TECHNICAL FIELD

The present disclosure relates to a water separator and hydrogen dilution device. Aspects of the invention relate to an apparatus for removing water and diluting purged hydrogen in an exhaust gas stream, to a method for removing water and diluting purged hydrogen in an exhaust gas stream, to a system comprising the aforementioned apparatus, to a fuel cell exhaust system comprising the aforementioned apparatus and to a vehicle comprising the aforementioned fuel cell exhaust system.

BACKGROUND

A fuel cell is an electrochemical cell that converts chemical energy of a fuel, such as hydrogen, and an oxidizing agent, such as oxygen, into electricity. A fuel cell consists of a negative electrode (or anode) and a positive electrode (or cathode) separated by an ion-conducting electrolyte. A fuel, such as hydrogen, is fed to the anode and air is fed to the cathode. In a hydrogen fuel cell, hydrogen molecules are separated at the anode by a catalyst, into their constituent protons and electrons, each of which takes a different path to the cathode. The electrons travel in an external circuit (supplying power). The protons move through the electrolyte to the cathode, where they combine with oxygen and the electrons (which have travelled through the external circuit) to produce water and heat.

Fuel cells can be used in a wide range of applications, providing power for those applications and have several benefits over conventional combustion-based technologies currently in use in many applications such as vehicles. For example, fuel cells have lower or zero emissions as compared to combustion engines, hydrogen fuel cells emit only water and therefore do not produce carbon dioxide emissions which may contribute to climate change, and fuel cells do not emit air pollutants that create smog and which may be detrimental to health.

Purging of hydrogen from the fuel cell is necessary to prevent fuel cell deterioration and to improve durability of the fuel cell. The purging process involves a controlled release of a proportion of the (gaseous) fuel and/ or oxidant (e.g. air) through an exhaust system. The purging process removes accumulated impurities, water and particulates from the fuel cell and restores fuel cell performance. However, release of hydrogen into the open air may present safety concerns if the concentration of the released hydrogen is above a level which is deemed safe. Currently, it is preferred that concentration of released hydrogen is 4% or less by volume. One method of diluting purged hydrogen in an exhaust gas stream and reducing the concentration of hydrogen released into the atmosphere is to pass the exhaust gas stream containing the purged hydrogen through a long conduit comprising a series of bends. As the exhaust gas stream passes around each of the bends in the long conduit, the bends create turbulence in the exhaust gas stream which mixes the purged hydrogen with air in the exhaust gas stream to which reduces the concentration of released hydrogen as compared to an unmixed stream.

When the hydrogen fuel cell system is applied to a vehicle, the long conduit with bends for mixing the exhaust gas stream is usually disposed along the length of the vehicle, such that advantage is taken of the vehicle’s length to provide numerous bends in the long conduit to improve mixing of the exhaust gases and thus reducing the concentration of hydrogen gas released. A disadvantage with this known arrangement is that the long conduit and multiple bends takes up a significant proportion of available space underneath the vehicle and placement of each of the bends and/or other components fitted to the vehicle’s underside must be carefully considered to ensure that each required component can be accommodated.

A further disadvantage of the aforementioned known method of diluting purged hydrogen in an exhaust gas stream is that water in the exhaust gas stream can reduce the efficacy of mixing of the purged hydrogen and exhaust gas stream. Water in the gas stream may also reduce the homogeneity of the resulting mixed stream of purged hydrogen and exhaust gas. This may cause an inconsistent dilution of purged hydrogen in the exhaust gas stream which is undesirable.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide an apparatus for removing water and diluting purged hydrogen in an exhaust gas stream, a method for removing water and diluting purged hydrogen in an exhaust stream, a system comprising the apparatus, a fuel cell exhaust system comprising the apparatus and a vehicle comprising the fuel cell exhaust system, as claimed in the appended claims. According to an aspect of the present invention there is provided an apparatus for removing water and diluting purged hydrogen in an exhaust gas stream, comprising: a conduit having a first inlet for receiving an exhaust gas stream; a water separation device configured to remove water from the exhaust gas stream by causing a helical rotating flow of the exhaust gas stream to produce a drier exhaust gas stream; one or more mixing means disposed in the conduit downstream of the water separation device and configured to mix the drier exhaust gas stream with purged hydrogen.

By using a water separation device to remove water from the exhaust gas stream prior to it being mixed with the purged hydrogen, the rate and efficiency of mixing can be improved, as well as improve the homogeneity of the mixed exhaust gas stream and purged hydrogen. The use of a water separation device configured to remove water by causing a helical flow of the exhaust gas stream has been found to be particularly efficient at removing water and producing a drier exhaust gas stream.

