EXHAUST SYSTEM FOR AN ENGINE

Description

[0001] The present invention relates to an exhaust system for an internal combustion engine, for example in a vehicle.

[0002] To reduce pollutant emissions, especially nitrogen oxide emissions from diesel combustion engines, it is known to add a reagent, for example a urea / hydrogen solution, to the exhaust gas emitted by such a combustion engine, so that in an exhaust gas treatment unit, in particular an SCR catalyst, through which the mixture of exhaust gas and reagent flows, water and nitrogen are formed by a catalytic reaction of the nitrogen oxides contained in the exhaust gas with ammonia.

[0003] For an efficient catalytic reaction for exhaust gas purification, it is necessary that the reagent, which is generally added to the exhaust gas in liquid form as a spray mist, is completely mixed with the exhaust gas and evaporated upstream of the exhaust gas treatment unit in order to avoid the formation of deposits, especially of urea contained in the reagent, as well as the entry of liquid reagent into the exhaust gas treatment unit.

[0004] US 2014 / 0196442 A1 discloses an exhaust system for an internal combustion engine according to the preamble of claim 1, in which an exhaust routing component downstream of a reactant delivery unit comprises an outer tube extending substantially in a straight line along an outer tube's longitudinal axis and, within the outer tube, an inner tube extending substantially in a straight line along an inner tube's longitudinal axis corresponding to the outer tube's longitudinal axis. An outer volume formed between the outer tube and the inner tube is at least partially permeable to exhaust gas. The inner volume formed in the inner tube is permeable to exhaust gas and to the reactant injected therein.

[0005] US Patent 2013 / 0239546A1 discloses an exhaust system for an internal combustion engine in which a mixing element is inserted into a tubular exhaust system extending downstream of a reactant discharge unit. The mixing element surrounds a longitudinal axis of the exhaust system in a helical fashion. An outer circumferential region of the mixing element rests against an inner surface of the tubular exhaust system. The mixing element forces the mixture of exhaust gas and reactant flowing through the exhaust system onto a helical flow path, at least in a radially outer cross-sectional region of the exhaust system.

[0006] The object of the present invention is to provide an exhaust system for an internal combustion engine which ensures efficient mixing of exhaust gas and reactant, particularly during a cold start phase.

[0007] According to the invention, this problem is solved by an exhaust system for an internal combustion engine according to claim 1, comprising: at least one exhaust gas treatment unit, an exhaust gas routing component leading to the at least one exhaust gas treatment unit, a reaction agent delivery unit for delivering reaction agent into the exhaust gas routing component.

[0008] The exhaust gas routing component comprises an outer pipe and, in a length range between the reaction agent delivery unit and the exhaust gas treatment unit, an inner pipe, wherein an outer volume through which exhaust gas flows is provided between the outer pipe and the inner pipe and an inner volume through which exhaust gas flows is provided in the inner pipe.

[0009] The mixing of exhaust gas and reactant is supported by the fact that the inner pipe extends in a helical fashion in the direction of a straight longitudinal axis of the inner pipe.

[0010] By providing the inner pipe and the internal volume it creates, contact between the reactant, which is to be mixed with and vaporized by the exhaust gas, and the outer pipe, which is comparatively cold and heats up only slowly, especially during a cold start phase, can be largely avoided. The reactant can be efficiently vaporized on the inner surface of the inner pipe, which is surrounded by exhaust gas and therefore heats up relatively quickly even at the start of an internal combustion engine. This prevents the formation of deposits and promotes mixing with the exhaust gas carrying the reactant.

[0011] In order to essentially completely exclude contact of the reactant with the outer pipe in the length range in which the inner pipe extends, it is proposed that the reactant delivery unit be arranged in such a way that the reactant delivered from the reactant delivery unit into the exhaust gas routing component is essentially only delivered into the inner volume.

[0012] For a simple design of the exhaust gas routing component in the length range comprising the outer pipe and the inner pipe, thus forming a double-walled structure, the outer pipe can extend essentially in a straight line in the length range in the direction of a straight outer pipe longitudinal axis.

