CLIAMS:We claim:
1. A mixing device (10) for mixing a reducing agent with exhaust gas of a combustion engine, the mixing device comprising:
? at least one exhaust pipe (12) bounding a duct (14) through which the exhaust gas can flow; and
? a dosing module adapter (20) configured to mount a dosing unit on the exhaust pipe (12);
characterized in that
the dosing module adapter (20) has an inclination angle (A) in a range of 58 degrees to 69 degrees with respect to the exhaust pipe (12).

2. The mixing device (10), according to claim 1,
characterized in that
the dosing module adapter (20) has a first cone-shaped portion (28) and a second cone-shaped portion (30), the first cone-shaped portion (28) and the exhaust pipe (12) confining a first angle (B) in a range of 110 degrees to 130 degrees, and the second cone-shaped portion (30) and the exhaust pipe (12) confining a second angle (C) in a range of 20 degrees to 50 degrees.

3. The mixing device (10), according to claim 1,
characterized in that
the mixing device (10) comprises:
? the dosing unit having an injector tip; and
? at least one mixing element (26) arranged in the duct, wherein a distance (D) between the injector tip and the mixing element (26), in particular a mixer reference plane (b) of the mixing element (26), ranges from 60 to 100 millimeters, the distance (D) extending in the axial direction of the exhaust pipe (12).

4. An exhaust aftertreatment device for a combustion engine, the exhaust aftertreatment device comprising at least one mixing device (10) according to any one of the preceding claims.
,TagSPECI:[001] DESCRIPTION OF THE INVENTION:
[002] The following specification particularly describes the invention and the manner in which it is to be performed:
[003] Technical Field of the Invention
[004] The invention relates to a mixing device according to the preamble of patent claim 1.
[005] Background of the Invention
[006] Such a mixing device for mixing a reducing agent with exhaust gas of a combustion engine can be found in DE 10 2005 061 145 A1. The mixing device comprises at least one exhaust pipe bounding a duct through which the exhaust gas of the combustion engine can flow. Thus, the exhaust pipe serves to guide the exhaust gas flowing through the duct. Moreover, the mixing device comprises a dosing module adapter configured to mount a dosing unit on the exhaust pipe. This means the dosing unit can be mounted on the exhaust pipe by clamping it on the dosing module adapter. The dosing unit is configured to feed the reducing agent into the exhaust gas. When the reducing agent is fed into the exhaust gas by means of the dosing unit the reducing agent leaves the dosing unit so that the reducing agent is fed into the exhaust gas at at least one feeding point.
[007] Conventional mixing devices are prone to wall wetting. The term “wall wetting” refers to a phenomenon where the injected reducing agent hits walls, in particular inner surfaces, of the exhaust pipe and the dosing module adapter before reducing agent droplets are atomized. This leads to spray distortion and subsequent crystallization and deposition of reducing agent on inner surfaces of the exhaust pipe and the dosing module adapter. From the general prior art liquid only (LO) dosing systems as well as air assisted dosing systems are known. In liquid only dosing systems only the liquid reducing agent is fed into the exhaust pipe. In air assisted dosing systems air is used to feed the reducing agent in the exhaust pipe, wherein the air and the reducing agent are fed into the exhaust pipe. It has been shown that liquid only dosing systems are more prone to wall wetting issues than air assisted dosing systems. However, the liquid only dosing systems offer the benefits of being cost effective and modular solutions for dosing in comparison with the air assisted dosing systems.
[008] It is therefore an object of the present invention to provide a mixing device of the kind indicated in the preamble of patent claim 1, by means of which mixing device the risk of crystallization and deposition of reducing agent on the exhaust pipe and the dosing module adapter can be kept particularly low in a particularly easy way.
[009] This object is solved by a mixing device having the features of patent claim 1. Advantageous embodiments with expedient developments of the invention are indicated in the other patent claims.
[010] Summary of the Invention
[011] In order to provide a mixing device of the kind indicated in the preamble of patent claim 1, by means of which the risk of crystallization and deposition of the reducing agent on the exhaust pipe and the dosing module adapter can be kept particularly low in a particularly easy way, according to the present invention the dosing module adapter has an inclination angle in a range of 58 degrees to 69 degrees with respect to the exhaust pipe. Moreover, by means of the mixing device according to the present invention cascading effects of crystallization and deposition of the reducing agent can be avoided so that the risk of failures of interfacing parts such as the dosing unit, a SCR catalytic converter (SCR – Selective Catalytic Reduction) and an ASC catalytic converter (ASC – Ammonia Slip Catalyst) can be kept particularly low as well as the risk of a loss of NOx conversion efficiency (NOx – Nitrogen Oxide) and an increase in backpressure.
[012] For example, the reducing agent is a liquid in the form of aqueous urea solution which can be fed into the duct at at least one feeding point by means of the dosing unit. The reducing agent is also referred to as DEF, i.e. Diesel Exhaust Fluid since the mixing device and the dosing unit can be used for internal combustion engines such as diesel engines to keep the emissions of nitrogen oxides particularly low. Preferably, the mixing device according to the present invention is used for internal combustion engines of vehicles, in particular commercial vehicles.
[013] Further advantages, features, and details of the invention derive from the following description of a preferred embodiment as well as from the drawing. The features and feature combinations previously mentioned in the description as well as the features and feature combinations mentioned in the following description of the figures and/or shown in the figures alone can be employed not only in the respectively indicated combination but also in other combination or taken alone without leaving the scope of the invention.
[014] Brief Description of Drawings
[015] Figure 1illustrates part of a schematic side view of an exhaust system for a combustion engine, the exhaust system comprising a mixing device for mixing a reducing agent with exhaust gas of the combustion engine;
[016] Figure 1illustrates a schematic sectional view of the mixing device according to Fig. 1