By improving the efficiency of mixing, the overall path length required to achieve the desired level of mixing and resultant hydrogen concentration emerging from the end of the mixing path, i.e. conduit, can be reduced as compared to known arrangements, such as an arrangement in which mixing of the gases is achieved in a long conduit comprising a series of bends for mixing the gases.

Efficiency of mixing is further enhanced by the one or more mixing devices positioned in the conduit downstream of the water separation device as claimed, which improve the rate and efficiency of mixing of the drier exhaust gas stream and purged hydrogen.

Optionally, the exhaust gas stream may comprise the purged hydrogen.

Optionally, the apparatus may comprise a second inlet for receiving the purged hydrogen.

The provision of a second inlet enables the purged hydrogen to be introduced into the conduit separately to the exhaust gas flow. By introducing the purged hydrogen into the conduit via a second inlet, the location of mixing of the purged hydrogen with the exhaust gas flow in the conduit can be altered by altering the position of the second inlet relative to the longitudinal axis of the conduit.

Optionally, the first inlet may be positioned upstream of the water separation device. Positioning the first inlet upstream of the water separation device allows the water separation device to receive the exhaust gas stream and thus enables water to be removed from the exhaust gas stream prior so as to expel a drier exhaust gas stream from the downstream side of the water separation device.

Optionally, the second inlet may be positioned downstream of the water separation device.

Positioning the second inlet downstream of the water separation device introduces the purged hydrogen into the conduit, via the second inlet, at a part of the conduit containing a drier exhaust gas stream. Mixing of purged hydrogen with a drier exhaust gas stream has been found to be more effective as compared to mixing of purged hydrogen with an exhaust gas stream having a significant water content.

Optionally, the water separation device may comprise a swirl generator configured to deflect the exhaust gas stream in the helical rotating flow.

The swirl generator causes rotation of the exhaust gas flow which assists with mixing of gases and assists with removal of any residual water in the gas flow.

Optionally, the water separation device may comprise a collection portion configured to collect separated water from the exhaust gas stream.

By providing a collection portion, separated water from the exhaust gas stream can be kept separate to the incoming, “wetter” exhaust gas stream and the outgoing “drier” exhaust gas stream and can be more easily removed from the conduit, if required.

Optionally, the water separation device may comprise a receiving portion for receiving the drier exhaust gas stream.

By providing a receiving portion adapted to capture all of the incoming exhaust gas stream, for example by being wider than more downstream section of the water separation device, the exhaust gas stream passes unhindered into the water separation device.

Optionally, the swirl generator may be positioned upstream of the receiving portion and/ or collecting portion. Optionally, at least a part of the collection portion of the water separation device may be frusto- conical.

Optionally, the conduit may comprise a drain for release of water separated from the exhaust gas stream.

Provision of a drain in the conduit prevents water removed from the exhaust gas stream from collecting within the conduit.

Optionally, the water separation device may be positioned to overlie the drain in the conduit.

Positioning the water separation device so that it overlies the drain reduces the path length between the water separation device and the drain in which water removed from the exhaust gas stream is required to travel. Therefore, water can be evacuated from the conduit via the drain quickly.

Optionally, the water separation device comprises hydrophobic materials and/ or a hydrophobic coating.

The hydrophobic materials and/ or hydrophobic coating assists in repelling water off the surface(s) of the water separation device, thus increasing the efficiency and speed of removal of water from the water separation device and out of the conduit.

According to another aspect of the invention, there is provided a method of removing water and diluting purged hydrogen in an exhaust gas stream, the method comprising the steps of: introducing an exhaust gas stream into a conduit; causing a helical rotating flow of the exhaust gas stream to produce a drier exhaust gas stream; introducing purged hydrogen into the conduit; mixing the purged hydrogen and the drier exhaust gas stream.

The presence of the water separation device in the conduit in the claimed position means that purged hydrogen is introduced into the exhaust gas stream once a proportion of water has been removed from the exhaust gas, which increases the ease with which the purged hydrogen and exhaust gas stream mix together, as compared to mixing of the purged hydrogen with a non-dried gas stream. The configuration of the present water separation device which causes the exhaust gas stream to be rotated to remove water has been found to be particularly efficient at drying the exhaust gas stream. This results in an improved efficiency of mixing and improved homogeneity of the mixed purged hydrogen and exhaust gas stream expelled from the conduit. The presence of the one or more mixing devices disposed in the conduit downstream of the water removal device more effectively mixes the purged gases, e.g. purged hydrogen and exhaust gas stream, in the conduit across a shorter path length as compared to the path length required to achieve a comparable level of mixing or dilution in a known system, e.g. a long conduit comprising bends.

Optionally, the method may comprise discharging the mixed purged hydrogen and drier exhaust gas from the conduit, wherein the concentration of hydrogen in the mixed purged hydrogen and drier exhaust gas discharged from the conduit is 4% or less, by volume.

