DRIVE SYSTEM FOR AN AIRCRAFT, AIRCRAFT HAVING A DRIVE SYSTEM AND METHOD FOR OPERATING AN AIRCRAFT

Abstract

The invention relates to a drive system for an aircraft which is constructed for operation with a liquid fuel and a gaseous fuel, including at least one engine having a combustion chamber for operation with the liquid fuel and/or the gaseous fuel and per fuel at least one separate tank chamber which is or can be brought into connection in flow terms with the combustion chamber via a fuel line for supplying it with the corresponding fuel.

A drive system which is optimized in terms of emissions and efficiency can be provided in that the drive system is constructed in such a manner that, in the event of firing at a great height, exclusively gaseous fuel is or can be used in the at least one engine during a firing operation at a great height.

Claims

1. A drive system for an aircraft which is constructed for operation with a liquid fuel and a gaseous fuel, comprising at least one engine having a combustion chamber for operation with the liquid fuel and/or the gaseous fuel and per fuel at least one separate tank chamber which is or can be brought into connection in flow terms with the combustion chamber via a fuel line for supplying it with the corresponding fuel, wherein the drive system is constructed in such a manner that, in the event of firing at a great height, exclusively gaseous fuel is or can be used in the at least one engine during a firing operation at a great height.

2. The drive system according to claim 1, wherein a minimum quantity of gaseous fuel can be or is stored in the drive system and is or can be used exclusively in the event of firing at a great height.

3. The drive system according to claim 2, wherein at least one additional tank chamber, which is or can preferably be brought via a separate additional fuel line into connection with the combustion chamber in flow terms, is provided for storing the minimum quantity.

4. The drive system according to claim 3, wherein at least one additional tank chamber is provided per available engine.

5. The drive system according to claim 3, wherein the additional tank chamber is arranged on the respective engine, with which the additional tank chamber is associated or at another location within the aircraft.

6. The drive system according to claim 3, wherein the additional tank chamber is constructed in a pressure-resistant additional tank container.

7. The drive system according to claim 6, wherein the additional tank container is constructed so as to comprise metal, in particular high-grade steel, and/or to include metal, or Is constructed so as to comprise plastics material, in particular reinforced plastics material, for example, polyamide and/or to include plastics material.

8. The drive system according to claim 3, wherein the volume of the where applicable respective additional tank chamber is configured in such a manner that at least, preferably precisely, one partial minimum quantity for carrying out, preferably precisely, at least one firing operation at a great height in the associated engine, can be or is stored.

9. The drive system according to claim 1, wherein the combustion chamber volume inside the combustion chamber is configured for the firing at a great height with the gaseous fuel, wherein the combustion chamber volume is constructed to be at least 10% smaller, preferably at least 20% or at least 30% smaller, for example, up to 50% smaller, than with a configuration of an equivalent engine for the firing at a great height with the liquid fuel.

10. The drive system according to claim 1, wherein the drive system is configured to operate with a kerosene-based and/or kerosene-like fuel as the liquid fuel and/or to operate with hydrogen and/or methane or a gas admixture which has at least one of these gases as the gaseous fuel.

11. An aircraft having a drive system according to claim 1.

12. A method for operating an aircraft which can be operated by means of a drive system which is constructed in particular according to claim 1, alternatively or simultaneously with a liquid fuel and a gaseous fuel, wherein at least one combustion chamber of at least one engine is supplied with the fuel(s) used via a fuel line from a separate tank chamber, wherein in the event of a firing at a great height, exclusively gaseous fuel is used in the at least one engine during a firing operation at a great height.

13. The method as claimed in claim 12, wherein a minimum quantity, which is stored in the drive system, of gaseous fuel is used for the firing operation at a great height.

14. The method as claimed in claim 12, wherein in the event of firing at a great height, there is connected in an additional fuel line an additional valve, via which a partial minimum quantity of gaseous fuel as required for the firing operation at a great height of the corresponding engine is directed out of an additional tank chamber to the combustion chamber, wherein in particular the pressure of the fuel is throttled via an interposed additional pressure reduction device to a pressure level which is necessary for the firing at a great height.

Description

[0029] The invention will be explained in more detail hereunder by means of exemplary embodiments with reference to the drawings, in which:

[0030] FIG. 1 shows an aircraft having a drive system which is constructed for operation with a liquid fuel and a gaseous fuel according to the prior art as a schematic illustration, and

[0031] FIG. 2 shows an aircraft according to the invention with a drive system comprising a separate additional tank chamber for storing gaseous fuel for firing at a great height as a schematic illustration.

