NO20170418A1

NO20170418A1 - Exhaust gas after-treatment system and internal combustion engine

Info

Publication number: NO20170418A1
Application number: NO20170418A
Authority: NO
Inventors: Andreas Döring; Plamen Toshev; Francis Nana
Original assignee: Man Diesel & Turbo Se
Priority date: 2016-03-31
Filing date: 2017-03-16
Publication date: 2017-10-02
Also published as: KR102299818B1; JP6893814B2; FI20175263A7; JP2017187034A; CN107269356B; KR20170113432A; DE102016003743A1; CN107269356A; FI20175263A

Description

Exhaust gas after-treatment system and internal combustion engine

The invention relates to an exhaust gas after-treatment system of an internal combustion engine. The invention, furthermore, relates to an internal combustion engine with an exhaust gas after-treatment system.

In combustion processes in stationary internal combustion engines, which are employed for example in power plants, and in combustion processes in non-stationary internal combustion engines, which are employed for example on ships, nitrogen oxides are created, wherein these nitrogen oxides are typically created during the combustion of sulphur-containing, fossil fuels such as coal, pit coal, crude oil, heavy fuel oil or diesel fuels. For this reason, such internal combustion engines are assigned exhaust gas after-treatment systems which serve for the cleaning, in particular denitrification of the exhaust gas leaving the internal combustion engine.

For reducing nitrogen oxides in the exhaust gas, so-called SCR catalytic converters are primarily employed in exhaust gas after-treatment systems known from practice. In an SCR catalytic converter, a selective catalytic reduction of nitrogen oxides takes place, wherein for the reduction of the nitrogen oxides ammonia (Nhb) as reduction agent is required. The ammonia or an ammonia precursor substance, such as for example urea, is introduced for this purpose into the exhaust gas in liquid form upstream of the SCR catalytic converter, wherein the ammonia or the ammonia precursor substance is mixed with the exhaust gas upstream of the SCR catalytic converter. To this end, mixing sections between the introduction of the ammonia or of the ammonia precursor substance and the SCR catalytic converter are provided according to practice.

Although with exhaust gas after-treatment systems known from practice, which comprise an SCR catalytic converter, an exhaust gas after-treatment, in particular a nitrogen oxide reduction, can already successfully take place, there is a need for further improving the exhaust gas after-treatment systems. There is in particular a need for making possible an effective exhaust gas after-treatment with a compact design of such exhaust gas after-treatment systems.

Starting out from this, the object of the present invention is based on creating a new type of exhaust gas after-treatment system of an internal combustion engine and an internal combustion engine with such an exhaust gas after-treatment system.

This object is solved through an exhaust gas after-treatment system of an internal combustion engine according to Claim 1. According to the invention, at least one blow-down device is positioned within the reactor chamber, which serves for purging the SCR catalytic converter. Clogging up of the SCR catalytic converter as a consequence of soot particles being deposited there can thus be avoided. A particularly effective exhaust gas after-treatment with compact design of the exhaust gas after-treatment system can be ensured.

According to an advantageous further development of the present invention, the or each blow-down device is orientated in such a manner that the same brings about a vortex flow or a swirl flow on a surface of the SCR catalytic converter running transversely to the flow direction, in particular on an upstream surface of honeycomb bodies of the SCR catalytic converter running transversely, preferentially perpendicularly to the flow direction. Clogging up of the SCR catalytic converter as a consequence of soot particles being deposited on the same can thus be particularly effectively avoided. An effective exhaust gas cleaning can be ensured with compact design of the exhaust gas after-treatment system.

According to an advantageous further development of the present invention, the reactor chamber has a wall that is round in cross section, in particular a circular wall. This is preferred for forming the vortex flow or swirl flow. This makes possible a particularly effective exhaust gas after-treatment with compact design.

