DE102010061753A1 - Exhaust gas treatment system for nitrogen oxide reduction for exhaust gas of internal combustion engine, has feeder tank, supply module and dosing module which is provided for introducing reduction medium to exhaust tract - Google Patents

Abstract

The exhaust gas treatment system (10) comprises a feeder tank (12), a supply module (22) and a dosing module (34) which is provided for introducing a reduction medium to an exhaust tract (48) of the internal combustion engine. A latent heat-accumulator is connected with a heat exchanger (18) in the feeder tank by a heat transfer medium, and is arranged in an external arrangement. An independent claim is also included for a method for operating an exhaust gas treatment system.

Description

State of the art

Currently used aftertreatment systems for self-igniting internal combustion engines, whether for commercial vehicles or passenger cars, use to reduce the NO _x components of the exhaust gas for exhaust aftertreatment urea dosing systems such as the SCR method (Selective Catalytic Reduction). By means of the SCR method, ammonia, NH ₃ , which is obtained on board the vehicle from urea, is injected into the exhaust tract of the internal combustion engine for the purpose of reducing the NO _x constituents of the exhaust gas. A urea solution stored in a separate tank, for example a urea-water solution (HWL), is metered by means of a metering pump or an injector into the hot exhaust gas stream which flows through an exhaust gas tract of an internal combustion engine. The urea decomposes to NH ₃ , which reduces the nitrogen oxides (NO _x ) in a downstream of the metering SCR catalyst. Here, the nitrogen oxides are converted into N ₂ and H ₂ O. The ratio of the reducing agent urea solution to diesel fuel is 1:20 to 1:30. The reducing agent has a freezing point which is at -11 ° C and a decomposition point at which decomposes the urea-water solution, which is approximately at + 60 ° C. At a temperature below -11 ° C, a complete crystallization of the reducing agent, so that this expands and occupies up to about 7% larger volume than before crystallization takes place. By heating, crystallized reducing agent can be thawed without any fear of adverse effects on the original quality of the reducing agent. The reducing agent can be used once all the crystalline structures are dissolved in it.

In order to prevent destruction of the reductant-filled system components of the exhaust aftertreatment system by crystallization at low ambient temperatures, after switching off the internal combustion engine all components of the exhaust aftertreatment system are emptied by reverse operation of pumps and valves in the storage tank in which the reducing agent is stored. Hot exhaust gases enter the components valves, lines and pump. Waiting times of up to several minutes are quite common in order to avoid overheating and the associated damage to the system components.

After starting the internal combustion engine, the reducing agent present in crystalline form is heated in the tank at low outside temperatures. As a result, all crystals are liquefied. In order to avoid crystallization of the reducing agent in the lines and in the metering valve during operation of the exhaust aftertreatment system at low ambient temperatures, these components of the exhaust aftertreatment system are generally electrically heated. Because of the associated burden on the electrical system of the motor vehicle, the heating within a defined voltage range between 8 volts and 16 volts, especially when the internal combustion engine is in operation, and the electrical system is at least partially powered by the generator.

DE 10 2004 052 107 B4 refers to an exhaust system and associated operating method. The exhaust system comprises in particular a NO _x storage catalytic converter, which is arranged in an exhaust gas line of the exhaust system. In the exhaust gas system, a heat accumulator is arranged upstream of the NO _x storage catalytic converter, which is designed such that it extracts heat from the exhaust gases of the internal combustion engine when the exhaust gases have an exhaust gas temperature which is greater than a predetermined storage temperature of the heat accumulator. The exhaust gases are supplied by the heat storage heat, as soon as the exhaust gas temperature is lower than the storage temperature. The heat accumulator is further configured such that the storage temperature corresponds to an upper limit temperature range of the NO _x storage catalytic converter. In particular, the heat accumulator is designed as a latent heat storage.

