WO2004091758A1

WO2004091758A1 - An improved fuel reformer and mixing chamber therefor

Info

Publication number: WO2004091758A1
Application number: PCT/AU2004/000503
Authority: WO
Inventors: Alexander Zubko; David John Longman
Original assignee: Orbital Engine Company (Australia) Pty Ltd
Priority date: 2003-04-16
Filing date: 2004-04-16
Publication date: 2004-10-28
Also published as: AU2003901841A0

Abstract

A reformer arrangement (10) for processing a fluid mixture wherein the reformer arrangement (10) comprises a mixture preparation portion and a reaction portion which together provide a reforming process. The reaction portion comprises one or more processing stages (16, 20, 22, 24) and one or more heat exchanger means (30, 32, 34) are arranged with respect to one or some of the processing stages (16, 20, 22, 24) such that heat may be extracted from a fluid mixture emanating from a corresponding processing stage (16, 20, 22, 24). The extracted heat is utilised according to a particular distribution strategy to enable a certain level of preheating of one or more fluid inputs required by the reforming process. A mixing chamber arrangement (14) to achieve mixing of at least two fluids and able to be used within the reformer arrangement is also described. The mixing chamber arrangement (14) is provided as a two-stage unit and comprises a mixture preparation section (40) and a mixture diffusing section (42) downstream of the preparation section (40). The mixing chamber arrangement (14) includes a first inlet (44) for directing a flow of a first fluid into the mixture preparation section (40) and at least one fluid delivery means (26) for directing a flow of at least a second fluid into the mixture preparation section (40). A second inlet (54) directs a flow of a fluid into the mixture diffusing section (42). Initial mixing of is effected in the mixture preparation section (40) and subsequent mixing of the fluids and diffusion thereof is effected by the mixture diffusing section (42). In a further embodiment a method of controlling dual fuel injection system is described. The method includes delivering multiple high frequency delivery injections events, including the steps of metering, in a single event, a volume of fluid sufficient to satisfy the requirements of at least two delivery injection events and delivering the volume of fluid by the way of the at least two delivery injection events.

Description

"An Improved Fuel Reformer and Mixing Chamber Therefor"

Field of the Invention

The present invention is related to an improved arrangement for a reforming process, and in particular to a fuel reformer as would be used in conjunction with a fuel cell. More particularly, the invention is related to a system for enhancing the thermal efficiency of the reforming process by way of controlling temperatures and more effectively using heat generated during the reforming process.

The present invention is also related to an arrangement for promoting the mixing of two or more fluids so as to achieve an effective and relatively uniform mixture. In particular, such an arrangement is applicable to the mixing of fluids prior to chemical processing in a fuel reformer for use with a fuel cell. Furthermore, the arrangement may also be applicable in the elimination or reduction of emissions in an exhaust flow by way of a controlled reaction.

Additionally, the present invention is related to a method of controlling an injection arrangement for use with the fuel reformer and/or mixing arrangement. In particular, the invention also relates to a method for increasing the frequency of an injection event when injecting a single fluid or dual fluid (i.e.. wherein one fluid is entrained by and/or delivered by a another fluid) for use in a fuel reformer. The invention is particularly relevant to those conditions where it is advantageous to adopt a higher frequency of injection events without the need to modify conventional injection apparatus.

Background Art

Hydrogen fuel cells are receiving a great deal of interest as potential candidates in future transport applications as an alternative to the use of internal combustion engines in vehicles. In their application to transportation, such fuel cells have the potential to offer certain advantages over the internal combustion engine. In addition to the environmental advantages of low direct emissions and reduced fuel consumption through high efficiency, they can also provide certain functional advantages such as a reduction of moving parts, and consequently may be relatively quiet and free from vibration.

The fuel cell is a device which converts chemical energy to electrical energy through an electrolytic reaction typically using inputs of hydrogen (or a hydrogen- rich fuel stream) and oxygen which react with an electrolyte so as to create outputs of electricity and heat. A typical fuel cell comprises an electrolyte (or membrane) in communication with an anode and cathode. The fuel cell functions by passing hydrogen across the anode and oxygen across the cathode so as to cause an electrolytic reaction. This typically results in the generation of electricity with by-products of heat and water vapour, the reaction having typically higher efficiencies than that of a conventional internal combustion engine. Unlike a conventional charge storage battery, the reactants that are supplied to a fuel cell are stored external to the cell and supplied as required, thus permitting a degree of control over the operation of the fuel cell and also permitting rapid refueling therefor.

The electrical energy produced- by the fuel cell may ultimately be used to supply all on-board requirements of an electric vehicle. In the most optimistic scenario, a fuel cell powered vehicle operating on hydrogen obtained from renewable, non- polluting sources has the potential to be a true zero pollution vehicle. The exhaust from such a fuel cell powered vehicle would contain only water and air and would potentially be free of greenhouse gases, NO_X) and unburned hydrocarbons.

However, there is currently one school of thought that in order to introduce fuel cells into mainstream transportation applications, hydrogen will need to be widely available in a distribution network similar to that of current petrol stations. Unfortunately, no widespread infrastructure currently exists to supply hydrogen and on-board storage of hydrogen is still under development. As it is presently not possible to deliver and store the required volumes of hydrogen in such a wide distribution network, significant work is being done in developing methods by which known hydrocarbon fuels can be converted, as driver demand requires, so as to deliver the required hydrogen load for a fuel cell.

In this regard, the on-board gasoline or fuel reformer has emerged as a promising interim (or possibly longer term) solution for providing hydrogen to a fuel cell while utilizing the existing refueling infrastructure. Such a solution enables the cracking of a hydrocarbon fuel within the fuel reformer located within a vehicle, disposing of the resulting emissions, and directing the hydrogen-rich fuel stream to a fuel cell. To date, most reformer development companies in the world have developed hydrogen reformers for methanol, liquefied petroleum gas (LPG) or natural gas (NG) because of their lower reaction temperatures and low sulphur levels. Such on-board reforming of a hydrocarbon fuel does however release the greenhouse gas CO₂. Nonetheless, with the expected high overall efficiency of a fuel cell powered vehicle, it is anticipated that the quantity of CO₂ produced should be less than that produced by an equivalent internal combustion engine powered vehicle.

In generating the hydrogen-rich fuel stream, a fuel reformer receives a hydrocarbon fuel which is added to air in order to achieve a desired fuel/air mix. Water vapour or steam is also added to the fuel/air mix either just prior to entering the reformer or after the fuel/air mix is elevated in temperature and just prior to the chemical reforming process. In essence the fuel reformer passes the fuel/air/steam mix over a catalyst at elevated temperatures so as to cause a reaction and, consequently, crack the hydrogen from the hydrocarbon fuel and remove the consequential emissions.

More specifically, the operation of a fuel reformer typically involves a hydrocarbon fuel undergoing steam reforming and/or partial oxidation under controlled conditions, whereby cracking of the hydrogen enables the delivery of a hydrogen-rich fuel stream to the anode of a fuel cell. However, failure to maintain an optimum mixture concentration may result in a reduced hydrogen concentration in the reformer. Further, it may sometimes be advantageous to operate the fuel reformer using a catalyst so as to promote the desired reactions at a reduced temperature. In each of these scenarios, it is important to avoid any inconsistent and incomplete reactions, or insufficient contact between the reactant compounds and the catalyst, which can each result from an inefficient mixing of the compounds introduced into the fuel reformer.

As such, a fuel reformer generally consists of several functional sections including mixture preparation and reaction sections. The mixture preparation section typically comprises a mixing chamber arrangement for satisfactorily mixing the air, steam and fuel constituents which are required in the reforming process. Ideally, the mixing chamber will contribute to atomizing a majority of the fuel which is input as well as enable a satisfactory level of homogeneity to be achieved in the resultant feed-gas. Furthermore, the mixture preparation section will ideally also effect a certain degree of diffusing of the resultant feed-gas as it is delivered from the mixture preparation section to the reaction section of the reformer.

The reaction section of a fuel reformer typically employs catalytic converters similar in construction to automotive exhaust catalysts. Higher fraction hydrocarbons can be reformed using nickel or precious metal based catalysts such as platinum. Hydrocarbon fuel (C_nH_n), steam (H2O) and air (O2, N2) are introduced to the catalyst resulting in the product gases hydrogen (H ), nitrogen (N₂), carbon dioxide (CO₂), carbon monoxide (CO) as well as water (H₂O), and non-methane and methane (CH ) hydrocarbons being produced. These constituents are subsequently treated by two types of primary chemical reactions, steam reforming and partial oxidation. Secondary chemical reactions are also employed, typically to produce additional hydrogen and for CO reduction. Each of these primary and secondary reaction stages will be further discussed hereinafter.

There are also certain temperature requirements that need to be addressed in the operation of a fuel reformer arrangement. Firstly, the temperatures of the air and steam which serve as inputs to the mixture preparation section of the reformer are preferably required to be preheated to a certain level to facilitate the satisfactory operation of the reformer. Furthermore, the feed-gas temperatures which are input to and resulting from the various stages of the reforming process within the reaction section of the reformer are also required to be of certain levels so as to enable a subsequent processing stage to function in a desired manner.

For certain stages of the reforming process, it is typically the case that some of the temperature differences between consecutive stages will require a certain degree of heat extraction to enable satisfactory operation of the reformer. Typically, heat exchangers may be arranged to extract this heat and in some cases use this extracted energy to heat the water and air prior to delivery into the reformer. However, it is believed that significant refinement may be possible to the way in which such heat exchangers are arranged within the reformer and also to the manner in which the heat extracted thereby may be more effectively used to enhance the efficiency of the overall reformer process. Still further, achieving said desired temperatures for the air, steam and fuel inputs prior to delivery to the reformer may be particularly challenging upon initial start-up operation of the reformer arrangement.

In regard to the mixture preparation section of the fuel reformer and in particular the configuration thereof, it is known that reasonably satisfactory mixing of fluids can be achieved by creating a confined environment whereby the fluids delivered thereto have sufficient residence time to fully combine. Unfortunately, for a fuel cell application, and particularly when used for transportation wherein responsiveness to changing load conditions is important, such a residence time may not be suitable as a continuous and fluctuating supply of fuel is typically required such that electricity can be produced throughout the operating range of a vehicle as driver load demands and/or driving conditions may require. In an alternative arrangement, the fluids could be combined within a conduit having a substantial mixing length in which mixing occurs as a result of turbulence generated within the conduit as the combined fluid achieves a steady uniform flow. With a transportation application however, size and weight parameters are typically very restricted and so it will rarely be convenient to provide a sufficiently long conduit that will achieve the desired level of mixing without adversely effecting the overall size and weight of the reformer and/or fuel cell arrangement. Furthermore, such long residence times and/or long mixing lengths tend to reduce the responsiveness of the system to load changes that may be imposed on the system (e.g. changing driver demands such as accelerating or driving up a hill).

In one prior art method, mixing is achieved by creating highly turbulent conditions in a confined zone into which the fluids are introduced. For example, it is known from US Patent No. 5,546,701 to provide a mixing zone by introducing two fluids to a rigid obstruction whereby turbulent conditions are created by the fluids as they impact with the obstruction. The two fluids are delivered into a mixing chamber at the same location and in the same direction. The fluids are introduced through parallel lines into the mixing chamber and the rigid obstruction is arranged adjacent the termination of the lines such that the fluids contact the obstruction and are subsequently directed into a larger mixing zone. The impact at the physical obstruction creates a turbulent flow that causes the fluids to inter-mix prior to the redirection of the resulting flow to a reformer. However, size and complexity are seen as potential significant drawbacks of such a system. It is also believed that further improvements are possible so far as the attainable degree of mixing of the fluids is concerned.

