RU2212929C2 - System with heated catalytic neutralizer and water catcher installed ahead of said neutralizer and method of system operation control - Google Patents

Abstract

FIELD: neutralization of exhaust gases of internal combustion engines. SUBSTANCE: system has the following components located in indicated sequence in direction of exhaust gases flow: the first water catcher 5, honeycomb member 7 with electric heating and honeycomb member 8 with catalytically active coating serving, at least, for oxidation catalysis. Honeycomb member 7 with electric heating and honeycomb member 8 with electric heating and honeycomb member 8 with catalytically active coating may also fully or partially form single design unit. Similar system may be installed as small additional system behind three-component catalytic neutralizer of exhaust gases for neutralization of exhaust gases during start of cold engine. Method of system operation control provides for heating of honeycomb member with electrical heating started not later than at the moment of start of internal combustion engine. EFFECT: reduced content of harmful substances in exhaust gases of vehicles. 16 cl, 2 dwg

Description

 The invention relates to a system for neutralizing exhaust gases (exhaust) of an internal combustion engine (ICE) and to a method for controlling the operation of such a system.

 In order to reduce the negative impact on the environment, there is a tendency to reduce the maximum permissible concentrations of harmful substances released into the atmosphere with exhaust gases. Particular problems with the treatment of exhaust gases in order to reduce their toxicity occur during the start-up of a cold internal combustion engine, when substantially large amounts of hydrocarbons are usually removed from the exhaust gas. In addition, it is also necessary to oxidize carbon monoxide to carbon dioxide, as a result of which, during the start-up of a cold engine, catalytically active materials should accelerate mainly oxidative processes. During the subsequent operation of the engine, as a rule, three-component catalytic converters are used to neutralize the exhaust gas, which are capable of simultaneously oxidizing oxidizable components and reducing nitrogen oxides.

 Systems specifically designed to neutralize exhaust gas during a cold engine start-up are described, for example, in EP 0 638 710 A2 and EP 0 485 179 A2. Such systems may consist of several components, namely, three-component catalytic converters, hydrocarbon adsorbers and heated honeycomb elements. Moreover, there are various systems of catalytic neutralization of exhaust gases, the individual components of which are supplied with catalytically active coatings of various types.

The most suitable electric heating components for such exhaust systems, which during the start-up of a cold engine ensure that the minimum temperature necessary to start the catalytic reaction is quickly achieved are described, for example, in WO 96/10127. In the case of systems with electrically heated honeycomb cells, it was initially assumed that the temperature that must be achieved so that the catalytically active coating can catalyze the required oxidation processes is approximately 250 ^° C.

However, as subsequent studies have shown, the temperature at which the catalytically active material can begin to catalyze the oxidation of carbon monoxide and hydrocarbons can be significantly reduced if it is possible to keep the substrate of this catalytically active material practically dry. Coatings have been developed that can be applied by conventional technology to a honeycomb cell coated with a γ-alumina ceramic layer and which act as oxidation catalysts even at temperatures well below 100 ^° C, in particular at 70-80 ^° C, unless the honeycomb and ceramic coating remain dry. At the same time, so-called “water traps”, i.e. water traps containing materials that are capable of trapping and storing water in large quantities at temperatures below a certain value. Exhaust systems with similar water traps in various designs and the materials required for this are described, for example, in WO 96/39576.

 Based on the foregoing, the present invention was based on the task of combining the components known from the prior art used to neutralize exhaust gases in such a way as to provide the most effective exhaust gas neutralization, which allows to reduce the content of harmful substances in exhaust gases emitted into the atmosphere to the lowest possible level. A special goal in this case is to increase the efficiency of exhaust gas neutralization during the start-up of a cold engine and at the same time to prevent the installation of components in the exhaust pipe close to the engine that are subject to high loads due to their proximity to the engine. Another objective of the invention is to develop the most simple in design, but at the same time highly efficient exhaust gas aftertreatment systems, while the electrically heated honeycomb components included in these systems should consume less energy compared to known systems. In addition, it is necessary to propose an appropriate way to control the operation of such systems.

 These tasks are solved using the proposed in the invention of the exhaust gas aftertreatment system of an internal combustion engine and a method for controlling the operation of such a system.

