DE102008012972A1 - Aqueous solution e.g. urea-water-solution, evaporation unit for use in exhaust gas system of motor vehicle, has heat layer formed outside thermal conductive layer and connected in material fit to thermal conductive layer - Google Patents

Abstract

The unit (1) has an evaporator cavity (2) that is limited by a wall (4) made of material containing titanium. A thermal conductive layer (5) lies outside the cavity and is made of a material e.g. copper or aluminum, including a thermal conductivity of 100 watt per mete Kelvin. The thermal conductive layer is connected to the unit in a heat-conducting manner. A heat layer (6) is formed outside the conductive layer and is connected in a material fit to the conductive layer. The conductive layer comprises a recess, and a heating conductor (7) is inserted into the recess.

Description

The The present invention relates to an evaporation unit for production a gas stream containing a reductant precursor such as For example, urea and / or a reducing agent such as Includes ammonia. Such an evaporation unit finds particular Application for providing gaseous ammonia from a Ammonia precursor, especially in liquid and / or solid form. The invention finds particular application in the context of exhaust aftertreatment in motor vehicles.

Especially In diesel internal combustion engines, it has proven to be the from the internal combustion engine generated exhaust urea in aqueous solution add ammonia directly or after an external gas hydrolysis. In this case, in known processes, a hydrolysis catalyst used, is obtained from the urea ammonia. The aqueous urea solution becomes upstream added to the hydrolysis catalyst, converted to the gaseous state and brought into contact with the hydrolysis catalyst. The generated For example, ammonia reacts with a so-called SCR catalyst further downstream in the exhaust stream with the nitrogen oxides contained there to molecular Nitrogen and water.

at the evaporation of the aqueous urea solution is the temperature control especially difficult. This is especially true if the required quantities the urea solution on the one hand and the available ones Temperatures in the exhaust on the other hand, for example, during a mobile application can vary greatly. Will not evaporate Completely achieved, can form intermediates, which may cause constipation lead the evaporation unit can. Such undesirable By-products are, for example, water-insoluble biuret, which is made up of isocyanic and urea forms, and cyanuric acid, which is the trimerization product the isocyanic acid represents. In the evaporation of an ammonia precursor, in particular a liquid Urea-water solution, was observed that the temperature introduction into the liquid very quickly over a critical temperature range must be in order to avoid the formation of mentioned unwanted, sometimes difficult to remove connections to avoid.

It Devices for external gas treatment of a urea-water solution are already described but they have been so far, at least for use in the automotive sector, not convincing. The known evaporation devices can not partially here for the desired completeness the evaporation over all operating states and / or quantities of the ammonia precursor to be evaporated. This is especially true when a highly dynamic control the evaporation unit taking into account operating conditions of a mobile internal combustion engine, as for example at a Diesel engine is given.

Of these, The present invention is based on the object, at least the problems associated with the prior art partially to be solved. In particular, an evaporation unit is to be specified, the a fast and complete Evaporating a urea-water solution to produce an ammonia comprehensive gas flow in exactly given quantitative quantities provides highly dynamic. The evaporation unit should be compact and be simple. Furthermore is desired that the evaporation unit cost can be produced.

These Tasks are solved with an evaporation unit according to the features of the claim 1. Advantageous embodiments of the evaporation unit are the subject the dependent claims. The in the dependent formulated claims individually specified features are in any, technologically more meaningful Way combined with each other and show other embodiments of the invention. The invention will be further understood by the description, in particular in connection with the figures, further characterized and clarified.

The evaporation unit according to the invention for evaporating an aqueous solution comprising at least one reducing agent precursor comprises:
at least one evaporator cavity bounded by a wall of a material comprising titanium, and
a lying outside the evaporator cavity heat transfer layer of a material having a thermal conductivity of at least 100 W / mk (watts per meter and Kelvin), which is thermally conductively connected to the evaporator cavity. According to the invention, a heating layer is formed outside of the heat-transfer layer and is connected to the heat-transfer layer in a material-like manner.