According to another aspect of the invention, there is provided a system comprising the apparatus disclosed herein, wherein the system comprises a hydrogen source in fluid communication with the at least one inlet of the conduit.

Optionally, the hydrogen source may comprise at least one hydrogen fuel cell.

Applying the apparatus in a fuel cell exhaust system means that mixing of the purged fuel (e.g. hydrogen) with exhaust gases is more efficient and homogenous as compared to known arrangements in which the exhaust gas stream is not dried before mixing with the purged hydrogen. This reduces the path length required for effective mixing of the drier exhaust gas stream with purged fuel from the fuel cell to achieve a desirable concentration of purged fuel in the mixed fuel and exhaust gas stream emerging from the fuel cell exhaust system.

According to another aspect of the invention, there is provided a vehicle comprising the system disclosed herein.

By applying the apparatus to a vehicle, the overall path length required for effective mixing and achieving the desired levels of dilution of purged hydrogen in the emergent exhaust gas stream from the apparatus as a result of the arrangement of one or more mixing devices in the conduit and the provision of the water separation device to dry the exhaust gas stream, is significantly reduced as compared to known methods of mixing exhaust gases emitted from cars, such as a long conduit extending substantially the length of the vehicle. The shorter path length required by the apparatus only takes up a fraction of the length of the vehicle, in contrast to the known, long conduit apparatus, thus freeing up vital space for other components on the underside of the vehicle. 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 invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows an exploded view of an embodiment of apparatus in accordance with the present invention, comprising a centrifugal type water separation device and a plurality of mixing devices positioned in a conduit;

Figure 2 shows a cross-sectional schematic illustration of an embodiment of apparatus in accordance with the present invention, and illustrating the various flow paths within the embodiment of the apparatus during use and thus illustrating an embodiment of method in accordance with the present invention;

Figure 3 shows a perspective view of a downstream face of the plurality of mixing devices shown in Figure 2;

Figure 4 shows a side view of a housing in the form of a conduit in which the mixing devices shown in Figure 3 are arranged in series along a longitudinal axis of the conduit and a water separation device is positioned in the conduit between some of the mixing devices;

Figure 5 shows a schematic representation of the profile of some of the individual fins of the plurality of mixing devices shown in Figure 3;

Figure 6 shows a schematic illustration of a vehicle to which an apparatus or a system according to the present invention may be fitted and/ or which may employ the method of the present invention; and Figure 7 shows a flow chart of an embodiment of a method in accordance with the present invention.

DETAILED DESCRIPTION

An apparatus in accordance with embodiments of the present invention is described herein with reference to the accompanying Figures. As described with reference to Figure 7, the apparatus can be installed in a vehicle. The vehicle 100 in the embodiment relating to Figure 7 is an automobile, such as a wheeled vehicle, but it will be understood that the apparatus may be used in other types of vehicle, such as but not limited to watercraft or any other type of vehicle having an exhaust gas system. Similarly, the method, system and fuel cell system described herein can be applied to a vehicle, such as a wheeled vehicle as shown in Figure 6, but as with the apparatus, the method, system and fuel cell system described herein can be applied to other types of vehicle such as but not limited to watercraft or any other type of vehicle having an exhaust gas system.

The apparatus 10 of the present invention is configured to dilute reacted fuel gas, such as hydrogen in the present example, and optionally other contaminants from a fuel cell to levels which are considered to be safe for release into the atmosphere. The reacted fuel gas is released from the fuel cell (not shown) when a valve (not shown) coupled to the fuel cell is opened. The valve is coupled to a conduit which fluidly connects the fuel cell and the apparatus 10 of the present invention so that when the valve is opened, the reacted fuel gas can transfer from the fuel cell into the apparatus 10 of the present invention via the conduit. As will be explained more fully, the conduit of the apparatus 10 comprises one or more mixing means for mixing an exhaust gas stream and purged hydrogen, and also comprises a water separation device which is configured to rotate the exhaust gas stream to remove water from the exhaust gas stream to facilitate mixing of the drier exhaust gas stream with the purged hydrogen. The water separation device may be positioned at different locations in the conduit relative to the one or more mixing devices, in different embodiments of the invention.

An embodiment of an apparatus 10 according to the present invention comprises a housing 12 which generally defines a conduit 12, as shown in each of the embodiments shown in Figures 1 and 2, respectively. Referring to Figures 1 and 2, the housing 12 comprises a first part 12a and a second part 12b. At the upstream end of the first part 12a is a first inlet 14 for receiving an exhaust gas stream A and the downstream end of the first part 12a comprises an annular flange 16 for securing the first part 12a to a corresponding annular flange 18 on the second part 12b of the housing 12. The conduit 12 comprises a second inlet 66 for receiving purged hydrogen, which is shown on Figure 2. The second inlet 66 is positioned downstream of the first inlet 14 and upstream of a plurality of mixing devices 28a, 28b, 30a, 30b, 34, 36 as will be described.

