WO2007113507A1

WO2007113507A1 - Power supply system

Info

Publication number: WO2007113507A1
Application number: PCT/GB2007/001165
Authority: WO
Inventors: Richard Keith Stobart; Zhijun Peng; Anita Raghunath Chaudhari; Morgan Raymond Heikal; Michael Louis Monaghan; Nicos Ladommatos; Ioannis Hardalupas; Alexander Marinos Kriton Peter Taylor; Hua Zhao; Xi Jiang; Thomas Tsoi-Hei Ma
Original assignee: The University Of Sussex; University Of Brighton; University College London; Imperial College Of Science; Brunel University
Priority date: 2006-03-31
Filing date: 2007-03-30
Publication date: 2007-10-11
Also published as: GB0606529D0; WO2007113509A1; EP2005507A1

Abstract

A power supply system comprises an internal combustion engine (1) and a fuel cell (2) arranged in series with each other, together with an appropriate fuel supply (6) and an air supply (3) for the fuel cell (2) and internal combustion engine (1). The stream of fuel gas (7) which is exhausted from the anode of the fuel cell (2) is provided as a fuel supply input to the fuel supply system of the internal combustion engine (1). The fuel cell (2) is controlled so as to control the composition of exhausted fuel supply stream (7) that is input from it into the internal combustion engine (1). This is achieved by controlling the fuel cell (2) to remove (consume) a desired amount of the combustible. material (fuel) in the fuel supplied to it, before that fuel is supplied to the internal combustion engine.

Description

Power Supply System

The present invention relates to a power supply system and more particularly to a system that combines both a fuel cell and an internal combustion engine to provide a power source that may be used, e.g., in a vehicle or other system. As is known in the art, it is becoming increasingly common to use so-called "hybrid" power supply systems that use two or more power sources in combination. A common example of such a system is th.e use of both a fuel cell and an internal combustion engine in a vehicle. In such an arrangement, the fuel cell may be used, e.g., to provide electrical power for auxiliary electrical systems of the vehicle and/or to drive the vehicle (e.g. when the internal combustion engine is not being used for that purpose) . Such arrangements can, e.g., be more fuel efficient and less polluting than simply using an internal combustion engine alone.

Although there have been many proposals regarding the combined use of fuel cells and internal combustion engines as "hybrid" power systems, the Applicants believe that there remains scope for improvement to such systems.

According to a first aspect of the present invention, there is provided a power supply -system, comprising: a fuel cell; an internal combustion engine; means , for providing a fuel supply to the fuel cell; means for providing the fuel supply exhausted from ^" the fuel cell as a fuel supply, to the internal combustion engine,- and means for controlling the operation of the fuel cell so as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell. According to a second aspect of the present invention, there is provided a method of operating a power supply system that comprises a fuel cell and an internal combustion engine, the method comprising: inputting the fuel supply stream exhausted from the fuel cell as a fuel supply to the internal combustion engine; and controlling the operation of the fuel cell so as to control a property or properties of the exhausted fuel supply stream that is supplied to the internal combustion engine from the fuel cell.

The power supply system of the present invention comprises a fuel cell and an internal , combustion engine, as in hybrid power supply systems that are known in the art. However, in the system of the present invention, the fuel exhausted from the fuel cell (i.e. the residual fuel supply stream after the fuel has passed through the fuel cell) is supplied as a fuel supply to the internal combustion engine (i.e. to be burnt by the internal combustion engine) and, moreover, the operation of the fuel cell is controlled so as to control a property or properties of the fuel that is supplied to the internal combustion engine in this manner. In other words, the fuel cell is used, at least in part, as a fuel processing unit to, in effect, condition or tailor the fuel that is supplied from it to the internal combustion engine. For example, the exhaust gas that is supplied from the fuel cell to the internal combustion can be used, as will be discussed further below, to dilute the air supply to the internal combustion engine and thereby modulate the subsequent combustion in the internal combustion engine and supply some fuel gases. Indeed, a key feature of the present invention is the recognition by the Applicants that in a hybrid system comprising a fuel cell and an internal combustion engine, the fuel^' cell may be used to condition or adapt fuel that is supplied to the internal combustion engine, and, furthermore, that that can be advantageous (as will be discussed further below) .

Thus, in a third aspect, the present invention is directed to the use of a fuel cell to condition fuel that is supplied to an internal combustion engine.

According to a fourth aspect of the present invention, there is provided a method of operating a power supply system that includes an internal combustion engine, the method comprising using a fuel cell to condition fuel that is supplied to the internal combustion engine.

According to a fifth aspect of the present invention, there is provided an apparatus for a power supply system that includes an internal combustion engine and a fuel cell, the apparatus comprising: means for using the fuel cell to condition fuel that is to be supplied to the internal combustion engine .

As discussed above, the Applicants have recognised that the use of a fuel cell to condition or adapt fuel supplied to an internal combustion engine can provide a number of significant advantages. For example, the fuel cell could be used to try to ensure that the fuel supplied from it to the internal combustion engine is, e.g., always of a particular quality and/or has particular properties, regardless of the, e.g., quality or properties of the initial input fuel that is supplied to the fuel cell. In other words, the fuel cell can be used to ensure the supply of fuel having consistent properties (e.g. in terms of the fuel's "quality" or composition) to the internal combustion engine, even where fuels of varying properties (e.g. "quality" or composition) are or have to be used in the system (e.g. because the available fuel supply changes or can change) . Moreover, the ability of the system of the present invention to tailor the fuel supplied to the internal combustion engine makes the system of the present invention particularly useful for use with engines that require more precise and less variable fuel supplies, such as engines that use the HCCI (homogeneous charge compression ignition) engine cycle (which engines, as is known in the art, can provide efficiency advantages, if they can be used) . Indeed, a significant advantage of the system of the present invention is that it facilitates the use of engines such as HCCI engines in situations where that may not otherwise or in the past have been possible.

The fuel cell used in the system of the present invention may take any suitable and desired form. In a preferred embodiment a solid oxide fuel cell (SOFC) is used. The use of a solid oxide fuel cell is advantageous because it, for example, will provide hot output gases, which facilitates use with engines that require warm intake conditions, such as an HCCI engine. The fuel cell is preferably in the form of, as is known in the art, a fuel cell stack (a stack of individual fuel cells) . It accordingly preferably comprises a plurality of individual cells arranged in series (in a series configuration) . The use of a fuel cell stack increases the electrical power that the fuel cell arrangement can provide, as is known in the art. Thus, there may be, in effect, a single fuel cell, or plural fuel cells arranged in a stack (in series) , as is known in the art . The fuel that is supplied (input) to the fuel cell may comprise any suitable such fuel (e.g., in the case of a fuel cell that reacts hydrogen and oxygen, a fuel that will at least comprise hydrogen for reaction in the fuel cell, such as a fuel gas or liquid that will typically, as is known in the art, comprise a mixture of carbon monoxide, hydrogen and/or light olefins (methane, ethane, propane and/or butane) .

Where the initial fuel supplied already includes hydrogen in a form suitable for consumption by the fuel cell, such as a blend of hydrogen and natural gas such as hythane, then the supplied fuel may be input to the fuel cell directly.