According to a further advantageous development of the present invention, each blow-down device is positioned adjacent to the wall of the reactor chamber that is round in cross section and blows, emanating from the wall to the inside into the reactor chamber, namely with a blowing cone, which intersects the blowing cone of at least one other blow-down device. This is preferred for forming the vortex flow or swirl flow and for the full-area purging of the soot particles.. This makes possible a particularly effective exhaust gas after-treatment with compact design

According to a further advantageous further development, the exhaust gas feed line opens with a downstream end into a reactor chamber receiving the SCR catalytic converter, wherein within the reactor chamber between the downstream end of the exhaust gas feed line and the SCR catalytic converter a device for increasing an exhaust gas backpressure is positioned upstream of the SCR catalytic converter. With the help of the device for increasing the exhaust gas backpressure upstream of the SCR catalytic converter, the exhaust gas flow upstream of the SCR catalytic converter is stemmed, as a result of which it can be achieved that the SCR catalytic converter is evenly supplied with the exhaust gas flow, namely seen in circumferential direction and also in radial direction. Because of this, an effective exhaust gas cleaning can be ensured with compact design of the exhaust gas after-treatment system. Furthermore, soot particles can be deposited on the device for increasing the exhaust gas backpressure, which can then no longer enter the region of the SCR catalytic converter clogging the same. This also serves for ensuring an effective exhaust gas cleaning with compact design of the exhaust gas after-treatment system

Preferentially, the or each blow-down device is positioned within the reactor chamber between the device for increasing an exhaust gas backpressure and the SCR catalytic converter. The or each blow-down device then serves at least for purging the SCR catalytic converter and preferentially additionally the purging of the device for increasing an exhaust gas backpressure. This further development makes possible a particularly effective exhaust gas after-treatment with compact design.

The internal combustion engine according to the invention is defined in Claim 11.

Preferred further developments of the invention are obtained from the subclaims and the following description. Exemplary embodiments of the invention are explained in more detail by way of the drawing without being restricted to this. There it shows: Fig. 1: a schematic perspective view of an internal combustion engine with an exhaust gas after-treatment system according to the invention; Fig. 2: a detail of the exhaust gas after-treatment system of Fig. 1; Fig. 3: a detail of Fig. 2;

Fig. 4 a cross section through the detail of Fig. 3.

The present invention relates to an exhaust gas after-treatment system of an internal combustion engine, for example of a stationary internal combustion engine in a power plant or in a non-stationary internal combustion engine employed on a ship. In particular, the exhaust gas after-treatment system is employed on a diesel engine on a ship operated with heavy fuel oil.

Fig. 1 shows an arrangement of an internal combustion engine 1 with an exhaust gas turbocharger system 2 and an exhaust gas after-treatment system 3. The internal combustion engine 1 can be a non-stationary or stationary internal combustion engine, in particular a non-stationarily operated internal combustion engine of a ship. Exhaust gas, which leaves the cylinders of the internal combustion engine 1, is utilised in the exhaust gas supercharging system 2, in order to extract mechanical energy from the thermal energy of the exhaust gas for compressing charge air to be fed to the internal combustion engine 1. Accordingly,

Fig. 1 shows an internal combustion engine 1 with an exhaust gas turbocharger system 2, which comprises a plurality of exhaust gas turbochargers, namely a first exhaust gas turbocharger 4 on the high-pressure side and a second exhaust gas turbocharger 5 on the low-pressure side. Exhaust gas which leaves the cylinders of the internal combustion engine 1 initially flows via a high-pressure turbine 6 of the first exhaust gas turbocharger 1 and is expanded in the same, wherein energy extracted in the process is utilised in a high-pressure compressor of the first exhaust gas turbocharger 4 in order to compress charge air. Seen in flow direction of the exhaust gas downstream of the first turbocharger 4 the second exhaust gas turbocharger 5 is arranged, via which exhaust gas, which has already flowed through the high-pressure turbine 6 of the first exhaust gas turbocharger 4, is conducted, namely via a low-pressure turbine 7 of the second exhaust gas turbocharger 5. In the low-pressure turbine 7 of the second exhaust gas turbocharger 5 the exhaust gas is further expanded and energy extracted in the process utilised in a low-pressure compressor of the second exhaust gas turbocharger 5 in order to likewise compress the charge air to be fed to the cylinders of the internal combustion engine 1.