[0013] A simple design with uniform flow through the exhaust system can be achieved if the outer pipe is essentially cylindrical in its length.

[0014] If it is provided that the longitudinal axis of the inner pipe extends throughout its entire length within the internal volume, it is simultaneously ensured that the inner pipe has a sufficiently large flow cross-section so that a correspondingly large proportion of the exhaust gas flowing through the exhaust gas routing component can flow through the internal volume and mix with the evaporating reactant.

[0015] When the inner pipe rests against the outer pipe along a connecting line that is spirally wound around the longitudinal axis of the inner pipe, the portion of the exhaust gas flowing through the exhaust gas guide component that flows through the outer volume is forced onto a spiral flow path, thereby promoting the mixing of these exhaust gas flows and thus also the mixing of the portion of the exhaust gas flowing through the outer volume with already vaporized reactants at the downstream end of the length section where the exhaust gas flows through the outer volume and the inner volume are combined.

[0016] In the area of ​​the connection line, the inner pipe can be connected to the outer pipe, for example, by material bonding, such as welding.

[0017] To avoid the occurrence of cross-sectional constrictions, particularly in the outer volume, it is proposed that the outer tube and the inner tube have an essentially identical cross-sectional geometry in the length region.

[0018] For example, in the length range, the outer tube and the inner tube can have an essentially circular cross-sectional geometry.

[0019] Uniform conditions that avoid excessive flow resistance can be further supported by ensuring that the inner tube, and thus the internal volume formed therein, has a substantially constant cross-sectional geometry and / or a substantially constant cross-sectional size along its length.

[0020] In order to combine the two exhaust gas flows flowing through the outer volume and the inner volume upstream of the exhaust gas treatment unit, and thus to supply the exhaust gas treatment unit with an exhaust gas flow that is essentially uniformly mixed with reactant, it is proposed that the inner pipe terminates upstream of a downstream end of the outer pipe and / or upstream of the exhaust gas treatment unit.

[0021] At least one exhaust gas treatment unit can, for example, include an SCR catalyst.

[0022] The present invention is described in detail below with reference to the accompanying figures. These show: Fig. 1 a schematic longitudinal section view of an exhaust system; Fig. 2 in its representations a), b) and c) cross-sectional views of an exhaust system component of the exhaust system of the Fig. 1 at an upstream end region of an inner pipe of the exhaust gas routing component (section II), at a middle length region of the inner pipe (section II-II) and at a downstream end region of the inner pipe (section III-III).

[0023] The Fig. 1 Figure 1 shows an exhaust system 10 for an internal combustion engine with an exhaust gas routing component 12 that receives the exhaust gas A emitted by an internal combustion engine and an exhaust gas treatment unit 14 connected downstream thereto. The exhaust gas treatment unit 14 can, for example, include an SCR catalyst 16 in which the exhaust gas A is reacted in a catalytic reaction with a reactant R, for example a urea / water solution, which is delivered into the exhaust gas routing component 12 by a reaction agent delivery unit 18 generally referred to as an injector, in order to reduce the nitrogen oxide content in the exhaust gas A.

[0024] The exhaust gas routing component 12 comprises an outer pipe 20, which is elongated in the direction of a straight longitudinal axis LA and, particularly in the section adjoining the exhaust gas treatment unit 14, is essentially cylindrical with, for example, a circular cross-sectional geometry. An inner pipe 22 is arranged inside the outer pipe 20. The inner pipe 22 is elongated in the direction of an inner pipe longitudinal axis LI corresponding, for example, to the longitudinal axis LA of the outer pipe and has a fundamentally helical structure, essentially corresponding to the geometry of a corkscrew.Since the inner tube 22 has a smaller cross-sectional dimension than the outer tube 20, an outer volume 24 is formed between the outer tube 20 and the inner tube 22, which, due to the helically wound structure of the inner tube 22, also has a ring-like and helically wound structure.