On the other hand, where the initial fuel supply is not suitable for direct use by the fuel cell, then it may be converted to a suitable form (e.g., a suitable carbon monoxide and hydrogen mixture that may then be consumed directly by the fuel cell stack) by means of a reformer, as is known in the art. The use of a reformer facilitates, as is known in the art, the use of a fuel cell with, e.g., more complex starting fuels, such as bio-fuels, diesel, coal, natural gas, biogas, ethanol, or gasoline. Indeed, the use of a reformer is advantageous because it further enhances the tolerance of the system of the present invention to a variety of fuels and varying quality fuels, such as those listed > above. Thus, in a particularly preferred embodiment, the system of the present invention includes a reformer or a reforming stage for reforming or converting fuel (a fuel supply) before it is supplied to the fuel cell.

Where a reformer is used, the reformer can be any suitable and desired such device, such as a reformer already known in the art, and can operate in any suitable and desired manner. In a preferred embodiment, a partial oxidation reformer is used.

Where a reformer is used, then the reforming process could similarly be used to tailor or adapt the fuel that is supplied via the fuel cell to the internal combustion engine. For example, . the reformer may be used to reduce and/or remove any sulphur from the fuel supplied to the fuel cell, thereby reducing the formation of hazardous sulphur compounds in the engine as discussed below. Thus, in a preferred embodiment, the present invention comprises a reformer for reforming or converting fuel before it is supplied to the fuel cell and means for or a step of controlling the operation of the reformer so as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell. In a preferred embodiment, the operation of the reformer is controlled based on one or more properties of the fuel supplied to the reformer, such as its hydrogen and/or hydrocarbon content. For example, the degree of reforming performed by the reformer can be varied so that either a partially reformed or completely reformed fuel is supplied to the fuel cell, e.g., and preferably, depending on the fuel required by the engine. The property or properties of the fuel supplied to the reformer can be _'determined in any suitable or desired manner. For example, the engine and/or the fuel cell can act as fuel sensors, as is discussed in more detail below. Accordingly, if it is determined that the fuel supplied to the reformer requires a greater hydrogen content, then the reformer preferably provides a completely reformed fuel to the fuel cell. Alternatively, if it is determined that a greater hydrocarbon content is required, then the reformer preferably provides a- partially reformed fuel to the fuel cell .

It is believed that the use of a reformer or a reforming stage for reforming or converting fuel before it is supplied to a fuel cell may be new and advantageous in its own right. Thus, according to a sixth aspect of the present invention, there is provided a power supply system, comprising: a fuel cell; an internal combustion engine; a fuel reformer for providing a fuel supply to the fuel cell; means for providing the fuel supply exhausted from the fuel cell as a fuel supply to the internal combustion engine; and means for controlling the operation of the reformer so as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell.

According to a seventh aspect of the present invention, there is provided a method of operating a power supply system that comprises a fuel cell and an internal combustion engine, the method comprising: inputting the fuel supply stream exhausted from the fuel cell as a fuel supply to the internal combustion engine; and controlling the operation of a reformer supplying fuel to the fuel cell so as to control a property or properties of the exhausted fuel supply stream that is supplied to the internal combustion engine from the fuel cell.

As will be appreciated by those skilled in the art, these embodiments and aspects of the invention can and preferably do include any one or more or all of the preferred and optional features of the invention described herein. For example, the fuel cell is preferably also controlled so¹ as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell. In a particularly preferred such arrangement the reformer and fuel cell are operated and controlled in combination, and, e.g., in a coordinated fashion, so as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell . The fuel input to the fuel cell is preferably provided under pressure, as is known in the art.

As well as a fuel supply as discussed above, the fuel cell will also, as is known in the art need to be provided with a supply of oxygen for its chemical reactions . The oxygen can be supplied to the fuel cell in any suitable and desired manner, and using any suitable means such as any suitable manner known in the art. In a preferred embodiment, the fuel cell is provided with an air supply stream as its source of oxygen, as is known in the art. Preferably this air supply is provided under pressure, e.g. by means of a turbocharging arrangement, again as is known in the art. Thus, in a preferred embodiment, the system includes means for or a step of providing a pressurised air stream to the fuel cell.

The fuel cell will, as is known in the art, in use cause fuel molecules (such as hydrogen) in the fuel supply and oxygen molecules in the air supply to react, and thereby generate an electric current (which may be used, e.g., as is known in the art, to drive an electric motor, power electric circuits, charge a battery, etc.).

The remains of the fuel supply stream and oxygen (e.g. air) supply stream, after they have passed through (and been, at least partially, consumed in) the fuel cell, are exhausted from the fuel cell, as is known in the art .

The fuel supply stream is exhausted from the fuel cell's anode and will comprise, as is known in the art, the residue of the fuel (e.g. reformate mixture (CO + H₂)) that was supplied to the fuel cell, i.e. the remaining fuel that has not been consumed by the fuel cell. The residual oxygen (air) supply stream is exhausted from the fuel cell's cathode and will comprise an oxygen depleted gas stream (e.g. an oxygen-depleted air stream, where air is used for the oxygen supply to the fuel cell) .

As discussed above, the resid.ua! fuel stream exhausted from the fuel cell is, in the present invention, input as a fuel supply to the internal combustion engine of the power supply system of the present invention, and can and will accordingly affect the operation of the internal combustion engine. For example, the addition of the exhausted, depleted gas from the fuel cell into the engine will change the properties of the air drawn into the engine, and modify the combustion of the liquid fuel in the engine. This will or can modify, e.g., the delay period, air-fuel ratio, burn rate and/or maximum pressure of the internal combustion engine.

The Applicants have recognised that the properties of the fuel input to the internal combustion engine in this manner will accordingly correspond to the residual fuel stream exhausted from the fuel cell, and will, accordingly, depend, inter alia, on how the fuel cell affects the fuel supplied to it as that fuel passes through the fuel cell (since the effect of the fuel cell on the supplied fuel will determine the properties of the residual, exhausted fuel supply that is input from the fuel cell to the internal combustion engine) . Moreover, the Applicants have recognised that by controlling and, e.g., varying, the effect of the fuel cell on the fuel supplied to it, properties of the fuel that is exhausted from the fuel cell and then provided to the internal combustion engine can accordingly be controlled and varied, which, as discussed above, can provide a number of advantages. A further advantage of providing the exhausted residual fuel supply stream from the fuel cell to the internal combustion engine is that that stream will typically be hot, and therefore particularly suitable as an input to an engine, such as an HCCI engine, that needs warm intake conditions (since, it can, for example, thereby remove the need to heat the fuel supply in some other way before it is input to the engine) .

The control and varying of the operation of the fuel cell to control the properties of the fuel that is supplied from the fuel cell to the internal combustion engine can be carried out in any suitable and desired manner .

In a preferred embodiment, the fuel cell is controlled so as to control > and preferably target, a particular, selected, preferably predetermined, property or properties (e.g. range values for a given parameter) in the residual fuel supply that is exhausted from the fuel cell and supplied to the internal combustion engine .

The property or properties that is controlled and/or targeted preferably comprises the composition of the fuel, such as it having a particular, preferably predetermined, composition or composition range (which composition or composition range could, e.g., relate to absolute amounts of, e.g., particular, selected components, in the exhausted residual fuel supply, and/or relative amounts of different fuel components in that supply) . In a particularly preferred embodiment, the control is based on a desired, preferably predetermined, hydrogen and/or hydrocarbon content of the exhausted fuel stream, for example so as to input a particular ratio range and/or range of absolute amounts of these components to the internal combustion engine from the fuel cell. Most preferably, the arrangement is so as to target a particular, selected, preferably predetermined, composition or composition range (e.g. in terms of its hydrogen and/or hydrocarbon absolute and/or relative content) in the fuel that will be output from the fuel cell and input to the internal combustion engine.