In addition to the exhaust gas supercharging system 2 comprising the exhaust gas turbochargers 4 and 5, the internal combustion engine 1 comprises the exhaust gas after-treatment system 3, which is an SCR exhaust gas after-treatment system. The SCR exhaust gas after-treatment system 3 is connected between the high-pressure turbine 6 of the first compressor 5 and the low-pressure turbine 7 , so that exhaust gas, which leaves the high-pressure turbine 6 of the first exhaust gas turbocharger 4, can be initially conducted via the SCR exhaust gas after- treatment system 3 before the same reaches the region of the low-pressure turbine 7 of the second exhaust gas turbocharger 5.

Fig. 1 shows an exhaust gas feed line 8, via which exhaust gas, emanating from the high-pressure turbine 6 of the first exhaust gas turbocharger 4 can be conducted in the direction of an SCR catalytic converter 9, which is arranged in a reactor chamber 10. Fig. 1, furthermore, shows an exhaust gas discharge line 11, which serves for discharging the exhaust gas from the SCR catalytic converter 9 in the direction of the low-pressure turbine 7 of the second exhaust gas turbocharger 5. Emanating from the low-pressure turbine 7, the exhaust gas flows via a line 21 in particular into the open. The exhaust gas feed line 8 leading to the reactor chamber 10 and thus to the SCR catalytic converter 9 positioned in the reactor chamber 10 and the exhaust gas discharge line 11 leading away from the reactor chamber 10 and thus from the SCR catalytic converter 9 are coupled via a bypass 12 in which a shut-off element 13 is integrated. With closed shut-off element 13, the bypass 12 is closed so that no exhaust gas can flow via the same. By contrast, in particular when the shut-off element 13 is opened, exhaust gas can flow via the bypass 12, namely past the reactor chamber 10 and accordingly past the SCR catalytic converter 9 positioned in the reactor chamber 10. Fig. 2 illustrates with arrows 14 the flow of the exhaust gas through the exhaust gas after-treatment system 3 with the bypass 12 closed via the shut-off element 13, wherein it is evident from Fig. 2 that the exhaust gas feed line 8 opens into the reactor chamber 10 with a downstream end 15, wherein the exhaust gas in the region of this end 15 of the exhaust gas feed line 8 is subjected to a flow deflection by approximately 180°, wherein the exhaust gas after the flow deflection is conducted via the SCR catalytic converter 9.

The exhaust gas feed line 8 of the exhaust gas after-treatment system 3 is assigned an introduction device 16, via which in the exhaust gas flow a reduction agent can be introduced, in particular ammonia or an ammonia precursor substance, which is required in order to convert nitrogen oxides of the exhaust gas in the region of the SCR catalytic converter 9 in a defined manner. This introduction device 16 of the exhaust gas after-treatment system 3 is preferentially an injection nozzle, via which the ammonia or the ammonia precursor substance is injected into the exhaust gas flow within the exhaust gas feed line 8. Fig. 2 illustrates with a cone 17 the injection of the reduction agent into the exhaust gas in the region of the exhaust gas feed line 8.

The section of the exhaust gas after-treatment system 3, which seen in flow direction of the exhaust gas is located downstream of the introduction device 16 and upstream of the SCR catalytic converter 9, is described as mixing section. In particular, the exhaust gas feed line 8 provides a mixing section 18 downstream of the introduction device 16, in which the exhaust gas can be mixed with the reduction agent upstream of the SCR catalytic converter 9.

