SE541714C2

SE541714C2 - Reducing agent dosing arrangement and exhaust gas system

Info

Publication number: SE541714C2
Application number: SE1750822A
Authority: SE
Inventors: Anders Gawell; Kurre Källkvist; Max Lindfors; Per Bremberg; Peter Engelke
Original assignee: Scania Cv Ab
Priority date: 2017-06-27
Filing date: 2017-06-27
Publication date: 2019-12-03
Also published as: DE102018004913A1; SE1750822A1

Abstract

The present invention relates to an exhaust gas system for an internal combustion engine (2). The exhaust gas system comprises a turbocharger turbine (6) and an exhaust gas duct (14) arranged downstream of the turbocharger turbine (6), the exhaust gas duct (14) being defined by a cylindrical duct wall with a longitudinally extending central axis (32). The exhaust gas system further comprises a dosing arrangement (20) for a reducing agent. The dosing arrangement comprises a dosing unit (22) comprising a valve means, and a dosing pipe (24) having an inlet end in contact with the dosing unit (22) and an outlet end (30) arranged in contact with exhaust gases in the exhaust gas duct (14), wherein the outlet end (30) of the dosing pipe is arranged in proximity to the longitudinally extending central axis (32) of the exhaust duct (14). The dosing arrangement further comprises an exhaust gas flow collector (26) fluidly connected to the dosing pipe (24) and arranged at a radial distance from the outlet end (30) of the dosing pipe in proximity to the cylindrical duct wall.

Description

Reducing agent dosing arrangement and exhaust gas system TECHNICAL FIELD The present invention relates to a reducing agent dosing arrangement for an exhaust gas system of an internal combustion engine. The present invention further relates to an exhaust gas system comprising such a reducing agent dosing arrangement as well as a vehicle comprising such an exhaust gas system.

BACKGROUND ART Due to strict environmental regulations, internal combustion engines, such as diesel engines, are provided with an exhaust gas purification system which comprises one or several devices to reduce both particles and emissions of environmentally harmful gases which result from the combustion of fuel during the operation of the internal combustion engine. Environmentally harmful discharges include e.g. carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (???) and particulate matter (PM). To regulate emissions or discharges from vehicles there are various standards and legal requirements which govern the permissible levels for exhaust discharges.

Emission reduction technologies suitable for diesel vehicles include exhaust gas recirculation (EGR), particulate filters, diesel oxidation catalysts (DOC), and selective catalytic reduction (SCR) system, which is used to reduce gaseous nitrogen oxide (NOx) -emissions from internal combustion engines. The SCR-system comprises a dosing system for dosing a reducing agent and a catalyst with an SCR-substrate. The reducing agent may be e.g. a mixture of 32.5% urea and water, often marketed with a trade name AdBlue<®>. In order to reduce substantially all NOx, large quantities of urea solution must be injected into the exhaust stream. If the exhaust stream is sufficiently hot, the solution will evaporate and decompose to ammonia. The exact temperature that this occurs at depends on the injected mass flow of urea: the greaterthe mass flow, the higher the temperature required. At sub-optimal temperatures the urea solution may instead form deposits on surfaces of the exhaust conduit. Such deposits may include crystallised urea, as well as urea decomposition by-products such as cyanuric acid. These deposits can be removed by heating the exhaust system at temperatures approaching 400 °C, but such temperatures are rarely achieved during normal operation of the vehicle and therefore, special procedures must be adopted to remove the exhaust deposits. Also, it may be difficult to reach efficient mixing of reducing agent with exhaust gases in order to achieve uniform distribution of the reducing agent over the entire surface area of SCR catalyst substrates. The space available for mixing is extremely limited and the reductant is commonly injected into the exhaust stream shortly upstream of the SCR catalyst substrates. In order to improve mixing a mixing device, often resembling a turbine blade, is arranged in the exhaust pipe. However, even when using a mixing device, it is difficult to achieve sufficiently uniform mixing. Moreover, the presence of a mixing device in the exhaust pipe acts as an obstruction to flow, causing higher pressure upstream of the mixer (backpressure) and reducing the engine efficiency.