Under a reducing agent precursor is understood in particular urea, preferably urea in aqueous solution. This aqueous solution may contain further ingredients, in particular further urea precursors, such as, for example, ammonium formate or the like. The evaporation unit according to the invention is in particular to be part of a line section of an auxiliary system opening into the exhaust line. Titanium as Material of the evaporator cavity has a very poor thermal conductivity. In order to be able to introduce enough heat into the fluid to be evaporated, the heat transfer layer is therefore made of a material having a thermal conductivity of at least 100 watts / mk, preferably more than 100 watts per meter and Kelvin, in particular more than 400 watts per meter and Kelvin educated. Heat transfer layers made of copper and / or aluminum are preferred here. In particular, the heat-transfer layer can be well potted, so that the evaporator cavity is embedded in the interior of the heat-transfer layer. A heat-conducting connection between the heat-transfer layer and the evaporator cavity is understood in particular to mean that the evaporator cavity is in intimate contact with the heat-transfer layer, so that conductive heat conduction can take place between the network layer and the evaporator cavity. By heating layer formed outside the heat-transfer layer, the heating of the heat-transfer layer takes place during operation. The heat-transfer layer simultaneously heats the evaporator cavity and the fluid inside this evaporator cavity. By the contact of the urea-water solution with the wall of the evaporator cavity, the urea-water solution is heated and evaporated. The steam can then be heated further, wherein partial conversion of the urea to ammonia occurs, in particular due to the formation of titanium oxides on the surface of the wall.

According to one advantageous embodiment of the evaporation unit according to the invention has the heat transfer layer at least one outside circumferential recess, in which at least one heating element inserted and with the heat transfer layer soldered is.

Prefers Here is that the heat-transfer layer externally has a thread-like recess into which a heating element or several heating conductors, circulating around the heat-transfer layer wound up on the heat-transfer layer become. So can a very uniform heating of the heat-transfer layer respectively.

Prefers Here is an embodiment in which at least two evaporation sections and accordingly two heating zones are formed in the heating layer. This means that the heating layer is formed in the partial areas is that the sections can be operated separately. So is it possible in particular in a first subregion the heating layer, and thus the evaporation unit, at a first temperature of for example 150 to 180 ° C and in a second portion at a significantly higher temperature such as 350 to 380 ° C to operate. This training in several areas, for example be achieved by two heat conductors in the recess be wound, wherein a first heating conductor, the first heating zone and a second heating conductor forms the second heating zone.

According to one further advantageous embodiment of the evaporation unit according to the invention the heating layer comprises at least one self-regulating heating resistor. Under a self-regulating heating resistor is in particular a PTC resistor (PTC, positive temperature coefficient) understood. Below this is a positive temperature coefficient understood that the heating conductor selbstregelnd to work at a setpoint temperature. Such self-regulating heating resistors are made of ceramic materials such as Barium titanate ceramics and / or doped polymers constructed. Such self-regulating heating resistors allow easy control of the evaporation unit according to the invention, because thereby the regulation in a simple manner by the heating resistor yourself.

According to one further advantageous embodiment of the evaporation unit according to the invention the heating layer has an inner and outer contact layer between the self-regulating heating resistor is formed.

About the inner and outer contact layer can the self-regulating heating resistor in a simple manner electrically be contacted and operated. Through a full-surface connection between the contact layers and the self-regulating resistor can low electrical resistance be reached in the contact layers, so that these are not themselves due to the ohmic heat significantly increased Have temperatures. Preferably, the inner contact layer is located between the self-regulating heating resistor and the heat transfer layer, while the outer contact layer the opposite side of the self-regulating heating resistor is trained.

• a) Kupfer;
• b) Aluminium.

According to a further advantageous embodiment of the evaporation unit according to the invention, the heat-transfer layer is made of a material comprising at least one of the following materials:

• a) copper;
• b) aluminum.

