TECHNICAL FIELD

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

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.

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 diluting purged hydrogen in an exhaust gas stream, a fuel cell exhaust system comprising the apparatus, a vehicle comprising the fuel cell exhaust system and a method for diluting purged hydrogen in an exhaust gas stream, as claimed in the appended claims

According to an aspect of the present invention there is provided an apparatus for diluting purged hydrogen in an exhaust gas stream, comprising a conduit having at least one inlet for receiving purged hydrogen and an exhaust gas stream, and one or more mixing devices disposed in the conduit, wherein the one or more mixing devices are configured to mix the purged hydrogen and the exhaust gas stream.

By providing a plurality of mixing devices, either in a single mixing plate or in a series of mixing plates disposed along the longitudinal axis of the conduit, the amount of turbulence that can be created in the flow of exhaust gas and purged hydrogen in the apparatus is increased, thus improving the mixing of the exhaust gas and purged hydrogen which leads to a reduction or dilution of the concentration of hydrogen present, by volume, in the exhaust gas stream emerging from the apparatus.

By 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 as compared with an arrangement which comprises a longer path length having alternative mixing means such as bends in the path or conduit.

According to another aspect of the invention, there is provided a fuel cell exhaust system comprising the apparatus disclosed herein.

Applying the apparatus in a fuel cell exhaust system reduces the path length required for effective mixing of the 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 fuel cell exhaust system according to the previous aspect of the invention.

According to another aspect of the invention, there is provided a vehicle comprising the apparatus 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, 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.

According to another aspect of the invention, there is provided a method for diluting purged hydrogen in an exhaust gas stream, the method comprising introducing purged hydrogen and an exhaust gas stream into a conduit, and deflecting the purged hydrogen and the exhaust gas stream using one or more mixing devices disposed in the conduit to achieve mixing of the purged hydrogen and the exhaust gas stream.

The use of one or more mixing devices disposed in the conduit 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 apparatus may comprise a plurality of mixing devices, the mixing devices may be disposed in substantially the same plane along a longitudinal axis of the conduit.

A plurality of mixing devices further improves the efficiency of mixing of the purged hydrogen and exhaust gas stream. Disposing the mixing devices in substantially the same plane along a longitudinal axis of the conduit, for example by mounting mixers in substantially the same plane, e.g. “twin mixers”, around an inner surface of the conduit can increase the turbulence and thus efficiency of mixing at a predetermined location in the conduit.

Optionally, the apparatus may comprise a plurality of mixing devices. The plurality of mixing devices may be spaced apart along a longitudinal axis of the conduit.

Spacing the plurality of mixing devices along a longitudinal axis of the conduit further improves the efficiency of mixing at least in part because the gases are being mixed by each of the plurality of mixing devices at more than one location in the conduit.

Optionally, the plurality of mixing devices may comprise at least one upstream mixing device and at least one downstream mixing device that is positioned in the conduit downstream of the at least one upstream device, wherein the at least one downstream mixing device may be configured to receive a turbulent stream of purged hydrogen and exhaust gas stream deflected from the at least one upstream mixing device.

By arranging at least one downstream mixing device to receive a turbulent stream of purged hydrogen and exhaust gas stream deflected from at least one upstream mixing device, turbulence in the flow of purged hydrogen and exhaust gas in the conduit can be increased, thus increasing the efficiency of mixing. Optionally, the downstream mixing device may be configured to deflect the purged hydrogen and exhaust gas stream in a different direction to the turbulent stream of purged hydrogen and exhaust gas stream deflected from the at least one upstream mixing device.

By deflecting the purged hydrogen and exhaust gas stream in different directions in the conduit, turbulence in the stream of purged hydrogen and exhaust gas is increased, thus increasing the efficiency of mixing.

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

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

Optionally, the apparatus may comprise a water separation device for removing a proportion of water from the exhaust gas stream.

Providing a water separation device to remove a proportion of water from the exhaust gas stream produces a drier exhaust gas stream which improves efficiency of mixing when the drier exhaust gas stream is mixed with the purged hydrogen in the conduit.

