AT512193B1 - INTERNAL COMBUSTION ENGINE WITH AN EXHAUST SYSTEM - Google Patents

Abstract

The invention relates to an internal combustion engine (1) having at least one exhaust gas line (2) in which at least one exhaust aftertreatment device (3), in particular at least one SCR catalytic converter (3a) is arranged, wherein upstream of the exhaust gas aftertreatment device (3) into the exhaust gas flow (S ) a metering device (4) for a particular ammonia-containing additive in the region of a mixing device (5) for introducing the additive into the exhaust stream (S) opens, and the mixing device (5) at least one heating device (7). In order to achieve an efficient treatment of the additive in the exhaust gas with the smallest possible space requirement, it is provided that the heating device (7) is formed by at least one flow guide surface (8) for the exhaust gas flow (S) in front of or in the mixing device (5) and the flow guide surface (8) merges into a concavely curved first guide surface (9) of the mixing device (5), the first guide surface (9) forming at its downstream end at least a first detaching edge (11).

Description

Austrian Patent Office AT512193B1 2013-10-15

The invention relates to an internal combustion engine having at least one exhaust gas line, in which at least one exhaust aftertreatment device, in particular at least one SCR catalyst is arranged, wherein upstream of the exhaust aftertreatment device in the exhaust gas flow metering for a particular ammonia-containing additive in the region of a mixing device for Introducing the additive opens into the exhaust stream, and the mixing device has at least one heating device.

WO 2008/122 724 A1 an internal combustion engine with an exhaust system is known in which an SCR catalyst is arranged, wherein upstream of the SCR catalyst, an additive is injected via a metering device and a mixing device in the exhaust line.

Due to the low injection pressures of the additive, relatively large drops are formed in the exhaust stream. This results in long evaporation times and long path lengths. The path lengths required for complete evaporation are usually unavailable in mobile applications.

A uniform distribution of the additive over the cross section of an exhaust system for all relevant operating points can hardly be achieved.

A large-scale mixing of non-uniform distributed gas components can be achieved with the usual pipe / mixing elements at the low available path lengths difficult or only with considerable pressure loss.

In addition, it often comes to wall contact of the injected droplets with the cold walls of the exhaust line, which can form unwanted deposits.

It is known to use mixers, which usually cause only a local mixing. On the other hand, vortex mixers (vortex mixers) are used, but they require a large pipe length.

WO 2008/024 535 A2 discloses an exhaust aftertreatment system for an internal combustion engine with a mixing device for supplying an additive, wherein in the mixing device, a spiral-shaped chamber is arranged. The mixer has a heater to enhance the evaporation of the additive.

WO 2006/014 129 A1 shows a mixing device for feeding a medium into an exhaust gas line of an internal combustion engine, wherein heating and evaporation of the injected medium takes place by the heat of the gas flowing around the mixing device. Another mixing device with porous plates for atomizing the injected additive is known from EP 1 748 162 A1.

EP 1 936 137 A1 discloses a device for admixing a reducing agent in an exhaust stream of an internal combustion engine, wherein the mixing device has wing-shaped heating ribs, which are wetted by the injected additive. The heating ribs are heated by the circulation of the exhaust gases.

The object of the invention is to allow with the least possible structural and spatial complexity, a uniform distribution of the additive at the entrance to the aftertreatment device while avoiding deposits.

According to the invention, this is achieved in that the heating device is formed by at least one flow guide for the exhaust stream before or in the mixing device and the flow guide merges into a concavely curved first guide surface of the mixing device, wherein the first guide surface at its downstream end at least a first Forming release edge.

The flow guide can form at least one flow separation edge at its downstream end. The use of the detaching edge leads to the fact that a wall film which has been obtained can be introduced into the flow. On the other hand, the introduction of the liquid phase or of the highly concentrated gaseous NH 3 in the main stream promotes thorough mixing, since propagation in all directions is made possible.