The exhaust gas feed line 8 opens with the downstream end 15 into the reactor chamber 10. This downstream end 15 of the exhaust gas feed line 8 is assigned a baffle element 20, which can be displaced relative to the downstream end 15 of the exhaust gas feed line 8. In the shown exemplary embodiment, the baffle element 20 can be linearly displaced relative to the end 15 of the exhaust gas feed line 8, which opens into the reactor chamber 10. The baffle element 20 can be displaced relative to the downstream end 15 of the exhaust gas feed line 8 in order to either shut off the exhaust gas feed line 8 at the downstream end 15 or open the same at the downstream end 15. In particular when the baffle element 20 shuts off the exhaust gas feed line 8 at the downstream end 15, the shut-off element 13 of the bypass 12 is preferentially opened in order to then conduct the exhaust gas completely past the SCR catalytic converter 9 or the reactor chamber 10 receiving the SCR catalytic converter 9. In particular when the baffle element 20 opens the downstream end 15 of the exhaust gas feed line 8, the shut-off element 13 of the bypass 12 can either be completely closed or at least partially opened.

In particular when the baffle element 20 opens the downstream end 15 of the exhaust gas feed line 8, the relative position of the baffle element 20 relative to the downstream end 15 of the exhaust gas feed line 8 is dependent in particular on the exhaust gas mass flow through the exhaust gas feed line 8 and/or on the exhaust gas temperature of the exhaust gas in the exhaust gas feed line 8 and/or on the quantity of the reduction agent introduced into the exhaust gas flow via the introduction device 16.

A further function of the baffle element 20 with opened downstream end 15 of the exhaust gas feed line 8 consists in that any droplets of liquid reduction agent present in the exhaust gas flow reach the baffle element where they are intercepted and atomised in order to avoid that such drops of liquid reduction agent reach the region of the SCR catalytic converter 9. By way of the relative position of the baffle element 20 relative to the downstream end 15 of the exhaust gas feed line 8 with opened downstream end 15 it can be determined in particular whether the exhaust gas, which is deflected in the region of the downstream end 15 of the exhaust gas feed line 8 in the region of the baffle element 20, is conducted or steered more in the direction of sections positioned radially inside or more in the direction of sections of the SCR catalytic converter 9 positioned radially outside.

According to a preferred embodiment, the exhaust gas feed line 8 is expanded funnel-like in the region of the downstream end 15 forming a diffuser. Because of this, the flow cross section of the exhaust gas feed line 8 increases in the region of the downstream end 15, wherein, as is evident in particular from Fig. 2, it can be provided that seen in flow direction of the exhaust gas upstream of the downstream end 15 of the exhaust gas feed line 8 the flow cross section of the same initially diminishes. Accordingly, Fig. 2 shows that the flow cross section of the exhaust gas feed line 8 seen in flow direction of the exhaust gas downstream of the introduction device 16 for the reduction agent is initially approximately constant, but then initially tapers gradually and finally expands in the region of the downstream end 15.

This expansion of the flow cross section at the downstream end 15 of the exhaust gas feed line 8 in this case is preferentially effected via a shorter section of the exhaust gas feed line 8 than that section via which the exhaust gas feed line 8 initially tapers in front of the downstream end 15.

Preferentially, the baffle element 20 is curved, preferentially bell-like curved on a side 22 facing the exhaust gas feed line 8 forming a flow guide for the exhaust gas. Accordingly, the side of the baffle element 20, which faces the downstream end 15 of the exhaust gas feed line 8, has a smaller distance on a radially inner section of the baffle element 20 to the downstream end 15 of the exhaust gas feed line 8 than on a radially outer section of the same. Accordingly, the baffle element 20 is drawn in or curved in the centre in the direction of the downstream end 15 of the exhaust gas feed line 8 against the flow direction of the exhaust gas.

As already explained, the exhaust gas feed line 8 with its downstream end 15 opens into the reactor chamber 10, which receives the SCR catalytic converter 9. Here, the exhaust gas feed line 8, according to Fig. 2, penetrates a lower side of the reactor chamber 10 and ends with its downstream end 15 adjacent to an upper side 23 of the reactor chamber 10 wherein, as already explained, the exhaust gas, which leaves the exhaust gas feed line at the downstream end 15, is deflected by 180° before the same subsequently flows via the SCR catalytic converter 9.

