BACKGROUND

[0001] 1. Field

[0002] Disclosed embodiments are generally related to gas turbine combustors and, more particularly to the application of ultrasonic waves in the gas turbine combustors.

[0003] 2. Description of the Related Art

[0004] Gas turbine engines employ dry low emissions (DLE) combustion in order to achieve stable, low emissions combustion for both gas and liquid fuels without water or steam injection. DLE gas turbine engines use lean premixed combustion to minimize nitrogen oxides and carbon monoxide emissions by maintaining uniform, low flame temperatures. Lean premixed combustion involves pre-mixing fuel with excess air before burning in the combustor chamber of a gas turbine engine. However, mixing fuel and air upstream of the combustion chamber produces a flammable mixture which at high pressures and temperatures typical of gas turbine engines can auto-ignite very rapidly. The time in which auto-ignition may occur reduces with the temperature and pressure of the mixture. Auto-ignition can prove to be a problem for gas turbine engines when using the types of natural gas usually used in gas turbine engines and can become even more problematic with more reactive fuels such as fuels with higher hydrocarbons.

[0005] Auto-ignition in the pre-mixer ducts located upstream of the combustion chamber is not desirable. During auto-ignition a flame can develop and stay in the pre-mixer ducts resulting in severe damage to the injector hardware. Therefore, fuel and air mixing is preferably achieved rapidly, on the order of milliseconds. The resulting mixture is also preferably convected into the combustion chamber rapidly as well. Additionally the pre-mixer ducts should be clean so as to improve aerodynamics and avoid recirculation zones where the flammable mixture could stay longer than its auto-ignition time. Additionally mixing is ideally achieved with minimum flow pressure drop as pressure drop can have a direct impact on gas turbine cycle efficiency. SUMMARY

[0006] Briefly described, aspects of the present disclosure relate to ultrasonic waves used in gas turbine engines.

[0007] An aspect of the disclosure may be a gas turbine engine having a premix injector connected to a combustion chamber, wherein the premix injector comprises, a mixing duct; a fuel inlet connected to the mixing duct; an air inlet aperture for injecting air into the mixing duct; a fuel injector for supplying fuel into the mixing duct; a first transducer connected to the premix injector at a first location, wherein the first transducer comprises a piezoelectric crystal; and a waveguide concentrator operably connected to the premix injector; and a rod operably connected to the waveguide concentrator, wherein the first transducer generates ultrasonic waves that are transmitted via the waveguide concentrator and the rod into the mixing duct for enhancing fuel-air mixing therein.

[0008] Another aspect of the present invention may be a method for mixing fuel and air in in a gas turbine engine comprising; actuating a first transducer having a piezoelectric crystal; transmitting ultrasonic waves to the premix injector via a waveguide concentrator and a rod; and adjusting a parameter of the ultrasonic waves transmitted by the first transducer to the premix injector, wherein the adjusting of the parameter of the ultrasonic waves achieves a desired level of fuel air mixing in the premix injector.

[0009] Still another aspect of the present invention may be a method for cleaning gas turbine engines comprising; actuating a first transducer comprising a piezoelectric crystal, transmitting ultrasonic waves via a waveguide concentrator and a rod, wherein the rod is connected to a component of gas turbine engine having deposits located thereon, and cleaning the deposits located on the component.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Fig. 1 shows a diagram of a premix injector and combustion chamber of a gas turbine engine.

[0011] Fig. 2 shows a schematic of a transducer made in accordance with an embodiment of the invention. [0012] Figs. 3A-3D show diagrams illustrating control of different parameters of the ultrasonic wave.

[0013] Fig. 4 is a diagram of a transducer and waveguide concentrator.

[0014] Figs. 5A-5C are diagrams illustrating different shapes of the waveguide concentrator.

[0015] Fig. 6 shows a surface of the premix injector having grooves formed therein.

[0016] Fig. 7 is a diagram illustrating grooves formed in the surface of components of the combustor having a half-step profile.

[0017] Fig. 8 is a flow chart of a method for transmitting ultrasound waves.

[0018] Fig. 9 shows a diagram of a premix injector and combustion chamber of a gas turbine engine having liquid fuel passages.

[0019] Fig. 10 is a flow chart of the method for cleaning components of the combustion chamber.

DETAILED DESCRIPTION

[0020] To facilitate an understanding of embodiments, principles, and features of the present disclosure, they are explained hereinafter with reference to implementation in illustrative embodiments. Embodiments of the present disclosure, however, are not limited to use in the described systems or methods.

