allows the zeolite to produce heat according to the principle of the heat pump. This heat exchanger is thus adapted to heat the fresh air taken from the atmosphere and to blow it into the exhaust aftertreatment system to increase its temperature. This rise in temperature remains limited, however, and does not significantly reduce the boot time of the aftertreatment system of the exhaust gas. Indeed, unless a very large amount of zeolite is provided, the temperature of the exhaust gas rapidly becomes higher than the temperature of the heated air, so that the heat exchanger has a questionable efficiency. Moreover, this heat exchanger, equipped with its closed circuit, is expensive to manufacture and bulky, which makes it difficult to board a motor vehicle. OBJECT OF THE INVENTION In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes a new internal combustion engine exhaust line that substantially promotes the heating rate of the gas after-treatment system. exhaust. More particularly, according to the invention there is provided an exhaust line as defined in the introduction, which comprises, between its exhaust manifold and its exhaust aftertreatment system, a gas heating module. exhaust system internally provided with at least one exhaust gas flow conduit whose wall is coated with zeolite adapted to generate an exothermicity by adsorption of water. Thus, at the start of the engine, a simple injection of water on this zeolite makes it possible artificially to raise the temperature of the exhaust gases and, consequently, that of the aftertreatment system of exhaust gases located downstream. The water naturally contained in the exhaust gas also makes it possible to raise this temperature artificially. This rise in temperature makes it possible to increase the heating rate of the exhaust gas aftertreatment system very substantially so as to prevent the engine from generating significant pollution in the minutes following its start or during the cold phases. . Thanks to its arrangement in the exhaust line, this heating module can also be easily disposed near the aftertreatment system of the exhaust gas, so as to limit heat losses and increase the yield of this zeolite . In addition, the water released by the zeolite (when it reaches a high temperature) mixes with the exhaust gas and is directly released into the atmosphere. The heating module, without a closed circuit, therefore has a reduced cost. Other advantageous and non-limiting features of the exhaust line according to the invention are the following: the heating module comprises a honeycomb structure defining a plurality of ducts and the zeolite forms an impregnation layer coating the walls of each conduit; the heating module and the aftertreatment system of the exhaust gases each comprise a separate stainless steel casing; the envelopes of the heating module and of the aftertreatment system of the exhaust gases are connected by a connecting duct of short length, at least less than 50 centimeters and preferably less than 10 centimeters; as a variant, the exhaust gas after-treatment system and the heating module comprise a single stainless steel casing; - In one embodiment, there is provided water injection means in the exhaust gas, equipped with an injector located upstream or at the entrance of the heating module; in the other embodiments, the water contained in the exhaust gas is sufficient to generate the desired exothermicity; the exhaust gas aftertreatment system comprises a structure defining a plurality of exhaust gas flow conduits, a catalytic impregnation layer covering the walls of the ducts of said structure, and a layer of zeolite which at least partially covers the walls of the conduits of said structure and which is adapted to generate an exothermicity by adsorption of water; the zeolite layer is merged with the catalytic impregnation layer or is superimposed on this catalytic impregnation layer, beneath it; the zeolite of the zeolite layer of the exhaust gas aftertreatment system has a water adsorption temperature higher than the water adsorption temperature of the zeolite of the heating module. The invention also relates to an internal combustion engine comprising an engine block equipped with cylinders, a fresh air intake line in the cylinders of the engine block and such an exhaust gas exhaust line. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description, with reference to the appended drawings, given by way of non-limiting example, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: FIG. 1 is a diagrammatic perspective view of an exhaust line according to the invention, equipped with a heating module and an aftertreatment system for the exhaust gases; FIG. 2 is a detailed view of zone II of FIG. 1, and FIG. 3 is a detailed view of a duct of the exhaust gas aftertreatment system. The invention applies to any type of internal combustion engine rejecting pollutants to be treated, and more specifically to any type of internal combustion engine with compression ignition (Diesel). Upstream of the cylinders, the internal combustion engine has an intake line which draws fresh air into the atmosphere and which brings and distributes this fresh air in each of the cylinders of the engine block. This intake line is equipped with a fresh air flow control valve. At the outlet of the cylinders, the internal combustion engine comprises an exhaust gas exhaust line. This exhaust line comprises, according to the direction of flow of the exhaust gas, an exhaust manifold for collecting the exhaust gases leaving each cylinder of the engine block, and at least one post-exhaust system. exhaust gas treatment to treat and / or filter the pollutants contained in the exhaust gas, before these exhaust gases are discharged into the atmosphere. Here, the exhaust line comprises, on the one hand, an oxidation catalyst for treating the HC unburned hydrocarbons and carbon monoxide CO contained in the exhaust gas, and, on the other hand, a particulate filter to capture solid particles suspended in these gases. Alternatively, it could include a NOx nitrogen oxide trap (Nox-Trap or SCR catalyst), or any other type of catalytic converter (three-way converter for treating HC unburned hydrocarbons, NOx nitrogen oxides and monoxide CO carbon in the case of a spark ignition engine). The internal combustion engine also comprises an exhaust gas recirculation line (also called EGR line) which originates in the exhaust line, which opens into the intake line and which is equipped with a gas valve. exhaust gas flow regulation.