In needing to provide a satisfactory degree of mixing and processing of the air, steam and fuel, it follows that at several stages in the process, fluids require injection into either the mixing chamber or directly into the fuel reformer. Whilst the delivery of air and steam into the mixing chamber may in most cases be relatively continuous, the mixing chamber must of course also be configured to receive a supply of fuel from a suitable delivery source. Typically, a fuel delivery means will be arranged such that a delivery end thereof is in fluid communication with the internal volume within the mixing chamber thereby permitting fuel to pass into the mixing chamber during operation. Such a fuel delivery means may take many different forms and may for example be of the type which can provide a continuous flow of fuel, or alternatively, be of the type which can be operated selectively so as to provide discrete intermittent metered quantities of fuel to the mixing chamber.

In this connection, the Applicant has developed and patented numerous different designs for fluid injection devices, and in particular fuel injectors and fuel injection systems for use with different automotive engine applications. More particularly, the Applicant has developed various dual fluid fuel injection systems wherein the fuel metering function is effectively separated from the fuel delivery function. In operation, discrete quantities of fuel are typically metered by a fuel metering means into a holding chamber which is in communication with a source of compressed gas, typically air. The holding chamber is comprised in or is in communication with a selectively openable fuel delivery injector such that, when opened, the metered quantity of fuel is entrained by and delivered from the holding chamber by the gas. Examples of such two fluid fuel injection systems are described in the Applicant's US Patent Nos. 4,693,224, RE36,768 and 6,463,916, and the Applicant's PCT Publication No. WO01/29406, the contents of which are each incorporated herein by way of reference. In recent times, the Applicant has investigated the application of its fuel system technologies to fuel reformers, and in particular, the use of a two fluid injection system to meter and supply fuel into a mixing chamber arrangement for mixing with air and steam.

In its application to a fuel reformer, a delivery injector of such a two fluid injection system is typically operatively arranged with respect to the mixing chamber or reformer and has a delivery end section with a delivery port through which fluid, typically a hydrocarbon based fuel, is injected. The delivery end section generally includes a valve seat, and a valve member movable into and out of sealing engagement with the valve seat for selectively opening and closing the delivery port. The valve member forms part of a valve having a valve stem, a first end of which supports the valve member. An electromagnetic arrangement typically controls the operation of the valve to selectively open and close the delivery port. The electromagnetic arrangement includes a solenoid coil located in the body of the injector about the valve stem, and a solenoid armature attached to a second end of the valve stem. Energisation of the solenoid coil typically induces movement of the armature to cause the valve member to move out of engagement with the valve seat against the influence of a spring, which normally retains the valve in the sealing or closed condition.

Where the fluid delivered by the injector into the mixing chamber or the reformer is entrained in a gas such as air (eg. by way of the arrangement disclosed in the Applicant's US Patent No. 4,693,224 or RE36,768), the injector is also typically connected to an air supply such as a gas compressor. A separate fuel metering means is typically also arranged to meter fuel from a suitable source to the injector for subsequent delivery thereby. Accordingly, metering and injection events at a particular frequency and in a predetermined timed sequence are required to control the operation of the fuel metering means and delivery injector respectively.

However, and in particular regard to the operation of the delivery injector, a low frequency pulsed injection event may typically produce variations in the air/fuel/water mixture which subsequently contacts the catalysts within the reaction section of the fuel reformer. Such variations may be most undesirable for the effective operation of the fuel reformer. As the fuel reformer generally requires a reasonably continuous supply of air, steam and fuel, the injection of air and steam should be of sufficient frequency so as to effectively emulate the continuous flow of fluid into the reformer. Further, in order to achieve sufficient mixing of the fluids prior to delivery to the reaction section of the reformer for conversion of the fuel into a hydrogen-enriched stream, it is advantageous if the fuel injection events were able to occur at a high a frequency as possible.

There is, however, a practical limit to the frequency at which a fluid can be metered prior to the injection event. It follows that the metering means must be sized so as to satisfy a full load condition. Having determined the ideal frequency of the metering events, the metering duration can then be calculated. This duration will define the time over which fuel during an injection event at a full load condition must be delivered. For a part load condition, the metering duration will be proportionally reduced so as to provide the delivery injector with the required volume of fuel for that operating condition.

The metering means may commonly be provided in the form of a pressure-time metering injector, the operation of which involves a lag time measured from the point at which the injector is first energised to when the injector is fully open. It follows that there is a related lag time from de-energisation until the injector is fully closed. For example, a typical lag time for energisation and de-energisation for a solenoid actuated injector of the type discussed may be approximately one millisecond. If it is considered that the upper limit of injector frequency for the metering means is, say, 200 Hz, this means the injector duration will be of the order of five milliseconds. For a part load of, say, 20% of the full load, the injector duration for the part load will hence be about 0.8 milliseconds, being less than the energisation or de-energisation lag time.

As a consequence, the ability of the metering injector to meter an accurate volume of fuel is compromised. Thus, the systemic need to provide a high frequency injection in a reformer application is limited by the ability of the standard metering injector to deliver a metered volume of fluid at the frequency required. Accordingly, certain challenges exist in adapting a pulse width modulated fuel metering injection process, such as is typically used in the applicant's two fluid injection system, for use with a fuel reformer arrangement.

The above discussion of the background to the invention is intended to facilitate an understanding of the present invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge in Australia or elsewhere as at the priority date of the application.

With the above challenges in mind, it is a first object of the present invention to provide a dynamically responsive, compact and effective mixing chamber arrangement which can provide relatively uniform mixing of a main fluid flow with a second fluid flow. It is a further object of the present invention to provide a fuel reformer arrangement which enhances the manner in which excess heat from the reaction stages of the reformer is used to improve the overall thermal efficiency of the reforming process.

It is yet a further object of the present invention to provide a fuel reformer arrangement which has the capability of operating more effectively in the period immediately following start-up.

It is yet a further object of the present invention to provide a method whereby a balance is struck between maximizing the delivery frequency of a fluid delivery injector without limiting the upper and lower duration limits of a corresponding metering means in a two-fluid injection system.

Disclosure of the Invention

Therefore, according to a first aspect of the present invention, there is provided a reformer arrangement for processing a fluid mixture, the reformer arrangement comprising a mixture preparation portion and a reaction portion which together provide a reforming process, the reaction portion comprising one or more processing stages and one or more heat exchanger means being arranged with respect to one or some of the processing stages such that heat may be extracted from a fluid mixture emanating from a corresponding processing stage, wherein the extracted heat is utilised according to a particular distribution strategy to enable a certain level of preheating of one or more fluid inputs required by the reforming process.

Preferably, the reformer arrangement is a fuel reformer for use with a fuel cell arrangement wherein a hydrogen-rich fluid mixture is processed by the fuel reformer and subsequently delivered to the fuel cell. Conveniently, the reaction portion is a chemical reaction portion.

Preferably, the mixture preparation portion is arranged to receive at least two fluid inputs, and the distribution strategy enables a certain level of preheating of one or more of the fluid inputs to the mixture preparation portion. As well as the fluid inputs to the mixture preparation portion, additional fluid inputs may also be required by one or more of the processing stages of the chemical reaction portion. Conveniently, the distribution strategy enables a certain degree of preheating of one or more of the fluid inputs to the mixture preparation portion and one or more of the additional fluid inputs required by the reaction portion. Conveniently, the distribution strategy is predetermined.

In the case of a fuel reformer for use with a fuel cell, the fluid inputs required by the mixture preparation portion preferably include air, steam and a hydrocarbon based fuel. Air and steam may also be used at various stages during the reaction portion to facilitate the overall reforming process.

Preferably, the mixture preparation portion may be provided in the form of a mixing chamber which receives the air, steam and fuel inputs and facilitates uniform mixing of these fluids prior to delivery of a resultant fluid mixture to the downstream reaction portion. Conveniently, the mixing chamber may be provided as a two stage unit comprising a swirl chamber and a diffuser. Conveniently, fuel may be delivered to the swirl chamber by way of a fluid delivery injector. An air/steam mixture may conveniently be delivered to the swirl chamber by an additional fluid delivery arrangement.

Conveniently, the reaction portion of the fuel reformer includes a steam reforming and a partial oxidation capability. Steam reforming is preferably carried out in the chemical reaction portion to facilitate the production of hydrogen from a hydrocarbon fuel and steam mixture. Partial oxidation is preferably carried out in the chemical reaction portion to facilitate the production of hydrogen from a hydrocarbon fuel and air mixture. Conveniently, other secondary reactions may also be carried out in the chemical reaction portion including processes to produce additional hydrogen and to facilitate a certain level of carbon monoxide reduction. Preferably, the chemical reaction portion also includes a two stage catalytic water-gas shift reactor to minimise the level of carbon monoxide in the resultant fluid mixture. Preferably, the water-gas shift reactor comprises a high temperature stage and a low temperature stage. The inlet temperature at the high temperature stage of the water-gas shift reactor conveniently requires to be of the order of 250°C. The inlet temperature at the low temperature stage of the water-gas shift reactor conveniently requires to be of the order of 200°C. It is however to be appreciated that the inlet temperatures at the high temperature and low temperature stages may vary dependant upon the type of catalyst used.

Conveniently, the steam reforming and partial oxidation may be carried out by a single catalytic means, typically an autothermal reactor or catalyst. However, as such an autothermal reactor may not be sufficient to satisfactorily reduce the carbon monoxide concentration in the resultant fluid mixture to levels acceptable by the fuel cell, the reaction portion may further include a preferential oxidation unit to further reduce any residual carbon monoxide in the resultant fluid mixture or gas stream to acceptable levels. The inlet temperature at the autothermal reactor preferably requires to be of the order of 400°C. However, it is again to be appreciated that the inlet temperature at the autothermal reactor may vary dependant upon the type of catalyst used.

Conveniently, the mixing chamber serves to satisfactorily mix the air, steam and fuel inputs prior to diffusing the resultant mixture for delivery to the autothermal reactor. Conveniently, the various gases and constituents produced by the autothermal reactor are subsequently delivered to the water-gas shift reactor such that a majority of the carbon monoxide produced in the autothermal reactor may be converted to carbon dioxide by a reaction with steam that also liberates additional hydrogen. Conveniently, the steam required by the water-gas shift reactor may be one of the additional inputs which is preheated by the heat extracted by the one or more heat exchangers.

Preferably, the mixture resulting from the water-gas shift reactor is delivered to the preferential oxidation unit which serves to further reduce any residual carbon monoxide from the gas stream to levels acceptable to the fuel cell. Preferably, a feed-gas temperature for the fuel cell requires to be of the order of 80°C. It is however to be appreciated that this temperature is typical for a polymer membrane fuel cell and that the feed-gas temperature may change based on future membrane developments. Carbon monoxide remaining after processing by the water-gas shift reactor is typically further processed in the preferential oxidation unit by a reaction with air.

Conveniently, two or more heat exchanger means are arranged with respect to two or more respective processing stages of the reaction portion of the fuel reformer.

Preferably, a first heat exchanger means is arranged between the autothermal reactor and the high temperature stage of the water-gas shift reactor. With the outlet temperature of the autothermal reactor typically being of the order of 730°C and the inlet temperature of the high temperature stage of the water-gas shift reactor being of the order of 250°C, the positioning of the first heat exchanger means at this point will facilitate a desired reduction in the inlet temperature to the high temperature stage of the water-gas shift reactor and hence enable the extraction of a significant degree of heat which may be used according to the above mentioned predetermined distribution strategy.

Preferably, a second heat exchanger means is arranged between the high temperature stage of the water-gas shift reactor and the low temperature stage of the water-gas shift reactor. With the outlet temperature of the high temperature stage of the water-gas shift reactor typically being of the order of 350°C and the inlet temperature of the low temperature stage of the water-gas shift reactor being of the order of 200°C, the positioning of the second heat exchanger means at this point will facilitate a desired reduction in the inlet temperature to the low temperature stage of the water-gas shift reactor and further enable the extraction of a considerable degree of heat which may be used according to the aforementioned predetermined distribution strategy.