The second part 12b of the housing 12 comprises an outlet 20 at the downstream end for discharging the exhaust gas stream A and the purged hydrogen B after they have been mixed together in the housing or conduit 12, as will be explained. The upstream end of the second part 12b of the housing 12 comprises an annular flange 18. The first and second parts 12a, 12b of the housing 12 are secured together using a plurality of fasteners 22 to couple the annular flanges 16, 18 of each of the first and second parts 12a, 12b together. Each of the first housing part 12a and second housing part 12b comprises a pair of mounting brackets (not shown) for mounting the housing or conduit 12 onto a surface. In the present example, the mounting brackets are intended to secure the housing 12 to a surface on the underside 100a of a vehicle 100, such as that schematically shown in Figure 6. It is to be understood that the configuration of the housing 12 in the present embodiment is not intended to be limiting. Other configurations of housing or conduit 12 may also be suitable for use in accordance with the present apparatus 10.

Positioned inside the housing or conduit 12 of the present embodiment is a plurality of mixing devices 28a, 28b, 30a, 30b positioned downstream of a water separation device 56, which is described in more detail below. Other embodiments of the apparatus 10 may comprise a single mixing device. In the present embodiment, the plurality of mixing devices 28a, 28b, 30a, 30b are secured to a generally planar, rectangular mounting plate 32 which is positioned substantially mid-way between the inlet 14 of the first part 12a of the housing 12 and the outlet 20 of the second part 12b of the housing 12. It is to be understood that this positioning is not necessarily essential and that the plurality of mixing devices 28a, 28b, 30a, 30b may be mounted elsewhere in the housing or conduit 12. It is also to be understood that the shape and/ configuration of the mounting plate 32 or, more generally, mounting means for mounting one or more mixing devices, may differ from that described and illustrated in respect of the present embodiment.

The plurality of mixing devices 28a, 28b, 30a, 30b are generally positioned to intersect the flow of the exhaust gas stream A and purged hydrogen B. In one embodiment, such as in accordance with the embodiment of Figure 1 and Figure 2, the exhaust gas stream A and purged hydrogen Beach enters the housing 12 at distinct locations, as shown in Figures 1 and 2. through the inlet 14 of the first housing part 12a. The exhaust gas stream A enters the housing, or conduit 12, through the inlet 14 of the first housing part 12a. The inlet 14 is positioned upstream of a water separation device 56 which is positioned in the conduit 12 for removing water from the incoming exhaust gas stream A, as will be explained. The purged hydrogen B is introduced into the conduit 12 via a separate inlet 66 which opens into the conduit in a position which is downstream of the water separation device 56 and upstream of the mixing devices 28a, 28b, 30a, 30b, such that the flow of purged hydrogen B does not pass through the water separation device 56 but does pass through the mixing devices 28a, 28b, 30a, 30b as is explained below.

However, in one or more different embodiments of the present invention, the water separation device 56 may be positioned elsewhere relative to the purged hydrogen inlet B. For example, the purged hydrogen B may enter the conduit 12 via the same inlet as the exhaust gas stream A. In such an embodiment, the purged hydrogen B may also pass through the water separation device 56 before flowing downstream in the conduit 12 with the exhaust gas stream A to one or more mixing devices which further mix the purged hydrogen and drier exhaust gas stream D before it is released through the outlet 20 of the conduit 12.

In the present embodiment, this is achieved by mounting the plurality of mixing devices 28a, 28b, 30a, 30b on first and second mixing plates 34, 36 which extend generally perpendicularly with respect to the planar mounting plate 32. This is explained in more detail below. The planar mounting plate 32 is then mounted in the housing or conduit 12 such that the longer side of the rectangular mounting plate 32 extends along a longitudinal axis of the housing or conduit 12, the longitudinal axis being generally in the direction of the arrow labelled C on Figure 1.

The mounting plate 32 is sized and shaped so as to conform with the internal dimensions of the housing or conduit 12. Similarly, the size and shape of the plurality of the mixing plates 34, 36 also conforms to the internal dimensions of the housing 12. By ensuring that the dimensions of the mixing plates 34, 36 and mounting plate 32 onto which they are secured conform to the internal dimensions of the housing or conduit 12, all or substantially all, of the exhaust gas stream A and purged hydrogen B is directed through the mixing devices 28a, 28b, 30a, 30b and is unable to bypass the mixing plates 34, 36. This arrangement ensures thorough mixing of the exhaust gas stream A and the purged hydrogen B within the housing or conduit 12. It is to be understood that in one or more other embodiments, it may be the shape and/ or dimensions of the one or more mixing devices which are configured to conform to the internal dimensions of the housing or conduit 12, for example, in an embodiment in which the one or more mixing devices are mounted directly to the housing or conduit 12 instead of on mixing plates as shown in the present example.

