Precision Temperature Detection Using a ...

Proceedings of ASME Turbo Expo 2012 GT2012 June 11-15, 2012, Copenhagen, Denmark

GT2012-6

PRECISION TEMPERATURE DETECTION USING A PHOSPHORESCENCE SENSOR COATING SYSTEM ON A ROLLS-ROYCE VIPER ENGINE J.P. Feist Southside Thermal Sciences London, United Kingdom

S. Berthier Southside Thermal Sciences London, United Kingdom

P.Y. Sollazzo Southside Thermal Sciences London, United Kingdom

B. Charnley Cranfield University Cranfield, United Kingdom

ABSTRACT By adapting existing thermal barrier coatings a sensor coating has been developed to enhance their functionality, such that they not only protect engine components from the high temperature gas, but can now also measure the material temperature accurately and 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 coating and by illuminating these coatings with excitation light phosphorescence can be observed. The phosphorescence carries temperature and structural information about the coating. Knowledge of the exact temperature could enable the design of advanced cooling strategies in the most efficient way using a minimum amount of air. The integration of an on-line temperature detection system would enable the full potential of thermal barrier coatings to be realized due to improved accuracy in temperature measurement and early warning of degradation. This in turn will increase fuel efficiency and reduce CO2 emissions. Application: The work carried out included the successful implementation of a sensor coating system on a Rolls-Royce Viper engine. The system consists of three components: industrially-manufactured robust coatings, advanced remote

J. Wells RWE npower Swindon, United Kingdom

detection optics and improved control and readout software. The majority of coatings were based on yttria stabilized zirconia doped with Dy, 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 the durability of specific coatings in excess of 4,500 effective operating hours. It is expected that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000hrs or even longer. An optical energy transfer system was designed and developed permitting scanning of coated components and also the detection of phosphorescence on rotating turbine blades (13,000 RPM) at probe-to-target distances of up to 400mm. The online measurement system demonstrated precision (around ±5K) comparable to commercial thermocouples and has shown calibration accuracy of ±4K. Transient temperatures were tracked at maximum at 8Hz which is fast enough to follow a typical power generation gas turbine. Repeatable measurements were successfully taken from the nozzle guide vanes (hot), the combustion chamber (noisy) and the rotating turbine blades (moving) and compared with thermocouple and pyrometer installations.

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NOMENCLATURE APS Atmospheric Plasma Spraying CO2 Carbone Dioxide Dy, Eu Dysprosium, Europium EBPVD Electron Beam Physical Vapour Deposition EPSRC Engineering and Physical Sciences Research Council FOV Field of View MCrAlY Metal Chromium Aluminum Yttrium Nd:YAG Neodymium-doped YAG NGV Nozzle Guide Vane OD Optical Density OPETS OPtical Energy Transfer System PMT Photo-Multiplier Tube RPM Rotations per minute SeCSy Sensor Coating System SEM Scanning Electron Microscope T1 Viper inlet temperature T2 Viper compressor delivery temperature T3 Gas stream temperature in front of the NGV T4 Viper Jet pipe exhaust temperature TBC Thermal Barrier Coating Tp Temperature measured by the pyrometer Ts Temperature using the novel sensor system YAG Yttrium Aluminum Garnet YSZ Yttria Stabilized Zirconia

Viper 201. The objective of this work is to demonstrate a fully working sensor system on an operating engine.

THEORY A sensor TBC can be defined as a refractory coating material doped with a rare earth. For example an yttrium aluminium garnet (YAG) doped with europium is notated YAG: Eu. When the sensor TBC is excited with light the rare earth electrons are excited from a ground energy level to a higher energy level. The energy levels are shown by the Dieke diagram [8] and an extract for Eu and Dy is shown in Fig.1. The relaxation of the excited electron into lower energy levels occurs by releasing energy either by photon or phonon emission. The photon emission usually is in the visible wavelength spectrum. Phonons release their energy nonradiatively into the crystal structure as heat. The lifetime of an excited state is linked to the probability of the occurrence of these two processes: (1) In the formula  is the lifetime decay, whilst PR and PNR are the radiative (photon) and non-radiative (phonon) relaxation probabilities respectively. The phonon relaxation is dependent on the temperature as can be seen from the following equation introduced by Hüfner [8] and Weber[9] using the theory of multiphonon emission:

INTRODUCTION Over the past 40 years engineers have increased the temperature on which gas turbines are operated. This increase in temperature allows a significant increase in gas turbine efficiency [1]. To achieve this goal dedicated techniques have been used to cool down components’ temperatures. Typically the gas temperature inside a combustion chamber is above the melting point of the metal from which it is composed. Among the solutions used to protect the engine components against the heat the combination of cooling air and thermal barrier coatings (TBC) is the most significant one. TBCs are refractory coatings usually based on zirconia (yttria stabilized zirconia (YSZ)). In addition to the heat protection, TBCs also provide oxidation protection. In an attempt to improve health monitoring of TBCs a new type of sensor TBC was developed over the past decade. The fundamental concept is to use phosphorescent materials such as the one used in TV screens, to dope standard TBC materials such as zirconia to produce a luminescent TBC [2,3,6,7]. When illuminated with light, the coating starts to phosphoresce. The observation of the phosphorescence with an instrument gives information on temperature and structural damage such as erosion, corrosion and ageing effects [2,4,5]. Previous work [7] explored suitable material for an engine application. This paper is a continuation of previous work and describes the application of a sensor coating for temperature detection on hot components in an operating engine: nozzle guide vanes, combustion chamber and rotating blades of a Rolls-Royce

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Figure 1: Extract of the Dieke diagram [8]. Energy level diagram for europium and dysprosium.

is the probability of spontaneous emission of n phonons at T=0K, Ephonon is the energy of the phonon studied which is equal to ωħ with ω the angular frequency and ħ the

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Dirac constant, k the Boltzmann constant and T the temperature. Usually PR is very small compared to PNR and does not depend on temperature. However PNR increases with temperature which as a result decreases the lifetime decay . Hence the temperature of a sensor TBC can be linked to the lifetime decay of its phosphorescence after excitation. The number of phonons n which will be emitted during the process can be computed from where ∆E is the energy gap. The energy gap between two levels is typically of the order of 1000cm-1, the maximum energy of a phonon is typically of the order of 500cm-1 and consequently the non-radiative decay from these levels is a multiphonon process. The constant is strongly dependent on the order n of the multiphonon process. Weber [9] and Riseberg&Moos [10] found that there is an exponential dependence on the energy gap to the next lowest level (ΔE).

When the sensor TBC is excited by a short laser pulse (5ns) it starts to phosphoresce. The phosphorescence decays exponentially and this decay time is usually much longer than that of the laser excitation pulse (typically of the order of micro- or milliseconds). Several publications have shown the dependency of the lifetime decay of the phosphorescence light on the temperature [6,7,12-14]. Figure 2 shows a simulation of phosphorescent signals at different temperatures as they appear after a 5ns laser pulse excitation. The lifetime decay becomes faster when the temperature increases. The life time decay is extracted by applying a commercial Levenberg-Marquardt algorithm [15] from LabVIEW to the measured signal. The exponential decay function used is shown below: (3) Equation (3) is the mathematical representation of the signals illustrated in Fig.2. I0 is the initial intensity,  is the lifetime decay, B0 is the base line, and t is the time.

(2) Therefore, the larger the energy gap is to bridge, the lower is . Hence, intense light emissions are observed for the transitions between energy levels which are separated by large gaps. The link between the temperature and the lifetime decay change is used to obtain the temperature. The calibration is generated under isothermal condition in a furnace. The application of equation 2 for TBC relevant materials was shown by Steenbakker et al. in 2008 [7].

A calibration curve is obtained by placing a sample inside a box furnace and obtaining the changing lifetime decay with changing temperature in controlled temperature steps. The sample used for the calibration is a 30mm diameter disk coated with the same coating as on the Viper components. The calibration set-up is similar to the one in Fig.4 for the engine measurements, the Viper is replaced with a furnace which has an optical access. The optical energy transfer system (OPETS) was placed in front of the observation window of the furnace.