A latent heat storage device is a device that conserves thermal energy with little loss and over many years of repetitive cycling. Phase Change Materials (PCM) are used whose latent heat of fusion, solution heat or heat of absorption is significantly greater compared to the heat that these materials can store due to their specific heat capacity, without the phase change effect. In heat pad often sodium acetate trihydrate is used. Under the action of heat, the salt hydrate is liquefied with a melting temperature of 58 ° C and remains liquid up to a temperature of -13 ° C, and is present as a supercooled melt in a metastable state. The salt dissolves in its water of crystallization, as the water molecules form a crystal lattice that dissolves first. If a metal plate is pressed into the heat pad, this triggers crystallization. The cushion heats up to 58 ° C, whereby the complete crystallization and thus the release of the latent heat extends over a longer period of time. The reason for the onset of crystallization is the release of nuclei. These store separated from the rest of the melt in Nanorissen of the metal plate and are released from there.

Presentation of the invention

The invention has for its object to achieve a reduction in electrical energy consumption via heating the components of an exhaust aftertreatment system or to achieve the possibility of warming the components of the exhaust aftertreatment system largely independent of the use of electrical energy and without consideration of the voltage range of the electrical system of a motor vehicle.

The present invention is further based on the object to achieve a shortening of the heating of the components of the exhaust aftertreatment system after the start of the internal combustion engine and thus to achieve a faster operational readiness of the exhaust aftertreatment system and thus the reduction of emissions. Furthermore, the solution proposed by the invention is based on the object to avoid the crystallization of the reducing agent during driving, especially at low ambient temperatures and counteract this crystallization by a temperature management of stored in a storage tank reducing agent to counteract its decomposition phenomena.

According to the invention, it is proposed to use a latent heat store which has a controlled initiation of the crystallization and a controlled initiation of the crystallization heat release, the latent heat storage via a liquid heat exchange medium with a heat exchanger of the exhaust system, in particular a heat exchanger, which is arranged in the storage tank, the the reducing agent stored, forms. The latent heat accumulator is designed either as an external heat exchanger, or as an enclosure around the reducing agent receiving storage tank, or in a further embodiment as a central heating unit in the tank of the reducing agent.

The arranged within a circuit of a neither freezing nor boiling heat transport medium latent heat storage gives when needed, such as the start of the internal combustion engine, heat to the reducing agent and can during operation of the exhaust aftertreatment system heat from the reducing agent to avoid exceeding its limit temperature of approx. Record 60 ° C. Additional heat sources for the regeneration of the material, which is used in the latent heat storage, may preferably be the catalyst housing of either the SCR catalyst or an oxidation catalyst, which is also included in the exhaust tract of an internal combustion engine.

By the proposed solution according to the invention can be advantageously achieve a faster operational readiness of the exhaust aftertreatment system after the start of the internal combustion engine, especially at low ambient temperatures; This also applies in the event that the vehicle electrical system voltage or the battery voltage of the motor vehicle is at a very low level, which is the case in general, especially at low outside temperatures. Another advantage of the proposed solution according to the invention is that excess waste heat energy can be used to regenerate the heat storage material of the latent heat storage, so that ultimately a lower fuel consumption of the internal combustion engine is achieved. Furthermore, can be achieved by the invention proposed solution, a reduction in the burden of the electrical system by reduced electrical power and performance design of heating elements and power amplifiers for heater control, creating a simpler integration of these components in engine control units or a complete elimination of the electric heater or their control can go along.

The solution proposed by the invention further advantageously prevents or at least reduces the decomposition of the reducing agent by dissipating heat to the latent heat accumulator.

The prerequisite is that the heat storage material that is used in the latent heat storage, even or, for example, by additives to temperatures specified in the automotive sector, for example, -40 ° C is supercooled without spontaneous self-crystallization occurs.

In the solution proposed according to the invention, a plurality of possible embodiments of the arrangement of the latent heat accumulator can be realized. In summary, the latent heat storage can be integrated externally in a cycle of a heat transfer medium, it is also possible to form the latent heat storage as a sheath to the storage tank stockpiling the reducing agent or finally integrate the latent heat storage as Zusatzheizeinheit in an inner pot of a storage tank receiving the reducing agent supply.