It also has fuel injectors that open into the cylinders of the internal combustion engine or, alternatively, upstream of the cylinders in the intake line. Finally, it comprises a control unit adapted to control the various engine components, in particular here the valves regulating the flow rates of exhaust gas and fresh air as well as the fuel injectors. In Figure 1, there is shown a portion of the exhaust line 1 with its post-processing system 20, namely here its oxidation catalyst and its particle filter. This post-treatment system 20 is here of conventional type, with an internal honeycomb structure covered with a catalytic coating for oxidizing the pollutants contained in the exhaust gas, and a cylindrical outer shell 25 of stainless steel . Of course, alternatively, it could also be provided that the particulate filter is not catalyzed and that it is devoid of catalytic coating. Anyway, here is defined with respect to this post-processing system 20 a threshold temperature Ts, generally between 150 and 250 degrees Celsius, below which it has an oxidation efficiency of HC hydrocarbons and carbon monoxide CO very greatly reduced, so that it does not fulfill its office properly. According to a particularly advantageous characteristic of the invention, as shown in FIG. 1, the exhaust line 1 comprises, between its exhaust manifold and its post-treatment system 20, a heating module 10 for the exhaust gases. internally provided with at least one exhaust gas conduit 11 whose wall is coated with zeolite capable of generating exothermicity by adsorption of water. This heating module 10 here comprises a honeycomb structure 12 made of ceramic and housed in an outer casing 15 of stainless steel. This outer casing 15 is here cylindrical and has conical ends provided with inlet openings 17 and outlet 18 of the exhaust gas. As shown in FIG. 1, the outer casings 15, 25 of the heating module 10 and the post-treatment system 20 are distinct and interconnected by a junction duct 30 of short length, less than 50 centimeters (and preferentially less than 10 centimeters). Alternatively, the honeycomb structures of the heating module and the post-treatment system could be housed in the same stainless steel envelope, one behind the other.

Be that as it may, the honeycomb structure 5 of the heating module 10 here defines a plurality of rectilinear conduits 11 parallel to one another, along which the exhaust gases flow. The number and the diameter of the rectilinear ducts 10 is designed to limit the pressure drops induced by the presence of the heating module 10 in the exhaust line 1.

The zeolite forms an impregnation layer 13 coating the walls of all of these rectilinear ducts 11. As shown in FIG. 2, this impregnation layer 13 completely covers the walls of the rectilinear ducts 11 of the honeycomb structure. bee 12. Thus, when it is sprinkled with water, the impregnation layer 13 releases heat and warms all the exhaust gases that pass through the heating module 10. This water is naturally found in the gases exhaust from the combustion of fuel (Diesel) and fresh air in the cylinders of the engine block. However, to enable the exhaust gases and the aftertreatment system 20 to be heated more rapidly, the internal combustion engine here comprises additional means (not shown) for injecting water into the exhaust line 1, upstream of the heating module 10.