[0025] If, as this is the case, Fig. 2a) bis 2cTo illustrate, if the inner tube 22, along its entire length B, which also contains the outer volume 24, has a substantially constant cross-sectional geometry and area (e.g., a circular cross-sectional geometry), then the outer volume 24 also has substantially the same cross-sectional area along its entire length B. Flow constrictions can thus be avoided in the outer volume 24. Simultaneously, with this design of the inner tube 22, the inner volume 26 formed within it has a constant cross-sectional geometry and area along its entire length B, where the inner tube 22 extends along its longitudinal axis LI. This ensures uniform flow conditions within the inner tube 22 and the inner volume 26 formed therein.

[0026] Due to the helically wound structure of the inner tube 22 and its dimensions, as well as its winding around the inner tube's longitudinal axis LI, a connecting line V is formed that helically surrounds the inner tube's longitudinal axis LI and the outer tube's longitudinal axis LA, extending in the direction of these longitudinal axes. Within this connecting line V, the inner tube 22 and the outer tube 20 are in contact with each other. In the region of this connecting line V, which preferably extends continuously along both longitudinal axes and thus contributes to the external flow SA leaving the outer volume 24 as a swirling flow, the inner tube 22 and the outer tube 20 can be firmly connected to each other, for example, by welding, such as laser welding, spot welding, or the like.

[0027] The exhaust gas A, emitted by the internal combustion engine and flowing along length B in the exhaust gas routing component 12, is split at the upstream end of the inner pipe 22, i.e., length B, into a portion flowing through the outer volume 24 and a portion flowing through the inner volume 26. Due to the helical structure of the inner pipe 22, and thus also of the outer volume 24, the portion of the exhaust gas A flowing through the outer volume 24 is accelerated circumferentially, so that this portion of the exhaust gas A essentially generates an outer flow SA with swirl. Similarly, the portion of the exhaust gas A flowing through the inner volume 26 is transformed into an inner flow SI with swirl due to the helical structure of the inner pipe 22, and thus also of the inner volume 26.

[0028] The reagent dispensing arrangement 18 is preferably positioned such that the reagent R dispensed by it is dispensed at the upstream end of the inner tube 22 essentially only into the inner volume 26. For example, the reagent dispensing unit 18 can be positioned such that, taking into account the opening angle of the spray cone dispensed by it with respect to the upstream inlet opening of the inner tube 22, it is ensured that essentially no reagent R flows into the outer volume 24. The reagent dispensing unit 18 could also be positioned such that its dispensing end extends into the inner volume 26.

[0029] The reactant R, which is introduced into the portion of the exhaust gas A flowing in the inner volume 26, is carried along by the internal flow SI and accelerated radially outwards by the resulting swirl, thus increasing its contact with the inner surface of the inner tube 22 and allowing it to evaporate there. Since the outer surface of the inner tube 22 is surrounded by the external flow SA, i.e., by comparatively warm exhaust gas, the inner tube 22 heats up relatively quickly even at the start of operation of an internal combustion engine. This ensures that, even during such a cold start phase, the reactant R undergoes essentially complete evaporation and mixing very early on, already within the length range B.

[0030] The downstream end of the inner pipe 22 is located upstream in the flow direction, i.e., at a distance from the exhaust gas treatment unit 14 or the SCR catalyst 16. Preferably, the inner pipe 22 terminates upstream of the downstream end of the outer pipe 20. Thus, a distance exists between the downstream end of the inner pipe 22 and the exhaust gas treatment unit 14 or the SCR catalyst 16, creating a flow path that ensures the mixing of the external flow SA with the internal flow SI. This ensures that even the portion of the exhaust gas A that does not contain any reactant R, which flows through the external volume 24 as external flow SA, can be mixed with the portion of the exhaust gas A flowing through the internal volume 26 as internal flow SI and containing reactant R, before entering the SCR catalyst 16.This ensures that the SCR catalyst 16 is exposed to a substantially uniform flow of exhaust gas and reaction agent across its entire upstream cross-section.

