Application of an Industrial Sensor Coating System on a Rolls-Royce Jet Engine for Temperature Detection

Abstract

Thermal barrier coatings are used to reduce the actual working temperature of the high pressure turbine blade metal surface and hence permit the engine to operate at higher more efficient temperatures. Sensor coatings are an adaptation of existing thermal barrier coatings to enhance their functionality, such that they not only protect engine components from the high temperature gas, but can also measure the material temperature accurately and determine the health of the coating e.g. ageing, erosion and corrosion. The sensing capability is introduced by embedding optically active materials into the thermal barrier coatings and by illuminating these coatings with excitation light phosphorescence can be observed. The phosphorescence carries temperature and structural information about the coating. Accurate temperature measurements in the engine hot section would eliminate some of the conservative margins which currently need to be imposed to permit safe operation. A 50K underestimation at high operating temperatures can lead to significant pre-mature failure of the protective coating and loss of integrity. Knowledge of the exact temperature could enable the adaptation of the most efficient coating strategies using the minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of thermal barrier coatings to be realised due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. Application: This paper describes the implementation of a sensor coating system on a Rolls-Royce jet engine. The system consists of three components: industrially manufactured robust coatings, advanced remote detection optics and improved control and readout software. The majority of coatings were based on yttria stabilized zirconia doped with Dy (dysprosium) and Eu (europium), although other coatings made of yttrium aluminium garnet were manufactured as well. Coatings were produced on a production line using atmospheric plasma spraying. Parallel tests at Didcot power station revealed survivability of specific coatings in excess of 4,500 effective operating hours. It is deduced that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000 hours or even longer. An advanced optical system was designed and manufactured permitting easy scanning of coated components and also the detection of phosphorescence on rotating turbine blades (13k RPM) at stand-off distances of up to 400mm. Successful temperature measurements were taken from the nozzle guide vanes (hot), the combustion chamber (noisy) and the rotating turbine blades (moving) and compared with thermocouple and pyrometer installations for validation purposes.

Temperature Sensing inside Thermal Barrier Coatings using Phosphor Thermometry

“…The flattening of the curve at around 850°C is due to the electronics of the collection system and results in a reduced precision for measurements above this temperature. However, the temperatures of interest in this study and in the previous application of the sensor [13][14][15][16] are located in the steepest part of the curve as shown in Figure 2. …”

“…The temperatures measured in the application of the TBC system in a Rolls-Royce jet engine [13][14][15][16] ranged from 500°C to about 650°C. The curve was obtained from over 500 data points, each consisting of 50 averaged single decays, recorded during the cooling down of the sample inside the furnace.…”

“…The output light of the fibre (NA=0.39) was imaged on the sample using a plano-convex lens (f=60mm) resulting in a spot size of about 9 mm. The emitted light was collected using an optical probe (OPETS) design by SCS [13,14]. The light was then coupled into a PMT using a narrowband interference filter tailored to the main emission line of dysprosium (592 nm).…”

“…Yttria stabilized zirconia (YSZ) is commonly used as a top layer of a TBC system and has become the industry standard. This material has been reported as a thermal sensor when doped with the rare earths Eu and Dy [7,10,12], and successfully used when integrated into a measurement system on a Rolls-Royce Viper engine to measure temperatures with an estimated precision of 5°C [13][14][15][16].…”

Ultrafast Laser Microprocessing of Transparent Dielectrics. New Schemes for the Fabrication of Photonic Devices

“…This ceramic is Yttria Stabilized Zirconia (YSZ) which is a material that currently have a wide variety of applications in different areas ranging from biomedicine to engineering and scientific research. Due to its excellent mechanical and chemical properties such as high hardness, high tolerance to thermal shock, high melting point, good phase stability, and excellent oxidation resistance [126], YSZ is used in the fabrications of tooth crowns [127], as a refractory in jet engines [128], thermal barrier coating in gas turbines [129][130][131], production of solid oxide fuel cell [132], etc. However, only recently has been considered as a material for optical applications [133,75].…”