GB2570313A

GB2570313A - Exhaust gas treatment apparatus

Info

Publication number: GB2570313A
Application number: GB1800846.6A
Authority: GB
Inventors: Ximena Odio Narvaez Maria
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-01-19
Filing date: 2018-01-19
Publication date: 2019-07-24
Anticipated expiration: 2038-01-19
Also published as: DE102019200161A1; GB201800846D0; GB2570313B

Abstract

The present disclosure relates to a system 1 for an internal combustion engine 3, comprising an exhaust conduit 8 and a bypass conduit 9. A selective catalytic reduction (SCR) catalyst 16 is disposed in the exhaust conduit. Means 17 for introducing a reductant upstream of the SCR catalyst is disposed in the bypass conduit. A vehicle V incorporates the system. The bypass conduit may bypass the engine and a turbine of a turbocharger 4. A bypass inlet valve 13 and a bypass outlet valve 15, may be check valves and may be controllable to control the mass flow rate of gas through the bypass conduit. The reductant introducing means may comprise an injector. The reductant introducing means may comprise a wick (21, fig 3A) having a gas permeable portion (23, fig 3A) through which gases pass, having a porous structure with a plurality of pores to draw a urea solution from a reservoir (24, fig 3A) through capillary action to the gas permeable portion.

Description

EXHAUST GAS TREATMENT APPARATUS

TECHNICAL FIELD

The present disclosure relates to exhaust gas treatment apparatus. Particularly, but not exclusively, the present disclosure relates to a system and to a vehicle.

BACKGROUND

It is known to introduce a reductant, such as a Urea Water Solution (UWS), into the exhaust system of a diesel engine to abate nitrogen oxides (NOx) present in exhaust gases. The UWS is typically sprayed into the exhaust as liquid droplets which change to a gaseous phase and decompose to form gaseous ammonia. The gaseous ammonia reacts with the NOx in the presence of a Selective Catalytic Reduction (SCR) catalyst to form nitrogen (N₂) and water (H₂O). The UWS is introduced into the exhaust system upstream of the SCR catalyst to allow mixing of the gaseous ammonia and the exhaust gases. There are, however, potential limitations of this approach. The introduction of the UWS into the exhaust gases as droplets is inefficient as it may decompose into biurets and melamine, which reduces the amount of ammonia produced. Additionally, at low temperatures urea can form solid deposits around the injector and on the walls, thus reducing the amount of ammonia available. Moreover, urea droplets may not evaporate completely in the exhaust free stream or when impinging on surfaces. The droplets may be transported with the exhaust gases to the inlet of the SCR catalyst, which may result in uneven distribution of ammonia.

At least in certain embodiments the present invention seeks to overcome at least some of the aforementioned problems.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a system and to a vehicle as claimed in the appended claims.

According to a further aspect of the present invention there is provided a system for an internal combustion engine, the system comprising:

an exhaust conduit;

a bypass conduit;

a selective catalytic reduction (SCR) catalyst disposed in said exhaust conduit; and means for introducing a reductant upstream of the SCR catalyst;

wherein said reductant introducing means is disposed in the bypass conduit. In use, the reductant is introduced into the bypass conduit and transported to the SCR catalyst. The internal combustion engine may be a diesel engine or a gasoline engine. In use, exhaust gas from the internal combustion engine travels through the exhaust conduit. The SCR catalyst is provided to abate nitrogen oxides (NOx) in the exhaust gases. In the presence of the SCR catalyst, the reductant converts nitrogen oxides (NOx) present in the exhaust gases into diatomic nitrogen (N₂) and water (H₂O). The reductant is introduced into the bypass conduit and is transported into the exhaust conduit. The reductant is introduced into the exhaust conduit upstream of the SCR catalyst.

The reductant may be a liquid reductant. The reductant may comprise a urea water solution (UWS).

The system may comprise a turbocharger having a turbine and a compressor. The compressor may be adapted to supply air to the internal combustion engine at a pressure greater than atmospheric pressure. The turbine may be adapted to be driven by the exhaust gases. The turbine may be disposed in a front section of the exhaust conduit. The SCR catalyst may be disposed in a rear section of the exhaust conduit.

The bypass conduit may comprise a bypass inlet and a bypass outlet. The bypass inlet and/or the bypass outlet may be connected to the exhaust conduit.

