WO2025238124A1

WO2025238124A1 - Pneumatic system for generating electricity for driving a means of transport

Info

Publication number: WO2025238124A1
Application number: PCT/EP2025/063320
Authority: WO
Inventors: Arvind GANGOLI RAO
Original assignee: Technische Universiteit Delft
Current assignee: Technische Universiteit Delft
Priority date: 2024-05-16
Filing date: 2025-05-15
Publication date: 2025-11-20
Anticipated expiration: 2026-11-16
Also published as: NL2037710B1

Abstract

The invention relates to a pneumatic system (1) for generating electricity. The pneumatic system (1) comprises a gas container (2) configured to contain a high-pressure oxygen containing gas, a fuel tank (3) and a combustion chamber (4). The combustion chamber (4) is fluidly connected to the gas container (2) and the fuel tank (3) to receive high-pressure oxygen containing gas. The combustion chamber (4) is configured to burn the fuel and discharge an expanding exhaust flow. The pneumatic system (1) comprises a prime mover (5) which is configured to receive the exhaust flow from the combustion chamber (4). The pneumatic system (1) comprises a generator (6) which is driven by the prime mover (5) to generate electricity.

Description

Pneumatic system for generating electricity for driving a means of transport

TECHNICAL FIELD

The invention relates to a pneumatic system.

BACKGROUND

In search for more environmentally friendly means of transport, different types of drive systems have been developed.

Today, electric vehicles are becoming the standard. Different types of electric vehicles are known, such as combustion-hybrid electrical vehicles (batteries charged by engine, no external charging), plug-in hybrid vehicles (fuel engine combined with chargeable batteries via plug-in), 100% battery vehicles, and fuel cell vehicles (hydrogen and oxygen are used to produce electricity).

Battery electric vehicles have several drawbacks. Electric vehicles have a limited range. Charging batteries is time-consuming. Recharging facilities are relatively expensive. Also, the batteries are heavy, making the vehicle heavy and thereby energy-intensive to move. The weight also causes increased tyre erosion and consequential particle emissions. Furthermore, manufacturing batteries requires a lot of rare earth materials and energy.

Less well known are vehicles that use compressed air as energy source, especially in a reciprocating engine for automotive use. However, these systems have a relatively low power density/range.

An example of such a vehicle is described in IN202321050022A. According to this publication, compressed oxygen is mixed with hydrogen before being introduced into a cylinder of a piston engine.

The company Solution Air BV (www.solutionair.nl) promotes high-pressure air engines for the propulsion of all vehicles and vessels that currently run or sail on diesel, petrol or gas (sea shipping excluded). The air bottles used have an air pressure of 600-800 atmospheres. Their product is based on preserving the reciprocating engine of the vehicle and converting it in such a way that it can run on high-pressure air as energy source.

More generally speaking, compressed air may also be used as a means to store energy, which may at some point in time be used to generate electricity.

These systems have the problem of condensation and temperatures going below 0°C caused by the cooling effect of expanding air.

SUMMARY

The object is to provide a pneumatic system which overcomes at least one of the disadvantages associated with the prior art.

According to an aspect there is provided a pneumatic system for generating electricity for driving a means of transport, the pneumatic system comprising a gas container configured to contain a high-pressure oxygen containing gas, a fuel tank and a combustion chamber, wherein the combustion chamber is fluidly connected to the gas container and the fuel tank to receive high-pressure oxygen containing gas from the gas container and fuel from the fuel tank, wherein the combustion chamber is configured to burn the fuel and discharge an expanding exhaust flow, wherein the pneumatic system further comprises a prime mover which is configured to receive the exhaust flow from the combustion chamber and wherein the pneumatic system further comprises a generator which is configured to be driven by the prime mover to generate electricity.

The gas container may contain a high-pressure oxygen containing gas (e.g. air) and the fuel tank may contain fuel (gaseous or liquid, pressurized or unpressurized). The pneumatic system is configured to supply high-pressure oxygen containing gas to the combustion chamber (4) at a pressure of more than 100 bar, preferably more than 500 bar or more preferably at a pressure of more than 800 bar. The pneumatic system is configured to supply the high-pressure oxygen containing gas to the combustion chamber (4) at substantially the storage-pressure, without the use of any pressure reducing mechanism or equipment. The system here provided is a low emission system, in which a combination of compressed oxygen containing gas (e.g. air) along with fuel is used to generate electricity. The system uses a combination of compressed oxygen containing gas along with fuel to drive a prime mover, such as a piston based or a turbine-based drive. The oxygen containing gas may be air or pure oxygen. The term 'air' refers to a mixture of gases, primarily composed of nitrogen (approximately 78 mol%), with oxygen being the second most abundant component (approximately 21 mol%). It also contains small amounts of other gases.

