Image conduit for fuel nozzle assemblies
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.
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.