EXPERIMENTAL ASPECTS - CALIBRATION The correlation between the lifetime decay  and the temperature is different for different host materials and can also vary with the concentration of the dopants or ageing processes involving the change of the crystal structure [7,11]. Hence it was necessary to calibrate the materials to obtain a robust calibration curve for the materials used during this study (YSZ: Dy and YAG: Eu). 1

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Figure 3: Calibration curve of YAG: Eu and YSZ: Dy sensor coatings.

The laser pulse is steered onto the sample by being reflected by a dichroic mirror located in the OPETS. The OPETS collected the phosphorescence signal and the signal was guided by an optical fibre to a remote photomultiplier tube (PMT). The phosphorescence signal was observed using a band pass filter centred at 590nm for dysprosium doped phosphors and a

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Figure 2: Simulated phosphorescent temperatures. Tc < Tb < Ta.

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Laser Beam Nd:YAG Laser 355nm

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Figure 4: Typical engine measurement setup. The laser power was measured before and after engine operation. For calibration measurements the engine can be replaced with a high temperature furnace with optical access.

mirror housed inside a cube. A typical power requirement for the laser pulse is 40mJ when it reaches the OPETS. From there the beam is steered towards the sensor TBC. The laser generates a phosphorescence spot of typically 9mm diameter.

620nm filter for YAG: Eu emission. The PMT signal was amplified and digitalized. Typically the temperature of the furnace was set 20 minutes prior the measurement, providing sufficient time for the temperature to stabilize. The goal was to generate one robust calibration curve for YSZ: Dy and to understand the sensitivities of the system when changing particular settings. Due to time limitations the same was not carried out for YAG: Eu. In this process the following settings were changed:  Laser power (10% variation)  Exchange of phosphorescence filters (OD12 to OD4)  Angle of observation (0° and 30°)  Variations in the data acquisition rate One calibration curve was generated for each setting and for the Viper measurement system the results of all calibration curves were averaged. The uncertainty associated with the changed settings was defined as the difference between the average calibration curve and each curve generated for a specific setting. For the Viper operational regime (673K to 973K) the maximum error was determined to be ±4K, but typically was less. Figure 3 represents the calibration curves of both YSZ: Dy and YAG: Eu. The YAG: Eu sensor TBC was excited at 532nm and observed at 620nm. The YSZ: Dy was excited with 355nm and observed at 580nm. The europium doped phosphor (YAG: Eu) demonstrated a dynamic range between room temperature and 860K. The YSZ: Dy dynamic range starts at 673K up to 973K.

Figure 5: OPETS – constant intensity collection over a wide field of view for measurements on moving components.

The phosphorescence was collected by the OPETS and transferred to the PMT through an optical fibre bundle. A selection of filters ensured that the desired wavelength was being observed while the background light was kept to a minimum. Measuring a phosphorescence lifetime decay signal on a rotating component is a challenging task as was demonstrated by researchers in the US on thermographic phosphors paints [12,13]. The main difficulty when using a standard imaging optic in combination with a fibre is the distortion of the lifetime decay signal as described by Allison&Gillies [12]. A second temperature independent phosphor was suggested to calibrate the distortion of the signal. This previous approach was unsuitable for the current setting as no second phosphor could have been integrated into the TBC. Consequently, a new approach was developed to use a non-

EXPERIMENTAL ASPECTS – ENGINE SET-UP Figure 4 presents a sketch of the instrumentation setup used to detect temperatures using a sensor TBC in the Rolls-Royce Viper 201. The set-up is similar to the calibration set-up described before. The Nd:YAG laser emits a 5ns long light pulse at a frequency of 10Hz. The laser beam is then directed with broadband laser mirrors to the OPETS beam steering

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imaging collection optic named OPETS. The novelty of this system is not only to obtain a constant intensity in a FOV of ±6° of angle, but also enabled a remote measurement with the benefit that the probe does not interfere with the hot gas stream. The detailed description of the OPTES goes beyond the scope of this paper and is reported elsewhere [16]. However, a typical characterisation curve is shown in Fig.5. This shows the normalized intensity collected from a constant light source which is moved from -8° to +8° observation angle. This was obtained by moving a LED across the FOV and recording the intensity vs. the observation angle. The Viper is equipped with six fused silica optical windows. Each window is 25.4mm in diameter. The stand-off distance between the coating and the OPETS can vary from window to window but is typically of the order of 400mm. This makes the technique truly remote and hence overcomes problems caused by intrusive probes directly exposed to the gas stream, which can cause catastrophic damage should they fail.

manufacturer learnt about the powders and deposition rates during the development and production work, it is expected that with a small amount of additional development the current spray process could be improved.

