High frequency-stabilized combustion in aircraft gas turbines

A gas turbine includes a combustion chamber and a microwave source to produce microwave radiation. The gas turbine is arranged to guide the microwave radiation into a cavity of the combustion chamber. Due to the microwave radiation, in the cavity of the combustion chamber, combustion in the cavity may be supported and thus lean operation of the gas turbine is made possible.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. §119 to German application number 10 2013 010 706.7, filed Jun. 27, 2013, the entire disclosure of which is herein expressly incorporated by reference.

BACKGROUND OF THE INVENTION

Exemplary embodiments of the invention relate to a gas turbine with a microwave source, an aircraft with a gas turbine, use of a microwave source to produce microwave radiation for a drive device, an electronic control for a gas turbine, and a method for controlling a gas turbine.

One requirement for gas turbines, especially aircraft gas turbines, is fuel efficient and low emissions operation. One possibility for this is operating the gas turbine with the highest possible excess air, i.e. lean operation.

One potential way to have lean operation is staged combustion. In staged combustion, a pilot flame with subsequent injection of the primary fuel quantity may be used to attain better homogenization, and, as a result of the intermediary combustion species, from the pilot flame the mixture may be rendered leaner. The pilot flame may be a kerosene flame, a hydrogen flame, or even a plasma-supported flame. Providing staged combustion may necessitate an extended combustion chamber.

SUMMARY OF THE INVENTION

Exemplary embodiments of the invention are directed to reducing fuel consumption of gas turbines.

In the following, operation with a large amount of excess air in the fuel-air mixture is also called lean operation. In the following the fuel-air ratio at which the combustion in the combustion chamber extinguishes without the introduction of microwaves or other measures is called the lean extinction limit.

A gas turbine is disclosed having a cavity for receiving and burning a fuel-air mixture. In addition, the gas turbine has a microwave source for producing microwave radiation, wherein the gas turbine is embodied to guide the microwave radiation into the cavity of the combustion chamber to support the combustion of the fuel-air mixture in the combustion chamber.

The combustion chamber may be, for example, an annular combustion chamber that extends annularly about the engine. Furthermore, the combustion chamber may be embodied as a can-type combustion chamber or as a can-annular combustion chamber, wherein a plurality of combustion chambers may be provided in the engine.

In the following, the term “microwave source” may also designate a high-frequency source for producing electromagnetic radiation. The microwave source may be e.g. a magnetron, a klystron tube, a Gunn diode, or an IMPATT diode. For instance, standard components for producing microwaves may be used for microwave sources. A magnetron may produce e.g. microwaves in the range of 0.9 to 25 GHz.

The microwave source may be disposed inside or outside of the combustion chamber. Furthermore, the microwave source may be disposed outside of the gas turbine, wherein the produced microwave radiation is guided to the combustion chamber of the gas turbine.

Introducing the microwave radiation into the cavity of the combustion chamber makes it possible to maintain lean operation. In other words, combustion in the combustion chamber, wherein the air portion in the fuel-air mixture is high, is made possible.

The microwave radiation introduced may cause coupling of ions, electrons, and/or neutral combustion fragments, e.g. OH, CH, CH2. This can make it possible to maintain a combustion reaction at a lean extinction limit.

Energy is supplied to the ions, electrons, and/or combustion fragments by the microwave radiation introduced, and this activates the fuel. The molecules absorb the energy and are activated, which supports and/or accelerates combustion. For instance, the molecules are activated using rotation energy, are caused to rotate and/or vibrate, so that the combustion reaction is enabled at the lean extinction limit.

In accordance with one embodiment of the invention, the microwave source is arranged outside of the combustion chamber.

By arranging the microwave source outside of the combustion chamber, the microwave source is not subjected to the high temperature in the combustion chamber. This makes it possible, for example, to use a standard component for the microwave source.

In accordance with another embodiment of the invention, the combustion chamber has a microwave-permeable window that is embodied to let the microwave radiation into the cavity of the combustion chamber.