As is evident in particular from Fig. 3, a device 25 for increasing an exhaust gas backpressure is positioned upstream of the SCR catalytic converter 9 between the downstream end 15 of the exhaust gas feed line 8 and the SCR catalytic converter 9. This device 25 for increasing the exhaust gas backpressure can for example be a grid, a perforated plate or the like.

With the help of the device 25 for increasing the exhaust gas backpressure upstream of the SCR catalytic converter 9, the exhaust gas flow upstream of the SCR catalytic converter 9 is stemmed, as a result of which it can be achieved that the SCR catalytic converter 9 is evenly supplied with the exhaust gas flow, namely seen in circumferential direction and also in radial direction.

The device 25 for increasing the exhaust gas backpressure furthermore has the advantage that soot particles, which are contained in the exhaust gas, can be deposited on the same. Those soot particles, which are deposited on the device 25 for increasing the exhaust gas backpressure can no longer reach the region of the SCR catalytic converter 9 clogging the same, namely honeycomb bodies 27 of the same. Fig 3 and 4 show a plurality of honeycomb bodies 27 of the SCR catalytic converter 9, which are round in cross section.

The device 25 for increasing the exhaust gas backpressure furthermore has a free flow cross section which corresponds to maximally 2 times, preferably maximally 1 times, particularly preferably maximally 0.5 times the free flow cross section of the SCR catalytic converter 9 or of the honeycomb bodies 27 of the SCR catalytic converter 9. In this way, evening-out of the exhaust gas flow over the SCR catalytic converter 9 can be ensured on the one hand while it can be ensured on the other hand that soot particles are already deposited in the region of the device 25 for increasing the exhaust gas backpressure and no longer reach the region of the SCR catalytic converter 9.

Preferentially, a ratio between the thickness or length of the device 25 for increasing the exhaust gas backpressure seen in flow direction or exhaust gas flow direction and the thickness or length of the SCR catalytic converter 9 or of the honeycomb bodies 27 of the SCR catalytic converter 9 seen in flow direction or exhaust gas flow direction amounts to at least 1:50, preferably at least 1:100, particularly preferably at least 1:200.

Preferentially, a ratio between the distance, which corresponds to the distance between the device 25 for increasing the exhaust gas backpressure and the SCR catalytic converter 9 seen in flow direction or in exhaust gas flow direction, and the thickness or length of the SCR catalytic converter 9 or of the honeycomb bodies 27 or the SCR catalytic converter 9 seen in flow direction amounts to maximally 2:1, preferably maximally 1:1, particularly preferably maximally 1:2.

By way of the device 25 for increasing the exhaust gas backpressure positioned in the reactor chamber 10, an even supply of the SCR catalytic converter 9 with exhaust gas can be ensured. By increasing the exhaust gas backpressure the exhaust gas flow is stemmed and because of this an even distribution of the exhaust gas over the SCR catalytic converter 9 ensured. A further advantage of the device 25 for increasing the exhaust gas backpressure is in that in the same likewise assumes the function of a pre-separator, on which soot particles, which are contained in the exhaust gas, can be deposited. Because of this it can be prevented that the soot particles reach the SCR catalytic converter 9 without obstruction, clogging the same.

Within the reactor chamber 10, at least one blow-down device 24 is positioned, which serves for purging the SCR catalytic converter 9. In the shown, preferred exemplary embodiment, the or each blow-down device 24 is positioned within the reactor chamber 10, in which the SCR catalytic converter 9 and additionally the device 25 for increasing the exhaust gas backpressure are received, wherein the or each blow-down device 24 seen in flow direction of the exhaust gas is arranged between the device 25 for increasing the exhaust gas backpressure and the SCR catalytic converter 9. The or each blow-down device 25 is preferentially an air nozzle. The or each blow-down device 24 serves at least for purging the SCR catalytic converter 9 with respect to soot particles being deposited on the same and preferentially also for purging the device 25 for increasing the exhaust gas backpressure, in order to avoid clogging up of the SCR catalytic converter 9 and preferentially also of the device 25 for increasing the exhaust gas backpressure. The or each blow-down device 24 is preferentially orientated in such a manner that the same brings about a vortex flow or swirl flow on a surface of the SCR catalytic converter 9 running transversely to the flow direction, namely on an upstream surface of honeycomb bodies 27 of the SCR catalytic converter 9 running perpendicularly to the flow direction.

