DE102014206907A1 - Emission control system for diesel engines - Google Patents

Abstract

An exhaust gas purification system (10) for an internal combustion engine, preferably a diesel engine, is described, comprising a catalytic converter (12), a reducing agent adding device (26), a mixing device (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. Between the catalyst (12) and the SCR filter (14), an exhaust passage (16) is arranged, which has an input portion (18) which is formed so that exhaust gas from the catalyst (12) at least in the input portion (18) from Input of the SCR filter (14) is led away.

Description

The invention relates to an emission control system.

It is known that the combustion gases of internal combustion engines contain polluting gases and particles harmful to the environment and health, and are therefore subject to ever stricter standards and requirements. In particular, CO ₂ , NOx and soot particles are the target of the developers of environmentally friendly combustion engines and applications. The efforts are directed on the one hand to lower consumption and on the other hand to the active cleaning of the combustion gases. The purifying measures include catalysts which chemically alter the noxious gases to 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 a while to reach it after a cold start.

In general, exhaust gas systems are known from the prior art, which include a catalyst and a selective catalytic reduction (SCRF). The catalyst can be designed either as an oxidation catalyst (DOC), as an active nitrogen oxide catalyst (NSC) or as a passive nitrogen oxide storage catalyst (PNA). The SCRF simultaneously reduces nitrogen oxides (NOx) and soot particles in exhaust gases of an internal combustion engine by combining two technologies in one, namely a selective catalytic reduction (SCR) catalyst that 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.

The catalyst (DOC, NSC or PNA) and the SCRF are typically connected to each other by means of an exhaust pipe, wherein within the exhaust pipe, a reducing agent is supplied to the exhaust gas to purify the exhaust gas. It has been found that the effectiveness and efficiency of the exhaust gas purification processes are dependent on several components, which, however, are in contradiction to the general requirements, such as compact design.

The invention has for its object to provide an exhaust gas purification system for an internal combustion engine, in particular a diesel engine, the exhaust gas cleaning is effective despite its compact design.

The object is achieved by an exhaust gas purification system comprising a catalyst, a reducing agent adding device, a mixing device for mixing the reducing agent with exhaust gases and an SCR filter, which are arranged in particular downstream of an exhaust gas turbocharger, wherein between the catalyst and the SCR filter an exhaust passage is arranged, which has an input portion which is formed so that the exhaust gas is led away from the catalyst at least in the input section from the input of the SCR filter. The basic idea of the invention provides that the exhaust gas is initially led away from the SCR filter through the exhaust gas channel, that is to say that the exhaust gas does not take the shortest route to the input of the SCR filter. The exhaust pipe has a diversion. This can be a better location for the other components in the emission control system can be realized. In addition, the exhaust gas can generally travel a greater distance within the exhaust pipe despite the small installation space.

An aspect of the invention provides that the exhaust gas duct also comprises an outlet section and a mixing section which is arranged between the inlet section and the outlet section, wherein the mixing section has a smaller cross-section than the inlet, the outlet section, the outlet of the catalyst and / or the Input of the SCR filter has. This ensures that the exhaust gas is compressed in the region of the mixing section, whereby the exhaust gas can be better mixed there with the reducing agent. Furthermore, the exhaust pipe is thus formed smaller in the region of the mixing section, so that more space is available for other components of the exhaust system.

According to a further aspect of the invention, a mixing section is formed in the mixing section, which in particular has a substantially circular cross-section and a high curvature. About the geometry of the mixing section, a large running distance of the exhaust gas is achieved in a small space. Further, the reducing agent can be more effectively and uniformly mixed with the exhaust gases. The circular or nearly circular cross section improves the uniformity of the distribution of the reducing agent in the exhaust gas before impinging on the subsequent component of the exhaust gas purification system.

The cross section of the holding section may in particular be of the order of magnitude of the remaining exhaust gas pipes. Typically, the cross section is predetermined depending on the working volume of the internal combustion engine.

Depending on the exhaust gas flow to be cleaned by the exhaust gas purification system, that is to say in proportion to the working volume of the internal combustion engine, a cross section can be predetermined according to the invention. The reduced cross section results in smaller outer Kühlabstrahloberflächen, whereby the mixing device reaches a higher temperature faster. The reducing agent can thereby be evaporated more effectively, so that the formation of non-evaporated droplets is prevented.

According to a further aspect of the invention, the mixing element within the mixing section, in particular in the mixing section, arranged such that a follow-up distance between the mixing element and the input of the SCR filter is longer than the inlet path 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 allows a smaller cross-sectional area for the mixing area, 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 noxious gas, in particular NOx.

According to a further aspect of the invention, the reducing agent-adding device is arranged such that the reducing agent-adding device has an acute angle to the exhaust gas flow direction, in particular less than 70 °. The reducing agent introduced into the exhaust gas channel thus does not slow down the exhaust gas flow, but has essentially the same flow direction. As a result, the beam drift can be minimized and a better mixing can be achieved even before the impact on the mixing device.