In order to achieve a good atomization, it can be provided that the heating device forms a baffle plate for the introduced additive, wherein the metering device is directed to the baffle plate, wherein preferably the baffle plate is arranged in the region of the inlet of the exhaust gas stream in the mixing device. Heating ribs may be arranged on the side of the baffle plate facing away from the injected additive. The atomization can be further improved if the flow guide surface has guide ribs which are arranged essentially parallel to one another in the direction of the exhaust gas flow and are preferably heatable.

In a preferred embodiment of the invention, preferably the baffle plate forming flow guide is arranged parallel to the entering into the mixing device exhaust stream.

Alternatively, it can also be provided that the flow guide is arranged inclined at a preferably acute angle to the entering into the mixing device exhaust stream and forms a deflection surface for the exhaust stream, which preferably forms the heater. In particular, in the case of an arrangement with purely axial exhaust gas flow metering of the additive directly onto the impact surface or onto a heating surface is not possible, so that the spray is transported by the flow onto the deflection surfaces of the cyclone. These deflection surfaces thus have the same function as heating surfaces.

It when the flow guide and / or the baffle tangentially merges into a concavely curved first guide surface of the mixing device, wherein preferably the first guide surface at its downstream end forms at least a first detachment edge is particularly advantageous.

The mixing device is preferably designed as a cyclone.

The preparation of the additive jet is thus carried out by a combination of pre-evaporation and atomization and subsequent mixing in the cyclone. The introduction of the additive into the cyclone via at least one detachment edge, so that the liquid phase or the high-centered gaseous additive (for example, a NH 3 -water mixture) is introduced in the main stream in the cyclone and on all sides and not from a wall can interfere with disabled.

To avoid deposits during the pre-evaporation on the baffle plate cooling of the baffle plate is avoided below the critical temperature by means of the heater.

In a particularly advantageous embodiment of the invention is provided, in the flow direction successively at least two, preferably helical or cylindrical, concave baffles are arranged, preferably facing each other ends of the baffles are arranged offset in a radial direction to each other so that the end an upstream guide surface in the region of the concave side of the downstream guide surface is arranged.

The mixing device has a central tube, wherein the at least one guide surface are arranged around the central tube at a distance, so that between the central tube and the guide surface is formed by an exhaust gas flowed annular space, preferably at least one end face of the annular space is closed.

With the central tube in the interior of the cyclone, the channel cross-section is reduced. This avoids poor mixing in the center of the cyclone. The central tube can be flowed through slightly to equalize the wall temperature to the gas temperature and thus to prevent wall film formation.

In a particularly preferred embodiment of the invention it is provided that the central tube has an upstream first end and a downstream second end, wherein the central tube in the region of the first end with the annulus fluidly connected and wherein the annular space is closed in the region of the second end. This results in an additional deflection in the region of the first end of the central tube by diverting the flow from the annulus into the interior of the central tube. This additional flow deflection can further enhance mixing. This is particularly advantageous if compromises have to be made in the positioning of the injector.

The preparation of the introduced additive can be done in this way with extremely low pressure losses. The evaporation and thermolysis of the additive is completed until it leaves the cyclone. Through the cyclone there is a global mixing, so that high uniformity of the gas components can be achieved.

The invention will be explained in more detail below with reference to FIG.

1 shows an internal combustion engine according to the invention, [0029] FIG. 2 shows a mixing device of this internal combustion engine in a first embodiment variant in an oblique view, [0030] FIG. 3 shows this mixing device in a view in the direction of the cyclone axis 4 shows a mixing device in a second embodiment in an oblique view, FIG. 5 shows a mixing device in a third embodiment in an oblique view, [0033] FIG. 6 shows a mixing device in a fourth embodiment in a side view and FIG 7 shows this mixing device in a section along the line VII-VII in FIG. 6.

Fig. 1 shows an internal combustion engine 1 with a plurality of cylinders 1a with an exhaust line 2, in which an exhaust gas aftertreatment device 3 formed by an SCR catalyst 3a is arranged. Upstream of the exhaust gas aftertreatment device 3, a metering device 4 for an additive, for example a urea-water mixture, is arranged. The injection nozzle 4 'of the metering device 4 is arranged in the region of the inlet 5a of the exhaust gas stream S in a mixing device 5, which is formed by a cyclone 6.

