EP2912375A1

EP2912375A1 - Metal burning vehicle engine system

Info

Publication number: EP2912375A1
Application number: EP12777918.9A
Authority: EP
Inventors: David John JARVIS; Martin Larsson
Original assignee: Agence Spatiale Europeenne
Current assignee: Agence Spatiale Europeenne
Priority date: 2012-10-25
Filing date: 2012-10-25
Publication date: 2015-09-02
Also published as: WO2014063740A1

Abstract

The present invention relates to a vehicle engine system (1) comprising a combustion part (2), a heat engine (3) arranged to convert heat from the combustion part (2) to kinetic energy, and an electrical generator (4) arranged to convert the kinetic energy from the heat engine (3) into electrical energy for directly or indirectly actuating propulsion means (5) of a vehicle on which the vehicle engine system (1) is arranged. The combustion part (2) comprises a metal burning unit 6 adapted to generate heat by burning of metal fuel (7), and this metal burning unit 6 comprises a metal burner (10). The combustion part (2) further comprises a metal fuel tank (8) for storing metal fuel (7) to be burned, and a metal fuel transport system (9) for transporting metal fuel (7) from the metal fuel tank (8) to the metal burner (10). The invention further relates to a vehicle comprising such a vehicle engine system (1) and to a method of driving such a vehicle.

Description

METAL BURNING VEHICLE ENGINE SYSTEM

FIELD OF THE INVENTION

The present invention relates to vehicle engine systems and in particular to vehicle engine systems comprising a metal burning unit.

BACKGROUND OF THE INVENTION

The increasing costs of fossil fuels have led to intensified focus on finding alternative energy sources. These efforts include developing substitutes for combustion engines used in vehicles.

Furthermore, the global increasing focus on the environment has resulted in car manufacturers investing intensely in the development of more environmentally friendly engines. Some examples are hybrid engines that can run on both fossil fuels and an alternative fuel, such as different types of biofuel. An example of a vehicle engine which is designed to use non-fossil fuel is described in

US2011/0005472. It relates to a vehicle engine system wherein the combustion part comprises a wood pellet burning unit. The generated heat is converted into kinetic energy by a heat engine, and the kinetic energy is then converted into electrical energy for actuating the wheels of the vehicle by an electrical generator. An advantage of this system is that it can use waste wood products for the production of energy. However, the ash must be removed from the vehicle at regular intervals, and the fuel has a relatively low energy output per unit fuel weight.

Hence, an improved vehicle engine system would be advantageous, and in particular a more efficient and environmentally friendly vehicle engine system would be advantageous. OBJECT OF THE INVENTION

It is an object of the present invention to provide a vehicle engine system which is more environmentally friendly than those using fossil fuel. It is another object of the present invention to provide a vehicle engine system which uses a fuel that has a higher energy output per unit fuel weight or volume than the presently used alternative fuels, such as different types of biofuel. It is another object of the present invention to provide a vehicle engine system which uses a fuel from a renewable energy source.

It is a further object of the present invention to provide an alternative to the prior art.

SUMMARY OF THE INVENTION

Thus, the above described object and several other objects are intended to be obtained in a first aspect of the invention by providing a vehicle engine system comprising :

- a combustion part having a combustion chamber,

- a heat engine arranged to convert heat from the combustion part into kinetic energy, and

- an electrical generator arranged to convert the kinetic energy from the heat engine into electrical energy for directly or indirectly actuating propulsion means of a vehicle on which the vehicle engine system is arranged,

in which system the combustion part comprises:

- a metal burning unit adapted to generate heat by burning of metal fuel, the metal burning unit comprising a metal burner,

- a metal fuel tank for storing metal fuel to be burned, and

- a metal fuel transport system for transporting metal fuel from the metal fuel tank to the metal burner.

The vehicle can e.g. be any type of vehicle comprising wheels, such as a car, truck, forest machine. It may also be e.g. a boat or ship of any type or size, a propeller aircraft, a farm machine, a train or a motor cycle.