There have been previous attempts have been made to improve mixing by utilising a turbocharger turbine for addition of additives to the exhaust stream. For example JP2007/128046 describes an exhaust gas purification device for an engine provided with a turbocharger. The exhaust gas purification device comprises an exhaust purification catalyst provided on a downstream side of the turbocharger in an exhaust passage of an engine and an injector which is provided at an upstream side of the exhaust purification catalyst and a downstream side of the turbocharger, and which faces the exhaust gas flow direction and injects the additive toward the discharge port of the turbocharger. However, there still remains a need for an improved means of adding a reductant to an exhaust stream.

SUMMARY OF THE INVENTION The inventors of the present invention have identified a number of shortcomings with regard to prior art solutions for providing a reducing agent to an exhaust stream. If the reductant dispensing device of a dosing unit is located too close to the exhaust duct, the high temperatures prevailing necessitate cooling of the dosing unit or risk leading to premature component failure, especially at locations upstream in the exhaust system such as at the outlet of a turbocharger turbine. However, if the dispensing device of the dosing unit is located remotely from the exhaust duct a means of conveying the reducing agent to the exhaust duct is required, such as a dosing pipe. Dispensed reducing agent may become trapped in such a dosing pipe, especially if the dispensing device of the dosing unit is not air-assisted and/or the dosing pipe is working against gravity. Trapped reducing agent may lead to clogging of the dosing pipe. Moreover, during start and stop of a dosing sequence there may be an error in the amount of reducing agent dosed to the exhaust duct due to reducing agent being trapped in the dosing pipe.

Therefore it would be desirable to achieve a dosing arrangement overcoming, or at least decreasing the above mentioned drawbacks. In particular, it would be desirable to obtain a dosing arrangement that permits use of an airless dosing device while reducing or alleviating problems with clogging, and/or errors in dosing quantity.

It is an objective of the present invention to better address one or more of these concerns. The objectives are attained by a dosing arrangement and an exhaust gas system having the features defined in the independent claims.

According to an aspect of the present invention, an exhaust gas system for an internal combustion engine is provided. The exhaust gas system comprises a turbocharger turbine and an exhaust gas duct arranged downstream of the turbocharger turbine, the exhaust gas duct being defined by a cylindrical duct wall with a longitudinally extending central axis. The exhaust gas system further comprises a dosing arrangement for a reducing agent. The dosing arrangement comprises a dosing unit comprising a valve means, and a dosing pipe having an inlet end in contact with the dosing unit and an outlet end arranged in contact with exhaust gases in the exhaust gas duct. The outlet end of the dosing pipe is arranged in proximity to the longitudinally extending central axis of the exhaust duct. The dosing arrangement further comprises an exhaust gas flow collector fluidly connected to the dosing pipe and arranged at a radial distance from the outlet end of the dosing pipe in proximity to the cylindrical duct wall. By radial distance is meant a distance in a plane perpendicular to the plane of the longitudinally extending central axis of the exhaust duct. The cross section of the exhaust duct can be circular, oval, elliptical or rectangular.

Such an exhaust gas system utilizes variations in exhaust gas velocities downstream of the turbocharger turbine in order to purge the dosing pipe of the dosing arrangement. In proximity to walls of the exhaust gas duct the exhaust gas velocity is much higher than at the central longitudinal axis of the exhaust gas duct, due to the wake of the turbocharger turbine. By arranging the exhaust gas flow collector in the high velocity region and the outlet of the dosing pipe in the low velocity region a pressure gradient is established in the dosing pipe which creates a directional flow from the inlet towards the outlet of the dosing pipe. This directional flow thus facilitates dosing of reducing agent from the dosing pipe and purging of trapped reducing agent from the dosing pipe. Thus, clogging of the dosing pipe is at least partly prevented and improved dosing accuracy is obtained.

The exhaust gas flow collector may be directly connected to the dosing pipe at a point within the interior of the exhaust gas duct. This permits the establishment of a purging flow in the dosing pipe without necessitating additional pipes traversing the wall of the exhaust duct.

