Exhaust gas purification system for diesel engines

Abstract

An exhaust gas purification system (10) for an internal combustion engine, preferably a diesel engine, comprising a catalyst (12), a reducing agent addition device (26), a mixing element (24) for mixing the reducing agent with exhaust gases, and an SCR filter (14), which are arranged in particular downstream of an exhaust gas turbocharger, wherein an exhaust gas duct (16) is arranged between the catalyst (12) and the SCR filter (14), which has an inlet section (18) coupled to the catalyst (12) and an outlet section (20) coupled to the SCR filter (14), as well as a mixing section (22) arranged between the inlet section (18) and the outlet section (20), and the exhaust gas duct (16) is designed such that the exhaust gas from the catalyst (12) is guided away from the inlet of the SCR filter (14), at least in the inlet section (18), characterized in thatthat the exhaust gas duct (16) is continuously curved and a 90° angle is included between an inlet of the inlet section (18) and an outlet of the outlet section (20).

Description

[0001] The invention relates to an exhaust gas purification system according to the preamble of claim 1.

[0002] It is known that the combustion gases from internal combustion engines contain gases and particles that are harmful to the environment and health and are therefore subject to increasingly strict standards and regulations. CO2, NOx, and soot particles are particularly in the sights of developers of environmentally friendly combustion engines and applications. Efforts are directed, on the one hand, at lower consumption and, on the other, at the active purification of combustion exhaust gases. Purification-oriented measures include catalysts, which chemically transform the harmful gases into a less harmful chemical element and filter out particulates, especially soot particles. The operation of catalysts requires a certain elevated operating temperature, so it takes time to reach this temperature after a cold start.

[0003] The generic EP 2 551 482 A1 shows an exhaust gas purification system in which an exhaust duct diverts the exhaust gas by 180° between a catalyst and an SCR filter.

[0004] DE 11 2010 004 966 T5, DE 10 2009 014 433 A1 and DE 600 16 218 T2 show further exhaust gas purification systems.

[0005] Generally, exhaust systems comprising a catalytic converter and a selective catalytic reduction filter (SCRF) are known from the prior art. The catalyst can be designed as an oxidation catalyst (DOC), an active nitrogen oxide catalyst (NSC), or a passive nitrogen oxide storage catalyst (PNA). The SCRF simultaneously reduces nitrogen oxide (NOx) and soot particles in the exhaust gases of an internal combustion engine by combining two technologies in one: an SCR (selective catalytic reduction) catalyst, which reduces NOx to nitrogen and water in the presence of a catalyst such as ammonia, and a particulate filter (DPF), which filters out the soot particles.

[0006] The catalyst (DOC, NSC, or PNA) and the SCRF are typically connected by an exhaust pipe, with a reductant being introduced into the exhaust gas to purify it. It has been found that the effectiveness and efficiency of exhaust gas purification processes depend on several components, which, however, conflict with general requirements, such as compact design.

[0007] The invention is based on the object of creating an exhaust gas purification system for an internal combustion engine, in particular a diesel engine, whose exhaust gas purification is effective despite its compact design.

[0008] This problem is solved by an exhaust gas purification system having the features of claim 1. The basic concept of the invention provides that the exhaust gas is initially guided away from the SCR filter through the exhaust duct, meaning that the exhaust gas does not take the shortest route to the inlet of the SCR filter. The exhaust pipe has a diversion. This allows for a better positioning of the other components in the exhaust gas purification system. Furthermore, the exhaust gas can generally travel a greater distance within the exhaust pipe despite the small installation space.

[0009] The exhaust duct comprises an outlet section and a mixing section located between the inlet section and the outlet section. The mixing section may have a smaller cross-section than the inlet section, the outlet section, the catalytic converter outlet, and / or the SCR filter inlet. This ensures that the exhaust gas is compressed in the area of ​​the mixing section, allowing the exhaust gas to be better mixed with the reducing agent. Furthermore, the exhaust pipe is smaller in the area of ​​the mixing section, thus providing more space for additional components of the exhaust system.

[0010] The exhaust duct is curved throughout. This curvature allows for a sufficiently long mixing section. Furthermore, the geometry of the exhaust duct allows for more precise and targeted exhaust flow.