Copper and / or aluminum have proven to be advantageous. On the one hand, they have sufficiently high thermal conductivities of over 200 watts / mK in the case of aluminum and over 400 watts / mK in the case of copper. Furthermore, these materials and their alloys can be applied to simple species and Be potted with the evaporation cavity of titanium. Furthermore, these materials allow machinability of their outer surface, which allows any shaping of the heat-transfer layer in the outside area, for example by introducing recesses or the like.

moreover can Heating conductor in a simple way with copper and / or aluminum or their alloys soldered be, especially brazed ("Brazed") or weichverlötet ( "Soldered"). This are the common ones cohesive Connection method between heating layer and heat-transfer layer, the in principle be used in the context of this invention in an advantageous manner can, around the heating layer with the heat-transfer layer connect to.

According to one further advantageous embodiment of the evaporation unit according to the invention the evaporator cavity comprises a channel.

in this connection becomes the watery solution demanded in an input-side end of the channel, where this through the contact with the heated walls the channel evaporates. The evaporated aqueous solution flows through the channel to an end portion where the steam leaves the evaporator cavity. By the design of the walls of the evaporator cavity of titanium form on these titanium oxides, a hydrolysis of the reducing agent precursor to reducing agent and especially the urea to catalyze ammonia. That's why already during traversing the evaporator to at least partial hydrolysis of the reducing agent precursor to reducing agent. The steam, which the evaporation cavity leaves, contains in an advantageous manner, therefore, reducing agent and in particular ammonia. The channel can meandered and in particular meandering d. H. especially with at least two changes of direction be educated. Furthermore, a straight channel can be formed. additionally can structures be formed, which protrude into the channel. So will be more advantageous Way, avoid dropping the aqueous solution without evaporating through pass through the evaporator. In the case of a channel is particular the heat transfer layer and / or the heating layer is formed concentrically or coaxially with the channel.

According to one further advantageous embodiment of the evaporation unit according to the invention the evaporator cavity has an inlet opening for the supply of an aqueous solution on, the opposite a part of the wall of the evaporator cavity is formed.

The means that in operation entering through the inlet opening aqueous solution the opposite heated wall of the evaporator cavity impinges. This comes it evaporates the aqueous Solution. The entrance opening can additionally have a dropper addition which is suitable at least for aqueous solutions partially in drop form on a part of the wall of the evaporator cavity give up.

These Drop additive may in particular comprise a nozzle which sprays the aqueous solution. alternative or additionally Here, too, a capillary can be formed, in which by detachment from Drop capillary drops into the evaporator cavity.

Especially Preferably, the drop addition comprises a nozzle and in particular a spray nozzle by means the watery one solution is entered in the form of droplets in the evaporator cavity. hereby will be a good distribution of the aqueous solution reached to different areas of the wall of the evaporator cavity, so that it does not become an excessive local Cooling comes from portions of the wall of the evaporator cavity.

According to one further advantageous embodiment, the drop addition is suitable at least one droplet jet on a part of the wall of the evaporator cavity give up.

One Droplet consists at least partially of drops of the aqueous Solution, which may preferably have different volumes. By such a drop addition is a good distribution of watery solution possible on the wall of the evaporator cavity.

According to one further advantageous embodiment of the evaporation unit according to the invention is the evaporator cavity, at least in some areas, tapered educated. This means that there is a free radius inside the evaporator cavity is reduced in at least one direction. Prefers Here is a funnel-shaped or cone-shaped Embodiment of the evaporator cavity, at least in at least one Subarea. Also, a frusto-conical configuration is possible and according to the invention.

By the converging formation of the evaporator cavity, at least in some areas, elevated in operation the possibility of contact the introduced into the evaporator cavity drops. The incoming one Subregion acts as a kind of drip that ensures that the appropriate drops of the aqueous solution safely with the wall in Come in contact.

According to another advantageous embodiment Design of the evaporation unit according to the invention, a hydrolysis catalyst body is formed downstream of the evaporator cavity.