Temperature [K]

Figure 6: Optical microscope image showing the microstructure of the top 3 layers of the coating achieved for a sensor coating for blade qualification (from the manufacturer coating qualification report).

One of the main achievements of this project was the introduction of production line air plasma spray (APS) coatings. In general the thickness of a TBC can vary between 150-1000μm depending on the component and application. To measure temperatures YSZ: Dy was applied on the combustion chamber liner and the nozzle guide vanes (NGV), whilst YAG: Eu was applied on the rotor blades. A backscattered scanning electron microscope (SEM) image of a sensor APS coating is shown in Fig.6. A parallel back-to-back test with standard type TBCs at Didcot power station revealed survivability of similar sensor coatings in excess of 4,500 effective operating hours [16]. This confirms previous tests where sensor coatings have shown equal or superior durability compared to standard TBCs. Hence, it is anticipated that the capability of these coatings is in the range of normal maintenance schedules of industrial gas turbines of 24,000hrs or even longer. Based on what the

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RESULTS AND DISCUSSION Nozzle guide vane (NGV) Figure 7 shows the measurements performed on Run A. The different graphs represent Ts, T3, T4 and the Viper rotor speed against operating time. Ts is the temperature measured by the phosphor thermometry technique on the NGV surface (spot size radius 4.5mm; location: half-way between the centre of the NGV and the engine casing). T3 is the gas stream temperature measured at 40mm upstream of the NGV. T4 is the jet pipe temperature. T3 and T4 are measured by K-type thermocouples. The thermocouple used to measure T3 has not been corrected for flow conditions and thermal radiation properties. However, the thermocouple was carefully shielded to allow for 98% measurement of the dynamic temperature and protection against radiation uncertainty [18]. The uninterrupted run lasted for approximately one hour. During this time the Viper rotor speed was manually adjusted, firstly, from 10k RPM to 13k RPM in steps of 500 RPM. At each step the speed was allowed to stabilize for about 5 minutes. Following this, the Viper rotor speed was decreased from 13k to 10k RPM again in 500 RPM steps. However, during the step changes in speed a fast transient was introduced at every other step to study the response of the sensor coating system to fast changing temperature variations. Figure 7 shows the three temperatures, T3, T4 and Ts, tracking the Viper rotor speed regime both in terms of transient response and stable running. 1300 14000

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Figure 7: Run A. Temperature detection using the STS system on a NGV at different operating regimes.

The gas stream temperature T3 shows a high signal-to-noise ratio from 12.5k to 13k RPM. The noise level is such that the first fast transient from 13k to 12k RPM is barely visible. The

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the NGV confirmed identical measurement areas for both runs. Therefore very little temperature variations between Run A and Run B were expected. Figure 8 compares standard deviations and averages for T4 and Ts for both runs. The bars at the bottom represent the sample standard deviation of T4 and Ts for a given speed. The diamonds represent the average value of T4 and Ts for a given speed. As expected the averaged values of T4 and Ts increase with speed for both runs. Also it is noted that the overall temperature of Run B is cooler by a minimum of 10K at 13k RPM and by a maximum of 30K at 12k RPM. This might be explained by the fact that the compressor inlet air temperature was 8K cooler (resulting into 10K cooler compressor delivery temperature) and globally the Viper fuel consumption was down during Run B. From Fig.8 it can be observed that with almost the same T4 temperature, the Ts temperature of Run B was about 70K cooler. A full explanation for this cannot be given but it is expected that a combination of the lower inlet air temperature and experimental uncertainties was the reason. Despite this variation the temperatures measured for Ts are in a range of temperatures which are plausible. Either by looking at T4 or by looking at the Viper manual and the turbine entry temperature predictions from Cranfield University’s TurboMatch program [17], the expected temperature for Ts should be from 800K to 1000K between 10k and 13k RPM. With reference to the standard deviation, T4 shows a precision which averages below 5K and coming from a thermocouple in a jet pipe flow this may be possible. In comparison the standard deviation for Ts , measuring on the NGV in the vicinity of the flame, is also around 5K for most operating regimes and only shows a higher value at 12k RPM during Run A when the optical probe was not decoupled from the engine frame. These results are equivalent to 0.5% and 0.6% measurement precision for Ts and T4 respectively. Taking into account that Ts is measured in the hot section of the engine, compared to T4, this is a major achievement. Figure 9 displays the average temperature in degrees Kelvin for T4 and Ts during Run A with rotor speed increasing to full 1050 Ts [K] 1000 T4 [K] 950