In a preferred embodiment, the selected target property or properties (e.g. composition) for the fuel that is exhausted from the fuel cell is based on, inter alia, the property or properties of any other fuel supplies that may be provided to the internal combustion engine. For example, the desired properties for the fuel exhausted from the fuel cell may be set so as to balance a property or properties of another fuel supply to the engine, so as to, for example, provide a desired, overall, combined fuel supply to the engine.

In a particularly preferred embodiment, the control of the fuel cell is also or instead, and preferably also, based on one or more properties (such as the hydrogen to carbon ratio, the hydrogen to carbon to oxygen ratio and/or the cetane number) of the fuel supplied to the fuel cell. These properties preferably include the composition of the fuel, such as its hydrogen and/or hydrocarbon content. In these arrangements, the relevant property or properties of the fuel supplied to the fuel cell could, e.g., be predetermined or taken from an external source, such as a database of fuel properties. This may be particularly appropriate, where, e.g.', the fuel supply is from a known (and reliable) source.

However, in a particularly preferred embodiment, the system can and preferably does determine in use one or more properties of the fuel supply for this purpose. This would facilitate, for example, using these arrangements of the present invention with variable and varying fuel supplies. Thus, --in a particularly preferred embodiment, the system or method of the present invention includes means for or a step of determining a property or properties of the fuel supplied to the fuel cell. In these arrangements , the property or properties of the fuel supply can be determined in any suitable and desired manner. For example, the engine itself can act as a fuel sensor. Probes inserted in the engine can detect, for example, delay period, pressure rise rate, fuel density and/or cetane number, etc., which information can be used to help classify the liquid fuel supplied to the engine and thereby the fuel supplied to (the reformer of) the fuel cell.

However, in a particularly preferred embodiment, the voltage and/or current, and preferably the voltage ' and the current, detected in a number (e.g., some or all) of the individual cells that make up the fuel cell is or are determined and assessed for this purpose. Preferably an analysis of the electric voltage and/or current profile and/or variation along the length of the fuel cell (the fuel cell stack) is used to determine property or properties of the fuel supplied to the fuel cell for this purpose.

As is known in the art, in a fuel cell stack, the chemical reaction that produces the electric current will proceed in the fuel cells of the stack as the input fuel passes through the overall fuel cell .

The Applicants have recognised that if the input fuel to the fuel cell contains a reactive gas, such as hydrogen, that gas will tend to react at the individual fuel cells closer to the input, and, the Applicants have recognised, thereby produce peaks in the current profile along the fuel cell stack that are towards the gas input and variations in the voltage profile along the fuel cell stack that are towards the gas input. The voltage prof-ile will also be dependent on the electro-chemical potential of the reacting gases . Similarly, a less reactive gas, such as methane, will tend to pass further through the fuel cell stack before it reacts, thereby, the Applicants have again recognised, producing a current profile and a voltage profile (that will again also be dependent on the electro-chemical potential of the reacting gases) that will or may tend to reach maximum values further along the fuel cell stack.

Thus, the Applicants have recognised that both the current profile and the voltage profile produced along the length of the fuel cell can be used as an indication of the composition (e.g. hydrogen and/or hydrocarbon content) of the fuel being supplied to the fuel cell. In effect, the current and voltage profiles can be thought of as being akin to an electro-chemical chromatograph of the fuel supplied to the fuel cell.

It would be possible in these arrangements to use the current profile on its own or the voltage profile on its own, but in a preferred embodiment both the current profile and the voltage profile are used to assess the fuel's composition.

In these arrangements, the system preferably also takes account of the fuel (gas) flow rate through the fuel cell stack and/or the fuel cell's and/or gas's operating temperature (preferably the operating temperature of the anode of the fuel cell (the anodes of the fuel cells in the stack) ) (at a steady state the fuel cell wall temperature and gas temperature should be equal), and preferably of both of these factors, as these factors will also influence where in the fuel cell stack the chemical reactions will take place (and hence the current and voltage profiles along the fuel cell produced by the reactions) .

The fuel cell can be controlled to control the properties of the fuel that is supplied from it to the internal combustion engine i-n any suitable and desired manner. In a particularly preferred embodiment the electrical load on the fuel cell is controlled (e.g. varied) to achieve this. For example, the fuel cell electrical output can be supplied to an ultra-capacitor unit, to a battery and/or to electrical functions in the vehicle.

The Applicants have recognised that the properties of the residual fuel in the fuel supply stream that is exhausted from a fuel cell will depend, for a given fuel supply, on the fuel which is consumed by the fuel cell. The fuel in the fuel supply that is consumed by a fuel cell depends, inter alia, on the electrical load placed, on the fuel cell. The Applicants have accordingly recognised that the electrical load on a fuel cell may be used to control the fuel that is consumed by the fuel cell, and, moreover, thereby control the residual fuel that remains in the fuel supply stream that is exhausted from the fuel cell. For example, by varying the electrical load imposed on a fuel cell, the amount of fuel (e.g. hydrogen and carbon monoxide) removed from a given fuel supply by (consumed by) the fuel cell may be . varied.

Thus, in a particularly preferred embodiment, the present invention includes means for or a step of controlling and/or varying the electrical load on the fuel cell, so as to control and/or vary the properties of the fuel that is supplied to the internal combustion engine from the fuel cell . ^■

Thus, as can be seen from the above, in a particularly preferred embodiment, the present invention will include steps of or means for determining one or more properties of fuel supplied to the fuel cell, and then controlling the operation of the fuel cell .(preferably by varying the electrical load placed on the fuel cell) on the basis of the determined property or properties, most preferably so as to try to target in the residual fuel supply exhausted from the fuel cell and input to the internal combustion engine, a particular, preferably selected, preferably predetermined, property or properties (e.g. composition range) .

In a preferred embodiment, a richer than stoichiometric fuel supply can be and preferably is provided to the fuel cell, as this will help to ensure that there can always be at least, some residue of fuel in the fuel supply stream exhausted from the fuel cell that is to be provided to the internal combustion engine .

The depleted oxygen (air) supply that is also exhausted from the fuel cell could, e.g., simply be exhausted to the atmosphere. However, in a particularly preferred embodiment, it is also input to the internal combustion engine. In other words, the (oxygen depleted), air supply exhausted from the fuel cell is preferably provided as an air supply input to the internal combustion engine.

Inputting the air supply exhausted from the fuel cell to the internal combustion engine has a number of advantages. In particular, the oxygen-depleted (air) stream from the fuel cell can be used as a diluent (like the recirculated exhaust gas in an EGR (Exhaust Gas Recirculation) system) for the internal combustion engine. Moreover, this air stream will, unlike in a conventional EGR systems, be substantially free of particulate and acidic matter, thereby making it a particularly clean form of diluent.

Thus, the oxygen-depleted air stream exhausted from the fuel cell can in effect, be used to substitute for exhaust gas recirculation (EGR) in the operation of the internal combustion engine (i.e. to act as an EGR source). This is advantageous, because, as discussed above, the air supply from, the fuel cell will typically be much cleaner than conventionally recirculated engine exhaust gas, thereby providing a cleaner form of "EGR".

