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Turbine Exhaust Gas Temperature Sensing using Fiber Optics Technologies




OBJECTIVE: Develop non-intrusive technologies for gas turbine exhaust temperature measurement that will enable future high performance engines. 


DESCRIPTION: The control and health management of modern turbine engines depends on sensing a wide variety of quantities throughout the engine, including temperatures, pressures, and vibration with different redundancy, reliability, and accuracy requirements. Exhaust gas temperature (EGT) is a critical parameter for gas turbine engine control and health management. EGT and other turbine temperature sensors are susceptible to degradation due to high temperature oxidation, erosion and contaminant intrusion into probes and wiring harnesses. Thermocouples acting as sensing elements provide microvolt signals that are easily affected by noise or other environmental factors. Military/commercial field experience indicates that gas path thermocouple removals affect aircraft availability and add maintenance time. Also, the adaptive engine of the future is driving the control system to outperform legacy design, and driving higher temperatures. “Best” entitlement for accuracy at higher than experience range 15-20F (20 deg temp margin ~1% thrust margin) allotment in redline stack is required. Additionally, calculated EGT entitlement is insufficient for future engine needs. Multicolor Pyrometers are not mature, complex, emissivity dependent, and expensive. With alternate technologies that use fiber optic technology to measure exhaust gas effects, measurement of significantly higher temperature should be possible. High temperature measurement requires innovation to survive the harsh environment while maintaining reliability, accuracy, ruggedness, and minimum size/weight/power. EGT sensors for military /commercial engines are located downstream from the highest temperature sections of the engine and can be used to infer the state/condition of the turbine blades/disks. As aircraft turbine engines continue to push the envelope on material capabilities, it is important to be able to sense how close to the material limits the system is operating. The new technology should be able to survive for the expected life of the engine between overhauls and measure temperatures in excess of 1600 degrees C (Life: 2000 EFH (immersive), 4000 Engine Flight Hours (EFH) ) (non-immersive). It is desired for the accuracy of the sensing systems to be 0.5% of full scale and stable over the life of the engine. Air temperature measurements in the exhaust gases must be taken outside of the wall boundary layer. Existing approaches for measuring EGT typically implement high temperature capability with thermocouples but extension to even higher temperatures is questionable. Other technologies that have been investigated include thin film thermocouples, pyrometers, spectroscopy, and radioactive isotope-based sensors. They are not mature, accurate or cost/effective for engine implementation. It is important that new technologies be ruggedized for installation in production aircraft. The high temperature measurement technology within the scope of this program should initially be developed for test cell demonstration and application. After successful technology demonstration and application in the test cell environment, other opportunities for Prognostics, Health management and controls may be considered. It is appropriate to design and fabricate a prototype EGT probe and interconnect system that is capable of passive testing in a turbine test rig on the ground. Bench testing the EGT probe in an environment that simulates engine operation should be accomplished. Demonstration of flight weight components and ruggedness of the system in Phase III will be critical for transition to insertion in a future program of record. It is recommended that that an engine or controls OEM be involved in the program to ensure future technology transition is facilitated. 


PHASE I: Work with at least one engine OEM to establish requirements for exhaust gas temperature measurement. Develop a new concept or adapt existing concepts for measuring exhaust gas temperature that meets the objectives of the system. Prove the feasibility of the concept through analysis and laboratory testing of representative devices. 


PHASE II: Based on the Phase I results, build and test a complete laboratory based EGT system that subjects the EGT sensors to realistic environments. Characterize the sensors with respect to accuracy and long term stability. 


PHASE III: Based on the Phase II & III (results & SOW), work with a sensor OEM to design and fabricate a prototype EGT probe (ground testing) in a turbine test rig. Bench test the EGT probe in an engine environment. Demonstration of flight weight components. 



1: Alexander Von Moll, Alireza R. Behbahani, Gustave C. Fralick, John D. Wrbanek, and Gary W. Hunter. "A Review of Exhaust Gas Temperature Sensing Techniques for Modern Turbine Engine Controls", 50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, AIAA Propulsion and Energy Forum, (AIAA 2014-3977)

2:  "Durable, Fiber-Optic Sensor for Gas Temperature Measurement in the Hot Section of Turbine Engines," Tregay, G., Calabrese, P., Finney, M., Stukey, K. Proc. SPIE 2295, Fly-by-Light, 156 (October 4, 1994).

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5:  "Sapphire Fiber Bragg Grating Sensor made using Femosecond Laser Radiation for Ultrahigh Temperature Applications," D. Grobnic, S. J. Mihailov, C.W. Smelser, and H. Ding. IEEE Photonics Technology Letters, Vol 16, No. 11, pp. 2505-2507, 2004.

6:  "Self-Calibrated Interferometric-Intensity-Based Optical Fiber Sensors," A.Wang, H. Xiao, J. Wang, Z. Wang, W. Zhao, R. G. May. Journal of Lightwave Technology, Vol 19, No. 10, pp. 1495-1501, 2001.

7:  "Fiber-Optic Temperature Sensor Based on Internally Generated Thermal Radiation," M. Gottlieb and G. B. Brandt. Applied Optics, No. 19, Vol. 20, pp. 3408-3414, 1981.



KEYWORDS: EGT, Fiber Optics Sensing, Turbine Engine Control, PHM, Exhaust Gas Temperature 


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