In the embodiment shown in Figure 1 and Figure 2, the apparatus is provided with a centrifugal-type water separation device 56 positioned downstream of the exhaust gas stream A inlet and upstream of a second inlet 66 for receiving purged hydrogen gas B. The inlet 66 is in fluid communication with the internal cavity of the conduit and introduces the purged hydrogen B into the conduit in the region of the “drier” exhaust gas stream emerging from the downstream side of the water separation device 56.

The apparatus 10 is provided with a centrifugal-type water separation device 56 positioned between the inlet 14 of the first part 12a of the housing 12 and the mixing devices 28a, 28b, 30a, 30b. The water separation device 56 removes a proportion of water from the exhaust gas stream A before the “drier” exhaust gas stream D passes through to the mixing devices 28a, 28b, 30a, 30b.. It is to be appreciated that any water separation device capable of causing a helical rotating flow may be employed in the present apparatus and that the examples of water separation devices described herein are by way of non-limiting example.

In the example embodiment shown in Figure 2, the water separation device 56 is mounted at an upstream end of the rectangular mounting plate 32 and upstream of the mixing devices 28a, 28b, 30a, 30b so as to intersect the flow of the exhaust gas stream A and purged hydrogen B entering the housing, or conduit 12 through inlet 14.

It is to be appreciated that varying housing/ conduit/ exhaust passage geometries will require an alteration of the water separation device 38 and/ or mixing devices 28a, 28b, 30a, 30b and/ or mixing plates 34, 36 and/ or mounting plate 32 to enable each of the aforementioned components to fit tightly within the housing or conduit 12 or an exhaust passage.

By way of example, Figure 4 illustrates, in cross section, an embodiment of apparatus 10 comprising a plurality of mixing devices 28a’, 30a’ spaced apart in a conduit 12’. As seen from Figure 3, a first mixing device 28a’ is positioned upstream of a second mixing device 30a’, and a water separation device 38’ is positioned adjacent the upstream side of the downstream, i.e. second mixing device 30a’. The mixing devices 28a’, 30a’ are, in the present example, of the same configuration as shown in the embodiment in Figure 2. A swirl generator 54, schematically illustrated in Figure 2, rotates the incoming exhaust gas stream A. The rotating exhaust gas stream A subsequently enters the water separation device 56. The generally conical shape of the water separation device 56 causes the incoming rotating gas stream to be deflected around the inner surface of the conical separation device 56 which maintains the rotational flow of the exhaust gas stream A initiated by the swirl generator. As the gas stream A rotates in the separator 56, water present in the gas stream A moves radially outward under centrifugal force, causing it to contact the inner surface of the water separation device 56. The water droplets W then move downwardly towards a drain 64 in the conduit 12 and underlying the water separation device 56, which allows water collected by the separation device 56 to drain out of the conduit.

The inventors found that by positioning the one or more mixing means, which may include simple mixing means such as one or more bends in a conduit (such as an exhaust tail pipe), downstream of the water separation device 56 and thus downstream of the “drier” exhaust gas stream and purged hydrogen inlet, mixing of the “drier” exhaust gas stream and purged hydrogen could be achieved more quickly because the drier exhaust gas stream more readily mixed with the purged hydrogen as compared to an exhaust gas stream from which the water had not been removed. An effect of this is that the path length of the conduit, which may, in an example embodiment, be in the form of an exhaust tail pipe, can be reduced as compared with known arrangements. A further effect of positioning the water separation device downstream of the exhaust gas inlet and upstream of the purged hydrogen inlet is that removal of a significant proportion of water from the exhaust gas stream prior to mixing it with the purged hydrogen produces a more homogenously mixed gas stream, and also allows for more rapid mixing of the exhaust gas stream and purged hydrogen as compared to mixing the two gas streams before water has been removed from the exhaust gas stream. The drier exhaust gas stream more readily mixing with the purged hydrogen gas produces a more homogenous mixture of exhaust gas and purged hydrogen, which in turn results in a more consistent dilution of purged hydrogen within the exhaust gas stream emerging from the apparatus.