 The exhaust gas aftertreatment system of the internal combustion engine according to the invention has at least the following components arranged in the indicated sequence in the direction of the exhaust gas flow: a first water trap, an electrically heated honeycomb and a catalytically active honeycomb, which serves at least , for catalysis of oxidation, while the honeycomb element with electric heating and the honeycomb element with a catalytically active coating can also fully or partially form e iny structural unit.

 It is preferable in this system to place behind the honeycomb element with a catalytically active coating a back damper, which serves to prevent the penetration of moisture into the system when the ICE is not working.

 In the same system, behind the honeycomb cell with a catalytically active coating, a second water trap can be located.

 In the proposed system, it is preferable to place a three-component exhaust gas catalytic converter in front of the first water trap, the dimensions and parameters of which would be selected so that it is individually or at least in combination with the rest of the system components capable of providing exhaust gas neutralization during engine operation under normal load conditions.

 In this case, it is desirable that the distance between the internal combustion engine exhaust outlet and the three-component exhaust gas catalytic converter be at least 30 cm, preferably 80 cm, and as a three-component exhaust gas catalytic converter, a catalytic converter located under the body floor is used primarily.

 In the proposed system between the internal combustion engine and its first component, it is advisable to have an air inlet.

 It is preferable to place a hydrocarbon adsorber in front of the electrically heated honeycomb element, especially behind the first water trap.

 In the proposed system, at least one of the traps can be electrically heated.

 It should be noted that in the proposed system, the honeycomb element with a catalytically active coating is a three-component exhaust gas catalyst with dimensions and parameters sufficient to neutralize the exhaust gas when the engine is operating at full load.

 In this case, the electrically heated honeycomb is a catalytically active coating section of the honeycomb.

 Said electrically heated honeycomb element is preferably installed directly in front of the catalytically active coated honeycomb element, preferably supported by the latter.

 In the proposed system, a device can be provided in front of the first water trap for removing heat from the exhaust gas stream.

 A method of controlling the operation of the proposed system is that the heating of the honeycomb cell with electric heating is started at the latest at the time of starting the engine.

 In accordance with the invention, the operation of the internal combustion engine during the start-up of a cold engine is first provided on an enriched combustible mixture with excess fuel, while secondary air is supplied through the air inlet until the internal combustion engine can operate on a stoichiometric combustible mixture or on a lean fuel mixture at the ratio of fuel and air is less than stoichiometric.

 Moreover, the internal combustion engine switching from working on an enriched combustible mixture to working on a stoichiometric combustible mixture or on a mixture with a fuel to air ratio less than the stoichiometric is carried out depending on the temperature in the three-component exhaust gas catalyst designed for normal load operation, namely, only when measured or calculated temperature sufficient for catalytic neutralization of the exhaust gas value.

 It should be noted that when implementing the method for controlling the operation of the proposed system, at least the first water catcher is electrically heated, which is turned on to drain this water catcher during the operation of the internal combustion engine and / or after the internal combustion engine is turned off.

 As described in more detail below, such a system, depending on its parameters, can be used to perform two different functions. With the relatively small size of the electrically heated honeycomb cell and the catalytically active honeycomb cell, this system can be installed behind a conventional exhaust gas aftertreatment system, for example a three-way catalytic converter. In this case, such a system serves primarily for the oxidation of carbon monoxide and hydrocarbons during the start-up of a cold engine, while the one located in front of it - the main one - the exhaust gas neutralization system takes over the functions of neutralizing exhaust gas during normal engine operation, while behind the specified main system, the system provides at most only the catalytic conversion of small residues of harmful substances.

The water trap keeps both components installed behind it dry, so that a catalytic reaction becomes possible even at temperatures of 70-80 ^o C. Since only a small stream of exhaust gases flows through the exhaust system during the start-up of a cold engine, an electrically heated honeycomb element can achieve this temperatures are much faster and / or less expensive than in conventional systems without a water catcher, in which it must be heated to a temperature of at least 250 ^o C. Usually The electrically heated element has at least one layer of oxidizing coating, so that immediately after reaching the temperature necessary for the catalytic reaction, it begins to catalyze exothermic oxidation reactions, which in this case additionally sharply increase the temperature of the exhaust gas, bringing the temperature of the next cellular element, which also has a catalytic coating having at least an oxidizing effect, also to the level necessary for the reaction to proceed. Therefore, the almost complete removal of carbon monoxide and hydrocarbons from the exhaust gas begins in a few seconds. The dimensions and parameters of the water trap should be selected so that it can accumulate water vapor coming from the internal combustion engine until a catalytic reaction begins in the honeycomb cell with electric heating and / or the cell cell behind it with a catalytically active coating. After this, the water trap can be heated by the exhaust gas flow and again return the accumulated water, which does not adversely affect the exhaust gas neutralization. Then, in the course of further engine operation, the catalytic exhaust gas aftertreatment system itself also reaches its operating temperature, after which it mainly assumes the functions of neutralizing the exhaust gas. The system installed behind it does not overheat, and under certain conditions it is even somewhat cooled again.