The microwave-permeable window comprises for instance ceramics, quartz, Al2O3, sapphire, or a combination of these materials.

Providing a microwave-permeable window permits the microwave source to be attached outside of the combustion chamber and/or microwave radiation to be introduced into the cavity of the combustion chamber. For instance, the combustion chamber has a plurality of microwave-permeable windows that are arranged on the combustion chamber annularly about a rotational axis of the gas turbine.

In accordance with another embodiment of the invention, the gas turbine has a horn antenna for radiating the microwave radiation into the cavity of the combustion chamber.

The horn antenna is, for example, attached to the microwave source or connected to the microwave source. Moreover, the horn antenna may be disposed outside of the combustion chamber on a microwave-permeable window so that the horn antenna can radiate the microwave radiation into the cavity of the combustion chamber.

In accordance with another embodiment of the invention, the gas turbine has a waveguide for guiding the microwave radiation from the microwave source to or into the combustion chamber.

This makes it possible for the microwave source to be a certain distance from the combustion chamber. For instance, the microwave source may be 10-30 cm from the combustion chamber. The microwave radiation may be guided with the waveguide from the microwave source to the combustion chamber and radiated by the waveguide into the cavity of the combustion chamber. Moreover, the microwave radiation may be guided by a waveguide to a horn antenna and radiated by the horn antenna into the cavity of the combustion chamber.

In accordance with another embodiment of the invention, the gas turbine has a plurality of microwave sources that are arranged annularly about a rotationally symmetrical axis of the gas turbine.

The annular arrangement of the microwave sources may, for example, describe an arrangement of the microwave sources on a circular path. The center point of this circular path is defined e.g. by a rotational axis of a drive shaft of the gas turbine.

For instance, the gas turbine has 8 microwave sources arranged annularly, as seen from the rotational axis, outside of the combustion chamber.

In accordance with another embodiment of the invention, the microwave source is embodied to produce the microwave radiation with a frequency between 1 and 100 GHz.

In accordance with another embodiment of the invention, the microwave source is embodied to produce pulsed microwave radiation.

The pulsed microwave radiation is absorbed by the fuel molecules and/or the oxygen molecules. The energy supplied by the pulsed microwaves is absorbed and the molecules are caused to vibrate and/or rotate so that the combustion reaction is made possible at the lean extinction limit.

In accordance with another embodiment of the invention, the gas turbine is an aircraft gas turbine.

The invention furthermore relates to an aircraft having a gas turbine described above and in the following.

The aircraft may be an airplane or a helicopter, for instance.

The invention furthermore relates to the use of a microwave source to produce microwave radiation, wherein the microwave radiation is guided into a cavity of a combustion chamber for a drive device of an aircraft.

The drive device is, for example, a gas turbine, a motor for driving a propeller, or a turboprop mechanism.

The invention furthermore relates to an electronic control for a gas turbine, wherein the gas turbine has a combustion chamber with a cavity for receiving and igniting a fuel-air mixture and has a microwave source for producing microwave radiation. Furthermore, the cavity is embodied to receive the fuel-air mixture and the microwave radiation and the electronic control is embodied for regulating the microwave source. A suitable sensor system is provided for this to make it possible for the control to evaluate when the microwave source should be activated.

For instance, the electronic control is designed to determine when the gas turbine should and/or may be operated in a lean operation. In the lean operation the electronic control may for instance activate the microwave source so that lean operation of the gas turbine is provided.

For instance, the electronic control is designed to determine the flying altitude so that lean operation of the gas turbine may be activated at a certain flying altitude. The electronic control may, for example, also determine the current operating mode of the gas turbine, for example whether the turbine must operate at full capacity for starting the aircraft or whether the turbine may be operated in a saving mode or in lean operation. As a result the electronic control may activate the microwave source for the lean operation.

Thus flexible and/or optimal operation of the gas turbine is made possible using the electronic control. The operation of the gas turbine may accordingly be adapted to the current requirement for performance and/or fuel consumption.