[0021] The components and materials described hereinafter as making up the various embodiments are intended to be illustrative and not restrictive. Many suitable components and materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of embodiments of the present disclosure.

[0022] There is a need to overcome the limitations found in existing gas turbine engines and in their premix injectors with respect to size, complexity, number of parts and emissions. The transmission of ultrasonic waves in gas turbine engines seeks to improve the performance of gas and/or liquid fuel turbine engines. The transmission of ultrasonic waves in DLE pre-mixers seeks to improve air and fuel (gaseous or liquid) mixing in primary and secondary mixing ducts as well as improve the reactivity of air and fuel in the combustion zone. One of the benefits of the improved mixing and combustion is the concurrent reduction of NOx and CO emissions. Additional benefits of transmitting ultrasonic waves to the gas turbine engines can be the removal of coking deposits from the components of the gas turbine engine.

[0023] Fig. 1 shows a combustor 100 of a gas turbine engine in which ultrasonic waves from transducers 45 are applied in order to enhance fuel mixing. The combustor 100 shown in Fig. 1 is a DLE combustor that has a premix injector 10 and combustion chamber 35. While the application of the transmission of ultrasonic waves disclosed herein is discussed with respect to a DLE combustor it should be understood that the ultrasonic gas mixing can be applied to other types of combustors as well, including liquid fuel combustors.

[0024] The pre-mix injector 10 has a fuel manifold 14 and a mixing duct 12. The fuel manifold 14 is supplied with gaseous or liquid fuel via a fuel inlet 16. The gaseous or liquid fuel is supplied from a fuel supply (not shown). The fuel manifold 14 shown in Fig. 1 has a manifold inner wall 22 and a manifold outer wall 24. Both the manifold inner wall 22 and the manifold outer wall 24 are substantially annular. While the fuel manifold 14 is described as being substantially annular it should be understood that the shape of the fuel manifold 14 is not limited to an annular shape.

[0025] The premix injector 10 further includes a mixing duct 12, which mixes fuel and air. The mixing duct 12 is substantially annular and is bordered by the manifold outer wall member 24 and the mixing duct wall member 26. While the mixing duct 12 is described as being substantially annular the mixing duct 12 is not limited to an annular shape.

[0026] A number of air inlet apertures 28 in the mixing duct wall member 26 allow air 3 to flow into mixing duct 12. A number of circumferentially spaced fuel injectors 29 in the manifold outer wall member 24 allow fuel to enter mixing duct 12. Combustors using liquid fuel may have additional passages that also can benefit from the transmission of ultrasonic waves; this is discussed below with respect to Fig. 5. It should be understood that the number of air inlet apertures 28 and fuel injectors 29 may vary depending on the intended fuel supply and desired mixture of the combustor 100.

[0027] Fuel 4 enters the mixing duct 12 and mixes with air 3 flowing therein. The fuel-air mixture 5 flows through mixing duct 12 toward a plurality of spaced apart vanes 32 that divide mixing duct 12 into a plurality of outlet flow streams 7 entering the combustion chamber 35. The vanes 32 reduce the exit area of the mixing duct 12 prior to the combustion chamber 35 and further accelerate the outlet flow streams 7 to prevent flashback. The vanes 32 further direct outlet flow streams 7 exiting pre-mix injector 10. Each outlet flow stream 7 exits the premix injector 10 through an outlet window 34 leading to a combustion chamber 35. The fuel-air mixture that is the outlet flow stream 7 exiting the pre-mix injector 10 is a lean combustible mixture.

[0028] Additionally a secondary fuel 6 may be supplied from a fuel supply (not shown) into a secondary fuel manifold 17. Air 3 may also enter into the secondary fuel manifold 17 through air inlet apertures 28 and mix with the fuel 6 in the combustion chamber 35.

[0029] The mixing that occurs in the premix injector 10 may be enhanced by introducing ultrasonic waves into the premix injector 10. By ultrasonic waves it is meant waves having a frequency greater than 20 kHz. Preferably the ultrasonic waves are between the range of 20 kHz and 100 kHz. The ultrasonic waves may be produced using piezoelectric crystals 40 and/or tuned masses 42 which form the transducer 45.