 It may be appropriate to install a water trap and a cell element with electric heating in a vehicle relatively far from the engine in order to maintain a low temperature load and prevent aging of this system when operating under normal load conditions.

 It should be noted that the electrically heated honeycomb element and the catalytically active coating honeycomb element can form a single structural unit, i.e. in the extreme case, it is necessary to have only one cell element with electric heating, having a sufficiently large surface with a catalytically active coating. However, the most preferred embodiment is when a very short electrically heated honeycomb cell is mounted directly in front of the catalytically active coated honeycomb body supported by the latter, as described, for example, in WO 96/10127.

 To keep the honeycomb element with a catalytically active coating and / or the honeycomb element electrically heated and in a vehicle with an inoperative engine dry, in the simplest case, an exhaust damper can be provided in the exhaust system to prevent moisture from entering the system when the engine is idle, which is opened by the exhaust gas flow, and in the absence of a flow, the exhaust gas is in a practically tightly closed position.

 Additionally or alternatively, it is also possible to provide at the end of the exhaust pipe a second water trap, capable of catching, if necessary, with an idle engine for a long period of time, moisture penetrating into the system from the air, preventing the moistening of the cellular elements located in front of it.

 When using the system proposed in the invention in combination with a conventional three-component exhaust gas catalytic converter, the latter is no longer required to be located near the engine, but can be installed at a distance of 30 cm or more from the engine exhaust outlet. Since the internal combustion engine during the start-up of a cold engine usually works on an enriched combustible mixture, i.e. when the ratio of fuel and air is higher than stoichiometric, at some point behind the internal combustion engine it is necessary to provide secondary air in order to ensure the catalytic conversion of excess fuel. Since this secondary air cools the exhaust gas flow moving from the engine, it was usually introduced at a point between the additional exhaust catalytic converter operating in the engine start-up and warm-up mode (the so-called pre-catalyst) and the primary catalytic converter to provide faster heating of this additional catalytic converter. In the solution proposed in the invention, this factor does not play any role, due to which secondary air can be let in at some point between the internal combustion engine and the first component of the exhaust gas aftertreatment system. In the case of particularly high requirements for exhaust gas neutralization during cold start of the engine, at some point in front of the electrically heated honeycomb cell, a hydrocarbon adsorber can also be provided, which at the initial stage of the internal combustion engine engulfs the hydrocarbons contained in the exhaust gas until the honeycomb cell electrically heated does not heat up to a sufficiently high temperature necessary for the catalytic reaction. In the exhaust gas aftertreatment system according to the invention, it is preferable to install such a hydrocarbon adsorber in front of the electrically heated honeycomb element, especially after the first water trap. Such hydrocarbon adsorbers are typically cell zeolite coated cellular elements, such as those described in the prior art.

 Very high temperatures can damage water traps, hydrocarbon adsorbers, and generally catalytically active coatings. This process is also called aging. Since the temperature of the incoming exhaust gas flow does not affect the operability of the system proposed in the invention, this entire system can be located in the vehicle at a relatively large distance from the engine, which reduces the risk of aging of its components. In the event that such an arrangement is not possible, a heat removal device may also be provided in front of the first water trap or, if necessary, in front of the hydrocarbon adsorber in front of it. In the simplest case, exhaust pipes made in the form of heat exchangers can serve as such a device. However, forced cooling is also possible, which in turn can be regulated or unregulated. This is especially useful when a conventional three-component exhaust gas catalyst is installed in front of the system of the invention, which, when operating under normal load conditions, increases the temperature of the exhaust gases additionally due to exothermic reactions occurring in it. In this case, the temperature of the exhaust gas is preferably reduced again before it enters the remaining components of the system.