The invention furthermore relates to a method for controlling a gas turbine wherein the method has the steps of determining an oxygen content of exhaust gases that are emitted by the gas turbine and regulating a microwave source as a function of the determined oxygen content of the exhaust gases. The method furthermore has the step of introducing the microwave radiation from the microwave source into a cavity of a combustion chamber of the gas turbine.

For instance, it may be determined whether the oxygen content of the exhaust gases exceeds a certain limit. In this case for example the output of the microwave source may be increased.

Thus automatic regulation of the microwave source is made possible. Measurement of the oxygen content in the exhaust gases may also make possible fine adjustment of the gas turbine.

The described exemplary embodiments also relate to a gas turbine, an aircraft having a gas turbine, use of a microwave source for a drive device of an aircraft, an electronic control for a gas turbine, and a method for controlling a gas turbine, regardless of whether individual embodiments are described exclusively with respect to a gas turbine.

Additional features, advantages, and potential applications of the invention result from the following description of the exemplary embodiments and drawings. All described and/or illustrated depictions of features constitute subject matter of the invention, alone or in any desired combination, even regardless of their composition in the individual claims or how they are referenced.

The drawings are diagrammatic and not to scale. In the following description, identical reference numbers used in different drawings indicate identical or similar elements. Identical or similar elements may also have different reference numbers, however.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In a combustion chamber of a gas engine, a flame that forms upstream of the entrance of air and fuel causes pre-evaporation of liquid fuel. This pre-evaporation of the liquid fuel may result in partial pre-mixing and/or partial homogeneity of a fuel-air mixture. Thus, the maximum occurring temperature of the combustion chamber may be lower than the temperature with diffusion flames, which may result in a reduction in the nitrogen oxides. However, when it is rendered very lean, i.e. when there is a high proportion of air in the fuel-air mixture, the flame may extinguish.

Reduced temperature of the combustion chamber may lead to a reduction in the nitrogen oxides. In particular Zeldovich nitrogen oxides and prompt nitrogen oxides may be reduced. Fuel nitrogen oxides may not be affected. On the other hand, portions of non-combusted hydrocarbons and carbon oxides increase, which may limit the operating range of the fuel-air ratio. This may derive from poor reaction kinetics due to reduced temperature, since the reaction speed is proportional to the exponential function of the inverse temperature. Consequently, when there is a large amount of excess air and the flame temperature is low, the reaction speed may be reduced and the combustion may therefore extinguish.

FIG. 1depicts a cross-section of a gas turbine101in accordance with one exemplary embodiment of the invention. The gas turbine has a compressor102that is embodied to compress the incoming air and then to guide it into the combustion chamber104. The compressor102includes a plurality of blades120with compressor vanes, wherein the blades120are attached axially to a drive shaft121. Moreover, the gas turbine has a combustion chamber104that is attached, for example, annularly behind the compressor102. Disposed in the combustion chamber104is the cavity of the combustion chamber119, in which the combustion of the fuel-air mixture takes place. The combustion chamber104furthermore has a first nozzle105and a second nozzle106for supplying fuel, for instance kerosene. For igniting the fuel-air mixture in the combustion chamber104, the combustion chamber104furthermore has a first igniter117and a second igniter118. For admitting microwave radiation into the combustion chamber104, the combustion chamber furthermore has a first microwave-permeable window107and a second microwave-permeable window108. Outside of the combustion chamber104is a first microwave source109with a horn antenna111and a second microwave source110that guides the microwave radiation to the combustion chamber with a waveguide112. The horn antenna111and the waveguide112are arranged at the first and second microwave-permeable windows107and108, respectively. The gas turbine may have additional nozzles, igniters, microwave-permeable windows, and microwave sources that are arranged about the drive shaft121. Disposed behind the combustion chamber104is the turbine103, which has blades122that are connected axially to the drive shaft121.