The combustion chamber may be a chamber suitable for burning a mixture of fuel and oxygen or air.

The term ‘fluidly connected’ is used to indicate that fluids, such as fuel, gas, exhaust, may flow from one component to the other component. The fluid connection may be direct in the sense that no other components are present in between other than components needed for establishing and managing the fluid connection (pumps, valves, conduits). The fluid connection may also be indirect in the sense that additional equipment may be present, such as a heat exchanger, additional prime mover etc.

So, the combustion chamber may be directly connected to the gas container, or the combustion chamber may be indirectly connected to the gas container in the sense that intermediate components may be present, such as a heat exchanger or an additional prime mover, as will be described in more detail below.

The prime mover may be a reciprocating engine or a turbine, such as a rotating turbine. The prime mover is connected to the combustion chamber to receive the expanding high-pressure exhaust flow and to be driven by the expanding exhaust flow.

The pneumatic system presented here has the advantage that the high-pressure oxygen containing gas is prevented from cooling down below 0°C as a result of the expansion by the heat generated by the burning of fuel.

The pneumatic propulsion system is a low emission power and propulsion system suitable for all sorts of means of transport, such as cars, trucks, busses, boats, airplanes etc. By using compressed oxygen containing gas and a fuel, such as hydrogen, as energy carriers, the recharging time can be reduced from 30 min or more (for a fast-charging electrical vehicle) to around 2 min or less. The amount of weight of this system will be slightly less than that of battery electrical vehicles. Moreover, the vehicle will become lighter during travel, thereby increasing the fuel efficiency. The other advantage is that the proposed system doesn’t require an expensive distributed electric charging infrastructure. Use can be made of existing fuel systems and relatively cost-efficient high-pressure oxygen containing gas filling systems. The oxygen containing gas compression system can be run when the cost of electricity is low or negative, thereby helping the grid to balance the load. Therefore, the cost of the here proposed system will be much less than that of a battery electric system.

When the pneumatic system is incorporated into a means of transport, the means of transport will be heavier than a conventional fossil-based means of transport, but lighter than a full battery electric means of transport.

The electricity generated by the generator can be used to drive the means of transport. It is noted here that that the prime mover is not mechanically coupled to the wheels, as the prime mover and the wheels are typically rotating in different rotational speed ranges, which would in practice require a large and complicated gear box. As an example, a turbine would typically rotate at 50.000 - 100.000 rpm, whereas wheels are typically rotating in the range of a couple of 100 rpm (rotations per minute). By decoupling the prime mover from the wheels there is no need for such a gear box. Furthermore, by decoupling the turbine from the wheels, the turbine can run optimally at one load point, rather than at the load that the vehicle is demanding.

The pneumatic system is comprised by the means of transport.

According to an embodiment the pneumatic system is configured to directly use at least part of the electricity generated by the generator to propel the means of transport.

The term directly is used to indicate that the electricity generated by the generator is directly used and not stored in a battery. The term at least partially is used to indicated that not all the generated electricity may be (immediately) used to propel the means of transport but part of it may be used for other purposes, such as for energizing other parts of the means of transport, for instance the lights, the control unit, the air-conditioning or may be stored in a battery. By way of example, where a 100% battery vehicle may travel 400 km when fully charged at 85-1 OOkW under normal running and temperature conditions, the here presented pneumatic system would use around 0,7 - 1 ,0 m³ of high-pressure oxygen containing gas at 350 bar and around 1 kg of hydrogen. The pneumatic system is capable of generating 30kW for small vehicles to 200kW for large vehicles or even 500kW for even larger vehicles.

According to an embodiment there is provided a pneumatic system, wherein the gas container is suitable to contain high-pressure oxygen containing gas at a pressure up to 100 bar, preferably up to 500 bar, more preferably up to 800 bar and more preferably at a pressure of more than 800 bar. One bar equals 100.000 Pa. It is noted that the higher the pressure, the more energy can be stored as pneumatic energy on board the vehicle.

The gas container can have any suitable volume, depending on the application and the storage volume available. The gas container may for example have a volume of more than 0,5 m3. The gas container may for example have a volume of less than 3 m3.

According to an embodiment there is provided a pneumatic system, wherein the fuel tank is suitable to contain fuel at a pressure up to 100 bar, preferably up to 500 bar, more preferably up to 800 bar and more preferably at a pressure of more than 800 bar.

The fuel tank may preferably contain hydrogen. Hydrogen fuel tanks are typically high- pressure tanks. Hydrogen is typically stored at 350 - 700 bar. The fuel tank is relatively small and may for instance be configured and dimensioned to contain 1 - 5 kg of fuel.

According to an embodiment the high-pressure oxygen containing gas is stored in the gas container at a first pressure, gaseous fuel is stored in the fuel tank at a second pressure, wherein the first pressure is equal to the second pressure or the first pressure is equal to R times the second pressure, where R is in the range of 0,8 - 1 ,2.