Of the Hydrolysekatalysatorkörper has a hydrolysis catalyst coating, which is the hydrolysis catalyzed by urea to ammonia This increases the proportion of ammonia clearly, in particular, such a gas flow can be generated in which 90% and more of the urea used have been converted to ammonia, in particular even more than 95%, more preferably more than 98%.

Farther a device is proposed which, in addition to an evaporation unit according to the invention a reservoir and a pump, at least partially through a connecting line section are connected.

By Such a device makes it possible to have a compact device for the provision of ammonia represent.

Farther is a motor vehicle with an internal combustion engine and a Exhaust system proposed in which the exhaust system at least one SCR catalyst body has and between the internal combustion engine and that at least an SCR catalyst body at least one connection with an evaporation unit according to the invention or a device according to the invention is provided so that gaseous Reducing agent and / or a gaseous reducing agent precursor so are introduced into the exhaust system, that this or this to the at least one SCR catalyst flows.

The for the Evaporation unit disclosed details and benefits are on the corresponding device and the motor vehicle transferable and applicable and vice versa.

in the The invention is explained in more detail below with reference to the attached figures, without that it would be limited to the details and embodiments shown there. Show it schematically:

1 an embodiment of an evaporation unit according to the invention;

2 a detail of another embodiment of an evaporation unit;

3 the construction of an SCR system in a motor vehicle;

4 schematically a further embodiment of an evaporation unit;

5 another embodiment of an evaporation unit;

6 a detail of an embodiment of an evaporation unit; and

7 another detail of another embodiment of an evaporation unit.

1 shows schematically a variant of an evaporation unit according to the invention 1 , This serves to evaporate an aqueous solution comprising at least one reducing agent precursor, in particular urea water solution. The evaporation unit 1 includes an evaporator cavity 2 , in the present embodiment as a channel 3 is trained. The evaporator cavity 2 is through a wall 4 limited in titanium. The channel 3 is wound or maanderförmig, that is formed with at least two deflections, which ensure that no non-evaporated urea-water solution, the channel 3 passes through without the wall 4 to get in touch.

By oxidation with atmospheric oxygen forms on the inner surface of the wall 4 Titanium oxide, which catalyzes the hydrolysis of urea to ammonia. Around the evaporator cavity 2 is a heat transfer layer 5 educated. In that sense, the channel 3 in a corresponding body, formed from the heat-transfer layer 5 embedded. This can in particular by casting the evaporator cavity 2 with a material comprising copper and / or aluminum. To the heat-transfer layer 5 around is a heating layer 6 educated. This consists in the present example of a layer of aluminum, in which a heating conductor 7 is incorporated. This is connectable to corresponding current sources (not shown), so that the heating layer 6 is heatable by ohmic heat. In the present embodiment, the evaporation unit 1 a first evaporation section 8th and a second evaporation section 9 on. These are through a gap 10 in heat transfer layer 5 and heating layer 6 separated.

In the operation of the evaporation unit 1 becomes the channel 2 through an enema 11 charged with liquid urea-water solution. The channel 2 is in the flow direction 22 flows through. The liquid urea-water solution is in the first evaporation section 8th evaporated in the channel. The then at least partially vaporous urea-water solution leaves the first evaporation section 8th through a straight intermediate piece 12 of the canal 2 and then flows through the channel in the second evaporation section 9 , There is through the heating layer 6 Heat introduced with the steam of the urea-water solution in this second Ver dampfungsabschnitt 9 of the canal 2 further heated and the existing liquid portions of the urea-water solution are evaporated. Through the titanium oxide areas inside the channel 2 the hydrolysis of urea to ammonia is catalyzed and improved.

The vaporized urea-water solution containing ammonia leaves the channel through the spout 13 and enters the reaction zone 14 one. This reaction zone 14 comprises a hydrolysis catalyst body 15 that has an inlet cone 16 with the spout 13 of the canal 2 connected is. The hydrolysis catalyst body 15 includes a honeycomb body 17 as a catalyst support body, which with a hydrolysis of urea to ammonia catalyzing coating 18 is provided.