As the arrow113depicts, air is drawn in due to the rotation of the blades120of the compressor102. The arrows115and116depict the air that is compressed by the compressor102and guided into the combustion chamber104. In the cavity119of the combustion chamber104fuel is supplied to the compressed air through the nozzles105and106. The resultant fuel-air mixture is ignited by the igniters117and118. To support the combustion, the microwave sources109and110produce microwave radiation, which is radiated by the horn antenna111or by the waveguide112through the windows107and108into the cavity. The gases from the combustion of the fuel-air mixture are then guided to the turbine103for driving the gas turbine and then out of the gas turbine101, as the arrow114depicts.

FIG. 2depicts a gas turbine101with a combustion chamber104, wherein a first microwave source109and a second microwave source110are positioned outside of the combustion chamber.

Also depicted is a control device201that has a processor202. The control device is connected with a first line205to the first microwave source109and with a second line206to the second microwave source110. In addition, the control device has an antenna207and the first microwave source has a second antenna208, so that the first microwave source109and the control device201may exchange data wirelessly. The control device201is embodied for controlling the microwave sources109and110via the lines205and206and via the wireless connection with the antennas207and208. Moreover, the control device201is connected to a reading device203for a computer-readable medium204, for instance a CD.

FIG. 3is a flowchart for a method in accordance with one exemplary embodiment of the invention. The method has a step301for determining a physical parameter, for instance the oxygen content of exhaust gases that are emitted by the gas turbine, the flying altitude, or the efficiency of the gas turbine, and a step302for regulating a microwave source as a function of the determined oxygen content of the exhaust gases. The method furthermore has a step of303for introducing the microwave radiation into a cavity of a combustion chamber of the gas turbine.

FIG. 4depicts an aircraft401in accordance with one exemplary embodiment of the invention. The aircraft401has a first turbine101and a second turbine402. To support the combustion in the combustion chamber104, the first turbine has a microwave source109and the second turbine402has a microwave source403. In addition, the aircraft contains a control device201for controlling the microwave sources109and402. For controlling the microwave sources109and402, the control device201is connected to the microwave source109via a first line205and to the microwave source403via a second line404.

FIGS. 5, 6 and 7depict different segments of a part of a gas turbine101in accordance with another exemplary embodiment of the invention.

FIG. 5depicts a combustion chamber104with a cavity119. The combustion chamber104is arranged annularly about a rotational axis and a drive shaft that are disposed below the visible area of the drawing. In addition, igniters117are attached to the combustion chamber104. A first microwave source109is attached to the combustion chamber104outside of the gas turbine and combustion chamber104as seen from the rotational axis.

The first microwave source109has a short-circuit switch502. In addition, the first microwave source109is connected to an antenna111that projects into a first chamber504. As seen from the rotational axis, the first chamber504is attached to the combustion chamber104outside of the combustion chamber104. Disposed inside the first chamber504is a second chamber503that is attached to the combustion chamber104. A plurality of microwave-permeable windows107are added to a limiting surface between the combustion chamber104and the second chamber503. In addition, the second chamber has a plurality of slits501that are arranged opposing the microwave-permeable windows107.

FIG. 6depicts an enlarged segment of the gas turbine101in which the first chamber504and the second chamber503are shown. It may also be seen inFIG. 6that a second microwave source601is arranged on the combustion chamber104on a circle about the rotational axis of the drive shaft. The second microwave source also has an ignition switch602and an antenna (not shown in this segment).

FIG. 7depicts a segment of the gas turbine101, wherein the first chamber504is depicted in a semi-transparent manner. The second chamber503is disposed inside the first chamber504. In addition, added to the second chamber503are slits501that are arranged annularly about the axis of rotation of the drive shaft.

In addition, the first microwave source109, the second microwave source601, and a third microwave source701are shown and are arranged annularly about a rotational axis of the drive shaft. The third microwave source701also has an antenna702and an ignition switch703.

It should also be noted that “including” or “having” does not exclude any other elements and “a” or “an” does not exclude more than one. In addition it should be noted that features that have been described referring to one of the above embodiments or exemplary embodiments may also be used in combination with other features of other embodiments or exemplary embodiments described above. Reference numbers in the claims shall not be construed as limitations.