The mixing device 5 has at least one heating device 7, which prevents deposition of additive drops on the wall of the mixing device 5.

In the embodiment variants shown in FIGS. 2 to 5, the mixing device 5 is formed by a cyclone 6 with tangentially or radially inflowing exhaust gas flow S. The cyclone 6 has in the region of its inlet 6a a flow guide 8 for the exhaust gas flow S, which forms a baffle plate 8a for the introduced additive, the nozzle 4 'of the metering device 4 is directed to the baffle plate 8a. The baffle plate 8a at the same time forms the heating device 7, which may be formed for example by heating ribs 7a on the back of the baffle plate 8a. The baffle plate 8a may also be ribbed in the impact area and / or form a number of heatable baffles directed parallel to the incoming exhaust gas flow S. The flow guide surface 8 is arranged tangentially to a concavely curved first guide surface 9 in the embodiments shown in FIGS. 2 to 4, which is partially guided around a central tube 10 by an angle α of, for example, at least about 90 °, for example 120 ° at a distance. The first guide surface 9 terminates in a first separation edge 11 for the exhaust gas flow S. The cyclone 6 has in the embodiments shown in FIGS. 2 to 4 a concave, preferably cylindrically curved second guide surface 12, which begins approximately in the region of the first detachment edge 11 and extends around the central tube 10 by an angle β of, for example, about 240 degrees. The second guide surface 12 terminates in a second detachment edge 13. Both the first guide surface 9 and the second guide surface 12 are radially spaced from the central tube 10, so that between the central tube 10 and the first or second guide surfaces 9, 12, an annular space 14 is spanned, wherein at least one end face 14a, 14b of the annular space 14 may be substantially closed. The beginning 12a of the second guide surface 12 is further spaced from the central tube 10 than the first detachment edge 11. The cyclone 6 has a closed first end face 6a located in FIGS. 2, 4 and 5 on the underside and one in FIGS , 4 and 5 shown at the top open second end face 6b. The laterally - in Figs. 2 to 4 tangentially - entering the cyclone 6 exhaust gas flows according to the arrows S along the baffle plate 8 and is passed through the baffle plate 6 and the first and second guide surface 11, 12 in the annular space 14 where a Ring flow is formed at high speed. Due to the geometric conditions in the cyclone 6, the annular flow 6 is deflected axially, whereby the exhaust gas flow S leaves the cyclone 6 at the second end face 6b. About the metering device 4, the additive - for example, a NH3-water mixture - introduced on the baffle plate 8a. In this case, an atomization occurs by impact on the baffle plate 8a, whereby it comes - with appropriate kinetic and / or thermal energy - drop breakage. In order to prevent the baffle plate 8 from being excessively cooled by the spraying process and thus the risk of wall film formation and deposits, the baffle plate 8 is heated via the heating device 7.

The cyclone 6 allows large-scale efficient gas mixing with low pressure drop. The mixture of exhaust gas and additive is passed via the guide surfaces 11 and 12 in the annular space 14, where an intense mixing takes place. The effect of the first and the second detachment edges 11, 13 is that a wall film possibly forming on the guide surfaces 9, 12 is introduced into the exhaust gas flow S. On the other hand, the introduction of the liquid phase or of the highly concentrated gaseous NH 3 in the main stream promotes thorough mixing, since propagation in all directions is made possible.

Through the central tube 10 in the interior of the cyclone 6, the channel cross-section of the annular space 14 is reduced. This avoids poor mixing in the center of the cyclone 6. The central tube 10 may optionally be slightly flowed through in order to equalize the wall temperature of the central tube 10 to the exhaust gas temperature and thus to prevent wall film formation on the outside of the central tube 10.

The preparation of the additive spray is thus carried out by a combination of pre-evaporation / atomization and subsequent mixing in the cyclone 6. The introduction of the additive in the cyclone 6 via the separation edges 11, 13, so that the liquid phase or the highly concentrated gaseous NH3 is introduced into the main stream in the cyclone 6 and can be mixed on all sides - and not hindered by a wall.

