GB2512896A

GB2512896A - A mixer module and an emissions cleaning module

Info

Publication number: GB2512896A
Application number: GB1306517.2A
Authority: GB
Inventors: Andrew Keen; David Heaton; Christopher Petto
Original assignee: Perkins Engines Co Ltd
Current assignee: Perkins Engines Co Ltd
Priority date: 2013-04-10
Filing date: 2013-04-10
Publication date: 2014-10-15
Anticipated expiration: 2033-04-10
Also published as: GB2512896B; GB201306517D0; CN203856551U

Abstract

An exhaust gas mixer module 2 comprises a coaxial arrangement of an outer conduit 10 and an inner conduit 20. An upstream end 11 of the outer conduit comprises an inlet 13 for receiving a fluid flow from a diesel oxidation catalyst 4. A downstream end 12 of the outer conduit is fluidly connected to the inner conduit, and the mixer module is configured to reverse the exhaust gas flow direction between the outer and inner conduits. An additive injector 30 is provided at the inlet to the inner conduit. A flow conditioner 14, for promoting uniform fluid flow, and/or a swirl inducer 16 may be provided in the outer conduit. A mixer element, such as a hydrolysis catalyst, may be provided in the inner conduit. The mixer module may be symmetric about its longitudinal axis. The mixer module may enable mixing of urea into a flow of exhaust gas upstream of a selective catalytic reduction module.

Description

A Mixer Module and an Emissions Cleaning Module

Technical Field

The present disclosure relates to an apparatus for cleaning exhaust fluids emitted during the operation of combustion engines. In particular, it relates to a mixer module, and an emissions cleaning module comprising such a mixer module.

Background

Engines, for example IC engines burning gasoline, diesel or biofuel, output various harmful substances which must be treated to meet current and future emissions legislation. Most commonly those substances comprise hydrocarbons (HC), carbon monoxides (GO), mono-nitrogen oxides (NO) and particulate matter, such as carbon (C), a constituent of soot. Some of those substances may be reduced by careful control of the operating conditions of the engine, bUt usually it is necessary to provide apparatus, such as an emissions cleaning module, downstream of the engine to treat at least some of those substances entrained in the exhaust gas. Various apparatus for reducing and/or eliminating constituents in emissions are known. For example, it is known to provide an oxidation device, such as a diesel oxidation catalyst (DOC), to reduce or to eliminate hydrocarbons (HG) and/or carbon monoxide (GO). Oxidation devices generally include a catalyst to convert those substances into carbon dioxide and water, which are significantly less harmful. As a further example, emissions cleaning modules may include a filter, such as a diesel particulate filter (DPF) to restrict the particulates present in the exhaust gas from being output to atmosphere.

In addition, it is known to reduce or eliminate mono-nitrogen oxides (NOr) in diesel combustion emissions by conversion to diatomic nitrogen (N2) and water (H2O) by catalytic reaction with chemicals such as ammonia (NH3) entrained in the exhaust gas.

Generally ammonia is not present in exhaust gases and must therefore be introduced upstream of a catalyst, typically by injecting a urea solution into the exhaust gas which decomposes into ammonia at sufficiently high temperatures.

By. these methods, exhaust gases can be cleaned, meaning that a proportion of the harmful substances which would otherwise be released to atmosphere are instead converted to carbon dioxide (GO2), nitrogen (N2) and water (H20).

It is also known to include an exhaust mixer to aid mixing of the injected urea with the exhaust gas flow. For example, De Rudder (De Rudder, K., "Tier 4 High Efficiency SGR for Agricultural.Applications," SAE Int. J. Commer. Veh. 5(1):386-394, 2012, doi:1O.4271/2012-O1-1087) describes an exhaust aftertreatment system, wherein the DOG has an annular shape with a tube in the middle. Exhaust gas flows through the outer section of the annular DOC and a swirl plate arranged at the outlet of the DOG before entering an inner tube of the annular DOC. This arrangement may lead to an exhaust aftertreatment system which is bulky and requires a relatively large DOG. The complex structure of the,DOC may also lead to increased manufacturing costs.

Against this background there is provided an emissions cleaning module comprising an improved mixer module.

Summary of the disclosure

The present disclosure provides a mixer module comprising: an outer conduit; and an inner conduit extending coaxially within the outer conduit; said outer conduit having: an upstream end comprising an inlet for receiving a fluid flow from an upstream diesel oxidation catalyst; and a downstream end of the outer conduit being fluidly connected to an inlet of the inner conduit such that the fluid flow exiting the outer conduit and entering the inner conduit reverses in direction; the mixer module further comprising an injector module located to inject an additive into the inlet of the inner conduit.

