Temperature sensing inside Thermal Barrier Coatings using phosphor thermometry

By introducing a few percent of rare earth oxides into existing Thermal Barrier Coating (TBC) materials, their functionality can be enhanced. The low fraction of the rare earth means the primary function of the coating as a thermal barrier can be maintained. However, it provides additional sensing capabilities. Embedded in the crystal, the rare earth ions act as optical centres making the material phosphorescent. The properties of the phosphorescence depend on temperature, among other parameters, such that the functional coating can be used to conduct phosphor thermometry. Accordingly, the temperature of the coating can be measured by exciting and detecting the phosphorescence from the coating. This technique has been under investigation for many years, although was only recently demonstrated on an operating gas turbine engine. Implementation of a phosphorescent measurement system was carried out in a Rolls-Royce jet engine using dysprosium doped yttrium stabilised zirconia as a sensor. During this implementation, a thermal gradient across the ceramic coating of some components of the engine existed due to cooling effects. This paper complements the previous work by investigating the effect on the temperature measurements accuracy of this thermal gradient.