The mixing devices of the present embodiment of the apparatus will now be described in more detail. The embodiment shown in Figures 1 and 2 comprises four static mixing devices 28a, 28b, 30a, 30b each of which, in very general terms, resembles a fan-like structure having a plurality of inclined surfaces S, S’ extending radially outward from a hub 44. The plurality of inclined surfaces S, S’ are referred to hereinafter as vanes S, S’. In the present embodiment, each vane S, S’ comprises at least one curved surface, as will be explained, although vanes comprising only generally planar surfaces may also be used in one or more embodiments. The vanes S, S’ are static. This arrangement is most clearly shown in Fig. 3. The four mixing devices 28a, 28b, 30a, 30b are arranged such that two mixing devices 28a, 28b are formed spaced apart side by side on a first mixing plate 34 which extends substantially perpendicularly from the planar mounting plate 32, and a further two mixing devices 30a, 30b are formed spaced apart and side by side on a second mixing plate 36 which extends substantially perpendicularly from the planar mounting plate 32. The first and second mixing plates 34, 36 are spaced apart along a longitudinal axis (in the direction of arrow, C) of the conduit 12, as shown in the Figures.

It is to be appreciated that other embodiments may have a different arrangement of mixing devices as compared with that of the present embodiment. For example, one or more embodiments may comprise a single mixing device which may or may not be mounted on a mixing plate, or may comprise a plurality of mixing devices having one or more mixing devices disposed on one or more mixing plates disposed throughout the conduit. One or more embodiments may use a series of bends in conduit to achieve mixing, for example such as embodiment relating to an exhaust tail pipe extending substantially the length of a vehicle to which it is fitted and comprising a series of bends for deflecting air and mixing exhaust gases within the tail pipe.

In the present example, the each mixing device 28a, 28b, 30a, 30b is integrally joined with its respective mixing plate 34, 36. However, in another example, each mixing plate 34, 36 may comprise one or more apertures into which a separate mixing device can be securely mounted. As perhaps best appreciated from Figures 1 and 2, each mixing device 28a, 28b, 30a, 30b comprises an inlet or upstream side 46 and an outlet or downstream side 48.

The inlet or upstream side 46 comprises, in the present example, a recessed annular flange 50 which is integrally joined with the outer-most edge of the upstream side of each of the vanes S, S’. The recessed portion of the flange 50 projects away from the downstream side of the mixing plate 34, 36 as best seen on Figure 1 . The inner-most edge of each of the vanes is connected to a central hub 44 around which the vanes S, S’ are radially mounted. The hub is generally cone-shaped on the inlet surface and extends from the inlet or upstream side in the direction of the incoming exhaust gas stream A and purged hydrogen flow B, as shown in Figure 1. In the present example, each of the mixing devices 28a, 28b, 30a, 30b comprises nine static vanes S, S1 extending radially from the central hub 44.

On the downstream or outlet side of each mixing device 28a, 28b, 30a, 30b, the static vanes S, S’ extend away from the downstream face 48 of each mixer plate 34, 36 such that they project from a first point on the annular flange 50 on downstream face of the mixing plate 34, 36 in a plane that is generally perpendicular to the upstream and downstream faces 46, 48 of the mixing plate 34, 36, before curving back towards a second point on the annular flange 50 on the downstream side of the mixer plate 34, 36 to define a vane S, S1 having a generally concave first, upstream side and corresponding convex second, downstream side. The vanes S, S1 are spaced apart around the annular flange.

The axial spacing 52 between the static vanes S, S’ creates space through which the exhaust gas stream A and purged hydrogen B can flow from the upstream side of the each mixing device 28a, 28b, 30a, 30b as the exhaust gas stream A and purged hydrogen B are deflected off the concave and convex surfaces of each vane S, S1 . As the exhaust gas stream A and purged hydrogen B moves through each mixing device 28a, 28b, 30a, 30b, the inclined surface of each vane causes the exhaust gas stream A and purged hydrogen flow B to change direction which causes mixing of the exhaust gas stream A and purged hydrogen B.

On the first mixing plate 34, the vanes of one mixing device 28a deflect the incoming drier exhaust gas stream and purged hydrogen in an anti-clockwise direction and the vanes of the second mixing device 28b are configured to deflect the incoming drier exhaust gas stream D and purged hydrogen B in a clockwise direction, to produce a tumbling flow of mixed exhaust gas and purged hydrogen AB emerging from the downstream side of the first mixing plate 34.

On the second mixing plate 34, the mixing devices 30a, 30b are configured such that the vanes of one mixing device 30a deflect the incoming mixed drier exhaust gas stream and purged hydrogen AB in an anti-clockwise direction and the vanes of the second mixing device 30b are configured to deflect the incoming mixed drier exhaust gas stream and purged hydrogen AB in a clockwise direction, to create further turbulence in the tumbling flow of mixed exhaust gas and purged hydrogen AB. The turbulent flow ABT of mixed exhaust gas and purged hydrogen AB is released out of the conduit 12 via outlet 20 positioned at the downstream end of the conduit.

It is to be appreciated that other embodiments of mixing may comprise a different number of vanes, or may arrange the vanes, or more generally a plurality of inclined surfaces in a different configuration so as to achieve mixing of the exhaust gas stream and purged hydrogen.