[0030] An exemplary transducer is shown in Fig. 2A. The transducer 45 may be a bolt Langevin type of transducer built from a pair of piezoelectric crystals 40 stacked between tuned masses 42 using a bolt 41. The bolt 41 passes through the centers of the stacked piezoelectric crystals 40 and tuned masses 42 and joins the stack along an axial direction A. The number of piezoelectric crystals 40 used in the transducer 45 impacts the intended vibrational power level. Typically the more piezoelectric crystals 40 used the larger the power level generated by the piezoelectric crystals 40. For example, in order to obtain a power level of 100 W with a frequency of 34.8 kHz, one pair of piezoelectric crystals would be used. More piezoelectric crystals 40 would be able to obtain greater power levels, for example five pairs of crystals with a frequency of 34.8 kHz could obtain a power level of 500 W.

[0031] The vibrating power level generated by ceramic piezoelectric crystals 40 depends on the materials used and its design. Incorporated into the transducer 45 is as many pairs of piezoelectric crystals 40 as necessary in order to obtain the power level needed for a to achieve a desired level of fuel air mixing. [0032] Under a variable electrical field the piezoelectric crystals 40 change mostly along their axial length A, and acts as an axial actuator. The elastic element of the transducer 45 is the bolt 41 which is impacted by the pair of piezoelectric crystals 40 which increase or decrease their lengths and impact the high strength bolt 41. The bolt 41 has a dual role of keeping the piezoelectric crystals 40 and tuned masses 42 together and providing also the spring element of the transducer 45. In this manner the transducer 45 creates a complete axial sinusoidal ultrasonic wave with a nodal point between the pair of piezoelectric crystals 40 shown in Fig. 2A. The piezoelectric crystals 40 work in pairs because in this way they establish the nodal point of the ultrasonic wave at the mating faces between them, and they can be fed different polarities on their faces. The amplitude of crystal deformation depends on the electrical field intensity in the piezoelectric crystal 40, which increases with the current intensity. More pairs of piezoelectric crystals 40 can be added to increase mixing in the premix injector 10 by generating different ultrasonic waves.

[0033] The tuned masses 42 shown in Fig. 2 A may be made of a metallic material. The diameter and length of the tuned masses 42 depend on the working frequency of the piezoelectric crystals 40 and the speed of sound in the metallic material of the tuned masses 42. In Fig. 2A the tuned masses 42 correspond to the piezoelectric crystals 40 located between the tuned masses 42.

[0034] The transducers 45 can be made to work for more than a single frequency by using two groups of piezoelectric crystals 40 stacked between the tuned masses 42. For example, Fig. 2B shows a transducer 45 that can generate two frequencies that can be made from a first tuned mass 42a, a second tuned mass 42b and a third tuned mass 42c. A pair of piezoelectric crystals 40 is stacked between the first tuned mass 42a and the second tuned mass 42b and another pair of piezoelectric crystals 40 is stacked between the second tuned mass 42b and the third tuned mass 42c. Each of the tuned masses 42a, 42b and 42c has an equal diameter to the piezoelectric crystals 40.

[0035] Referring back to Fig. 1, more than one transducer 45 may be used and it should be understood that it is possible to use more than one transducer 45 at various locations on, or outside of, the combustor 100. The transducer 45 may be situated outside of the premix injector 10. For example, the transducer 45 may be fixed to a flange 43 or located within a flange 43. Flange 43 shown in Fig. 1 provides support for the reaction force of the combustor 100 The flange 43 may be located at a nodal point of the ultrasonic wave being transmitted. In the embodiment shown in Fig. 1 the nodal point of the flange 43 may be second nodal point of the ultrasonic wave generated by the transducer 45.

[0036] Transducer 45 may be connected with bolts 49 to the premix injector 10, or be brazed, or integrally formed with the premix injector 10. The transducer 45 may be cylindrical following the shape of the piezoelectric crystals 40. However, it should be understood that other shapes for the transducer 45 may be used depending on the ultrasonic waves desired. For example the transducer 45 may be rectangular, radial, or irregular. Further, one may use only one transducer 45 depending on the desired mixing to be achieved by ultrasonic waves.

[0037] Connected to the transducers 45 is a controller 55 which can control the frequency, phase and amplitude of the ultrasonic wave that is produced by the transducer 45. Controller 55 may be located remotely or proximate to the combustor 100. Figs. 3A-3D diagrammatically show interactions between the ultrasonic wave and the molecules of fuel and air that occur through various control features generated by the controller 55.