Preferably, a third heat exchanger means is arranged downstream of the preferential oxidation unit and upstream of the fuel cell. With the outlet temperature of the preferential oxidation unit typically being of the order of 200°C and the feed-gas temperature to the fuel cell typically needing to be 80°C, the positioning of the third heat exchanger means at this point will again facilitate a desired reduction in the feed-gas temperature to the fuel cell and also enable the extraction of some heat which may be used according to the aforementioned predetermined distribution strategy.

Preferably, the predetermined distribution strategy includes the heat extracted by the third heat exchanger means being utilised to heat the water which is required as an input to the low temperature stage of the water-gas shift reactor. Conveniently, this preheating results in 1.19g/sec of steam and 1.77g/sec of water at 100°C. It is however to be noted that the resulting g/sec of steam and water is dependant upon the quantity of hydrogen being generated and that the figures specified are in no way intended to be limiting of the present invention. Similar comments apply in respect of the related figures specified hereafter.

Preferably, the predetermined distribution strategy includes the heat extracted by the second heat exchanger means being utilised to heat the water which is required as an input to the high temperature stage of the water-gas shift reactor. Conveniently, the heat extracted by the second heat exchanger is alternatively or also utilised to heat the steam which is required as an input to the mixing chamber.

Conveniently, the low temperature stage of the water-gas shift reactor serves to further heat the water which is initially preheated by the third heat exchanger and provided thereto. Conveniently, the predetermined distribution strategy includes the heat extracted at the low temperature stage of the water-gas shift reactor serving to further heat the water resulting in 2.08g/sec of steam and 0.88g/sec of water at 100°C.

Conveniently, the predetermined distribution strategy includes the heat extracted at the second heat exchanger means serving to further heat the steam mixture which is initially heated by the low temperature stage of the water-gas shift reactor and provided thereto. Conveniently, the steam mixture is increased to 250°C with 0.61 g/sec of steam being diverted to the high temperature stage of the water-gas shift reactor and the remainder of the steam being directed to the mixing chamber.

Preferably, the predetermined distribution strategy includes the heat extracted by the first heat exchanger means being utilised to heat the air which is required as an input to the mixing chamber. Conveniently, the air is heated to 650°C prior to being delivered to the mixing chamber.

Conveniently, the predetermined distribution strategy may include any combination of one or more of the above-mentioned utilisations for heat extracted by the heat exchangers.

Preferably, the fuel reformer arrangement includes an electrically heated catalyst arranged downstream of the mixing chamber and upstream of the autothermal reactor. Conveniently, the electrically heated catalyst is operated upon cold starting of the reforming process. Conveniently, the electrically heated catalyst is turned-off once the fuel reformer has achieved a self-sustaining point with respect to heat generation. The autothermal reactor, which is itself a catalyst, may also or alternatively include electrical heating for start-up operation.

According to a second aspect of the present invention, there is provided a reformer arrangement for processing a fluid mixture, the reformer arrangement comprising a reaction portion which consists of one or more processing stages, wherein an electrically heated catalyst is also provided in the reaction portion to provide additional heat input within the reformer arrangement under various operating conditions.

Preferably, the reformer arrangement is a fuel reformer for use with a fuel cell arrangement wherein a hydrogen-rich fluid mixture is processed by the fuel reformer and subsequently delivered to the fuel cell. Preferably, the reformer arrangement comprises a mixture preparation portion as well as the reaction portion which together define a reforming process, the electrically heated catalyst providing additional heat input during part of the reforming process. Preferably, the electrically heated catalyst is arranged downstream of the mixture preparation portion and upstream of an autothermal reactor in the reaction portion of the fuel reformer. Conveniently, the electrically heated catalyst is specifically operated upon cold starting of the reforming process. Conveniently, the electrically heated catalyst is turned-off once the fuel reformer has achieved a self-sustaining point with respect to heat generation. Conveniently, the autothermal reactor may also or alternatively include electrical heating for startup operation.

According to a third aspect of the present invention, there is provided a mixing chamber to achieve mixing of at least two fluids, the mixing chamber including an inlet for directing a flow of a first fluid into the chamber, and at least one fluid delivery means for directing a flow of at least a second fluid into the mixing chamber, the mixing chamber comprising an annular portion arranged about a central passage, the annular portion being in fluid communication with the central passage for delivering fluid from the mixing chamber, the fluid delivery means being arranged to deliver the second fluid downstream of and in the path of the flow of the first fluid into the chamber, wherein the inlet for the first fluid is arranged with respect to the annular portion such that a swirl flow is established in the mixing chamber to promote mixing of the first and second fluids prior to their delivery through the central passage and from the mixing chamber.

Preferably, the inlet for the first fluid is arranged tangentially to the annular portion in order to promote the formation of the swirl flow in the mixing chamber. Conveniently, a plurality of inlets are provided for delivering the first fluid into the mixing chamber, each of the inlets being arranged in a spaced apart relationship and tangential to the annular portion.

Conveniently, the swirl flow is established in the annular portion of the mixing chamber. Conveniently, the central passage is arranged axially within the mixing chamber and includes an opening at a first end thereof which communicates with the annular portion. The fluid mixture is hence delivered from the mixing chamber in a direction perpendicular to the direction at which the first fluid enters the annular portion.

According to a fourth aspect of the present invention, there is provided a mixing chamber arrangement to achieve mixing of at least two fluids which is provided as a two-stage unit, the mixing chamber arrangement comprising a mixture preparation section and a mixture diffusing section downstream of the preparation section, the mixing chamber arrangement including a first inlet for directing a flow of a first fluid into the mixture preparation section, and at least one fluid delivery means for directing a flow of at least a _. second fluid into the mixture preparation section, and a second inlet for directing a flow of a fluid into the mixture diffusing section, wherein initial mixing is effected in the mixture preparation section and subsequent mixing of the fluids and diffusion thereof is effected by the mixture diffusing section.

Preferably, the first inlet directs a first flow of a first fluid into the mixture preparation section and the second inlet directs a second flow of the first fluid into the mixture diffusing section. In this way, initial mixing of the first and second fluids is effected in the mixture preparation section and subsequent mixing of the two fluids and diffusion thereof is effected by the mixture diffusing section. In certain arrangements, the second inlet may direct a second flow of the second fluid into the mixture diffusing section. Alternatively, the second inlet may direct a flow of third fluid into the mixture diffusing section.

Preferably, the first and second inlets are arranged so that the fluid flows delivered thereby are directed towards one another. Preferably, a turbulent region is created at the point at which the flows of the fluids delivered by the first and second inlets impinge. Conveniently, the turbulent region is generated at a location central to the mixing chamber. Conveniently, the turbulent region is generated at a location within the diffusing section.

Conveniently, the mixture preparation section comprises an annular portion arranged about a central passage, the annular portion being in fluid communication with the central passage for delivering a fluid mixture from the mixture preparation section. Preferably, the first flow of the first fluid is delivered into the annular portion of the mixture preparation section. Preferably, the fluid delivery means is arranged to deliver the second fluid downstream of and in the path of the first flow of the first fluid into the annular portion.

Conveniently, the first inlet is arranged with respect to the annular portion such that a swirl flow is established in the mixture preparation section to promote mixing of the first and second fluids prior to their delivery through the central passage and from the mixture preparation section. Preferably, the first inlet is arranged tangentially to the annular portion in order to promote the formation of the swirl flow in the mixture preparation section. Conveniently, a plurality of first inlets are provided for delivering the first fluid into the preparation section, each of the first inlets being arranged in a spaced apart relationship and tangential to the annular portion.

Conveniently, the swirl flow is established in the annular portion of the preparation portion. Conveniently, the central passage is arranged axially within the preparation portion and includes an opening at a first end thereof which communicates with the annular portion. The fluid mixture is hence delivered from the preparation portion in a direction perpendicular to the direction at which the first fluid enters the annular portion. Preferably, the fluid mixture is delivered from the preparation section by way of the central passage and into the diffusing section.

Preferably, the second inlet to the diffusing section is provided as a central inlet which directs the second flow of the first fluid into the diffusing section. Conveniently, an inner end of the central inlet to the diffusing section is arranged to correspond with a delivery end of the central passage from the preparation section. In this way, the second flow of the first fluid is directed towards the fluid mixture emanating from the preparation portion. Alternatively, a flow of a different fluid may be directed by the second inlet towards the fluid emanating from the preparation portion. Conveniently, the turbulent region is created adjacent the inner end of the central inlet. The establishment of this desired turbulent region within the mixing chamber arrangement serves to promote the efficient and relatively uniform mixing of the fluid inputs to the preparation portion and the diffusing portion. The turbulent region conveniently forms only a small portion of the overall volume of the diffusing section of the chamber arrangement.

It may be advantageous, in order to optimise uniform mixing, to vary the relative velocities of the mixture flow from the preparation portion and/or the flow of the first fluid delivered by the second inlet as they are delivered into the mixing chamber arrangement. For example, a higher velocity flow may be directed into a lower velocity flow to facilitate generation of the turbulent region.

Preferably, 50% of the first fluid is delivered into the mixing chamber arrangement by way of the first inlet whilst the remaining 50% of the first fluid is delivered into the mixing chamber arrangement by way of the second inlet.

Preferably, the diffusing section further comprises an annular diffusing portion arranged about the central inlet for diffusing and delivering a resultant fluid mixture from the mixing chamber. Conveniently, the resultant fluid mixture is delivered from the annular diffusing portion in a parallel but opposite direction to the flow of the first fluid into the diffusing section. Conveniently, the annular diffusing portion communicates with the turbulent region by way of an intermediate portion arranged therebetween.

Conveniently, the mixing chamber arrangement may be used in a fuel reformer to uniformly mix fluid inputs required thereby prior to being processed in a downstream reaction section of the fuel reformer. Air, steam and a hydrocarbon based fuel are typically the fluid inputs delivered to the mixing chamber arrangement when used as part of a fuel reformer. It is however to be appreciated that similar mixing chamber arrangements may also have applicability within subsequent stages of the reforming process where there exists a need to effectively mix two or more fluids. Preferably, air and steam are delivered to the mixing chamber arrangement by way of the first and second inlets with 50% of the air and steam mixture delivered into the preparation section and the remaining 50% of the air and steam mixture being delivered into the diffusing section. Preferably, fuel is delivered into the preparation section by way of the fluid delivery means.

Conveniently, the flow of fuel from the fluid delivery means may be arranged such that it is directed across the flow of air and steam delivered into the preparation section by one of the first inlets so as to facilitate a shearing effect of the air/steam on the fuel and to promote intermixing of the fluids. Alternatively, the flow of fuel from the fluid delivery means may be arranged such that it is directed at or into the flow of air and steam delivered into the preparation section by one of the first inlets.

Alternatively, the mixing chamber arrangement may be adapted for use in relation to the control of emissions within an exhaust system for an engine. Conveniently, the fluid delivered into the first and second inlets may be exhaust gases from the exhaust system. Conveniently, the second fluid injected by the fluid delivery means may facilitate a particular reaction within the exhaust gases to reduce the level of emissions therein.

More particularly, the exhaust gases delivered into the mixing chamber by the first and second inlets may be exhaust gases generated from combustion within a diesel engine. Conveniently, the second fluid injected by the delivery means may be urea which is required to satisfactorily mix with the exhaust gases to promote the reduction of NOx in a catalytic reaction with the exhaust gases.

Preferably, the fluid delivery means is provided as part of a dual fluid injection system such that the second fluid delivered into the mixing chamber arrangement is entrained by and delivered by a quantity of gas, typically air. Conveniently, the fluid delivery means is a delivery injector arranged to deliver the second fluid, typically fuel, into the mixing chamber arrangement such that a fuel spray or plume of finely atomised droplets and/or vapour is directed towards or into the flow of air and steam through the first inlet(s). Conveniently, a fuel metering means is arranged with respect to the delivery injector such that discrete metered quantities of fuel from the fuel metering means may subsequently be delivered by the fuel delivery injector. Furthermore, such an arrangement enables the fuel metering and fuel delivery events to be separated.