According to an embodiment there is provided a pneumatic system, wherein the pneumatic system comprises a fuel pump configured to supply fuel from the fuel tank to the combustion chamber. The fuel may be stored at a pressure that is different, e.g. lower, than the pressure at which the oxygen containing gas is stored in the gas container. According to an embodiment, the fuel is stored at atmospheric pressure.

The fuel pump may be provided to overcome the pressure difference between the fuel and the oxygen containing gas and allow the oxygen containing gas and fuel to be mixed in or upstream of the combustion chamber.

According to an embodiment there is provided a pneumatic system, wherein the pneumatic system further comprises a heat exchanger, which heat exchanger is configured to preheat the high-pressure oxygen containing gas against a prime mover exhaust flow and discharge pre-heated high-pressure oxygen containing gas to the combustion chamber.

The prime mover is configured to receive the exhaust flow from the combustion and discharge a prime mover exhaust flow. The prime mover exhaust flow is at a much lower pressure than the exhaust flow received by the prime mover, but is still at a considerable high temperature. This temperature can advantageously be used by the pneumatic system to preheat the high- pressure oxygen containing gas before being provided to the combustion chamber.

This increases the efficiency of the system significantly as the waste heat in the exhaust after the prime mover is utilised by the compressed air.

According to an embodiment there is provided a pneumatic system, wherein the pneumatic system further comprises an additional prime mover, wherein the additional prime mover is configured to receive high-pressure oxygen containing gas from the gas container or receive pre-heated high-pressure oxygen containing gas from the heat exchanger, and wherein the additional prime mover is configured to discharge expanded high-pressure oxygen containing gas to the combustion chamber.

The additional prime mover is configured to receive high-pressure oxygen containing gas from the gas container, which may be pre-heated high-pressure oxygen containing gas received from the heat exchanger. This embodiment has the advantage that the expansion of the high-pressure gas stream from the gas container is split over stages, i.e. two prime movers. This allows for optimization of the efficiency.

According to an embodiment there is provided a pneumatic system, wherein the pneumatic system further comprises an additional generator, wherein the additional generator is coupled to the additional prime mover to generate electricity driven by the additional prime mover.

This embodiment makes the pneumatic system suitable for heavier loads, as for instance needed by large means of transport, such as busses or trucks. In general, the efficiency of components like a turbine, combustion chamber and heat exchanger increase with size.

The prime movers may be provided by two turbines.

According to an embodiment there is provided a pneumatic system wherein the pneumatic system comprises a compressor, wherein the compressor is configured to provide an additional compressed oxygen containing gas stream to the combustion chamber, wherein the additional compressor is preferably configured to be driven by the additional prime mover.

This embodiment may advantageous be used in a system wherein the high-pressure oxygen containing gas is stored at a relatively low pressure, being a pressure up to 100 bar, 150 bar or 200 bar. The compressor is used to generate extra high pressure oxygen containing gas to be provided to the combustion chamber in addition to oxygen containing gas obtained from the gas container. The compressor preferably compresses ambient air to a pressure substantial equal to the pressure of the gas from the gas container, e.g. being a pressure up to 100 bar, 150 bar or 200 bar. The additional compressed oxygen containing gas stream is mixed with the expanded high-pressure oxygen containing gas discharged by the additional prime mover to be provided to the combustion chamber.

This embodiment has the advantage that a high mass flow rate through the combustion chamber and the subsequent prime mover is high. This might be required in some niche applications such as aeronautics where there are strict limitations to the maximum pressure of air or gas stored on-board. According to an embodiment there is provided a pneumatic system, wherein the pneumatic system comprises a prime mover exhaust flow path that is at least partially in contact with the gas container to allow the prime mover exhaust flow to heat the gas container.

The prime mover exhaust flow path may be at least partially in thermal contact with the gas container to allow the prime mover exhaust flow to exchange heat with the gas container and thereby preheat the gas contained by the gas container.

The gas tank may at least partially be configured as a double-walled tank, comprising an inner wall, an outer wall and an intermediate space created in between the inner wall and the outer wall. The intermediate space is part of the prime mover exhaust flow path. The prime mover exhaust flow is, in use, guided through the intermediate space. The intermediate space may be configured to receive a prime mover exhaust flow to preheat the high-pressure oxygen containing gas contained by the gas container 2.

This embodiment makes even more use of the energy I heat contained in the prime mover exhaust flow. Also, the temperature of the prime mover exhaust flow is further reduced.

According to an embodiment there is provided a pneumatic system, wherein the pneumatic system comprises a controller configured to control the amount of high-pressure oxygen containing gas and amount of fuel to be supplied to the combustion chamber.