The exhaust gas flow collector may be connected to the dosing pipe at a point exterior to the exhaust duct via an exhaust conveying pipe. This allows the dosing unit to be located remotely from the walls of the exhaust duct while still permitting a purging flow along substantially the entire length of the dosing pipe.

The exhaust gas flow collector may be fluidly connected to the dosing pipe at a point proximal to the inlet end of the dosing pipe. This facilitates a purging flow along substantially the entire length of the dosing pipe.

The exhaust gas flow collector may be a vane having an orifice arranged to collect a flow of exhaust gas downstream of the turbocharger turbine.

The dosing unit may comprise an airless injector as a dispensing device. Airless injectors are less energy-demanding since they do not require the production of compressed air. Moreover, airless injectors are a convenient solution in applications where a ready source of compressed air is not typically available, such as in marine engines.

The dosing pipe may be arranged to introduce dispensed reducing agent in a downstream direction within the exhaust duct. Due to the turbulence created by the turbocharger turbine, as well as because the turbocharger turbine is located far upstream in the exhaust system and has low thermal inertia, the reducing agent drops from such a pipe will be adequately vaporized and mixed with exhaust gas before reaching any after-treatment catalysts downstream of the turbine.

The dosing pipe may be arranged to introduce dispensed reducing agent in an upstream direction within the exhaust duct. For example, the dosing pipe may be arranged to introduce reducing agent onto a reducing agent dosing or distribution device mounted to a shaft or a hub of the turbocharger turbine. Such a distribution device utilizes the spinning motion of the turbine rotor to effectively distribute the reducing agent in the exhaust gas.

The dosing pipe may extend through a stopping device arranged centrally in an outlet of the turbocharger turbine. Such a stopping device may prevent the turbine rotor from escaping the turbine housing in the event of turbine failure, thus preventing damage to further engine components.

According to a further aspect of the present invention, the objects of the invention are achieved by a reducing agent dosing arrangement according to the appended claims.

The reducing agent dosing arrangement is suitable for an exhaust gas system of an internal combustion engine, and comprises a dosing unit comprising a valve means, a dosing pipe having an inlet end in contact with the dosing unit and an outlet end arranged at a distance from the dosing unit, and an exhaust gas flow collector fluidly connected to the dosing pipe and arranged at a distance from the outlet end of the dosing pipe.

The reducing agent dosing arrangement may comprise any of the features that are described herein in association with the dosing arrangement of the exhaust system. Specifically, the exhaust gas flow collector may be directly connected to the dosing pipe, or connected to the dosing pipe via an exhaust conveying pipe. The exhaust gas flow collector may be connected to the dosing pipe at a point proximal to the inlet end of the dosing pipe.

According to another aspect of the present invention, the objects of the invention are achieved by an internal combustion engine comprising an exhaust gas system or reducing agent dosing arrangement as described herein.

According to yet another aspect of the present invention, the objects of the invention are achieved by a vehicle comprising an exhaust gas system or reducing agent dosing arrangement as described herein.

Further objects, advantages and novel features of the present invention will become apparent to one skilled in the art from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of the present invention and further objects and advantages of it, the detailed description set out below should be read together with the accompanying drawings, in which the same reference notations denote similar items in the various diagrams, and in which: Fig. 1 schematically illustrates a vehicle comprising an exhaust system according to an embodiment of the invention.

Fig. 2 schematically illustrates an exhaust gas system wherein the dosing pipe is directed upstream and the exhaust gas flow collector in fluid communication with the dosing pipe via an exhaust conduit pipe.

Fig. 3 schematically illustrates an exhaust gas system wherein a distribution device is mounted to the shaft of the turbocharger turbine.

Fig. 4 schematically illustrates an exhaust gas system wherein a dosing pipe is directed downstream in the exhaust gas duct.

Fig. 5 schematically illustrates an exhaust gas system wherein the exhaust gas flow collector is directly attached to the dosing pipe.

Fig. 6 schematically illustrates an exhaust gas system wherein the dosing pipe extends through a stopping device.