The angle and shape of each of the inclined surfaces or vanes S, S’ may differ between embodiments of mixing device, to cause a suitable deflection to achieve the required mixing pattern of the exhaust gas stream and purged hydrogen. The vanes S, S’ may be configured to have generally planar faces in one or more embodiments. Figure 5 illustrates the profile of some of the outer-most tips 52 of the surfaces of the vanes S, S’ of the mixer devices shown in Fig. 1. The effect of the positioning of the water separation device relative to the exhaust gas and purged hydrogen inputs will be described in more detail and with reference to Figure 2, as an example embodiment. Figure 2 also illustrates a method according to an embodiment of the present invention, as will be described. Referring to the embodiment of Figure 2, the apparatus 10 of the present invention is shown comprising a centrifugal-type water separation device 56.

The exhaust gas stream A enters a swirl generator 54 in the water separation device 56 which is upstream of the plurality of mixing devices 28, 30. The mixing devices 28, 30 in the present example are as per those described above and illustrated in Figures 1 and 3. The swirl generator 54 is in accordance with known swirl generators 54 and so will not be described in detail. The swirl generator 54 is configured to receive a generally laminar flow of exhaust gas stream A and rotate the exhaust gas stream A to produce a swirling flow of exhaust gas A. The swirling motion causes water droplets W in the exhaust gas stream W to be forced radially outward out of the exhaust gas stream A, as they are heavier than the remaining exhaust gases, so that they collect on the inner surface of the water separation device 56, which, in the present embodiment, is generally conical in shape and comprises an inwardly extending annular rim 58 which extends inwardly from an outer wall 62 of the water separation device 56 and towards the upstream end of the conduit 12, terminating before it reaches a downstream side of the swirl generator 54, to define an inner wall 60 of the water separation device 56 which is spaced apart from the outer wall 62. The outer wall 62 may or may not be integrally formed with the conduit 12.

For ease of reference, the “incoming” exhaust gas stream which comprises the full amount of water discharged from the exhaust gas system is identified on the Figures as A, whereas the “drier” exhaust gas stream emerging from the water separation device is identified as D. Mixed exhaust gas and purged hydrogen is identified as AB on Figure 2.

The inwardly extending annular rim 58 prevents collected water droplets W from being forced through the conduit 12 under the pressure associated with the exhaust gas. Instead, the collected water droplets W are able to drain out of the water separation device 56 and the conduit 12 via a drain 64 which underlies a part of the inwardly extending annular rim 58 and inner wall 60.

The exhaust gas stream D emerging from the downstream side of the water separation device 56 is therefore drier than the exhaust gas stream A entering the swirl generator 54 on the upstream side of the water separation device 56. This can be advantageous in that the drier exhaust gas stream D improves ease of mixing with purged hydrogen B as compared to an exhaust gas stream having a higher water content, which improves the homogeneity of the resulting mixture of purged hydrogen and exhaust gas stream, thus producing a more consistent dilution of purged hydrogen in the exhaust gas stream emerging from the outlet 20 of the conduit 12.

In the present example shown in Figure 2, the conduit 12 is provided with an inlet 66 for introducing purged hydrogen B into the conduit. The inlet 66 is positioned downstream of the water separation device in the present embodiment. This positioning can be advantageous in that the purged hydrogen B is introduced to the drier exhaust gas stream D and so may more easily mix.

The purged hydrogen B initially combines with the drier exhaust gas stream D emerging from the downstream side of the water separation device 56 before, under pressure from the exhaust system, the drier exhaust gas stream D and purged hydrogen B move downstream towards the first upstream mixing device 28. The first, upstream mixing plate 34 is in accordance with the embodiment of mixing plate 34 shown on Figure 1 and Figure 3 and thus is configured so that the vanes of one mixing device 28a on the mixing plate 34 deflect the incoming drier exhaust gas stream and purged hydrogen in an anti-clockwise direction and the vanes of the second mixing device 28b on the mixing plate 34 are configured to deflect the incoming drier exhaust gas stream D and purged hydrogen B in a clockwise direction, to produce a tumbling flow of mixed exhaust gas and purged hydrogen AB, ABT emerging from the downstream side of the first mixing plate 34.

The second mixing plate 36 which comprises two mixing devices in accordance with the embodiment of mixing plate 36 shown on Figure 3, receives the emergent mixed exhaust gas and purged hydrogen AB, ABT from the downstream side of the first mixing plate 34. As with the first mixing plate 34, the second mixing plate 36 is configured so that the vanes of one mixing device 30a on the mixing plate deflect the incoming mixed drier exhaust gas stream and purged hydrogen AB in an anti-clockwise direction and the vanes of the second mixing device 30b on the mixing plate 36 are configured to deflect the incoming mixed drier exhaust gas stream and purged hydrogen AB in a clockwise direction, to create further turbulence in the tumbling flow of mixed exhaust gas and purged hydrogen AB, ABT. The turbulent flow of mixed exhaust gas and purged hydrogen AB is released out of the conduit 12 via outlet 20 positioned at the downstream end of the conduit. In general terms, an embodiment of method of diluting purged hydrogen gas is schematically illustrated by the flow chart in Figure 7.