The bypass conduit may be adapted to bypass the turbine of the turbocharger. The bypass inlet may be connected to the exhaust conduit upstream of the turbine. For example, the bypass inlet may be disposed between an exhaust port of the internal combustion engine and the turbine. The bypass inlet may be disposed in an exhaust manifold connected to the internal combustion engine. The bypass outlet may be connected to the exhaust conduit downstream of the turbine. The bypass outlet may be connected to the exhaust conduit between the turbine and the SCR catalyst.

The bypass conduit may be arranged to supply air from the compressor to the SCR catalyst at a pressure greater than atmospheric pressure. The bypass conduit may be adapted to bypass the internal combustion engine. The bypass conduit may be arranged to bypass the turbine. The bypass inlet may be connected downstream of the compressor. The bypass inlet may be connected between the compressor and an inlet of the internal combustion engine. The bypass outlet may be connected to the exhaust conduit downstream of the turbine. The bypass outlet may be connected to the exhaust conduit between the turbine and the SCR catalyst.

The system may comprise a bypass inlet valve and a bypass outlet valve. The bypass inlet valve and/or the bypass outlet valve may comprise a check valve. The bypass inlet valve and/or the bypass outlet valve may be controllable to control the mass flow rate of gas through the bypass conduit. The system may comprise a controller for controlling said bypass inlet valve and/or said bypass outlet valve. The controller may be configured to control said bypass inlet valve and/or said bypass outlet valve to control the dosage of the reductant supplied to the SCR catalyst.

The bypass outlet may be connected to the exhaust conduit. The bypass outlet may be connected to the exhaust conduit upstream of the SCR catalyst. The bypass outlet may be disposed downstream of the turbocharger. More particularly, the bypass outlet may be disposed downstream of the turbine of the turbocharger. The bypass outlet may connect to said exhaust conduit upstream of the SCR catalyst.

The reductant introducing means may comprise an injector nozzle or a vaporizer. Alternatively, the reductant introducing means may comprise a wick. The wick may be disposed in said bypass conduit. The wick may extend into a reductant reservoir. The wick may, for example, comprise a stem disposed into said reductant reservoir. The wick may comprise a wick structure suitable for supplying the reductant through capillary action. Suitable wick structures include a wire screen, a sintered metal, a metal foam, a metal felt, a woven wire mesh and axial grooves. In use, capillarity forces may draw the reductant through the wick. The reductant may be evaporated from a surface of the wick. Thus, the reductant may be dispersed into the gas in said bypass conduit.

The wick may comprise a gas permeable portion through which gases pass in use. The gas permeable portion may have a porous structure comprising a plurality of pores. The pores may be open to draw a urea solution from a reservoir through capillary action to said gas permeable portion. The pores may be sixed to control the flow rate of gas through the gas permeable member. The wick may, for example, comprise a plurality of micro-pores.

In use, gas may pass over an outer surface of said wick. The gas may evaporate the reductant from the outer surface of said wick.

Alternatively, or in addition, the gas permeable portion may be arranged at least partially to obstruct the flow of gas through the bypass conduit. The gas permeable portion may be adapted such that, in use, gas flowing through the bypass conduit passes through the gas permeable portion. The gas may help to clean the wick, for example by displacing solid deposits. Alternatively, or in addition, solid deposits in the wick may be eliminated when the gas passing through the wick is at a high temperature.

The gas permeable portion could extend at least partially across the bypass conduit. The gas permeable portion may comprise an annular wall which forms a hollow chamber in said wick. The hollow chamber may have a gas inlet in fluid communication with the bypass inlet. In use, gas may be introduced into said hollow chamber through the gas inlet and passes through the annular wall. In use, at least a portion of the gas in the bypass conduit may be introduced into said hollow chamber.

Alternatively, the hollow chamber may comprise a gas outlet in fluid communication with the bypass outlet. In use, gas may pass through the annular wall into said hollow chamber and exit through the gas outlet.

The reductant introducing means may comprise a pump for pumping the reductant. The reductant introducing means may comprise an injector for injecting the urea solution into said bypass conduit. The injector may comprise a vaporiser or an atomiser.