These water injection means may for example comprise a pressurized water tank, connected to an injector opening into the inlet opening 17 of the heating module 10. Such injection means may thus allow water the impregnation layer 13 from the start of the engine or during its cold operation, so as to warm up very quickly the exhaust gas and, therefore, the after-treatment system 20 so that the temperature of the latter exceeds quickly the threshold temperature Ts. There are various kinds of zeolites. The zeolite used in the heating module 10 is here chosen to have a very low water adsorption temperature, preferably close to 0 degrees Celsius. It can release heat very soon after starting the engine or during cold operation. It is furthermore selected for heating the exhaust gases to a temperature greater than 100 degrees, preferably equal to 200 degrees. It is finally chosen to release the water vapor that it has accumulated when the exhaust gas reaches a high temperature, preferably greater than 200 degrees Celsius. A zeolite satisfying these characteristics will preferably have a low silicon to aluminum (Si / Al) ratio, so that it is hydrophilic and can adsorb a high quantity of water (for example a zeolite A, X, Y, etc. ...). In operation, the control unit controls the water injection means in the following manner. When starting the internal combustion engine or during its cold operation, the control unit reads the temperature of the exhaust gas. As long as this temperature remains below the threshold temperature Ts, the control unit controls the injection of water into the heating module 10. This water is housed in the cavities of the crystal lattice of the zeolite, which has the effect of effect of producing heat that heats the exhaust.

The exhaust gases then leave the heating module 10 with a high temperature and enter the post-treatment system 20 by heating it (even though the exhaust gas temperature at the inlet of the heating module 10 n is not yet high). The temperature rise of this post-treatment system 20 is thus rapid, so that the pollutants contained in the exhaust gas begin to be effectively treated very soon after the engine is started or during the cold phases.

Then, when the temperature of the exhaust gas exceeds the threshold temperature Ts, the engine control unit stops the injection of water. As the engine continues to heat up, the water contained in the zeolite escapes from the cavities of its crystal lattice and mixes with the exhaust gases released into the atmosphere. Then, when the temperature of the post-processing system 20 returns below the threshold temperature Ts, for example because the engine is operating at low speed, the control unit again controls the injection of water into the exhaust gas . This injection makes it possible to maintain the post-treatment system 20 at a temperature as high as possible. This injection is particularly advantageous when the engine is in an active regeneration phase of its particulate filter. This active regeneration consists, when the particle filter is congested with a large amount of solid particles, to inject excess fuel into the cylinders or directly into the exhaust line, resulting in an exothermic oxidation phase of the fuel in the oxidation catalyst or directly in the catalyzed particulate filter. The exhaust gases then exit the oxidation catalyst with a very high temperature (500 to 650 degrees Celsius) and enter the particulate filter by burning most of the solid particles that fill the particulate filter. It is understood that the maintenance of the post-processing system 20 at a very high temperature thus makes it possible to continue the regeneration of the filter, even if the engine speed decreases, the temperature of the exhaust gas at the inlet of the heating module 10 decreases. .

The present invention is not limited to the embodiments described and shown, but the skilled person will be able to make any variant within his mind. In particular, it will be possible to incorporate zeolite directly into the post-treatment system 20.

This post-processing system 20 comprises, as shown in FIG. 3, a honeycomb structure 22 defining a plurality of exhaust gas flow conduits 21. The walls of its ducts 21 are covered with a catalytic impregnation layer 24. Here, the post-treatment system 20 further comprises a layer of zeolite 23 which at least partially (preferably completely) covers the walls of the ducts 21 of the structure 22 of the post-treatment system 20. The layers of zeolite 23 and catalytic impregnation 24 may be either merged or superimposed. As shown in FIG. 3, the layers of zeolite 23 and catalytic impregnation 24 are superimposed and the zeolite layer 23 is located under the catalytic impregnation layer 24.