According to a fifth aspect of the present invention, there is provided a method for controlling a dual fluid injection system for use with a reformer arrangement, the method including delivering multiple high frequency delivery injection events, including the steps of metering, in a single event, a volume of fluid sufficient to satisfy the requirements of at least two delivery injection events and delivering the volume of fluid by way of the at least two delivery injection events.

Conveniently, the dual fluid injection system is arranged to deliver fuel to the reformer arrangement for processing thereby. Conveniently, the fuel reformer arrangement comprises a mixing chamber arrangement including a fuel delivery injector for enabling the delivery of fuel thereto. A fuel metering means is conveniently arranged with respect to the fuel delivery injector such that discrete metered quantities of fuel from the fuel metering means may subsequently be delivered by the fuel delivery injector. Furthermore, such an arrangement enables the fuel metering and fuel delivery events to be separated.

The present invention offers a solution to the problem of requiring high frequency fuel metering events in light of the typical limitations of the fuel metering means to provide accurate metered quantities of fuel at such higher operating frequencies. In one preferred embodiment, where the fuel delivery injector is required to operate at 200 Hz, the fuel metering means could be set to operate at 100 Hz and have a metering duration of twice that which would be required at 200 Hz. Hence, the metered quantity of fuel could be provided in one fuel metering event in sufficient quantities to satisfy two fuel delivery events.

It will be appreciated by the person skilled in the art that the metering duration may be extended so as to provide sufficient fuel to satisfy more than two injection events and that therefore, the frequency of the fuel metering events are for all intents and purposes independent of the frequency of the fuel delivery events. To this end, a single fuel metering event may be of sufficient duration so as to satisfy two, three, four or more delivery injection events.

Brief Description of the Drawings

It will be convenient to further describe the present inventions with respect to the accompanying drawings which illustrate possible embodiments of the inventions. Other embodiments of the inventions are possible and, consequently, the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the inventions.

- Figure 1 is a schematic representation of the different processing stages comprised in a prior art fuel reformer arrangement;

- Figure 2 is a schematic representation of the different processing stages comprised in a fuel reformer arrangement according to a first embodiment of the present invention;

- Figure 3 is a further schematic representation of the different processing stages and certain operating characteristics therefor of the fuel reformer arrangement according to the first embodiment of the present invention;

- Figure 4 is a partial cross-sectional isometric side view of an improved mixing chamber according to one embodiment of the present invention;

- Figure 5 is a schematic flow direction and velocity map for the improved mixing chamber as shown in Figure 4;

- Figure 6 is a schematic fuel vapour concentration map for the improved mixing chamber as shown in Figure 4;

- Figure 7 is a schematic temperature variation map for the improved mixing chamber as shown in Figure 4; - Figure 8(a) is a timing diagram of the timing sequences for the fuel metering and fuel delivery events of a two-fluid fuel injection system according to the prior art; and

- Figure 8(b) is a timing diagram of the timing sequences for the fuel metering and fuel delivery events of a two-fluid fuel injection system adapted for use with the mixing chamber arrangement according to the present invention.

Best Mode(s) for Carrying Out the Invention

One aspect of the present invention is directed at more effectively using the heat generated throughout the reforming process in a fuel reformer arrangement and particularly to how this heat can be used to raise the temperature of the fluid inputs to a reformer to enhance the thermal efficiency thereof. As part of the fuel reformer arrangement, there is also described a means for effectively mixing the three main constituents of hydrocarbon fuel, air and steam prior to its reformation. In this regard, it is to be noted that, whilst the mixing means is particularly suited for use as a mixing chamber of a fuel reformer arrangement for use with a fuel cell, the mixing means described hereafter is by no means restricted to its application to a fuel reformer. That is, the mixing chamber may advantageously be applied in other arrangements to provide an improved level of mixing of two or more fluids, with one such alternative application, namely urea injection in diesel exhaust systems, being briefly discussed hereinafter.

As alluded to hereinbefore, a typical fuel reformer consists of several functional sections to enable mixture preparation and subsequent chemical reactions to be effected. Steam reforming and partial oxidation are two types of primary chemical reactions which are employed in gasoline or fuel reformers whilst other secondary reactions to produce additional hydrogen and for CO reduction are also employed.

Steam reforming is an endothermic process that produces hydrogen from a hydrocarbon fuel and steam mixture. The process requires a significant amount of thermal energy which typically equates to a long start-up time since heating will be required to initiate the reaction. In general, steam reforming produces the highest yield of hydrogen per mass of fuel due to the additional hydrogen liberated from the water.

Partial oxidation is an exothermic process that produces hydrogen from a hydrocarbon fuel and oxygen mixture. A rapid start-up time is expected since no initial heating is required. During partial oxidation the desired reaction generates extremely high temperatures, especially if the excess air ratio is higher than a certain level. The influence of the excess air ratio is critical to avoid overheating problems.

Carbon monoxide is a strong poison for the anode in some fuel cells, and most notably in proton exchange membrane fuel cells. In conventional reformer processing for hydrogen production, a two-stage catalytic water-gas shift reactor, followed by pressure-swing adsorption, catalyst selective methanation, or catalyst selective oxidation, is used to remove carbon monoxide. Various efforts are however currently being undertaken seeking to develop highly active and thermally rugged catalysts to yield compact and lightweight shift reactors for automotive use. Alternative techniques including reversible complexing with a suitable sorbent, non precious metal selective oxidation catalysts, and other carbon monoxide oxidation processes are being examined. It is hoped that such approaches will offer the potential for ease of control and excellent dynamic response to frequent start-up and transient operation, as would be expected in an automotive fuel cell application.

The water gas shift is an equilibrium reaction between CO & H₂0 and CO₂ & H₂. The equilibrium concentrations are temperature dependant with high temperatures favoring CO.

In regard to the above described reactions, it has been found possible to combine the endothermic steam reforming, exothermic partial oxidation and water gas shift reactions in a single catalytic process called autothermal reforming (ATR). ATR uses the water gas shift reaction for further hydrogen generation and for CO removal. However, it is not possible to reduce the carbon monoxide concentration to levels acceptable for the fuel cell as the reaction is limited by thermal equilibrium and hence additional CO removal is required.

With the above background comments in mind, it is evident that an on-board gasoline or fuel reformer is likely to comprise a number of functional sections, each of these sections which will now be discussed further with reference to Figure 1. In Figure 1 there is shown what is understood to be a typical fuel reformer arrangement 10 for use with a fuel cell 12 in a manner as has been alluded to hereinbefore. The reformer 10 comprises a mixing chamber 14, an auto thermal reformer (ATR) or ATR catalyst 16, a water gas shift means 18 and a preferential oxidation unit (PrOx) 20. The water gas shift means 18 comprises a high temperature stage 22 and a low temperature stage 24.

The mixing chamber 14 comprises a fluid injector 26 for delivering a hydrocarbon based fluid such as gasoline into the mixing chamber 14, the workings of the injector 26 which will be described in further detail hereinafter. The mixing chamber 14 also receives fluid inputs from a delivery arrangement 28 which enables the supply of steam and air into the mixing chamber 14. The mixing chamber 14 serves to satisfactorily mix the steam, air and gasoline prior to diffusing the resultant mixture for delivery to the ATR 16. Further details of the workings of the mixing chamber 14 and one specific arrangement which may be adopted therefor will be provided hereinafter.

As alluded to hereinbefore, the ATR 16 effectively serves to promote the simultaneous steam reforming and partial oxidation reactions involving the air, steam and gasoline mixture it receives from the mixing chamber 14. The various gases and constituents which are produced by the ATR 16 are subsequently acted on by the water gas shift arrangement (WGS) 18 which serves to convert most of the CO produced in the ATR 16 to CO₂ by a reaction with water that also liberates additional H₂. As suggested, the WGS reaction is completed in two stages using a High Temperature Shift (HTS) stage 22 and a Low Temperature Shift (LTS) stage 24 with each of the HTS and LTS stages 22 and 24 being provided as specific catalysts.

The resultant gases and constituents from the WGS 18 are then passed to the preferential oxidation unit (PrOx) 20 which serves to reduce the residual CO from the gas stream to levels acceptable to the fuel cell 12. The predominantly H based gas which remains is then fed to the anode of the fuel cell 12 wherein the electrochemical reaction which has been discussed hereinbefore can be effected resulting in electricity being produced for use by, for example, a suitably coupled electric motor.

It is suggested by the Applicant that durable and efficient operation of the reformer 10 such as to produce a maximum H₂ yield can be achieved with the following temperatures:

• The inlet temperature at the ATR 16 being of the order of 400°C with its operating or outlet temperature being of the order of 730°C;

• The inlet temperature at the HTS stage 22 of the WGS 18 being of the order of 250°C with its operating or outlet temperature being of the order of 350°C;

• The inlet temperature at the LTS stage 24 of the WGS 18 being of the order of 200°C with its operating or outlet temperature also being of the order of 200°C; and

• The feed-gas temperature for the fuel cell 12 ideally being of the order of 80°C.

From a consideration of the above-noted temperatures, it will be evident that some of the temperature differences between consecutive stages of the reforming process will require a certain degree of heat extraction to enable satisfactory operation of the reformer 10. Typically, this heat extraction will be effected by way of one or more suitably arranged heat exchangers which can reduce the feed-gas temperature for a subsequent stage to that desired or required at the inlet for the stage. In some cases, the heat which is recovered in the heat exchanger(s) may be used to heat the water and air prior to delivery into the mixing chamber 14.

One advantageous arrangement of heat exchangers in the reformer arrangement as described with respect to Figure 1 will now be discussed with reference to Figure 2. The discussion of Figure 2 will also assist in understanding how the heat extracted during the reforming process may be more effectively used to improve the thermal efficiency of the fuel reformer 10. For ease of reference, like reference numerals have been used to identify corresponding components of the fuel reformer 10 as shown in , Figure 2 with those components described with reference to Figure 1.

Accordingly, Figure 2 shows a fuel reformer 10 which, as well as a mixing chamber 14, ATR 16, WGS 18 and PrOx 20, also comprises a first heat exchanger (HX1) 30, a second heat exchanger (HX2) 32 and a third heat exchanger (HX3) 34. Also shown in Figure 2 is a two fluid fuel injection system 36 adapted to deliver metered quantities of fuel entrained in air to the mixing chamber 14 via the fluid delivery injector 26. Further details pertaining to the arrangement and function of the fuel injection system 36 will be provided hereinafter.

In regard to the arrangement of the heat exchangers 30, 32 and 34, it will be evident from Figure 2 that HX1 30 is arranged between the ATR 16 and the HTS stage 22 of the WGS 18. Noting that the outlet temperature of the ATR 16 is typically of the order of 730°C whilst the desired inlet temperature of the HTS stage 22 of the WGS 18 requires to be in the order of 250°C, the positioning of HX1 30 between these stages in the reforming process will facilitate a reduction in the feed-gas temperature such that the HTS stage 22 will not receive a feed- gas at a temperature far in excess of that required for the effective functioning thereof. Similarly, HX2 32 is positioned between the HTS stage 22 and LTS stage 24 of the WGS 18 such that heat can be removed from the feed-gas emanating from the HTS stage 22 prior to being input to the LTS stage 24. This is required in that the outlet temperature of the HTS stage 22 is typically of the order of 350°C whilst the inlet temperature of at the LTS stage 24 is required to be of the order of 200°C. For similar reasons, HX3 34 is ideally positioned after the PrOx 20 and upstream of the fuel cell 12 such that the temperature of the final hydrogen rich fluid stream can be reduced prior to its delivery to the fuel cell 12. This is necessary due to the feed-gas temperature of the fuel cell 12 ideally needing to be of the order of 80°C whilst the outlet temperature of the PrOx 20 is typically of the order of 200°C.