The system may comprise an inlet bypass control valve for controlling the flow of gas through said bypass inlet; and/or an outlet bypass control valve for controlling the flow of gas through said bypass outlet. The inlet bypass control valve and/or the outlet bypass control valve may control the flow of gas through the bypass conduit. The inlet bypass control valve and/or the outlet bypass control valve may be controlled in dependence on one or more operating parameters of the internal combustion engine.

According to a further aspect of the present invention there is provided a vehicle comprising an exhaust system as described herein.

Any control unit or controller described herein may suitably comprise a computational device having one or more electronic processors. The system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller” or “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. To configure a controller or control unit, a suitable set of instructions may be provided which, when executed, cause said control unit or computational device to implement the control techniques specified herein. The set of instructions may suitably be embedded in said one or more electronic processors. Alternatively, the set of instructions may be provided as software saved on one or more memory associated with said controller to be executed on said computational device. The control unit or controller may be implemented in software run on one or more processors. One or more other control unit or controller may be implemented in software run on one or more processors, optionally the same one or more processors as the first controller. Other suitable arrangements may also be used.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which:

Figure 1 shows a schematic representation of a vehicle incorporating an exhaust system in accordance with an embodiment of the present invention;

Figure 2 shows a schematic representation of the exhaust system of the vehicle shown in Figure 1;

Figure 3A shows a vertical section through a dispensing wick for use in the exhaust system shown in Figure 2;

Figure 3B shows a horizontal section through the dispensing which Figure 3A; and Figure 4 shows a schematic representation of a system in accordance with a further embodiment of the present invention.

DETAILED DESCRIPTION

A system 1 incorporating an exhaust system 2 in accordance with an embodiment of the present invention will now be described with reference to Figures 1 to 3. The system 1 described herein is for use in a vehicle V, such as an automobile, but it will be understood that the present invention is applicable in other applications.

As shown in Figure 1, the system 1 is connected to an internal combustion engine 3. In the present embodiment the internal combustion engine 3 is a diesel engine configured to combust diesel fuel. In alternative embodiments, the internal combustion engine 3 may combust other fuels, such as gasoline. The exhaust gases from the combustion process are expelled from the internal combustion engine 3 into the exhaust system 2. The system 1 comprises a turbocharger 4 to provide forced induction of the internal combustion engine 3. The turbocharger 4 comprises a turbine 5 disposed in a turbine chamber and driven by the exhaust gases from the internal combustion engine 3. The turbine 5 is drivingly connected to a compressor 6 (shown in Figure 2) which supplies air to the internal combustion engine 3 at a pressure greater than atmospheric pressure. The system 1 comprises one or more aftertreatment systems (denoted generally by the reference numeral 11) for treating the exhaust gases. The aftertreatment system(s) 11 are disposed in the rear section 8B of the exhaust conduit 8 downstream of the turbine 5.

The exhaust system 2 comprises an exhaust manifold 7, an exhaust conduit 8, a bypass conduit 9 and a tailpipe 10. The exhaust conduit 8 comprises a front section 8A and a rear section 8B. The exhaust manifold 7 connects to the internal combustion engine 3 and, in use, receives exhaust gases. The turbine chamber is disposed in the front section 8A of the exhaust conduit 8 and, in use, exhaust gas from the internal combustion engine 3 enters the turbine chamber and rotates the turbine 5. The bypass conduit 9 is arranged to bypass the turbocharger 4 such that a portion of the exhaust gases introduced into the exhaust system 2 is diverted around the turbocharger 4. The bypass conduit 9 comprises a bypass inlet 12, a bypass inlet valve 13, a bypass outlet 14 and a bypass outlet valve 15. In the present embodiment the bypass inlet 12 is connected to the front section 8A of the exhaust conduit 8 and the bypass outlet 14 is connected to the rear section 8B of the exhaust conduit 8. The bypass inlet valve 13 and the bypass outlet valve 15 are operable to control the flow of exhaust gas through the bypass conduit 9. In the present embodiment the bypass inlet valve 13 and the bypass outlet valve 15 are both (one-way) check valves.

With reference to Figure 2, the aftertreatment system(s) 11 are adapted to treat the exhaust gases before they are expelled from the tailpipe 10. In the present embodiment, the aftertreatment system(s) 11 comprise a selective catalytic reduction (SCR) catalyst 16 for abating NOx emissions. A reductant (reducing agent), such as anhydrous ammonia, aqueous ammonia or urea, is introduced to the exhaust gas. The reductant is stored in a liquid form and in the present embodiment is a urea water solution (UWS). In the presence of the SCR catalyst 16, the reductant converts nitrogen oxides (NOx) present in the exhaust gases into diatomic nitrogen (N₂) and water (H₂O) which are emitted from the tailpipe 10.

