DE102013012909B4 - Mixing chamber - Google Patents

Abstract

Mixing chamber (1) for mixing an additive in an exhaust system of an internal combustion engine a) with a one-part or multi-part housing (11) which has an inlet opening (12) for exhaust gas with a flow cross-section (S12) and with a central inlet axis (M12) and a downstream of the Having an inlet opening (12) arranged outlet opening (13) for exhaust gas with a flow cross section (S13) and with a central outlet axis (M13), whereby a flow guide element (2) is arranged within the housing (11) between the two openings (12, 13) , c) the flow guide element (2) is tubular and forms at least one channel (20) having a channel axis (K2) with an inlet (22) and with an outlet (23), via which the entire exhaust gas flow in one direction to the channel axis (K2 ) parallel flow direction (S) up to the outlet opening (13), whereby) the flow direction (S) differs relative to the central outlet axis (M13) by an angle a between 20 ° and 80 ° characterized in that the outlet (23) has an outlet cross-section (A23) running at right angles to the central outlet axis (M13), the outlet cross-section (A23) being a maximum of 20% larger or smaller than the flow cross-section (S13) of the outlet opening (13).

Description

The invention relates to a mixing chamber for mixing an additive in an exhaust system of an internal combustion engine with a one-part or multi-part housing. For this purpose, the housing has an inlet opening for exhaust gas with a flow cross section and with a central inlet axis and an outlet opening for exhaust gas arranged downstream of the inlet opening with a flow cross section and with a central outlet axis. A flow guide element is arranged in the housing between the two openings.

It's already in the DE 11 2010 002 589 T5 a mixing chamber arranged between two monoliths (substrates) is described. This mixing chamber is arranged between an upstream and a downstream monolith arranged in series for treating the exhaust gases circulating in the exhaust line. The mixing chamber has a channel formed by a shell and running around the central axis for the circulation of the exhaust gas flow, which channel is at least 20% longer than the mixing chamber along the central axis.

After US 2010 0005790 A1 a mixing chamber for mixing an additive is known in which the flow guide element arranged in a housing is tubular and guides the exhaust gas flow in a flow direction which is set at an angle between 45 ° and 60 ° relative to the central outlet axis. The outlet cross-section of the flow guide element is arranged at an angle to the central axis of the housing and corresponds to approximately 1/5 of the flow cross-section of the housing.

In the JP 2009 030560 A describes a duct wall for a flow guide element arranged in a housing, which can be perforated or free of perforations. The flow guide element forms a flow direction parallel to the central exit axis of the housing.

The US 2011 0 107 749 A1 shows an exhaust gas purification unit. This includes an injection nozzle, a pre-catalytic converter, an expansion section and a further catalytic converter. After the primary catalytic converter, the majority of the exhaust gas flow within the funnel deviates between approximately ± 20 ° to ± 30 ° from a mean flow direction which corresponds to the axis L1. The mean flow direction is not inclined with respect to the central exit axis, which also corresponds to the axis L1.

From the US 2011 0094206 A1 a housing with a dome is known on which an injection device is arranged. The flow guide element is arranged outside the exhaust gas flow.

The invention is based on the object of designing and arranging a mixing chamber in such a way that, with a reduced overall length, an improved distribution of the mixture of exhaust gas and additive on the substrate surface and, at the same time, deposits of the additive are achieved.

The object is achieved according to the invention in that the flow guide element is tubular and forms at least one channel having a channel axis with an inlet and an outlet, via which the entire exhaust gas flow is directed in a flow direction parallel to the channel axis to the outlet opening, the flow direction being relative deviates from the central outlet axis by an angle a between 20 ° and 80 ° and the outlet has an outlet cross-section running at right angles to the central outlet axis, the outlet cross-section being a maximum of 20% larger or smaller than the flow cross-section of the outlet opening. The angle a is preferably between 55 ° and 75 °. At an angle of 65 °, the substrate was wetted with a gamma greater than 0.9.

This ensures that all flow threads of the exhaust gas flowing into the inlet opening are deflected by the flow guide element in such a way that all flow threads are guided out of the mixing chamber through the flow guide element in approximately the same direction of flow inclined to the outlet opening, on which a downstream substrate is then arranged. Since the exhaust gas is distributed over the flow cross section of the outlet opening, it is also distributed over the cross section of the downstream substrate. The downstream substrate is thus flowed at an angle over its entire end face with flow threads approximately parallel to the direction of flow, which leads to a very good distribution of the additive introduced into the mixing chamber without the additive forming larger deposits. The person skilled in the art understands by approximately parallel to the flow direction deviations from the flow direction defined as the main flow direction of a maximum of 5 ° to 8 °.