The present disclosure also provides an emissions cleaning module comprising a mixer module as just described.

Brief description of the drawings

Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a schematic representation of a portion of an emissions cleaning module including a first embodiment of mixer module in accordance with the present

disclosure;

Figure 2 shows a schematic representation of a portion of an emissions cleaning module including a second embodiment of mixer module in accordance with the present

disclosure;

Figure 3 shows an enlarged view of a portion of Figure 2; and Figure 4 shows a schematic representation of a portion of an emissions cleaning module including a third embodiment of mixer module in accordance with the present

disclosure.

Detailed description

A mixer module 2 according to the present disclosure may form a component part of an emissions cleaning module, which itself may form a part of an engine exhaust system.

The emissions cleaning module 1 may comprise a diesel oxidation catalyst (DOC) module, a selective catalyst reduction (SCR) module and an ammonia oxidation catalyst (AMOX) module. The emissions cleaning module 1 may comprise a plurality of interconnected conduits housing the modules. The DOC module 3 may be housed in a first conduit 4 which may have an inlet 45 for receiving exhaust gases requiring treatment. The first conduit 4 may also contain a diesel particulate filter (OFF) module (not shown in Figure 1), which may be downstream of the DOC module 3. An outlet 46 of the first conduit 4 may be connected to a second conduit 5 by means of a first flowhood 40. The second conduit 5 may form a part of the mixer module 2 which will be described in more detail below. An outlet of the mixer module 2 may be connected via a second flowhood to a third conduit which may house the SCR module and AMOX module. For clarity the second flowhood and the third conduit are omitted from Figure 1.

The first conduit 4 and second conduit 5 may be elongate, having an axis of elongation, and may have a substantially constant cross-section along the axis of elongation. The first conduit 4 and the second conduit 5 may be substantially cylindrical and may be arranged parallel to one another.

The DOC module 3 may be located in a first portion of the first conduit 4. The DOC module 3 may co.mprise one or more catalysts, such as palladium or platinum. These materials serve as catalysts to cause oxidation of hydrocarbons ([HCI) and carbon monoxide (CO) present in the fluid flow in order to produce carbon dioxide (C02) and water (H20). The catalysts may be distributed in a manner so as to maximise the surface area of catalyst material in order to increase effectiveness of the catalyst in catalysing reactions.

A first embodiment of mixer module 2 is shown in Figure 1. The mixer module 2 comprises an outer conduit 10 and an inner conduit 20 extending coaxially within the outer conduit 10.

An upstream end 11 of the outer conduit 10 may comprise an inlet 13 for receiving a fluid flow from the upstream DOG module 3 via the first flowhood 40. The first flowhood 40 may be configured to reverse the flow of fluid passing therethrough, such that the direction of flow of fluid in the first conduit 4 may be opposite the direction of flow of fluid in the outer conduit 10 of the second conduit 5.

A downstream end 12 of the outer conduit 10 is fluidly connected to an inlet 21 of the inner conduit 20 such that a fluid flow exiting the outer conduit 10 and entering the inner conduit 20 reverses in direction. The mixer module 2 further comprises an injector module 30 located to inject an additive into the inlet 21 of the inner conduit 20. The downstream end 12 of the outer conduit 10 may be fluidly connected to the inlet 21 of the inner conduit 20 by means of a mixer flowhood 50. The mixer flowhood 50 may comprise a bowl-shaped endpiece having an annular concave region 51 surrounding a centrally-located elevated section 52 that forms the mounting point for the injector module 30. The mixer flowhood 50 may be mounted to the downstream end 12 of the outer conduit 10 by mounting flanges 53, 54.

An outlet 26 of the inner conduit 20 may be provided at an outlet end 24 of the inner conduit 20. The second flowhood (not shown) may be fluidly connected to the outlet 26.

The outer conduit 10 and the inner conduit 20 may be rotationally symmetric about a common longitudinal axis. The outer conduit 10 may be cylindrical and may have a constant diameter along the majority of its length. The inner conduit 20 may be cylindrical and may have a constant diameter.

The inner conduit 20 may extend along greater than 50% of the length of the outer conduit I 0.The inner conduit 20 may extend along greater than 75% of the length of the outer conduit 10. The outlet end 24 of the inner conduit 20 may project beyond the outer conduit 10. The outlet end 24 of the inner conduit 20 may extend through an aperture 41 in the first flowhood 40. The first flowhood 40 may act as a structural support for the inner conduit 20 in spaced relationship with respect to the outer conduit 10.