The reductant is introduced into the exhaust gas upstream of the SCR catalyst 16. In accordance with an aspect of the present invention the reductant is introduced into the exhaust gas in the bypass conduit 9.

The exhaust system 2 comprises apparatus 17 for distributing the UWS in the exhaust gases in the bypass conduit 9. The apparatus 17 comprises means (denoted generally by the reference numeral 18 in Figure 1) for introducing the reductant into the exhaust gas. The reductant introducing means 18 is disposed between a gas inlet 19 and a gas outlet 20 of said apparatus 17. In the present embodiment the reductant introducing means 18 comprises a wick 21 disposed in the bypass conduit 9. The wick 21 has a wick structure for supplying the UWS through capillary action. The wick 21 is composed of a material having hydrophilic properties. In the present embodiment the wick 21 comprises a metal foam having an open-cell structure, but it will be understood that other compositions may be used. The wick 21 may be composed of a non-metallic material, such as a ceramic material, for example an open-cell ceramic foam.

With reference to Figures 3A and 3B, the wick 21 comprises a stem 22 and a gas permeable member 23. The stem 22 and the gas permeable member 23 are formed integrally as a single component. In the present embodiment the stem 22 and the gas permeable member 23 both have a wick structure. The stem 22 extends into a reservoir 24 for storing the UWS. The wick 21 has a porous structure comprising a plurality of capillary pores (not shown) to promote capillary action. The wick 21 draws the UWS stored in said reservoir 24 through the stem 22 and supplies the UWS to the gas permeable member 23. The gas permeable member 23 comprises an annular wall 25 and a hollow chamber 26. The gas inlet 19 is in fluid communication with the hollow chamber 26 via an aperture 27 formed in the annular wall 25. The hollow chamber 26 is closed by an end plate 28 which functions as a flow guide to divert the exhaust gases radially outwardly through the annular wall 25. The gas inlet 19 is arranged to introduce exhaust gas from the bypass conduit 9 into the hollow chamber 26 through said aperture 27. The annular wall 25 of the gas permeable member 23 has an open-cell structure through which the exhaust gas may permeate. In use, exhaust gases are introduced into the hollow chamber 26 through the aperture 27. The exhaust gases pass through the annular wall 25. The flow of exhaust gas through the annular wall 25 promotes evaporation of the UWS from the wick 21, producing water and urea in a gaseous state. This may also lead to a thermolysis reaction which produces ammonia (NH₃). The thermal energy of the exhaust gas in the bypass conduit 9 is relatively high since the exhaust gas has not been used to drive the turbocharger 4. The elevated temperature of the exhaust gas may further promote evaporation of the reductant. The exhaust gases and the vaporized reductant exit the reductant introducing means 18 through the gas outlet 20. The gas outlet 20 is connected to the rear section 8B of the exhaust conduit 8. The gaseous urea, ammonia and water vapour mix with the exhaust gas in the bypass conduit 9.

A first operating pressure P1 measured at the bypass inlet 12 is greater than a second operating pressure P2 measured in the bypass conduit 9 downstream of the wick 21. The second operating pressure P2 is greater than a third operating pressure P3 at the bypass outlet 14. The pressure differential within the exhaust system 2 helps to transport the water vapour and gaseous ammonia to the SCR catalyst 16. The exhaust gas functions as a transportation medium which transports the gaseous ammonia and water vapour to the SCR catalyst 16. By spacing the reductant introducing means 18 and the SCR catalyst 16 apart from each other, thorough mixing of the gaseous ammonia and the exhaust gas is facilitated upstream of the SCR catalyst 16. The gaseous ammonia may be dispersed evenly throughout the exhaust gas. At least in certain embodiments, this may improve distribution of the gaseous ammonia over the surface of the SCR catalyst 16.

In the present embodiment it is not necessary to provide a pump to supply the UWS since the liquid is drawn into the wick 21 due to capillarity forces and the mass gradient caused by the evaporation in the gas permeable member 23. It will be understood that modified arrangements may use other means, such as a pump, a syphon or a gravity feed, to supply the UWS to the gas permeable member 23.