DETAILED DESCRIPTION The present invention is based upon the realisation by the inventors that the exhaust gas velocity differential created downstream of the turbocharger can be utilized to create a pressure gradient within the dosing pipe, which in turn may be used to purge reducing agent from the dosing pipe. Immediately downstream of the turbocharger turbine, the swirl caused by the turbine results in high velocity gas flow at the walls of the exhaust duct, whereas in the wake of the turbine the exhaust gas velocity is low. By placing an exhaust gas flow collector in proximity to the wall of the exhaust duct and fluidly connecting the exhaust gas flow collector to the dosing pipe having its outlet in the wake of the turbine, a static pressure difference is created over the length of the dosing pipe, with high pressure at the dosing pipe inlet and low pressure at the dosing pipe outlet. The resulting pressure gradient drives fluid flow along the dosing pipe from the inlet to the outlet, purging any reducing agent deposited in the dosing pipe. This ensures that the dosing pipe if fully emptied of reducing agent, thus preventing clogging and ensuring accurate dosing of the reducing agent to the exhaust gas, even when the dosing pipe is orientated such that it is working against gravity. Thus, no external gas supply, such as pressurized air, is required to assist in purging the dosing pipe. A further advantage is that the hot exhaust gas flowing through the dosing pipe assists in vaporizing the reducing agent.

The reducing agent dosing arrangement of the present disclosure is located in an exhaust gas system for an internal combustion engine. The internal combustion engine may be any internal combustion engine, but is preferably a four-stroke combustion engine, even more preferably a compression ignition four-stroke combustion engine. The engine may be used in any application commonly known for internal combustion engines. It may for example be merchandized as a free-standing engine, for use for example in power generation or industrial settings. However, application in a vehicle is preferred. By vehicle it is meant any machine utilising an internal combustion engine to provide motive force, either directly, or indirectly as in the case of series hybrid vehicles. This includes, but is not limited to, motor vehicles such as cars, trucks and buses; railed vehicles such as trains and trams; watercraft such as ships and boats; and aircraft. The reducing agent is preferably diesel exhaust fluid comprising a solution of urea in water, in accordance with standard AUS 32 of ISO 22241. However, the reducing agent may also be another liquid additive added to the exhaust stream, such as hydrocarbon fuel to "burn off" a diesel particulate filter arranged downstream in the exhaust system. The reducing agent may alternatively be termed "reductant" or "reduction agent".

The exhaust gas system of the present invention comprises a turbocharger turbine, an exhaust gas duct arranged downstream of the turbine, and a reducing agent dosing arrangement.

The exhaust gas system is equipped with a turbocharger for recovering energy from the exhaust gases. The turbocharger comprises a turbine housed in turbine housing. A shaft connects the turbine to the impeller of a compressor for compressing the charge air of the internal combustion engine. This shaft may traverse the turbine, in which case the end of the turbine shaft extends outwardly at the outlet side of the turbine, or the shaft may terminate at a hub of the turbine, within the turbine. As described herein, the turbine may be equipped with a distribution device to assist in distributing the reducing agent in the exhaust gas.

An exhaust duct is connected downstream of the turbocharger for conveying exhaust gas from the turbocharger through the exhaust system towards downstream components, such as for example particulate filters, selective reduction catalysts, ammonia slip catalyst, etc. The exhaust duct is defined by a cylindrical duct wall with a longitudinally extending central axis. By cylindrical it is meant a cylinder having any cross-sectional shape known in the art, but most commonly circular-cylindrical. Any exhaust duct known in the art may be used. The velocity of the exhaust gas in the exhaust duct downstream of the turbocharger is uneven, with a high velocity flow in proximity to the walls of the exhaust duct and a low velocity flow centrally in the exhaust duct due to the wake of the turbine. It is this velocity differential that is utilized by the reducing agent dosing arrangement in order to improve dosing of the reducing agent.

The reducing agent dosing arrangement comprises a dosing unit, a dosing pipe and an exhaust gas flow collector.