[0011] In particular, an angle of essentially 90 degrees or slightly deviating therefrom is formed between the inlet of the inlet section and the outlet of the outlet section. This allows for a compact exhaust system layout. The exhaust duct or outlet section simultaneously serves as an inlet connection for the downstream SCRF. Likewise, this allows for a close arrangement of the exhaust gas purification system components and a close-to-engine arrangement of the entire exhaust system, which facilitates rapid warm-up of the catalysts and filters after a cold start.

[0012] According to a further aspect of the invention, a mixing section is formed in the mixing portion, which in particular has a substantially circular cross-section and a pronounced curvature. The geometry of the mixing portion allows the exhaust gas to travel a long distance within a small installation space. Furthermore, the reducing agent can be mixed with the exhaust gases more effectively and evenly. The circular or nearly circular cross-section improves the uniform distribution of the reducing agent in the exhaust gas before it impinges on the downstream component of the exhaust gas purification system.

[0013] The cross-section of the retaining section can, in particular, be of the same size as the remaining exhaust pipes. Typically, the cross-section is specified depending on the working volume of the combustion engine.

[0014] Depending on the exhaust gas flow to be purified by the exhaust gas purification system, i.e., proportional to the working volume of the combustion engine, a cross-section can be specified according to the invention. The reduced cross-section creates smaller external cooling radiation surfaces, allowing the mixing device to reach a higher temperature more quickly. This allows the reducing agent to be evaporated more effectively, preventing the formation of unevaporated droplets.

[0015] According to a further aspect of the invention, the mixing element is arranged within the mixing section, in particular in the mixing path, such that a downstream section between the mixing element and the inlet of the SCR filter is longer than the inlet section between the outlet of the catalyst and the mixing element. In the mixing element, the exhaust gas is mixed with the introduced reducing agent. The mixing section with a smaller cross-section enables a smaller cross-sectional area for the mixing region, whereby a more uniform distribution of the reducing agent and mixing with the exhaust gas can be achieved. As a result, a more effective reduction reaction is achieved and thus a lower proportion of the corresponding pollutant gas, in particular NOx.

[0016] According to a further aspect of the invention, the reducing agent addition device is arranged such that the reducing agent addition device has an acute angle to the exhaust gas flow direction, in particular less than 70°. The reducing agent introduced into the exhaust duct thus does not slow down the exhaust gas flow, but rather has essentially the same flow direction. This minimizes jet drift and achieves better mixing even before it hits the mixing device.

[0017] In particular, the reducing agent addition device is arranged on the exhaust duct, wherein the exhaust duct has a mounting section for the reducing agent addition device, which is designed in particular as a base element protruding outward from the outer surface of the exhaust duct. This ensures that the reducing agent addition device is arranged in the correct orientation so that the reducing agent is introduced efficiently, thereby improving the purification of the exhaust gas. By arranging the reducing agent addition device on the outer surface of the exhaust duct, it is also ensured that the reducing agent addition device does not collide with other parts of the exhaust gas purification system and remains easily accessible. A urea-water solution is preferably used as a reducing agent.

[0018] According to a further preferred embodiment, the mixing device has an edge gap to the holding section. The edge gap can be used to limit the exhaust backpressure at high mass flow rates.

[0019] A further aspect of the invention provides that the inlet section and / or the outlet section is designed as a Fischer funnel. Fischer funnels are exhaust gas inlet or exhaust gas outlet nozzles which feed the exhaust gas coming from a motor vehicle's internal combustion engine from a pipe with a comparatively small cross-section over a large area to a catalyst coating of an exhaust gas aftertreatment device. As nozzle-like transition pieces, they have a conically widening funnel and, on the outlet side, an oblique cut of the component. The oblique cut generally pivots the gas flow. However, a Fischer funnel can be designed in the opposite way if it is used as an exhaust gas outlet nozzle which feeds the exhaust gas coming from a catalyst to another treatment unit, whereby the cross-section is reduced. The inlet section is designed, in particular, as an inverted Fischer funnel.The entrance and exit sections, designed as a Fischer funnel, allow a long running distance to be achieved despite limited installation space.