For example, one particular problem with conventional EGR systems is the recirculation of hazardous sulphur compounds, such as sulphur dioxide (SO₂), into the engine. Sulphur dioxide, as is well known in the art, is formed by the oxidation of sulphur present in the fuel supplied to the engine, and which when recirculated, may be further oxidised to form sulphur trioxide (SO₃) that can in turn form sulphuric acid. Thus, by using the oxygen-depleted air stream exhausted from the fuel cell, which may be and preferably is substantially, if not completely, free from sulphur or sulphur compounds, as an EGR source, the recirculation of any sulphur compounds in the engine exhaust that arise from the combustion of the fuel in the engine as in conventional EGR systems can be reduced or avoided, and any sulphur compounds can instead be directed into the particulate filter within the engine. Further benefits are provided by the possibility of NO_x control, with a much lower, in particular, risk of particulate generation. For example, recent studies have shown that it is possible to reduce NO_x emissions by adding diluents, such as water and nitrogen, to the fuel supplied to an internal combustion engine so as to lower combustion temperatures. The addition of diluents, such as helium and nitrogen, has also been shown to reduce knocking in internal combustion engines, particularly when using fuels with relatively low cetane numbers. In a preferred embodiment of the present invention therefore, the fuel supply and depleted oxygen air stream exhausted from the fuel cell are used to provide a source of diluents, such as nitrogen and water, for the internal combustion engine so as to reduce NO_x formation and/or knocking. As would be understood by a -•-person skilled in the art, the fuel cell is well, .adapted for this purpose as it is able to provide a relatively- large volume of oxygen-depleted air. Accordingly, though the use of the fuel cell, the internal combustion engine is, inter alia, able to achieve low NO_x emissions without the need to resort to conventional EGR or after-treatment systems . ,

In a particularly preferred embodiment, the exhaust, from the fuel cell is used to provide an oxygen depleted air stream (which will accordingly serve as a source of nitrogen) and a water vapour stream (which will serve as a source of water) to the engine. These streams are preferably separate. This will help, as discussed above, to reduce NO_x formation and inhibit knocking behaviour. In such arrangements (and otherwise) , the water vapour exhausted from the fuel cell is preferably partly condensed (into droplets) before being supplied (injected) into the engine.

The air supply to the fuel cell is preferably controlled and controllable independently of the fuel supply, so that the fuel supply and air supply may be independently controlled. This could be achieved, e.g., by the fuel cell having separate supplies for air and fuel .

The oxygen depleted air stream exhausted from the fuel cell and supplied to the engine may be, and preferably is, also controlled and controllable independently of the fuel supply exhausted from the fuel cell, so that the fuel supply and depleted oxygen gas stream may be independently controlled. Similarly, where the fuel cell is used to provide both an oxygen-depleted air stream and a water vapour stream into the engine, those streams can preferably be controlled independently (of each other) .

The Applicants have again recognised that in an arrangement' where the depleted oxygen air supply exhausted from the fuel-cell is supplied to the internal combustion engine, then the fuel cell can be controlled so as to control the degree of oxygen depletion of the, e.g., input air stream, caused by the fuel cell, and thereby the, e.g., oxygen depletion (oxygen content) of the (air) supply exhausted from the fuel cell and provided to the internal combustion engine.

Thus, in a particularly preferred embodiment, the fuel cell is or can also be controlled to control and/or vary a property or properties of the air supply that is exhausted from the fuel cell, and, most preferably to control the oxygen content of that air supply (e.g. to target a particular range of oxygen content) .

Such control of the properties of the exhausted air supply can be carried out in any suitable manner, such as, and preferably, in one or more or all of the manners discussed above in relation to controlling the properties of the fuel supply stream exhausted from the fuel cell and input to the internal combustion engine.

Thus, for example, preferably the oxygen content of the input air supply is determined, and the fuel cell is then controlled (e.g. by setting an appropriate electrical load on it) to consume a desired amount of oxygen, so as, e.g., to provide an exhausted air supply having a particular, desired oxygen content (e.g. oxygen composition range) . For example, the electrical load on the fuel cell can be varied and/or the flow rate varied _\to control the depleted air supply to the engine.

It is believed that the idea of using a. fuel cell to condition an oxygen-depleted air stream that is then provided as a diluent to an internal combustion engine may be new and advantageous in its own right, and not just when used in combination with providing a conditioned fuel supply from the fuel cell to the internal combustion engine. Thus, according to an eighth aspect of the present invention, there is provided a power supply system, comprising: a fuel cell; an internal combustion engine; means for providing an air supply to the fuel cell;- means for providing the air supply exhausted from the fuel cell as an air supply to the internal combustion engine; and means for controlling the operation of the fuel cell so as to control a property or properties of the exhausted air supply that is supplied to the internal combustion engine from the fuel cell.

According to a ninth aspect of the present invention, there is provided a method of operating a power supply system that comprises a fuel cell and an internal combustion engine, the method comprising: inputting the air supply stream exhausted from the fuel cell as an air supply to the internal combustion engine; and controlling the operation of the fuel cell so as to control a property or properties of the exhausted air supply stream that is supplied to the internal combustion engine from the fuel cell. In a tenth aspect, the present invention is directed- to the use of a fuel cell to condition an air supply that is supplied to an internal combustion engine .

According to an eleventh aspect of the present invention, there is provided a method of operating a power supply system that includes. an internal combustion engine, the method comprising using a fuel cell to condition air that is supplied to the internal combustion engine. According to a twelfth aspect of the present invention, there is provided an apparatus for a power supply system that includes an internal combustion engine and a fuel cell, the apparatus comprising: means for using the fuel cell to condition air that is to be supplied to the internal combustion engine. As will be appreciated by those skilled in the art, these aspects and embodiments of the invention may and preferably do include any one or more or all of the preferred and optional features of the invention described herein, as appropriate. Thus, for example, the property of the exhausted air stream is preferably controlled by setting the electrical load on the fuel cell . Similarly, a reformer may be used to further or instead control a property or properties of the oxygen-depleted air exhausted from the fuel cell. The internal combustion engine can be any suitable such engine. It is preferably a reciprocating internal combustion engine. In a preferred embodiment it is a diesel engine. Most preferably it is an HCCI engine.

As discussed above, the fuel supply exhausted from the fuel cell's anode will comprise the residue of the fuel that was supplied to the cell, e.g. H₂, carbon monoxide (CO) and unreformed fuel. The air supply from the cathode meanwhile will comprise an oxygen depleted gas stream, water vapour and carbon dioxide (CO₂) . In a preferred embodiment, the system of the present invention further comprises a reactor in which the fuel and air supplies exhausted from the fuel cell can be (and preferably are) combined. The reactor preferably facilitates a water gas shift reaction between the carbon monoxide and water vapour, i.e. CO + H₂O —> CO₂ + H₂ (which occurs when carbon monoxide is combined with water (in the form of stream) at around 130⁰C) .

This will allow the fuel cell to act as a controllable source of hydrogen, and/or allow the system of the present invention to actively control the hydrogen content (e.g., of fuel supplied to the engine), . e.g., to allow "trimming" of the hydrogen content to meet desired requirements.

