Method Of Supplying A Propulsion Device With Fuel

Abstract

A propulsion system for a submarine includes an electric motor driving a propeller supplied with current from a fuel cell battery and a hydrocarbon burning engine. The fuel in the form of a hydroaromatic hydrocarbon or a mixture of such hydrocarbons is stored near the propulsion system. The hydroaromatic hydrocarbon is split to form hydrogen and the corresponding aromatic hydrocarbon. The hydrogen is supplied to the fuel cell and the hydroaromatic hydrocarbon is supplied as fuel to the other propulsion device.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to propulsion devices for submarines including an electric motor propulsion system for slow speed and a hydrocarbon-powered device for higher speeds.

2. The Prior Art

Propulsion devices for submarines are known which comprise a propulsion system for low speed comprising an electric motor which is supplied with current from a fuel cell battery running on hydrogen and oxygen and a driving system for high speed comprising a steam turbine which is supplied with over-heated steam developed in a combustion chamber by combustion of hydrogen and oxygen. The hydrogen and oxygen are stored in liquid form in fuel tanks in the submarine.

Disadvantages with the known propulsion device are the difficulties of storing the fuel and the military vulnerability due to the extreme temperature requirements. Also the great weight of the storage vessels in comparison with the weight of the fuel in them is a disadvantage.

SUMMARY OF THE DISCLOSURE

According to the invention it has been found that considerable advantages can be gained if the fuel is stored in the form of hydroaromatic hydrocarbons which split during operation of the propulsion device into hydrogen which is supplied to the fuel cell as fuel and into the corresponding aromatic hydrocarbon which is supplied to the combustion chamber of the steam turbine or the equivalent as fuel. The hydroaromatic hydrocarbons are liquid or solid at room temperature and can therefore be stored in simple and light fuel tanks. Further, it has been found that the aromatic hydrocarbon produced can be completely consumed in the combustion chamber of the turbine or the equivalent. In this way an extremely compact fuel system is obtained for the propulsion device from the fuel/energy point of view.

The invention thus relates to a method of supplying a propulsion device with fuel, comprising a first propulsion system comprising an electric motor which is supplied with current from a fuel cell battery and a second propulsion system comprising machinery with a combustion chamber for combustion of a fuel, such as a combustion motor, a Stirling motor, a steam turbine or a gas turbine, characterized in that the fuel of the propulsion device is stored near the propulsion device in the form of a hydroaromatic hydrocarbon or a mixture of at least two hydroaromatic hydrocarbons which split during operation to form hydrogen and the corresponding aromatic hydrocarbon(s), the hydrogen produced being supplied as fuel to the fuel cell and the aromatic hydrocarbon(s) produced being supplied as fuel to the machinery with the combustion chamber.

The propulsion device according to the present invention is also suitable for other purposes than submarines where a high energy: fuel ratio is required, for example space-research vehicles.

The hydroaromatic hydrocarbon may consist, among other things, of hexahydrobenzene C.sub.6 H.sub.12 (cyclohexane), decahydronaphthalene C.sub.10 H.sub.18 (decaline), tetrahydronaphthalene C.sub.10 H.sub.12 (tetraline), dihydrobenzene C.sub.6 H.sub.8 (cyclohexadiene), tetrahydrobenzene C.sub.6 H.sub.10 (cyclohexene), dihydronaphthalene C.sub.10 H.sub.10 and hexahydronaphthalene C.sub.10 H.sub.14, or mixtures of such hydrocarbons. In certain cases even other hydroaromatic hydrocarbons having more benzene rings may be used. Hydroaromatic hydrocarbons are particularly preferred which are liquid at room temperature, for example hexahydrobenzene, decahydronaphthalene and tetrahydronaphthalene or mixtures of these hydrocarbons. Hexahydrobenzene is particularly preferred since this substance produces the greatest quantity of energy per weight unit. Solid hydroaromatic hydrocarbons are also usable but they should suitably be used with other hydrocarbons which, together with the solid hydrocarbon, produce liquid mixtures.