The outer conduit 10 may comprise a flow conditioner 14 for increasing the uniformity of flow of the fluid flow within the outer conduit 10. The flow conditioner 14 may comprise one or more perforated baffles or a plurality of fins. In the illustrated example a single perforated baffle is provided. As shown in Figure 1, the flow conditioner 14 may be located at or towards the upstream end 11 of the outer conduit 10. The flow conditioner 14 may be annular and may be sized to fit the annular gap between outer conduit 10 and the inner conduit 20 such that all fluid flow through the outer conduit 10 passes through the flow conditioner 14. The flow conditioner 14 may also act as a structural support to hold the inner conduit 20 in sp?ced relationship with respect to the outer conduit 10.

The outer conduit 10 may comprise a swirl inducer 16 for inducing rotation of the fluid flow about the longitudinal axis of the outer conduit 10. Jhe swirl inducer 16 may be located at or towards the downstream end 12 of the outer conduit 10. An elongate, annular void space may therefore be defined between the flow conditioner 14 and the swirl inducer 16. The swirl inducer 16 may comprise one or more vanes. The swirl inducer 16 may comprise a plurality of vanes spaced around the circumference of the outer conduit 10. The vanes may be equally spaced around the circumference of the outer conduit 10. In one example, the swir! inducer 16may comprise 5 or 6 vanes. The swirl inducer 16 may also act as a structural support to hold the inner conduit 20 in spaced relationship with respect to the outer conduit 10.

In addition to, or in place of, the swirl inducer 16, a structural support may be provided at or near the inlet 21 of the inner conduit 20 to hold the inner conduit 20 in spaced relationship with respect to the outer conduit 10. The structural support may be a plurality of support members extending between the inner conduit 20 and the outer conduit 10.

As shown in Figure 1, the injector module 30 may be located directly upstream of the inlet 21. An outlet 31 of the injector module 30 may be configured to inject an additive, for example urea, as a spray having a spray pattem centred along, or parallel to, the longitudinal axis 25 of the inner conduit 20. The injected additive fluid may be injected as a spray having a substantially conical spray pattern.

The injector module 30 may be associated with or attachable to a pump electronic tank unit (PETU). The pump electronic tank unit may comprise a tank for providing a reservoir for additive fluid to be injected by the injector. Such additive fluids may include urea or ammonia. The PETU may further comprise a controller configured to control a volume of additive fluid to be injected from the tank by the injector. The controller may have as inputs, for example, temperature information and quantity of NOX information which may be derived from sensors in the SCR module.

A mixing element 22 may be located within the inner conduit 20, downstream of the injector module 30. The mixing element 22 may be a hydrolysis catalyst. The mixing element 22 may be located at or towards the inlet 21.

In use, exhaust gas may enter the emissions cleaning module I through inlet 45. The exhaust gas then passes through the DOC module 3 within the first conduit 4 and via the first flowhood 40 into the mixer module 2 through inlet 13. As the exhaust gas passes through the first flowhood 40 its direction of flow may be reversed. The incoming fluid may impact on an outside of the inner conduit 20 and be thus diverted so that the fluid flows through the full annulus between the inner conduit 20 and the outer conduit 10.

The exhaust gas may then pass through the flow conditioner 14 and the swirl inducer 16.

The flow conditioner 14 may act to condition the flow of exhaust gas and may produce a more uniform pattern of flow within the outer conduit 10. The swirl inducer 16, where present, may induce swirl to the exhaust gas before it reaches the injector module.

Next the exhaust gas passes out of the downstream end 12 of the outer conduit 10 through the mixer flowhood 50 and into the inlet 21 of the inner conduit 20. Transfer of the exhaust gas from the outer conduit 10 to the inner conduit 20 causes the direction of flow of the exhaust gas to be reversed. In addition, the difference in the cross-sectional areas of the inlet 21 of the inner conduit 20 and the downstream end 12 of the outer conduit 10 may be configured to lead to an increase in the flow speed as the exhaust gas enters the inner conduit 20.

As the exhaust gas transits the mixer flowhood 50 it passes the outlet 31 of the injector module 30. Additive fluid, for example urea, may be injected into the exhaust gas flow before the exhaust gas reaches the inlet 21 of the inner conduit 20 and the resultant mixture of exhaust gas and additive fluid, may then pass into the inner conduit 20 via the inlet 21.

