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Sensing for Controls and Propulsion Health Management in Turbine Engines

New methods can mitigate deleterious effects on turbine engine safety and performance.

Advances in engine performance and reliability require sensor components that operate reliably under extreme engine operating conditions (e.g., takeoff, max thrust) and in harsh environments (e.g., high temperature and radiation). The design of advanced controls and Propulsion Health Man agement (PHM) also depend on the use of components with increased susceptibility to atmospheric radiation. Current and future engine operating temperature environments that provide major challenges in sensor design for control and propulsion health management are being explored.

High-Temperature Regimes for Sensors with aerospace applications.
Eliminating the life-reducing effects of high cycle fatigue (HCF), combustion instabilities, compressor surge, and combustion instability control will require the use of sensors with high-temperature tolerance and high-frequency response. This requirement cannot be met by currently available technology. As a result, accurate, high-frequency sensors capable of operating in harsh environments are being developed. The need for accurate high-temperature dynamic pressure measurements is an integral step to the implementation of active surge control methodologies. For high-frequency applications, it is generally necessary to reduce the distance from the sensor to the environment to a minimum.

Typical aerospace pressure transducers are limited to about 500°F, while in today’s large gas turbine engines, compressor exit temperatures can be on the order of 1,200 to 1,400°F, meaning that current pressure transducers are not sufficient for measuring these conditions. The normal technique used to handle this temperature environment is to cool the transducer or locate the transducer in a benign environment.

Modern turbines have Full Authority Digital Engine Controls (FADECs) that provide safe and stable engine operation. These FADECs govern and limit operation of the combustion system. To minimize emissions of carbon monoxide and nitric oxides (NOx), and ensure design life, combustion systems may include control scheduling algorithms that receive input measurements of the exhaust temperature of the turbine and the actual compressor operating pressure ratio.

In a turbine engine control system, the fuel control uses a fuel metering valve assembly that is responsive to electrical signals generated by the FADEC. The FADEC response depends on sensors that measure turbine speed, pressure, and temperature, indicative of the operator thrust request. A fuel bypass valve provides a means for returning excess (unmetered) fuel from the main pump to the inlet low pressure supply. Sensors are also required to measure compressor discharge pressure for operating bypass valves to control pressure fluctuations. A high-response sensor is needed to measure differential pressure for controlling the main fuel-metering valve to achieve a rate of metered fuel flow corresponding to compressor discharge pressure. The figure shows the high-temperature regimes for the sensors needed for future aerospace applications.

The future challenges for turbine engine sensors and controls are implementation of specific technologies for diagnostics, stability management, and reconfiguration for damage tolerance. These challenges include tip clearance control, active combustion control, data fusion, integration of the turbine engine with the flight control, and high-frequency analysis for turbine engine controls. These technologies will prolong the life of the engine, increase reliability, as well as reduce lifecycle cost. In all techniques, the objective is to reduce engine wear and tear and obtain maximum life from the components.

This work was done by Alireza Behbahani and Kenneth Semega of the Air Force Research Laboratory. AFRL-0122

Topics:
Engine components Engine control systems Engines Fuel control Fuel systems Machinery Mechanical Components Powertrains
This Brief includes a Technical Support Package (TSP).
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Sensing for Controls and Propulsion Health Management in Turbine Engines

(reference AFRL-0122) is currently available for download from the TSP library.

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    Defense Tech Briefs Magazine

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    Overview

    The document titled "Sensing Challenges for Controls and PHM in the Hostile Operating Conditions of Modern Turbine Engine" by Alireza Behbahani and Kenneth Semega discusses the critical role of sensor technologies in the operation and management of advanced gas turbine engines. It highlights the evolution of these engines, which have become dominant in both commercial and military aviation, and emphasizes the need for reliable sensor components that can withstand extreme operating conditions, such as high temperatures and radiation.

    The paper outlines the challenges faced in sensor design for control systems and Prognostics and Health Management (PHM) due to the harsh environments encountered during engine operation, particularly during takeoff and maximum thrust scenarios. It addresses the increasing susceptibility of sensor components to atmospheric radiation, which can adversely affect their performance and reliability. The authors discuss the implications of these challenges for the design and operation of engine electronics and PHM systems.

    Key topics covered include the current and future temperature environments of turbine engines, which present significant challenges for sensor technology. The document also explores the effects of atmospheric radiation on sensor performance and the necessity for innovative design solutions to mitigate these effects. The authors propose methods to enhance system safety and performance, ensuring that sensors can operate effectively under the demanding conditions of modern turbine engines.

    Furthermore, the paper anticipates changes in engine operating conditions over the coming decades and discusses potential solutions for improving sensing and control capabilities. The authors emphasize the importance of developing advanced sensors that can provide accurate data for engine control and health management, ultimately contributing to improved engine performance and reliability.

    In summary, this document serves as a comprehensive overview of the challenges and considerations in sensor technology for turbine engines, highlighting the need for ongoing research and development to address these issues. It underscores the critical role of sensors in ensuring the safe and efficient operation of modern aviation propulsion systems, paving the way for future advancements in aerospace technology.

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