In further embodiments of the solution proposed by the invention, for example, the latent heat storage may be formed as a sheath of the urea tank, wherein the Latent heat storage comprises a material such as sodium acetate trihydrate. By means of a first heat exchanger, which is arranged in the region of the exhaust system of the internal combustion engine, the exhaust gas heat is absorbed. Another second heat exchanger releases the heat of exhaust gas to the material of the latent heat accumulator, for example sodium acetate trihydrate, which forms an envelope of the urea tank. In this case, this further heat exchanger is arranged only within the envelope of the tank for receiving the reducing agent, so that it surrounds the tank and the latent heat storage material, such as NaAc heated completely above 58 ° C. A heat transfer to the reducing agent, such as urea, is not provided.

In a further embodiment of the invention underlying idea, the material of the latent heat storage, such as NaAc, sodium acetate trihydrate, as a central heating unit, for example columnar or block-like arranged inside the reducing agent receiving tank.

Brief description of the drawings

With reference to the drawing, the invention will be described below in more detail.

It shows:

1 the individual components of an exhaust aftertreatment system,

2 an inner pot of a storage tank is stored in the reducing agent with delivery module and a perspective view of the storage tank for receiving the reducing agent,

3 the representation of an integrated into a cycle of a heat transfer medium externally arranged latent heat storage,

4 individual steps of the operating sequence which occur during operation of the exhaust aftertreatment system proposed according to the invention,

5 A variant of the latent heat storage as the reducing agent tank surrounding sheath,

6 the design of the latent heat storage as integrated in the storage tanks columnar or block-like central heating unit.

Embodiments of the invention

The representation according to 1 is an exhaust aftertreatment system can be seen.

An exhaust aftertreatment system 10 which is in particular an exhaust aftertreatment system operated according to the SCR method 10 traded in a storage tank 12 for receiving a reducing agent such as urea or a urea-water solution (HWL), which freezes below temperatures of -11 ° C, a delivery module 22 and a dosing module 34 , In the storage tank 12 in which the freezable reducing agent is stored, for example, urea-water solution, there are a level sensor 14 and a temperature sensor 16 , Inside the storage tank 12 there is a heat exchanger 18 , which may be formed, for example, as an electrically heatable heating element and above the bottom of the pot-shaped configured storage tank 12 located. A conveyor module 22 includes a switching valve 20 and a feed pump 24 , a backflow restrictor 26 and a pressure sensor 28 and a filter 30 , One from the filter 30 to the dosing module 34 extending line is with a line heating 32 Mistake. The dosing module 34 is located in the area of an exhaust tract 38 the internal combustion engine. The exhaust pipe 48 is traversed by the hot exhaust gas and takes next to an oxidation catalyst 44 optionally a diesel particulate filter 42 an SCR catalyst 40 on. Between the dosing point for introducing the reducing agent at the exhaust gas tract of the internal combustion engine below the dosing 34 and the input side of the SCR catalyst 40 there is a mixing device 46 , through which a uniform swirling over the dosing module 34 To achieve in the exhaust stream registered reducing agent, before this the SCR catalyst 40 flows through there and reduces the nitrogen oxides to N ₂ and H ₂ O.

The exhaust pipe 48 the internal combustion engine are further a NO _x sensor 36 associated, downstream side downstream of the SCR catalyst 40 located as well as a temperature sensor 38 which is upstream of the SCR catalyst 40 in front of the dosing module 34 located.

The representation according to 2 a storage tank is to be taken.

2 shows an inner pot 50 standing in storage tank 12 for receiving the reducing agent is located at the top of the delivery module 22 is included. The arrangement of delivery module 22 and inner pot 50 is in an approximately mature-shaped outer pot 52 , which is also part of the storage tank 12 is, let in. From the according to perspective rendering 2 shows that the delivery module 22 in a trough-shaped depression 54 on the top of the storage tank 12 located. The lateral surface of the inner pot 50 as well as the inner wall of the outer pot 52 define the cavity in which the reducing agent is accommodated. In the inner pot 50 as shown in 2 is the in 1 schematically indicated heat exchanger 18 as well as the also indicated there level sensor 14 and a built-in temperature sensor 16 ,

The representation according to 3 is shown in a circuit for a heat transfer medium, with which a heat exchanger of the storage pot is connected to a latent heat storage.