The mixture of exhaust gas and additive fluid may then pass through the mixing element 22. The exhaust gas may then pass via outlet 26 into the third conduit which may contain the SCR and/or AMOX modules for further treatment.

A second embodiment of mixer module 2 according to the present disclosure is shown in Figures 2 and 3. Like components to the first embodiment have been referenced using like reference numerals. In the following, only the differences between the first and second embodiments will be discussed. In other respects, the construction, features and utilisation of the mixer module 2 are as described above with respect to the first embodiment.

As before, the mixer module 2 comprises an outer conduit 10 and an inner conduit 20 extending coaxially within the outer conduit 10. However, in this embodiment, the length of the outer conduit 10 may be significantly reduced compared to the first embodiment.

As before, an upstream end 11 of the outer conduit 10 may comprise an inlet 13 for receiving a fluid flow from the upstream DOC module 3. However, the orientation of the first conduit 4 relative to the second conduit 5 may be reversed so that the outlet 46 of the first conduit 4 may be located nearer the end of the second conduit 5 housing the injector module 30 rather than nearer the outlet 26 of the inner conduit 20.

A first flowhood 40 may interconnect the first conduit 4 and the inlet 13 of the outer conduit 10. The first flowhood 40 may comprise a dog-legged shape configured to deflect the flow of fluid passing therethrough through an angle of 90°. For example, the direction of flow of fluid into the first flowhood 40 from the first conduit 4 may be in an axial direction aligned with the longitudinal axis of the first conduit 4, but the direction of flow of fluid into the outer conduit 10 may be in a radial direction perpendicular to the direction of flow in the first conduit 4. The inlet 13 of the outer conduit may be an aperture in a section of the wall of the second conduit 5.

As before, a downstream end 12 of the outer conduit 10 is fluidly connected to an inlet 21 of the inner conduit 20 such that a fluid flow exiting the outer conduit 10 and entering the inner conduit 20 reverses in direction.

The downstream end 12 of the outer conduit 10 may be fluidly connected to the inlet 21 of the inner conduit 20 by means of a mixer flowhood as described previously..

Alternatively, as illustrated in Figure 2, the downstream end 12 of the outer conduit 10 may be closed off by an end plate 56. As shown most clearly in Figure 3, the end plate 56 may comprise a flat outer section 57 and a conically-shaped protrusion 58 that forms the mounting point for an injector module 30 of the type described previously. The conically-shaped protrusion 58 may allow the outlet 31 of the injector module 30 to be located closer to the inlet 21 of the inner conduit 20. The end plate 56 may be mounted to the downstream end 12 of the outer conduit 10 by mounting flanges or by welding.

As with the first embodiment, an outlet 26 of the inner conduit 20 may be provided at an outlet end 24 of the inner conduit 20. The second flowhood (not shown) may be fluidly connected to the outlet 26.

The inner conduit 20 may extend along greater than 50% of the length of the outer conduit 1 0.The inner conduit 20 may extend along greater than 75% of the length of the outer conduit 10. The outlet end 24 of the inner conduit 20 may project beyond the outer conduit 10. The proportion of the inner conduit 20 projecting beyond the outer conduit 10 may be greater than 50% and significantly greater compared to the first embodiment.

The outlet end 24 of the inner conduit 20 may extend through an aperture 41 in the first flowhood 40. A mounting flange 43 may surround the aperture 41. The first flowhood 40 may act as a structural support to hold the inner conduit 20 in spaced relationship with respect to the outer conduit 10.

A flow conditioner 14 which may be of the general type described previously may be located in the outer conduit 10 and may comprise one or more perforated baffles. In the illustrated example two perforated baffles are provided. Due to the truncated length of the second conduit 5, the flow conditioner 14 may be located approximately in the middle of the axial extent of the outer conduit 10. In particular, as illustrated, one of the perforated baffles may be located proximate to the inlet 13 of the outer conduit 10 and the other perforated baffle may be located proximate the end of the inner conduit 20 nearest the inlet 21 thereof. The flow conditioner 14 may also act as a structural support to hold the inner conduit 20 in spaced relationship with respect to the outer conduit 10.

The outer conduit 10 may not require the inclusion of a swirl inducer.

A mixing element 22 of the type described previously may be located within the inner conduit 20, downstream of the injector module 30.