It can also be advantageous for this purpose if the channel axis intersects the central exit axis at an angle α between 20 ° and 80 °. The flow guide element collects all the flow threads and channels them in the direction of the outlet opening, the additive being mixed into the exhaust gas flow in the flow guide element.

For this purpose, it is advantageous that the flow guide element in the direction of the channel axis has an inlet opposite the outlet upstream with an inlet cross section whose size is 10% to 70% compared to the outlet cross section is reduced. In addition to an adaptation to the respective hydraulic cross-sections of the downstream and upstream substrates, a reduction in the inlet cross-section can accelerate the exhaust gas flow beginning at the inlet of the channel and into the channel, through which the additive introduced in the area of the inlet is better mixed and in its Droplet size is reduced.

For this purpose, it is provided that the channel is encased by a channel wall and the channel wall is closed or formed without perforations so that the described deflection of all flow threads can take place. The inlet and the outlet form the only openings in the flow guide element.

It can be particularly advantageous if the channel along the channel axis, starting at the central exit axis, has a length which corresponds at least to the quotient of a mean radius of the entrance opening to sine a, ie L2 ^R12 / _{sin a} . As a result, the flow guide element closes the flow cross section for the exhaust gas in the direction of the central inlet axis and initially forces it from the axial direction into a radial direction before the exhaust gas flows into the flow guide element.

If the cross-sectional area of the upstream substrate is a certain maximum amount smaller than the flow cross-section of the inlet opening, then the channel has a reduced length that corresponds at least to the quotient of a mean radius of a substrate to sine a, i.e. L2 ≥ ^R51 / _{sin a} .

It is advantageously provided that the housing has a dome which protrudes beyond the flow cross section in the radial direction to the central inlet axis, which at least partially forms the channel or into which the channel protrudes at least partially. So that the outermost stream filament can also be deflected in the radial direction, the dome forms a volume outside the radial limits of the rest of the housing.

It can be of particular importance for the present invention that one or more mixing elements for mixing the additive injected into the mixing chamber are arranged on the channel adjoining the inlet and / or in the channel. Regardless of whether the inlet is formed by a single opening or by several slots or a perforation through which the exhaust gas is swirled when flowing into the channel, mixing elements are provided which are arranged downstream of the injection device.

In connection with the design and arrangement according to the invention, it can be advantageous if an injection device is arranged on the dome or on the flow guide element, which injects the additive in one injection direction into the flow guide element, the injection direction being set at up to 90 ° to the channel axis. Due to a possible adjustment to the channel axis, the additive can be injected with or against the flow direction of the exhaust gas.

It can also be advantageous if the cross section of the channel increases steadily from the inlet to the outlet.

It can also be advantageous if the housing and the downstream converter housing and / or the upstream converter housing form a one-part or multi-part common component.

It can furthermore be advantageous if the mixing element is a static mixer with one or more mixing stages.

Finally, it can be advantageous if the flow cross section of the inlet opening is different from the flow cross section of the outlet opening.

It can also be advantageous if the mixing chamber or the flow guide element or parts thereof are at least partially catalytically coated on the sides facing the exhaust gas.

The arrangement is particularly advantageous when the upstream substrate is designed as a catalyst and the downstream substrate is designed as a particle filter.

• 1 eine Schnittansicht eines Ausführungsbeispiels mit angestellter Einspritzrichtung;
• 2 eine Schnittansicht eines Ausführungsbeispiels mit koaxialer Einspritzrichtung;
• 3 eine Prinzipskizze der geometrischen Verhältnisse;
• 4 eine Schnittansicht entgegen der Strömungsrichtung gemäß Schnittebene A-A';
• 5 ein Ausführungsbeispiel mit einem Mischelement in einem Strömungsleitelement mit einem schlitzförmigen Einlass;
• 6 ein Ausführungsbeispiel mit einem konischen Strömungsleitelement;
• 7 ein Ausführungsbeispiel mit einem perforierten Strömungsleitelement;
• 8 ein Ausführungsbeispiel mit parallel versetzt angeordneten Substraten;
• 9 ein Ausführungsbeispiel mit schräg zueinander angeordneten Substraten;
• 10 ein Ausführungsbeispiel mit parallel in radialer Richtung nebeneinander angeordneten Substraten.

Further advantages and details of the invention are explained in the patent claims and in the description and shown in the figures. It shows:

• 1 a sectional view of an embodiment with adjusted injection direction;
• 2 a sectional view of an embodiment with a coaxial injection direction;
• 3 a basic sketch of the geometric relationships;
• 4th a sectional view counter to the flow direction according to section plane A-A ';
• 5 an embodiment with a mixing element in a flow guide element with a slot-shaped inlet;
• 6th an embodiment with a conical flow guide element;
• 7th an embodiment with a perforated flow guide element;
• 8th an embodiment with substrates arranged offset in parallel;
• 9 an embodiment with substrates arranged obliquely to one another;
• 10 an embodiment with substrates arranged parallel to one another in the radial direction.