It is envisaged that for most practical applications, each of the specific components of the fuel reformer 10 will require to be packaged together into a single integral unit. For example, heat exchangers may conveniently be provided as co-axial tubes within other components of the reformer 10. This packaging aspect is particularly important for transportation applications where size and weight will require to be minimised as much as possible. These comments apply equally to the mixing chamber 14 itself which requires to be a very compact arrangement and this will be elaborated on further hereinafter.

The typical or required inlet and outlet temperatures at the various stages of the reforming process are further described with reference to the schematic representation of the fuel reformer 10 arrangement as shown in Figure 3. Again, for ease of reference, like components of the fuel reformer when compared to Figures 1 and 2 are referenced with the same numbers. In the schematic, Q represents heat with the appropriate subscript + or - representing heat removal from or heat addition to the system respectively. Furthermore, certain of the products and reactants at each stage are also shown in Figure 3.

As can be seen, the inputs to the mixing chamber 14 ideally comprise water, gasoline and air. Prior to any pre-heating steps, the initial temperature of these constituents is of the order of 80°C, 40°C and 40°C respectively. As will be further discussed hereinafter, certain of these inputs are preferably preheated prior to their delivery to the mixing chamber 14 to enable effective operation of the reformer 10. The fluid mixture which is output from the mixing chamber 14 and which comprises water, gasoline and air (including O₂ and N₂) is passed to the ATR 14 for which the desired input temperature is of the order of 400°C.

From an analysis of the physical properties of the reactants, conditions which would represent a durable and efficient operating point for the ATR catalyst 16, the ideal yield of the ATR 16 at these conditions and various fuel composition and ATR reaction parameters, the Applicant has determined through its research that the combined chemical reaction of steam reforming and partial oxidation promoted by the ATR catalyst 16 can be represented as follows:

C7.33H12+ 5.86H2O + 19.1 (0.19O₂ + 0.82N₂) ->

8.5H₂ + 4.9CO + 2.43CO₂ + 3.37H₂0

Products of the ATR 16 include hydrogen, carbon monoxide, carbon dioxide and water with the outlet temperature of the fluid mix from the ATR 16 being of the order of 730°C. HX1 30 which is arranged downstream of the ATR 16 then serves to extract a significant amount of heat from this resultant fluid mixture such that fluid may be fed to the HTS stage 22 of the WGS 18 at a temperature which will enable durable and effective operation thereof.

The water gas shift reaction is an equilibrium reaction described by the following equation:

CO + H₂O <=> H₂ + CO₂

The reaction is exothermic in nature with a heat output of 41 kJ/mole. The equilibrium concentration of products and reactants is temperature dependant. As already discussed, a two-stage system consisting of a high temperature catalyst and a low temperature catalyst is used to minimise carbon monoxide in the gas stream. At each stage, water which has previously undergone some degree of preheating (as will be discussed further hereinafter) is also introduced as a reactant such that it may react with CO to convert most of the CO to CO as well as liberate some additional H₂.

The inlet temperature of the HTS stage 22 is desirably of the order of 250°C whilst the outlet temperature of the fluid mixture emanating therefrom is of the order of 350°C. HX2 32 is arranged downstream of the HTS stage 22 to extract heat from the fluid mixture at this point so as to bring the temperature thereof down to the 200°C inlet temperature ideally required at the LTS stage 24. With a certain degree of heat being removed from the fluid mixture during the low temperature shift reaction, the outlet temperature thereof (i.e. the fluid mixture typically comprising H₂, N2, CO₂, H₂O and CO) as it is delivered from the LTS stage 24 is also typically of the order of 200°C.

As the fluid mixture at this point still contains carbon monoxide, a constituent which essentially needs to be reduced or eliminated due to its potential to effectively "poison" the fuel cell 12, the further reaction stage represented by the PrOx 20 is required. The PrOx 20 receives the fluid mixture at a temperature of the order of 200°C and serves to reduce the residual carbon monoxide from the gas stream to levels acceptable to the fuel cell 12. At this stage, air from a suitable source is also introduced as a reactant such that it may react with CO to convert most of the remaining CO to CO₂. The preferential oxidation reaction is defined by the following equation:

CO + 0.5O₂ -> CO₂

The outlet temperature of the fluid mixture emanating from the PrOx 20 is of the order of 200°C and, as alluded to hereinbefore, HX3 34 is arranged downstream of the PrOx 20 stage to extract heat from the fluid mixture at this point so as to bring the temperature thereof down to the 80°C inlet temperature ideally required by the fuel cell 12 (i.e. generally referred to as a Polymer Electrolyte Fuel Cell (PEFC)). Following this final stage of the reforming process, the gas stream comprises H₂, N₂ and CO₂. With HX1 30, HX2 32 and HX3 34 arranged between stages of the reforming process as described above, once operating, the reforming process is effectively self-sufficient in terms of heat. The heat recovered in the heat exchangers may then be used to heat the air, water and fuel at the inlet to the mixing chamber 14 as well as to heat the additional water supplied to the WGS 18 stage. In this regard, the Applicant through its research activities has developed one particularly advantageous heat exchanger arrangement which improves the overall effectiveness of the reforming process. This arrangement will now be described by way of example with reference to Figure 2. It is to be noted that the specified g/sec flow rates for steam and water detailed hereafter are in no way intended to be limiting of the present invention and have been derived by using a typical automotive fuelling level.

Water is provided from a suitable source to HX3 34 where it is preheated by way of the heat extracted subsequent to the PrOx 20 stage. This preheating results in 1.19g/sec of steam and 1.77g/sec of water at 100°C. This steam mixture is subsequently passed to the LTS stage 24 of the WGS 18 where it is continued to be heated. The heat extraction at the LTS stage 24 serves to further heat the mixture resulting in 2.08g/sec of steam and 0.88g/sec of water at 100°C. From the LTS stage 24, the steam mixture is passed to HX2 32 where the heat extracted subsequent to the HTS stage 22 is used to further heat the mixture. At this point, the mixture temperature is increased to 250°C.

From HX2 32, 0.61 g/sec of steam is diverted to the HTS stage 22 where it is used in the reaction process at that stage to react with the carbon monoxide delivered to the HTS stage 22. As alluded to hereinbefore, at this stage, most of the carbon monoxide produced in the ATR 16 is converted to carbon dioxide by the reaction with water, the reaction also resulting in the liberation of some additional hydrogen. The remainder of the steam is directed to the delivery arrangement 28 upstream of the mixing chamber 14.

Air which is delivered from the same source as that which is provided to the PrOx 20 is directed through HX1 30 where it is heated to 650°C. The air is then also directed to the delivery arrangement 28 where it is able to mix with the steam resulting in a steam/air mixture at 539°C. This steam/air mixture is subsequently provided to the mixing chamber 14. At the mixing chamber 14 stage, fuel is injected into the steam/air mixture by way of the delivery injector 26 resulting in a 400°C fluid mixture in the mixing chamber 14. This fluid then proceeds to be processed by the fuel reformer 10 in the manner as previously discussed.

Under certain operating conditions, it may be required to remove an additional small quantity of heat at HX1 30 and HX2 32. For instance, for the particular example as described above, the Applicant has found that an additional 4.8kW of heat was required to be removed at HX1 30 and/or HX2 32.

Figure 2 also shows an optional electrically heated catalyst (EHC) 38 arranged after the mixing chamber 14 and upstream of the ATR 16. In certain applications, the EHC 38 may be used to heat the fluid mixture upon starting of a cold system and quickly bring the mixture temperature up to a more desirable level. Typically, the EHC 38 would not be used throughout the entire operating regime of the fuel reformer 10, but predominantly at start-up such that the reformer 10 could more rapidly attain a higher level of operating efficiency. Once the system was able to achieve a self-sustaining point with respect to heat generation, the EHC 38 would typically be turned off. In certain arrangements, the EHC 38 may alternatively be integrated into a single unit with the ATR 16.

The function of the EHC 38 is further highlighted in the following comments which also relate to the air to steam ratio and air to fuel ratio as provided to the mixing chamber 14 (and hence to the ATR 16). As previously described, the ATR 16 effectively promotes simultaneous steam reforming (endothermic) and partial oxidation (exothermic) reactions involving air, steam and gasoline received from the mixing chamber 14. At start-up, there may however be insufficient heat available from the reformer arrangement 10 to generate satisfactory levels of steam and so the ATR 16 may initially function in a predominantly oxidation mode. In such circumstances, the gas delivered to the mixing chamber 14 is predominantly air, and essentially results in the fuel delivered thereto being atomised by and mixed with air alone.

When functioning in this primarily oxidation mode, the heating process can advantageously be optimised through control of the air to fuel ratio to increase heat generation at the expense of reduced Hydrogen formation. This process can be further enhanced by way of the EHC 38 as mentioned above which serves to more rapidly heat the fluid mixture from the mixing chamber 14 during start-up and hence promote the oxidation reaction at the ATR 16. In this way, the oxidation reaction at the ATR 16 is enhanced and can more readily generate a significant amount of heat to enable satisfactory levels of steam to be produced sooner in the reformer 10. As the mixture temperature increases and more steam is able to be produced, the ATR 16 also begins to effect steam reforming with the reformer 10 eventually being able to operate in a self- sustaining manner without the need for heat input from the EHC.

Hence, by way of the above described heat exchanger arrangement, the reformer process may be enhanced such that durable and effective operation can ensue at each functional stage. As such, overall operation of the fuel reformer 10 is improved. Apart from the optional use of the EHC 38, the heat exchanger and heat transfer properties of the above described system result in no external energy sources being required to heat the water and air inputs which are used by the fuel reformer 10. That is, utilization of the heat released in the process of reforming fuel to pre-heat the air and water supplied to the reformer 10 is rendered more optimum.

As alluded to hereinbefore, mixture preparation is also an important step in the reforming process with the mixing chamber 14 of the fuel reformer 10 being predominantly responsible for performing this function prior to the fluid mixture undergoing any subsequent chemical reactions as discussed above. Further detail regarding the configuration and function of the mixing chamber 14 will now be provided with particular reference being made to Figures 4, 5, 6 and 7. Figure 4 shows the mixing chamber 14 as being an essentially two-stage arrangement wherein a first section 40 is in series with a second section 42 and wherein each of the first and second sections 40, 42 have a generally circular cross-sectional shape. In the particular embodiment described, the first section 40 effectively serves as a swirl chamber whilst the downstream second section 42 provides for the further mixing and diffusing of the resultant fluid mixture from the first section 40. The first section 40 is configured such that first and second fluids may be directed thereinto by an inlet or inlets 44 and the delivery injector 26. After passing to the second section 42 and being further processed therein (as will be further described), the resultant fluid mixture is delivered from the mixing chamber 14 by way of an annular delivery portion 46. Whilst the operation of the mixing chamber 14 will in the main be described with reference to a fuel reformer, it is to be noted that the mixing chamber 14 may of course be adapted for use in various alternative applications where the effective mixing of two or more fluids may be required.

When adapted for use as a component of the fuel reformer 10, the first portion 40 which is provided as a swirl chamber serves to effectively enable liquid fuel which is delivered thereinto to be evapourated. The evapourated air/steam/fuel mixture is subsequently mixed with additional air/steam in the second portion 42 prior to being diffused for supply to the next stage of the fuel reformer 10. Hence, the second portion 42 effectively serves as a mixing and diffusing chamber.

The inlets 44 are arranged to receive the air/steam mixture from the delivery arrangement 28. The delivery arrangement 28 may be provided in the form of one or more simple conduits to direct the air/steam mixture into the mixing chamber 14 or may alternatively be provided in the form of a more involved arrangement which serves to impart some degree of pre-mixing to the air and steam. So as to provide the continuous supply of air and steam to the fuel reformer 10, the inlet(s) 44 are in communication with an air pump or an intermediary air rail supplying air and/or steam to the mixing chamber 14, further details of which will be provided hereinafter. The delivery injector 26 is adapted to introduce into the mixing chamber 14 a fluid for mixing with the incoming air/steam, said second fluid typically being an unreformed hydrocarbon based fuel. As previously described, the air/steam and fuel promote conversion within the fuel reformer 10 and consequently the supply of a hydrogen enriched gas supply to the corresponding fuel cell 12.