The invention also relates to a means for carrying out the method described, comprising a propulsion device which comprises a first propulsion system consisting of an electric motor which is supplied with current from a fuel cell battery and a second propulsion system comprising machinery with a combustion chamber for combustion of a fuel such as a combustion motor, a Stirling motor, a steam turbine or a gas turbine, characterized in that a reactor for splitting the hydroaromatic hydrocarbons to hydrogen and the corresponding aromatic hydrocarbon is connected to the propulsion device with a connection to the fuel cell for the supply of hydrogen produced as fuel to the fuel cell and with a connection to the combustion chamber in the machinery with combustion chamber for the supply of aromatic hydrocarbon produced to the combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described with reference to the accompanying drawings in which

FIG. 1 shows schematically a means for carrying out the method according to the invention,

FIG. 2 shows schematically a fuel cell in the fuel cell battery of the means and

FIG. 3 shows schematically a common power transmission from the two propulsion systems in the propulsion device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, 10 designates a fuel cell battery driven by hydrogen gas and oxygen gas, which generates electric energy in known manner. The fuel cell battery charges an accumulator battery 12, for example a lead battery, through conduits 11. The accumulator battery is connected by conduits 13 to a DC motor 14 which directly drives the propeller shaft 15 of a submarine. Since the DC motor is directly connected to the propeller shaft a low speed motor can be used, which runs more quietly since there is no noisy gear in the propulsion system. For low speed preferably only this fuel cell battery is used with its accumulator and motor to provide the propulsion system for the submarine.

The propulsion device also includes a second propulsion system comprising machinery with a combustion chamber, in the example shown a gas turbine 16 with a combustion chamber 17. The turbine is connected to the propeller shaft 15 over a gear 18 and a coupling 19. When the coupling 19 is connected the turbine 16 and the DC motor 14 drive the propeller shaft 15 simultaneously so that the highest driving power can be obtained. This is of course the case at high speed. During silent running the turbine 16 and gear 18 are completely disconnected with the help of the coupling 19.

The fuel for the propulsion device is stored in the tank 20 and consists in the example of hexahydrobenzene C.sub.6 H.sub.12 (cyclohexane). It is led through the conduit 21 to a heated reactor 22 containing a catalyst, for example platinum, palladium or nickel. Hexahydrobenzene is split in the reactor at 200.degree.-300.degree. C to form hydrogen gas and benzene C.sub.6 H.sub.6. The mixture of hydrogen gas and benzene is led through the conduit 23 to a cooler 24 in which the benzene condenses to a liquid while the hydrogen remains a gas. The hydrogen gas is led from the cooler through the conduit 25 to a fuel chamber in the fuel cell battery 10. Hydrogen gas which is not consumed in the fuel cell battery is returned through the conduit 26 to the cooler 24. The benzene is led through the conduit 27 to a storage tank 36 and from there to the combustion chamber 17 of the turbine.

The oxidant of the propulsion device is stored in the tank 28 and consists in the example of liquid oxygen. The oxygen is led through a conduit 29 which penetrates the cooler 24 to the oxidant chamber in the fuel cell battery. From there unconsumed oxygen is led off through the conduit 30 by a circulation pump, not shown, to a point in the conduit 29. The oxygen which is vaporized on its way to the fuel cell battery is used as coolant in the cooler 24. Oxygen is also led through the conduit 31 to the combustion chamber 17 of the turbine where it reacts with benzene at a high temperature, preferably 800.degree.-1,000.degree. C. The gaseous reaction products are led from the combustion chamber through a conduit 32 to the turbine 16 and then to a condenser 33 in which the pressure is kept very low with the help of a vacuum pump 34 in known manner. The condensate is led off through the conduit 35.

Instead of oxygen, hydrogen peroxide, for example, may be used as oxidant. In this case both the fuel and the oxidant may be stored as liquids at normal pressure. The decomposition heat when the hydrogen peroxide splits to from oxygen and water, which can be done, for example, with platinum as catalyst, can advantageously be used for the catalytic splitting of the hydrogen gas from the hexahydrobenzene or other hydroaromatic hydrocarbon used.