A heat engine may be defined as a system that performs the conversion of heat or thermal energy into mechanical work. It does this by bringing a working

substance from a high temperature state to a lower temperature state. A heat source, which in this context is the burning of metal fuel in the metal burner, generates thermal energy that brings the working substance to the high temperature state. The working substance generates work in the "working body" of the heat engine while transferring heat to the colder "sink" until it reaches a low temperature state. During this process some of the thermal energy is converted into work by exploiting the properties of the working substance. The working substance can be any system with a non-zero heat capacity, but it usually is a gas or liquid.

An advantage of using metal fuel is that the burning thereof offers a high energy output per unit fuel; either measured as per weight or per volume. Due to the relatively high density of metal compared with conventional fuels, the advantage of burning metal will often be largest when comparing energy output per unit volume. Another advantage is that the combustion does not produce greenhouse gasses and thereby is more environmentally friendly than a number of other energy sources, in particular fossil fuels. Furthermore, huge amounts of metal scrap are produced in the machining industry, and the present invention provides for an efficient use of this scrap.

In preferred embodiments of the invention, the combustion chamber comprises a heat protective pipe arranged within an outer wall of the combustion chamber, and cooling means for guiding cooling gas to a space between the outer wall of the combustion chamber and the heat protective pipe.

The heat protective pipe and the cooling means are used to protect the remainder of the system from the very high temperatures in the burner flame environment and the combustion zone, since the burning of metal will typically create temperatures in the order of 1800°C or more. Such high temperatures could result in a superheating and potential melting or break down of the system, if a burner unit from other types of fuel was used without modification.

The vehicle engine system may further comprise a cyclone arranged in the combustion chamber and being adapted to guide particles left after combustion towards the outer wall of the combustion chamber. In some embodiments of the invention, the cyclone comprises circumferentially arranged deflector fins adapted to guide the particles towards the outer wall of the combustion chamber. From there they can be removed from the combustion chamber so that the heated gas being led towards the heat engine is as clean as possible.

The metal burning unit may further comprise an air regulator system providing air to the combustion zone, and/or an exhaust and filtering system for removing combustion gasses and particles from the combustion chamber. In some embodiments, the vehicle engine system further comprises a mid storage for storing an amount of metal fuel near the metal burner, and wherein the metal fuel transportation system is adapted to transport the metal fuel from the metal fuel tank to the mid storage. The advantages of having such a mid-storage are described in relation to the figures.

The vehicle engine system may further comprise a blower for directing air past the exhaust system and into a space to be heated. This space will typically comprise a part of the heat engine. It may also be relevant to direct heated air or gas towards other parts of the system, e.g. in order to counteract large

temperature gradients in the systems. Large variations in temperature could lead to build up of undesired thermal stresses in the system.

In some embodiments of the invention, the heat engine is a Stirling engine or a Rankine type heat engine. However, use of any type of heat engine is considered to be covered by the scope of the present invention.

The metal fuel may be selected from metal chips, metal shavings, and metal powder; powder may also be referred to as particles. It could also be

combinations thereof. Typical sizes of metal chips are in the order of 1 to 100 mm in the length direction of the chips, such as in the order of 10 to 50 mm or 50 to 100 mm. Typical sizes of metal shavings are in the order of 0.1 to 300 mm, such as in the order of 0.1 to 1mm, 1 to 10 mm, 10 to 100 mm, or 100 to 500 mm. Typical sizes of metal powder is in the order of 1 to 100 microns, such as 10 to 50 microns or 50 to 100 microns. A particularly preferred size is 1 to 10 microns, at least for iron carbonyl powder particles. This size has proven to give a stabilized flame. The used powder of this size is also easily captured using a cyclone separator or filters which is not the case for smaller particle sizes. Once captured, the iron oxide particles could be collected in a canister and then subsequently regenerated using regular de-oxidation technology in a factory. An option would be to use a part of the metal fuel tank for storing used fuel. This could e.g. be done by dividing the tank into two sections separated by a movable partition, such as a membrane. Hereby the spent fuel would not take up additional space provided that it could be compacted to near original volume. The metal originally being in the form of chips or shavings may be used as it is, or it may be ground into powder before being led into the metal burner. Such grinding would typically take place at a factory, but if desired, it may also take place on the vehicle by use of a grinder. In this case the metal fuel may e.g. be stored in the original form of chips or shavings and ground before being led to the metal burner. It may also be ground at regular intervals and stored in a powder buffer chamber until needed. Such a powder buffer chamber may e.g. be or resemble a mid storage as described above and in relation to the figures.