Figure 7 illustrates a method 200 according to an embodiment of the present invention. The method 200 comprises introducing 202 an exhaust gas stream A into a conduit 12, causing 204 a helical rotating flow of the exhaust gas stream A to produce a drier exhaust gas stream by forcing water W out of the exhaust gas stream under centrifugal force, introducing 206 purged hydrogen B into the conduit 12, mixing 208 the purged hydrogen B and the drier exhaust gas stream D, discharging 210 the mixed purged hydrogen and dried exhaust gas stream from the conduit 12. The final step in Figure 7 of discharging 210 the mixed purged hydrogen and exhaust gas stream from the conduit 12 is intended to illustrate an example of a flow path taken by the mixed purged hydrogen and exhaust gas stream after the mixing stage within the conduit when the method is in use in a particular application, such as in an exhaust gas system. However, it is to be appreciated that the step of discharging 210 the mixed purged hydrogen and exhaust gas stream from the conduit 12 is not an essential step of the invention.

It is to be appreciated that other embodiments of mixing devices may be configured to deflect the exhaust gas stream and purged hydrogen in a different manner which may or may not include a rotational flow element as per the present embodiment. In general terms, the mixing devices are configured to receive a flow of gas, either substantially laminar or non-laminar in flow, and deflect the received flow to produce a turbulent flow, i.e. a flow in different directions, which may or may not have a rotational element as per the tumbling flow described in relation to the present example.

The position of the water separation device 56 downstream of the exhaust gas inlet 14, allows for more effective mixing and thus dilution of the purged hydrogen B in the exhaust gas stream A as compared to an arrangement in which the purged hydrogen is mixed with the exhaust gas stream prior to removal of water from the exhaust gas.

By arranging the water separation device to “dry” the exhaust gas stream before mixing with the purged hydrogen, the rate and homogeneity of mixing of the exhaust gas stream and purged hydrogen is increased, which improves the efficiency of mixing. An effect of this is that the path length of the conduit, which may, in an example embodiment, be in the form of an exhaust tail pipe, can be reduced as compared with known arrangements. The present inventors have also found that the above-mentioned advantages can also be achieved even if the water separation device is positioned downstream of both the exhaust gas stream inlet and purged hydrogen inlet, such that the combined stream of exhaust gas and purged hydrogen enters the upstream side of the water separation device. The present invention is not therefore necessarily limited to an arrangement in which the water separation device is positioned in a particular location in the conduit relative to the purged hydrogen inlet.

This above-mentioned technical effect can be further supplemented by providing a plurality of mixing devices that are configured to deflect, i.e. change the direction of the gas stream flow, in the conduit as described herein, to further improve efficiency of mixing of the drier exhaust gas stream and purged hydrogen and thus also enables effective mixing of the purged hydrogen with an exhaust gas stream across a much smaller path length as compared with an arrangement which comprises a longer path length having alternative mixing means such as bends.

The addition of a plurality of mixing devices as described herein, either in a single mixing plate or in a series of mixing plates disposed along the longitudinal axis of the conduit increases the amount of turbulence that can be created in the flow of exhaust gas and purged hydrogen in the apparatus, thus even further improving the technical effect of the present invention. Therefore, it will be appreciated that employing a plurality of mixing devices either in a single plane or on a single mixing plate in the conduit and/or by providing a series of mixing devices disposed along the longitudinal axis of the conduit, the path length required for effective mixing and achieving the desired levels of dilution of purged hydrogen in the emergent exhaust gas stream from the apparatus, can be substantially reduced. This is of particular benefit when the apparatus is used in applications where space is at a premium, for example on the underside of a vehicle, such as that illustrated in Figure 6. Instead of employing, for example, a long conduit extending substantially the length of the vehicle and comprising bends for creating turbulence to mix various exhaust gases, the present invention can be applied to achieve effective mixing of the exhaust gas stream and purged hydrogen across a much smaller path length and thus takes up only a fraction of the length of the vehicle, thereby freeing up vital space for other components on the underside of the vehicle.

As a further consequence of the reduced path length, design considerations for accommodating the various components on the underside of the vehicle are significantly simplified by using the present invention, as it is no longer necessary for designers to have to accommodate a long exhaust conduit with its multiple bends that traditionally are required to extend substantially the length of the vehicle. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.