Instead of the cooler 24 the separation of the hydrogen gas and benzene can be done by means of a membrane which is only permeable to hydrogen gas. This membrane may consist, for example, of palladium-silver and is suitably arranged in the immediate vicinity of the reactor so that it obtains the required operating temperature in a simple manner. The hydrogen gas is led from behind the membrane to the fuel cell, while the benzene remains at the front of the membrane and is led to a smaller cooler to be condensed and carried to the storage tank 36.

A fuel cell battery usually consists of a very large number of fuel electrodes and oxidant electrodes stacked successively with spaces for fuel, oxidant and electrolyte between them. Part of such a fuel cell battery is shown in FIG. 2. It contains the porous fuel electrodes 40 consisting of, for example, nickel activated with platinum and the porous oxidant electrodes 41 consisting of, for example nickel activated with silver. The electrodes 40 are attached in the frames 42 and the electrodes 41 in the frames 43. The frames may consist, for example, of a thermosetting resin. The frames are held together by clamp means, not shown, in the stacking direction and may be sealed to each other, for example by O-rings or by welded joints of thermosetting resin. The electrodes are connected by outer conductor rails, not shown, either in series with each other or in parallel. The porous electrodes 40 form separating walls between the fuel in the gas chamber 44 and the electrolyte in the electrolyte chamber 45. In the same way the porous electrodes 41 form separating walls between the oxidant in the gas chamber 46 and the electrolyte in the electrolyte chamber 45.

The fuel, that is the hydrogen gas, is led through the channel 47 connected to the conduit 25, into the gas chamber 44 and is withdrawn through the channel 48 connected to the conduit 26. Oxidant, that is oxygen gas, is supplied through the channel 49 connected to the conduit 29, to the gas chamber 46 and withdrawn through the channel 50 connected to the conduit 30. The electrolyte, with the electrode material used in the example for instance potassium hydrate, is supplied through the channel 51 to the electrolyte chamber 45 and withdrawn through the channel 52. The electrolyte thus flows in an outer circulation circuit which is not shown in FIG. 1. FIG. 3 shows a suitable way of arranging the power transmission from the first propulsion system with the DC motor and the second propulsion system with the turbine. The motor 14 comprises a stator 60 and a rotor 61. The stator 60 is journalled by means of bearings 62 directly on the propeller shaft 15. The rotor 61 is supported by a hollow shaft 63 which is also journalled on the propeller shaft 15 by means of bearings 64. With the help of a coupling 65 the rotor 61 can be connected to the shaft 15 or disconnected from it. If it is not desired to disconnect the motor 14 from the propeller shaft 15, the coupling 65 may be made permanent. As previously described, the turbine 16 is connected to the propeller shaft 15 over the gear 18 and coupling 19. The propeller shaft can thus be driven either by the motor 14 or the turbine 16, or by both simultaneously.

Claims

I claim:

1. Method of supplying a propulsion device with fuel, said propulsion device comprising a fuel cell battery and a first propulsion system comprising an electric motor which is supplied with current from said fuel cell battery and a second propulsion system comprising machinery with a combustion chamber for combustion of a hydrocarbon fuel, which comprises storing the fuel of the propulsion device near the propulsion device in the form of at least one hydroaromatic hydrocarbon, splitting said hydroaromatic hydrocarbon to form a mixture consisting essentially of hydrogen and the corresponding aromatic hydrocarbon, supplying the hydrogen produced as fuel to the fuel cell and supplying the aromatic hydrocarbon produced as fuel to the machinery with the combustion chamber.

2. Method according to claim 1, in which hexahydrobenzene is the hydroaromatic hydrocarbon.

3. Method according to claim 1, in which decahydronaphthalene is the hydroaromatic hydrocarbon.

4. Method according to claim 1, in which tetrhydronaphthalene is the hydroaromatic hydrocarbon.

5. Method according to claim 1, in which the hydroaromatic hydrocarbon fuel consists essentially of a mixture of at least two of the substances selected from the group consisting of hexahydrobenzene, decahydronaphthalene and tetrahydronaphthalene.