As well as the fuel supply from the fuel cell, the internal combustion engine could also, and, indeed, does preferably also, have a separate, additional fuel supply that is and can be used to provide fuel, e.g., liquid fuel such as diesel fuel, to the engine. Thus, in a preferred embodiment, the internal combustion engine has two fuel supplies (inputs), the fuel supplied from (via) the fuel cell, and a separate fuel supply. In other words, the engine preferably has two fuel supplies, a main fuel supply and a supply comprised of the exhaust from the fuel cell stack (which is, e.g., and preferably, mixed with the air that is ingested into the engine) . The provision of an additional, "normal" fuel supply to the internal combustion engine facilitates its operation, and also, e.g., helps to facilitate using the fuel supply from the fuel cell to modify and condition the overall, combined fuel supply that the internal combustion engine receives. In such an arrangement, any residual fuel produced by the fuel cell, but which is not required and/or desired for use in the engine, can be, and preferably is, recycled. In a particularly preferred embodiment, the fuel ^' cell is controlled so as to achieve optimum performance of the internal combustion engine instead of, or addition to, for example, achieving low NO_x emissions. In such an arrangement, one or more criteria for achieving this optimum performance are determined by and/or supplied to a control system. The control system preferably compares these criteria with one or more properties of the fuel supplied to the fuel cell and adjusts and/or varies the operation of the fuel cell as required. The one or more properties of the fuel applied to the fuel-cell can be determined in any suitable manner, for example using the engine itself as a fuel sensor.

For example, and preferably, the engine can have an engine control system designed to give optimum performance as well as low emissions. In the case where the fuel quality in the engine does -not fit the criteria required by the engine control system, the exhausts from the fuel cell can be used to condition the fuel to, e.g., and preferably, change the hydrogen/carbon and/or hydrogen/carbon/oxygen ratio and/or other fuel properties such as the cetane number. The fuel cell may, e.g., be controlled for this purpose using information from a fuel quality detector of the engine^' (e.g., to provide the required quantity and/or quality of fuel) .

The power supply system of the present application may be. used in any suitable manner and for any desired and suitable application. It is believed that it will have particular, but not exclusive, application as a ^' power supply for vehicles. Thus, according to another aspect, the present invention extends to a vehicle including or operated in accordance with the system or method of the present invention.

In use of the system of the present invention, the power supplied by the fuel cell and the internal combustion engine can, be used as desired. For example, the fuel cell could be used to power (auxiliary) electrical circuits and components, and the internal combustion engine used, e.g., to drive the vehicle. In a preferred embodiment, where the system is used in a vehicle, both the fuel cell and the internal combustion engine can be used to drive the vehicle, preferably both independently of each other and together- (at the same time) . It is also preferred for both the fuel cell and the internal combustion engine to be able to provide an electrical output, which outputs can then be distributed as desired to the required electrical loads .

The fuel cell and internal combustion engine can be used and operated in combination in any desired manner, e.g., depending on the current load and operating conditions, e.g., of the vehicle in which the system is provided. For example, where it is desired to reduce emissions from the internal combustion engine, the fuel cell may preferentially be used to provide the desired output power. On the other hand, in a situation where the output loads can vary significantly, both the fuel cell and the engine can be used to provide power.

As will be appreciated by those skilled in the art, all of the aspects and embodiments of the invention described herein may, and preferably do, include one or more or all of the preferred and optional features of the invention described herein, as appropriate. The methods in accordance with the present invention may be implemented at least partially using software e.g. computer programs. It will thus be seen that when viewed from further aspects the present invention provides computer software specifically adapted to carry out the methods herein described when installed on data processing means, a computer program element comprising computer software code portions for performing the methods herein described when the program element is run on data processing means, and a computer program comprising code means adapted to perform all the steps of a method or of the methods herein described when the program is run on a data-processing system. The invention also extends to a computer software carrier comprising such software which when used to operate a radio system comprising data processing means causes in conjunction with said data processing means said system to carry out the steps of the method of the present invention-. Such a computer software carrier could be a physical storage medium such as a ROM chip, CD ROM or disk, or could be a signal such as an electronic signal over wires, an optical signal or a radio signal such as to a satellite or the like. It will further be appreciated that not all steps of the method of the invention need be carried out by computer software and thus from a further broad aspect the present invention provides computer software and such software installed on a computer software carrier for carrying out at least one of the steps of the methods set out .herein.

The present invention may accordingly suitably be embodied as a computer program product for use with a computer system. Such an implementation may comprise a series of computer readable instructions either fixed on a tangible medium, such as a computer readable medium, for example, diskette, CD-ROM, ROM, or hard disk, or transmittable to a computer system, via a modem or other interface device, over either a tangible medium, including but not limited to optical or analogue communications lines, or intangibly using wireless techniques, including but not limited to microwave, infrared or other transmission techniques. The series of computer readable instructions embodies all or part of the functionality previously described herein.

Those skilled in the art will appreciate that such computer readable instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Further, such instructions may be stored using any memory technology, present or future, including but not limited to, semiconductor, magnetic, or optical, or transmitted using any communications technology, present or future, including but not limited to optical, infrared, or microwave. It is contemplated that such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation, for example, shrink-wrapped software, pre-loaded with a computer system, for example, on a system ROM or fixed disk, or distributed from a server or electronic bulletin board over a network, for example, the Internet or World Wide Web .

A number of preferred embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 shows schematically an embodiment of a power supply system that is in accordance with the present invention; and

Figure 2 shows schematically a second embodiment of a power supply system that is in accordance with the present invention.

As shown in Figure 1, the power supply system of the present embodiment comprises an internal combustion engine 1 and a fuel cell 2 arranged in series with each other, together with an appropriate fuel supply 6 and an air supply 3 for the fuel cell 2 and internal combustion engine 1. As is known in the art, the fuel cell 2 will in use operate to consume fuel and oxygen and generate an electrical output 10. The internal combustion, engine 1 will similarly consume fuel and oxygen and generate a mechanical output 11. As shown in Figure 1, the exhaust 8 from the internal combustion engine 1 can also be used to provide a mechanical output 12, for example using a turbocharger arrangement 9, if desired. In this embodiment the internal combustion engine 1 is in the form of a diesel engine. However, as will be appreciated by those skilled in the art, other forms of internal combustion engine could be used if desired. For example, as discussed herein, the present invention is particularly suited to the use of engines that operate using the homogeneous charge compression ignition (HCCI) engine cycle.

The fuel cell 2 is, in the present embodiment, in the form of a solid oxide fuel cell stack, and thus comprises a plurality of individual (fuel) cells arranged in a series configuration. (Other arrangements and forms of fuel cell- would, of course, be possible) . As shown in Figure 1, and as discussed above, the fuel cell 2 is arranged in series with and in front of the engine 1.

The fuel cell 2 has an air supply input 3 which is passed via a compression device with an electric motor to supply additional torque (or, e.g., an electric supercharger) 4 working in series to provide a pressurised air supply (at a pressure of about 2 bar) to the cathode of the fuel cell 2. This input air supply may be controlled independently of the input of the fuel supply 6.

The oxygen depleted air supply 5 exhausted from the cathode of the fuel cell 2 is supplied to the inlet manifold of the internal combustion engine 1 to act as a diluent (EGR source) to the internal combustion engine 1, as shown in Figure 1. This air stream is loaded with moisture that should be at the point of condensing. The pressure drop in the fuel cell 2 is minimal and thus a full "boost pressure" is available.

The fuel cell 2 and internal combustion engine 1 are also provided with a fuel supply 6. As shown in Figure 1 , this fuel supply β is divided into two streams, one to supply fuel to the fuel cell 2, and the other to supply fuel to the internal combustion engine 1. The division of the fuel flow into two streams in this manner helps to facilitate a more flexible control strategy for the operation of the fuel cell and engine. In the present embodiment, the fuel supply 6 comprises a liquid (e.g. diesel) fuel. The portion of — 9 7 —

this fuel that is to be provided directly to the internal combustion engine 1 is provided in its "raw", liquid diesel, form to the internal combustion engine 1 by direct liquid fuel injection of this fuel supply to the internal combustion engine 1.