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noise increases with increasing speed. The flows through the engine main gas path at speeds above 80% of the design speed are significant and any obstacle in the path would be subject to severe buffeting. The induced turbulence may account for the decreased precision of the gas path thermocouple. Ts shows a high signal-to-noise ratio only at 12k RPM. The noise can be observed each time the Viper rotor speed reaches 12k RPM during Run A. When the light collector was mechanically decoupled from the Viper frame, during Run B, the signal-to-noise ratio was reduced to levels observed at other speeds. This is indicated in Fig.8 by a decrease in the standard deviation for Ts at 12k RPM for Run B. T4 follows the Viper rotor speed variations very well and does not exhibit similar problems associated with the other temperature measurements. The Ts data trace is between T3 and T4. This is expected as T4 is the exhaust gas temperature, which is lower, and the NGV is being externally cooled by compressor air meaning that it should show a lower temperature reading than the gas stream temperature T3. During the same test, Run A, T2 (compressor delivery temperature - not shown in Fig.7) increased from 373K to 473K when the speed increased from 8k to 13.5k RPM. With the cooling air on average 500K cooler than T3 it is not improbable that the surface temperature measured on the NGV could be 100K cooler than the gas temperature heating it up. Standard deviations and averages for T4 and Ts have been derived to characterize the precision of the phosphor thermometry technique. The jet pipe exhaust temperature T4 has been used as a reference in comparison to Ts due to its low signal-to-noise ratio. Statistics were applied only during stable operating regimes from 10k to 13k RPM comparing Run A and Run B.

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Run B has been measured following the dismantling and reassembling of the phosphor thermometry system used for Run A, hence providing a good test case to demonstrate the repeatability of the sensor coating system. Visual inspection of

Figure 9: Comparison between the average temperature for Ts and T4 when the engine speed is increasing and decreasing during Run A.

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temperature, however they were not measuring at the exactly the same position. Ts and Tp measurement spots were measured on opposite side of the inner flame tube (180° apart). Also Tp was measured a few centimetres upstream from Ts. As the temperature measurements were taken at different positions on the inner flame tube, it would be expected that there would be some difference as Tp was upstream of Ts and certainly Tp shows a slight increase in temperature at the design condition (13k RPM). However the combustor is designed to provide even distribution of heat by a symmetrical shape and careful cooling to avoid any localized hot spots, therefore it might be expected that the temperature would be reasonably balanced around the flame tube. A temperature difference of several hundred Kelvin is not being expected. After operation inspection of the inner flame tube showed no evidence of localized heating so the assumption is that the flame tube operated as designed. The pyrometer used on this measurement was a LAND SOLOnet SN11 with a measurement range between 823K and 2023K. The pyrometer has a spectral response of 1m and a response time of 10ms. The emissivity was set to 1. By using the Wien’s law approximation the real temperature of the component can be calculated once the component emissivity is known. Because the measurements were performed with an emissivity of 1, the calculated temperature with a lower emissivity will always be higher. At the given wavelength a typical emissivity of a ceramic surface such as a TBC would be around 0.5 [19]. This however would increase the temperature reading of the pyrometer and an example is being given later. During Run D (Fig.10) the Viper rotor speed was varied to change the engine conditions. The speed was firstly increased from 7k RPM to 13.5k RPM decreased from the 13.5k RPM to 10k RPM, and finally a rapid transient from 5k to 11k RPM was performed. When the speed was increased, it was stabilized for about 5 minutes at 7k, 9k, 11k, 12k, 13k and 13.5k RPM. When the speed was decreased three fast transients were performed. A fast transient begins with a rapid decrease in speed, followed by a rapid increase in speed. The first transient started at 13.5k RPM, the second at 12.5k and the last one at 11k RPM. The temperatures measured by Tp at 5k, 7k, and 9k RPM are similar. This is thought to be due to the measurable temperature range limitation of the pyrometer. Above these speeds the pyrometer has the tendency to measure exactly the same temperature as T3 except at 13.5k RPM where the difference between T3 and Tp is about 60K. Only the temperature measurement at Tp and T3 recorded a drop when the Viper was stabilized at 13k RPM. When the speed was decreased the pyrometer followed the transients except when the temperature is expected to go below the minimum measurable limit. The final transient was followed by the pyrometer once the temperatures were high enough to be measured. The temperature measured by the pyrometer at 13.5k RPM was around 1200K. The Viper manual states that temperature inside the Viper should not exceed the 1073K mark. The pyrometer was measuring a temperature which is 130K higher with an emissivity setting of 1. However, it is estimated that the