[0020] The Fischer funnel design of the outlet section, with the exhaust flow deflected at an angle to the front face of the SCR filter, ensures that gas flow separation and uneven distribution of the reducing agent across the cross-sectional area of ​​the SCR filter are avoided. This is especially true when not all of the reducing agent evaporates at the mixing element and droplets are allowed to pass through.

[0021] Further advantages and features of the invention will become apparent from the following description and the drawings, to which reference is made.

[0022] The single drawing shows an exhaust gas purification system 10, which can preferably be arranged directly downstream of a turbocharger (not shown). The arrows indicate the exhaust gas flow direction.

[0023] The exhaust gas purification system 10 comprises a catalyst 12, an SCR filter 14 and an exhaust duct 16 connecting these two components. The catalyst 12 can be a DOC, NSC or PNA.

[0024] The exhaust duct 16 has several sections: an inlet section 18 coupled to the catalytic converter 12, and an outlet section 20 coupled to the SCR filter 14. Furthermore, the exhaust duct 16 has a mixing section 22, which has a smaller cross-section than the inlet section 18 and the outlet section 20. A mixing element 24 is also arranged and secured in the mixing section 22.

[0025] The cross-section of the mixing section 22 is also smaller than the cross-section of the outlet of the catalyst 12 and the inlet of the SCR filter 14.

[0026] The exhaust gas purification system 10 further comprises a reducing agent addition device 26 arranged on an outer side of the exhaust pipe 16. For this purpose, the exhaust pipe 16 has a mounting section 28, which is designed as a base element that protrudes outward from the outer side of the exhaust pipe 16. The reducing agent addition device 26 can be inserted into this mounting section 28.

[0027] In the mixing section 22, the introduced reducing agent is mixed with the exhaust gas, wherein the entire mixing section 22 forms a mixing section 29 which extends from the assembly section 28 to the outlet section 20 and comprises an inlet section and a follow-up section, as explained below.

[0028] The operation of the exhaust gas purification system 10 is described below.

[0029] The exhaust gas generated by an internal combustion engine is preferably guided downstream of the turbocharger through a first exhaust inlet nozzle 30 designed as an inverted funnel. The exhaust gas expands due to the provided widening and is introduced into the catalytic converter 12.

[0030] In the catalyst 12, which can be designed as a two-way oxidation catalyst, for example, up to 90% of carbon monoxide and hydrocarbons are removed. It can also reduce particulate matter by up to 30%, although this value is typically around 8-10%.

[0031] After the catalytic converter 12, the exhaust gases enter the inlet section 18 of the exhaust duct 16, which is designed as a funnel tapering in the direction of the exhaust flow, in particular as an inverted Fischer funnel. In the inlet section 18, the exhaust gas is compressed again due to the changing cross-section. Due to the compactness of the entire exhaust system 10, the inlet section 18 is designed with a tapered cross-section offset from the center and curved according to the invention.

[0032] The inlet section 18 initially directs the exhaust gas coming from the catalytic converter 12 away from the SCR filter 14, as can be seen from the walls of the inlet section 18, which are both oriented upwards in the figure, i.e. pointing away from the SCR filter 14.

[0033] The inlet section 18 of the exhaust pipe 16 is followed by the mixing section 22, wherein the fastening section 28 in the embodiment shown is provided at the transition from the inlet section 18 to the mixing section 22, in which the reducing agent addition device 26 is arranged.

[0034] In general, the mixing section 22 extends to the outlet section 20, wherein the mixing section 22 is continuously curved.

[0035] In the mixing section 22 itself, the mixing element 24 is arranged such that the mixing element 24 interacts with the reducing agent addition device 26. This means that the reducing agent addition device 26 is arranged in the fastening section 28 such that its spray pattern is precisely aligned with the mixing element 24, in particular impinging vertically.

[0036] The reducing agent addition device 26 is arranged upstream of the mixing element 24 in the exhaust gas flow direction, so that the exhaust gases can entrain the sprayed reducing agent, in particular a urea water solution, and apply it to the mixing element 24 evenly distributed over the circular cross section.

[0037] Furthermore, according to the invention, the reducing agent addition device 26 is arranged at an angle α inclined to and in the direction of the exhaust gas flow direction A on the pipe bend section of the exhaust duct 16. This is illustrated in the figure by the dashed line shifted parallel to the central axis of the reducing agent addition device 26.