Prior art arrangements typically atomize the UWS and the resulting droplets are sprayed into the exhaust gas directly. These droplets may not evaporate completely in the free stream of exhaust gas and may be transported to the SCR catalyst 16. The droplets may then evaporate due to impingement on the heated surfaces of the SCR catalyst 16. The evaporation on the SCR catalyst 16 may result in the formation of secondary decomposition products, such as biurets and melamine, which may reduce the amount of ammonia produced. The transportation of the droplets may be affected by localised flow characteristics within the exhaust system 2 which may result in an uneven distribution of ammonia within the SCR catalyst 16.

The wick 21 is operative to diffuse the UWS into the exhaust gas upstream of the SCR catalyst 16. The use of the wick 21 should help to reduce or prevent secondary decomposition products (such as biurets and/or melamine) reaching the SCR catalyst 16. By evaporating the UWS upstream of the SCR catalyst 16, the ammonia may mix thoroughly with the exhaust gas resulting in a more uniform distribution within the SCR catalyst 16.

Moreover, since the UWS is introduced into the bypass conduit 9, the UWS is not present in the main line of the rear section 8B of the exhaust conduit 8. Rather, gaseous ammonia is released into the rear section 8B of the exhaust conduit 8 from the bypass conduit 9.

By controlling the bypass inlet valve 13 and the bypass outlet valve 15, the mass flow rate of the exhaust gas through the bypass conduit 9 can be controlled. The bypass inlet valve 13 and the bypass outlet valve 15 may be controlled such that the phase change and thermolysis of the UWS occurs within a predetermined temperature range, for example within the temperature range 100°C to 150°C. Furthermore, controlling the bypass inlet valve 13 and the bypass outlet valve 15 in order to control the mass flow rate of the exhaust gas (m_exh) through the bypass conduit 9 may be used to control the dosage of UWS introduced into the exhaust system 2, thereby controlling the mass flow of the urea (m_urea) and water (m_water) supplied to the SCR catalyst 16. The flow of exhaust gas through the annular wall 25 may help to reduce the build-up of deposits from the UWS within the wick 21. At least in certain embodiments, the wick 21 may be self-cleaning. A controller 29 comprising at least one electronic processor 30 and a system memory 31 may be provided for controlling said bypass inlet valve 13 and said bypass outlet valve 15. The controller 29 could, for example, be configured to control the bypass inlet valve 13 and/or the bypass outlet valve 15 in dependence on a determined temperature of the wick 21. The temperature of the wick 21 could be measured by a temperature sensor (not shown); or the temperature could be modelled, for example in dependence on operating conditions of the internal combustion engine 3.

The stem 22 and the gas permeable member 23 may have different properties. The stem 22 may be adapted to provide enhanced capillary action for drawing the UWS from the reservoir 24. The gas permeable member 23 may be adapted to provide enhance gas permeability. For example, the size of the cells in the gas permeable member 23 may be larger than those in the stem 22. The properties could be varied within a single component, or the stem 22 and the gas permeable member 23 may be formed separately.

A system 1 in accordance with a further embodiment of the present invention will now be described with reference to Figure 4. Like reference numerals are used for like components.

The system 1 comprises an exhaust system 2 for expelling exhaust gases from an internal combustion engine 3 disposed in a vehicle V. The system 1 comprises a turbocharger 4 to provide forced induction of the internal combustion engine 3. The turbocharger 4 comprises a turbine 5 drivingly connected to a compressor 6. The compressor 6 is arranged to supply air to the internal combustion engine 3 at a pressure greater than atmospheric pressure. In particular, the compressor 6 supplies air to an inlet 33 of the internal combustion engine 3. The exhaust system 2 comprises an exhaust manifold 7, an exhaust conduit 8 and a tailpipe 10. The exhaust manifold 7 connects to exhaust ports (not shown) of the internal combustion engine 3. The exhaust conduit 8 comprises a front section 8A and a rear section 8B. The turbine 5 is disposed in the front section 8A of the exhaust conduit 8. The system 1 comprises one or more aftertreatment systems (denoted generally by the reference numeral 11) for treating the exhaust gases. The aftertreatment system(s) 11 are disposed in the rear section 8B of the exhaust conduit 8 downstream of the turbine 5.