The controller controls the ratio and quantity of high-pressure oxygen containing gas and fuel discharged to and received by the combustion chamber. This allows to control the amount of electricity being generated. The controller may be arranged to receive an input signal based on which the controller controls the amount of high-pressure oxygen containing gas and fuel being discharged. The input signal is indicative for the amount of electricity that is required to be generated.

According to an aspect there is provided a means of transport comprising a pneumatic system as provided above, wherein the means of transport is one of: car, van, truck, bus, boat, aircraft.

According to an aspect there is provided a method of operating a pneumatic system as provided. According to an embodiment, a method of operating a pneumatic system for generating electricity for driving a means of transport comprises: supplying high-pressure oxygen containing gas from a gas container to a combustion chamber; supplying fuel from a fuel tank to the combustion chamber; burning the fuel in the combustion chamber to generate an expanding exhaust flow; directing the expanding exhaust flow to a prime mover; and generating electricity with a generator driven by the prime mover, wherein the high-pressure oxygen containing gas is supplied to the combustion chamber at a pressure of more than 100 bar, preferably more than 500 bar or more preferably at a pressure of more than 800 bar.

According to an embodiment, the method further comprises directly using at least part of the electricity generated by the generator to propel the means of transport.

According to an embodiment, the method further comprises preheating the high-pressure oxygen containing gas in a heat exchanger against a prime mover exhaust flow before supplying the high-pressure oxygen containing gas to the combustion chamber.

According to an embodiment, the method further comprises: directing the high-pressure oxygen containing gas from the gas container or pre-heated high-pressure oxygen containing gas from the heat exchanger to an additional prime mover; expanding the high-pressure oxygen containing gas in the additional prime mover; and directing the expanded high- pressure oxygen containing gas to the combustion chamber.

According to an embodiment, the method further comprises generating additional electricity with an additional generator driven by the additional prime mover.

According to an embodiment, the method further comprises: operating a compressor to provide an additional compressed oxygen containing gas stream to the combustion chamber, wherein the compressor is driven by the additional prime mover.

According to an embodiment, the method further comprises heating the gas container with a prime mover exhaust flow by directing the prime mover exhaust flow along a flow path that is at least partially in contact with the gas container. According to an embodiment, the method further comprises controlling, with a controller, the amount of high-pressure oxygen containing gas and the amount of fuel supplied to the combustion chamber to optimize combustion efficiency and power output.

According to an embodiment, the method comprises burning the fuel in the combustion chamber at a burning temperature of less than 1200°C, preferably less than 1100°C.

According to an embodiment, the method comprises controlling the amount of high-pressure oxygen containing gas and fuel supplied to the combustion chamber such that the amount of oxygen exceeds the stoichiometric requirement for complete combustion of the fuel with at least a factor of two, preferably at least with a factor of five.

In the combustion chamber, the amount of oxygen provided may exceed the stoichiometric requirement for complete combustion of the fuel. This approach ensures that a significant portion of the energy driving the system is derived from the pressure of the high-pressure oxygen containing gas, rather than solely or primarily from the combustion of fuel. The equivalence ratio, which is the ratio of the actual fuel-to-air ratio to the stoichiometric fuel-to- air ratio, may be maintained between approximately 0.2 to 0.5. This low equivalence ratio indicates that the system primarily harnesses the energy stored in the compressed gas, with the fuel serving mainly to prevent temperature drops that could compromise system efficiency. By maintaining an oxygen-rich environment where the amount of oxygen exceeds stoichiometric requirements by a factor of two to five, the system maximizes the utilization of pneumatic energy while using minimal fuel, resulting in a more efficient and environmentally favorable operation.

The pneumatic system as described above may be configured to supply high-pressure oxygen containing gas from the gas container (2) and fuel from the fuel tank (3) to the combustion chamber such that an amount of high-pressure oxygen containing gas exceeds the stoichiometric requirement for complete combustion of the fuel by at least a factor of two, preferably at least with a factor of five.

The method may comprise

• receiving a signal indicative of the electricity required by the means of transport, controlling the amount of fuel being provided to the combustion chamber and controlling the amount of high-pressure oxygen containing gas being provided to the combustion chamber in response to the signal.

The signal may be generated based on a user input provided by a user, for instance by means of a foot pedal operated by the user.

The method may be performed by the control unit.

According to an aspect there is provided a use of a pneumatic system as provided for propelling a means of transport. In use, the electricity generated by the pneumatic system is at least partially used directly for propelling the means of transport.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures, the subject-matter of the invention is schematically shown, wherein identical or similarly acting elements are usually provided with the same reference signs.

Figure 1 shows a schematic view of an embodiment.

Figure 2 - 5 show schematic views of further embodiments.

DESCRIPTION OF EMBODIMENTS

Embodiments will be described with reference to the figures.