The dosing device of the dosing unit in the reducing agent dosing arrangement may be a liquidonly device, otherwise known as an airless injector. This means that the dosing unit does not utilize compressed air in order to facilitate injection of the reductant into the exhaust conduit. Since a compressor requires energy to run, this represents an energy saving compared to airassisted systems. Moreover, some applications such as marine applications do not necessarily have a ready source of compressed air to hand, and thus the use ofextra, costly components can be avoided. However, the dosing device of the dosing unit may alternatively be an airassisted device, i.e. a device that utilises compressed air to facilitate injection of the reductant. The dosing unit may be a component of a reductant dosing system. Further components of the reductant dosing system may include a reductant storage tank, a control unit, and a pressurising device such as a pump.

Pressurised reductant may be supplied to the dosing unit via a supply channel. The dosing unit comprises a dispensing device which can be an electrically controllable valve means for dosing the required amount of reductant to the exhaust system. After passing the dosing unit, the reductant is transported from the dispensing device along a dosing pipe to the outlet of the dosing pipe. The dosing pipe may traverse the wall of the exhaust system at any suitable location, preferably downstream of the turbine. For example, the dosing pipe may pass through a port provided in the wall of the turbine housing, exhaust duct, or any exhaust system component located immediately downstream of the turbocharger, such as an exhaust brake.

The outlet of the dosing pipe is arranged to be located centrally in the exhaust gas duct, in a region having a lower exhaust gas velocity, and therefore a lower dynamic pressure, than regions located in the periphery of the exhaust gas duct. The outlet of the dosing pipe is preferably located in proximity to or at the central longitudinal axis of the exhaust gas duct.

The outlet opening of the dosing pipe may be directed in an upstream direction, such that reducing agent exiting the outlet is directed back towards the turbocharger turbine. In such a case, the turbochargerturbine may be equipped with a distribution device mounted on a central shaft or hub of the turbine. Such a distribution device is arranged to receive reducing agent and distribute it radially outwards by the centrifugal force generated by the spinning motion of the turbine. Suitable forms for a distribution device include cup-shaped, disc shaped, or nozzleshaped, and the distribution device may comprise channels to aid in the distribution of reducing agent in the exhaust gas.

Alternatively, the outlet opening of the dosing pipe may be directed in a downstream direction, away from the turbocharger turbine.

A stopping device may be located along the central longitudinal axis of the exhaust duct or turbine housing. Such a stopping device prevents the turbine from escaping the turbine housing or dismounting the turbine shaft in the event of failure, and may essentially abut the turbine or distribution device if present. If such a stopping device is present, the dosing pipe may pass through or be integrated in the body of the stopping device.

The reducing agent dosing arrangement comprises an exhaust gas flow collector. The exhaust gas flow collector is arranged to be located peripheral in the exhaust gas duct, in proximity to a wall of the exhaust gas duct. Such peripheral regions have higher exhaust gas velocity, and therefore higher dynamic pressure, than regions located more centrally in the exhaust gas duct. The exhaust gas flow collector is in fluid communication with the dosing pipe. By collecting the high velocity exhaust gas, the dynamic pressure difference between the exhaust gas flow collector and the outlet of the dosing pipe is converted to a static pressure gradient. This gradient causes a unidirectional fluid flow through the dosing pipe, from the inlet where the dosing unit is located, to the outlet. Therefore, reducing agent being dispensed in the dosing pipe by the dispensing device is conveyed by the directional fluid flow into the exhaust gas duct. This reduces the tendency of the dosing pipe to clog and increases the proportion of reducing agent that is successfully conveyed to the exhaust gas duct for each dosing event.

The exhaust gas flow collector may be any form suitable for collecting exhaust gas and converting it to a static pressure. For example, the exhaust gas flow collector may resemble a static vane having an orifice in fluid communication with the dosing pipe, or it may be shell-like.

The exhaust gas flow collector may be arranged directly in fluid communication with the dosing pipe, in which case the orifice of the exhaust gas flow collector opens directly into the dosing pipe. Alternatively, the exhaust gas flow collector may be connected in fluid communication with the dosing pipe via an exhaust conveying pipe. The point at which the exhaust gas flow collector is fluidly connected to the dosing pipe, either directly or via an exhaust conveying pipe, may be proximal to the inlet end of the dosing pipe. This ensures a pressure gradient along substantially the entire length of the dosing pipe and facilitates emptying of the dosing pipe.