However, the portion of the fuel supply 6 that is to be provided to the fuel cell 2 must, as is known, in the art, first be converted to an appropriate form for consumption by the fuel cell 2. This is done by providing the fuel supply 6 to a reformer (not shown) which will, as is known in the art, convert the liquid fuel supply 6 to a suitable reformate (e.g. carbon monoxide and hydrogen) mixture that may then be consumed directly by the fuel cell 2. The reformed fuel (the reformate) is then passed to the fuel cell 2 under pressure for consumption in the fuel cell 2. In the present embodiment a partial oxidation reformer is used, although other arrangements would, of course, be possible. As shown in Figure 1, the stream of fuel gas 7 which is exhausted from the anode of the fuel cell 2 is provided as a fuel supply input to the fuel supply system of the internal combustion engine 1. In other words, the internal combustion engine 1 in effect receives fuel from two sources, directly from the fuel supply 6, and the residual fuel exhausted by the fuel cell 2. This enables, inter alia, the fuel exhausted from the fuel cell 2 to be used to modify (e.g. balance) the overall fuel supply to the engine 1, for example to facilitate the engine 1 achieving desired efficiency and/or emissions targets .

The fuel supply stream exhausted from the fuel cell 2 will comprise, as is known in the art, any residual reformate (CO + H₂) mixture that has not been consumed by the fuel cell 2. For example, if the primary fuel supply to the fuel cell was a liquid hydrocarbon mixture, the reformed liquid fuel supplied to the fuel cell would tend to contain a mixture of hydrogen, carbon monoxide and methane, and the residue reformate gas exhausted from the anode of the fuel cell would thus comprise small quantities of all of these gases in a gaseous form. On the other hand, if the fuel supply to the fuel cell 2 was a gas mixture of methane and hydrogen, then hydrogen would be mostly converted in the fuel cell 2 with some carry over (exhausting) of a little hydrogen and some methane into the exhaust gas.

In the present embodiment, a richer than stoichiometric supply of fuel gas is provided to the fuel cell 2, so as to ensure that a small residue of fuel that can be burnt and supplied to the internal combustion engine will always be left in the fuel supply stream that is exhausted from the fuel cell.

In use of the fuel supply system of the present embodiment, the fuel cell 2 is controlled so as to control the composition of exhausted fuel supply stream 7 that is input from it into the internal combustion engine 1. This is achieved by controlling the fuel cell 2 to remove (consume) a desired amount of the combustible material (fuel) in the fuel supplied to it, before that fuel is supplied to the internal combustion engine. This allows the fuel cell 2 to be used to, for example, modify and condition the fuel that is supplied from it to the internal combustion engine 1, for example so as to ensure a desired overall fuel supply to the internal combustion engine 1. The amount of fuel in the input fuel supply that is consumed by the fuel cell 2 before that fuel is supplied to the internal combustion engine 1 is controlled in this embodiment by setting the electrical load (current drawn) on the fuel cell 2 to a value such that the fuel cell 2 consumes the desired amount of fuel from its input fuel supply 6.^' In other words, the load on the fuel cell 2 is used to control how much combustible material is removed from the fuel supply 6 before that fuel supply is provided to the internal combustion engine 1. As is known in the art, the current drawn from a fuel cell determines the chemical reactions which occur in the fuel cell, and thus the amount of fuel that is consumed by the fuel cell in use. Thus, as recognised by the Applicants, varying the electrical load on the fuel cell 2 can be used to remove varying amounts of fuel (hydrogen and carbon monoxide) from the fuel supplied to the fuel cell 2, and thereby control the composition of the exhausted fuel supply that is then ■for input to the internal combustion engine 1. The amount of fuel that the fuel cell 2 is arranged (set) to consume from the fuel supply 6 in use is determined in this embodiment using the composition of the fuel supply 6 to the fuel cell 2 and the desired input fuel conditions or properties for the internal combustion engine 1. In particular, the composition of the fuel supplied to the fuel cell 2 is used, in \ combination with the desired composition of the fuel that is to be input from the fuel cell 2 to the internal combustion engine 1, to control the operation of ^" the fuel cell 2, so that the fuel cell 2, in effect, converts the input fuel supply to the form desired for input to the internal combustion engine 1.

The desired fuel characteristics for the fuel to be input to the internal combustion engine 1 will typically be known and, e.g., predetermined, and so these known, desired conditions can be used to set "target" fuel characteristics for the fuel that is exhausted from the fuel cell 2. For example, the optimum fuel combination for the engine can be evaluated through experiments and some predictive modelling, to determine and evaluate in advance, for -example, optimum combinations of exhaust- gas and liquid fuel that can then be, e.g., pre-programmed into the control system. It would also be possible to instead or additionally use the engine's ability to detect fuel quality (e.g. via its sensors) in use to further optimise and control the system in use.

As the input fuel supply 6 may be likely to vary in use, such that it may not be so readily possible or desirable simply to "predetermine" the input fuel supply's characteristics, in the present embodiment, the relevant characteristics,, and in particular the composition, of the input fuel 6 supplied to the fuel cell are determined in use.

In this- embodiment, the current profile and the voltage profile along the length of the fuel cell 2, together with the temperature of the fuel cell anode and the flow rate of the fuel supply 6 to the fuel cell, are used to estimate the composition of the fuel supply 6 provided to the fuel cell .

As is known in the art, in operation of the fuel cell 2, the fuel gas 6 will flow through the fuel cell and react with oxide ions conducted from the cathode as the gas passes through the stack of cells making up the fuel cell 2. More reactive gases, such as hydrogen, in the fuel will tend to react in cells closer to the gas -entry point into the fuel cell stack 2, whereas gases that are slower to react will tend to react further into the stack. Since it is the reaction of the gases that generates the electric current output by the fuel cell, there will be a corresponding arrangement of the current profile along the fuel cell 2. (The chemical activity will affect the current that is generated, although because of internal resistance, this can be detected as ^• a voltage variation. ) For example, a more reactive gas such as hydrogen, will produce a current peak in the cells of the fuel cell 2 closer to the gas entry point, whereas gases that are slower to react, such as methane, will produce a voltage profile that will reach its maximum value further into the 'fuel cell stack.

Similar comments apply in respect of the voltage profile along the fuel cell stack. Again, a variation in the voltage will occur where the fuel gas is reacting. In addition, the voltage values will be dependent upon the electro-chemical potentials of the reacting gases.

Thus, for example, considering an input fuel supply comprising a mixture of hydrogen and methane, the hydrogen will react quickly (i.e. at the beginning of the fuel cell 2), producing a peak in the current profile and a variation in the voltage profile close to the fuel entry, whereas the methane will react more slowly, indicating some electrical activity in cells downstream of where the hydrogen content of the gas stream has been fully depleted.

In the case of a fuel comprising hydrogen, carbon monoxide and methane, both the hydrogen and carbon monoxide will react quickly but their reaction rates are different, and will be, for example, dependent on the partial pressure of the gases in the mixture. The methane will again react more slowly, and may therefore create' current and voltage activity downstream of where the hydrogen and carbon monoxide have been (fully) depleted.