[017] Detailed Description of the Invention
[018] In the figures the same elements or elements having the same functions are indicated by the same reference signs.

[019] Fig. 1 shows part of an exhaust system for a combustion engine in the form of an internal combustion engine which is configured as, for example, a diesel engine. For example, the combustion engine is configured to drive a vehicle, in particular a commercial vehicle. The exhaust system is configured to guide and aftertreat exhaust gas of the combustion engine. Thus, the exhaust system comprises an exhaust aftertreatment device having a mixing device 10 which is shown in a schematic sectional view in Fig. 2. As can be seen from Figs. 1 and 2, the mixing device 10 comprises at least one exhaust pipe 12 bounding a duct 14 through which the exhaust gas can flow. A directional arrow 16 illustrates the direction of flow of the exhaust gas, wherein a directional arrow 18 illustrates the longitudinal direction of the exhaust pipe 12, the longitudinal direction corresponding to the axial direction of the exhaust pipe 12.

[020] The mixing device 10 is configured to mix a reducing agent with the exhaust gas flowing through the duct 14. For this purpose the mixing device 10 comprises a dosing module adapter 20 configured to mount a dosing unit on the exhaust pipe 12, wherein the dosing unit is not shown in the figures. The dosing module adapter 20 is attached to the exhaust pipe 12 and has a through opening 22 which opens into the duct 14. For example, the dosing module adapter 20 is welded to the exhaust pipe 12. The dosing unit which is also referred to as a dosing module is configured to be attached to the dosing module adapter 20 so that the dosing unit is mounted on the exhaust pipe 12 via the dosing module adapter 20.

[021] The reducing agent is a liquid in the form of an aqueous urea solution, wherein the dosing unit comprises at least one duct through which the reducing agent can flow. The duct comprises at least one through opening through which the reducing agent flowing through the duct of the dosing unit can flow out of the duct and thus the dosing unit. When the reducing agent is fed into the exhaust gas by means of the dosing unit the reducing agent leaves the dosing unit via said through opening arranged at an injector tip of the dosing unit. The reducing agent is fed into the duct 14 along a feeding direction illustrated by a line 24 which is, for example, the center line of a spray of the reducing agent. When feeding the reducing agent into the duct 14 and thus into the exhaust gas, the reducing agent is fed into the exhaust gas at at least one feeding point at which the exhaust gas is supplied with the reducing agent.
[022] The reducing agent is used to reduce nitrogen oxides (NOx) in the exhaust gas. For example, the exhaust aftertreatment device further comprises at least one catalytic converter such as an SCR catalytic converter (SCR – Selective Catalytic Reduction) and/or an ASC (ASC – Ammonia Slip Catalyst), wherein the at least one catalytic converter is arranged downstream of the mixing device 10 with respect to the direction of flow of the exhaust gas. Preferably, a temperature dependent release of the reducing agent is implemented. In other words, preferably, the reducing agent is fed into the exhaust gas on the basis of at least one temperature. Preferably, the temperature is a temperature of the SCR catalytic converter. For example, the temperature ranges from 220 degrees Celsius to 280 degrees Celsius.