[0038] The positioning is defined by the mounting section 28. This inclined orientation further improves the uniform distribution of the reducing agent across the cross-section. Improved uniform distribution, in turn, increases the effectiveness of mixing the reducing agent with the exhaust gases.

[0039] The reducing agent is premixed from the reducing agent addition device 26 via an injection section or an inlet section 32 before the exhaust gases with the reducing agent impinge on the actual mixing element 24.

[0040] The premixing section 32 is provided between the mixing element 24 and the inlet section 18, starting from the fastening section 28.

[0041] As already described, the mixing section 22 has a reduced cross-section compared to the inlet section 18. Furthermore, the cross-section of the mixing section 22 is essentially circular. Consequently, the cross-section of the mixing element 24 is also circular or nearly circular. The circular cross-section achieves a more uniform distribution of the reducing agent supplied to the mixing element 24, provided the center axis of the spray direction coincides with the center axis of the mixing element 24. This is the case in the illustrated embodiment. Therefore, the manufacture of an injection device of the reducing agent addition device 26 is also simplified compared to an elliptical cross-section, thereby reducing costs.

[0042] During operation, the mixing element 24 is hot due to the exhaust gases and causes the reducing agent to evaporate without droplet formation, so that it mixes evenly with the exhaust gases in the gaseous state in the downstream outlet section 20 before being fed to the SCRF 14 for further aftertreatment.

[0043] A trailing section 33 extends from the mixing element 24 to the outlet section 14, which, like the inlet section 32, is part of the mixing section 29. The trailing section 33 has a length that is greater than that of the inlet section 32, which is achieved by arranging the mixing element 24 in the mixing section 22.

[0044] The exhaust gas passing through the after-run section 33 reaches the SCR filter 14 via the outlet section 20.

[0045] The exhaust gases treated with the reducing agent are cleaned in the SCR filter 14. Before this conversion, the urea and water react chemically in a hydrolysis reaction to form ammonia and CO2. The produced ammonia reacts with NOx in the exhaust gases at operating temperature in the presence of the catalyst, producing nitrogen and water. Furthermore, soot particles are filtered out in the particulate filter. From the SCR filter 14, the cleaned exhaust gases flow through an exhaust outlet 34 into an exhaust pipe system (not shown).

[0046] The outlet section 20 can be designed as a Fischer funnel. This ensures that the exhaust gas flow impinges on the SCR filter 14 in a uniformly distributed manner. This allows for a uniform distribution of the mixed exhaust gas flow containing the reducing agent across the cross-section of the particulate filter or SCR catalyst or a single-piece SCRF unit.

[0047] Furthermore, the greatest possible running distance can be achieved in the smallest space.

[0048] The drawing also clearly shows that the exhaust duct 16 is curved overall, and even curved throughout. The curvature is selected such that, for example, a 90° angle is enclosed between the inlet of the inlet section 18 and the outlet of the outlet section 20. The inlet and outlet are the respective connection areas to the catalytic converter 12 and the SCR filter 14, respectively. The curvature of the exhaust duct 16 can vary in order to achieve the most compact arrangement possible for the exhaust gas purification system 10.

[0049] Due to the compact arrangement of the exhaust duct 16 and the entire exhaust gas purification system 10, the mixing element 24 is heated very quickly after a cold start of the internal combustion engine, so that the cold start phase with impaired exhaust gas purification performance is greatly shortened according to the invention.

[0050] Furthermore, according to the invention, the connecting channel 16 is capable of combining effective distribution of the reducing agent, preferably a urea-water solution, across the cross-section with a very short overall length due to the very sharp bend, which is expressed at an acute angle, through the inlet section 18 and the outlet section 20. This allows for greater compactness of a close-coupled exhaust gas purification system 10 with an SCR filter 14.

[0051] Furthermore, the distance between the components of the exhaust gas purification system 10 is very short. For example, a distance a between 10 and 50 mm can exist between the catalytic converter 12 and the SCR filter 14. This allows for rapid heat transfer through radiation and the short exhaust gas flow path in the exhaust duct 16, allowing both the SCR filter 14 and the mixing element 22 to reach their respective operating temperatures very quickly after a cold start. The exhaust gas purification system 10 has only one exhaust flow deflection, so that gas backpressure is not a problem at high gas mass throughput.