Thus, the Applicants have recognised that the current profile and voltage profile developed along the fuel cell 2 in use will depend, inter alia, on¹ the composition of the fuel supplied to the fuel cell 2, and as such be used as an indicator of the fuel's composition. The process can, in effect, be thought of as an electrochemical chromatograph.

The operating temperature of the anode, and the flow rate of the fuel gas supplied to the fuel cell 2 are also taken into account when assessing the voltage and current profiles along the fuel cell 2 for this purpose, since these factors will also affect the reaction rates of the fuel in the fuel cell 2, and accordingly where, for example, peaks in the current profile and variations in the voltage profile will occur. For example, at higher gas flow rates, the number of cells in the fuel cell stack 2 over which the reactions take place will be lengthened, but this lengthening effect will be in proportion to the flow rate of the gases .

The determined current and voltage profiles and gas flow rates, etc., can be used to determine the fuel's composition in any desired manner. For example, a set of references profiles for known fuel compositions could be determined and then used as references to compare profiles determined in use against (e.g. using pattern or curve matching techniques) , so as to identify the reference profile (and hence fuel composition) that the determined profile most closely matches. The composition of the fuel supplied to the fuel cell 2 determined in this manner is then compared to the desired composition of the gas to be input from the fuel cell to the internal combustion engine 1, and the electric load on the fuel cell is then set in accordance with the results of that comparison, i.e. so as to try to ensure that the fuel cell will consume the appropriate proportions of input fuel supply so as to provide the desired output fuel supply for input to the internal combustion engine 1. Since the composition of the fuel supplied to the internal combustion engine 1 from the fuel cell 2 is known from the initial conditions and the power drawn from the fuel cell 2, the input conditions to the internal combustion engine 1 may be controlled in this manner in a feed-forward sense. For example, by varying the electrical load on the fuel cell (e.g. by making different' .uses of electricity on the vehicle and/or charging a battery, etc.)/ varying the air and fuel flow rate and/or varying the ratio of flows of the air and fuel respectively, the ratios of depleted air, fuel gas and the total flow rate supplied to the internal combustion engine can be varied and controlled.

As discussed above, as well as the fuel supply 7 exhausted from the fuel cell 2 being supplied to the internal combustion engine 1, the oxygen depleted air supply 5 exhausted from the fuel cell 2 is also input to the internal combustion engine 1, and, in effect, acts as an exhaust gas recirculation (EGR) source for the internal combustion engine 1. This can be used to help the internal combustion engine 1 to achieve low NO_x emissions without the need to resort to conventional exhaust gas recirculation or other after treatment systems.

The properties, and in particular the oxygen content, of this oxygen depleted air 5 that is exhausted from the fuel cell 2 and provided to the internal combustion engine 1 can be, and preferably are, controlled and adapted by the fuel cell 2 in a similar way to the controlling of the composition of the fuel supply stream effected by the fuel cell discussed above. Thus, in a preferred arrangement of the present embodiment,' the fuel cell 2 is also controlled, in the same way as described above in relation to the control of the fuel's composition, to control the composition of the oxygen depleted air supply 5 exhausted from the fuel cell 5. Thus, the electrical load of the fuel cell 2 is varied, so as to provide a desired oxygen depleted air supply 5 for input to the internal combustion engine 1. The fuel cell 2 and the internal combustion engine 1 and in particular their outputs, can be operated and used in combination in any desired and suitable manner, for example depending on the desired application of the system.

For example, in a_. situation where the loads on the system vary significantly, both the internal combustion engine 1 and fuel cell 2 can be operated. At low loads, the internal combustion engine 1 may, for example, be operated very lean, while the fuel cell 2 also operates at a low load. In this configuration, the system may be highly efficient and have very low emissions. Where there is a high sensitivity to emissions, then the fuel cell 2 could preferentially be operated at a high output, with the internal combustion engine 1 being operated at a low or intermediate load, and, preferably, the fuel cell being used to provide warm oxygen-depleted air to the engine to help control the formation of oxides of nitrogen.

In the face of varying input fuel quality, the fuel cell 2 may be used to adjust the amount of fuel gas in the fuel 7 that is provided from it to the internal combustion engine 1, so that the internal combustion engine 1 sees a more constant fuel quality.

The fuel cell 2 and the internal combustion engine 1 can be and preferably are used to supply power simultaneously to meet any desired load requirements. In a preferred embodiment the internal combustion engine 1 is used to provide an electrical output, which output is then combined with the electrical output from the fuel cell 2. These outputs can be combined in any suitable and desired manner. For example, a three-phase^' variable frequency alternating current provided by the internal combustion engine 1 could be rectified and connected to a DC link which is connected to the output of the fuel cell (which, as is known in the art, will be a varying voltage direct current (which may be and preferably is buffered (in a DC/DC link) ) ) , and the combined DC link then be provided as an overall output, for example via a three-phase inverter.

Figure 2 shows a second embodiment of a power supply system that is in accordance with the present invention.

As can be seen from Figure 2, the system shown in Figure 2 shows many similar components and will operate in a similar manner to the preceding embodiment. Like reference numerals have been used for like components in Figure 2.

The significant features of the Figure 2 arrangement will now be described. Unless otherwise stated, the arrangement of Figure 2 and its components operate in the same manner as and are similar to the arrangement and components described with reference to Figure 1.

Firstly, as shown in Figure 2, the air supply compressor 4 and the exhaust expander 9 are shown to be coupled together to an electrical machine 16 which can also be used to generate electrical power. The electrical power generated by the electrical machine 16 can be used, as can the electrical output 10 from the fuel cell stack 2, to supplement the mechanical output 11 to the main load 18, if desired. In a preferred arrangement of this embodiment (and in general) , the electric machine -(motor) 16 is also able to produce (regenerative) electric energy (e.g., during change of the load on the system) .

Figure 2 also shows the inclusion of a reformer 13 which receives the input fuel supply 6 and reforms that fuel supply before its provision to the fuel cell stack 2.

As shown in Figure 2, the air supply 3, and fuel¹ supply 6 to the reformer 13, to the fuel cell 2, and to the internal combustion engine 1 are independent of each other. This facilitates control of these various supplies in use, and, for example, altering the fuel supply 6 to the fuel cell, and the fuel supply 6 to the internal combustion engine 1 independently, for example depending on the main load requirement of the internal combustion engine 1.

In use of the Figure 2 arrangement, the residual fuel 7 and oxygen depleted air 5 exhausted from the fuel cell stack are sent to the internal combustion engine via a mixing valve 19. There is also a fuel recycling line 17 that can be used to recycle excess residual fuel back to the fuel cell stack 2 when desired.

The (hot) exhaust gas 20 from the internal combustion engine 1 is provided to the exhaust expander 9. This exhaust flow could be provided directly to the exhaust expander 9 as shown in Figure 2, or it could, e.g., be used to heat and/or maintain the temperature of, e.g., the reformer 13 and/or fuel cell stack 2, e.g., by passing it through appropriately arranged heat-exchangers in the reformer and/or fuel cell stack before it is exhausted via the exhaust expander 9. Finally, Figure 2 also shows some additional electrical loads, such as an ultra-capacitor/battery pack 15 and auxiliary loads 14 (such as, for example, auxiliary power consuming elements of the vehicle) to which, for example, excess electrical power 10 from the fuel cell 'stack (e.g. when there is excess residual fuel from the fuel cell stack such that more fuel needs to be burnt) can be sent, thereby to consume additional electrical power 10 (and hence fuel in the fuel cell stack 2) .

