GAS TEMPERATURE MEASUREMENT AT THE EXIT PLANE OF A TYPICAL GAS TURBINE COMBUSTOR

This paper describes an attempt to use a technique called thin filament pyrometry (TFP) to measure simultaneously multiple temperature lines at the exit plane of a gas turbine combustor. This technique diverges significantly from the widely used setup that characterizes the TFP method [W. M. Pitts, H. C. Smyth, and D. A. Everest in 27th Symp. (Intl.) on Combustion, The Combustion Institute, pp. 563−569, 1998; V. Vilimpoc and L. P. Goss in 22nd Symp. (Intl.) on Combustion, The Combustion Institute, pp. 1907−1917, 1988; W. M. Pitts in 26th Symp. (Intl.) on Combustion, pp. 1171−1179, 1996; P. B. Kuhn, B. Ma, B. C. Connelly, M. D. Smooke, and M. B. Long in Proc. 33rd Int. Symp. on Combustion, pp. 743−750, 2010]. Although the same physics apply, the approach will be discussed to indicate required changes. The experiment will utilize multiple 15-µm β-SiC fibers, which will be simultaneously imaged at 10,300 points over a total length of 525 mm. Typically, the measurable temperature range is known to be between 500 and 2100 K with the proper filter, the temperature range having a spatial resolution of ~100 µm, a temporal resolution of 1.5 ms, and an accuracy of 1.5 ± 1.0 K for temperature on the order of 2000 K [Kuhn et al., 2010]. Unlike usual TFP experiments, the filament will be calibrated with a thermocouple, with data from a Fourier transform infrared (FTIR) gas analyzer allowing a thermochemical equilibrium calculation to provide low but sufficient accuracy. Temperature at different positions along the filament will then be determined by recording relative emission intensities and assuming that the filament acts as a gray body emitter. The calibrated TFP would then be used to make a multiple-filament temperature measurement across the exit plane of a typical combustion chamber at various operating conditions. For each flame type, emissions measured with an FTIR and a calibration done with thermocouples are both necessary to provide knowledge of flow temperature and molecular composition. The flow conditions need to be well characterized to provide enough accuracy with the technique. Most studies were done with laminar diffusion flames. The case under study is a highly turbulent high-speed gas flow. The convective properties are to be validated and the mechanical resistance of the 15-µm β-SiC fibers is to be demonstrated under relatively much harsher conditions.

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