[0038] Fig. 3A shows an ultrasonic wave mixing an air molecule and fuel molecule (not to scale). It should be understood that Fig. 3 A is meant to illustrate the concept and that in actuality many air and fuel molecules are located between individual wave peaks. By controlling the input frequency of the electrical current transmitted into the piezoelectric crystals 40 the precise resonant tuning of the transducer 45 can be achieved. A pair of piezoelectric crystals 40 of certain dimensions typically produces only one frequency for the ultrasonic wave along with a small domain of frequencies around the one frequency which can be used to produce wave phase variation. The maximum axial elongation along axis A, shown in Fig. 2A, of the piezoelectric crystal 40 is achieved at resonance when the current frequency fed to the piezoelectric crystal 40 is the same as its nominal frequency (i.e. the center vibrational frequency of the piezoelectric crystal 40). Along the axis A of the piezoelectric crystal 40 the deformation takes place and generates a compression- decompression sinusoidal ultrasonic axial wave. When at resonance the maximum axial displacement amplitude is achieved and therefore the maximum mixing effect is obtained.

[0039] The variable phase may be controlled via controller 55. Fig. 3B diagrammatically shows the phase control of the ultrasound wave, with two ultrasound waves out of phase. Phase control permits the generation of ultrasound waves with variable phase so that the pattern of a stationary wave inside an air fuel mixture is broken and the nodes and antinodes are mobile instead of being stationary in space. Phase control can generate a generalized stirring of the air fuel mixture. Fig. 3C diagrammatically shows the frequency control of the ultrasound wave, with ultrasound waves of different frequency. The use of different frequencies can increase the mixing effect. A transducer 45 that can generate more than one frequency can be used, such as that shown in Fig. 2B. By increasing current transmitted to the piezoelectric crystals 40 the power of the broadcasted ultrasonic wave can be increased and consequently the stirring and mixing effects are increased.

[0040] The longitudinal wave propagated by the transducer 45 may have a limited variable phase which makes the sinusoidal ultrasonic wave move alternatively back and forth. The back and forth movement of the ultrasonic wave may cause a diminishing of the ultrasonic wave amplitude. The diminished ultrasonic wave amplitude is diagrammatically illustrated in Fig. 3D. This movement can break stationary wave patterns, which in turn can increase the mixing effects.

[0041] The longitudinal ultrasound wave may propagate through a waveguide concentrator 46 and ultrasonic wave conductor 50, in the embodiment shown in Fig. 1 the ultrasonic wave conductor 50 is a rod, however it should be understood that other geometries may be used to conduct the ultrasonic wave. Alternatively, the transducer 45 may transmit the ultrasonic wave directly to a different component of the premix injector 10 such as the secondary fuel manifold 17. As shown in Fig. 1, waveguide concentrator 46 may be connected to and extending from the transducer 45. Flange 43 can be coaxial with the waveguide concentrator 46 and situated at the first nodal point of the ultrasonic wave produced by the piezoelectric crystals 45 in the waveguide concentrator 46. The transducer 45 may be attached to the waveguide concentrator 46 through a screw connection and the face of the transducer 45 may mate with a face of the waveguide concentrator 46. However the waveguide concentrator 46 may be arranged at different locations on the combustor 100 and in some instances may be part of the existing combustor 100.

[0042] The waveguide concentrator 46 joined to the transducers 45 through a screw connection further carries and amplifies the ultrasonic wave. When connected to the transducer 45 the portion of the waveguide concentrator 46 that has the largest diameter is connected to the transducer 45. As shown in Fig. 4 is the waveguide concentrator 46 has a diameter Dl at a portion of the waveguide concentrator 46 that is smaller than the diameter D2 of the portion of the waveguide concentrator 46 that is located closest to the transducer 45.

[0043] Figs. 5A-5C show various shapes that the waveguide concentrator 46 can take. Fig. 5A shows a waveguide concentrator 46 that is conical shaped. Fig. 5B shows waveguide concentrator 46 that uses an exponential shape. Fig. 5C shows a waveguide concentrator 46 that is catenoidal shaped. When used the waveguide concentrator 46 can guide the ultrasonic waves and further amplify the ultrasonic wave amplitude. A waveguide concentrator 46 with decreasing cross-sectional area produces an increase in the wave amplitude as a consequence of the volume conservation. The portions of the waveguide concentrator 46 having a larger diameter may have a smaller amplitude axial displacement, while the portion of the waveguide concentrator 46 with a smaller diameter may have a larger amplitude axial displacement, while the volume variation produced by the piezoelectric crystals 40 will remain the same. "Volume variation" with respect to piezoelectric crystals 40 refers to their change in volume primarily in the axial direction under an electrical field as a result of the application of an electrical current.