In this embodiment, a series of inlets 44 are positioned such that the air, and/or steam, is introduced into the mixing chamber 14 tangentially. In this case, the injector 26 is also located tangentially to the mixing chamber 14 with the second fluid being directed into or towards the center of the first section 40. Swirl is generated in the first section or swirl chamber 40 by the introduction of the air/steam mixture through the tangential inlets 44. In the embodiment described, 4 equispaced tangential inlets 44 are provided (though only 3 are visible in Figure 4). 50% of the air/steam mixture delivered to the mixing chamber 14 is introduced into the swirl chamber 40 through the inlets 44.

As best seen in Figure 5, the swirl chamber 40 comprises an annular chamber 48 arranged about a central conduit 50. The central conduit 50 extends from the swirl chamber 40 through to the second section or diffuser 42. The central conduit 50 serves as the outlet for the swirl chamber 40 with the annular chamber 48 being in communication with a first open end 52 of the central conduit 50.

Fuel is introduced into the swirl chamber 40 at a single injection point 53 which is conveniently arranged downstream of one of the tangential inlets 44. As will be further discussed hereinafter, the fuel is injected in the form of a highly atomised spray plume via delivery injector 26 which forms part of the air assist or two fluid fuel injection arrangement 36 as previously described with reference to Figure 1. The particular arrangement discussed promotes a certain degree of shearing by the air/steam mixture of the fuel which is particularly beneficial in assisting in the mixing of the air/steam and fuel. That is, the arrangement whereby the fuel is delivered tangential to and downstream of one of the inlets 44 results in a certain degree of interference between the fluids which is conducive to the intermixing thereof.

In certain arrangements, the degree of interference may be further increased by having the injector 26 arranged such that the fuel delivered thereby is aimed at a certain angle into or towards the air/steam flow out of an inlet 44. The tangential orientations of the inlets 44 further serve to promote mixing within the swirl chamber 40 as the air/steam/fuel mixture is to a certain extent caused to swirl around the central conduit 50 within the annular portion 48 prior to being delivered through to the diffuser 42 by way of the central conduit 50. This further mixing arises primarily due to the increased residence time of the fluid mixture within the swirl chamber 40 and the enhanced turbulence therebetween which gives the air/steam and fuel greater opportunity to interact or interfere with one another and become mixed.

It is evident that the position of the injector 26 in the mixing chamber 14 will have a significant bearing on the effectiveness of the mixing action in that the momentum of the second fluid, typically liquid fuel, must be sufficient to have the plume of the second fluid interact with the first fluid. Thus, the position of the injector 26 relative to the inlet 44 will generally be a function of the fluid properties of the first and second fluids, the size of the swirl chamber 40, and the inlet and injection speed of the first and second fluids which will be readily understood and discernible by the person skilled in the art so as to place the injector 26 adjacent to the inlet 44 to achieve the degree of mixing desired in the swirl chamber 40. Similarly, the orientation of the inlet(s) 44 in the swirl chamber 40 will have a significant bearing on the efficiency thereof in that the residence time is typically desired to be maximised to permit the greatest degree of mixing as is possible of the first and second fluids. Nonetheless, in certain applications, there may exist certain benefits in having the inlets 44 angled from the tangential orientation and such a variant is also deemed within the scope of the present invention. For example, a certain degree of such angling may permit an initial degree of interference between the various air/steam streams as they enter the swirl chamber 40 which may be conducive to effective mixing thereof. Furthermore, at the expense of additional cost and complexity, multiple injection points can be utilised to further increase the degree of mixing and atomisation and/or provide less cyclic introduction of fuel to the mixing chamber 14, for example, by phasing the multiple injection points to deliver fuel at different times to each other.

As best seen in Figure 5, the second section or diffuser 42 is fed with opposing flows from the swirl chamber 40 and the remaining 50% of the air/steam mixture which is delivered into the diffuser 42 by way of a central inlet 54. As with the inlets 44, the central inlet 54 receives the air/steam mixture from the delivery arrangement 28 which could be of various different forms depending upon the particular application. An inner end 56 of the central inlet 54 corresponds with a delivery end 58 of the central conduit 50 from the swirl chamber 40. In this way, the fluid flows delivered into the diffuser 40 by the conduit 50 and inlet 54 converge in a highly localised region where further mixing takes place. That is, each of the fluid flows in part act as obstructions or blockages to the opposing fluid flow. Consequentially, the point of impact between the two fluids becomes highly turbulent because of the interchange between the two fluids within this region causing further mixing of the two fluids.

Hence, a turbulent region 60 is generated at the point of impact of the two fluids and significantly contributes to the uniform mixing of the air/steam and fuel prior to the resultant fluid being delivered from the mixing chamber 14. Ideally, a first fluid flow has a high relative velocity and is directed into a second fluid flow to generate the turbulent region 60.

An annular diffusing section 62 is arranged about the central inlet 54, the diffusing section 62 communicating with the turbulent region 60 by way of an intermediate section 64. An axial angled flow guiding portion 66 extends from the inner end 56 of the central inlet 54 towards a dividing wall 67 which isolates the annular portion 48 of the swirl chamber 40 from the diffusing section 62 of the diffuser 42. The axial angled flow guiding portion 66, together with the outside surface of the delivery end 58 of the central conduit 50, serve to in part define the intermediate section 64. After the fluid flows have converged in the turbulent region 60 where further mixing takes place, the resultant mixture enters the diffusing section 62 by way of the intermediate section 64. In being made to traverse through the intermediate section 64 and around the axial angled flow guiding portion 66, further mixing of the fluid takes place such that the final mixture which enters the diffusing section 62 is essentially a relatively uniform or homogenous mixture.

The diffusing section 62 then serves to direct the final mixture axially towards the face of the ATR catalyst 16 of the fuel reformer 10 via the annular delivery portion 46. Within this diffusing section 62, the mixture is able to disperse annularly such that an evenly distributed flow of fluid is able to be fed to the ATR 16 via the annular delivery portion 46, hence avoiding any undesirable concentrated or dilute pockets of the mixture at the face of the ATR catalyst 16.

Accordingly, the two stage mixing chamber 14 arrangement enables a compact, responsive and lightweight mixing chamber to be provided which can be incorporated as part of an effective and reliable fuel reformer arrangement. By virtue of the effective mixing with the hot air/steam fed into the swirl chamber 40, the injected liquid fuel is able to in most cases be totally evapourated in the swirl chamber 40 before being delivered to the diffusing section 62. The evapourated air/steam/fuel mixture is mixed with additional air/steam in the diffuser 42 in which gas flows are ideally arranged to oppose each other with a higher velocity flow being directed into a lower velocity flow to generate the turbulent mixing region 60. The uniform mixture is then delivered to the ATR catalyst 16 by way of the annular delivery portion 46 with a uniform velocity and temperature distribution as will be further explained hereinbelow.

Whilst the above discussion of the mixing chamber 14 has primarily focused on the fluid delivered by the central conduit 50 and the central inlet 54 to the diffuser 42 being first and second flows of the same first fluid (i.e. typically air/steam), it is to be appreciated that the central conduit 50 and the central inlet 54 may in certain arrangements provide for the delivery of different fluids into the diffuser 42. For example, and as alluded to hereinbefore, the fluid delivered into the diffuser 42 by the central inlet 54 may be the same as that delivered by the injector 26, or may be a different third fluid.

Various tests and simulations have been carried out by the Applicant confirming the operation and performance of the embodiment described and some of these results are discussed herebelow to highlight the effectiveness of the mixing chamber 14. Figure 5, which shows a lateral cross-section of the mixing chamber 14, provides an indication of the gas flow field which results within the mixing chamber 14 due to the two-stage swirl chamber 40 and diffuser 42 sections. The swirl chamber 40 is on the left side of the Figure with the exiting parallel flow on the right representing the face of the ATR catalyst 16. The four tangential inlets 44 are not visible in this Figure, but are directed approximately at the center of the vortex in the annular chamber 48. The plot shows that the resultant flow and velocity of the fluid mixture at the face of the ATR 16 is approximately uniform in magnitude and free of any reverse flow.

As well as showing the configuration of the mixing chamber 14, Figure 4 also provides an indication of the particle trajectories of the injected fuel droplets 65 with these droplets typically having a size in the range of 1 micron to 80 microns. The trajectories of the droplets 65 are terminated when either a fuel droplet has evapourated or when a fuel droplet impinges on a wall of the annular chamber 48. Figure 4 aids in highlighting that the performance of the mixing chamber 14 is more than satisfactory as it is evident that no fuel droplets reach the face of the ATR 16 and that for small droplets, the evapouration time is very short with the small droplets only penetrating a few mm from the point of injection. For medium size droplets in the order of 20 microns, the penetration is greater with a small proportion of these droplets traveling more than halfway across the annular chamber 48 before evapourating. During this passage these medium sized droplets are clearly influenced by the flow established within the annular chamber 48 by way of the tangential inlets 44. Some large droplets may also impinge on the central conduit 50 although these are expected to evapourate upon contact with this hot surface. Figure 6 is a further lateral cross-section through the mixing chamber 14 which shows the vapour concentration of fuel within the mixing chamber 14. The darkest regions 68 represent low vapour concentration (i.e. inlets for air/steam mixture) whilst the region 70 of medium darkness (e.g. beneath the upper inlet 44) represents a high fuel concentration region (i.e. point of entry for fuel). The regions of differing darkness/lightness show that mixing of the air/steam and the fuel within the swirl chamber 40 progressively improves with the passage of the fluid through the annular chamber 48 and then the central conduit 50. The swirl chamber 40 gases are reasonably well mixed at the entrance to the diffuser 42 as can be seen from the light region 72. Further substantial mixing of the diffuser 42 air/steam and the swirl chamber 40 fluid mixture occurs in the high localised region where the two gas streams meet, this localised region corresponding to , the turbulent region 60. Further downstream within the diffusing section 62, the fuel vapour concentration at the face of the ATR catalyst 16 is relatively uniform with minimal variation (see region 74), hence highlighting that the fuel has successfully been uniformly mixed with the air and steam.

Figure 7, yet a further lateral cross-section through the mixing chamber 14 shows the variation of gas temperature throughout the mixing chamber 14. In this Figure, the darkest region 76 corresponds to the 80°C injected fuel and the next darkest region corresponds to the 539°C incoming air/steam (region 78). The results of the Applicant's analysis of the performance of the mixing chamber 14 are close to those obtained for the analysis of vapour concentration and show that there is only minimal temperature variation at the face of the ATR catalyst 16 (see region 80).

By way of the embodiment of the present invention, the turbulent region 60 only forms a small portion of the overall volume of the mixing chamber 14. Hence it is evident how an arrangement according to the present invention may enable the overall volume and/or size of the mixing chamber 14 to be reduced to provide a more compact design. The mixing chamber 14 as described achieves this compact design whilst still providing a high level of homogeneity of the fluid mixture which is delivered to the ATR 16. Furthermore, the swirl-diffuser type mixing chamber 14 satisfies certain other criteria which are key to the operation of such a mixer when used in a fuel reformer, namely that it ensures no droplet impingement occurs at the face of the ATR 16 and that uniform velocities, temperature and vapour concentrations are attained prior to delivery of the resultant mixture to the ATR catalyst 16.

As alluded to hereinbefore, the mixing chamber 14 arrangement of the present invention is not necessarily restricted to the field of fuel reformers and fuel cells and one possible alternative application of the present invention is in relation to the control of emissions within an exhaust system. For example, the inlet(s) 44 of the mixing chamber 14 as shown in Figure 4 may be arranged to be in communication with one or more combustion chambers of an internal combustion engine. Thus, the first fluid directed into the mixing chamber 14 may be exhaust gases from said combustion chambers carrying polluted emissions. In order to reduce the emissions, a particular reaction may assist, but may be dependent upon the injection of a second fluid. Such a reaction may or may not involve a catalyst to process the exhaust emissions. The second fluid may be delivered into the mixing chamber 14 by way of the injector 26. Being a chemically driven reaction, it may be necessary to optimise the reaction and so uniform mixing of the two fluids is highly desirable which is satisfied by this embodiment of the present invention.

