EP2005507A1

EP2005507A1 - Methods and apparatus for use with power supply system

Info

Publication number: EP2005507A1
Application number: EP07732221A
Authority: EP
Inventors: Richard Keith Stobart; Zhijun Peng; Anita Raghunath Chaudhari; Morgan Raymond Heikal; Michael Louis Monaghan
Original assignee: Loughborough University; University of Sussex; University of Brighton
Current assignee: Loughborough University
Priority date: 2006-03-31
Filing date: 2007-03-30
Publication date: 2008-12-24
Also published as: GB0606529D0; WO2007113509A1; WO2007113507A1

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 voltage and current profile along the fuel cell (2) is determined in use so as to determine the composition of the fuel supply stream (6) that is input to the fuel cell (2). This allows the nature, e.g., quality, of the supplied fuel to be determined.

Description

Methods and Apparatus For Use With Power Supply Systems

The present invention relates to methods and apparatus for use with power supply systems, such as, and in particular, for use with internal combustion engines that may be used as a power source in, e.g., a vehicle or other system. In many internal combustion engine arrangements, for example, it is desirable to know the nature, e.g., quality, of the fuel that is being supplied to the engine, as this may assist in relation to, for example, the operation and management of the engine in use. Although a number of techniques are known for this purpose, the Applicants believe that there remains scope for improved and alternative such techniques .

According to a first aspect of the present invention, there is provided a fuel cell system, comprising: a fuel cell; means for determining a property or properties of the fuel cell in use; and means for using the determined property or properties of the fuel cell to determine a property or properties of the fuel supplied to the fuel cell. According to a second aspect of the present invention, there is provided a method of operating a fuel cell system, comprising: determining a property or properties of the fuel cell in use; and using the determined property or properties of the fuel cell to determine a property or properties of the fuel supplied to the fuel cell . According to a third aspect of the present invention, there is provided a method of operating a fuel cell system, comprising using a property or properties of the fuel cell in use to determine a property or. properties of the fuel supplied to the fuel cell. In the present invention, a property or properties of a fuel cell are used to determine a property or properties of the fuel supplied to the fuel cell. In other words, a fuel cell is used to determine a property or properties of the fuel (e.g., and preferably, as a fuel quality detector) .

The Applicants have found, as will be discussed further below, that a fuel cell may advantageously be used in this manner to determine one or more properties of a fuel. For example, the system can determine in use one or more properties of the fuel supply. This could be used to facilitate, for example, the use of variable and varying fuel supplies.

Thus, according to a fourth aspect, the present invention extends to the use of a fuel cell to determine a property or properties of a fuel.

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 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) . In a preferred embodiment, the system includes means for or a step of supplying fuel to the fuel cell .

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), e.g., and preferably, 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. 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.

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 property or properties of the fuel cell that are determined in order to determine a property or properties of the fuel can be any suitable such property ' or properties and can be selected as desired. In a preferred embodiment, they comprise a property or properties relating to the operation and/or activity of the fuel cell (in use) (e.g., and preferably, as it processes (consumes) the fuel that is being assessed). In a particularly preferred embodiment, a measure of the electric voltage and/or current of or in or developed by the fuel cell is determined and assessed. Preferably, the voltage and/or current, and preferably the voltage and the current, detected in a number of (e.g., some or all of) the individual cells that make up the fuel cell is determined and assessed for this purpose. Preferably an analysis of the variation of, and most preferably the profile of, ^'the electric voltage and/or current along the length of the fuel cell (the fuel cell stack) is used to determine a property or properties of the fuel supplied to the fuel cell. In other words, the current and/or voltage developed by the fuel cell in use is preferably used to determine a property or properties of the fuel .

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 profile 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/or variation) and the voltage profile (and/or variation) 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. - S -

In particular, any variation in gas concentrations in the fuel stack can be detected by monitoring the voltage and current. For example, the equilibrium concentrations of gases and therefore the voltage developed by the fuel cell will vary with the current density. Thus, the relationship between the voltage and current can be related to the particular gas concentration and therefore the fuel supplied to the system. 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/or variation) and the voltage profile (and/or variation) are used to assess the fuel's composition. Preferably the voltage-current relationship in the fuel cell (stack) is assessed.

Thus, according to an fourth aspect o.f the present invention, there is provided a fuel cell system comprising: a fuel cell; means for determining a current and/or voltage variation along the length of the fuel cell in use; and means for using the determined current and/or voltage variation along the length of the fuel cell in use to determine a property or properties of the fuel supplied to the fuel cell.

According to a fifth aspect of the present invention, there is provided a method of operating a fuel cell system, comprising: determining a current and/or voltage variation along the length of the fuel cell in use; and using the determined current and/or voltage variation along the length of the fuel cell in use to determine a property or properties of the fuel supplied to the fuel cell. According to a sixth aspect of the present invention, there is provided a method of operating a fuel cell system, comprising using the voltage and/or current variation along the length of the fuel cell to determine a property or properties of the fuel supplied to the fuel cell.

As will be appreciated by those skilled in the art, these aspects and embodiments 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. Thus, for example, preferably a current or voltage profile (and preferably both) along the length of the fuel cell is determined, and the fuel cell is preferably in the form of a fuel cell stack. In a preferred embodiment, the system and method of the present invention 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) .

In a particularly preferred embodiment, the fuel exhausted from the fuel cell (stack) is provided as a fuel supply to an internal combustion engine. Thus, in a preferred embodiment the system of the present invention comprises a power supply system, comprising a fuel cell and an internal combustion engine, and means for or steps of. providing a fuel supply to the fuel cell, and providing the fuel supply exhausted from the fuel cell as a fuel supply to the internal combustion engine .

In a preferred embodiment, the exhaust gas that is supplied from the fuel cell to the internal combustion can also or instead 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 . As is known in the art, the fuel supply stream that is exhausted from the fuel cell's anode will comprise 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) . If the residual fuel stream exhausted from the fuel cell is then input as a fuel supply to the internal combustion engine, it 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. This may be desirable.

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 property or properties of the fuel that is or are determined can be selected as desired. In a preferred embodiment, the fuel cell is used to determine a particular, selected, preferably predetermined, property or properties (e.g. range of values for a given parameter) in the fuel supply. Most preferably a property or properties relating to the quality of the fuel (a measure of the fuel's quality) is ^"determined.

The fuel property or properties that is determined preferably comprises and/or relates to the composition of the fuel, such as its 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) , such as its hydrogen and/or hydrocarbon content. Most preferably a property or properties relating to and/or indicating the ratio between carbon, hydrogen and oxygen in the fuel supplied to the fuel cell is determined.

In a particularly preferred embodiment, where the fuel cell is used in combination with an internal combustion engine, then as well as using the fuel cell to determine a property or properties of the supplied fuel, a property or properties of the engine itself (such as a property or properties relating to its operation or activity) is or are determined and used to determine a property or properties of the fuel supply.

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.

Most preferably, engine instrumentation is used to detect aspects of engine operation that are particularly affected by the fuel property or properties in question.

One preferred such example is the delay reactions that take place between the injection of diesel fuel into the engine cylinder and the beginning of the combustion. During the delay period low temperature reactions take place whose progress is dictated by the chemical properties of the fuel. For example, a low cetane fuel will produce longer delay times that can be measured (cetane number is a measure of the ignitability of the fuel: high values (above 50 typically) imply easy , to ignite fuel) . During operation on such a fuel, the engine will need a different injection strategy if emissions are to be controlled. An on-board control system can be used to both monitor delay reactions and then set up the changed strategy as required. As discussed above, the result of using^' the voltage-current relationship in the fuel cell stack can be an understanding of the ratio between carbon, hydrogen and oxygen in the fuel supplied to the fuel cell .• The combination of this gross chemical information with other properties arising from the physical and chemical processes in the engine in this ^■ manner provides additional information. For example, a short delay time in the engine would indicate a GTL fuel typified by its high cetane number, while the presence of oxygen from the fuel cell measurements may indicate a blend with a bio-derived fuel.

The Applicants believe that the use of a property or properties of an engine to determine a property or properties of fuel supplied to the engine may be new and , advantageous in its own right. Thus, according to a seventh aspect of the present invention, there is provided an engine system, comprising: an engine; means for determining a property or properties of the engine in use; and means for using the determined property or properties of the engine to determine a property or properties of the fuel supplied to the engine. ^' According to an eighth aspect of the present invention, there is provided a method of operating an engine system, comprising: determining a property or properties of the engine in use; and using the determined property or properties of the engine to determine a property or properties of the fuel supplied to the engine.

According to a ninth aspect of the present invention, there is provided a method of operating an engine system, comprising using a property or properties of the engine in use to determine a property or properties of the fuel supplied to the engine.

As will be appreciated by those skilled in the art, these aspects and embodiments 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, as appropriate. Thus, for example, the engine is preferably an internal combustion engine.

Similarly, the property or properties of the engine that is or are used to determine a property or properties of the supplied fuel preferably comprise a property or properties relating to operation or activity of the engine (in use). Equally, aspects of engine operation that are particularly affected by the fuel property or properties in question, such as, and preferably, the delay period (delay time) and/or pressure rate rise of the engine, are preferably used for this purpose. Preferably the delay reactions (e.g. the delay time(s)) that take place between the injection of (e.g. and preferably diesel) fuel into an engine cylinder or the engine cylinder or cylinders and the beginning of the combustion are assessed for this purpose.

Similarly, where the engine is used in combination with a fuel cell, a property or properties of the fuel cell is preferably also used to, assess the supplied fuel, as discussed above.

The Applicants further believe that the use of a fuel cell and/or an engine to determine a property or properties of supplied fuel in a system that comprises both a fuel cell arrangement and an engine may be new and advantageous in its own right.

Thus , according to a tenth aspect of the present invention, there is provided a power supply system, comprising: a fuel cell system and an engine; means for determining a property or properties of the fuel cell and/or engine in use; and means for using the determined property or properties of the fuel cell and/or engine to determine a property or properties of the fuel supplied to the fuel cell and/or engine.

According to an eleventh aspect of the present invention, there is provided a method of operating a power supply system that comprises a fuel cell system and an engine, the method comprising: determining a property or properties of the fuel cell and/or engine in use; and using the determined property or properties of the fuel cell and/or engine to determine a property or properties of the fuel supplied to the fuel cell and/or engine . According to a twelfth aspect of the present invention, there is provided a method of operating a power supply system that comprises a fuel cell system and an engine, comprising using a property or properties of the- fuel cell and/or engine in use to determine a property or properties of the fuel supplied to the fuel cell and/or engine.

As will be appreciated by those skilled in the art, these aspects and embodiments 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, as appropriate. Thus, for example, preferably properties of both the fuel cell and of the engine are used to determine a property or properties of the supplied fuel, and preferably the ^"property or properties of the fuel cell and/or engine that are assessed are as discussed above.

In a particularly preferred embodiment of the present invention, the operation of the fuel cell is controlled (in use) to probe and/or access the properties of the fuel that is supplied to it. This can be done in any suitable and desired manner, but 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 found that, for example, a change in current density affects different gases to different degrees in a fuel cell, thereby allowing, for example, the possibility of the system probing the reaction of the fuel cell to identify the ratios of the gases .

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 probe and/or test the properties of the fuel that is supplied to it.

In a preferred embodiment, where appropriate, 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 can be provided to an 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, where appropriate input to an (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 an internal combustion engine.

Inputting the air supply exhausted from the fuel cell to an 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 system, 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" and the possibility of NO_x control, with a much lower, in particular, risk of particulate generation. The fuel cell can also provide a relative large volume of oxygen-depleted air for this purpose. It can accordingly help the internal combustion engine to achieve low NO_x emissions without the need to resort to conventional EGR or after-treatment systems.

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.

In the arrangement of the present invention where the fuel cell is used in combination with an internal combustion engine, 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 (Homogenous Charge-Compression Ignition) engine.

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 such embodiment, the internal combustion engine will have 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. The system of the present invention may be used, e.g., and preferably, as a power supply system in any suitable manner and for any desired and suitable application. It is believed that it will have particular, but not exclusive, application for and as power supplies 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 such systems 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 airstream 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 6 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 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^1' 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 composit-Lon 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 fμel 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, on 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 NOx 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, with preferably, the fuel cell also being used to provide I - 28 -

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. ^'

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 fuel 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 systems of the present embodiments can be used as a power supply for a variety of applications, including both stationary and mobile applications. In a preferred embodiment, they are used as power supply systems for vehicles. 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 using a fuel cell, preferably together with the engine, as a fuel quality detector.

Claims

1. A fuel cell system, comprising: a fuel cell; means for determining a property or properties of the fuel cell in use; and means for using the determined property or properties of the fuel cell to determine a property or properties of the fuel supplied to the fuel cell .

2. The system of claim 1, wherein the property or properties of the fuel Cell that is or are determined comprise an electric voltage and/or current developed in the fuel cell in use.

3. The system of claim 1 or 2, comprising: means for determining a current and/or voltage variation along the length of the fuel cell in use; and means for using the determined current and/or voltage variation along the length of the fuel cell in use to determine a property or properties of the fuel supplied to the fuel cell .

4. The system of any one of the preceding claims, wherein an analysis of the voltage profile and/or current profile along the length of the fuel cell is used to determine a property or properties of the fuel supplied to the fuel cell .

5. The system of any one of the preceding claims, further comprising: means for providing the fuel supply exhausted from the fuel cell as a fuel supply to an internal combustion engine .

6. The system of any one of the preceding claims, wherein the fuel cell comprises a fuel cell stack.

^■ 7. The system of any one of the preceding claims, wherein the fuel cell is a solid oxide fuel cell.

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

9. 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 probe and/or test the properties of the fuel that is supplied to the fuel cell.

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

11. The system of any one of the preceding claims, further comprising: means for providing the fuel supply exhausted from the fuel cell as a fuel supply to an internal combustion engine; and means for using the engine to determine a property or properties of the fuel.

12. A fuel cell system, comprising a fuel cell and means for determining a property or properties of the^' fuel supplied to the fuel cell.

13. A method of operating a fuel cell system, comprising: determining a property or properties of the fuel cell in use; and using the determined property or properties of the fuel cell to determine a property or properties of the fuel supplied to the fuel cell .

14. A method of operating a fuel cell, comprising using a property or properties of the fuel cell in use to determine a property or properties of the fuel supplied to the fuel cell.

15. The method of claim 13 or 14, wherein the property or properties of the fuel cell that is or are determined comprise an electric voltage and/or current developed in the fuel cell in use.

16. The method of claim 13, 14 or 15, comprising: determining a current and/or voltage variation along the length of the fuel cell in use; and using the determined current and/or voltage variation along the length of the fuel cell in use to determine a property or properties of the fuel supplied to the fuel cell .

17. The method of any one of claims 13 to 16, comprising using an analysis of the voltage profile and/or current profile along the length of the fuel cell to determine a property or properties of the fuel supplied to the fuel cell .

18. The method of any one of claims 13 to 17, comprising: inputting the^* fuel supply stream exhausted from the fuel cell as a fuel supply to an internal combustion engine .

19. The method of any one of claims 13 to 18, wherein the fuel cell comprises a fuel cell stack.

20. The method of any one of claims 13 to 19, wherein the fuel cell is a solid oxide fuel cell.

21. The method of any one of claims 13 to 20, further comprising reforming the fuel before it is supplied to the fuel cell .

22. The method of any one of claims 13 to 21, comprising controlling and/or- varying the electrical load on the fuel cell, so as to probe and/or test the properties of the fuel that is supplied to the fuel cell.

23. The method of any one of claims 13. to 22, comprising providing the air supply exhausted from the fuel cell as an air supply to an internal combustion engine.

24. The method of any one of claims 13 to 23, comprising: providing the fuel supply exhausted from the fuel cell as a fuel supply to an internal combustion engine; ^■and using the engine to determine a property or properties of the fuel .

25. A method of operating a fuel cell system, comprising determining a property or properties of the fuel supplied to the fuel cell.

26. A method of operating an engine system, comprising: determining a property or properties of the engine in use,- and using the determined property or properties of the engine to determine a property or properties of the fuel supplied to the engine.

27. A method of operating an engine system, comprising using a property or properties of the engine in use to determine a property or properties of the fuel supplied to the engine .

28. A method of operating a power supply system that comprises a fuel cell system and an engine, the method comprising: determining a property or properties of the fuel cell and/or engine in use; and using the determined property or properties of the fuel cell and/or engine to determine a property or properties of the fuel supplied to the fuel cell and/or engine .

29. A method of operating a power supply system that comprises a fuel cell system and an engine, comprising using a property or properties of the fuel cell and/or engine in use to determine a property or properties of the fuel supplied to the fuel cell and/or engine.

30. An engine system, comprising: an engine; means for determining a property or properties of the engine in use; and means for using the determined property or properties of the engine to determine a property or properties of the fuel supplied to the engine.

31. A power supply system, comprising: a fuel cell system and an engine; means for determining a property or properties of the fuel cell and/or engine in use; and means for using the determined property or properties of the fuel cell and/or engine to determine a property or properties of the fuel supplied to the fuel cell and/or engine.

32. A vehicle or a power supply system including the system of any one of claims 1 to 12, 30 or 31, or operated in accordance with the method of any one of claims 13 to 29.

33. The use of a fuel cell and/or an engine to determine a property or properties of fuel that is supplied to the fuel cell and/or engine.

34. A computer program element comprising computer software code portions for performing the method of any one of claims 13 to 29 when the program element is run on data processing means.

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

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

37. An engine system substantially as herein described with reference to any one of the accompanying drawings .

38. A method of operating an engine system substantially as herein described with reference to any one of the accompanying drawings.

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

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

41. A vehicle or a power supply system substantially as herein described with reference to any one of the accompanying drawings .