A vehicle engine system may be designed for burning of any size of metal, but it may also be designed for burning metal within a predefined size range. This may e.g. be relevant with respect to how the used fuel is collected for possible regeneration. The means for transportation of the metal fuel may also be particularly suitable for a given size of metal. It has previously been suggested to use metal nano-particle fuel for internal and external combustion engines and vehicle propulsion; see e.g. the article "Metal : The fuel of the future" in issue 2522 of "New Scientist", 22 October 2005, page 34ff. However, the storage, handling and in particular combustion of nano- particles provide a number of health and safety risks. Therefore, in preferred embodiments of the invention, it should be avoided to use nano-particles as they will typically need special safety precautions to avoid fire and explosions.

Furthermore, they are difficult to capture and collect within the exhaust system, and they may also have a number of health precautions to take into account before, during and after use. Metal chips and shavings will typically be waste products from industrial machining processes. This may also be the case for metal powder, but powder may also be produced specifically for the purpose of using it for fuel in a vehicle engine system if desired. Metal powder may e.g. be produced by direct reduction, gas atomization or carbonyl processing.

The metal is preferably a combustible oxidizing metal, and it may be selected from the group consisting of iron, iron carbide, aluminium, magnesium, silicon, titanium, boron or alloys or compounds thereof.

A second aspect of the invention relates to a vehicle comprising an electrical motor and a vehicle engine system as described above. The vehicle may further comprise a battery set up rechargeable by the electrical energy generated by the generator.

The vehicle may have a hybrid engine so that it is adapted to also run on another fuel than the metal fuel, such as gasoline, diesel, hydrogen, ethanol or plant based oil. Hereby it can be ensured that the engine can also be used in situations where there is not enough metal fuel readily available or where use of metal fuel is not profitable.

A third aspect of the invention relates to a method of driving such a vehicle, the method comprising :

- transporting metal fuel from a metal fuel tank to a metal burning unit,

- burning metal fuel in the metal burning unit,

- converting heat from the metal burner system into kinetic energy by means of a heat engine,

- using the kinetic energy to generate electrical energy by means of a generator, and

- using the electrical energy directly or indirectly to actuate propulsion means of the vehicle.

By "directly" is preferably meant that the shaft of the heat engine is directly connected to the propulsion means. By "indirectly" is preferably meant the following connection : shaft-generator-electric engine-propulsion means; i.e. that a generator and an electric engine is arranged between the shaft of the heat engine and the propulsion means. In both cases, the connection may further include a gear box. The method may further comprise the step of using cooling means to guide cooling gas to a space between an outer wall of a combustion chamber of the metal burning unit and a heat protective pipe arranged within the outer wall of the combustion chamber. The first, second and third aspects of the present invention may each be combined. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

The vehicle engine system according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. For example some of the figures illustrate vehicles with four wheels which may e.g. be a car. However, any number of wheels and also other types of propulsion means, such as the propeller of a boat or ship, are covered by the scope of the present invention.

Figure 1 shows schematically the overall design of a vehicle engine system according to the present invention.

Figure 2 shows schematically the conversion of forms of energy within the vehicle engine system. Figure 3 shows schematically the metal fuel transport system connecting the metal fuel tank and the metal burner.

Figure 4 shows an exploded view of a possible design of a metal burner. Figure 5 shows a three-dimensional view of a metal burning unit. Figure 6 shows the cooling gas distribution ring of the metal burning unit in figure 5. Figure 7 shows the heat protective pipe of the metal burning unit in figure 5.

Figure 8 shows the cyclone of the metal burning unit in figure 5.

Figure 9 shows a three-dimensional view of the metal burner connected to the combustion chamber.

Figure 10 shows a cross sectional view of the metal burner and combustion chamber in figure 9. Figure 11 shows schematically the possibility of having a main metal fuel tank arranged at one location of the vehicle and a mid storage arranged at another location close to the metal burner.