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load and then decreasing. The temperature differences between T4 and Ts is, on average, 65K and is more or less constant for the speed range between 10k and 12k RPM. However for the 13k RPM speed this temperature difference almost doubled to 115K. The heat energy used in part to drive the turbine is being used inefficiently at the off-design condition below 13k RPM so there is a reduced temperature difference across the turbine. When the engine reaches the design condition at 13k RPM the turbine will be extracting the heat energy as designed so the upstream NGV temperature increases (Ts) but the downstream jet pipe temperature (T4) rise is limited by the more efficient extraction of heat energy, leading to a larger temperature difference. Also the temperatures are slightly lower when the speed decreased compared to when the speed increased. This may be due to inaccuracies in the positioner on the Viper engine fuel control system. Indeed the average speed is always 30 RPM slower when the speed decreases compared to when the speed increases. 1550 14000

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Figure 10: Shows the temperature reading for the combustion chamber during Run D.

Combustion chamber Figure 10 presents the data collected during Run D. Four different temperatures and the Viper rotor speed have been measured for approximately one hour. The data for Ts, now the temperature measured on the inner flame tube surface using the sensor coating technology, and Tp, the temperature of the inner flame tube measured by a pyrometer, were recorded with an acquisition rate of 1 sample per second when the speed was lower than 12k RPM. When the speed was higher than 12k RPM the acquisition rate was decreased to 1 sample every 8 seconds for both techniques. This change in acquisition rate was adopted due to the increase in the background light from the flame above 11k RPM. Typically, when the signal is collected every second the number of averaged signals is 10, whilst when collected every 8 seconds the number of signals is 80. T4 is the jet pipe exhaust temperature and T3 is the gas stream temperature as were defined for Run A and B. The acquisition rate of T3 and T4 was 1Hz. As mentioned previously, Ts and Tp were both measuring the inner flame tube

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When the speed was decreased Ts could not follow the first transient as the integration time of the measurement was set to 8 seconds. Below 12k RPM the integration time was set to 1 second which allowed the sensor coating system to follow the two last transients. As for T4 when the Viper rotor speed was decreased from 10k to 5k RPM the temperature at first decreased and then increased to a stable condition. As for T4, when the final transient from 5k to 11k started, the measured temperature started to decrease and then finally to follow the Viper rotor speed. But unlike T4 at the end of the final transient, the temperature stabilized almost exactly to the previous stable condition when the Viper was at 5k RPM. Despite the fact that the temperature measured with the pyrometer did not accurately represent the temperature of the inner flame tube surface, pyrometers have the advantage of showing high measurement repeatability. Hence the pyrometer data were used to compare with the sensor coating data. Figure 11 shows the average temperature of Tp and Ts calculated for different speeds between 7k and 13.5k RPM. Run C and D were performed with the exact same engine and instrumentation settings. Figure 11 shows that Ts and Tp have a permanent offset where Tp is always above Ts. This offset is constant from 7k to 11k RPM and increases from 12k to 13.5k RPM. The repeatability of the pyrometer measurement was such that the average temperature variation between the two runs was around 15K. In comparison the repeatability of Ts shows an average variation of 5K.