Optionally, the water separation device may be positioned upstream of the one or more mixing devices.

Positioning the water separator upstream of the one or more mixing devices means that water is removed from the exhaust gas stream before the exhaust gas stream is mixed with the purged hydrogen by the one or more mixing devices, thus improving efficiency of mixing by mixing a drier exhaust gas stream with the purged hydrogen.

Optionally, the plurality of mixing devices may be disposed on an inner surface of the conduit. The plurality of mixing devices may be disposed around on an inner circumferential surface of the conduit.

Disposing the mixing devices on an inner surface, optionally an inner circumferential surface of the conduit means that no additional space is taken up by the mixing devices. Optionally, each of the one or more mixing devices may comprise a plurality of planar and/or curved surfaces for deflecting the purged hydrogen and exhaust gas stream.

Providing a plurality of planar and/ or curved surfaces changes the deflection angle of the gases so that the nature of the turbulent mixing can be modified in dependence on the angle of the planar and/or curved surface, to achieve the desired flow/ mixing pattern.

Optionally, the configuration of the plurality of planar and/or curved surfaces may cause clockwise and/or anti-clockwise air flow.

Clockwise and/or anti-clockwise air flow causes rotational flow of the purged hydrogen and exhaust gas stream which has been found to produce effective mixing. An arrangement comprising both clockwise and anticlockwise air flow, such as via a plurality of mixing devices, produces a folding or tumbling effect of gas flow which significantly improves mixing.

Optionally, the plurality of planar and/or curved surfaces may be arranged at one or more inclined angles relative to a longitudinal axis of the conduit. Such a configuration may assist in deflecting the air flow in one or more different directions relative to the longitudinal axis of the conduit. This improves the efficiency of mixing of the purged hydrogen and exhaust gas stream.

Optionally, the plurality of planar and/or curved surfaces of each of the one or more mixing devices may comprise fins or blades.

Optionally, the fins or blades of the plurality of planar and/ or curved surfaces of each of the one or more mixing devices may extend radially outward from one or more hubs on each of the one or more mixing devices. This provides a convenient arrangement for providing a plurality of surfaces for deflection of the gases.

Optionally, the apparatus may be disposed in a fuel cell exhaust system.

Provision of the apparatus in a fuel cell exhaust system enables purged fuel from the fuel cell to be effectively mixed and diluted in the exhaust system prior to release into the atmosphere.

Optionally, a concentration of a concentration of hydrogen in the mixed purged hydrogen and exhaust gas stream discharged from the conduit is 4% or less, by volume. A concentration of 4% or less of purged hydrogen in the exhaust gas stream and discharged from the conduit is optimal according to present emissions standards.

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 an apparatus for diluting purged hydrogen in an exhaust gas stream, according to the present invention;

Figure 2 shows a perspective view of a downstream face of the plurality of mixing devices shown in Figure 1 ;

Figure 3 shows a side view of a housing in the form of a conduit in which the mixing devices shown in Figure 2 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 4 shows a schematic representation of the profile of some of the individual fins of the plurality of mixing devices shown in Figure 1 ;

Figure 5 shows a schematic illustration of an embodiment of apparatus in accordance with the present invention, shown in cross-section and illustrating the various flow paths within the embodiment of the apparatus during use; 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

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.

An embodiment of an apparatus 10 according to the present invention comprises a housing 12 which generally defines a conduit 12, as shown in Figure 1. The housing 12 comprises a first part 12a and a second part 12b. At the upstream end of the first part 12a is an inlet 14 for receiving an exhaust gas stream A and, in the present example, purged hydrogen B, in a combined stream AB, hereinafter “combined stream”, 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 second part 12b of the housing 12 comprises an outlet 20 at the downstream end for discharging the combined stream AB after the combined stream AB has been mixed together in the housing or conduit 12 to dilute the proportion of hydrogen in the gas stream discharged from the outlet 20, 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. 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 combined stream AB which enters the housing 12 through the inlet 14 of the first housing part 12a. 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 combined stream AB 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 components of the combined stream AB, namely the exhaust gas 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 , the apparatus 10 is also provided with a generally planar water separation device 38 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 38 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. The water separation device 38 in the present example is a known condensation plate and therefore will not be described in detail, but in general terms, comprises a filter screen which traps a proportion of the water from the combined stream AB as the combined stream AB passes through the filter, which “dries” the combined stream AB prior to it reaching the mixing devices 28a, 28b, 30a, 30b.