The 1 and 2 show a mixing chamber 1 between a downstream converter housing 4th and an upstream converter housing 5 is arranged. The mixing chamber 1 has a housing 11 with an entrance opening 12 and an exit port 13 on, according to these two embodiments with respect to a central input axis M12 and a central exit axis M13 are arranged coaxially.

One between the entrance opening 12 and the exit port 13 arranged tubular flow guide element 2 causes the exhaust gas flow after entering through the inlet opening 12 from an axial direction along the central entrance axis M12 is deflected in the radial direction because the flow guide element 2 an axial flow cross section S12 locks.

The flow guide element is for this purpose 2 as a channel 20th with a channel wall 21st formed and closes with its outlet 23 against the direction of flow to the outlet opening 13 of the housing 11 at. As an outlet cross-section A23 of the outlet 23 essentially a flow cross section S13 the exit opening 13 is the exit port 13 through the flow guide element 2 in the direction of the central entrance axis M12 locked. After the radial deflection, the exhaust gas flow is via an inlet 22nd in the canal 20th guided and at an angle a of 65 ° from the outlet opening 13 out onto an end face of a downstream substrate 41 directed.

So as possible all flow threads at the end of the channel 20th approximately in a flow direction S parallel to a channel axis K2 aligned, the channel 20th or the flow guide element 2 a certain length L2 so that the outermost stream filament is also deflected outward in the radial direction.

The exhaust gas flow deflected in the radial direction collects in a dome 14th going through part of the case 11 is formed, which in the radial direction over the inlet opening 12 stands out. The inlet 22nd of the flow guide element 2 is in the cathedral 14th arranged. At the cathedral 14th is in the area of the inlet 22nd an injector 6th provided for introducing an additive in an injection direction E.

According to the embodiment according to 1 the additive is from the injection direction E in the channel 20th in the direction of the channel axis K2 diverted. The inlet 22nd has an inlet cross section E22 on, in which a static mixing element 3 is arranged and through which the additive is injected.

According to the embodiment according to 2 are the injection direction E and the channel axis K2 coaxial or at least parallel.

In front of and behind the housing 11 are a downstream converter housing 4th with a downstream substrate 41 and an upstream converter housing 5 with an upstream substrate 51 arranged. These two housings 4th , 5 are according to 2 in the housing 11 , in the entrance opening 12 and into the exit opening 13 plugged in. The substrates 41 , 51 are coaxial with the central entrance axis M12 the entrance opening 12 and to the central exit axis M13 the exit opening 13 arranged.

Determining the necessary length L2 is according to the schematic diagram 3 clarified. So that the entire exhaust gas flow or each flow thread after entering the inlet opening 12 can be deflected in the radial direction, the duct wall protrudes 21st of the canal 20th in the radial direction with a dimension above the central entrance axis M12 that is larger than a radius R12 the entrance opening 12 or a radius R51 of the upstream substrate 51 . Taking into account the angle a with which the channel axis K2 opposite the central exit axis M13 is employed, must be the length L2 must be at least greater than the quotient of the mean radius R51 of the substrate 41 to sine a. Depending on how the diameter of the upstream converter housing 5 to the diameter of the upstream substrate 51 behaves or what construction geometry is used, it may be sufficient that the length L2 is greater than the quotient of the mean radius R12 the entrance opening 12 to sine a.

In 4th is the section AA 'according to 2 shown, after which the curved duct wall 21st is shown in the direction of the central exit axis M13 the outlet 23 over its entire outlet cross-section A23 locks. The radius of the outlet cross section A23 in this case corresponds to both a radius R41 of the downstream substrate 41 as well as the radius R51 of the upstream substrate 51 .

In 5 an embodiment is shown in which in the channel 20th after the entrance opening 12 a mixing element 3 is arranged. The entrance opening 12 is designed like a grid, with partial areas of the duct wall 21st are bent in the radial direction as a flap like a wing inwards or outwards.

After 6th is the channel 20th in the area of the entrance opening 12 conical. After 7th instead of a lattice-like structure, a perforation P is provided which, like the lattice-like structure, has a corresponding flow cross section S12 forms.

After 8th are the two substrates 41 , 51 arranged axially parallel so that the central input axis M12 and the central exit axis M13 are arranged in parallel.

After 9 the two substrate central axes are arranged at an angle b of 30 ° to one another. The angle b can vary between 0 ° and 180 °. 0 ° corresponds to the embodiment according to 1 and 2 . 180 ° corresponds to the embodiment according to 10 .