The bypass conduit 9 is arranged to divert a portion of the air from the compressor 6 to the exhaust conduit 8. The proportion of the air diverted to the exhaust conduit 8 may be fixed or may be variable. The bypass conduit 9 comprises a bypass inlet 12, a bypass inlet valve 13, a bypass outlet 14 and a bypass outlet valve 15. In the present embodiment the bypass inlet 12 is connected to an inlet 33 of the internal combustion engine 3; and the bypass outlet 14 is connected to the rear section 8B of the exhaust conduit 8. The bypass inlet valve 13 and the bypass outlet valve 15 are operable to control the flow of exhaust gas through the bypass conduit 9. In the present embodiment the bypass inlet valve 13 and the bypass outlet valve 15 are both (one-way) check valves. In use, the bypass conduit 9 is operative selectively to bypass the internal combustion engine 3.

The aftertreatment system(s) 11 comprise a selective catalytic reduction (SCR) catalyst 16 for abating NOx emissions. A reductant (reducing agent), such as anhydrous ammonia, aqueous ammonia or urea, is introduced to the exhaust gas. The reductant is stored in a liquid form and in the present embodiment is a urea water solution (UWS). In the presence of the SCR catalyst 16, the reductant converts nitrogen oxides (NOx) present in the exhaust gases into diatomic nitrogen (N₂) and water (H₂O) which are emitted from the tailpipe 10. The reductant is introduced into the exhaust gas upstream of the SCR catalyst 16. In accordance with an aspect of the present invention the reductant is introduced into the exhaust gas in the bypass conduit 9. The exhaust system 2 comprises distributing apparatus 17 for distributing the UWS into means (denoted generally by the reference numeral 18) for introducing the reductant into the exhaust gas. The reductant introducing means 18 comprises a wick 21 disposed in the bypass conduit 9. The configuration of the wick 21 is unchanged from the arrangement described herein in respect of the previous embodiment. It will be appreciated that the reductant introducing means 18 may usefully take other forms, such as an injector or a vaporizer.

The gas introduced into the bypass conduit 9 from the compressor 6 is at a higher pressure than the exhaust gas in the rear section 8B of the exhaust conduit 8. Moreover, the gas in the bypass conduit 9 is at an elevated temperature, for example in the range 45°C to 180°C. If required, the bypass conduit 9 may be disposed adjacent to the exhaust conduit 8 to provide additional thermal heating. Alternatively, or in addition, means may be provided for heating the gas as it flows through the bypass conduit 9. The flow of gas through the bypass conduit 9 promotes evaporation of the UWS from the wick 21, producing water vapour and gaseous ammonia (NH₃) through thermolysis. The gaseous ammonia and water vapour mix is introduced into the rear section 8B of the exhaust conduit 8 upstream of the SCR catalyst 16.

A first operating pressure P1 measured at the bypass inlet 12 is greater than a second operating pressure P2 measured in the bypass conduit 9 downstream of the wick 21. The second operating pressure P2 is greater than a third operating pressure P3 at the bypass outlet 14. The pressure differential helps to transport the water vapour and gaseous ammonia to the SCR catalyst 16. The gas introduced into the bypass conduit 9 from the compressor 6 functions as a transportation medium which transports the gaseous ammonia and water vapour to the SCR catalyst 16.

By controlling the bypass inlet valve 13 and the bypass outlet valve 15, the mass flow rate of the gas through the bypass conduit 9 can be controlled. The bypass inlet valve 13 and the bypass outlet valve 15 may be controlled such that the phase change and thermolysis of the UWS occurs within a predetermined temperature range, for example within the temperature range 100°C to 150°C. Furthermore, controlling the bypass inlet valve 13 and the bypass outlet valve 15 in order to control the mass flow rate of the exhaust gas (m_exh) through the bypass conduit 9 may be used to control the dosage of UWS introduced into the exhaust system 2, thereby controlling the mass flow of the urea (m_urea) and water (m_water) supplied to the SCR catalyst 16.

It will be appreciated that various modifications may be made to the system 1 described herein without departing from the scope of the appended claims. The wick 21 may have a uniform pore size. Alternatively, the size of the pores may vary within the wick 21. For example, the pores may be larger in the gas permeable member 23 than in the stem 22 such that the passage of exhaust gas through the annular wall 25 is facilitated whilst promoting capillary action in the stem 22 to draw reductant from the reservoir.

