Image conduit for fuel nozzle assemblies

Abstract

A fuel nozzle for a gas turbine engine includes a feed arm including a fuel passage for issuing a spray of fuel. A nozzle assembly is fixed at an upstream end of the feed arm having a fuel inlet in fluid communication with the fuel passage. A fiber optic cable is configured to collect burner radiation for a pyrometer input and has a first end centered within an optical connector of the nozzle assembly and a second end exposed from the spray outlet. The fiber optic cable fitted within the feed arm and nozzle assembly has a permanent bend radius preformed in the fiber optic cable. The bend radius can be equal to or greater than the minimum bend radii for the fiber optic cable to serve as a wave guide in wavelengths for monitoring combustion.

Claims

1. A method of constructing a fiber optic cable for a fuel nozzle, the steps comprising: inserting seven wave guides into a metal sheath with alumina powder spaced apart from the other wave guides; drawing the metal sheath through a round reduction die to compress the alumina powder and fibers together; annealing the metal sheath; and forming at least one bend of a predetermined radius in the metal sheath by heating the metal sheath and applying a bending force, wherein the bend radius is formed so as not to exceed the minimum bend radius of the wave guides with respect to wavelengths for monitoring combustion, wherein each waveguide is 0.017 inches in diameter such that the metal sheath has a minimum bend radius of three times the diameter of one of the wave guides.

2. The method of claim 1, further comprising annealing the metal sheath again after the step of forming.

3. The method of claim 1, further comprising spacing each waveguide apart from the other waveguides.

4. The method of claim 1, further comprising filling interstitial sites between each waveguide with compacted alumina powder.

5. The method of claim 1, wherein forming the predetermined bend radius comprises forming the predetermined bend radius to a bend radius of about 0.5 inches.

6. The method of claim 1, wherein inserting the seven waveguides includes arrange one of the waveguides as a center waveguide and circumferentially spacing six waveguides about the center waveguide.

7. The method of claim 1, further comprising forming each of the waveguides with a common diameter such that a 1/7th reduction in expected signal strength indicates breakage of one of the waveguides.

8. The method of claim 1, wherein the waveguides are configured to pass light through the waveguide within a range of 430 nm to 1400 nm.

9. The method of claim 1, further comprising forming each waveguide by coating and bonding adjacent fibers to one another.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:

(2) FIG. 1 is a cross-sectional view of an exemplary embodiment of a fuel nozzle constructed in accordance with the present disclosure, showing a fiber optic cable threaded therethrough including a minimum bend radius; and

(3) FIG. 2 is a cross-sectional view of the fiber optic cable of FIG. 1, showing a plurality of wave guides.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(4) Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of an image conduit for a fuel nozzle in accordance with the disclosure is shown in FIG. 1 and is designated generally by reference character 100. Other embodiments of the image conduit in accordance with the disclosure, or aspects thereof, are provided in FIG. 2, as will be described.

(5) With reference to FIG. 1, a cross-sectional view of a fuel nozzle 10 is shown. The fuel nozzle 10 is associated with a gas turbine engine. Gas turbine engines, such as those which power modern aircrafts, include a compressor for pressurizing a supply of air, a combustor for burning a hydrocarbon fuel in the presence of the pressurized air, and a turbine for extracting energy from the resultant combustion gases. The combustor generally includes radially spaced apart inner and outer liners that define an annular combustion chamber therebetween. A plurality of circumferentially distributed fuel injectors axially project into a forward section of the combustion chamber to supply the fuel to be mixed with the pressurized air. The fuel nozzle 10 injects/atomizes the fuel into the combustor air stream. The fuel nozzle 10 includes a feed arm 12 with a fuel passage 14 for directing fuel from a fuel inlet 15 of a nozzle assembly 18 to a spray outlet 13 of the feed arm 12. During operation, compressed air flows past the nozzle assembly 18 while fuel is injected continuously and a flame occupies two to six inches from the tip. A fiber optic cable 100 is threaded through the fuel nozzle 10 and configured to collect burner radiation from the flame for pyrometer input for analysis and real-time combustion control.