Outside the heating layer 6 is a thermal insulation in this embodiment 19 provided a ceramic layer 20 and a ceramic tube 21 includes.

The 2 shows a detail of another embodiment of the evaporation unit 1 in partial cross-section. Down in 2 is shown as the flow channel 4 around a central axis 23 regularly commutes. The channel 3 has a diameter 24 for example, 4 mm. Inside the canal 2 or on the wall 4 is also a hydrolysis coating 18 intended. The channel 2 4 however, is in a heat transfer layer 5 cast in, the material fit with a heating layer 6 is connected, in which also the heating conductor 7 are provided in the manner of a helical winding. In the left area is a heating conductor 7 indicated with a certain distance 25 to the canal 2 is positioned. Further to the right are several, partially overlapping, heating conductors 7 , In particular provided in a closer arrangement to each other, here now the distance 25 towards the evaporation unit 1 surrounding housing 26 or the thermal insulation 19 was enlarged, so that these heating conductors 7 closer to the canal 3 are provided. By the variation of the distance 25 between heating conductor 7 and channel 2 the temperature profile in the channel can be varied.

3 now shows schematically a motor vehicle 27 , in particular a passenger car or a truck. That in the internal combustion engine 28 generated exhaust gas is now via a corresponding exhaust system 29 cleaned and released to the environment. The exhaust gas flows through in the flow direction 22 first a catalytic converter 30 (eg, an oxidation catalyst) to further downstream on an SCR catalyst body 31 hold true. Between the catalytic converter 30 and the SCR catalyst body 31 is the connection 32 for the evaporation unit according to the invention 1 provided so that there the gas stream comprising ammonia 32 is initiated. The flow of exhaust gas supplied with ammonia then optionally reaches a flow influencer 34 (eg a static mixer) before this mixture contains the SCR catalyst body 31 reached. For completeness, it should be noted that the SCR catalyst in the inlet area 35 and / or in the exit area 36 may be provided with further exhaust treatment components, such as a particle separator in the inlet region 35 and / or an oxidation catalyst in the exit region 36 , It should also be noted that other exhaust treatment facilities in the exhaust system 29 can be provided.

The evaporation unit according to the invention 1 is now over several line sections 37 with a reservoir 38 connected. In the reservoir 38 For example, liquid urea-water solution is provided, which then by means of a metering pump 39 time and / or volume of the evaporation unit 1 is supplied. Alternatively, instead of a metering pump 39 a pump is provided which holds a pressure, wherein the dosage in the evaporation unit 1 via a valve, not shown.

The dosing pump 39 , the evaporation unit 1 and / or the internal combustion engine 28 can with a controller 40 (data technology and / or technical) to be here to a controlled admixture of urea-water solution to the evaporation unit 1 or to ensure ammonia gas to the exhaust gas.

For the sake of completeness, it should also be noted that a device 41 comprising at least one reservoir 38 , a line section 37 , a dosing pump 39 and an evaporation unit 1 in any quantities also separately as a component set with / or without control 40 can be offered. Alternatively, the device 41 instead of a dosing pump 39 a pump and a metering valve.