The wick 21 in the embodiment described herein comprises an aperture 27 arranged to introduce exhaust gas from the bypass conduit 9 directly into the hollow chamber 26. The arrangement of the wick 21 may be modified to provide an exhaust gas outlet through which the exhaust gas may exit the hollow chamber 26. In this modified arrangement the exhaust gas travel through the annular wall 25 into the hollow chamber 26.

The exhaust system 2 described herein may be modified to provide additional aftertreatment systems, such as filters and catalysts. For example, the exhaust system 2 may include a diesel particulate filter (DPF) and/or a lean NOx trap (LNT). These aftertreatment systems may be disposed in the rear section 8B of the exhaust conduit 8 either upstream or downstream of the bypass outlet 14 depending on their function.

It will also be understood that the SCR catalyst 16 referenced herein may be replaced with a Selective Catalytic Reduction Filter SCRF (RTM). The present invention may be utilised to supply a reductant to an SCRF (RTM).

Claims

CLAIMS:

1. A system for an internal combustion engine, the system comprising:

an exhaust conduit;

a bypass conduit;

wherein said reductant introducing means is disposed in the bypass conduit.

2. A system as claimed in claim 1 comprising a turbocharger having a turbine and a compressor, wherein said bypass conduit is arranged to bypass the turbine.

3. A system as claimed in claim 2, wherein the bypass conduit comprises a bypass inlet and a bypass outlet, the bypass inlet being connected to the exhaust conduit upstream of the turbine and the bypass outlet being connected to the exhaust conduit between the turbine and the SCR catalyst.

4. A system as claimed in claim 1, wherein said bypass conduit is arranged to bypass the internal combustion engine.

5. A system as claimed in claim 4 comprising a turbocharger having a turbine and a compressor, the bypass conduit being arranged to bypass the turbine.

6. A system as claimed in claim 4, wherein the bypass conduit comprises a bypass inlet and a bypass outlet, the bypass inlet being connected downstream of the compressor and the bypass outlet being connected to the exhaust conduit between the turbine and the SCR catalyst.

7. A system as claimed in any one of the preceding claims comprising a bypass inlet valve and a bypass outlet valve.

8. A system as claimed in claim 7, wherein said bypass inlet valve and/or said bypass outlet valve comprise a check valve.

9. A system as claimed in claim 7 or claim 8, wherein said bypass inlet valve and/or said bypass outlet valve are controllable to control the mass flow rate of gas through the bypass conduit.

10. A system as claimed in claim 9 comprising a controller for controlling said bypass inlet valve and/or said bypass outlet valve, the controller being configured to control said bypass inlet valve and/or said bypass outlet valve to control the dosage of the reductant supplied to the SCR catalyst.

11. A system as claimed in any one of the preceding claims, wherein the reductant introducing means comprises a wick disposed in said bypass conduit.

12. A system as claimed in claim 11, wherein the wick comprises a gas permeable portion through which gases pass in use.

13. A system as claimed in claim 12, wherein said gas permeable portion has a porous structure comprising a plurality of pores.

14. A system has claimed in claim 13, wherein said pores are sized to draw a urea solution from a reservoir through capillary action to said gas permeable portion.

15. A system as claimed in any one of claims 12, 13 or 14, wherein the gas permeable portion is arranged at least partially to obstruct the flow of gas through the bypass conduit.

16. A system as claimed in any one of claims 12 to 15, wherein the gas permeable portion comprises an annular wall which forms a hollow chamber in said wick.

17. A system as claimed in claim 16, wherein the hollow chamber has a gas inlet in fluid communication with the bypass inlet and, in use, gas is introduced into said hollow chamber through the gas inlet and passes through the annular wall.

18. A system as claimed in claim 17, wherein the hollow chamber has a gas outlet in fluid communication with the bypass outlet and, in use, gas passes through the annular wall into said hollow chamber and exits through the gas outlet.

19. A system as claimed in any one of claims 1 to 10, wherein the reductant introducing means comprises an injector for injecting the urea solution into said bypass conduit.

20. A system as claimed in any one of the preceding claims comprising an inlet bypass control valve for controlling the flow of gas through said bypass inlet; and/or an outlet bypass control valve for controlling the flow of gas through said bypass outlet.

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21. A vehicle comprising a system as claimed one of the preceding claims.