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Accurate high temperature engine aero-thermal measurements for gas-turbine life optimisation, performance and condition monitoring

Final Report Summary - HEATTOP (Accurate high temperature engine aero-thermal measurements for gas-turbine life optimisation, performance and condition monitoring)

The HEATTOP project aimed to address the need for improved instrumentation to be used in development, design evaluation and performance monitoring of aero engines and industrial gas turbines for power generation. In the middle of interest were the hottest regions of engines, the combustors and HP turbines where temperatures reach 2 000 K. The objective of the HEATTOP project was to develop accurate high temperature sensors for measurement of pressure, temperature and tip clearances.

The temperatures affect directly engine efficiency and life time of components. As current sensors cannot be placed in the hottest regions, knowledge of conditions inside the turbine is gathered from outside measurements which are then extrapolated by using models and assumptions. Turbine parts and other hot gas components are very expensive, have a shorter life time due to heavy mechanical and thermal loads and are critical for engine reliability. Accurate knowledge of temperatures would be very beneficial in predicting their life time and verify the performance of a design. Other aerodynamic parameters as dynamic and static pressure and clearances affect efficiency, operation and health of an engine.

To achieve the project's goals within a period of 45 months, a work programme was set up to develop measurement technologies for high temperatures in four areas with specific development objectives:
1. Advanced thermocouple technology
2. Measurement of surface temperatures
3. Gas path aerodynamic measurements
4. Tip clearance measurement system
5. Testing and validation of all developed techniques in rigs and engines.
6. Dissemination of technology developments by the developers

The responsibilities and work were structured in three main areas and nine work packages (WPs):
- Specification and validation: containing WP 1 - Definitions, and two WPs for sensor validation in test facilities: WP 6 - Sensor rig tests and WP 7 - Sensor engine tests.
- Sensor design and development: containing four technical development WPs.
- Coordination and dissemination: dedicated to coordination and project management (WP 0) and dissemination of results (WP 8).

More specifically, the WPs included:
WP 0 - Project management
WP 1 - Definitions and specifications
WP 2 - Life and accuracy optimisation of current instrumentation for high temperature measurement
WP 3 - Advanced solid temperature measurements
WP 4 - Gas path aerodynamic measurements
WP 5 - Tip clearance measurement
WP 6 and WP 7 - Validation of technologies
WP 9 - Dissemination of results.

Among the most important results obtained, the following can be reported:
1 - 2. Improved fast response thermocouples. High frequency response time thermocouple for wall temperature measurement in engine environment. High stability K type thermocouples, after several thousands of hours on engine.
3. Advanced stable thermocouple system as results of design of experiment. Optimised thermocouple system for exhaust gas temperature measurement. Better than class 1 accuracy (about 0.25 %) over the life of the thermocouple for temperatures up to 1 050 degrees Celsius.
4. Advanced high temperature thermocouple. A new Ni-based thermocouple in MIMS configuration has been designed at the Department of Materials Science and Metallurgy of the University of Cambridge. The new thermocouple allows temperature measurements up to 1 200 degrees Celsius with a total drift of about 2 degrees Celsius: this is a significant improvement compared to the conventional Ni-based thermocouples which can have drift as high as 15-20 degrees Celsius.
5. Ceramic-based thermocouple for temperature measurement up to 1 500 degrees Celsius, in engine environment.
6. Embedded fibre optic sensors. Siemens has developed and demonstrated fibre Bragg gratings sensors embedded in high temperature components of gas turbines for solid temperature measurement. Together with the partners IPHT and AOS the first sapphire Bragg grating (FBG) sensor multiplexing was achieved. A sapphire-based FBG sensor was inscribed in IPHT Jena by high-energy FS laser and has been demonstrated at temperatures up to 1 200 degrees Celsius with temperature drifts below ±5 K. As a further unique feature, the highest temperature stability has been achieved with T > 1 750 degrees Celsius, as the most severe conditions a fibre-optic temperature sensor can be used.
7. A pyrometer corrected / calibrated for transmission and fouling. A boroscope hole pyrometer has been designed and constructed. It includes a facility for on-line calibration for fouling and transmission losses, thus enhancing the instrument with self-inspection capability.
8 - 9. Advanced pyrometer design know-how. Advanced pyrometer system that is insensitive to most types of lens contaminant for HP turbine blade measurement.
10. Thermographic phoshors for quasi 2D temperature measurement on airfoils, under high temperature and pressure.
11. A high temperature water-cooled fast response total pressure probe for hot gas path measurements (in combustion chambers and turbine hot sections). This concept is based on the use of a conventional miniature piezoresistive pressure sensor, located in the probe tip to achieve a bandwidth of at least 40 kHz.
12. An optical fibre multiplexable pressure sensor (< 1 000 degrees Celsius).
13. An intermittent choked nozzle probe for total pressure and temperature.
14. A non-intrusive IR sensor for turbine inlet gas temperature measurements. The research teams have developed and tested a non intrusive temperature probe for on line real time measurements of the turbine inlet temperature (TIT) based on the detection of the infrared (IR) radiation emitted in a selected wavelength band by the CO2 molecules in the combustion gases. The sensor is suitable for stationary GT applications. The sensor can be operated without damage or environment disturb up to temperatures as high as T = 1 500 degrees Celsius and pressure of the order of P = 9 bar. However, reliable temperature measurements have been demonstrated only in a limited temperature range (up to around 1 300 degrees Celsius).
15. Tip clearance sensor. A mm-wave sensor for measurement of tip clearances in the hot section of a turbine was developed by Siemens in collaboration with partners Vibro-Meter and Farran. The sensor uses electromagnetic waves with 77 GHz that propagate through wave guide channels and radiate through an antenna towards the turbine blades where they are reflected.
16. Thin film thermocouple for temperature measurements at the surface of metallic components or at the interface between thermal barrier coating and metallic component. The product consists of a sputtered multilayer (bond coat, insulating layer, thin film thermocouple, connection pads and protecting layer) deposited on metallic substrates by ONERA.
17. Uncooled fast-insertion temperature and pressure probes for gas turbine engine measurements. Uncooled fast-insertion temperature and pressure probes have been developed that are capable of surviving in the hottest parts of gas turbine engines. The pressure probe is capable of measuring total pressure with a bandwidth from DC to 100 kHz, from which turbulence information can be derived.

The HEATTOP project developed sensors and probes which are critical for efficient, economic, reliable and environmentally friendly operation of gas turbines in aero engines and in stationary power generation facilities. The current limits of instrumentation had to be stretched, while at the same time accuracy and reliability needed to be improved.