[0031] By splitting the exhaust gas stream emitted by an internal combustion engine into the outer flow SA and the inner flow SI, efficient mixing of the exhaust gas and reactant is ensured very quickly during a cold start phase, thus initiating a catalytic reaction in the exhaust gas treatment unit 14. The time during which essentially untreated exhaust gas is emitted to the environment can therefore be significantly reduced.Furthermore, since the helical structure of the inner tube 22 promotes the mixing of exhaust gas A and reaction agent R within the inner volume 26, as well as the evaporation of the reaction agent, and since the resulting swirl flow at the downstream end of the inner tube 22 mixes the internal flow SI and the external flow SA, uniform utilization of the catalyst volume provided in the exhaust gas treatment unit 14 is simultaneously ensured. The rapid and uniform mixing of exhaust gas A and reaction agent R also reduces the formation of deposits, particularly urea deposits, which could impair the flow through the exhaust gas routing component 12 over the service life.

Claims

1. An exhaust gas system for an internal combustion engine, comprising: - at least one exhaust gas treatment unit (14), - an exhaust gas guide component (12) conducting exhaust gas (A) to the at least one exhaust gas treatment unit (14), - a reactant discharge unit (18) for the discharge of reactant (R) into the exhaust gas guide component (12), wherein the exhaust gas guide component (12) comprises an outer pipe (20) and an inner pipe (22) in a longitudinal region (B) between the reactant discharge unit (18) and the exhaust gas treatment unit (14), wherein an external volume (24) through which exhaust gas (A) can flow and an internal volume (26) through which exhaust gas (A) can flow in the inner pipe (22) are provided between the outer pipe (20) and the inner pipe (22), characterized in that the inner pipe (22) extends so as to be wound in a helical manner in the direction of an inner pipe longitudinal axis (LI) extending in a linear manner.

2. The exhaust gas system as claimed in claim 1, characterized in that the reactant discharge unit (18) is arranged such that reactant (R) discharged by the reactant discharge unit (18) into the exhaust gas guide component (12) is discharged substantially only into the internal volume (26).

3. The exhaust gas system as claimed in claim 1 or 2, characterized in that the outer pipe (20) extends substantially in a linear manner in the longitudinal region (B) in the direction of an outer pipe longitudinal axis (LA) extending in a linear manner.

4. The exhaust gas system as claimed in one of claims 1 - 3, characterized in that the outer pipe (20) is configured to be substantially cylindrical in the longitudinal region (B).

5. The exhaust gas system as claimed in one of claims 1 - 4, characterized in that the inner pipe longitudinal axis (LI) extends in the internal volume (26) in the entire longitudinal region (B).

6. The exhaust gas system as claimed in one of claims 1 - 5, characterized in that the inner pipe (22) bears against the outer pipe (20) along a connecting line (V) wound in a helical manner about the inner pipe longitudinal axis (Li).

7. The exhaust gas system as claimed in claim 6, characterized in that the inner pipe (22) is connected to the outer pipe (20) in the region of the connecting line (V).

8. The exhaust gas system as claimed in one of claims 1 - 7, characterized in that the outer pipe (20) and the inner pipe (22) have substantially the same cross-sectional geometry to one another in the longitudinal region (B).

9. The exhaust gas system as claimed in one of claims 1 - 8, characterized in that the outer pipe (20) and the inner pipe (22) have a substantially circular cross-sectional geometry in the longitudinal region (B).

10. The exhaust gas system as claimed in one of claims 1 - 9, characterized in that the inner pipe (22) has a substantially uniform cross-sectional geometry and / or a substantially uniform cross-sectional size in the longitudinal region (B).

11. The exhaust gas system as claimed in one of claims 1 - 10, characterized in that the inner pipe terminates upstream of a downstream end of the outer pipe (20) and / or upstream of the exhaust gas treatment unit (14).

12. The exhaust gas system as claimed in one of claims 1 - 11, characterized in that the at least one exhaust gas treatment unit (14) comprises an SCR catalytic converter (16).