 The parameters of the system proposed in the invention can also be selected in such a way that it can, without installing a three-component catalytic converter in front of it, completely take over all the functions of neutralizing the exhaust gas, starting from the start-up period of a cold engine. Obviously, in this case, the cell element with a catalytically active coating, located behind the cell element with electric heating, should have a sufficiently large volume to fully ensure the catalytic conversion of the exhaust gas during engine operation under normal load conditions. In this case, it should have a three-component coating. An electrically heated honeycomb element must have at least one layer of a catalytically active coating catalyzing the oxidation reaction. Therefore, in a preferred embodiment for such an application, the proposed system has the following components arranged in the indicated sequence in the direction of the exhaust gas flow: a water trap, a catalytic converter with electric heating, a honeycomb cell with a catalytically active three-component coating and, if necessary, a second water trap and / or back flap. In addition, a hydrocarbon adsorber may be included in such a system if necessary.

 It should be noted that components such as an electrically heated honeycomb and a catalytically active honeycomb can have various designs. Thus, for example, an electrically heated honeycomb cell may be supported by a honeycomb cell located behind it, or even be integrated into a larger honeycomb cell. In addition, the catalytically active coated honeycomb may also be made up of several separate sections.

According to the method of the invention, the heating of the honeycomb cell with electric heating is started at the latest at the time of starting the engine. In systems without a hydrocarbon adsorber, heating could be started as early as 1-5 s before starting the engine to ensure exhaust gas neutralization from the very beginning. Electric circuits that promptly turn on the heating, for example, when opening the door, when sitting the driver in the driver's seat or when inserting the ignition key into the ignition switch-lock, are known. Since the temperature required to initiate the catalytic reaction is very low for dry honeycomb cells and amounts to, for example, 70-80 ^° C, only a short period of time and / or lower electric power is required for heating. For this reason, there is a fairly large freedom of choice of the parameters of the cell element with electric heating.

 The proposed system allows the easiest way to ensure the mode of operation of the internal combustion engine, which is necessary for the optimal start of a cold engine. During the start-up of a cold engine, it is possible to supply enriched combustible mixture to the internal combustion engine while supplying secondary air through the air inlet until the internal combustion engine can operate on the stoichiometric combustible mixture or even on the lean fuel mixture. It should be noted that the system proposed in the invention is also suitable for use as an additional component used to neutralize exhaust gases during the start-up of a cold engine in exhaust systems for exhaust engines operating on lean mixtures. It is preferable to switch the engine from operating on an enriched mixture to operating on a stoichiometric mixture or a mixture with a fuel / air ratio less than the stoichiometric depending on the measured or calculated temperature in the three-component exhaust gas catalyst intended for normal load operation, namely, only when temperature sufficient for catalytic neutralization of the exhaust gas value.

 When using water traps in the exhaust system, these conditions may occur and operating modes are possible in which the water catcher can reach the limit of its moisture absorption capacity and lose the ability to perform its functions if appropriate additional measures are not taken. In order to avoid such situations, it is advisable to provide a water trap with electric heating, which is turned on to drain this water trap during operation of the internal combustion engine and / or after the internal combustion engine is turned off.

 It should be noted that for sulfur-containing fuels that are still in use today, in order to avoid damage or poisoning of the components of the exhaust gas aftertreatment system, a sulfur trap may be provided, i.e. a honeycomb element with a sulfur-absorbing coating. It is preferable to install such a trap in front of the component of the system that is most at risk of damage by sulfur, but at such a distance from the engine to avoid thermal damage to this trap. It is most advisable to install this trap, for example, immediately in front of the first water trap of the system.

Other advantages and distinguishing features of the invention are discussed in more detail below on the example of two options for its implementation, which the scope of the invention is not limited, with reference to the accompanying drawings, which show:
in FIG. 1 - exhaust gas aftertreatment system with a three-component exhaust gas catalytic converter and the system of the invention proposed for neutralizing exhaust gas during the start-up of a cold engine installed behind it, and
in FIG. 2 - proposed in the invention system, intended for use during the start-up of a cold engine and when operating in normal load mode.