A third embodiment of mixer module 2 according to the present disclosure is shown in Figure 4. Like components to the first and second embodiments have been referenced using like reference numerals. In the following, only the differences between the second and third embodiments will be discussed. In other respects, the construction, features and utilisation of the mixer module 2 are as described above with respect to the second embodiment.

According to the third embodiment, a flow conditioner 14 may be located in the outer conduit 10 and may comprise a plurality of straightening fins 17. As previously described, the flow conditioner 14 may be annular and may be sized to fit the annular gap between outer conduit 10 and the inner conduit 20 such that all fluid flow through the outer conduit 10 passes through the flow conditioner 14. Each fin may comprise a rectangular plate-like element of uniform thickness and may extend radially from the inner conduit 20 to the outer conduit 10. The fins 17 may be spaced around the circumference of the outer conduit 10. The fins 17 may be equally spaced around the circumference of the oUter conduit 10. The fins 17 may be individually mounted to the inner conduit 20 and/or the outer conduit 10. The fins 17 may be mounted to a housing which may in turn be mounted to the inner conduit 20 and/or outer conduit 10.

The outer diameter of the outer conduit 10 may be larger than in the second embodiment so as to provide a larger annular gap between the inner conduit 20 and outer conduit 10.

As previously described, due to the truncated length of the second conduit 5, the flow conditioner 14 may be located approximately in the middle of the axial extent of the outer conduit 10. In particular, as illustrated, the fins 17 may be located proximate to the inlet 13 of the outer conduit 10.

The flow conditioner 14 may also act as a structural support to hold the inner conduit 20 in spaced relationship with respect to the outer conduit 10. The outer conduit 10 may not require the inclusion of a swirl inducer.

The downstream end 12 of the outer conduit 10 may be fluidly connected to the inlet 21 of the inner conduit 20 by means of a mixer flowhood as described previously.

Alternatively, as illustrated in Figure 4, the downstream end 12 of the outer conduit 10 may be closed off by an end plate 56. The end plate 56 may comprise a flat outer section 57 and a conically-shaped protrusion 58 that forms the mounting point for an injector module 30 of the type described previously. The conically-shaped protrusion 58 may allow the outlet 31 of the injector module 3D to be located closer to the inlet 21 of the inner conduit 20. Alternatively, the injector module 30 may be mounted such that the outlet 31 is in proximity to the end plate 56. The injector module 30 may be mounted using a v-band clamp. The end plate 56 may be mounted to the downstream end 12 of the outer conduit 10 by mounting flanges or by welding.

Industrial Applicability

The present disclosure provides a mixer module and an emissions cleaning module which may improve the efficiency of mixing an additive, such as urea, in a flow of exhaust fluid, such as exhaust gas.

In use, exhaust gas may enter the emissions cleaning module 1 through inlet 45. The exhaust gas then passes through the DOC module 3 within the first conduit 4 and via the -11 -first flowhood 40 into the mixer module 2 through inlet 13. As the exhaust gas passes through the first flowhood 40 its direction of flow may be deflected through 9Q0 The incoming fluid may impact on an outside of the inner conduit 20 and be thus diverted so that the fluid flows through the full annulus between the inner conduit 20 and the outer conduit 10. The exhaust gas may then pass through the perforated baffles of the flow conditioner 14. The flow conditioner 14 may act to condition the flow of exhaust gas and may produce a more uniform pattern of flow within the outer conduit 10.

Next the exhaust gas passes out of the downstream end 12 of the outer conduit 10 and may be deflected by the end plate 56 into the inlet 21 of the inner conduit 20. Transfer of the exhaust gas from the outer conduit 10 to the inner conduit 20 causes the direction of flow of the exhaust gas to be reversed. In addition, the difference in the cross-sectional areas of the inlet 21 of the inner conduit 20 and the downstream end 12 of the outer conduit 10 may be configured to lead to an increase in the flow speed as the exhaust gas enters the inner conduit 20.

As the exhaust gas transits between the outer conduit 10 and the inner conduit 20 it passes the outlet 31 of the injector module 30. Additive fluid, for example urea, may be injected into the exhaust gas flow before the exhaust gas reaches the inlet 21 of the inner conduit 20 and the resultant mixture of exhaust gas and additive fluid, may then pass into the inner conduit 20 via the inlet 21.

The mixture of exhaust gas and additive fluid may then pass through the mixing element 22. The exhaust gas may then pass via outlet 26 into the third conduit which may contain the 5CR and/or AMOX modules for further treatment.

