<title>Durable fiber optic sensor for gas temperature measurement in the hot section of turbine engines</title>

Abstract

An optical sensor system extends gas temperature measurement capability in turbine engines beyond the present generation of thermocouple technology. The sensing element which consists of a thermally emissive insert embedded inside a sapphire lightguide is capable of operating above the melting point of nickel-based super alloys. The emissive insert generates an optical signal as a function of temperature. Continued development has led to an optically averaged system by combining the optical signals from four individual sensing elements at a single detector assembly. The size of the signal processor module has been reduced to overall dimensions of 2 x 4 x 0.7 inches.The durability of the optical probe design has been evaluated in an electric-utility operated gas turbine under the sponsorship of the Electric Power Research Institute. The temperature probe was installed between the first stage rotor and second stage nozzle on a General Electric MS7001B turbine. The combined length of the ceramic support tube and sensing element reached 1 .5 inches into the hot gas stream. A total of over 2000 hours has been accumulated at probe operation temperatures near 1600°F.An optically averaged sensor system was designed to replace the existing four thermocouple probes on the upper half of a GE F404 aircraft turbine engine. The system was ground tested for 250 hours as part of GE Aircraft Engines IR&D Optical Engine Program. Subsequently, two flight sensor systems were shipped for use on the FOCSI (Fiber Optic Control System Integration) Program. The optical harnesses, each with four optical probes, measure the exhaust gas temperature in a GE F404 engine.

A zirconia single-crystal fibre-optic sensor for contact measurement of temperatures above 2000 °C

“…The commonly used radiation-based high-temperature fibreoptic sensors, using sapphire fibres as high-temperature waveguides, have many advantages, such as high accuracy, intrinsic immunity to electromagnetic interference and long life, making them very successful in many applications. Some aspects of their excellent performance cannot be achieved by other pyrometers [1][2][3]. However, the melting point of the sapphire crystal, 2045 • C, limits their application to operation below 2000 • C [4].…”

Review on an Advanced High‐Temperature Measurement Technology: The Optical Fiber Thermometry

“…The optical fiber thermometer mentioned above has many advantages, such as high accuracy, intrinsic immunity to electromagnetic inference, and long lifetime, which make it very successful in various applications. Some of these excellent performances cannot be achieved by other pyrometers [30][31][32]. However, these sensors have their own shortcomings.…”