Here, Fig. 4 shows the preferred orientation of the or each blow-down device 24 which is preferentially orientated in such a manner that the vortex flow or swirl flow is generated within the reactor chamber 10, namely on the upstream surface of the SCR catalytic converter 9 running perpendicularly to the flow direction or exhaust gas flow direction and preferentially also on a downstream surface of the device 25 for increasing the exhaust gas backpressure running perpendicularly to the flow direction or exhaust gas flow direction, wherein the surfaces in each case face the or each blow-down device 24. By way of a vortex flow or swirl flow, the purging of soot particles from the SCR catalytic converter 9, namely the honeycomb bodies 27 of the same, and preferentially also from the device 25 for increasing the exhaust gas backpressure, can take place particularly effectively.

The reactor chamber 10, in which the SCR catalytic converter 9 and preferentially also the device 25 for increasing the exhaust gas backpressure are received, preferentially has a wall 19 that is preferentially round in cross section, in particular circular, which extends between the lower side 22 and the upper side 23 of the reactor chamber 10. At least the wall 19 is round or circular in cross section on an inside, which defines an interior space of the reactor chamber 10 receiving at least the catalytic converter 9. By way of such a wall 19 combined with the orientation of the or each blow-down device 24, the vortex flow or swirl flow within the reactor chamber 10, which serves for purging the SCR catalytic converter 9 and preferentially also the purging of the device 25 for increasing the exhaust gas backpressure, can be designed particularly advantageously with respect to the soot particles being deposited on the same.

Preferentially, a plurality of blow-down devices 24 is positioned in the reactor chamber 10, preferentially at least there, particularly preferably at least four blow-down devices 24.

Here, the blow-down devices 24 are positioned adjacent to the reactor chamber 10 that is round in cross section and blow air or compressed air, emanating from this wall 19, to the inside into the reactor chamber 10 namely with a blowing cone 26, which intersects the blowing cone 26 of at least one other blow-down device 24 thus partly overlapping the same. Because of this, a full-area purging of the SCR catalytic converter 9 and preferentially also of the device 25 for increasing the exhaust gas backpressure on the abovementioned surfaces can be realised or ensured.

The invention makes possible an effective exhaust gas after-treatment with compact design.

In the case of the internal combustion engine 1 of Fig. 1, the exhaust gas after-treatment system 3 is positioned upright upstream of the exhaust gas supercharging system 2. Access to the cylinders of the internal combustion engine 1 is free but accessibility of the turbochargers 4 and 5 is restricted. However, the reactor chamber 10 can be simply disassembled when maintenance work becomes necessary on the exhaust gas turbochargers 4, 6.

In contrast with the upright arrangement of the exhaust gas after-treatment 3 upstream of the exhaust gas supercharging system 2 shown in Fig. 1, a horizontal arrangement of the exhaust gas after-treatment system 3 tilted by 90° next to the exhaust gas supercharging system 2 is also possible, wherein however in the case of such a horizontal arrangement the length of the arrangement grows. However, internal combustion engine 1 and exhaust gas supercharging system 2 are then available for maintenance operations without restrictions without the need for disassembling the reactor chamber 10.