According to the embodiments, energy is provided in terms of two energy sources: a compressed oxygen containing gas, e.g. air, and fuel, in particular hydrogen. The compressed oxygen containing gas may be generated in any suitable manner, including using renewable energy. The fuel may be any kind of suitable fuel, such as any hydrocarbon fuel (e.g. petrol, diesel, ethanol, methanol), including gas (e.g. methane, CNG or LPG). Hydrogen may be used, in particular hydrogen made with the use of renewable energy. The hydrogen may be created in any suitable manner, including with the use of renewable energy (electrolysis), nuclear energy and/or as an industrial by-product. Fig. 1 shows a schematic view of a pneumatic system 1 according to an embodiment.

The pneumatic system 1 comprises a high-pressure oxygen containing gas container 2 suitable for being filled with and storing a compressed oxygen containing gas. The gas container 2 is suitable for storing oxygen containing gas at a maximum pressure of up to 100 bar, preferably at up to 500 bar and more preferably up to 700 bar, more preferably up to 800 bar and most preferably at a pressure more than 800 bar. The gas container 2 may have a storage volume in the range of 0,5 m³ to 3 m³. The gas container 2 comprises an inlet (not shown) for filling the gas container 2 with oxygen containing gas from an external high- pressure oxygen containing gas supply, e.g. a high-pressure air filling station. The gas container 2 further comprises a (high-pressure) gas outlet 21 for discharging the oxygen containing gas from the gas container 2. To control the amount of oxygen containing gas being released from the gas container 2 a controllable gas valve 22 may be provided. The controllable oxygen containing gas valve 22 may be controlled by a controller 100, as will be described in more detail below, to control the amount of oxygen containing gas being released from the gas container 2.

The pneumatic system 1 further comprises a fuel tank 3 suitable for being filled with and storing fuel. The fuel may be hydrogen. The fuel tank 3 is suitable for storing fuel at a maximum pressure of up to 100 bar, preferably at up to 500 bar and more preferably up to 700 bar, more preferably up to 800 bar and most preferably at a pressure more than 800 bar. The fuel tank 3 comprises an inlet (not shown) for filling the fuel tank with fuel from an external fuel supply, e.g. a fuel filling station. The fuel tank 3 further comprises a fuel outlet 31 for discharging fuel from the fuel tank 3. To control the amount of fuel being released from the fuel tank 3 a controllable fuel valve 32 may be provided. The controllable fuel valve 32 may be controlled by the controller 100, as will be described in more detail below, to control the amount of fuel being released from the fuel tank 3. In the embodiment shown an optional fuel pump 33 is provided to pump fuel into the combustion chamber 4. The fuel pump 33 may be required in situations in which the pressure of the oxygen containing gas is higher than the pressure of the fuel. If a fuel pump 33 is present, the fuel valve 32 may be omitted.

The pneumatic system 1 further comprises a combustion chamber 4. The combustion chamber 4 comprises a (high pressure) gas inlet 41 and a fuel inlet 42. The gas inlet 41 is fluidly connected to the gas outlet 21 to receive gas from the gas container 2. The fuel inlet 42 is fluidly connected to the fuel outlet 31 to receive fuel from the fuel tank 3. The combustion chamber has a fixed volume. According to an alternative embodiment, the combustion chamber 4 comprises a single inlet for receiving a mixture of gas and fuel, where the gas and fuel are mixed upstream of the inlet and downstream of the gas outlet 21 and fuel outlet 31.

The combustion chamber 4 is configured to receive high-pressure oxygen containing gas and fuel. The combustion chamber 4 is configured to ignite the mixture of oxygen containing gas and fuel thereby create an expanding, hot exhaust flow. The combustion chamber 4 operates in a continuous matter. This means that when the combustion chamber 4 is in operation there is a constant supply of high-pressure oxygen containing gas and fuel. The combustion chamber 4 may be a low NOx combustion system. The mixture may be ignited by a spark plug, a glow plug or any other similar device.

The exhaust flow is expanded through a prime mover 5, in this embodiment provided by turbine 5. In the turbine 5 the exhaust flow is used to drive the turbine 5 and generate rotational movement. According to an alternative embodiment, the exhaust flow is expanded through a reciprocating engine, an axial turbine, a radial turbine or any other prime mover capable of being driven by the exhaust flow (hot gases).

In this text the term prime mover is used to refer to devices, such as turbines or reciprocating engines, that are configured to convert a fluid flow (in this case the exhaust flow) into mechanical motion (e.g. a rotational movement), which can then be used to perform work. A prime mover is designed to receive and modify force and motion as supplied to the prime mover and apply them to drive machinery, e.g. a rotational shaft. In the embodiments described, the energy of the exhaust flow is converted into rotational motion, which can be used to generate electricity.