Incomplete mixing of the urea, and hence adequate decomposition of the urea to ammonia, when it is injected into a mixing conduit can lead to a build-up of solid urea deposits on the internal surfaces of the mixing conduit, including any exhaust mixer present therein. It has also been found that impingement of the injected additive spray on relatively cold walls of a mixing conduit can also promote such deposit build-up. This can lead to the need for overly-frequent disassembly and maintenance of the emissions cleaning module or an emissions cleaning module regeneration strategy.

The location of the injector module allows injection of the additive into the inlet of the inner conduit. This may lead to a reduction of impact of the additive spray on the surfaces of the outer conduit which may be relatively cold. This may help to avoid build-up of solid additive deposits within the mixer module which may impact performance.

In addition, the co-axial arrangement of the inner conduit within the outer conduit may beneficially help to maintain a raised temperature of the surfaces of the inner conduit *which may come into contact with the additive spray since the outer conduit may act as an insulating layer.

The present mixer module may also provide a more compact arrangement for use in an emissions cleaning module by housing the DOC module separately from the mixer module. The mixer module may therefore be made smaller. This may allow for easier integration of the emissions cleaning module in an engine exhaust arrangement. In addition, an annular DOC module is not required. Therefore, the DOC module may be smaller and less complicated.

The mixer module may be rotationally symmetric about its longitudinal axis. This may be beneficial in promoting increased flow uniformity of the exhaust gas and, in addition, the flow uniformity may be less sensitive to changes in fluid flow rate and/or changes in the engine geometry upstream of the emissions cleaning module.

The mixer module may comprise a flow conditioner in the form of fins which may be beneficial in reducing the overall pressure drop across the mixer module compared to the use of perforated baffles.

The mixer module may be beneficially utilised in an arrangement where the outlet of the injector module may only project a small distance,say approximately 6mm, into the module. The use of the flow conditioner and the reversal of the exhaust gas flow direction may compensate and still produce a uniform mixing of the injected fluid and the exhaust gas.

The mixer module and emissions cleaning module may be utilised with IC engines burning gasoline, diesel or biofuel.

Claims

Claims 1. A mixer module comprising: an outer conduit; and an inner conduit extending coaxially within the outer conduit; said outer conduit having: an upstream end comprising an inlet for receiving a fluid flow from an upstream diesel oxidation catalyst; and a downstream end of the outer conduit being fluidly connected to an inlet of the inner conduit such that the fluid flow exiting the outer conduit and entering the inner conduit reverses in direction; the mixer module further comprising an injector module located to inject an additive into the inlet of the inner conduit.
2. A mixer module as claimed in claim 1, wherein the outer conduit comprises a flow conditioner for increasing a uniformity of flow of the fluid flow within the outer conduit.
3. A mixer module as claimed in claim 2, wherein the flow conditioner comprises one or more perforated baffles or a plurality of fins.
4. A mixer module as claimed in any preceding claim, wherein the outer conduit comprises a swirl inducer for inducing rotation of the fluid flow about a longitudinal axis of the outer conduit.
5. A mixer module as claimed in claim 4 when dependent on claim 3, wherein the one or more perforated baffles are located at or towards the upstream end of the outer conduit and the swirl inducer is located at or towards the downstream end of the outer conduit so as to define an elongate, annular void space therebetween.
6. A mixer module as claimed in any preceding claim, wherein the inner conduit contains a mixing element.
7. A mixer module as claimed in claim 6, wherein the mixing element contains a hydrolysis catalyst. -14-
8. A mixer module as claimed in any preceding claim, further comprising a first flowhood connected to the upstream end of the outer conduit.
9. A mixer module as claimed in claim 8, wherein an outlet end of the inner conduit extends through an aperture in the first flowhood.
10. A mixer module as claimed in any preceding claim, further comprising a mixer flowhood connected to the downstream end of the outer conduit.
11. A mixer module as claimed in claim 1 d, wherein the injector module is mounted in the mixer flowhood.
12. A mixer module as claimed in any preceding claim, wherein the outer conduit and the inner conduit are rotationally symmetric about a common longitudinal axis.
13. An emissions cleaning module comprising a mixer module as claimed in any preceding claim.
14. An emissions cleaning module as claimed in claim 13, further comprising an upstream conduit fluidly connected to the inlet of the outer conduit, wherein said upstream conduit contains a diesel oxidation catalyst module.
15. An emissions cleaning module as claimed in claim 13 or claim 14, further comprising a downstream conduit fluidly connected to an outlet of the inner conduit, wherein said downstream conduit contains a selective catalyst reduction nodule.