In particular, the reducing agent-adding device is arranged on the exhaust gas passage, wherein the exhaust gas channel has a mounting section for the reducing agent-adding device, which is in particular designed as a base element projecting outwardly from the outer surface of the exhaust gas channel. By doing so, it can be ensured that the reducing agent adding device is properly oriented, so that the reducing agent is efficiently introduced, thereby improving the purification of the exhaust gas. The arrangement of the reducing agent-adding device on the outer surface of the exhaust passage also ensures that the reducing agent-adding device does not collide with other parts of the emission control system and remains easily accessible. As a reducing agent, a urea water solution is preferably used.

Another aspect of the invention provides that the exhaust duct is curved, in particular continuously curved. Due to the curvature, a sufficiently long mixing section can be provided. Furthermore, the exhaust gas flow can be better directed via the geometry of the exhaust gas duct.

In particular, an angle may be formed between the input of the input section and the output of the output section that is substantially 90 degrees or slightly different therefrom. As a result, a compact arrangement of the exhaust system can be achieved. The exhaust passage or the output section also serves as an inlet port of the downstream SCRF. Likewise, this allows a close arrangement of the components of the exhaust gas purification system with each other and a close-coupled arrangement of the entire exhaust system, which allows rapid heating of the catalysts and filters after a cold start.

According to a further preferred embodiment, the mixing device has an edge gap to the holding section. The exhaust gas backpressure can be limited at high mass flow rates via the marginal gap.

Another aspect of the invention provides that the input section and / or the output section is designed as a Fischer funnel. Fischer funnels are Abgaseinlass- or Abgasauslassstutzen which supply the coming of an internal combustion engine of a motor vehicle exhaust gas from a tube with a relatively small cross section over a large area of a catalyst coating an exhaust aftertreatment device. As nozzle-like transition pieces, they have a conically widening funnel and on the outlet side an oblique section of the component. The oblique cut generally swivels the gas flow. However, a Fischer funnel may be reversed when used as an exhaust outlet port which supplies exhaust gas from a catalyst to another treatment unit, the cross-section decreasing. The input section is designed in particular as a reverse Fischer funnel. About the trained as a Fischer funnel entrance and exit section a large running distance is achieved despite limited space.

The design of the output section as a Fischer funnel, with an exhaust flow skewed obliquely to the face of the SCR filter, ensures that gas flow separations and non-uniform distribution of the reductant across the cross-sectional area of the SCR filter are avoided. This is especially true if not all the reducing agent is vaporized at the mixing element and droplets are allowed to pass through.

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

The only drawing shows an emission control system 10 which may preferably be arranged directly after a turbocharger (not shown). The arrows indicate the exhaust gas flow direction.

The emission control system 10 includes a catalyst 12 , an SCR filter 14 and an exhaust duct connecting these two components 16 , With the catalyst 12 it can be a DOC, NSC or PNA.

The exhaust duct 16 has several sections, an input section 18 that with the catalyst 12 is coupled, and an output section 20 that with the SCR filter 14 is coupled. Furthermore, the exhaust duct 16 a mixing section 22 on, which has a smaller cross section than the input section 18 and the exit section 20 Has. In the mixing section 22 is also a mixing element 24 arranged and fastened.

The cross section of the mixing section 22 is also smaller than the cross-section of the exit of the catalyst 12 and the input of the SCR filter 14 ,

Furthermore, the emission control system includes 10 a reductant addition device 26 located on an outside of the exhaust pipe 16 is arranged. The exhaust pipe 16 has a mounting section for this purpose 28 on, which is designed as a base element, that of the outside of the exhaust pipe 16 protrudes outwards. In this mounting section 28 may be the reducing agent adding device 26 be used.

In the mixing section 22 the introduced reducing agent is mixed with the exhaust gas, wherein the entire mixing section 22 a mixed route 29 forms, extending from the mounting section 28 to the outlet section 20 extends and includes an inlet section and a caster track, as will be explained below.

Furthermore, the mode of action of the exhaust gas purification system 10 described.

The exhaust gas produced by an internal combustion engine is preferred after the turbocharger by a first exhaust inlet port designed as an inverted funnel 30 guided. Due to the expansion provided, the exhaust gas expands and becomes the catalyst 12 initiated.

In the catalyst 12 For example, which may be embodied as a 2-way oxidation catalyst, for example, up to 90% of the carbon monoxide and hydrocarbons are removed. It can also reduce particulate matter by up to 30%, with the value typically around 8-10%.

