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Photomultiplier tube (PMT) nonlinearities relevant for single shot high-speed lifetime phosphor thermometry were investigated by simulating decay curves with a light emitting diode (LED) at repetition rates between 1 Hz and 10 kHz. The PMT gain, LED decay time, and background radiant flux were also varied to investigate their impact on the measured decay time error. Errors in the measured decay time due to nonlinear PMT performance lead to temperature measurement errors; therefore, having the measured decay time sensitive to only phosphor temperature is highly valuable for more reliable temperature measurements. Photocathode bleaching had a significant impact on the signal level linearity for PMTs with excitation frequency in the kHz regime but had a smaller impact on the decay time error. Space charge effects were most noticeable at high radiant flux levels and high repetition rates. Strong background radiant flux may lead to decay time errors, and a gateable photocathode could be an effective method to reduce decay time errors. The best decay time measurement configuration to maximize precision without sacrificing accuracy is to use PMT gain in the recommended range and the highest radiant flux where the PMT response is still linear. The degree of nonlinearity in the PMT response is partly detector dependent; therefore, the results in this work may differ among detectors; however, the analysis presented in this work provides guidelines for improving the temperature accuracy of kHz lifetime phosphor thermometry measurements.

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A method is specified which enables lifetime calibration of multiple phosphors and emission lines at the same time to temperatures above 1900 K. The experimental setup and algorithm used for data collection and experimental equipment control are described. The phosphors were coated on an alumina oxide disc and the reference temperature was measured using three type B thermocouples. The algorithm automates the data collection process such that no input from an operator is required during operation. The potential systematic error in calibration temperature was evaluated and was less than 1 % around 1400 K.

Online wall temperatures were measured with fiber-coupled phosphor thermometry in a full-scale gas turbine combustor. The combustor was operated with natural gas and up to 100 vol% hydrogen at engine-relevant conditions. Two phosphors were tested for this application, namely YAG:Dy and YAG:Tm;Li. Although YAG:Tm;Li seemed to be the most promising phosphor for this application, it turned out to be incompatible with the used setup due to a strong interfering signal generated by the laser in the used fiber setup. A strategy to compensate for interferences from flame emissions during natural gas operation was developed. With this strategy it was possible, to obtain single-shot temperature measurements at 15 Hz and a precision of 2 – 7 K for a 1 s average.