The catalytic impregnation layer 24 is thus directly in contact with the exhaust gas, which allows it to effectively oxidize the polluting elements contained in these gases. Here it is made to be permeable to water, so that the water can reach the zeolite layer 23. The zeolite layer 23 is also in direct contact with the catalytic impregnation layer 24, so that warm it effectively when it receives water. Preferably, this layer of zeolite 23 is made with a zeolite of a type different from that used in the heating module 10, so that it has a water adsorption temperature greater than that of the zeolite used in the process. heating module 10. Thus, when the engine starts, when the control unit controls the injection of water into the heating module 10, the water is housed only in the cavities of the crystal lattice of the zeolite. this module. This zeolite then generates heat and thus heats the exhaust gas and hence the catalytic impregnation layer 24 of the post-treatment system 20. Then, when this zeolite reaches the temperature above which it ceases to generate heat, the steering unit stops the injection of water. This zeolite then begins to reject water vapor. Part of this water vapor escapes into the exhaust gas while another part enters the zeolite layer 23 of the post-treatment system 20. The zeolite layer 23 thus produces in turn the heat. In summary, these two types of zeolite can produce heat over a wider temperature range.

Claims (10)

REVENDICATIONS1. Exhaust line (1) of an internal combustion engine having, according to the direction of flow of the exhaust gas, an exhaust manifold and an exhaust after-treatment system (20), characterized in that it comprises, between said exhaust manifold and said exhaust aftertreatment system (20), an exhaust gas heating module (10) internally provided with at least one duct (11) exhaust gas flow whose wall is coated with zeolite adapted to generate exothermicity by adsorption of water. 2. Exhaust line (1) according to the preceding claim, wherein the heating module (10) comprises a honeycomb structure (12) defining a plurality of ducts (11) and wherein the zeolite forms a layer impregnating device (13) coating the walls of each conduit (11). 3. Exhaust line (1) according to one of the preceding claims, wherein the heating module (10) and the exhaust after-treatment system (20) each comprise a casing (15, 25) in separate stainless steel. 4. Exhaust line (1) according to the preceding claim, wherein the envelopes (15, 25) of the heating module (10) and the exhaust after-treatment system (20) are connected by a conduit junction (30) of short length, less than 50 centimeters. 5. Exhaust line according to one of claims 1 and 2, wherein the exhaust after-treatment system and the heating module comprise a single stainless steel casing. 6. Exhaust line (1) according to one of the preceding claims, comprising means for injecting water into the exhaust gas, equipped with an injector located upstream or at the entrance of the heating module. (10). 7. Exhaust line (1) according to one of the preceding claims, wherein the exhaust after-treatment system (20) comprises a structure (22) defining a plurality of flow conduits (21). exhaust gas, a catalytic impregnating layer (24) covering the walls of the conduits (21) of said structure (22), and a zeolite layer (23) which at least partially covers the walls of the conduits (21). ) of said structure (22) and which is adapted to generate an exothermicity by adsorption of water. 8. Exhaust line (1) according to the preceding claim, wherein the zeolite layer (23) is merged with the catalytic impregnation layer (24) or is superimposed on this catalytic impregnation layer (24), under that -this. 9. Exhaust line (1) according to one of the two preceding claims, wherein the zeolite of the zeolite layer (23) of the exhaust gas aftertreatment system (20) has an adsorption temperature. water greater than the water adsorption temperature of the zeolite of the heating module (10). 10. Internal combustion engine comprising an engine block equipped with cylinders and a fresh air intake line in the cylinders of the engine block, characterized in that it comprises an exhaust line (1) of exhaust gas out of the cylinders according to one of the preceding claims.