For this purpose, the combustion chamber 4 has an exhaust outlet 43 which is fluidly connected to a prime mover inlet 51 of a prime mover 5, in this embodiment provided a turbine inlet 51 of a turbine 5. The turbine 5 may comprise a rotor assembly. The rotor assembly comprises a rotational shaft 52 with blades (not shown). The exhaust flow received from the combustion chamber 4 causes the blades to move and thereby the rotational shaft 52 to rotate. The turbine 5 comprises a turbine outlet 53 to discharge a prime mover exhaust flow 9, in this case a turbine exhaust flow. The pneumatic system 1 further comprises a generator 6. The generator 6 is driven by the rotational shaft 52 and is configured to transform the rotational movement of the rotational shaft 52 into electricity.

The generated electricity can directly be used to power a transport means (not shown).

Further provided may be a controller 100. The controller 100 may be a stand-alone controller or embedded in an over-all controlling system of the means of transport. The controller may be dedicated computer hardware, programmable computer hardware, or any other suitable type of controller.

In use, the embodiment shown in Fig. 1 may function as follows. The controller 100 sends control signals to the controllable fuel valve 32 and the controllable gas valve 22 to discharge fuel and compressed oxygen containing gas towards the combustion chamber 4. If needed, a control signal is sent to the fuel pump 33 to pressurize the fuel to an appropriate pressure. The controller 100 may further send control signals to the combustion chamber 4 to initiate ignition, e.g. by activating the spark plug, glow plug or similar device. The exhaust flow from the combustion chamber 4 is guided to the prime mover 5 and is used to drive the prime mover 5 and consequently the rotational axis 52. The generator 6 produces electricity driven by the rotational axis 52. The electricity generated by the generator 6 is used directly at least partially to propel and optionally further energize the means of transport.

It is noted that depending on the application the amount of fuel and oxygen containing gas that is used varies. But for a normal situation in which the pneumatic system is used to propel a car, a few milligrams of fuel and a few grams of air would be released per second. As the oxygen containing gas is provided at high pressure, there is only a small amount of fuel required. Preferably a lean mixture of oxygen and fuel is used to avoid Nox production.

In use, the temperature reached at the end of the combustion chamber is in the range of 300°C - 1000°C, of course depending on the load and operating condition. In use, the pressure in the gas container 2 may drop from 800 bar when fully loaded to 50 bar when almost depleted.

Fig. 2 schematically depicts a further embodiment. Same reference numbers are used to refer to the same components. For clarity, the control unit 100 is not repeated in Fig. 2 and further figures, but it will be understood that the control unit 100 may also be part of the embodiments shown in the further figures.

Fig. 2 shows an embodiment wherein the pneumatic system 1 further comprises a heat exchanger 8. The heat exchanger 8 may be used to re-use at least some of the heat present in the prime mover exhaust flow 9 by pre-heating the high-pressure oxygen containing gas discharged from the gas container 2. The heat exchanger comprises a first inlet 81 and a second inlet 82, wherein the first inlet 81 is fluidly connected to the turbine outlet 53 to receive the prime mover exhaust flow 9 and wherein the second inlet 82 is fluidly connected to the gas outlet 21 of the gas container 2 to receive high-pressure oxygen containing gas. The heat exchanger 8 is configured to allow the turbine exhaust flow 9 and the gas stream received from the gas container to exchange heat. As the turbine exhaust flow is relatively warm, this will preheat the gas stream. The heat exchanger 8 further comprises a first outlet 83 to discharge the prime mover exhaust flow 9 and a second outlet 84 to discharge pre-heated high-pressure oxygen containing gas to the combustion chamber 4.

Fig. 3 schematically shows a further embodiment wherein the pneumatic system 1 comprises an additional prime mover 7, e.g. a turbine. The additional prime mover 7 is configured to receive high-pressure oxygen containing gas from the gas container 2 via an additional prime mover inlet 71 directly from the gas container 2 or via the heat exchanger 8 as shown in Fig. 3, in which case the additional prime mover 7 receives pre-heated high-pressure oxygen containing gas. The high-pressure oxygen containing gas drives the additional prime mover 7. Further provided is an additional generator 10 which is configured to be driven by the additional prime mover 7, e.g. by means of an additional rotational shaft 72 and generate electricity. The additional prime mover 7 comprises an additional prime mover outlet 73 to discharge the high-pressure oxygen containing gas to the combustion chamber 4. The embodiment shown in Fig. 3 is typically more suitable for relatively large applications, such as a truck or a bus, where the system can be optimised further by splitting the expansion into different streams.