Temperature [K]

emissivity of the coated surface of the Viper inner flame tube is around 0.5 at the given wavelength [19]. Consequently, applying the new emissivity value and correcting with Wien’s law the measured temperature would increase by about 60K bringing the maximum temperature recorded by the pyrometer to 1260K. This seems an unrealistic value and it is concluded that the pyrometer technique is not suitable to obtain accurate temperature readings at this location. It is speculated that the high temperature readings are caused by additional intensity contributions from the flame either through reflections on the combustion liner wall or from hot radiating particles in the flow. 1400 Run C 1200 Run D 1000 800 600

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Figure 11: Repeatability of the measurement systems for two independent runs C and D. Ts demonstrates repeatability equal to the commercial pyrometric system Tp over a wide range of operating conditions.

This demonstrates that the repeatability of the temperature data for the novel sensor coating system is comparable to a commercially available pyrometer system.

When the Viper reached 13k RPM Ts measured a drop in temperature which was shorter in duration than the one measured by T3 and Tp. Also, as for T3, the maximum temperature measured at 13k RPM was the same as the temperature measured at 13.5k RPM. It is noted that the temperature of the inner flame tube surface was reasonably constant when the Viper was between 13k and 13.5k RPM.

Rotating blades The last performed test, Run E, was accomplished on the rotor blades. The main difficulty of this measurement comes from the fact that the phosphorescence spot moves with the blades. For that reason the OPETS was used to measure the temperature on blades coated with YAG: Eu. One of the measured phosphorescence signals is plotted in Fig.12.

2 – Signal partly outside the OPETS FOV

1 – Signal fully inside the OPETS FOV

3 – Signal totally outside the OPETS FOV

. Figure 12: Lifetime decay of the sensor coating (Yag:Eu) after a laser pulse excitation (355nm, 5ns) measured on a rotor blade speeding at more than 350m/s

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REFERENCES [1] Ruud, J., Lau, Y. C. and Kwasniewski V., 2003, “Increased Fuel Efficiency And Decreased Emissions Through TBCs”, Published in Performance of the Third 50 Completed ATP Projects, Status Report - Number 4 NIST Special Publication 950-4, Septembre 2006, pp. 5758 [2] Amano, K., Takeda, H; Suzuki, T.; Tamatani, M; Itoh, M.; Takahashi, Y., 1987, “Thermal Barrier Coating.”: Patent 4774150. [3] Choy, K.L., Heyes, A.L., and Feist, J.P., 1998, “Thermal Barrier Coating With Thermoluminescent Indicator Material Embedded Therein”. Patent 6974641. [4] Feist, J.P and Nicholls, J.R , 2009, “Multi-Functional Material Compositions, Structures Incorporating The Same And Methods For Detecting Ageing In Luminescent Material Compositions,” patent application number EP20090750110. [5] Feist, J.P. and Heyes, A.L., 2003, “Coatings And An Optical Method For Detecting Corrosion Process In Coatings,” GB. Patent 0318929.7. [6] Feist, J. P., and Heyes, A. L., 2000, “Europium-Doped Yttria-Stabilized Zirconia For High-Temperature Phosphor Thermometry”, Proceedings of the Institution of Mechanical Engineers, 214 Part L, pp. 7-11.. [7] Steenbakker, R.J.L., Feist, J.P., Nicholls, J.R. and Wellman, R.G., 2008, “Sensor Tbcs: Remote In-Situ Condition Monitoring Of EB-PVD Coatings At Elevated Temperatures”, Berlin, Germany: AMSE Turbo Expo 2008, June 9-13. [8] Hüfner, S., 1978, Optical Spectra Of Transparent Rare Earth Compounds, New York, San Francisco, London: Academic press. [9] Weber, M. J., 1968, “Radiative And Multiphonon Relaxation Of Rare-Earth Ions In Y2O3”, The Physical Review, 171(2), pp. 283-291. [10] Riseberg, L. A. and Moos H. W., 1968, “Multiphonon Orbit-Lattice Relaxation Of Excited States Of Rare-Earth Ions In Crystals”, The Physical Review, 174(2), pp. 429438. [11] Feist J.P., Nicholls J.R., Fraser M.J., and Heyes A.L., 2006, “Luminescent Material Compositions And Structures Incorporating The Same”, Patent PCT/GB2006/003177. [12] Allison, S. A. and Gillies, G. T., , July 1997, “Remote Thermometry With Thermographic Phosphors: Instrumentation And Applications” Scient. Instrum. [13] Tobin, K. W.; Allison, S. W.; Cates, M. R.; Capps, G. J.; Beshears, D. L.; Cyr, M.; Noel, B. W., 1990, "HighTemperature Phosphore Thermometry of Rotating Turbines Blades," 28(8), pp.1485-1490. [14] Hussain Khalid, A. and Kontis, K., 2008, “Thermographic