The person skilled in the art will recognise the benefits of thorough mixing so as to preferably limit emissions such as uncombusted hydrocarbons which may be removed by bringing said emissions into contact with a catalyst at an elevated temperature and pressure. More particularly, the present invention may be used to promote the reduction of NOx in the exhaust gases of diesel engines by promoting mixing with a suitable regeneration substance such as urea. In this connection, it is currently the practice to seek to inject urea subsequent to combustion and once the exhaust emissions have been delivered to the vehicle exhaust system. At this point, there typically exists a very homogenous gas environment and so significant mixing of the urea with the exhaust gases is required in order to provide the desired benefit. Accordingly, the mixing chamber 14 as previously described may offer certain advantages in such an environment. In other alternative arrangements, the mixing chamber arrangement of the present invention may be used to further process or prepare fluids necessary to promote combustion, such as air, prior to being drawn into the combustion chambers of an engine.

Referring again to Figure 2, further detail will now be given in relation to the fuel injection system 36, which in this case is a dual fluid or air-assist fuel injection system. Delivery injector 26 is a key component of the injection system 36 as it is the component which interfaces with the mixing chamber 14 and delivers the fuel thereinto. The delivery injector 26 receives pressurised gas, in this case air, from an air compressor 82 via an air supply line 84. An air pressure regulator 86 is interposed between the delivery injector 26 and the compressor 82 along the air supply line 84 and eliminates any undesirable irregularities in the air supply pressure. Air is supplied to the air compressor 82 from an air pump 88 which also supplies air to HX1 30, the PrOx 20 and fuel cell 12.

A fuel metering means 90 is axially arranged with respect to the delivery injector 26 and delivers metered quantities of fuel to a working or holding chamber of the delivery injector 26. This metered fuel is subsequently entrained by air from the compressor 82 and is delivered from the holding chamber and into the mixing chamber 14 upon operation of the delivery injector 26, the holding chamber being in fluid communication with the air supply line 84. Fuel is delivered to the fuel metering means 90 from a fuel source via a fuel supply line 92. The fuel source in this case is a fuel tank 94 from which fuel is delivered into and along the fuel supply line 92 by way of a suitably arranged fuel pump 96. A fuel-air pressure regulator 98 is interposed between the fuel metering means 90 and the fuel pump 96 and along the fuel supply line 92 to regulate the fuel pressure with respect to the air pressure such that a suitable differential may be maintained therebetween at all times. The fuel-air regulator 98 communicates back to the fuel tank 94 by way of a fuel return line 100 and similarly, the air regulator 86 returns any excess air back to the air line from the air pump 88 via air return line 102. The injector 26 typically includes a delivery end section with a delivery port through which the second fluid, typically fuel, is injected into the mixing chamber 14. The delivery end section generally includes a valve seat, and a valve member movable into and out of sealing engagement with the valve seat for selectively opening and closing the delivery port. The valve member forms part of a valve having a valve stem, one end of which supports the valve member. An electromagnetic system is typically utilised for operation of the valve to selectively open and close the delivery port. The electromagnetic system includes a solenoid coil located in the body of the injector about the valve stem, and a solenoid armature attached to the valve stem. Energisation of the solenoid coil typically induces movement of the armature to cause the valve member to move out of engagement with the valve seat against the influence of a spring which normally retains the valve in the sealing or closed condition. The valve stem may in certain applications be of hollow construction to provide a central bore which forms part of the fuel flow path. Openings are provided in the wall of the valve stem to permit the fluid charge to pass from the central bore to an outer zone from where it can be delivered into the mixing chamber 14 upon opening of the delivery port. Such a hollowed valve stem is disclosed in the Applicant's US Patent No. RE 36,768, the contents of which are incorporated herein by reference. Further detail regarding the operation of electromechanical injectors of this type should be well know to the skilled addressee in the art and will not elaborated on further herein.

Referring further to the function of the delivery injector 26, whilst the introduction of the air/steam in a reformer arrangement will generally be continuous in nature, the injection of the second fluid, typically fuel, may in certain circumstances be discontinuous depending on the type of injector 26 adopted. In such an arrangement and in order to maintain a desired degree of mixing and to emulate a continuous flow, the injector 26 may ideally operate at a high frequency such as up to 100 to 200 Hz. The injector 26 may be of any known type that can provide an injection of a second fluid such as fuel at a required frequency and of a required volume. In this regard, the injector 26 may be of the single fluid type where fuel at a relatively high pressure is delivered in the form of a fine spray into the first portion 40 of the mixing chamber 14 such that it functions according to know pressure-time metering principles. Alternatively, the injector 26 may be of the dual fluid type as described above wherein the fuel is entrained and delivered by way of a quantity of compressed gas, typically air, in the form of a spray plume. An example of such a two fluid delivery injector is given in the Applicant's US Patent No. RE 36,768. Other suitable injectors may also be adapted for use in the above described mixing chamber arrangement.

In regard to the above described two-fluid injection system, under normal circumstances, a metered quantity of fluid entrained in air is delivered to the mixing chamber 14 upon opening of the delivery port. The metering and injection events are thus arranged in a timed sequence so as to inject the full metered quantity of fluid in one event. Figure 8(a) shows a timing diagram with plot 110 representing the metering timing signal and plot 112 showing the injection timing signal. As can be seen, for a typical two-fluid injection system, prior art methods generally sequence the metering event with the injection event so as to have the same duration and the same frequency in timed sequence.

However, when such a dual fluid injection system is applied to a fuel reformer, a low frequency pulsed injection event may produce unwanted variations in the air/fuel/water mixture which subsequently contacts the ATR catalyst 16. As previously highlighted, such variations are most undesirable for the effective operation of the reformer 10. As the fuel reformer 10 generally requires a reasonably continuous supply of air, steam and fuel, the injection of air/steam should be of sufficient frequency so as to effectively emulate the continuous flow of fluid into the reformer. Further, in order to achieve sufficient mixing of the fluids prior to delivery to the reaction section of the reformer 10 for conversion of the fuel into a hydrogen-enriched stream, it is advantageous if the fuel injection events were able to occur at a high a frequency as possible.

Hence, in order to enhance mixing between the air/steam and the fuel, the rate of injection should preferably be maximised and in this embodiment is preferred to be at a frequency of 200 Hz. However, the ability of the metering means 90 to accurately meter a fluid charge is diminished as the frequency increases and there exists a practical limit to the frequency at which a fluid can be metered prior to the injection event. For example, it is evident that the metering means, which in the embodiment discussed is a solenoid actuated device, must be sized so as to satisfy a full load condition. At an injection rate of 200 Hz, the corresponding metering time will be 5 milliseconds. The lag time involved in the actuation and de-actuation of the fuel metering means 90 is approximately 1 millisecond and, thus, the effective time in which the fluid may be metered is 4 milliseconds. On the basis that the metering means 90 is designed to meter a sufficient fluid charge to satisfy a full load condition at the designated frequency of 200 Hz, then the metering of fluid to satisfy the full load conditions must occur within 4 milliseconds.

However, the same assembly, when used to meter a part load fuel quantity, say 20% of the full load, will meter the required part load fluid within 20% of 4 milliseconds, or 0.8 milliseconds. It has been found through operation of the assembly that as a result of the actuation and de-actuation lag time that a duration of less than 1.5 milliseconds will be overly influenced by the lag time and thus push the proportional metering output outside the linear range.

As one method of overcoming this problem, the Applicant has devised a multiple fuel injection strategy that enables the use of established dual fluid fuel injection system features on fuel reformer arrangements without affecting the efficiency of operation thereof. Figure 8(b) shows the timing diagram for a multiple injection strategy wherein the injection timing signal 112 has the same frequency as the prior art with each injection duration 114 being of the same period. The metering timing signal 116 for the multiple injection strategy is however quite different and has a duration 118 which is considerably longer than the injection duration 114 reflecting a frequency of metering somewhat less than that of the injection frequency. In this embodiment, where the injection frequency is 200 Hz, the metering frequency is 100 Hz, thus doubling the opening time of the fuel metering means 90. As a consequence, by doubling the duration, the volume of fluid metered is doubled satisfying the requirements of two injection events. Hence, an equal amount of fuel can be metered by suitable phasing of the metering event between the two fuel delivery events. A multiple injection strategy, in this case a dual injection arrangement, is embraced permitting a longer metering duration and so maintaining the output of the metering means 90 within the linear range without sacrificing the injection frequency, which is required for satisfactory operation of the fuel injection system 36 when applied to the fuel reformer 10.

Accordingly, the above described strategy enables the convenience of a high frequency injection rate with the ability of the fuel injection system 36 to accurately meter a fuel charge for injection. A key advantage of the strategy is to provide a method of balancing the metering and injection needs required for a fuel reformer arrangement whilst still enabling conventional injection apparatus to be utilised.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Modifications and variations as would be deemed obvious to the person skilled in the art are included within the ambit of the present invention.

Claims

The Claims Defining the Invention are as Follows

1. A reformer arrangement for processing a fluid mixture, the reformer arrangement comprising a mixture preparation portion and a reaction portion which together provide a reforming process, the reaction portion comprising one or more processing stages and one or more heat exchanger means being arranged with respect to one or some of the processing stages such that heat may be extracted from a fluid mixture emanating from a corresponding processing stage, wherein the extracted heat is utilised according to a particular distribution strategy to enable a certain level of preheating of one or more fluid inputs required by the reforming process.

2. The reformer arrangement according to claim 1 wherein the reformer arrangement is a fuel reformer for use with a fuel cell arrangement wherein a hydrogen-rich fluid mixture is processed by the fuel reformer and subsequently delivered to the fuel cell.

3. The reformer arrangement as claimed in claim 2 wherein the fluid inputs required by the mixture preparation portion include air, steam and a hydrocarbon based fuel.

4. The reformer arrangement according to claim 2 wherein the mixture preparation portion is arranged to receive at least two fluid inputs, and the distribution strategy enables a certain level of preheating of one or more of the fluid inputs to the mixture preparation portion.

5. The reformer arrangement according to claim 4 wherein the distribution strategy also enables a certain degree of preheating of one or more additional fluid inputs to the reaction portion.

6. The reformer arrangement according to any one of claims 1 to 5 wherein the mixture preparation portion is provided in the form of a mixing chamber which receives the fluid inputs and facilitates uniform mixing of the fluids prior to delivery of a resultant fluid mixture to the reaction portion.

7. The reformer arrangement according to claim 6 wherein the mixing chamber is provided as a two stage unit comprising a swirl chamber and a diffuser.

8. The reformer arrangement according to claim 7 wherein fuel is delivered to the swirl chamber by way a fluid delivery injector.

9. The reformer arrangement according to claim 1 wherein the reaction portion includes steam reforming and partial oxidation capability.

10. The reformer arrangement according to claim 9 wherein steam reforming and partial oxidation are carried out by a single catalytic means such as an autothermal reactor.

11. The reformer arrangement according to claim 9 wherein the reaction portion further includes a preferential oxidation unit to further reduce any residual carbon monoxide in the resultant fluid mixture or gas stream to acceptable levels.

12. The reformer arrangement as claimed in claim 11 wherein the reaction portion also includes a two stage catalytic water-gas shift reactor to minimise the level of carbon monoxide in the resultant fluid mixture.

13. The reformer arrangement as claimed in any one of claims 1 to 12 wherein two or more heat exchanger means are arranged with respect to two or more respective processing stages of the reaction portion.

14. The reformer arrangement as claimed in claim 11 wherein a first heat exchanger means is arranged between the autothermal reactor and a high temperature stage of the water-gas shift reactor.