Figure 12 shows a partly transparent view of a mid storage connected to a rotating wheel.

Figure 13 shows schematically a three-dimensional view of the mid storage in figure 12 connected to the metal burner via a rotating wheel. Figure 14 shows examples of relationships between cleanness of a gas and the size of particles in the gas after filtering with different kinds of filters.

Figure 15 shows schematically three possible overall designs of vehicles equipped with a vehicle engine system according to the present invention.

DETAILED DESCRIPTION OF AN EMBODIMENT

Figure 1 shows an example of a vehicle engine system 1 according to the present invention. It comprises a combustion part 2, a heat engine 3 and an electrical generator 4. The combustion part 2 is an external heating system. The heat engine 3 may e.g. be a Stirling engine or a Rankine type heat engine, but any type of heat engine is considered to be covered by the scope of the present invention. In the heat engine 3, the heat energy is transformed into kinetic energy, such as a rotational movement used to rotate the driving shaft of the electrical generator 4. The generator 4 may e.g. be an induction generator. The generator 4 produces electricity which is typically fed to an electric motor (not shown here; please refer to figure 15) used to drive the propulsion means 5 of the vehicle.

As shown schematically in figure 2, the heat engine 3 is arranged to convert heat from the combustion part 2 into kinetic energy, and the electrical generator 4 is arranged to convert the kinetic energy from the heat engine 3 into electrical energy for directly or indirectly actuating propulsion means 5 of the vehicle of which the vehicle engine system 1 forms a part. The propulsion means 5 will depend on the type of vehicle. It will e.g. be wheels of a car or truck or propellers of a boat. The system will also comprise further components not shown in the figure, such as a cooling system for the heat engine.

The combustion part 2 comprises a metal burning unit 6 (see figure 5) adapted to generate heat by burning of metal fuel 7. The metal fuel 7 will typically be metal chips, metal shavings, metal powder or a combination thereof. It may be waste products from industrial machining processes, or it may be specially manufactured for the purpose of using it as fuel. The metal is preferably a combustible oxidizing metal, and it may be selected from the group consisting of iron, iron carbide, aluminium, magnesium, silicon, titanium, boron or alloys or compounds thereof.

The combustion part 2 further comprises a metal fuel tank 8 for storing metal fuel 7 to be burned, and a metal fuel transport system 9 for transporting metal fuel 7 from the metal fuel tank 8 to the metal burner 10 as shown schematically in figure 3. The tank and transport system will preferably be made from a material, or coated with a material, which can resist the contact with the metal fuel 7 both chemically and mechanically. It may e.g. have an inner ceramic coating having a high abrasive resistance against the potentially sharp-edged metal chips and shavings. The system also comprises means (not shown) for re-fuelling. A possible solution will be a system wherein the whole empty fuel tank is replaced with another full tank. Hereby the tanks can be filled with the metal fuel 7 at a central station, especially set up to safely handle the metal fuel 7. Alternatively, the means for re- fuelling comprises a closeable opening for pumping the metal fuel 7 into the metal fuel tank 8, e.g. by use of vacuum or compressed air.

The combustion part 2 has a combustion chamber 11 which surrounds the burning flame during use of the system. The part of the combustion chamber 11 where the combustion takes place is also referred to as the combustion zone. Due to the high temperatures arising during the burning of metal fuel 7, the combustion zone is preferably protected by a heat protective pipe 12 arranged within an outer wall 13 of the combustion chamber 11. The metal burning unit 6 (see figure 5) comprises a metal burner 10 handling the metal fuel 7 to be burned in the combustion zone of the combustion chamber 11. It may further comprise an air regulator system (not shown) providing air to the combustion zone, and an exhaust and filtering system for removing combustion gasses and particles from the combustion chamber.