[0044] Additionally, the waveguide concentrator 46 may be axisymmetric with the curve of the combustor 100 and may have a curved surface that is linear, exponential, hyberbolic or non-uniform. The shape of the waveguide concentrator 46 may be chosen to obtain maximum amplitude amplification of the ultrasonic vibrations. Also, cylindrical step shapes for the waveguide concentrator 46 may be chosen in order to minimize manufacturing costs.

[0045] At the end of the waveguide concentrator 46 may be connected to an ultrasonic wave conductor 50 which can transmit the ultrasonic wave to the desired place of excitation in the premix injector 10 and the combustor 100. The ultrasonic wave conductor 50 may extend from the waveguide concentrator 46 to any location in the combustor 100 that requires mixing of fuels or additional cleaning. The ultrasonic wave conductor 50 shown in Fig. 1 extends to the surface of the mixing duct 12. In this instance to the surface of the outer wall manifold 26. Alternatively, as discussed above, the waveguide concentrator 46 may connect directly to the second fuel manifold 17 which may then perform the same function as the ultrasonic wave conductor 50.

[0046] The length of the waveguide concentrator 46 and the ultrasonic wave conductor 50 should provide an integer number of half wavelengths so that the maximum of displacement occurs where the fuel and air mixing occurs. For example, the speed of sound in stainless steel at 20° is 5790 m/s. The full wavelength length is obtained by dividing the above speed by the frequency. For a frequency of 30 kHz a wavelength of 193 mm is derived. The integer number of half wavelengths can be counted from the end of the transducer 45 connected to the waveguide concentrator 46 to the end of the ultrasonic wave conductor 50. The maximum of the ultrasonic wave produced by the transducer 45 is reached at any half wave integer multiple of the sinusoidal oscillation of the ultrasonic wave. The ultrasonic wave produced by the waveguide concentrator 46 is also dependent on the curve profile of the waveguide concentrator 46, with a steeper curve profile generating allowing for an increased end displacement in a shorter waveguide concentrator 46.

[0047] The ultrasonic waves produced by the transducer 45 may be amplified with the assistance of the waveguide concentrator 46 and ultrasonic wave conductor 50. The length of the waveguide concentrator 46 and ultrasonic wave conductor 50 is dependent upon the desired number of half wavelengths and can be made as long as needed by attaching ultrasonic wave conductors 50 to the end of the waveguide concentrator 46. The sinusoidal ultrasonic wave generated by the transducer 45 travels through the waveguide concentrator 46 from the larger diameter and low amplitude of the transducer 45 to a smaller diameter and higher amplitude of the waveguide concentrator 46. The waveguide concentrator 46 can be connected to the underlying structure of the combustor 100 at one of its travelling wave zero displacement points (i.e. nodal points), preferably at a second nodal point, such as at the flange 43 in Fig. 1 (with the first nodal point being located between the pair of piezoelectric crystals 40 shown in Fig. 2A). [0048] The waveguide concentrator 46 or ultrasonic wave conductor 50 may be connected to the surfaces of the fuel manifold 14 or the other components of the combustor 100 where the surface then radiates the ultrasonic wave into the fuel-air mixture. The connection of the waveguide concentrator 46 or ultrasonic wave conductor 50 to the surface of a component of combustor 100, such as mixing duct 12 or fuel manifold 14, can be done through bolting, brazing or other appropriate procedure. The acoustical coupling between the vibrating modes of the surface of the component of the combustor 100 and the fuel-air mixture enables the transmission of the ultrasonic wave to the fuel air mixture. By using the ultrasonic wave conductor 50, the transducer 45 and its piezoelectric crystals 40 may stay out of the hot region of the combustor 100 and in such instances the ultrasonic wave conductor 50 will carry the wave to the hot radiating surfaces of the components of the combustor 100. In this way the piezoelectric crystals 40 stay sheltered from the high temperature of the combustor 100.