[0032] FIG. 1 shows a schematic illustration of an aircraft 1 having a drive system 11 which is constructed for operation with a liquid fuel and a gaseous fuel as generally known from the prior art.

[0033] The liquid fuel is particularly a kerosene-based or kerosene-like fuel (that is to say, a fuel comparable with kerosene). The gaseous fuel is particularly hydrogen and/or methane or another highly reactive gas or a gas admixture which has at least one of these gases.

[0034] The drive system 11 has for the gaseous fuel a tank chamber 3 in a tank container 30 which is connected in flow terms via a fuel line 5.1 to a combustion chamber 6 of an engine 2 of the drive system 11 for supplying it during operation with the gaseous fuel. For the liquid fuel, the drive system 11 has a tank chamber 4 in a tank container 40 which is connected in flow terms via a fuel line 5.2 to the combustion chamber 6 of the engine 2 for supplying it during operation with the liquid fuel.

[0035] The aircraft 1 can be operated both alternatively with one of the two fuels, that is to say, exclusively with the liquid fuel or the gaseous fuel, and simultaneously with an admixture of the two fuels.

[0036] For this purpose, at least one engine 2 or generally all the engines 2 present in the drive system 11 of the aircraft is/are in the form of a so-called dual fuel engine 2. In this instance, a gas turbine arrangement with the combustion chamber 6 of the respective engine 2 is configured in such a manner that it can be operated in every operating situation with each of the two fuels, that is to say, during take-off, cruising, landing, etc., irrespective of the external conditions, such as pressure, temperature and height. This also includes the fact that the engine 2 can start both with the gaseous fuel and with the liquid fuel, similarly irrespective of the external conditions, that is to say, also at a great height (for example, 30,000 ft), that is to say, during firing at a great height.

[0037] In order to ensure reliable firing at a great height of the combustion chamber 6 at a height, for example, of 30,000 ft with the liquid fuel, a combustion space of the combustion chamber 6 must have a comparatively large volume. In order to ensure safe flight operation, the combustion chamber 6 is configured for the emergency situation of firing at a great height, in accordance with which the combustion space volume is directed. Accordingly, the combustion chamber 6 has a comparatively large construction size with a great combustion space volume which has a disadvantageous effect on the NOx emissions, the spatial requirement in the engine 2, the weight and the costs of the combustion chamber 6 and therefore of the entire engine 2. Furthermore, the degree of efficiency of the combustion chamber 6 in the event of firing with kerosene as the liquid fuel under firing conditions at a great height is very low (less than 30%) so that large quantities of kerosene during the start operation of the engine remain unburnt.

[0038] For the benefit of the emission level and the combustion efficiency, it is proposed according to the invention to fire the combustion chamber 6 exclusively with the gaseous fuel in the event of firing at a great height. The gaseous fuel generally has a very much higher reactivity (for example, characterized by a firing delay time or a flame speed) and a substantially greater firing range (for example, characterized by the firing limits) than the liquid fuel so that the combustion of the gaseous fuel can also be carried out substantially more efficiently at low load points and in the sub-atmospheric region and at a great height. Furthermore, the combustion space volume of the combustion chamber 6 can advantageously be configured for firing at a great height with hydrogen or another generally (comparatively) highly reactive fuel and not for firing at a great height with kerosene, which allows a smaller combustion space volume and therefore a combustion chamber 6 with a smaller construction size.

[0039] In this case, it is extremely advantageous to ensure in technical safety terms that at any time for each engine 2 which is intended to be fired during firing at a great height a sufficient quantity of gaseous fuel is present, irrespective of how much gaseous fuel is still available for the onward flight.

[0040] The sufficient quantity is referred to below as a minimum quantity. The minimum quantity forms the quantity, which is required for firing of all the engines 2 intended to be fired during a firing operation at a great height (or a plurality of firing operations at a great height), of gaseous fuel. In this instance, a corresponding partial minimum quantity is required for firing at a great height of a single engine 2.

[0041] The partial minimum quantity for a firing operation at a great height per engine 2 is the quantity which is required in order to achieve firing and start-up of the engine 2 to an idling state and varies depending on the size, in particular thrust, of the engine 2 and the duration of the firing operation at a great height. Typically, a firing operation at a great height (firing and start-up of the engine 2 to an idling state) takes, for example, from 60 seconds to 180 seconds for starting up an engine 2 (with, for example, up to 100 klbf full load thrust).

[0042] FIG. 2 shows a construction according to the invention of the aircraft 1 having a drive system 11 which is constructed in such a manner that the minimum quantity of gaseous fuel which is used exclusively in the event of firing at a great height is stored.