The OPETS was installed at 400mm from the blade. It is possible to observe three distinct parts in the measured signal. The first part, (noted 1 in Fig.12), shows when the phosphorescence spot is entirely in the field of view. The second part, (noted 2 in Fig.12), shows when part of the phosphorescence spot is outside the FOV, and the third part (noted 3 in Fig.12) shows when the phosphorescence spot is totally outside the OPETS field of view. By using the calibration curve presented in Fig.3, the temperature associated with the lifetime decay shown in Fig.12 is 733K. However, while a full assessment of the data will follow at a later stage it can be noted that measurements of rotating phosphorescence signals can be performed at relevant engine speeds.

SUMMARY AND CONCLUSION Successful temperature measurements were conducted using a Sensor TBC on an operating jet engine. The aim was to bring together all sub-components of a system: production line coatings, advanced instrumentation and data acquisition. The application of the system has proved that a phosphorescent based system integrated into a TBC can be used for high precision measurements. The precision of the system is comparable to a standard thermocouple in the exhaust gas stream. Further, measurements were conducted looking through flames or hot gases inside the combustion chamber. The temperature readings correlated well with the engine operating conditions. The new sensor system shows the same repeatability as a commercial pyrometer. The advanced optic enabled the detection of signals from a rotating turbine blade at 350m/s. The system promises highly precise measurements on operating engines.

ACKNOWLEDGEMENT The authors are grateful to Scott Booden from Cranfield University, for operating and maintaining the Rolls-Royce Viper, to Prof John Nicholls and Tim Rose from Cranfield University, for advice on coating manufacturing technology, to Andy Heyes, Chris Pilgrim and Abderahman Rabhiou from Imperial College London, for their fruitful discussions. Also the authors like to acknowledge Geoff Beynon from Land Instruments, for his expertise in pyrometry and Prof Robert Vaβen from Forschungs Zentrum Jülich, Germany, for his advice on APS coating manufacturing. Most of the work of this paper has been co-funded by the Technology Strategy Board and the EPSRC under the programme Materials for Energy 2007 with the title ‘Sensor Coating System – SeCSy’. A demonstration video can be found here [20].

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Phosphors for High Temperature Measurements: Principles, Current State of the Art and Recent Applications,” Sensors, 8(9), pp 5673-5744. [15] Press, W. H., Teukolsky, S. A., Vetterling, W. T. and Flannery, B. P., 1992, Numerical Recipies in Fortran, Second edition ed.: Press Syndicate of the University of Cambridge. [16] Feist, J. P., Sollazzo, P. Y., Berthier, S., Charnley, B. and Wells J., 8 & 9 November 2011, "Application Of An Industrial Sensor Coating System On A Rolls-Royce Jet Engine For Temperature Detection", Proceedings Of The 6th Gas Turbines Conference, Gas Turbine In The Market Tomorow , Milton Keynes. [17] Cranfield University, 2010, “TurboMatch”, Cranfield Publications. [18] Cohen, H., Rogers, G. F. C., and Saravanamuttoo, H. I. H., 2001, “Gas Turbine Theory”, Pearson Education Ltd, fifth edition, pp 279. [19] Land Instruments International, 2006, “SOLOnet Digital Infrared Thermometer User Guide”, Publication PP307 (B 10/06). [20] Southside Thermal Science, 14 February 2012, "Video," http://www.stscience.com/focus-and-press/video.

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