The ever-increasing requirements on gas turbine efficiency and the simultaneous demand for reduced emissions, necessitate much more accurate calculations of the combustion process and combustor wall temperatures. Thermal history paints (THPs) is an innovative alternative to the established measurement techniques, but so far only a limited number of tests have been conducted under real engine conditions. A typical THP comprises oxide ceramic pigments and a water-based binder. The ceramic is synthesized to be amorphous and when heated it crystallizes, permanently changing the microstructure. The ceramic is doped with lanthanide ions to make it phosphorescent and as the structure of the material changes, so do the phosphorescent properties of the material. By measuring the phosphorescence, the maximum temperature of exposure can be determined, enabling postoperation measurements at ambient conditions. This paper describes a test in which THP was applied to an impingement-cooled front panel from a combustor of an industrial gas turbine. The panel was instrumented with a thermocouple (TC), and thermal paint was applied to the cold side of the impingement plate. The THP was applied to the hot-gas side of this plate for validation against the other measurement techniques and to evaluate its resilience against the reacting hot gas environment. The durability and temperature results of the three different measurement techniques are discussed. It is shown that the THP exhibited greater durability compared to the conventional thermal paint. Furthermore, the new technology provided detailed measurements indicating local temperature variations and global variations over the complete component.

To improve the efficiency of gas turbines, the turbine inlet temperature needs to be increased. The highest temperature in the gas turbine cycle takes place at the exit of the combustion chamber and it is limited by the maximum temperature turbine blades, vanes and discs can withstand. A combination of advanced cooling designs and Thermal Barrier Coatings (TBCs) are used to achieve material surface temperatures of up to 1200°C. However, further temperature increases and materials that can withstand the harsh temperatures are required for next-generation engines. Research is underway to develop next-generation CMCs with 1480 °C temperature capability, but accurate data regarding the thermal load on the components must be well understood to ensure the component life and performance. However, temperature data is very difficult to accurately and reliably measure because the turbine rotates at high speed, the temperature rises very quickly with engine startup and the blades operate under harsh environments. At the operating temperature range of CMCs, typically platinum thermocouples are used, however, this material is incompatible with silicon carbide CMCs. Other temperature techniques such as infrared cameras and pyrometry need optical access and the results are affected by changes in emissivity that can take place during operation. Offline techniques, in which the peak temperature information is stored and read-out later, overcome the need for optical access during operation. However, the presently available techniques, such as thermal paint and thermal crystals cannot measure above ∼1400°C. Therefore, a new measurement technique is required to acquire temperature data at extreme temperatures. To meet this challenge, Sensor Coating Systems (SCS) is focused on the development of Thermal History Coatings (THC) that measure temperature profiles in the 900–1600 °C range. THC are oxide ceramics deposited via air plasma spraying process. This innovative temperature profiling technique uses optically active ions in a ceramic host material that start to phosphoresce when excited by light. After being exposed to high temperatures the host material irreversibly changes at the atomic level affecting the phosphorescence properties which are then related to temperature through calibration. This two-part paper describes the THC technology and demonstrates its capabilities for high-temperature applications. In this second part, the THC is implemented on rig components for a demonstration on two separate case studies for the first time. In one test, the THC was implemented on a burner rig assembly on metallic alloys instrumented with thermocouples, provided by Pratt & Whitney Canada. In another test, the THC was applied to environmental barrier coatings developed by NASA, as part of a ceramic-matrix-composite system and heat-treated up to 1500°C. The results indicate the THC could provide a unique capability for measuring high temperatures on current metallic alloys as well as next-generation materials.

The operating temperature of turbomachinery components are increasing the drive towards higher efficiency, lower fuel consumption and reduced emissions. Accurate thermal models are required to simulate the operating temperature of gas turbine components and hence predict service life or other qualities. These models require validation through measurement. Therefore, the quality of the models and prediction are dependent on the uncertainty of the measurements used to validate them. Currently available temperature measurement techniques have limitations in the harsh operating conditions inside gas turbines. Thermocouples are widely used, however, are practically very challenging to apply on rotating components and only provide point measurements. Furthermore, over 80% of the surface must be measured to validate complex thermal models. A new technique under development called thermal history paints (THP) and coatings (THC) overcomes some of these limitations. While the uncertainty estimation model described in this work is directly related to THP, the principles can be applied in general to thermographic phosphors. The paint comprises a proprietary phosphor powder and a water-based silicate binder. The paint is applied to the surface of the test component. When the component is operated the paint records the maximum temperature of exposure across the complete surface of the component. After operation, the paint is read-out using automated instrumentation. The measurements are related to temperature through calibration to deliver a high-resolution temperature profile. An uncertainty model has been developed and described for the first time. The model assesses the uncertainty sources related to the generation of the calibration data and the measurement of the component. It has been applied to determine the uncertainty of the THP in the temperature range 400–750 °C. The estimated uncertainty in this case was, for most samples, ±3–6 °C (67% confidence level). The maximum estimated uncertainty was ±6.3 °C or ±13 °C for 67% or 95% confidence levels respectively. This is believed to be well within the uncertainty of thermal models and the requirements for temperature measurements in harsh environments on gas turbines. These results combined with the fact that the THP can record the temperature at many locations demonstrates that it is a very useful tool for the validation of thermal models and lifing predictions. The uncertainty model was validated by measuring separate test samples and comparing the temperature measured from the THP with the thermocouple data from the heat treatment. The difference was within ±7 °C and the uncertainty bounds determined by the model.

Compliance with incoming new emission standards such as Euro6d and China6b will require new approaches to the design of thermally loaded automotive components e.g. turbochargers, exhaust valves and manifolds. However, the validation of those new designs and the need for a rapid market entry will require new temperature measurement technologies to provide accurate data across the entire component. A limited number of techniques are currently available, and all have limitations in the harsh operating conditions of turbomachinery. A new technique, called Thermal History Paint (THP), has been developed to overcome these limitations to enable accurate temperature profiles to be recorded in harsh environments. There are limited publications that cover the use of this technique and this paper demonstrates the capability of the THP through the implementation on turbocharger turbine wheels. A cooled, hollow radial turbine wheel was designed, manufactured via 3D printing and tested. A solid wheel of the same external dimensions was manufactured and tested under the same conditions to act as a baseline. The THP was used to measure the temperature profile of the blade surfaces and to quantify the effectiveness of the cooling. The paint exhibited good durability through the tests of both wheels in a hot gas rig at the University of Bath. Specific calibration data were generated for the test and the repeatability of the measurements was determined to be within 8K. Both the cooled and baseline wheels were measured at many locations and the THP recorded a significantly higher temperature on the baseline solid wheel. The measured temperature profiles were in good agreement with expectation and CFD simulations. The results enable the validation of thermal models and demonstrate the capability of the new measurement technique.