List of reference numbers

Claims

1. An exhaust gas after-treatment system (3) of an internal combustion engine, namely SCR exhaust gas after-treatment system of an internal combustion engine, with an SCR catalytic converter (9) received in a reactor chamber (10), with an exhaust gas feed line (8) leading to the reactor chamber (10) and thus to the SCR catalytic converter (9) and with an exhaust gas discharge line (11) leading away from the reactor chamber (10) and thus from the SCR catalytic converter (9) with an introduction device (16) assigned to the exhaust gas feed line (8) for introducing a reduction agent, in particular ammonia or an ammonia precursor substance, into the exhaust gas, and with a mixing section (8) provided by the exhaust gas feed line (8) downstream of the introduction device (16) for mixing the exhaust gas with the reduction agent upstream of the reactor chamber (10) or SCR catalytic converter (9),characterized in thatwithin the reactor chamber (10) at least one blow-down device (24) is positioned, which serves for purging the SCR catalytic converter (9).

2. The exhaust gas after-treatment system according to Claim 1,characterized inthat the or each blow-down device (24) is orientated in such a manner that the same brings about a vortex flow or swirl flow on a surface of the SCR catalytic converter (9) running transversely, in particular perpendicularly to the flow direction.

3. The exhaust gas after-treatment system according to Claim 2,characterized inthat the or each blow-down device (24) is orientated in such a manner that the same brings about the vortex flow or swirl flow on an upstream surface of honeycomb bodies (27) of the SCR catalytic converter (9) running transversely, in particular perpendicularly to the flow direction.

4. The exhaust gas after-treatment system according to any one of the Claims 1 to 3,characterized in thatthe reactor chamber (10) has a wall (19) that is round in cross section, in particular a circular wall.

5. The exhaust gas after-treatment system according to Claim 4,characterized inthat each blow-down device (24) is positioned adjacent to the wall (19) of the reactor chamber (10) that is round in cross section and blows emanating from the wall (19) to the inside into the reactor chamber (10), namely with a blowing cone (26) which intersects the blowing cone (26) of at least one other blow-down device (24).

6. The exhaust gas after-treatment system according to any one of the Claims 1 to 5,characterized in thatthe exhaust gas feed line (8) with a downstream end (15) opens into the reactor chamber (10) and in that within the reactor chamber (10) between the downstream end (15) of the exhaust gas feed line (8) and the SCR catalytic converter (9) a device (25) for increasing an exhaust gas backpressure upstream of the SCR catalytic converter (9) is positioned.

7. The exhaust gas after-treatment system according to Claim 6,characterized inthat the or each blow-down device (24) is positioned within the reactor chamber (10) between the device (25) for increasing an exhaust gas backpressure and the SCR catalytic converter (9).

8. The exhaust gas after-treatment system according to Claim 6 or 7,characterized in thatthe device (25) for increasing the exhaust gas backpressure has a free flow cross section which corresponds to maximally two times, preferably maximally one times, particularly preferably 0.5 times of a free flow cross section of the SCR catalytic converter (9).

9. The exhaust gas after-treatment system according to any one of the Claims 6 to 8,characterized in thata ratio between the thickness or length of the device (25) for increasing the exhaust gas backpressure seen in flow direction and the thickness or length of the catalytic converter (9) seen in flow direction amounts to at least 1:50, preferably at least 1:100, particularly preferably at least 1:200.

10. The exhaust gas after-treatment system according to any one of the Claims 6 to 9,characterized in thata ratio between a distance, which corresponds to the distance between the device (25) for increasing the exhaust gas backpressure and the SCR catalytic converter (9) seen in flow direction, and the thickness or length of the SCR catalytic converter (9) seen in flow direction, amounts to maximally 2:1, preferably maximally 1:1, most preferably maximally 1:2.

11. An internal combustion engine (1), in particular with an internal combustion engine operated with a diesel fuel or with a heavy fuel oil fuel, with an exhaust gas after-treatment system (3) according to any one of the Claims 1 to 10.

12. The internal combustion engine according to Claim 11,characterized in thatthe same comprises a multi-stage exhaust gas supercharging system (2) with a first exhaust gas turbocharger (4) comprising a high-pressure turbine (6) and a second exhaust gas turbocharger (5) comprising a low-pressure turbine (7), wherein the exhaust gas after-treatment system (3) is connected between the high-pressure turbine (6) and the low-pressure turbine (7).