The present invention will now be further illustrated with reference to the appended figures.

Figure 1 illustrates schematically a side view of a vehicle 1 according to an embodiment of the invention. The vehicle 1 includes a combustion engine 2, a first exhaust duct 4 leading to a turbocharger turbine 6, and a second exhaust duct 8 leading from the turbocharger turbine 6 to an SCR catalyst 10. A reductant dosing arrangement (not shown) is arranged in conjunction with the turbocharger turbine 6 and second exhaust duct 8. The vehicle 1 may be a heavy vehicle, e.g. a truck or a bus. The vehicle 1 may alternatively be a passenger car. The vehicle may be a hybrid vehicle comprising an electric machine (not shown) in addition to the combustion engine 2.

Figure 2 illustrates schematically an exhaust gas system according to an embodiment of the present invention. A turbocharger turbine 6 is shown in cross-section, the turbine 6 comprising a turbine housing 12. Located in the turbine housing 12 is a turbine rotor 18. Exhaust gas duct 14 is connected to the turbine housing 12 to lead exhaust gas away from the turbine 6. A reducing agent dosing arrangement 20 is arranged in association with the exhaust gas duct 14.

The reducing agent dosing arrangement 20 comprises a dosing unit 22 comprising a dosing device such as a valve means (not shown), dosing pipe 24, exhaust gas flow collector 26 and exhaust gas conveying pipe 28. The outlet end 30 of the dosing pipe 24 is arranged at the longitudinal central axis 32 of the exhaust duct 14 and is arranged to direct reducing agent upstream towards the turbine rotor 12. The exhaust gas flow collector 26 is arranged at the wall of the exhaust gas duct 14. Exhaust gas exiting the turbine 12 has an uneven velocity, with exhaust gas closer to the walls of the exhaust duct 14 having a higher velocity than exhaust gas in proximity to the central longitudinal axis 32 of the exhaust duct 14. By locating the exhaust flow collector 26 in the high velocity region and the dosing pipe outlet 30 in the low velocity region, a flow of exhaust gas is established along the length of the dosing pipe 24, from the inlet to the outlet 30. Thus, whenever reducing agent is dispensed to the dosing pipe by dosing unit 22, the flow of exhaust gas in the dosing pipe 24 ensures that substantially all of the reducing agent is conveyed to the exhaust gases in the exhaust duct 14 and that the dosing pipe 24 does not clog.

Figure 3 illustrates an embodiment of the present invention wherein a reductant distribution device 34 is fixed on the outlet end of the turbine shaft 36. In operation, the distribution device 34 spins in unison with the turbine rotor 18 and shaft 36 whenever exhaust gas passes through the turbine 6. Reductant such as urea solution, upon being deposited to the distribution device 34 from the dosing pipe 24, is dispersed in the exhaust gas passing through the turbine 6 by the spinning motion of the distribution device 34. The distribution device 34 is illustrated as a disc, but may be any other suitable form such as a cup or nozzle.

Figure 4 illustrates an embodiment of the present invention wherein the dosing pipe outlet 30 is directed downstream, away from turbine 6. Reducing agent leaving the outlet end 30 of the dosing pipe is entrained and vaporized by the swirling exhaust gas flow through the exhaust gas duct 14.

Figure 5 illustrates an embodiment wherein exhaust gas flow collector 26 is arranged directly on the dosing pipe 24, i.e. the orifice of the exhaust gas flow collector 26 leads directly into the dosing pipe 24.

Figure 6 illustrates an embodiment wherein a stopping device 38 is arranged in the exhaust gas duct 14 and turbine outlet in order to prevent the turbine rotor 18 from escaping the turbine housing 12 in the event of turbine failure. The stopping device is nearly abutting a distribution device 34 mounted on the shaft 36 of the turbine. The dosing pipe 24 extends through the stopping device 38, such that the outlet 30 of the dosing pipe 15 is flush with the end of the stopping device.