After the catalyst 12 enter the exhaust gases in the input section 18 the exhaust duct 16 formed as a funnel tapering in the exhaust gas flow direction, in particular as a reverse Fischer funnel. In the entrance section 18 the exhaust gas is compressed again due to the changing cross section. The entrance section 18 is due to the compactness of the entire exhaust system 10 formed with a displaced from the center and bent inventive tapered cross-section.

The entrance section 18 directs this out of the catalyst 12 coming exhaust first by the SCR filter 14 away, as from the walls of the entrance section 18 which are both oriented upwards in the figure, ie from the SCR filter 14 groundbreaking.

To the entrance section 18 of the exhaust pipe 16 closes the mixing section 22 on, wherein the attachment portion 28 in the embodiment shown at the transition from the input section 18 to the mixing section 22 is provided, in which the reducing agent-adding device 26 is arranged.

Generally, the mixing section extends 22 to the outlet section 20 , where the mixing section 22 is formed continuously curved.

In the mixing section 22 itself is the mixing element 24 arranged such that the mixing element 24 with the reducing agent adding device 26 interacts. This means that the reducing agent adding device 26 such in the attachment section 28 arranged is that her spray pattern exactly on the mixing element 24 is aligned, in particular perpendicular.

The reductant addition device 26 is in the exhaust gas flow direction in front of the mixing element 24 arranged so that the exhaust gases entrain the sprayed reducing agent, in particular a urea water solution, and on the mixing element 24 distributed over the circular cross-section can apply evenly.

The reductant addition device 26 is further inclined according to the invention at an angle α to and in the direction of the exhaust gas flow direction A at the pipe bend portion of the exhaust duct 16 arranged. This is indicated in the figure by the center axis of the reducing agent adding device 26 parallel dashed line illustrates,

The positioning is via the attachment section 28 Are defined. By this inclined orientation, a further improvement in the uniform distribution of the reducing agent over the Cross section reached. An improved uniform distribution in turn increases the effectiveness of the mixing of the reducing agent with the exhaust gases.

The reducing agent is removed from the reducing agent adding device 26 via an injection section or an inlet section 32 premixed before the exhaust gases with the reducing agent to the actual mixing element 24 incident. The premix route 32 is between the mixing element 24 and the entrance section 18 provided, from the attachment section 28 emanates.

As already described, the mixing section 22 a reduced cross-section compared to the input section 18 on. Further, the cross section of the mixing section 22 formed substantially circular. In the sequence is also the cross section of the mixing element 24 also circular or nearly circular. Due to the circular cross-section, a more even distribution of the mixing element 24 supplied reducing agent, provided that the central axis of the spray direction with the central axis of the mixing element 24 matches. This is the case in the embodiment shown. Therefore, the manufacture of an injector of the reducing agent adding device is also simplified 26 compared to an elliptical cross-section, which can reduce costs.

The mixing element 24 is hot in operation by the exhaust gases and causes evaporation of the reducing agent without droplet formation, so that they are in the gaseous state in the downstream output section 20 mixed evenly with the exhaust gases before proceeding to a further aftertreatment of the SCRF 14 be supplied.

From the mixing element 24 to the exit section 14 extends a caster track 33 that are like the inlet section 32 Part of the mixing section 29 is. The caster track 33 has a running length that is greater than that of the inlet section 32 is, this being the arrangement of the mixing element 24 in the mixing section 22 is reached.

That the trail distance 33 Passed exhaust gas reached via the outlet section 20 the SCR filter 14 ,

The exhaust gases acted upon by the reducing agent are in the SCR filter 14 cleaned. Before this conversion, the urea and water react chemically in a hydrolysis reaction to ammonia and CO ₂ . The generated ammonia reacts with NOx of the exhaust gases at an operating temperature in the presence of the catalyst and produces nitrogen and water. Furthermore, soot particles in the particulate filter are filtered out. From the SCRF 14 The cleaned exhaust gases pass through an exhaust outlet 34 in an exhaust pipe string (not shown).

The exit section 20 can be designed as a Fischer funnel. This ensures that the exhaust gas flow evenly on the SCR filter 14 distributed impinges. Thus, a uniform distribution of the mixed exhaust gas flow applied with the reducing agent can be effected across the cross section of the particulate filter or SCR catalyst or a one-piece SCRF unit.

Furthermore, the largest possible running distance can be achieved in a small space.

From the drawing is also easy to see that the exhaust duct 16 is curved overall, where it is even curved throughout. The curvature is chosen so that, for example, a 90 ° angle between the input of the input section 18 and the output of the output section 20 is included. The input and the output are the respective connection areas to the catalyst 12 or the SCR filter 14 , The curvature of the exhaust duct 16 can vary to a compact arrangement of the emission control system 10 to reach.

Due to the compact arrangement of the exhaust duct 16 and the entire emission control system 10 becomes the mixing element 24 heated very quickly after a cold start of the internal combustion engine, so that the cold start phase with deteriorated emission control performance is greatly reduced according to the invention.