[0043] In FIG. 2, there is provided according to a preferred variant at least one additional tank space 7 in which the minimum quantity is stored. Preferably, at least one additional tank chamber 7 is present per engine 2 which is intended to be fired during the firing at a great height. The respective additional tank chamber 7 stores the partial minimum quantity which is sufficient for at least one firing operation at a great height of the corresponding engine 2.

[0044] The combustion space volume of the combustion chamber 6 is configured for firing at a great height with the gaseous fuel, not for liquid fuel, and consequently has, for example, a combustion space volume which is smaller by at least 10% or 20%, for example, by up to 50%, than a combustion chamber 6 which is configured for the equivalent engine 2 for the firing at a great height with the liquid fuel.

[0045] The additional tank chamber 7 can be arranged on the respective engine 2, with which the additional tank chamber is associated (in particular inside the external engine covering) or at a different location within the aircraft 1. The additional tank chamber 7 is preferably arranged separately from the tank chamber 3 and the tank chamber 4.

[0046] The additional tank chamber 7 is connected to the combustion chamber 6 via a separate additional fuel line 10. An additional valve 8 and an additional pressure reduction device 9 are arranged in the additional fuel line 10.

[0047] In the event of firing at a great height, the additional valve 8 is switched and the flow connection between the additional tank chamber 7 and the combustion chamber 6 is therefore produced by means of the additional fuel line 10. The gaseous fuel is directed to the combustion chamber 6 via the additional fuel line 10, wherein the pressure of the gaseous fuel is throttled via the additional pressure reduction device 9 to a pressure level, which is necessary for the firing, of, for example, up to 15 bar excess pressure.

[0048] In the example shown in FIG. 2, the additional tank chamber 7 is constructed in a pressure-resistant additional tank container 70 which is arranged separately from the tank containers 30 and 40, in this case by way of example on the engine 2. In the case of hydrogen as the gaseous fuel, the additional tank container 70 is configured, for example, for a maximum storage pressure between 300 bar and 700 bar. The additional tank container 70 comprises metal, in particular high-grade steel, and/or is constructed so as to include metal. Alternatively, the additional tank container 70 comprises in particular, for example, plastics material which is reinforced with glass fibre, for example, polyamide, and/or is constructed so as to include plastics material.

[0049] The volume of the additional tank chamber 7 is configured in such a manner that the partial minimum quantity for at least one firing operation at a great height can be stored. Consequently, the volume of the additional tank chamber 7 is directed towards the characteristics of the engine 2, in particular the fuel consumption thereof during the firing operation at a great height.

[0050] By way of example, the necessary partial minimum quantity of hydrogen during a firing operation at a great height for firing and starting up the engine 2 (full-load thrust approximately 20 klbf) to flight idle within 90 seconds is approximately 0.8 kg. This corresponds to a hydrogen volume of approximately 20 l at a storage pressure of 700 bar. The additional tank chamber 7 is consequently configured for a volume of approximately 20 l, wherein it may have, for example, a diameter of approximately 20 cm and a length of approximately 70 cm.

[0051] For a relatively large engine, for example, the additional tank chamber 7 may be configured to be larger or a plurality of additional tank chambers 7 of the same size may be provided (not shown in FIG. 2).

[0052] The size of the additional tank chamber 7 or all the necessary additional tank chambers 7 is so small that, when the combustion chamber 6 is configured with the reduced combustion space volume in total, a total weight saving is possible.

[0053] The storage of the minimum quantity is also possible in technical control terms by obtaining a minimum filling level in the tank chamber 3, wherein no additional tank chamber 7 is present (not shown in FIG. 2).

[0054] By means of the modified construction of the drive system 11 in relation to the ability to fire at a great height not for both fuels, but instead only with the gaseous fuel, it is possible to configure the combustion chamber 6 with a substantially reduced volume. This is associated with a decreasing dwell time of the air/fuel admixture within the combustion chamber 6 and consequently a reduction of the NOx emissions. Furthermore, the engine weight and associated costs can be reduced.

LIST OF REFERENCE NUMERALS

[0055] 1 Aircraft [0056] 2 Engine [0057] 3 Tank chamber [0058] 30 Tank container [0059] 4 Tank chamber [0060] 40 Tank container [0061] 5.1 Fuel line [0062] 5.2 Fuel line [0063] 6 Combustion chamber [0064] 7 Additional tank chamber [0065] 70 Additional tank container [0066] 8 Additional valve [0067] 9 Additional pressure reduction device [0068] 10 Additional fuel line [0069] 11 Drive system