Claims (15)

Mixing chamber (1) for mixing an additive in an exhaust system of an internal combustion engine a) with a one-part or multi-part housing (11) which has an inlet opening (12) for exhaust gas with a flow cross-section (S12) and a central inlet axis (M12) and a downstream the inlet opening (12) has an outlet opening (13) for exhaust gas with a flow cross section (S13) and with a central outlet axis (M13), b) inside the housing (11) a flow guide element (2) between the two openings (12, 13) is arranged, c) the flow guide element (2) is tubular and forms at least one channel (20) having a channel axis (K2) with an inlet (22) and with an outlet (23) via which the entire exhaust gas flow in one direction to the channel axis (K2) parallel flow direction (S) is passed to the outlet opening (13), d) the flow direction (S) relative to the central outlet axis (M13) deviates by an angle a between 20 ° and 80 ° characterized in that the outlet (23) has an outlet cross-section (A23) running at right angles to the central outlet axis (M13), the outlet cross-section (A23) being a maximum of 20% larger or smaller than the flow cross-section (S13) of the outlet opening (13). Mixing chamber (1) Claim 1 , characterized in that the channel axis (K2) intersects the central exit axis (M13) at an angle a between 20 ° and 80 °. Mixing chamber (1) Claim 2 , characterized in that the flow guide element (2) in the direction of the channel axis (K2) opposite the outlet (23) has an inlet (22) with an inlet cross section (E22), the size of which is 10% to 70% compared to the outlet cross section (A23) ) is reduced. Mixing chamber (1) according to one of the preceding claims, characterized in that the channel (20) is encased by a channel wall (21) and the channel wall (21) is designed to be closed or free of perforations. Mixing chamber (1) according to one of the preceding claims, characterized in that the channel (20) along the channel axis (K2), starting at the central exit axis (M13), has a length (L2) which is at least the quotient of a mean radius (R12) the inlet opening (12) corresponds to sine a, ie L2 ≥ ^R12 / _{sin α} . Mixing chamber (1) according to one of the preceding claims, characterized in that a substrate (51) is provided upstream of the inlet opening (12) and the channel (20) along the channel axis (K2), starting at the central outlet axis (M13), has a length ( L2), which corresponds at least to the quotient of a mean radius (R51) of a substrate (41) to sine a, ie L2 ≧ ^R51 / _{sin α} . Mixing chamber (1) according to one of the preceding claims, characterized in that the housing (11) has a dome (14) which protrudes beyond the flow cross section (S12, S13) in the radial direction to the central inlet axis (M12) and which at least partially defines the channel (20 ) or into which the channel (20) protrudes at least partially. Mixing chamber (1) according to one of the preceding claims, characterized in that on the channel (20) adjoining the inlet (22) and / or in the channel (20) one or more mixing elements (3) for mixing the in the mixing chamber (1) injected additive are arranged. Mixing chamber (1) after one of the Claims 7 to 8th , characterized in that an injection device (6) is arranged on the dome (14) or on the flow guide element (2), which injects the additive in an injection direction (E) into the flow guide element (2), the injection direction (E) by up to at 90 ° to the duct axis (K2). Mixing chamber (1) according to one of the preceding claims, characterized in that a downstream converter housing (4) with a downstream substrate (41) is provided following the output inlet opening (13), wherein the downstream substrate (41) is fluidically connected to the outlet (23). Mixing chamber (1) according to one of the preceding claims, characterized in that an upstream converter housing (5) with the upstream substrate (51) is provided in front of the inlet opening (12), the upstream substrate (51) with the inlet (22) in terms of flow connected is. Mixing chamber (1) according to one of the preceding claims, characterized in that the central inlet axis (M12) and the central outlet axis (M13) are arranged parallel or coaxially or intersect at an angle between 10 ° and 80 °. Mixing chamber (1) according to one of the preceding claims, characterized in that the inlet opening (12) and the outlet opening (13) are arranged one behind the other in the direction of the central inlet axis (M12) or next to one another in the radial direction to the central inlet axis (M12). System consisting of a mixing chamber (1) according to one of the preceding claims and an exhaust system for an internal combustion engine. A method for flowing against a substrate (41) with a mixing chamber (1) according to one of the Claims 1 to 14th , which is aligned in the direction of the central exit axis (M13), with a mixed flow of exhaust gas and an additive, characterized in that the entire flow in parallel flow directions deviating by a maximum of 5 ° from a mean, straight flow direction (S) directly onto the Substrate (41) is passed, the flow direction (S) being inclined at an angle a between 20 ° and 80 ° with respect to the central exit axis (M13).

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