The connection channel 16 is also according to the invention by the very strong bend, which is reflected at an acute angle, through the input section 18 and the exit section 20 capable of combining an effective distribution of the reducing agent, preferably a urea water solution, over the cross section with a very short overall length. This allows a higher compactness of a near-engine exhaust purification system 10 with an SCR filter 14 be achieved.

In addition, there is a very short distance between the components of the emission control system 10 , So can between the catalyst 12 and the SCR filter 14 there is a distance a between 10 and 50 mm. As a result, the heat by radiation and the short exhaust gas flow path in the exhaust duct 16 transferred quickly, so that both the SCR filter 14 as well as the mixing element 22 can be brought to their respective operating temperature very quickly after a cold start. The emission control system 10 has only one exhaust flow deflection, so that thereby the gas back pressure at high gas mass flow rate is not a problem.

It can be provided that the mixing device has an edge gap 36 to the holding section, can be limited by the exhaust backpressure at high mass flow rates.

The reductant addition device 26 is on the outer side of the curved exhaust duct 16 arranged so that they do not interfere with other components of the exhaust system 10 or the internal combustion engine comes into collision. This makes it possible, without or with only minor changes an emission control system 10 to arrange at different sized and in longitudinal or transverse arrangement trained internal combustion engines and so to reduce manufacturing costs. The reductant addition device 26 is preferably controlled by a controller (not shown) in accordance with the combustion process depending on engine load.

This is due in particular to the fact that the input section 18 of the exhaust pipe 16 is formed so that the exhaust pipe 16 the exhaust gas first from the SCR filter 14 leads away. This has a hook shape of the exhaust pipe 16 result, which corresponds in particular to a gooseneck shape. Because the mounting section 28 in the upper region of the hook-shaped exhaust pipe 16 is provided, this is thermally decoupled from the hot engine components despite the positioning close to the engine.

About the curved design of the exhaust pipe 16 and the arrangement of the mixing element 24 and the execution of the input and output sections 18 . 20 As a Fischer funnel is a large mixing section 29 possible in a small space. This increases the effectiveness and efficiency of the emission control system 10 ,

The emission control system 10 Further, it can be isolated from heat to protect it against overheating as well as allowing a shorter warm-up period to reach operating temperature.

Claims (9)

Emission control system ( 10 ) for an internal combustion engine, preferably a diesel engine, with a catalyst ( 12 ), a reducing agent adding 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, characterized in that between the catalyst ( 12 ) and the SCR filter ( 14 ) an exhaust duct ( 16 ) is arranged, which has an input section ( 18 ), which is designed so that the exhaust gas from the catalyst ( 12 ) at least in the input section ( 18 ) from the input of the SCR filter ( 14 ) is led away. Emission control system ( 10 ) according to claim 1, characterized in that the exhaust duct ( 16 ) an output section ( 20 ) and a mixing section ( 22 ) located between the input section ( 18 ) and the output section ( 20 ), wherein the mixing section ( 22 ) has a smaller cross section than the input, the output section ( 18 . 20 ), the output of the catalyst ( 12 ) and / or the input of the SCR filter ( 14 ) Has. Emission control system ( 10 ) according to claim 1 or 2, characterized in that a mixing section ( 29 ) in the mixing section ( 22 ) is formed, which in particular has a substantially circular cross-section and a strong curvature. Emission control system ( 10 ) according to one of claims 1 to 3, characterized in that the mixing element ( 24 ) within the mixing section ( 22 ), especially in the mixing section ( 29 ), is arranged such that a caster track ( 33 ) between the mixing element ( 24 ) and the input of the SCR filter ( 14 ) longer than an inlet line ( 32 ) between the exit of the catalyst ( 12 ) and the mixing element ( 24 ). Emission control system ( 10 ) according to one of the preceding claims, characterized in that the reducing agent adding device ( 26 ) is arranged such that the reducing agent adding device ( 26 ) has an acute angle (α) to the exhaust gas flow direction, in particular less than 70 °. Emission control system ( 10 ) according to one of the preceding claims, characterized in that the reducing agent adding device ( 26 ) at the exhaust duct ( 16 ), wherein the exhaust duct ( 16 ) a mounting section ( 28 ) for the reducing agent adding device ( 26 ), in particular as from the outer surface of the exhaust passage ( 16 ) is formed outwardly projecting base element. Emission control system ( 10 ) according to one of the preceding claims, characterized in that the exhaust gas channel ( 16 ) is curved, in particular continuously curved. Emission control system ( 10 ) according to one of the preceding claims, characterized in that the mixing element ( 24 ) an edge gap ( 36 ) to the mixing section ( 22 ) having. Emission control system ( 10 ) according to one of the preceding claims, characterized in that the input section ( 18 ) and / or the output section ( 20 ) is designed as a Fischer funnel.

Images