High-Pressure Optical Measurements of Temperature at Turbine Rotor Inlet Conditions

In gas turbine engines, the measurement of the rotor inlet temperature remains particularly challenging because of harsh operating conditions and limited access. The integrated spectral band ratio (ISBR) method is a nonintrusive optical emission gas temperature measurement technique suitable for this application. