VEHICLE SYSTEM COMPRISING A FUEL CELL

Abstract

A vehicle system comprising a fuel cell, at least one container for the storage of ammonia precursor, and a first and second fuel generator. The first and second fuel generators are configured to convert the ammonia precursor into fuel for use in the fuel cell. The first fuel generator is configured to carry out the ammonia precursor conversion within a lower temperature range than the second fuel generator.

Claims

1. A vehicle system comprising: a fuel cell, at least one container for the storage of ammonia precursor, and a first and second fuel generator, wherein the first and second fuel generators are configured to convert the ammonia precursor into fuel for use in the fuel cell, and wherein the first fuel generator is configured to carry out the ammonia precursor conversion within a lower temperature range than the second fuel generator.

2. The vehicle system of claim 1, wherein the ammonia precursor is urea.

3. The vehicle system of claim 1, wherein the first and second fuel generators convert the ammonia precursor into the same fuel.

4. The vehicle system of claim 1, wherein the first and second fuel generators convert the ammonia precursor into different types of fuel.

5. The vehicle system of claim 1, wherein the first and second fuel generators are configured to convert the ammonia precursor into ammonia.

6. The vehicle system of claim 1, wherein the first fuel generator comprises a catalyst suitable for decomposing the ammonia precursor into ammonia, wherein the catalyst is a biological catalyst.

7. The vehicle system of claim 6, wherein the biological catalyst is a urease.

8. The vehicle system of claim 1, wherein the second fuel generator comprises a catalyst suitable for decomposing the ammonia precursor into ammonia.

9. The vehicle system of claim 8, wherein the catalyst is a vanadium pentoxide.

10. The vehicle system of claim 1, further comprising at least one hydrogen generator, wherein the hydrogen generator is configured to at least partially decompose ammonia formed from the ammonia precursor into hydrogen.

11. The vehicle system of claim 10, wherein it comprises an ammonia-hydrogen effluents buffer tank.

12. The vehicle system of claim 1, wherein a single container for the storage of ammonia precursor is connected to both the first fuel generator and the second fuel generator.

13. The vehicle system of claim 1, wherein the fuel cell is a solid oxide fuel cell.

14. The vehicle system of claim 1, wherein at least one of the first fuel generator and the second fuel generator comprises a heat transfer means configured to transfer heat generated by the fuel cell to the fuel generator.

15. The vehicle system of claim 1, further comprising at least one buffer tank for storing fuel produced by at least one of the first fuel generator and the second fuel generator.

16. The vehicle system of claim 1, wherein the system further comprises an additional fuel cell configured to generate electricity at a lower temperature than the fuel cell, and wherein the additional fuel cell is an anionic fuel cell.

17. The vehicle system of claim 1, wherein the additional fuel cell is an alkaline fuel cell or an alkaline membrane fuel cell.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0073] The accompanying drawings are used to illustrate presently preferred non-limiting exemplary embodiments of devices of the present invention. The above and other advantages of the features and objects of the invention will become more apparent and the invention will be better understood from the following detailed description when read in conjunction with the accompanying drawings, in which:

[0074] FIG. 1 is a diagram illustrating an embodiment of a vehicle system according to the present invention;

[0075] FIG. 2 is a diagram illustrating another embodiment of a vehicle system according to the invention;

[0076] FIG. 3 also shows an embodiment of a vehicle system according to the invention;

[0077] FIG. 4 illustrates a further embodiment of a vehicle system according to the invention;

[0078] FIG. 5 illustrates another embodiment of a vehicle system according to the invention.

DESCRIPTION OF EMBODIMENTS

[0079] FIGS. 1 to 5 illustrate embodiments of a vehicle system according to the present invention.

These embodiments all comprise a fuel cell 1, a first fuel generator 2, a second fuel generator 3, a container 4 for holding an ammonia precursor and a buffer tank 5 for collecting effluents produced by the first fuel generator 2 and/or the second fuel generator 3.

[0080] In the embodiments of FIGS. 1 to 5, the fuel cell 1 is preferably a solid oxide fuel cell (SOFC). Therefore, in the following description, the fuel cell will be described as being a solid oxide fuel cell 1. However, it would be possible to use other fuel cells in these embodiments.

[0081] The container 4 for holding an ammonia precursor may be any form of tank suitable for storing an ammonia precursor. Preferably, the container 4 is configured to hold a solution of an ammonia precursor, most preferably a urea solution such as AdBlue (also known as diesel exhaust fluid, DEF). If the container 4 is configured to hold AdBlue or another urea solution, in some embodiments, this solution may be boosted with extra urea before it is added to the container 4.

[0082] In all of the illustrated embodiments, a single container 4 for the ammonia precursor is connected to both the first fuel generator 2 and the second fuel generator 3. The first fuel generator 2 and the second fuel generator 3 are able to generate ammonia from the ammonia precursor held in the container 4. The generated ammonia can then be fed to the solid oxide fuel cell 1 where it can be oxidised to generate electricity.

[0083] In the illustrated embodiments, the second fuel generator 3 is configured to operate at higher temperatures than the first fuel generator 2 (i.e. the first fuel generator 2 is configured to operate at lower temperatures than the second fuel generator 3). For example, the second fuel generator 3 may be configured to operate at temperatures above 80 C., such as temperatures around 200 C. In contrast, the first fuel generator 2 is configured to operate at lower temperatures, for example, below 80 C.

[0084] A first fuel generator 2 will be particularly well adapted to operate at temperatures below 80 C. if the fuel generator contains a biological catalyst such as urease.

[0085] The second fuel generator 3 may contain a catalyst such as vanadium pentoxide. In this case, the conversion of ammonia precursor to ammonia in the second fuel generator is performed by a catalyst in the adequate thermal activation conditions.

Alternatively the conversion of the ammonia precursor to ammonia in the second fuel generator may be performed without any catalyst by thermal degradation only.

[0086] Effluents from both fuel generators 2, 3 may be directed to the solid oxide fuel cell 1 or to an ammonia effluents buffer tank 5.

[0087] The system illustrated in the figures may also be provided with a controller (not shown) for controlling the flow of the effluents generated by the first fuel generator 2 and/or the second fuel generator 3.

[0088] Furthermore, the system shown in the figures may additionally comprise a temperature sensor (not shown) configured to measure a temperature of the vehicle system. The controller may then be configured to control at least one of the first fuel generator 2 and the second fuel generator 3 as a function of this measured temperature.

[0089] The temperature sensor may measure the temperature of the first fuel generator 2 or the second fuel generator 3. The temperature sensor may alternatively be configured to measure the temperature in a line (for example, a conduit, tube or pipe) connecting a fuel generator to the solid oxide fuel cell 1. The temperature sensor may also measure the temperature of the solid oxide fuel cell 1 itself.

In some embodiments, the system may comprise multiple temperature sensors. In such embodiments, the controller may be configured to control one or more system components as a function of multiple measured temperatures.

[0090] In the systems of FIGS. 1 to 4, if the temperature detected by the temperature sensor is below a first temperature, the controller may be configured to use the first fuel generator 2 to generate fuel as this fuel generator is configured to operate at a lower temperature. Conversely, if the temperature detected by the temperature sensor is equal to or above a second temperature, the controller may be configured to use the second fuel generator 3 to generate fuel.

[0091] In the illustrated systems, at least some of the output of the solid oxide fuel cell 1 is sent to the exhaust system 11.

[0092] At start-up of the vehicle system shown in FIG. 1, the solid oxide fuel cell 1 can be electrically heated using electrical heaters (not shown in the figures). For example, the means for heating may be an electrical resistive heating device powered by batteries carried on board the vehicle. The solid oxide fuel cell 1 needs to be heated to an operational temperature before it can be used to oxidise fuel.

[0093] The first fuel generator 2 can also be started on start-up. For example, if the solid oxide fuel 1 does not contain enough fuel to be able to operate when it reaches the required temperature, the effluents produced by the first fuel generator 2 may be sent to the solid oxide fuel cell 1.

[0094] Therefore, on start-up of the vehicle, the controller may be configured to start the first fuel generator 2.

[0095] Once the solid oxide fuel cell 1 has enough ammonia for start-up, the first fuel generator 2 may continue to generate ammonia which is then sent to the ammonia effluents buffer tank 5 by the controller.

[0096] When an operating temperature of the solid oxide fuel cell 1 is reached, ammonia effluents may be sent directly from the first fuel generator 2, and/or from the second fuel generator 3, and/or from the ammonia effluents buffer tank 5 to the solid oxide fuel cell 1 where the ammonia will be oxidised.

[0097] In addition to sending ammonia to the solid oxide fuel cell 1, the system is also configured to provide the solid oxide fuel cell 1 with an oxidant. This oxidant is typically provided by supplying the solid oxide fuel cell with a flow of air. The fuel and/or oxidant directed to the solid oxide fuel cell 1 may be preheated before they reach the solid oxide fuel cell 1.

[0098] The heat generated by the solid oxide fuel cell 1 after it has been turned on may be used to heat up one or more of the first and second fuel generators 2, 3. Therefore, in some embodiments, the first and second fuel generators 2, 3 may comprise a heat transfer means configured to harness waste heat energy generated by the solid oxide fuel cell 1. For example, these heat transfer means may permit direct contact between the fuel generator 2, 3 and the solid oxide fuel cell, or the heat transfer means may be a heat exchanger.

[0099] In one embodiment, once the solid oxide fuel cell 1 has heated the second fuel generator 3 to an appropriate temperature (i.e. to a temperature at which it can operate), the second fuel generator 3 begins to operate and the first fuel generator 2 is shutdown by the controller. The shutdown of the first fuel generator 2 prevents catalysts such as urease from being used up as quickly. The heat generated by the solid oxide fuel cell 1 is then used by the second fuel generator 3 to decompose the ammonia precursor to ammonia fuel for use in the solid oxide fuel cell 1.

[0100] In some embodiments, the heating of the first fuel generator 2 and/or the second fuel generator 3 can be supplemented by heat provided by additional heating means such as an electrical resistive heating device. A means for regulating the heat (for example, a fan) may also be provided.

[0101] When the solid oxide fuel cell 1 is shut down, heat will still be emitted by the solid oxide fuel cell 1 as it cools down.

[0102] During this cool down, the second fuel generator 3 continues operating whilst the heat generated is sufficient to keep it at its operating temperature. In addition, the second fuel generator will continue to operate during cool down provided the ammonia effluents buffer tank 5 has space to contain the effluents generated by the fuel generator 3.

[0103] When the amount of heat emitted by the solid oxide fuel cell 1 is no longer sufficient to keep the second fuel generator 3 operating but there is an enough heat to reach the operating temperature of the first fuel generator 2, the controller will shut down the second fuel generator 3 and start up the first fuel generator 2. The first fuel generator 2 will then continue to decompose the ammonia precursor to ammonia until there is no longer enough heat to perform this process or until the buffer tank 5 is full of ammonia or until the amount of ammonia in the buffer tank 5 is above a threshold value.

[0104] In order to determine how much effluent is being stored in the buffer tank 5, the buffer tank 5 may be provided with some form of sensor, for example, a weight sensor or a device for sensing the level of the effluents in the buffer tank 5. The controller would then be configured to use the information provided by the buffer tank 5 sensor to control the operation of one or more of the fuel generators 2, 3.

[0105] In using the heat produced by the solid oxide fuel cell 1 whilst it is shutting down, less energy is wasted by the system. Instead, some of the energy lost as heat whilst the solid oxide fuel cell 1 shuts down can be recovered by harnessing the waste heat energy and using it to convert an ammonia precursor into ammonia.

[0106] In some embodiments, the ammonia effluents buffer tank 5 may be placed inside the urea solution tank 4.

[0107] As shown in FIG. 1, a portion of the gases emitted by the solid oxide fuel cell 1 can be recycled and fed back to the solid oxide fuel cell 1 so as to increase the efficiency of the system. The recycling of the gases emitted by the solid oxide fuel cell is illustrated by line 20.

[0108] The part of the output from the solid oxide fuel cell 1 which is not recycled is directed towards the exhaust where it can be subjected to further processing. For example, ammonia that escapes from the solid oxide fuel cell can be combusted in the exhaust in a post-combustion step, or the ammonia could be catalytically oxidised. In addition, the heat of the gases emitted by the solid oxide fuel cell 1 can, in turn, be used to heat up the solid oxide fuel cell 1 and/or other parts of the system, for example, the first and second fuel generators 2, 3.

[0109] The gases emitted by the solid oxide fuel cell 1 can also be used in selective catalytic reduction (SCR) to eliminate or reduce the emission of nitrogen oxides.

[0110] The gases emitted by the solid oxide fuel cell 1, if they contain excessive amounts of nitrogen oxides can also be cleaned using for instance selective catalytic reduction.

[0111] As described above, in the embodiment of FIG. 1, both the first and second fuel generators 2, 3 are used to generate fuel during the cooling down of the solid oxide fuel cell 1. For example, if 1 kWh of energy is stored as heat in the solid oxide fuel cell 1 at shutdown, the system of FIG. 1 could, for instance, recover 50% of this energy, i.e. the system could recover 0.5 kWh of energy. This is achieved by using both of the fuel generators 2, 3 to convert the ammonia precursor such as urea to ammonia which is then stored in the system. The stored ammonia is then able to be used directly in the solid oxide fuel cell 1 upon start-up, reducing the amount of energy that needs to be input into the system on start-up to generate ammonia fuel.

[0112] Converting the ammonia precursor to ammonia raises the energy level of the urea (2.5 kWh) to 3.0 kWh. Thanks to the fuel generators 2,3, 3.0 kWh in the form of ammonia effluents are therefore made available for the next start-up and about 0.5 kWh electrical energy will be saved (from the energy needed to generate the ammonia effluents).

[0113] Preferably, the system illustrated by FIG. 1 would be able to recover at least 20% of the energy lost from the solid oxide fuel cell 1 during shutdown, more preferably around 40%.

[0114] In an alternative embodiment, only a single fuel generator may be used to produce fuel during the cooling down process. For example, the fuel generator configured to be used at a lower temperature may be used. The use of the first fuel generator 2 alone may achieve a similar performance to systems comprising two fuel generators but it will take more time to reach the same result and be more demanding on the enzymatic catalyst. Alternatively, only the fuel generator configured to be used at a higher temperature, the second fuel generator 3, may be used. However, use of the higher temperature fuel generator alone would reduce the amount of generated ammonia effluents as the conversion will stop once the solid oxide fuel cell 1 is not generating enough heat to keep the second fuel generator 3 at its operational temperature.

[0115] As the system illustrated by FIG. 2 is substantially identical to that of FIG. 1, this system operates in predominately the same way as the system of FIG. 1.

[0116] The system of FIG. 2 is different to that of FIG. 1 as it additionally comprises a second fuel cell 6. This further fuel cell (a second fuel cell) 6 is configured to operate at lower temperature than the solid oxide fuel cell 1.

[0117] In some embodiments, the second fuel cell 6 may be an alkaline fuel cell (AFC) Alkaline fuel cells typically have low operating temperatures. For example, the alkaline fuel cell may be configured to operate at ambient temperature or slightly above ambient temperature (say <120 C.).

The alkaline fuel cell may also be an alkaline membrane fuel cell (AMFC).

[0118] At system start-up, the second fuel cell 6 can be put in operation much faster than the solid oxide fuel cell 1. During operation, the second fuel cell 6 may use the ammonia effluents stored in the buffer tank as fuel. Alternatively (or additionally), fuel for use in the second fuel cell 6 may be generated by the lower temperature first fuel generator 2. The second fuel cell 6 can then be used to generate electricity which can be used to heat-up the rest of the system (such as the solid oxide fuel cell 1, the second fuel generator 3) and/or support the electrical power demand from the motor(s) powering the vehicle.

[0119] The heat generated by the losses of the secondary fuel cell 6 can also be used to sustain the temperature of the lower temperature first fuel generator 2. For example, the first fuel generator 2 may be provided with a heat transfer means configured to transfer waste heat from the secondary fuel cell 6 to the first fuel generator 2.

[0120] When the solid oxide fuel cell 1 of the system of FIG. 2 reaches its operating temperature, a controller (not shown) shuts down the second fuel cell 6. In addition, the first fuel generator 2, the fuel generator that is able to operate at a lower temperature may also be shut down at this point by the controller, and the controller may be configured to turn on the higher temperature second fuel generator 3.

[0121] When the solid oxide fuel cell 1 is shut down, the procedure is essentially same as described in relation to the system of FIG. 1: the second fuel generator 3 continues operating as long as temperature allows (and provided there is room in the buffer tank 5 for the effluents formed).

When the solid oxide fuel cell 1 no longer produces enough heat the keep the second fuel generator 3 at its operating temperature, the controller turns off this higher temperature second fuel generator 3 and turns on the first fuel generator 2. This is provided the temperature of the system is high enough to operate this lower temperature first fuel generator 2 and if there is enough room in the buffer tank 5 to store the effluents generated.

[0122] If needed, the second fuel cell 6 can be turned on during shut down of the solid oxide fuel cell 1 to charge up any electrical batteries in the system to ensure that the system is ready for start-up.

[0123] Considering for instance that 3.0 kWh of ammonia effluents have been generated by the fuel generators as described in relation to FIG. 1, the alkaline fuel cell could generate 1.5 kWh of electrical energy at start-up. If the electrical power needed to move the vehicle in the first 10 minutes and first 20 minutes amounts to 2 kWh and 4 kWh respectively, this represents 75% and 37.5% of the electrical needs. This electrical energy will not have to be extracted from the electrical batteries, allowing thus these to be downsized.

[0124] The system as shown in FIG. 3 is similar to the one shown in FIG. 2. Therefore, the system of FIG. 3 operates in substantially the same way as the system of FIG. 2 (and, therefore, also the system of FIG. 1).

[0125] A hydrogen generator 7 and an additional buffer tank 8 have been added to the system of FIG. 2 to form the system of FIG. 3.

[0126] In the system of FIG. 3, effluents comprising both ammonia and hydrogen are generated by the hydrogen generator 7 and the solid oxide fuel cell 1. In alternative embodiments, the ammonia and hydrogen buffer tank 8 can be fed only from the outlet of the solid oxide fuel cell 1 or by the hydrogen generator 7.

[0127] In the embodiment shown in FIG. 3, the ammonia produced by the first fuel generator 2 and/or the second fuel generator 3 may be divided into two portions, where a first portion is sent to the solid oxide fuel cell 1 for use as fuel, and the second portion of the ammonia is directed by the controller to a hydrogen generator for at least partial decomposition into hydrogen. Therefore, in the system of FIG. 3, some of the ammonia generated by the first fuel generator 2 and/or the second fuel generator 3 is converted to hydrogen as this produces a mixture that is easier to oxidize and so allows heat to be generated more readily.

[0128] In the system illustrated by FIG. 3, the ammonia and hydrogen buffer tank 8 is positioned at a different location in the system to the other buffer tank 5 and the container 4 of the ammonia precursor. However, in alternative embodiments, the ammonia-hydrogen effluents buffer tank 8 may be placed inside the ammonia precursor tank 4 and/or inside the ammonia effluents buffer tank 5 for increased safety.

[0129] FIG. 4 illustrates a further embodiment of a system which, like the system of FIG. 3, generates ammonia-hydrogen effluents.

[0130] In the system of FIG. 4, ammonia-hydrogen effluents produced by the system, for example, by the hydrogen generator 7 and the solid oxide fuel cell 1 can be burnt by an ammonia-hydrogen burner 9. In the system of FIG. 4, the controller (not shown) is configured to direct the ammonia-hydrogen mixture stored in the ammonia-hydrogen effluents buffer tank 8 to the burner 9. Burning ammonia-hydrogen effluents generates heat that can be distributed to other parts of the system such as the solid oxide fuel cell 1, the first fuel generator 2, and/or the second fuel generator 3.

[0131] In order to harness the heat produced by the ammonia-hydrogen burner 9, the system of FIG. 4 is provided with multiple heat exchangers 10a, 10b, 10c, 10d, 10e, 10f, 10g, 10h, 10i, 10j. These heat exchangers are able to transfer heat generated by the ammonia-hydrogen burner 9 to the part of the system to which the heat exchanger is attached. For example, the heat exchanger 10a joined to the solid oxide fuel cell 1 can be used to capture heat generated by the burner 9 and use it to heat up the solid oxide fuel cell 1. As another example, there can be a heat exchanger 10j attached to at least part of the exhaust system 11. For example, a heat exchanger 10j may be attached to a device (such as a SCR) provided in the exhaust system 11 for treating exhaust gases.

[0132] In the system of FIG. 4, most of the system components are provided with a heat exchanger.

However, in alternative embodiments, only one or a few of the system components may be provided with a heat exchanger.

[0133] In the system of FIG. 4, air is fed to the burner 9 to insure proper combustion (the air supply is not illustrated in the figure). Furthermore, in this embodiment, at least a portion of the gases produced by the burner are directed back to the burner 9 so that they can be recycled and used to generate more heat.

[0134] At the start-up of the system shown in FIG. 4, the system operates in a similar manner to the system of FIG. 3 (and, therefore, the systems of FIGS. 1 and 2). However, as the system of FIG. 4 comprises a ammonia-hydrogen burner 9, if there is any ammonia-hydrogen effluent stored in the ammonia-hydrogen buffer tank 8 on start-up of the system, this mixture can be combusted in the burner 9. The combustion of the ammonia-hydrogen effluent in the burner 9 generates heat. The heat generated by the burner 9 can be distributed to the solid oxide fuel cell 1 and/or other components of the system. Therefore, by burning an ammonia-hydrogen mixture on start-up, the demand on other energy generating mean (for example, on any batteries on board the vehicle) is reduced.

[0135] When the solid oxide fuel cell 1 and/or other system components (for example, the first and/or second fuel generator 2, 3) reaches its operating temperature, the burner 9 can be shutdown.

[0136] During operation of the system of FIG. 4, the depleted ammonia-hydrogen effluents tank 8 is progressively refilled with gases produced by the solid oxide fuel cell 1 and/or the output of the hydrogen generator 7. Ammonia-hydrogen effluents will be sent to the relevant buffer tank 8 by the controller until the tank 8 is deemed to contain an appropriate level of effluents so as to insure optimal restart conditions.

[0137] In some embodiments, if the output from the solid oxide fuel cell 1 is deemed not sufficient to refill the ammonia-hydrogen buffer tank 8, the hydrogen generator 7 starts to produce ammonia-hydrogen effluents for storage in the buffer tank 8.

[0138] When the solid oxide fuel cell 1 is shut down, the system of FIG. 4 follows a similar procedure to that of the system of FIG. 1. However, in the system of FIG. 4, both the second fuel generator 3 and the hydrogen generator 7 continue to operate as long as the solid oxide fuel cell 1 is producing enough heat to maintain the operating temperature of these devices, and provided the relevant buffer tank 5, 8 has space for more effluent. As with the system of FIG. 1, when the second fuel generator 3 gets too cold, the controller shuts down this second fuel generator 3 and turns on the lower temperature first fuel generator 2. This first fuel generator 2 will then continue to operate for as long as the solid oxide fuel cell 1 is generating enough heat to allow the first fuel generator to generate ammonia, and whilst there is space for more ammonia in the ammonia buffer tank 5.

[0139] As with the systems illustrated in FIGS. 2 and 3, the system of FIG. 4 also comprises a second fuel cell 6. After the solid oxide fuel cell 1 has been shut down, the second fuel cell 6 may use the waste heat generated by the solid oxide fuel cell 1 to generate electricity. This electricity can be used to recharge one or more electrical batteries provided on board the vehicle, for example.

[0140] FIG. 5 illustrates another embodiment of a vehicle system according to the present invention.

This particular embodiment comprises a fuel cell 1, a first fuel generator 2 based on catalytic decomposition, a second fuel generator 3 based on thermal decomposition, a container 4 for holding an ammonia precursor and a buffer tank 5 for collecting effluents produced by the first fuel generator 2 and/or the second fuel generator 3.

[0141] In the embodiment of FIG. 5, the fuel cell 1 is preferably a solid oxide fuel cell (SOFC).

Therefore, in the following description, the fuel cell will be described as being a solid oxide fuel cell 1. However, it would be possible to use other fuel cells in this particular embodiment.

[0142] The container 4 for holding an ammonia precursor may be any form of tank suitable for storing an ammonia precursor. Preferably, the container 4 is configured to hold a solution of an ammonia precursor, most preferably a urea solution such as AdBlue (also known as diesel exhaust fluid, DEF). If the container 4 is configured to hold AdBlue or another urea solution, in some embodiments, this solution may be boosted with extra urea before it is added to the container 4.

[0143] In the illustrated embodiment, a single container 4 for the ammonia precursor is connected to both the first fuel generator 2 and the second fuel generator 3. The first fuel generator 2 and the second fuel generator 3 are able to generate ammonia from the ammonia precursor held in the container 4. The generated ammonia can then be fed to the solid oxide fuel cell 1 where it can be oxidised to generate electricity.

[0144] In the illustrated embodiment, the second fuel generator 3 is configured to operate at higher temperatures than the first fuel generator 2 (i.e. the first fuel generator 2 is configured to operate at lower temperatures than the second fuel generator 3).

For example, the second fuel generator 3 may be configured to operate at temperatures between 200 C. and 800 C. and the first fuel generator 2 may be configured to operate at temperatures between 20 C. to 350 C.

[0145] A first fuel generator 2 based on thermal decomposition will be particularly well adapted to operate at temperatures between 20 C. and 350 C. if the fuel generator contains no catalyst.

Thus, the first fuel generator 2 will be able to generate ammonia from the ammonia precursor held in the container 4 by thermal decomposition and with no need of catalyst.

[0146] The first fuel generator 2 can be electrically heated using electrical heaters (not shown in the figures). For example, the means for heating may be an electrical resistive heating device powered by batteries carried on board the vehicle. The electrical resistive heating device may be metallic heating filaments (wires), flexible heaters, (that is to say heaters comprising one or more resistive track(s) affixed to a film or placed between two films (that is to say two substantially flat supports, the material and thickness of which are such that they are flexible)) or any other type of resistive elements that have a shape, size and flexibility suitable for being inserted into and/or wound around the components of the SCR system.

In some embodiments, the first and second fuel generators 2, 3 may comprise a heat transfer means, such as a heat exchanger, configured to harness waste heat energy generated by the solid oxide fuel cell 1.
A means for regulating the heat (for example, a fan) may also be provided.
The first fuel generator 2 needs to be heated to an operational temperature before it can generate ammonia.

[0147] The second fuel generator 3 may contain a catalyst such as vanadium pentoxide.

[0148] Effluents from both fuel generators 2, 3 may be directed to the solid oxide fuel cell 1 or to an ammonia effluents buffer tank 5.

[0149] The system illustrated in the figure may also be provided with a controller (not shown) for controlling the flow of the effluents generated by the first fuel generator 2 and/or the second fuel generator 3.

[0150] Furthermore, the system shown in the figure may additionally comprise a temperature sensor (not shown) configured to measure a temperature of the vehicle system. The controller may then be configured to control at least one of the first fuel generator 2 and the second fuel generator 3 as a function of this measured temperature.

[0151] The temperature sensor may measure the temperature of the first fuel generator 2 or the second fuel generator 3. The temperature sensor may alternatively be configured to measure the temperature in a line (for example, a conduit, tube or pipe) connecting a fuel generator to the solid oxide fuel cell The temperature sensor may also measure the temperature of the solid oxide fuel cell 1 itself. In some embodiments, the system may comprise multiple temperature sensors. In such embodiments, the controller may be configured to control one or more system components as a function of multiple measured temperatures.

[0152] In the system of FIG. 5, if the temperature detected by the temperature sensor is below a first temperature, the controller may be configured to use the first fuel generator 2 to generate fuel as this fuel generator is configured to operate at a lower temperature. Conversely, if the temperature detected by the temperature sensor is equal to or above a second temperature, the controller may be configured to use the second fuel generator 3 to generate fuel.

[0153] In the illustrated system, at least some of the output of the solid oxide fuel cell 1 is sent to the exhaust system 11.

[0154] At start-up of the vehicle system shown in FIG. 5, the solid oxide fuel cell 1 can be electrically heated using electrical heaters (not shown in the figures). For example, the means for heating may be an electrical resistive heating device powered by batteries carried on board the vehicle. The solid oxide fuel cell 1 needs to be heated to an operational temperature before it can be used to oxidise fuel.

[0155] The first fuel generator 2 can also be started on start-up. For example, if the solid oxide fuel 1 does not contain enough fuel to be able to operate when it reaches the required temperature, the effluents produced by the first fuel generator 2 may be sent to the solid oxide fuel cell 1.

Therefore, on start-up of the vehicle, the controller may be configured to start the first fuel generator 2.

[0156] Once the solid oxide fuel cell 1 has enough ammonia for start-up, the first fuel generator 2 may continue to generate ammonia which is then sent to the ammonia effluents buffer tank 5 by the controller.

[0157] When an operating temperature of the solid oxide fuel cell 1 is reached, ammonia effluents may be sent directly from the first fuel generator 2, and/or from the second fuel generator 3, and/or from the ammonia effluents buffer tank 5 to the solid oxide fuel cell 1 where the ammonia will be oxidised.

[0158] In addition to sending ammonia to the solid oxide fuel cell 1, the system is also configured to provide the solid oxide fuel cell 1 with an oxidant. This oxidant is typically provided by supplying the solid oxide fuel cell with a flow of air. The fuel and/or oxidant directed to the solid oxide fuel cell 1 may be preheated before they reach the solid oxide fuel cell 1.

[0159] The heat generated by the solid oxide fuel cell 1 after it has been turned on may be used to heat up one or more of the first and second fuel generators 2, 3. Therefore, in some embodiments, the first and second fuel generators 2, 3 may comprise a heat transfer means configured to harness waste heat energy generated by the solid oxide fuel cell 1. For example, these heat transfer means may permit direct contact between the fuel generator 2, 3 and the solid oxide fuel cell, or the heat transfer means may be a heat exchanger.

[0160] In some embodiments, the heating of the first fuel generator 2 and/or the second fuel generator 3 can be supplemented by heat provided by additional heating means such as an electrical resistive heating device. A means for regulating the heat (for example, a fan) may also be provided.

[0161] When the solid oxide fuel cell 1 is shut down, heat will still be emitted by the solid oxide fuel cell 1 as it cools down.

[0162] During this cool down, the second fuel generator 3 continues operating whilst the heat generated is sufficient to keep it at its operating temperature. In addition, the second fuel generator 3 will continue to operate during cool down provided the ammonia effluents buffer tank 5 has space to contain the effluents generated by the fuel generator 3.

[0163] When the amount of heat emitted by the solid oxide fuel cell 1 is no longer sufficient to keep the second fuel generator 3 operating but there is an enough heat to reach the operating temperature of the first fuel generator 2, the controller will shut down the second fuel generator 3 and start up the first fuel generator 2. The first fuel generator 2 will then continue to decompose the ammonia precursor to ammonia until there is no longer enough heat to perform this process or until the buffer tank 5 is full of ammonia or until the amount of ammonia in the buffer tank 5 is above a threshold value.

[0164] In order to determine how much effluent is being stored in the buffer tank 5, the buffer tank 5 may be provided with some form of sensor, for example, a weight sensor or a device for sensing the level of the effluents in the buffer tank 5. The controller would then be configured to use the information provided by the buffer tank 5 sensor to control the operation of one or more of the fuel generators 2, 3.

[0165] In using the heat produced by the solid oxide fuel cell 1 whilst it is shutting down, less energy is wasted by the system. Instead, some of the energy lost as heat whilst the solid oxide fuel cell 1 shuts down can be recovered by harnessing the waste heat energy and using it to convert an ammonia precursor into ammonia.

[0166] In some embodiments, the ammonia effluents buffer tank 5 may be placed inside the urea solution tank 4.

[0167] As shown in FIG. 5, a portion of the gases emitted by the solid oxide fuel cell 1 can be recycled and fed back to the solid oxide fuel cell 1 so as to increase the efficiency of the system. The recycling of the gases emitted by the solid oxide fuel cell is illustrated by line 20.

[0168] The part of the output from the solid oxide fuel cell 1 which is not recycled is directed towards the exhaust where it can be subjected to further processing. For example, ammonia that escapes from the solid oxide fuel cell can be combusted in the exhaust in a post-combustion step, or the ammonia could be catalytically oxidised. In addition, the heat of the gases emitted by the solid oxide fuel cell 1 can, in turn, be used to heat up the solid oxide fuel cell 1 and/or other parts of the system, for example, the first and second fuel generators 2, 3.

[0169] The gases emitted by the solid oxide fuel cell 1 can also be used in selective catalytic reduction (SCR) to eliminate or reduce the emission of nitrogen oxides.

[0170] The gases emitted by the solid oxide fuel cell 1, if they contain excessive amounts of nitrogen oxides can also be cleaned using for instance selective catalytic reduction.

[0171] As described above, in the embodiment of FIG. 5, both the first and second fuel generators 2, 3 are used to generate fuel during the cooling down of the solid oxide fuel cell 1. For example, if 1 kWh of energy is stored as heat in the solid oxide fuel cell l at shutdown, the system of FIG. 5 could, for instance, recover 50% of this energy, i.e. the system could recover 0.5 kWh of energy. This is achieved by using both of the fuel generators 3, 2 to convert the ammonia precursor such as urea to ammonia which is then stored in the system. The stored ammonia is then able to be used directly in the solid oxide fuel cell 1 upon start-up, reducing the amount of energy that needs to be input into the system on start-up to generate ammonia fuel.

[0172] The energy content of the effluents (3 kWh) is higher than the energy content of the initial urea solution (2.5 kWh) which is involved in the conversion process.

Thanks to the fuel generators 2 and/or 3, the ammonia effluents resulting from the conversion of the urea solution provide an energy content of 3.0 kWh which is is available for the next start-up and about 0.5 kWh electrical energy will be saved (from the energy needed to generate the ammonia effluents).

[0173] Preferably, the system illustrated by FIG. 5 would be able to recover at least 20% of the energy lost from the solid oxide fuel cell 1 during shutdown, more preferably around 40%.

[0174] In an alternative embodiment, only a single fuel generator (i.e. the second fuel generator) may be used to produce fuel during the cooling down process. However, the use of the second fuel generators alone requires a larger optimized operational temperature range compared to a system with two fuel generators in which each of the two generators are optimized for their operational temperature ranges. Such system with the second fuel generator alone would therefore be less efficient and produce a reduced amount of generated ammonia effluents compared to a system with two fuel generators.