[023] As can be seen from Fig. 2, the mixing device 10 comprises at least one mixing element 26 arranged in the duct 14. The mixing element 26 is configured to cause turbulences of the exhaust gas and the reducing agent so that the exhaust gas and the reducing agent are mixed particularly advantageously.

[024] In order to keep the risk of crystallization and deposition of the reducing agent on the dosing module adapter 20 and the exhaust pipe 12 particularly low, the dosing module adapter 20 has an inclination angle A in a range of 58 degrees to 69 degrees with respect to the exhaust pipe 12. As can be seen from Fig. 2, the orientation of the dosing module adapter 20 is defined by the line 24, wherein the line 24 and the axial direction of the exhaust pipe 12 confine said inclination angle A.

[025] Moreover, the dosing module adapter 20 has a first cone-shaped portion 28 and a second cone-shaped portion 30. This means the first cone-shaped portion 28 is a first cone and the second cone-shaped portion 30 is a second cone of the dosing module adapter 20. The first cone-shaped portion 28 and the exhaust pipe 12, in particular an outer circumferential surface 32 of the exhaust pipe 12, confine a first angle B in a range of 110 degrees to 130 degrees. Moreover, the second cone-shaped portion 30 and the exhaust pipe 12, in particular the outer circumferential surface 32, confine a second angle C in a range of 20 degrees to 50 degrees. In the present case, the first angle B is 115 degrees, wherein the second angle C is 50 degrees.

[026] Moreover, a distance D between said injector tip and the mixing element 26 ranges from 60 to 100 millimeters and extends in the axial direction of the exhaust pipe 12. Preferably, the distance D is 89 millimeters. The distance D is defined as the linear distance between the injector tip, in particular an injector plane a and a mixer reference plane b along the axis of the axial direction of the exhaust pipe 12. Moreover, E is a distance between the injector tip and the exhaust pipe 12, in particular its outer circumferential surface 32, along the line 24.

[027] The first cone-shaped portion 28 is a first short cone for steeper and guided injection in order to mitigate deposition of the reducing agent on the mixing element 26. The second cone-shaped portion 30 is a second cone for preventing deposition due to fine mist and spray of the reducing agent in the dosing module adapter 20. By using the second cone a gap for fine mist and spray of the reducing agent can be realized to that the reducing agent is hydrolyzed without causing deposition. Thus, the effect of wall wetting, i.e. reducing agent hitting the wall can be avoided or kept particularly low in the dosing module adapter 20 as well as in the exhaust pipe 12. Hence, the risk of crystallization in the dosing module adapter 20, the exhaust pipe 12 and the mixing element 26 can be kept particularly low or eliminated. The spray of reducing agent is evenly distributed, in particular on respective flaps 34 of the mixing element 26. Consequently the area of peak spray surface load can be kept particularly low. Moreover, an improved flow and ammonia uniformity (UI) can be realized. Furthermore, a loss of NOx conversion efficiency can be avoided so that a particularly high conversion efficiency of nitrogen oxides can be realized. Failures of interfacing parts like the dosing module and the catalytic converter can be prevented. Additionally, the reducing agent consumption, especially in city driving cycles, can be reduced in comparison with conventional mixing devices. Furthermore, the risk of backpressure increase due to crystallization of the reducing agent is minimized.

[028] Since the exhaust gas and the reducing agent can be mixed particularly advantageously by the mixing device 10, the dosing unit can be configured as a liquid only dosing system by means of which only the liquid reducing agent and no gas, in particular no pressurized air is fed into the duct 14. This means a particularly advantageous mixture of the exhaust gas and the reducing agent is obtained without using an air assisted dosing system. The practical implementation of such a liquid only dosing system is mainly dependent on addressing the challenge of wall wetting. By using the mixing device 10 a liquid only dosing system can be implemented instead of an air assisted dosing system so that the cost of the exhaust aftertreatment device can be kept particularly low.