Fig. 4 schematically shows a further embodiment comprising a compressor 11. The compressor 11 is configured to provide an additional compressed oxygen containing gas stream. The additional compressor 11 is driven by a compressor rotational shaft 112 which is driven by the additional prime mover 7. The compressor 11 comprises a compressor inlet 111 to take in oxygen containing gas, preferably air and a compressor outlet 113 to discharge an additional compressed oxygen containing gas stream. The compressor 113 outlet is fluidly connected to the combustion chamber 4 to discharge the additional compressed oxygen containing gas stream to the combustion chamber 4. The embodiment shown in Fig. 4 may advantageously be used in situations where the gas container 2 is at relatively low pressure (e.g. order of 100 bars) and there is a need for an additional high pressure gas stream.

Fig. 5 schematically shows a further embodiment in which the prime mover exhaust flow 9 is guided along the gas container 2 such that it is in thermal contact with the gas container 2 and the prime mover exhaust flow 9 is used to heat the gas container 2 and thereby the high- pressure oxygen containing gas inside the gas container 2.

The gas tank may at least partially be configured as a double-walled tank, comprising an inner wall 23, an outer wall 24 and a double-walled intermediate space 25 created in between the inner wall 23 and the outer wall 24. The double-walled intermediate space 25 is part of the prime mover exhaust flow path 9. The prime mover exhaust flow is, in use, guided through the double-walled intermediate space 25. The double-walled tank may comprise a double-walled inlet 26 configured to receive the prime mover exhaust flow 9 to preheat the high-pressure oxygen containing gas contained by the gas container 2. The double-walled tank may comprise a double-walled outlet 27 configured to discharge the prime mover exhaust flow.

Further disclosed is a pneumatic system as described above, wherein the pneumatic system, instead of being for driving a means of transport, is a pneumatic system for a stationary power generator for powering one or more external devices and wherein the pneumatic system is configured to directly at least partially use the electricity generated by the generator to power one or more of such external devices.

Again, the term directly is used to indicate that the electricity generated by the generator is directly used and not stored in a battery. The term at least partially is used to indicated that not all the generated electricity may be (immediately) used to power one or more devices, but part of it may be used for other purposes, such energizing the control unit or may be stored in a battery.

The devices may be any kind of electrical external devices that may be connected to the pneumatic system. All embodiments described above may be used for such a stationary power generator.

REFERENCE LIST

1. Pneumatic drive system

2. High-pressure oxygen containing gas container

21. Gas outlet

22. Controllable gas valve

23. Inner wall

24. Outer wall

25. Double-walled intermediate space

26. Double-walled inlet

27. Double-walled outlet

3. Fuel tank

31. Fuel outlet

32. Controllable fuel valve

33. Fuel pump

4. Combustion chamber

41. High-pressure gas inlet

42. Fuel inlet

43. Exhaust outlet

5. Prime mover

51. Prime mover inlet

52. Rotational shaft

53. Prime mover outlet

6. Generator

7. Additional prime mover

71. Additional prime mover inlet

72. Additional rotational shaft

73. Additional prime mover outlet

8. Heat exchanger 81. First inlet

82. Second inlet

83. First outlet

84. Second outlet 9. Prime mover exhaust flow

10. Additional generator

11. Compressor

111. Compressor inlet

112. Compressor rotational shaft 113. Compressor outlet

100. Controller

Claims

1. Pneumatic system (1) for generating electricity for driving a means of transport, the pneumatic system (1) comprising a gas container (2) configured to contain a high-pressure oxygen containing gas, a fuel tank (3) and a combustion chamber (4), wherein the combustion chamber (4) is fluidly connected to the gas container (2) and the fuel tank (3) to receive high-pressure oxygen containing gas from the gas container (2) and fuel from the fuel tank (3), wherein the combustion chamber (4) is configured to burn the fuel and discharge an expanding exhaust flow, wherein the pneumatic system (1) further comprises a prime mover (5) which is configured to receive the exhaust flow from the combustion chamber (4) and wherein the pneumatic system (1) further comprises a generator (6) which is configured to be driven by the prime mover (5) to generate electricity.

2. Pneumatic system (1) according to claim 1 , wherein the pneumatic system (1) is configured to directly use at least part of the electricity generated by the generator (6) to propel the means of transport.

3. Pneumatic system (1) according to any one of the preceding claims, wherein the gas container (2) is suitable to contain high-pressure oxygen containing gas at a pressure up to 100 bar, preferably up to 500 bar, more preferably up to 800 bar and more preferably at a pressure of more than 800 bar.

4. Pneumatic system (1) according to any one of the preceding claims, wherein the fuel tank (3) is suitable to contain fuel at a pressure up to 100 bar, preferably up to 500 bar, more preferably up to 800 bar and more preferably at a pressure of more than 800 bar.

5. Pneumatic system (1) according to any one of the preceding claims, wherein the pneumatic system (1) comprises a fuel pump (33) configured to supply fuel from the fuel tank (3) to the combustion chamber (4).