The vehicle engine system 1 may be optimized during the design phase to obtain the best combustion conditions to ensure an efficient burning process. This optimization may comprise computer simulations as well as experimentation. A large number of parameters may be adjusted during the development phase, such as how rich the metal/air mix should be, the air flow speed and the ignition system parameters. Some or all of these parameters may also be controlled and adjusted during running of the system. They may e.g. be monitored and controlled constantly or at predefined regular intervals. Figure 4 shows an exploded view of a possible design of a metal burner 10 to be used in a vehicle engine system 1 according to the present invention. It comprises a dispersion disc 14 where the metal fuel 7 is mixed with pressurized air used to de-agglomerate the metal fuel 7 and force it towards the combustion zone. First it is led to a laminarization pipe 15 which creates a laminar flow. A laminar flow is characterized by a high momentum diffusion and low momentum convention. The laminarization pipe 15 is connected to the main housing 16 inside which an air spread 17 and a swirl 18 are arranged. The air spread 17 is used to obtain an even distribution of the flow of metal fuel 7 across the cross section, and the swirl 18 imposes a swirling motion to the metal fuel 7 which results in a better mixing of the metal fuel 7 and the air. At the other end of the metal burner 10, the mixed metal fuel 7 leaves via the exit tube 19. Gas is added via a gas nozzle 20, and the burning of the fuel is started by the igniter 21. The gas is normally only added in the startup phase when ignition of the metal fuel 7 takes place. In the illustrated embodiment, the metal burner 10 in figure 4 is mounted to an end surface of the combustion chamber 11 as shown in figure 5 which is a three- dimensional view of the metal burning unit 6. The combustion chamber 11 is shown as transparent for illustrative purposes only. Some of the components are shown on their own in the following figures. Figure 6 shows the cooling gas distribution ring 22, figure 7 shows the heat protective pipe 12, and figure 8 shows the cyclone 24. The heat protective pipe 12 is used since the burning of metal fuel 7 typically results in temperatures of 1800°C or more which is more than what the other components of the system can withstand. The heat protective pipe 12 surrounds the flame and is made from a very heat resistant material, typically a ceramic, such as Yttria-stabilized zirconia (YSZ). These types of ceramics survive well up to 2200 to 2400°C, and since it is already an oxide, such a material is inherently oxidation resistant. It also has a low thermal conductivity of 2.2 W/mK. Thermal shock resistance would also be an important property to take into account in the selection of materials, since a combustion chamber 11 could experience quite rapid temperature changes. Smaller YSZ tubes might also be considered.

The conical shape of the first section of the heat protective pipe 12 prevents heat from being led backwards in the system. The cylindrical part of the heat protective pipe 12 comprises protrusion, typically in the form of ribs 25, so that an annular space 26 is obtained between the outer wall 13 of the combustion chamber 11 and the heat protective pipe 12. The ribs 25 are arranged and sized to fit inside the combustion chamber 11 and may be fastened thereto e.g. by use of screws (not shown). Cooling gas, such as atmospheric air, is led to this space 26 via cooling means which in the illustrated embodiment is in the form of a cooling gas inlet pipe 23 and a cooling gas distribution ring 22; see figure 6. The cooling gas distribution ring 22 has circumferentially arranged holes 27 so that it is ensured that the space 26 is cooled around the whole outer surface of the heat protective pipe 12. From the circumferential space 26, the cooling air flows into the central part of the combustion chamber 11 and thereby also cools the flue gas from the combustion. Hereby the risk of inducing thermal stresses and wear is lowered. At the other end of the combustion chamber 11 is a cyclone 24 comprising circumferentially arranged deflector fins 28 which are used to deflect particles, e.g. iron oxides, left after the combustion towards the outer wall 13 of the combustion chamber 11. From there they can be removed e.g. via a removal pipe 29 and collected in a canister 30; see figure 11. Hereby the heated gas leaving the combustion chamber and flowing towards the heat engine is as clean as possible. The cyclone 24 can be seen as a "normal" cyclone running backwards with the combustion gas turning round the inner perimeter of the combustion chamber 11. It will be desired to be able to tune the cyclone 24 so that a good separation of particles from the gas is ensured.