[0049] In the premix injector 10, the ultrasonic wave couples with the pressurized fuel-air mixture within the premix injector 10 and travels inside the flowing fuel-air mixture as a phase variable acoustical wave. The coupling quality of the ultrasonic wave with the fuel-air mixture can be increased by the high density of the gases after the compression, which occurs further upstream of the premix injector 10.

[0050] Grooves 48 may be formed in the surface of a component of the combustor 100, such as shown in Fig. 6. The grooves 48 can be formed according to the desired ultrasonic wave length. The grooves 48 shown in Fig. 6 may be formed in the surface of the mixing duct 12 or fuel manifold 14 by any art recognized technique. The grooves 48 may be formed to follow the first vibration mode orientation of the surface in which they are formed. For example, a circular plate component may have grooves 48 that are circular. Modal analysis of a surface can help find these shapes by studying the dynamic properties of a component under vibrational excitation. The surfaces in which the grooves 48 are formed are in contact with the fuel air mixture and the ultrasonic wave travels out from the surface of the combustor component, such as mixing duct 12, into the fuel-air mixture and performs the controlled stirring, as illustrated diagrammatically in Figs. 3A-3D. The coupling to the fuel-air mixture is increased by having the increased density of the air provided by a turbine compressor. In this way a higher percentage of the ultrasonic wave will be transmitted to the fuel- air mixture.

[0051] The grooves 48 may occur at half of the ultrasonic wavelengths so that the grooves 48 may present a stepped profile as shown in Figure 7. In this way the sinusoidal oscillations of the ultrasonic wave are moving in phase increasing their radiation efficiency. Fig. 7 shows a stepped profile formed by the grooves 48 on the surface of the mixing duct 12. Having the grooves 48 formed at half of the wavelengths means that the depth of the groove 48 is ½ the ultrasonic wavelength generated by the transducer 45 and that is produced by the vibration of the surface of the mixing duct 12.

[0052] The stepped profile for the grooves 48 makes it possible to overcome problems that occur when using flat surfaces. The surfaces of the components of the combustor 100 driven at ultrasonic frequencies may vibrate in a flexural mode and consequently can have a poor directivity pattern due to phase cancellation. This means that the ultrasonic wavelengths emanating from a flat surface may interfere with each other in such a manner that the overall mixing that occurs between the fuel and the air is decreased. This drawback can be eliminated if the surface of the component of the combustor 100 has grooves 48 formed in it that cause the ultrasonic waves that are vibrating in counter-phase on the two sides of the nodal lines shifted along the acoustic axis to half a wavelength of the ultrasonic wave in the propagation medium. This is accomplished by having grooves 48 formed having a depth of ½ the wavelength of the desired wavelength for the particular fuel air mixture. The result is that the ultrasonic wave emanating from the surface of the component of the combustor 100 is in phase across the whole surface of a component and can have a directivity pattern similar to using a piston.

[0053] The grooves 48 may improve the coupling between the metal of the mixing duct 12 and the fuel air mixture thereby increasing the amount of transmitted ultrasonic energy. While the grooves 48 are shown on the surface of the mixing duct 12, it should be understood that other portions of the combustor 100 may have grooves 48 formed therein, for example this may also occur in the combustion chamber 35. Having grooves 48 formed in the combustion chamber 35 can allow more uniform dispersion of combustion in the combustion chamber 35 Additionally, grooves 48, while shown as straight may form other patterns depending of the vibrating mode shape of the component of the combustor 100 and the ultrasonic frequency used to generate the vibrating mode shape. Grooves 48 may be wavy, checked, cross-hatched or whatever the modal shape of the component of the combustor 100 may be.

[0054] Set forth in Fig. 8 is a flow chart depicting a method of transmitting ultrasonic waves in a gas turbine combustor 100. In step 801, the transducer 45 is activated. In step 802 the ultrasonic waves are transmitted to the pre-mix injector 10. The ultrasonic waves may be transmitted via a flange 43, through a wave guide concentrator 46, or through ultrasonic wave conductor 50. In step 803 a parameter of the ultrasonic wave may be adjusted in order to optimize mixing such as phase, amplitude and/or frequency. The adjustment of the parameters of the ultrasonic wave may be achieved through the controller 55.