From the illustration according to 3 shows that a cycle 62 for a heat transport medium 96 , which is in liquid form and does not freeze and does not boil, by means of a delivery unit 74 is circulated. A pressure side of the delivery unit 74 is by reference numerals 80 marked, the suction side of the delivery unit 74 by reference numerals 78 , From the illustration according to 3 shows that the liquid heat transport medium 96 which is within the cycle 62 is circulated, the heat exchanger 18 , the inner pot 50 of the storage tank 12 , in which the reducing agent is stored, flows through. The inner pot 50 is like in 2 shown in the outer pot 52 of the storage tank 12 embedded and includes the fittings described above. After flowing through the heat exchanger 18 in the inner pot 50 leaves the liquid heat transport medium 96 the storage tank 12 and flows to a latent heat storage 64 to. in the in 3 illustrated embodiment is the latent heat storage 64 in external arrangement 66 shown. The latent heat storage 64 can on top and bottom - as in 3 indicated - with a ribbing 90 be provided. Furthermore, the latent heat storage 64 in the in 3 illustrated external arrangement 66 a device for initiating crystallization, in this case designed as a Peltier element 92 assigned.

The crystallization initiator 94 in the general case, for example, as a Peltier element 92 be formed, wherein both the crystallization initiator 94 as well as the heat transport medium 56 circulating pump 74 via a control unit 84 to be controlled. With the control unit 86 in which the crystallization initiator 94 as well as the delivery unit 74 can be controlled independently, for example, a variable pump speed of the delivery unit 94 can be given, so that the adjusting heat exchange through the circuit 62 is effected, can be variably controlled and regulated.

As shown in the illustration 3 Furthermore, it is indicated by reference numerals 82 a heat input direction indicated, while by reference numerals 84 a waste heat utilization direction to the latent heat storage 64 is designated.

The latent heat storage 64 represented in. 3 in external arrangement 66 , includes a heat storage material 88 which stores heat with low loss in many repetitive cycles and over a long period of time. In the heat storage material 88 the latent heat storage 64 they are preferably Phase Change Materials (PCMs) whose latent heat of fusion, solution heat or heat of adsorption is significantly greater than the heat that these materials can store due to their normal specific heat capacity without the phase change effect. As a heat storage material 88 For example, sodium acetate trihydrate can be used. Under heat, the heat storage material NaAc, see position 88 in 3 , in latent heat storage 64 liquefied at a melting temperature of 58 ° C and remains up to a temperature of -13 ° C in the liquid phase as a supercooled melt in a metastable state. The salt dissolves in its water of crystallization, as the water molecules form their own crystal lattice that dissolves first. Now a metal plate in the heat storage material 88 pressed, its crystallization is triggered. The heat storage material 88 heats up to 58 ° C, whereby the complete crystallization and thus the release of the latent heat of the heat storage material can extend over a longer period. The reason for the onset of the crystallization process is the release of crystallization nuclei.

Based on the presentation of 4 be the functional sequence with regard to the heat dissipation and heat absorption within the in 3 illustrated circuit explained in more detail.