4 schematically shows an evaporation unit 1 with an evaporator volume 2 which of a wall construction 42 is limited, the example in the 6 and 7 is shown. The evaporator cavity 2 has an entrance opening 43 for the supply of urea-water solution, which is opposite to a part of the wall structure 42 and with it the wall 4 is trained. In operation, through a through the inlet opening 43 passing through as a tube 44 , For example, as a capillary, formed drop drops 45 the urea-water solution in the evaporator cavity 2 given on the inside 46 the Wall 4 of wall construction 42 hit and evaporate there. The wall construction 42 also includes the heating layer, by means of an electrical heating of the evaporator volume 2 he follows. The evaporated urea-water solution, due to the formation of the wall 4 Titanium and the corresponding present titanium oxide may already contain amounts of ammonia leaves the evaporator cavity 2 through a spout 13 on. This has projections 46 on, prevent the not yet evaporated urea-water solution from evaporating the spout 13 crosses. Alternatively or additionally, the spout 13 be wound and / or formed with multiple deflections. The projections 46 are in thermal contact with the heating layer 6 so that upon contact of the urea-water solution with the protrusions 46 an evaporation takes place. To the outlet 13 For example, a hydrolysis catalyst body (not shown) may join to increase the ammonia content of the gas. The evaporator cavity 2 has a tapered section 47 on, the funnel-shaped design. Furthermore, the evaporator cavity has an opening portion 48 on.

5 schematically shows a further embodiment of an evaporation unit 1 , which is tapered tapered. The evaporation unit 1 indicates one of a wall construction 42 limited evaporator cavity 2 on, its inner wall 4 made of titanium. The evaporation unit 1 also has a dropper addition, which serves as a nozzle 53 is formed, which in operation several Tropfensträhle with drops 45 of urea-water solution on the wall 4 of the evaporator cavity. The spout 13 is designed similarly as in the embodiment in 4 , The in the 4 and 5 shown embodiment of the evaporation unit 1 can also be advantageously in a device 47 be used.

6 shows an example of a wall structure 42 , which in one embodiment according to the 4 respectively. 6 , but also in an embodiment with a Kahal 3 as evaporator cavity 2 can be chosen. The evaporator cavity 2 gets through the wall 4 limited, which is made of titanium. With the wall 4 thermally conductive is the heat-transfer layer 5 made of aluminum and / or copper. With this heat transfer layer 5 is a heating layer 6 on the outside materially connected, in particular soldered. The heating layer 6 includes in this embodiment, from inside to outside, an inner contact layer 49 , a self-regulating heating resistor 50 and an outer contact layer 51 , Through the inner 49 and outer contact layer 51 becomes the self-regulating heating resistor 50 electrically contacted and operated. This heating layer 6 may be surrounded on the outside by a thermal insulation and heats the heat-transfer layer 5 , Inner contact layer 49 , self-regulating heating conductor 50 and outer contact layer 51 are formed as coaxial and concentrated tric to each other and can also form coaxial and concentric tubes.

7 schematically shows a section of another example of a wall structure 42 , In the heat-transfer layer 5 are recesses on the outside 52 introduced, in the at least one heat conductor 7 inserted and with the heat-transfer layer 5 is soldered. The recesses 52 are in particular thread-like and circumferentially around the evaporator cavity 2 executed.

The evaporation unit according to the invention 1 can be used advantageously for the provision of gaseous ammonia from urea-water solution. Due to the structure with a heating layer, which is preferably electrically heated, a highly dynamic control can be constructed with which a sufficiently large amount of ammonia can be provided even with rapid load changes and consequent large increases in nitrogen oxide concentrations in the exhaust gas of the internal combustion engine. Due to the compact design of the evaporation unit 1 This can be advantageously used in mobile applications such as in the exhaust systems 29 used by motor vehicles.

1

Evaporation unit

2

evaporator cavity

3

channel

4

wall

5

Heat network layer

6

heating layer

7

heating conductor

8th

first Evaporation section

9

second Evaporation section

10

gap

11

enema

12

connecting piece

13

outlet

14

reaction zone

15

Hydrolysekatalysatorkörper

16

intake cone

17

honeycombs

18

hydrolysis coating

19

thermal insulation

20

ceramic layer

21

ceramic tube

22

flow direction

23

central axis

24

diameter

25

distance

26

casing

27

motor vehicle

28

Internal combustion engine

29

exhaust system

30

catalytic converter

31

SCR catalyst body

32

connection

33

ammoniacal gas flow

34

Flow influencer

35

entry area

36

exit area

37

line section

38

reservoir

39

metering

40

control

41

contraption

42

wall construction

43

entrance opening

44

tube

45

drops

46

head Start

47

tapering subregion

48

opening subregion

49

inner contact layer

50

self-regulating heating resistor

51

outer contact layer

52

recess

53

jet

Claims (15)