In this way it is achieved that the evaporation and the thermolysis of the additive is completed until it leaves the mixing device 5. Through the cyclone 6 there is a global mixing, so that a high uniformity of the gas species can be achieved.

Fig. 4 shows a variant in which the entire exhaust gas flow S is passed through the central tube 10, wherein the mixing can be further enhanced upon entry into the central tube 10 by an additional flow deflection, which is represented by the arrows St. The axial extent b of the central tube 10 is smaller than the axial extent a of the first and second guide surfaces 9, 12. An upstream first end of the central tube 10 is designated 10a, a downstream second end of the central tube 10b. A second end face 14b of the annular space 14 is substantially closed in the region of the second end 10b of the central tube 10. In the region of the first end 10a and the first end face 14a of the annular space 14, the central tube 10 is made shorter than the guide surfaces 9, 12, whereby an annular flow passage between the annular space 14 and the central tube 10 is formed. The exhaust gas flows according to the arrows S along the baffle plate 8 in the cyclone 6 and is guided along the first and second guide surfaces 9, 12 annularly around the central tube 10 in the annular space 14. Since the annular space 14 is closed in the region of the second end face 14b, the exhaust gas flows according to the arrows Si in the region of the first end 10a of the Austrian Patent Office AT512193B1 2013-10-15

Central tube 10 in the central tube 10 and further in the axial direction within the central tube 10 to the second end 10 b, where it leaves the cyclone 6. This embodiment variant is particularly advantageous if the metering device 4 for the additive can not be optimally positioned. In this case, the additional deflection nevertheless achieves excellent mixing of the additive with the exhaust gas.

In Fig. 5, an embodiment is shown, in which the baffle plate 8 is not arranged tangentially, but radially with respect to the cyclone 6. In this way, an additional separation edge 15 is formed by a step in the transition region between the baffle plate 8 and the first guide surface 9, which allows an early detachment of a wall film.

6 and 7 show a further embodiment in which a purely axial flow of the mixing device 5 takes place. The heating device 7 is formed by deflecting surfaces 16a, 16b forming flow guide 8 of the cyclone 6, which are arranged tangentially to substantially cylindrical first and second guide surfaces 17, 18 and pass into this. The first and second guide surfaces 17, 18 are formed substantially cylinder-segment-like and extend over an angular range γ between about 120 ° - 170 °, wherein between the first deflection surface 16a and the second guide surface 18, a first gap 19, and between the second deflection surface 16b and the first guide surface 17, a second gap 20 is formed, which forms a flow passage to a central space 21 for the exhaust gas flow S. The metering of the additives takes place via the metering device 4 arranged upstream of the mixing device 5. The exhaust gas flows in a substantially cylindrical annular space 23 formed between the exhaust pipe 22 and the guide surfaces 17, 18, which is closed at its downstream end face 24. About the deflection surfaces 16a, 16b, the exhaust gas is passed through the first and the second gap 19, 20 in the central space 21, wherein the exhaust gas flow S is imparted a twist. A liquid film possibly adhering to the first and second guide surfaces 17, 18 is released at the detachment edges 17a, 18a of the guide surfaces 17, 18, whereby liquid particles are entrained by the exhaust gas flow S. The fact that the deflection surfaces 16a, 16b also fulfill the function of heaters 7, the evaporation and thermolysis of the additive can be significantly accelerated.