6. Pneumatic system (1) according to any one of the preceding claims, wherein the pneumatic system (1) further comprises a heat exchanger (8), which heat exchanger (8) is configured to preheat the high-pressure oxygen containing gas against a prime mover exhaust flow (9) and discharge pre-heated high-pressure oxygen containing gas to the combustion chamber (4).

7. Pneumatic system (1) according to any one of the preceding claims, wherein the pneumatic system (1) further comprises an additional prime mover (7), wherein the additional prime mover (7) is configured to receive high-pressure oxygen containing gas from the gas container (2) or receive pre-heated high-pressure oxygen containing gas from the heat exchanger (8), and wherein the additional prime mover (7) is configured to discharge expanded high-pressure oxygen containing gas to the combustion chamber (4).

8. Pneumatic system (1) according to claim 7, wherein the pneumatic system (1) further comprises an additional generator (10), wherein the additional generator (10) is coupled to the additional prime mover (7) to generate electricity driven by the additional prime mover (7).

9. Pneumatic system (1) according to any one of the claims 7 - 8, wherein the pneumatic system (1) comprises a compressor (11), wherein the compressor (11) is configured to provide an additional compressed oxygen containing gas stream to the combustion chamber (4), wherein the additional compressor (11) is preferably configured to be driven by the additional prime mover (7).

10. Pneumatic system (1) according to any one of the preceding claims, wherein the pneumatic system (1) comprises a prime mover exhaust flow path that is at least partially in contact with the gas container (2) to allow the prime mover exhaust flow (9) to heat the gas container (2).

11. Pneumatic system (1) according to any one of the proceeding claims, wherein the pneumatic system (1) comprises a controller (100) configured to control the amount of high- pressure oxygen containing gas and amount of fuel to be supplied to the combustion chamber (4).

12. Means of transport comprising a pneumatic system (1) according to any one of the proceeding claims, wherein the means of transport is one of: car, van, truck, bus, boat, aircraft.

13. Method of operating a pneumatic system (1) according to any one of the preceding claims 1 - 12.

14. Use of a pneumatic system (1) according to any one of the preceding claims 1 - 12 for propelling a means of transport.

15. Method of operating a pneumatic system (1) for generating electricity for driving a means of transport according to claim 13, the method comprising:

• supplying high-pressure oxygen containing gas from a gas container (2) to a combustion chamber (4);

• supplying fuel from a fuel tank (3) to the combustion chamber (4);

• burning the fuel in the combustion chamber (4) to generate an expanding exhaust flow;

• directing the expanding exhaust flow to a prime mover (5); and

• generating electricity with a generator (6) driven by the prime mover (5), wherein the high-pressure oxygen containing gas is supplied to the combustion chamber (4) at a pressure of more than 100 bar, preferably more than 500 bar or more preferably at a pressure of more than 800 bar.

16. Method according to claim 15, further comprising directly using at least part of the electricity generated by the generator (6) to propel the means of transport.

17. Method according to any one of claims 15-16, further comprising preheating the high- pressure oxygen containing gas in a heat exchanger (8) against a prime mover exhaust flow (9) before supplying the high-pressure oxygen containing gas to the combustion chamber (4).

18. Method according to any one of claims 15-17, further comprising: • directing the high-pressure oxygen containing gas from the gas container (2) or preheated high-pressure oxygen containing gas from the heat exchanger (8) to an additional prime mover (7);

• expanding the high-pressure oxygen containing gas in the additional prime mover (7); and

• directing the expanded high-pressure oxygen containing gas to the combustion chamber (4).

19. Method according to claim 18, further comprising generating additional electricity with an additional generator (10) driven by the additional prime mover (7).

20. Method according to any one of claims 18-19, further comprising:

• operating a compressor (11) to provide an additional compressed oxygen containing gas stream to the combustion chamber (4), wherein the compressor (11) is driven by the additional prime mover (7).

21. Method according to any one of claims 15-20, further comprising heating the gas container (2) with a prime mover exhaust flow (9) by directing the prime mover exhaust flow (9) along a flow path that is at least partially in contact with the gas container (2).

22. Method according to any one of claims 15-21 , further comprising controlling, with a controller (100), the amount of high-pressure oxygen containing gas and the amount of fuel supplied to the combustion chamber (4) to optimize combustion efficiency and power output.

23. Method according to any one of the claims 15 - 22, wherein burning the fuel in the combustion chamber (4) is done at a burning temperature of less than 1200°C, preferably less than 1100°C.

24. Method according to any one of the claims 15 - 23, wherein the method comprises controlling the amount of high-pressure oxygen containing gas and fuel supplied to the combustion chamber such that the amount of oxygen exceeds the stoichiometric requirement for complete combustion of the fuel with at least a factor of two, preferably at least with a factor of five.