Figures 9 and 10 show the metal burner 10 and the combustion chamber 11 in three-dimensional views. Figure 10 shows a cross sectional view of the metal burner 10 and combustion chamber 11 in figure 9. It shows how the ribs 25 on the outer surface of the heat protective pipe 12 are used to support the pipe in a position resulting in forming of a space 26 for the cooling gas between the heat protective pipe 12 and the outer wall 13 of the combustion chamber 11. It is also shown where the cooling gas leaves the space to be mixed with and thereby cooling the flue gas resulting from the combustion. Some embodiments of the invention comprise a mid storage 31 for storing an amount of metal fuel 7 near the metal burner 10 whereas the remainder of the metal fuel 7 is stored in the main metal fuel tank 8. Figure 11 shows schematically a possible design of such a system having a main metal fuel tank 8 arranged at one location of the vehicle and a mid storage 31 arranged at another location close to the metal burner 10. In this way the major part of the metal fuel 7 can be stored where there is most room therefore and transported to the mid storage 31 by use of ordinary transportation means without any need for precise

measurements of the amounts being transported. The transportation means may e.g. be by use of pressurized air or vacuum or other transport technologies suitable for the actual metal fuel 7 being used. It may also be fed partly or fully by gravity or by a screw feeder. From the mid storage 31 the metal fuel 7 can then be led to the metal burner 10 in precisely metered amounts to ensure efficient combustion conditions. This transportation will be over a short distance only and can be effectuated precisely e.g. by use of a screw feeder 32 in combination with a rotary wheel feeder 33 as shown in figures 12 and 13. Such a rotary wheel feeder 33, which may also be called a rotary valve, and the functioning thereof will be well known to a person skilled in the art. The mid storage 31 preferably comprises stirrers 34 rotationally arranged on central axes 35 so that rotation thereof can be used to prevent that the metal fuel 7 close to the inner surfaces does not move forwards. The capacity of the mid storage 31 will typically be in the order of containing metal fuel 7 for approximately an hour's use. If desired, there could be more than one mid-storage 31. Figure 11 also shows a possible location of the canister 30 used to collect particles removed from the combustion chamber 11. Other locations, such as close to the metal fuel tank 8, will also be possible.

Figure 12 shows a partly transparent view of a mid storage 31 connected to a rotating wheel 33, and figure 13 shows schematically a three-dimensional view of the mid storage 31 in figure 12 connected to the metal burner 10 via a rotating wheel 33. Other types of feeding mechanisms may be used instead of or in combination with the rotational wheel 33. Examples of such feeding mechanisms are one or more pistons, and pressurized air feed through a piezo pinch valve. The feeding may be assisted by gravity. The mid storage 31 may further comprise a sub-chamber 36 to obtain that only a small amount of metal fuel 7 is contained in the sub-chamber which may make it easier to ensure an even and precisely metered flow of metal fuel 7 towards the rotating wheel 33 and thereby the metal burner 10. Sensors (not shown) may be arranged to provide signals for a control system (not shown) to ensure the desired flow of metal fuel 7. Figure 14 shows examples of relationships between the obtainable cleanness of a gas and the size of particles in the gas after filtering with different kinds of filters. As seen from the figure, a cyclone will be most efficient for relatively large particles, whereas smaller particles are more efficiently removed by e.g. a hose filter. In a system as described as described above, a cyclone can be used to remove particles from inside the combustion chamber. This may be combined with other types of filters arranged e.g. where the hot gas leaves the combustion chamber and is led towards the heat engine. A vehicle provided with a vehicle engine system according to the present invention and described above typically also comprises an electrical motor used to drive the propulsion means of the vehicle. This may be done either directly or indirectly including via a gear box or the like. The vehicle preferably also comprises a battery set up rechargeable by the electrical energy generated by the generator. This battery is also used to power the fuel and air injection systems.

Figure 15 shows schematically three possible overall designs of vehicles equipped with a vehicle engine system 1 according to the present invention. As shown in the figure, the vehicle may comprise different combinations of the following components: rechargeable battery 37, charger 38, converter 39, electric motor 40, and flywheel or capacitor 41. The design and use thereof will be known from an ordinary vehicle and will be well known for a person skilled in the art.