The system of the present invention can be used as a power supply for a variety of applications, including both stationary and mobile applications. In a preferred embodiment, it is used as a power supply system for a vehicle. It also, as will be appreciated from the above, provides flexible power output that can include both electrical and mechanical forms of output.

Although the present embodiment has been described above with particular reference to, for example, the use of a solid oxide fuel cell and a diesel engine, etc., as will be appreciated by those skilled in the art, the present invention is not limited to such arrangements, but can, for example, equally be applied to, for example, other forms of fuel cell and engine, etc.. It can be seen from the above that the present invention, in its preferred embodiments at least, offers a number of advantages. For example, the ability of the system to, in effect, manage and control in real time the fuel quality and fuel provided to the internal combustion engine facilitates, for example, more efficient and optimum operation and usage of the fuel cell and engine, and can provide enhanced versatility and tolerance that can, e.g., allow the system to cope with a wide range of fuel quality and fuel types, whilst still matching its operation to achieve, for example, desired efficiency and emission targets.

This is achieved, in the preferred embodiments of the present invention at least, by providing a fuel gas containing hydrogen to a fuel cell, controlling the amount of hydrogen and carbon monoxide that is removed from the fuel gas by the fuel cell , and then providing the hydrogen depleted gas from the fuel cell to an internal combustion engine as a fuel gas .

In effect, the fuel cell (together with its control system) acts as a fuel processing unit, for example to provide (produce) fuel of certain qualities for an engine. It also provides and has inherent fuel flexibility.

The use of a fuel cell to supply hydrogen depleted fuel and oxygen depleted air to an internal combustion engine 1 is, in particular, very well suited for the homogeneous charge compression ignition (HCCI) engine cycle, -and, moreover, can provide the ability to use an HCCI engine where that may otherwise have been difficult or not possible. The ability to use an HCCI cycle engine is a significant advantage, as such an engine can, as is known in the art, achieve a reduction of. pollutants and an increase in thermal efficiency when compared to both the Otto and the Diesel cycle.

Claims

1. A power supply system, comprising: a fuel cell; an internal combustion engine; means for providing a fuel supply to the fuel cell; means for providing the fuel supply exhausted from the fuel cell as a fuel supply to the internal combustion engine; and means for controlling the operation of the fuel cell so as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell .

2. An apparatus for a power supply system that includes an internal combustion engine and a fuel cell, the apparatus comprising: means for using the fuel cell to condition fuel that is to be supplied to the internal combustion engine .

3. The system or apparatus of claim 1 or 2 , wherein the fuel cell comprises a fuel cell stack.

4. The system or apparatus of any one of the preceding claims, further comprising a reformer for reforming fuel before it is supplied to the fuel cell .

5. The system or apparatus of claim 4, further comprising means for controlling the operation of the reformer so as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell .

6. A power supply system, comprising: a fuel cell ; an internal combustion engine; a fuel reformer for providing a fuel supply to the fuel cell ; means for providing the fuel supply exhausted from the fuel cell as a fuel supply to the internal combustion engine; and means for controlling the operation of the reformer so as to control a property or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell.

7.. The system or apparatus of any one of the preceding claims, wherein the control of the operation of the fuel cell is based on one or more properties of the fuel supplied to the fuel cell.

8. The system or apparatus of any one of the preceding claims, comprising means for controlling and/or varying the electrical load on the fuel cell, so as to control and/or vary the properties of the fuel that is supplied to the internal combustion engine from the fuel cell.

9. The system or apparatus of any one of the preceding claims, comprising means for providing the air supply exhausted from the fuel cell as an air supply to the internal combustion engine.

10. The system or apparatus of claim 9, comprising means for controlling the operation of the fuel cell so as to control and/or vary a property or properties of the exhausted air supply that is supplied to the internal combustion engine from the fuel cell.

11. A power supply system, comprising: a fuel cell; an internal combustion engine; means for providing an air supply to the fuel cell; means for providing the air supply exhausted from the -fuel cell as an air supply to the internal combustion engine; and means for controlling the operation of the fuel cell so as to control a property or properties of the exhausted air supply that is supplied to the internal combustion engine from the fuel cell.

12. An apparatus for a power supply system that includes an internal combustion engine and a fuel cell, the apparatus comprising: means for using the fuel cell to condition air that is to be supplied to the internal combustion engine.

13. A method of operating a power supply system that comprises a fuel cell and an internal combustion engine, the method comprising: inputting the fuel supply stream exhausted from the fuel cell as a fuel supply to the internal combustion engine; and controlling the operation of the fuel cell so as to control a property or properties of the exhausted fuel supply stream that is supplied to the internal combustion engine from the fuel cell.

14. A method of operating a power supply system that includes an internal combustion engine, the method comprising using a fuel cell to condition fuel that is supplied to the internal combustion engine.

15. The method of claim 13 or 14, further comprising reforming fuel before it is supplied to the fuel cell; and controlling the reforming operation so as to control a property- or properties of the exhausted fuel supply that is supplied to the internal combustion engine from the fuel cell .

16. A method of operating a power supply system that comprises a fuel cell and an internal combustion engine, the method comprising: inputting the fuel supply stream exhausted from the fuel cell as a fuel supply to the internal combustion engine; and controlling the operation of a reformer supplying fuel to the fuel cell so as to control a property or properties of the exhausted fuel supply stream that is supplied to the internal combustion engine from the fuel cell.

17. The method of any one of claims 13 to 16, wherein the control of the operation of the fuel cell is based on one or more properties of the fuel supplied to the fuel cell.

18. The method of any one of claims 13 to 17, comprising controlling and/or varying the electrical load on the fuel cell, so as to control and/or vary the properties of the fuel that is supplied to the internal combustion engine from the fuel cell.

19. The method of any one of claims 13 to 18, comprising providing the air supply exhausted from the fuel cell as an air supply to the internal combustion engine .

20. The method of claim 19, comprising controlling the operation of the fuel cell so as to control and/or vary a property or properties of the exhausted air supply that is supplied to the internal combustion engine from the fuel cell.

21. A method of operating a power supply system that comprises a fuel cell and an internal combustion engine, the method comprising: inputting the air supply stream exhausted from the fuel cell as an air supply to the internal combustion engine; and controlling the operation of the fuel cell so as to control a property or properties of the exhausted air supply stream that is supplied to the internal combustion engine from the fuel cell.

22. A method of operating a power supply system that includes an internal combustion engine, the method comprising using a fuel cell to condition air that is supplied to the internal combustion engine.

23. A vehicle including the system or apparatus of any one of claims 1 to 12 , or operated in accordance with the method of any one of claims 13 to 22.

24. The use of a fuel cell to condition fuel and/or an air supply that is supplied to an internal combustion engine .

25. A computer program element comprising computer software code portions for performing the method of any one of claims 13 to 22 when the program element is run on data processing means .

26. A power supply system substantially as herein described with reference to any one of the accompanying drawings .

27. An apparatus for a power supply system substantially as herein described with reference to any one of the accompanying drawings .

28. A fuel cell system substantially as herein described with reference to any one of the accompanying drawings .

29. A method of operating a power supply system substantially as herein described with reference to any one of the accompanying drawings .

30. A method of operating a fuel cell substantially as herein described with reference to any one of the accompanying drawings.

31. A vehicle substantially as herein described with reference to any one of the accompanying drawings .