The exhaust gas flow leaves the central space 21 in the axial direction and exits axially from the cyclone 6 according to the arrow S to - mixed with additive - to enter the subsequent SCR catalyst 3. Again, evaporation and thermolysis of the additive at the outlet of the cyclone 6 are largely completed. 5.9

Claims (14)

1. Internal combustion engine (1) with at least one exhaust line (2), in which at least one exhaust aftertreatment device (3), in particular at least one SCR catalytic converter (3a), is arranged upstream of the exhaust gas aftertreatment device (3) in the exhaust gas flow (S) a metering device (4) for a particular ammonia-containing additive in the region of a mixing device (5) for introducing the additive into the exhaust stream (S) opens, and the mixing device (5) at least one heating device (7 ), characterized in that the heating device (7) is formed by at least one flow guide surface (8) for the exhaust gas flow (S) in front of or in the mixing device (5) and the flow guide surface (8) into a concavely curved first guide surface (9). merges the mixing device (5), wherein the first guide surface (9) at its downstream end at least a first separation edge (11) forms et. 2. Internal combustion engine (1) according to claim 1, characterized in that in the flow direction successively at least two, preferably helical or cylindrical, concave guide surfaces (9, 12) are arranged, preferably facing each other ends of the guide surfaces (9, 12) in one Radial direction are arranged offset to one another such that the end of the upstream first guide surface (9) in the region of the concave side of the downstream second guide surface (12) is arranged, wherein preferably the second guide surface terminates in a second detachment edge (13). 3. internal combustion engine (1) according to claim 1 or 2, characterized in that the Strömungsleitfläche (8) at its downstream end at least one flow separation edge (15) is formed. 4. Internal combustion engine (1) according to one of claims 1 to 3, characterized in that the flow device formed as a flow heating device (7) forms a baffle plate (8a) for the introduced additive, wherein the metering device (4) directed to the baffle plate (8a) is, wherein preferably on the downstream side of the baffle plate (8a) heating ribs (7a) are arranged. 5. Internal combustion engine (1) according to claim 4, characterized in that the baffle plate (8a) in the region of the inlet (5a) of the exhaust gas stream (S) in the mixing device (5) is arranged. 6. Internal combustion engine (1) according to one of claims 1 to 5, characterized in that the flow guide surface (8) arranged substantially parallel to each other in the direction of the exhaust gas flow (S), preferably heatable, guide ribs. 7. Internal combustion engine (1) according to one of claims 1 to 6, characterized in that the preferably the baffle plate (8a) forming the flow guide (8) is arranged substantially parallel to the in the mixing device (5) entering the exhaust stream (S). 8. Internal combustion engine (1) according to one of claims 1 to 6, characterized in that the Strömungsleitfläche (8) at a preferably acute angle (a) to the mixing device (5) entering the exhaust stream (S) is arranged inclined. 9. Internal combustion engine (1) according to any one of claims 1 to 8, characterized in that the Strömungsleitfläche (8) and / or the baffle plate (8a) merges tangentially into a concavely curved first guide surface (9) of the mixing device (5). 10. Internal combustion engine (1) according to one of claims 1 to 8, characterized in that the heating device (7) by two flow guide surfaces (8) forming the deflection surfaces (16a, 16b) is formed, wherein the deflection surfaces (16a, 16b) are arranged tangentially to substantially cylindrical first and second guide surfaces (17, 18) and merge into them. 11. Internal combustion engine (1) according to one of claims 1 to 10, characterized in that the mixing device (5) is designed as a cyclone (6). 6/9 Austrian Patent Office AT512193B1 2013-10-15 12. Internal combustion engine (1) according to any one of claims 2 to 11, characterized in that the mixing device (5) has a central tube (10), wherein the at least one guide surface (9, 12) arranged around the central tube (10) at a distance are, so that between the central tube (10) and the guide surface (9,12) an exhaust gas flowed through the annular space (14) is formed, preferably at least one end face (14a, 14b) of the annular space (14) is closed. 13. An internal combustion engine (1) according to claim 12, characterized in that the central tube (10) has an upstream first end (10 a) and a downstream second end (10 b), wherein the central tube (10) in the region of the first end (10 a) is fluidly connected to the annular space (14), and wherein preferably an end face (14b) of the annular space (14) in the region of the second end (10b) is closed. 14. internal combustion engine (1) according to one of claims 1 to 11, characterized in that the mixing device (5) within an exhaust pipe (22) is arranged and between the exhaust pipe (22) and the guide surfaces (17, 18) is a substantially cylindrical Annular space (23) is formed, which is closed at a downstream end face (24). For this 2 sheets drawings 7/9