Evaporation unit ( 1 ) for evaporating an aqueous solution comprising at least one reducing agent precursor, comprising: at least one evaporator cavity ( 2 . 3 ), which through a wall ( 4 ) is bounded by a material comprising titanium and one outside the evaporator cavity ( 2 ) lying heat transfer layer ( 5 ) made of a material with a thermal conductivity of at least 100 W / mK (watts per meter and Kelvin), which is connected to the evaporator cavity ( 2 ) is thermally conductively connected, characterized in that outside the heat-transfer layer ( 5 ) a heating layer ( 6 ) is formed, the cohesively with the heat transfer layer ( 5 ) connected is. Evaporation unit ( 1 ) according to claim 1, wherein the heat transfer layer ( 5 ) at least one outer circumferential recess ( 52 ), into which at least one heating conductor ( 7 ) and with the heat transfer layer ( 5 ) is soldered. Evaporation unit ( 1 ) according to one of the preceding claims, in which the heating layer ( 6 ) at least one self-regulating heating resistor ( 50 ). Evaporation unit according to claim 3, wherein the heating layer ( 6 ) an inner ( 49 ) and an outer contact layer ( 51 ), between which the self-regulating heating resistor ( 50 ) is trained. Evaporation unit ( 1 ) according to one of the preceding claims, in which the heat transfer layer ( 5 ) is constructed of a material comprising at least one of the following materials: a) copper; and b) aluminum. Evaporation unit ( 1 ) according to any one of the preceding claims, wherein the evaporator cavity ( 2 ) a channel ( 3 ). Evaporation unit ( 1 ) according to one of claims 1 to 5, wherein the evaporator cavity ( 2 ) an entrance opening ( 43 ) for the supply of aqueous solution which is opposite to a part of the wall ( 4 ) of the evaporator cavity ( 2 ) is trained. Evaporation unit ( 1 ) according to claim 7, in which a dropping addition ( 44 . 53 ), which is suitable, aqueous solution at least partially in drop form ( 45 ) on a part of the wall ( 4 ) of the evaporator cavity ( 2 ) give up. Evaporation unit ( 1 ) according to claim 8, in which the addition of the drop is a spray nozzle ( 53 ). Evaporation unit ( 1 ) according to claim 8 or 9, in which the drop addition is suitable for applying a droplet jet to a part of the wall ( 4 ) of the evaporator cavity ( 2 ) give up. Evaporation unit ( 1 ) according to one of claims 7 to 10, wherein the evaporator cavity ( 2 ) at least in subareas ( 47 ) is formed tapering. Evaporation unit ( 1 ) according to one of claims 7 to 11, wherein the evaporator cavity ( 2 ) is funnel-shaped at least in at least a portion. Evaporation unit ( 1 ) according to one of the preceding claims, in which a hydrolysis catalyst body ( 15 ) downstream of the evaporator cavity ( 2 ) is trained. Contraption ( 41 ) comprising at least one reservoir ( 38 ), a pump ( 39 ), an evaporation unit ( 1 ) according to one of the preceding claims, as well as at least one, the aforementioned components at least partially connecting line section ( 37 ). Motor vehicle ( 27 ) with an internal combustion engine ( 28 ) and an exhaust system ( 29 ), Where at the exhaust system ( 29 ) at least one SCR catalyst body ( 31 ) and between the internal combustion engine ( 28 ) and the at least one SCR catalyst body ( 31 ) at least one connection ( 32 ) with an evaporation unit ( 1 ) according to one of claims 1 to 13 or an apparatus according to claim 14, so that gaseous reducing agent and / or a gaseous reducing agent precursor so into the exhaust system ( 29 ) can be introduced, that this or this to the at least one SCR catalyst body ( 31 ) flows.