In the present example shown in Figure 1 , the water separation device 38 is mounted onto an end plate 40 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 combined stream AB entering the housing, or conduit 12. The end plate 40 extends from the planar rectangular mounting plate 32 at an angle between around 90 degrees and 110 degrees relative to the mounting plate 32 so as to be able to intersect the incoming combined stream AB when the mounting plate 32 is situated in the housing or conduit 12. As with the mixing plates 34, 36, the shape and configuration of the end plate 40 conforms to the internal dimensions of the housing or conduit 12 so as to force all or substantially all of the combined stream AB (in the present example) through the water separation device 38 and to prevent any of the combined stream AB from bypassing the filter of the water separation device 32. It is to be appreciated that in one or more alternative embodiments, the purged hydrogen may be introduced into the housing or conduit 12 downstream of the water separation device 38 and will therefore not pass through it as the exhaust gas stream A will.

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 3 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 1 . The water separation device 38’ in this embodiment is generally conical, in contrast to the generally planar water separation device 38 of the embodiment of Figure 1. The conduit 12’ also comprises a drain 42 in the present embodiment, for draining water collected by the water separation device 38’, out of the conduit 12’.

The water separation device is not an essential feature of the present invention. The apparatus 10 of the present invention effectively mixes the components (exhaust gas and purged hydrogen) of the combined stream AB without necessarily requiring the water separation device to do so, as will be described below. The apparatus 10 of the present invention is also able to achieve the technical effects of the invention, which include a reduction in the path length of a conduit or similar space in which the purged hydrogen and exhaust gas stream are mixed, irrespective of whether the purged hydrogen is introduced into the apparatus 10 with the exhaust gas stream, as described in relation to Figure 1 , or separately, as described in relation to Figure 5, so as to dilute the purged hydrogen to an acceptable percentage concentration, as compared with known arrangements. The water separation device may be useful in further improving the ease with which the purged hydrogen and exhaust gas stream are mixed as mixing of “drier” gas streams, i.e. after removal of a significant proportion of water from the exhaust gas stream is generally easier and produces a more homogenous mixed gas stream.

The mixing devices of the present embodiment of the apparatus will now be described in more detail. The embodiment shown in Figure 1 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. 2. 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.

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 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 2. 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 combined stream AB, 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 combined stream AB (Figure 1) (or separate exhaust gas stream A and purged hydrogen B as shown in Figure 5) can flow from the upstream side of the each mixing device 28a, 28b, 30a, 30b as the combined stream AB/ exhaust gas stream A and purged hydrogen B are deflected off the concave and convex surfaces of each vane S, S1. As the combined stream AB (or separate exhaust gas stream A and purged hydrogen B (Fig. 5) moves through each mixing device 28a, 28b, 30a, 30b, the inclined surface of each vane causes the combined stream AB/ exhaust gas stream A and purged hydrogen flow B to change direction which causes mixing of the components of the combined stream AB, namely the exhaust gas A and purged hydrogen in the example shown in Figure 1 , or the separate exhaust gas stream A and purged hydrogen B if referring to Figure 5.