[0055] The ultrasonic wave that is formed has linear and non-linear effects acting on the fuel-air mixture. The linear effects are given by the sinusoidal shape of the wave and comprise creating maximum and minimum fuel-air mixture density regions. The application of a variable phase shift in the ultrasonic wave moves alternatively back and forth in these regions thereby producing a generalized stirring of the fuel-air mixture. In this way momentum is communicated to the fuel and air molecules. The non-linear streaming effects of the ultrasonic wave impacts the fuel-air mixture and further mix it. This mixing occurs at a molecular level and increases the probability of contact between gas molecules and the air. Downstream in the combustion chamber 35, the gas molecules that are well mixed with oxygen will burn when ignited at lower temperatures. Because they burn at lower temperatures this will result in lower levels of NOx and CO concurrently.

[0056] The alternating ultrasonic wave mixing at a molecular level is imposed with very high frequency on the steady continuous air flow and carried downstream afterwards. More or less ultrasonic energy can be injected. This can be used to optimize mixing and reactivity of the fuel-air mixture. The ability to provide higher or lower amounts of ultrasonic energy via the ultrasonic wave further permits control of the mixing process independent of air flow speed. Moreover, the intensity and efficiency of downstream combustion can be modified and controlled through the continuously adjustable mixing action in the premix injector 10. [0057] Once present in the fuel-air mixture the ultrasonic wave is carried downstream and continues mixing until the ultrasonic wave is completely dispersed and its energy is absorbed in the fuel-air mixture. The increase in reactivity caused by the ultrasonic wave in the combustor is tuneable on a continuous basis and can be achieved by the controller 55. In this manner one engine design geometry can accommodate fuels with widely different calorific values.

[0058] The provision of the ultrasonic waves in the combustors 100 can result in producing gas turbine engines which burn cleaner by having concurrent lower NOx and CO emissions. This offers the ability to reduce emissions without adding substantial cost or complexity or requiring major modification to existing combustor designs and can be applicable to all scales of gas turbine engines.

[0059] Fig. 9 is a diagram depicting an alternative embodiment of the present invention. Like numerals present in Fig. 9 correspond to similar structure shown in Fig. 1. Fig. 9 specifically includes a liquid fuel inlet 61 and corresponding liquid fuel passages 62 that supply liquid fuel to the fuel manifold 14. In this embodiment the ultrasonic wave conductor 50 contacts the structures that are prone to coking in the premix injector 10. Coking is the solid material that can remain due to imperfect combustion. In other embodiments the ultrasonic wave conductor 50 may be placed in other locations in the combustor 100 that may require cleaning, such as liners. Having the ultrasonic wave conductor 50 contact the structures that may be prone to coking, or that require cleaning, such as the liquid fuel passage 62, the fuel manifold 14 and the combustion chamber 35 permits ultrasonic waves to be applied to these surfaces and remove any particulate material that remains due to coking.

[0060] Fig. 10 is a flow chart that shows the application of the ultrasonic waves to the portions of the combustor 100 prone to coking or that require cleaning. In step 1001, the transducer 45 is activated. In step 1002, the transducer 45 generates an ultrasonic wave and transmits it to the component of the combustor 100 that requires cleaning, such as components prone to coking or that may accumulate soot, such as liners. The transducer 45 may generate an ultrasonic wave that is transmitted to a waveguide concentrator 46 to an ultrasonic wave conductor 50 that contacts liquid fuel passage 62. In step 1003 the ultrasonic waves clean the surface of the liquid fuel passage 62. In the embodiment shown in Fig. 9 the coking deposits from the surface of the liquid fuel passage 62 are removed. The removal of coking deposits in this manner can reduce engine maintenance downtime. Also, the liquid fuel passages 62 found within combustors 100 are cleaned of the coking deposits that are produced by the high temperature of the manifold 14, and obstruction of the liquid fuel passages 62 is precluded, thus improving performance. This can also reduce liquid fuel wetting of surfaces of the combustor 100 that can lead to erosion. Additionally, the application of ultrasonic waves to the combustor 100 may be used to remove soot deposits on downstream turbine components, such as combustor liners. The elimination of soot deposits via the ultrasonic waves can reduce maintenance downtime as well as increase the productive time of the combustor 100.

[0061] When using the process for fuel-air mixture discussed above the creation of deposits is reduced because fuel molecules are burning in a more efficient manner. The cleaning process described above may be implemented during operation of the combustor 100 in order to further prevent deposits from forming on components.

[0062] While embodiments of the present disclosure have been disclosed in exemplary forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions can be made therein without departing from the spirit and scope of the invention and its equivalents, as set forth in the following claims.