 Figure 1 shows a diagram of the proposed invention, the exhaust gas aftertreatment system (exhaust), made according to the first embodiment. The exhaust gas stream exhausting from the internal combustion engine 1 (ICE) passes through the exhaust pipe 2a, 2b, 2c, 2e, 2f in the direction S. An inlet 3 is provided in the pipe for supplying secondary air, preferably during the start-up of a cold engine. This opening is followed by a three-component catalytic converter 4 exhaust gas, which, when the internal combustion engine operates under normal load conditions, provides exhaust gas neutralization by oxidizing carbon monoxide and hydrocarbons and reducing nitrogen oxides. Next, a section 2b follows in the exhaust pipe, which preferably has devices 11 for removing heat Q in order to prevent aging of the components behind it under the influence of high temperatures. This is followed by the first water trap 5, which accumulates all the moisture contained in the exhaust gas and secondary air until a catalytic reaction begins in the system components located behind it. Then, an additional hydrocarbon adsorber 6 may be provided in the exhaust pipe if the hydrocarbon yield must be reduced to a particularly low level. This is followed by a cell element 7 with electric heating and a cell element 8 with a catalytically active coating. The electrically heated honeycomb element 7 also preferably has a catalytically active coating that at least catalyzes the oxidation, especially the oxidation of carbon monoxide. The catalytically active coated cell 8 preferably also serves to catalyze oxidation.

 Behind it, in the exhaust system, an additional water trap 9 can be additionally installed, which, when the engine is idle, prevents moisture from entering the exhaust system through its outlet. The back flap 10 can additionally or alternatively serve the same purpose.

 One of the water traps, or both of them can also be electrically heated, if conditions can arise in the entire exhaust gas aftertreatment system in which the complete dehumidification of one or both water traps cannot be achieved during the operation of the internal combustion engine. Similar situations can occur under certain conditions with frequent short periods of starting a cold engine without subsequent longer periods of its operation under normal load conditions. According to an embodiment of the invention, the proposed system having at least one first water trap 5, an electrically heated honeycomb element 7 and a catalytically active coating honeycomb element 8 is used as an additional system to a conventional three-component exhaust gas catalytic converter in order to increase the neutralization efficiency Exhaust gas and during the start-up of a cold engine. In this case, the honeycomb element 7 with electric heating and the honeycomb element 8 with a catalytically active coating can also form a single structural unit and, if necessary, together make up only one single cell element with a catalytically active coating and electric heating. The proposed system allows you to abandon the use of the catalyst used in the start-up and warm-up of the engine, and thereby provides the opportunity to install a three-component catalytic converter exhaust gas at a sufficient distance from the engine, which prevents exposure to extremely high thermal loads. In addition, secondary air can be supplied anywhere in front of the components of the exhaust gas aftertreatment system.

 In FIG. 2 shows a second embodiment of the invention, in which case the proposed system fully assumes all the functions of exhaust gas neutralization without the need to place it close to the engine. Moreover, it is even preferable to remove this system from the engine so that it is not exposed to extremely high exhaust gas temperatures. In accordance with the variant of FIG. 2, the exhaust gas flow from the internal combustion engine 1 passes in the S direction through the exhaust pipe 12a, 12b, 12c, 12d, 12e. The inlet 3 for supplying secondary air is located on the first section 12A of the exhaust pipe. The first water trap 5 accumulates all the moisture contained in the exhaust gas until the catalytic conversion of the exhaust gas begins in the electrically heated honeycomb element 17 located behind it and the catalytically active coating located after the last honeycomb element 18. And in this case, closer to the end of the exhaust pipe, a second water trap 9 and / or a back flap 10 can be provided, which serve to keep the entire system dry when the engine is not running. Similarly, in the embodiment of FIG. 2, a hydrocarbon adsorber not shown in the drawing may also be provided. It is important in the embodiment of FIG. 2 that the catalytically active coated honeycomb element 18 is large enough to ensure complete catalytic conversion of the harmful exhaust components even when the engine is operating under normal load conditions. Thus, we are talking about the main catalyst, which is located relatively far from the engine and in front of which is installed a honeycomb element with electric heating, having a catalytically active coating that catalyzes at least oxidation. Obviously, conventional measuring systems should also be provided for regulating the exhaust gas aftertreatment process and engine control.