With reference number 100 Let a start of the journey be designated, at its beginning via the crystallization initiator 54 , For example, the Peltier element 52 , a local subcooling of the heat storage material 88 is triggered. Here is the heat storage material 88 the latent heat storage 64 Heat to the in the cycle 62 circulating heat transport medium 96 , which is liquid and does not freeze and does not boil off. There is a release of latent heat to the urea-water solution. This release of latent heat is in 3 by reference numerals 104 characterized. A urea / water temperature is ambient temperature plus a temperature due to the release of latent heat. There is a release of the injection of a reducing agent, in particular a urea-water solution 106 , Due to the exhaust heat emitted by the internal combustion engine, the regeneration of the heat storage material takes place 88 the latent heat storage 64 , but in a short-distance journey of less than 8 km in length, the latent heat storage 64 can not be charged due to the low usable waste heat. A regeneration of the heat storage material 88 Example, sodium acetate trihydrate, is carried out in a temperature range between 58 ° C and 77 ° C. The regeneration of the heat storage material 88 is in the illustration in 4 by reference numerals 108 indicated. Upon further heating of the heat storage material 88 as the drive continues, saturation of the heat storage material occurs 88 , For example, NaAc and its melt due to the continuously supplied engine waste heat in a temperature range between 77 ° C <T ≤ 120 ° C. This condition is shown in the illustration 4 by reference numerals 110 indicated. After the end of the journey, compare reference numbers 114 , turns a cooling phase 112 one. During the cooling phase 112 decreases the temperature of the reducing agent, in particular the urea-water solution to ambient temperature T _Umg , the heat storage material 88 Cools slowly and the temperature of the melt of the heat storage material 88 decreases to ambient temperature. If extremely low outside temperature prevails, the addition of alcohol can become a heat storage material 88 a cooling below 25 ° C whose spontaneous crystallization can be prevented.

From the illustration according to 4 shows that the regeneration of the heat storage material 88 the latent heat storage 64 due to the engine waste heat emitted by the internal combustion engine after its start. The latent heat storage 64 in 3 represented as an external arrangement 66 , is above the heat transport medium 64 which is in circulation 62 circulates with heat-emitting components, such as catalytic converters, such as in the oxidation catalyst 44 or hot gas piping, such as the exhaust pipe 48 connected. To its coupling serve the heat exchanger, see comparison according to 3 as well as lines and pumps as in 3 are shown. This ensures that the temperatures are sufficiently long above the regeneration temperature of the latent heat storage material 88 can be kept in the drive cycle. In the 3 arrangement shown is particularly suitable when the regeneration temperature of the latent heat storage material 88 above the decomposition temperature of the urea solution, ie about 60 ° C. In the storage tank 12 Frozen reducing agent or a risk of freezing the same in operation, the crystallization of the latent heat storage material 88 via the control unit 86 by appropriate activation of the crystallization initiator 94 , compare illustration according to 3 , initiated. For the transport of heat, the onset of crystallization in the circulating heat transport medium 96 generated heat to the heat exchanger 18 in the inner pot 50 of the storage tank 12 is arranged, there is a corresponding control of the delivery unit 74 via the control unit 86 such that a heat-transporting heat-input direction 82 , compare illustration according to 3 is triggered.

From the illustration according to 5 shows a further embodiment of a latent heat storage in the sense of the invention proposed solution.

Out 5 it appears that the storage tank 12 for receiving the reducing agent, in particular a urea-water solution from an enclosure 68 from heat exchanger material 88 , so for example NaAc is enclosed. into the serving 68 from heat exchanger material 88 is the heat exchanger 18 embedded. An in the cycle 62 circulating heat transport medium 56 is through a delivery unit 74 circulated. The suction side of the delivery unit 74 is by reference numerals 78 , whose print page by reference numerals 80 indicated. A heat exchanger 118 is the exhaust aftertreatment system of an internal combustion engine 116 downstream. How out 5 it shows that it is in circulation 62 circulating heat transport medium 96 the heat absorbed in the heat exchanger 18 to the heat exchanger material 88 which is preferably a salt hydrate such as sodium acetate trihydrate. The heat exchanger 18 is according to the in 5 illustrated embodiment within the enclosure 68 arranged so that he has the storage tank 12 encloses and the heat exchanger material 88 In particular, the NaAc can warm completely above 58 ° C. In this case, a heat release to the reducing agent, such as a urea-water solution is not provided.

With reference number 24 is the feed pump designates which the reducing agent from the storage tank 12 about that in 1 shown dosing module 34 in the exhaust tract of the internal combustion engine 116 metered.

The representation according to 6 the embodiment of the proposed solution according to the invention can be seen, after which a central heating unit through the heat exchanger material 88 which is in particular a salt hydrate, for example NaAc.