Note that that features may be added, modified or deleted as appropriate from the illustrated embodiments. Specifically, dosing pipe 24 may be directed upstream or downstream within the exhaust duct 14, turbine rotor 18 may or may not be equipped with a distribution device 34, and the exhaust flow collector 26 may or may not be fluidly coupled to the dosing pipe 24 via an exhaust conveying pipe 28.

Claims

1. An exhaust gas system for an internal combustion engine (2), wherein the exhaust gas system comprises a turbocharger turbine (6), an exhaust gas duct (14) arranged downstream of the turbocharger turbine (16), the exhaust gas duct (14) being defined by a cylindrical duct wall with a longitudinally extending central axis (32), and a dosing arrangement (20) for a reducing agent, wherein the dosing arrangement (20) comprises a dosing unit (22) comprising a valve means, and a dosing pipe (24) having an inlet end in contact with the dosing unit and an outlet end (30) arranged in contact with exhaust gases in the exhaust gas duct (14), characterised in that the outlet end (30) of the dosing pipe (15) is arranged in proximity to the longitudinally extending central axis (32) of the exhaust duct (14), and in that the dosing arrangement (20) further comprises an exhaust gas flow collector (26) arranged at a radial distance from the outlet end (30) of the dosing pipe in proximity to the cylindrical duct wall and wherein the exhaust gas flow collector (26) is fluidly connected to the dosing pipe (24).

2. An exhaust gas system according to claim 1, wherein the exhaust gas flow collector (26) is directly connected to the dosing pipe (24) at a point within the interior of the exhaust gas duct (14).

3. An exhaust gas system according to claim 1, wherein the exhaust gas flow collector (26) is connected to the dosing pipe (24) at a point exterior to the exhaust duct (14) via an exhaust conveying pipe (28).

4. An exhaust gas system according to any one of the preceding claims, wherein the exhaust gas flow collector (26) is fluidly connected to the dosing pipe (24) at a point proximal to the inlet end of the dosing pipe.

5. An exhaust gas system according to any one of the preceding claims, wherein the exhaust gas flow collector (26) is a vane having an orifice arranged to collect a flow of exhaust gas downstream of the turbocharger turbine (6).

6. An exhaust gas system according to anyone of the preceding claims, wherein the dosing unit (22) comprises an airless injector.

7. An exhaust gas system according to anyone of the preceding claims, wherein the dosing pipe (24) is arranged to introduce dispensed reducing agent in a downstream direction within the exhaust duct (14).

8. An exhaust system according to any one of the preceding claims, wherein the dosing pipe (24) is arranged to introduce dispensed reducing agent in an upstream direction within the exhaust duct (14).

9. An exhaust system according to claim 8, wherein the dosing pipe (24) is arranged to introduce reducing agent onto a reducing agent distribution device (34) mounted to a shaft (36) or a hub of the turbocharger turbine.

10. An exhaust system according to any one the preceding claims, wherein the dosing pipe (24) extends through a stopping device (38) arranged centrally in an outlet of the turbocharger turbine (6).

11. A reducing agent dosing arrangement (20) for an exhaust gas system of an internal combustion engine, wherein the dosing arrangement (20) comprises a dosing unit (22) comprising a valve means, and a dosing pipe (24) having an inlet end in contact with the dosing unit (22) and an outlet end (30) arranged at a distance from the dosing unit (22), characterised in that the dosing arrangement (20) further comprises an exhaust gas flow collector (26) fluidly connected to the dosing pipe (24) and arranged at a distance from the outlet end (30) of the dosing pipe.

12. A reducing agent dosing arrangement according to claim 11, wherein the exhaust flow collector (26) is directly connected to the dosing pipe (24).

13. A reducing agent dosing arrangement according to claim 11, wherein the exhaust flow collector (26) is connected to the dosing pipe (24) via an exhaust conveying pipe (28).

14. A reducing agent dosing arrangement according to any one of claims 11-13, wherein the exhaust gas flow collector (26) is connected to the dosing pipe (24) at a point proximal to the inlet end of the dosing pipe.

15. A vehicle (1), comprising an exhaust gas system according to any one of claims 1-10 or a reducing agent dosing arrangement (20) according to any one of claims 11-14.