The vehicle may comprise a hydraulic system and a hydraulic engine used to perform the movement of the vehicle or parts thereof. This is e.g. often seen on forest machines where the wheels and possibly also other parts of the equipment are moved by use of hydraulics.

An engine system according to the present invention preferably further comprises a particulate filter system (not shown) connected to the exhaust pipe of the vehicle. This filter system is used to remove metal oxide particles from the combustion process. Some filters are disposable filters while others are designed to burn off the accumulated particles. To sum up the above, a method of driving a vehicle according to the present invention comprises the following steps:

- transporting metal fuel 7 from a metal fuel tank 8 to a metal burning unit 6,

- burning metal fuel 7 in the metal burning unit 6,

- converting heat from the metal burning unit 6 into kinetic energy by means of a heat engine 3,

- using the kinetic energy to generate electrical energy by means of an electrical generator 4, and

- using the electrical energy directly or indirectly to actuate propulsion means 5 of the vehicle.

The method preferably further comprises using cooling means to guide cooling gas to a space 26 between an outer wall 13 of a combustion chamber 11 and a heat protective pipe 12 arranged within the outer wall 13 of the combustion chamber 11.

The automatic collection of the particles collected after combustion will preferably be made when re-fuelling of the vehicle. They will then be transported back to the fuel plant for regeneration using regular de-oxidation technology in the factory. It might also be possible to have a corresponding miniature process implemented in the vehicle. This could e.g. be advantageous on board larger ships that do not often arrive at harbours.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. E.g. the shapes and relative dimensions of the

components may vary from those shown.

The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

1. A vehicle engine system comprising :

- a combustion part having a combustion chamber,

in which system the combustion part comprises:

- a metal fuel tank for storing metal fuel to be burned, and

2. The vehicle engine system according to claim 1, wherein the combustion chamber comprises:

- a heat protective pipe arranged within an outer wall of the combustion chamber, and

- cooling means for guiding cooling gas to a space between the outer wall of the combustion chamber and the heat protective pipe.

3. The vehicle engine system according to claim 1 or 2, further comprising a cyclone arranged in the combustion chamber and being adapted to guide particles left after combustion towards the outer wall of the combustion chamber.

4. The vehicle engine system according to claim 3, wherein the cyclone comprises circumferentially arranged deflector fins adapted to guide the particles towards the outer wall of the combustion chamber.

5. The vehicle engine system according to any of the preceding claims, wherein the metal burning unit further comprises:

- an air regulator system providing air to the combustion zone, and/or

- an exhaust and filtering system for removing combustion gasses and particles from the combustion chamber.

6. The vehicle engine system according to any of the preceding claims, further comprising a mid storage for storing an amount of metal fuel near the metal burner, and wherein the metal fuel transportation system is adapted to transport the metal fuel from the metal fuel tank to the mid storage.

7. The vehicle engine system according to any of the preceding claims, wherein the heat engine is a Stirling engine or a Rankine type heat engine.

8. The vehicle engine system according to any of the preceding claims, wherein the metal fuel is selected from metal chips, metal shavings, and metal powder.

9. The vehicle engine system according to any of the preceding claims, wherein the metal is a combustible oxidizing metal selected from the group consisting of iron, iron carbide, aluminium, magnesium, silicon, titanium, boron or alloys or compounds thereof.

10. A vehicle comprising an electrical motor and a vehicle engine system according to any of the preceding claims.

11. A vehicle according to claim 10, further comprising a battery set up rechargeable by the electrical energy generated by the electrical generator.

12. A vehicle according to claim 10 or 11, wherein the vehicle has a hybrid engine so that it is adapted to also run on another fuel than the metal fuel.

13. A method of driving a vehicle according to any of claims 10 to 12, the method comprising :

- transporting metal fuel from a metal fuel tank to a metal burning unit,

- burning metal fuel in the metal burning unit,

- converting heat from the metal burning unit into kinetic energy by means of a heat engine,

- using the kinetic energy to generate electrical energy by means of an electrical generator, and

14. The method according to claim 13, further comprising using cooling means to guide cooling gas to a space between an outer wall of a combustion chamber of the metal burning unit and a heat protective pipe arranged within the outer wall of the combustion chamber.