Again, the heat exchanger 118 in the exhaust aftertreatment system 10 the internal combustion engine 116 assigned. In the cycle 62 becomes analogous to in 5 illustrated embodiment, the heat transport medium 96 using the delivery unit 74 circulated. The suction side of the delivery unit 74 is by reference numerals 78 , whose print page by reference numerals 80 characterized. In the heat exchanger 18 the heat is released in the heat exchanger 118 was taken to the storage tank 12 , With reference number 24 is the feed pump designated by which in the storage tank 12 stored reducing agent in the exhaust aftertreatment system 10 by means of the in 1 shown dosing modules 34 is introduced. Out 6 shows that the heat exchanger material 88 the latent heat storage essentially columnar or block shaped as Zentralheizeinheit 98 is arranged in the center of the reducing agent receiving storage tank. In the exhaust aftertreatment system 10 the SCR catalyst is arranged, which in the illustration according to 6 by reference numerals 40 is marked.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102004052107 B4 [0004]

Claims (10)

Exhaust aftertreatment system ( 10 ) to NO _x reduction in the exhaust gas of internal combustion engines with a storage tank ( 12 ), a conveyor module ( 22 ) and a dosing module ( 34 ) for introducing a reducing agent into an exhaust gas tract ( 48 ) of the internal combustion engine, characterized in that a latent heat storage ( 64 ) via a heat transport medium ( 96 ) with a heat exchanger ( 18 ) in the storage tank ( 12 ) and (a) either in an external arrangement ( 66 ), b) or as an envelope ( 68 ) of the storage tank ( 12 ), c) or as a central heating unit ( 98 ) in the storage tank ( 12 ) is trained. Exhaust aftertreatment system ( 10 ) according to claim 1, characterized in that the latent heat storage ( 64 ) a heat storage material ( 88 ), in particular a salt hydrate, for example sodium acetate trihydrate. Exhaust aftertreatment system ( 10 ) according to claim 1, characterized in that the latent heat store ( 64 ) a crystallization initiator ( 94 ) for initiating the heat release, in particular a Peltier element ( 92 ) assigned. Exhaust aftertreatment system ( 10 ) according to claim 1, characterized in that the latent heat storage ( 64 ) by means of a cycle ( 62 ), which is a delivery unit ( 74 ), with the storage tank ( 12 ), in particular of the heat exchanger arranged therein ( 18 ). Exhaust aftertreatment system ( 10 ) according to claims 3 and 4, characterized in that the crystallization initiator ( 94 ) and the delivery unit ( 74 ) with a control device ( 86 ), which provides independent control of the crystallization initiator ( 94 ) and in particular a variable speed of the delivery unit ( 74 ). Exhaust aftertreatment system ( 10 ) according to claim 1, characterized in that the latent heat storage ( 64 ) with at least one heat-emitting component, such as a diesel particulate filter ( 42 ), or an oxidation catalyst ( 44 ) in the exhaust tract ( 48 ) of the internal combustion engine, so that a generation of the heat storage material ( 88 ) takes place above its regeneration temperature. Exhaust aftertreatment system ( 10 ) according to claim 1, characterized in that the latent heat storage ( 64 ) as a wrapper ( 68 ) of the storage tank ( 12 ) is trained. Exhaust aftertreatment system ( 10 ) according to claim 1, characterized in that the latent heat storage ( 64 ) as a central heating unit ( 98 ) columnar or block of the reducing agent flows around in the storage tank ( 12 ) is arranged. Method for operating an exhaust aftertreatment system ( 10 ) according to any one of claims 1 to 8, characterized in that when freezing or frozen reducing agent in the storage tank ( 12 ) the crystallization in the heat storage material ( 88 ) of the latent heat storage ( 64 ) by driving the crystallization initiator ( 94 ) is initiated and a heat transfer to that in the circulation line ( 76 ) of the cycle ( 62 ) circulating heat transfer medium ( 96 ) he follows. A method according to claim 9, characterized in that during operation of the exhaust aftertreatment system ( 10 ) occurring temperatures in the storage tank ( 12 ) above the regeneration temperature of the latent heat storage ( 64 ) and below the decomposition temperature of the reducing agent, this through the circulating heat transfer medium ( 96 ) is heated.

Images