On the first mixing plate 34, the vanes of one mixing device 28a deflect the incoming drier combined stream AB (e.g. Figure 1 embodiment)/ exhaust gas stream A and purged hydrogen B (e.g. Figure 5 embodiment) 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 emerging from the downstream side of the first mixing plate 34. The combination of a mixer 28a configured to deflect the gas stream in an anti-clockwise direction and a mixer 28b configured to deflect the gas stream in a clockwise direction has found to be particularly effective at mixing the purged hydrogen and exhaust gas stream, irrespective of whether the purged hydrogen is introduced to the apparatus 10 with the exhaust gas stream in a combined stream AB, or separately such as shown in Figure 5. The “tumbling flow” produced by this configuration acts to “fold” the components of the gas stream together to achieve extremely effective mixing and thus dilution of purged hydrogen relative to the exhaust gas stream. In one example, the mass flow rate of the gas stream is 75kg/ hr.

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 in an anti-clockwise direction and the vanes of the second mixing device 30b are configured to deflect the incoming mixed drier combined stream ABT in a clockwise direction, to create further turbulence in the tumbling flow of mixed exhaust gas and purged hydrogen ABT. The turbulent flow of mixed exhaust gas and purged hydrogen ABT 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 4 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. 2.

The effect of the mixers of the present invention will be described in more detail and with reference to Figure 5, as an example embodiment. Figure 5 also illustrates a method according to an embodiment of the present invention, as will be described. In the embodiment of Figure 5, the apparatus 10 of the present invention is shown in conjunction with a centrifugal-type water separation device 56 which is an optional feature of the invention. In this embodiment, the purged hydrogen stream B is introduced into the conduit 12 separately to the exhaust gas stream A.

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 2. 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.

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 moisture content.

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. However, the effective mixing provided by the present invention is achieved by the one or more mixing devices which are positioned downstream of the purged hydrogen inlet 66, and is not necessarily dependent on the presence of the water separation device 56 in the apparatus 10 to achieve effective mixing.

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 2 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 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 2, receives the emergent mixed exhaust gas and purged hydrogen AB 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. 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.

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. For example, although an embodiment described above relates to a plurality mixing devices which are configured to deflect gas flow in anti-clockwise and clockwise directions, respectively, one or more embodiments may relate to one or more mixing devices which are each configured to deflect gas flow in only a clockwise direction, or only an anti-clockwise direction.

The number of vanes, and/ or the shape of the vanes, and/or the position of the vanes may also be different to the embodiments shown in the Figures and described herein. For example, the number of vanes, and/or the shape of the vanes, and/or the position of the vanes may be changed depending on the flow rate and/ or direction of gas coming from the stack.

As another example, the shape of the mixer can be varied. In the embodiments described herein, a circular mixing device is provided as an example. However, this shape is not essential. For example, a square-shaped mixing device may be used, or any other shape which may be better suited to the environment in which it is disposed.

By providing a plurality of mixing devices that are configured to deflect, i.e. change the direction of the gas stream flow, effective mixing of the purged hydrogen with the exhaust gas stream is achieved. The above-described configuration of the mixing devices 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, 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 improving the mixing of the exhaust gas and purged hydrogen which leads to a reduction or dilution of the concentration of hydrogen present, by volume, in the exhaust gas stream emerging from the apparatus. 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 and takes up only a fraction of the length of the vehicle, thus 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.

It is to be appreciated that in different embodiments, the one or more mixing devices may be configured to cause a different deflection of the exhaust gas stream and purged hydrogen than the example embodiment shown in Figure 5 and as such, a different flow pattern may be utilized to achieve mixing of the exhaust gas stream and purged hydrogen.

Figure 7 illustrates a method 200 according to an embodiment of the present invention. The method 200 comprises introducing 202 purged hydrogen B and an exhaust gas stream A into a conduit 12, deflecting 204 the purged hydrogen B and the exhaust gas stream A using one or more mixing devices disposed in the conduit 12 to achieve mixing of the purged hydrogen and exhaust gas stream ABT, and discharging 206 the mixed purged hydrogen and exhaust gas stream ABT from the conduit 12.

The discharge step 206 in Figure 7 which includes discharging 206 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 ABT after the mixing stage when the method is in use with in a particular application, such as in an exhaust gas system. However, it is to be appreciated that the step 206 of discharging the mixed purged hydrogen and exhaust gas stream from the conduit 12 is not an essential step of the invention.

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.