 In both of the above embodiments, the electrically heated honeycomb element can be turned on directly when starting the engine or even a few seconds before. In particular, in the absence of a hydrocarbon adsorber located in front of it, its inclusion 1-5 s before the start of the internal combustion engine can provide exhaust gas neutralization from the very beginning of the engine operation.

 The solution proposed in the present invention is most suitable for use in vehicle exhaust systems, since when using inexpensive means, it provides effective exhaust gas neutralization taking into account even the most stringent legislative requirements.

Claims (16)

 1. The exhaust gas aftertreatment system (exhaust gas) of an internal combustion engine (1) internal combustion engine, having at least the following components arranged in the indicated sequence in the direction (S) of the exhaust gas flow: first water trap (5), honeycomb element ( 7; 17) electrically heated and a honeycomb cell (8; 18) with a catalytically active coating that serves at least to catalyze oxidation, while the honeycomb cell (7; 17) is electrically heated and a honeycomb (8; 18 ) with a catalytically active coating can also fully and whether to partially form a single structural unit.  2. The system according to claim 1, in which behind the honeycomb element (8; 18) with a catalytically active coating there is a back flap (10), which serves to prevent moisture from entering the system when the ICE is not working (1).  3. The system according to claim 1 or 2, in which a second water trap (9) is located behind the honeycomb element (8; 18) with a catalytically active coating.  4. The system according to any one of the preceding paragraphs, in which in front of the first water catcher (5) there is a three-component exhaust gas catalytic converter (4), the dimensions and parameters of which are selected so that it is individually or at least in combination with the other components (7 , 8) the system was able to provide exhaust gas neutralization during the operation of the internal combustion engine (1) in normal load mode.  5. The system according to claim 4, in which the distance between the exhaust port of the internal combustion engine (1) and the three-component exhaust catalyst (4) is at least 30 cm, preferably 80 cm, while the exhaust gas is three-component catalyst (4) total catalytic converter located under the body floor.  6. The system according to any one of the preceding paragraphs, in which there is an air inlet (3) between the ICE (1) and the first component (4; 5) of the exhaust gas aftertreatment system.  7. The system according to any one of the preceding paragraphs, in which a hydrocarbon adsorber (6) is located in front of the electrically heated honeycomb element (7), primarily behind the first water trap (5).  8. The system according to any one of the preceding paragraphs, in which at least one of the water traps (5, 9) is electrically heated.  9. The system according to claim 1, in which the honeycomb element (18) with a catalytically active coating is a three-component exhaust gas catalyst (4) with dimensions and parameters sufficient to neutralize exhaust gases when the engine is operating at full load.  10. The system according to claim 9, in which the cell element (7; 17) with electric heating is a section of the cell element (8; 18) with a catalytically active coating.  11. The system according to claim 9, in which the honeycomb element (7; 17) with electric heating is installed directly in front of the honeycomb element (8; 18) with a catalytically active coating, preferably based on the latter.  12. The system according to any one of the preceding paragraphs, in which a device (11) is provided in front of the first water trap (5) for removing heat (Q) from the exhaust gas stream.  13. The method of controlling the operation of the system according to any one of the preceding paragraphs, in which the heating of the honeycomb element (7; 17) with electric heating is started at the latest at the time of starting the engine (1).  14. The method according to p. 13, in which the operation of the internal combustion engine (1) during the start-up of a cold engine is first provided on an enriched fuel mixture with excess fuel, while secondary air is supplied through the air inlet (3) until the internal combustion engine ( 1) will not be able to work on a stoichiometric combustible mixture or on a lean fuel mixture when the ratio of fuel and air is less than the stoichiometric.  15. The method according to p. 14, in which the switch of the internal combustion engine (1) from working on an enriched combustible mixture to working on a stoichiometric combustible mixture or on a mixture with a fuel to air ratio less than the stoichiometric is carried out depending on the temperature intended for normal load operation a three-component catalytic converter (4; 18) of exhaust gas, namely only when the measured or calculated temperature in it reaches a value sufficient for catalytic neutralization of exhaust gas.  16. The method according to PP. 13, 14 or 15, in which at least the first water trap (5) is electrically heated, which is turned on to drain this water trap during operation of the internal combustion engine (1) and / or after the internal combustion engine (1) is turned off.

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