(6) With continued reference to FIG. 1, the fiber optic cable 100 has a first end 102 centered within an electrical/optical connector 16 and a second end 104 exposed from the spray outlet 13. The second end 104 can optionally include a sapphire lens 106. The light from the flame is transmitted through the sapphire lens 106 to the optical connector and pyrometer for analysis. The fiber optic cable 100 includes a formable metal sheath 110 assembly that is formed under heat to a tight bend radius to fit through the fuel nozzle 10. Once the correct bend radius is formed, the metal sheath assembly 100 is allowed to cool to a fixed rigid shape such that the bend radius is preformed in the fiber optic cable 100.

(7) With reference to FIG. 2, a cross-sectional view of the fiber optic cable 100 is shown. The metal sheath 110 of the fiber optic cable 100 encloses a plurality of individual wave guides 112a-g. As shown, seven wave guides 112a-g are enclosed within the metal sheath 100. Seven wave guides are included and shown, but any suitable number can be used. The use of seven wave guides 112a-g improves the redundancy and reliability in addition to reducing the bend radius. The wave guides 112a-g allow for burner radiation to be transmitted from the first end 102 of the fiber optical cable 100 to the second end 104 substantially without a loss of light transmission. The bend radius is greater than or equal to the minimum bend radius for the wave guides 112a-g to serve as wave lengths for monitoring combustion. Typical fiber optical cables with tight bends lose light transmission as the light travels through a core or inner channel due to light striking the core at more than a critical angle. However, with the configuration and wave guides 112a-g of the present disclosure, each wave guide 112a-g has a minimum bend radius limited to three times the wave guide diameter. In keeping with this minimum bend radius, the fiber optic cable 100 is formed with one or more bends without noticeable loss of wave guide effectiveness. Therefore, signal strength at the second end 104 of the fiber optic cable 100 is the same as or comparable to the signal strength detected at the first end 102. Each wave guide 112a-g is 0.017 inches in diameter allowing for a minimum bend radius of 0.5 inches. As each of the wave guides 112a-g are the same diameter, a 1/7th reduction in expected signal strength indicates breakage of one of the wave guides 112a-g.

(8) Each wave guide 112a-g is comprised of approximately 918 fibers that are 12 m in diameter. Those skilled in the art will appreciate that any number of fibers may used without departing from the scope of the present disclosure. The fibers are coated and bonded to adjacent fibers to help prevent the loss of light transmission through the wave guides 112a-g. Radiation transmitted through each wave guide 112a-g is approximately within the range of 430 nm to 1400 nm. The wave guides 112a-g are similar to fused glass optical fiber rods known in the art, for example, fiber optic image conduits manufactured by Edmunds Scientific Corporation of Barrington, N.J. As shown in FIG. 2, the fiber optic cable 100 includes a center wave guide 112g with six wave guides circumferentially 112a-f spaced around the center wave guide 112g. Each of the wave guides 112a-g are spaced apart from the other wave guides 112a-g with the interstitial sites 116 between each wave guide 112a-g filled with compacted alumina powder to provide compliance and reduce mechanical stress due to thermal expansions and vibrations.

(9) During construction of the fiber optic cable, seven wave guides, e.g., wave guides 112a-g, are inserted into a metal sheath, e.g. metal sheath 110, with alumina powder filling the interstitial sites, e.g., interstitial sites 116. The metal sheath is then drawn through a round reduction die to compress the alumina powder together. The metal sheath is then annealed. After annealing the metal sheath, the fiber optic cable is heated to about 1300 F. and a bending force is applied to form the desired shape including at least one bend radius so as not to exceed the minimum bend radius of the wave guides. The metal sheath can then be annealed again, if required. The metal sheath is cooled thereby maintaining the preformed shape required for compatibility with the fuel nozzle.

(10) The methods and systems of the present disclosure, as described above and shown in the drawings, provide for a fiber optic cable with superior properties including having a minimum bend radius without a loss of light transmission. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.