15. The reformer arrangement as claimed in claim 14 wherein a second heat exchanger means is arranged between the high temperature stage of the water-gas shift reactor and a low temperature stage of the water-gas shift reactor.

16. The reformer arrangement as claimed in claim 15 wherein a third heat exchanger means is arranged downstream of the preferential oxidation unit and upstream of the fuel cell.

17. The reformer arrangement as claimed in claim 16 wherein the predetermined distribution strategy includes the heat extracted by the third heat exchanger means being utilised to heat the water which is required as an input to the low temperature stage of the water-gas shift reactor.

18. The reformer arrangement as claimed in any one of claims 15, 16 or 17 wherein the predetermined distribution strategy includes the heat extracted by the second heat exchanger means being utilised to heat the water which is required as an input to the high temperature stage of the water-gas shift reactor.

19. The reformer arrangement as claimed in claim 15 wherein the heat extracted by the second heat exchanger is utilised to heat the steam which is required as an input to the mixing chamber.

20. The reformer arrangement as claimed in claim 18 wherein the predetermined distribution strategy includes the heat extracted at the low temperature stage of the water-gas shift reactor serving to further heat the water which is initially preheated by the third heat exchanger and provided thereto.

21. The reformer arrangement as claimed in claim 18 wherein the predetermined distribution strategy includes the heat extracted at the second heat exchanger means serving to further heat the steam mixture which is initially heated by the low temperature stage of the water-gas shift reactor and provided thereto.

22. The reformer arrangement as claimed in claim 18 wherein the predetermined distribution strategy includes the heat extracted by the first heat exchanger means being utilised to heat the air which is required as an input to the mixing chamber.

23. The reformer arrangement as claimed in claim 16 including an electrically heated catalyst arranged downstream of the mixing chamber and upstream of the autothermal reactor.

24. The reformer arrangement as claimed in claim 23 wherein the electrically heated catalyst is operated upon cold starting of the reforming process.

25. A reformer arrangement for processing a fluid mixture, the reformer arrangement comprising a reaction portion which consists of one or more processing stages, wherein an electrically heated catalyst is also provided in the reaction portion to provide additional heat input within the reformer arrangement under various operating conditions.

26. The reformer arrangement as claimed in claim 25 wherein the reformer arrangement is a fuel reformer for use with a fuel cell arrangement wherein a hydrogen-rich fluid mixture is processed by the fuel reformer and subsequently delivered to the fuel cell.

27. The reformer arrangement as claimed in claim 26 wherein the reformer arrangement comprises a mixture preparation portion as well as the reaction portion which together define a reforming process, the electrically heated catalyst providing additional heat input during part of the reforming process.

28. The reformer arrangement as claimed in claim 27 wherein the electrically heated catalyst is arranged downstream of the mixture preparation portion and upstream of an autothermal reactor in the reaction portion of the fuel reformer.

29. The reformer arrangement as claimed in claim 28 wherein the electrically heated catalyst is specifically operated upon cold starting of the reforming process.

30. The reformer arrangement as claimed in claim 29 wherein the autothermal reactor also includes electrical heating for start-up operation.

31. A mixing chamber to achieve mixing of at least two fluids, the mixing chamber including an inlet for directing a flow of a first fluid into the chamber, and at least one fluid delivery means for directing a flow of at least a second fluid into the mixing chamber, the mixing chamber comprising an annular portion arranged about a central passage, the annular portion being in fluid communication with the central passage for delivering fluid from the mixing chamber, the fluid delivery means being arranged to deliver the second fluid downstream of and in the path of the flow of the first fluid into the chamber, wherein the inlet for the first fluid is arranged with respect to the annular portion such that a swirl flow is established in the mixing chamber to promote mixing of the first and second fluids prior to their delivery through the central passage and from the mixing chamber.

32. The mixing chamber as claimed in claim 31 wherein the inlet for the first fluid is arranged tangentially to the annular portion in order to promote the formation of the swirl flow in the mixing chamber.

33. The mixing chamber as claimed in claim 31 wherein a plurality of inlets are provided for delivering the first fluid into the mixing chamber, each of the inlets being arranged in a spaced apart relationship and tangential to the annular portion.

34. The mixing chamber as claimed in claim 31 or 32 wherein the swirl flow is established in the annular portion of the mixing chamber.

35. The mixing chamber as claimed in claim 31 wherein the central passage is arranged axially within the mixing chamber and includes an opening at a first end thereof which communicates with the annular portion.

36. A mixing chamber arrangement to achieve mixing of at least two fluids which is provided as a two-stage unit, the mixing chamber arrangement comprising a mixture preparation section and a mixture diffusing section downstream of the preparation section, the mixing chamber arrangement including a first inlet for directing a flow of a first fluid into the mixture preparation section, and at least one fluid delivery means for directing a flow of at least a second fluid into the mixture preparation section, and a second inlet for directing a flow of a fluid into the mixture diffusing section, wherein initial mixing is effected in the mixture preparation section and subsequent mixing of the fluids and diffusion thereof is effected by the mixture diffusing section.

37. The mixing chamber arrangement according to claim 36 wherein the first inlet directs a first flow of a first fluid into the mixture preparation section and the second inlet directs a second flow of the first fluid into the mixture diffusing section.

38. The mixing chamber arrangement according to claim 36 wherein the second inlet directs a flow of a third fluid into the mixture diffusing section.

39. The mixing chamber arrangement according to claim 36 wherein the first and second inlets are arranged so that the fluid flows delivered thereby are directed towards one another.

40. The mixing chamber arrangement according to claim 39 wherein a turbulent region is created at the point at which the flows of the fluids delivered by the first and second inlets impinge.

41. The mixing chamber arrangement according to claim 40 wherein the turbulent region is generated at a location central to the mixing chamber.

42. The mixing chamber arrangement according to claim 41 wherein the turbulent region is generated at a location within the diffusing section.

43. The mixing chamber arrangement according to claim 36 wherein the mixture preparation section comprises an annular portion arranged about a central passage, the annular portion being in fluid communication with the central passage for delivering a fluid mixture from the mixture preparation section.

44. The mixing chamber arrangement according to claim 43 wherein a first flow of the first fluid is delivered into the annular portion of the mixture preparation section.

45. The mixing chamber arrangement according to claim 44 wherein the fluid delivery means is arranged to deliver the second fluid downstream of and in the path of the first flow of the first fluid into the annular portion.

46. The mixing chamber arrangement according to claim 45 wherein the first inlet is arranged with respect to the annular portion such that a swirl flow is established in the mixture preparation section to promote mixing of the first and second fluids prior to their delivery through the central passage and from the mixture preparation section.

47. The mixing chamber arrangement according to claim 46 wherein the first inlet is arranged tangentially to the annular portion in order to promote the formation of the swirl flow in the mixture preparation section.

48. The mixing chamber arrangement according to claim 46 wherein a plurality of first inlets are provided for delivering the first fluid into the preparation section, each of the first inlets being arranged in a spaced apart relationship and tangential to the annular portion.

49. The mixing chamber arrangement according to claim 46 wherein the swirl flow is established in the annular portion of the preparation portion.

50. The mixing chamber arrangement according to claim 46 wherein the central passage is arranged axially within the preparation portion and includes an opening at a first end thereof which communicates with the annular portion.

51. The mixing chamber arrangement according to claim 50 wherein the fluid mixture is delivered from the preparation section by way of the central passage and into the diffusing section.

52. The mixing chamber arrangement according to claim 51 wherein the second inlet to the diffusing section is provided as a central inlet which directs a second flow of the first fluid into the diffusing section.

53. The mixing chamber arrangement according to claim 52 wherein an inner end of the central inlet to the diffusing section is arranged to correspond with a delivery end of the central passage from the preparation section.

54. The mixing chamber arrangement according to claim 53 wherein the turbulent region is created adjacent the inner end of the central inlet.

55. The mixing chamber arrangement according to claim 54 wherein the diffusing section further comprises an annular diffusing portion arranged about the central inlet for diffusing and delivering a resultant fluid mixture from the mixing chamber.

56. The mixing chamber arrangement according to claim 55 wherein the resultant fluid mixture is delivered from the annular diffusing portion in a parallel but opposite direction to the flow of the first fluid into the diffusing section.

57. The mixing chamber arrangement according to claim 56 wherein the mixing chamber arrangement may be used in a fuel reformer to uniformly mix fluid inputs required thereby prior to being processed in a downstream reaction section of the fuel reformer.

58. The mixing chamber arrangement according to claim 57 wherein air, steam and a hydrocarbon based fuel are typically the fluid inputs delivered to the mixing chamber arrangement when used as part of a fuel reformer.

59. The mixing chamber arrangement according to claim 58 wherein air and steam are delivered to the mixing chamber arrangement by way of the first and second inlets with 50% of the air and steam mixture delivered into the preparation section and the remaining 50% of the air and steam mixture being delivered into the diffusing section.

60. The mixing chamber arrangement according to claim 59 wherein fuel is delivered into the preparation section by way of the fluid delivery means.

61. The mixing chamber arrangement according to claim 60 wherein the flow of fuel from the fluid delivery means may be arranged such that it is directed across the flow of air and steam delivered into the preparation section by one of the first inlets so as to facilitate a shearing effect by the air/steam on the fuel and to promote intermixing of the fluids.

62. The mixing chamber arrangement according to claim 60 wherein the flow of fuel from the fluid delivery means may be arranged such that it is directed at or into the flow of air and steam delivered into the preparation section by one of the first inlets.

63. The mixing chamber arrangement according to claim 36 wherein the mixing chamber arrangement is adapted for use in relation to the control of emissions within an exhaust system for an engine.

64. The mixing chamber arrangement according to claim 63 wherein the fluid delivered into the first and second inlets may be exhaust gases from the exhaust system.

65. The mixing chamber arrangement according to claim 64 wherein the second fluid injected by the fluid delivery means may facilitate a particular reaction within the exhaust gases to reduce the level of emissions therein.

66. The mixing chamber arrangement according to claim 65 wherein the exhaust gases delivered into the mixing chamber by the first and second inlets may be exhaust gases generated from combustion within a diesel engine.

67. The mixing chamber arrangement according to claim 66 wherein the second fluid injected by the delivery means may be urea which is required to satisfactorily mix with the exhaust gases to promote the reduction of NOx in a catalytic reaction with the exhaust gases.

68. The mixing chamber arrangement according to claim 36 wherein the fluid delivery means is provided as part of a dual fluid injection system such that the second fluid delivered into the mixing chamber arrangement is entrained by and delivered by a quantity of gas, typically air.

69. The mixing chamber arrangement according to claim 68 wherein the fluid delivery means is a delivery injector arranged to deliver the second fluid, typically fuel, into the mixing chamber arrangement such that a fuel spray or plume of finely atomised droplets and/or vapour is directed towards or into the flow of air and steam through the first inlet(s).

70. The mixing chamber arrangement according to claim 69 wherein a fuel metering means is arranged with respect to the delivery injector such that discrete metered quantities of fuel from the fuel metering means may subsequently be delivered by the fuel delivery injector.

71. A method for controlling a dual fluid injection system for use with a reformer arrangement, the method including delivering multiple high frequency delivery injection events, including the steps of metering, in a single event, a volume of fluid sufficient to satisfy the requirements of at least two delivery injection events and delivering the volume of fluid by way of the at least two delivery injection events.

72. The method according to claim 71 wherein the dual fluid injection system is arranged to deliver fuel to the reformer arrangement for processing thereby.

73. The method according to claim 72 wherein the fuel reformer arrangement comprises a mixing chamber arrangement including a fuel delivery injector for enabling the delivery of fuel thereto.

74. The method according to claim 73 wherein a fuel metering means is conveniently arranged with respect to the fuel delivery injector such that discrete metered quantities of fuel from the fuel metering means may subsequently be delivered by the fuel delivery injector.