[0052] It can be provided that the mixing device has an edge gap 36 to the holding section, via which exhaust gas back pressure can be limited at high mass flow rates.

[0053] The reducing agent addition device 26 is arranged on the outer side of the curved exhaust duct 16, so that it does not collide with other components of the exhaust system 10 or the internal combustion engine. This makes it possible to install an exhaust gas purification system 10 on internal combustion engines of different sizes and arranged longitudinally or transversely with little or no modification, thus reducing manufacturing costs. The reducing agent addition device 26 is preferably controlled by a controller (not shown) in accordance with the combustion process, depending on the engine load.

[0054] This is particularly due to the fact that the inlet section 18 of the exhaust pipe 16 is designed such that the exhaust pipe 16 initially guides the exhaust gas away from the SCR filter 14. This results in a hooked shape of the exhaust pipe 16, which in particular corresponds to a gooseneck shape. Since the mounting section 28 is provided in the upper area of ​​the hooked exhaust pipe 16, it is better thermally decoupled from the hot engine components despite its close positioning.

[0055] The curved design of the exhaust pipe 16 and the arrangement of the mixing element 24, as well as the design of the inlet and outlet sections 18, 20 as Fischer funnels, enable a large mixing section 29 in a small space. This increases the effectiveness and efficiency of the exhaust gas purification system 10.

[0056] The exhaust gas purification system 10 can also be insulated from heat in order to protect it against overheating and to enable a shorter warm-up phase until the operating temperature is reached.

Claims

[1] An exhaust gas purification system (10) for an internal combustion engine, preferably a diesel engine, comprising a catalyst (12), a reducing agent addition device (26), a mixing element (24) for mixing the reducing agent with exhaust gases, and an SCR filter (14), which are arranged in particular downstream of an exhaust gas turbocharger, wherein an exhaust gas duct (16) is arranged between the catalyst (12) and the SCR filter (14), which has an inlet section (18) coupled to the catalyst (12) and an outlet section (20) coupled to the SCR filter (14), as well as a mixing section (22) arranged between the inlet section (18) and the outlet section (20), and the exhaust gas duct (16) is designed such that the exhaust gas from the catalyst (12) is guided away from the inlet of the SCR filter (14), at least in the inlet section (18), characterized bythat the exhaust gas duct (16) is continuously curved and a 90° angle is included between an inlet of the inlet section (18) and an outlet of the outlet section (20). [2] Exhaust gas purification system (10) according to claim 1, characterized by that the mixing section (22) has a smaller cross-section than the inlet, the outlet section (18, 20), the outlet of the catalyst (12) and / or the inlet of the SCR filter (14). [3] Exhaust gas purification system (10) according to claim 1 or 2, characterized by that a mixing section (29) is formed in the mixing portion (22), which in particular has a substantially circular cross-section and a strong curvature. [4] Exhaust gas purification system (10) according to one of claims 1 to 3, characterized bythat the mixing element (24) is arranged within the mixing section (22), in particular in the mixing section (29), such that a trailing section (33) between the mixing element (24) and the inlet of the SCR filter (14) is longer than an inlet section (32) between the outlet of the catalyst (12) and the mixing element (24). [5] Exhaust gas purification system (10) according to one of the preceding claims, characterized by that the reducing agent addition device (26) is arranged such that the reducing agent addition device (26) has an acute angle (α) to the exhaust gas flow direction, in particular less than 70 °. [6] Exhaust gas purification system (10) according to one of the preceding claims, characterized bythat the reducing agent addition device (26) is arranged on the exhaust gas duct (16), wherein the exhaust gas duct (16) has a mounting section (28) for the reducing agent addition device (26), which is designed in particular as a base element projecting outwards from the outer surface of the exhaust gas duct (16). [7] Exhaust gas purification system (10) according to one of the preceding claims, characterized by that the mixing element (24) has an edge gap (36) to the mixing section (22). [8] Exhaust gas purification system (10) according to one of the preceding claims, characterized by that the inlet section (18) and / or the outlet section (20) is designed as a Fischer funnel.

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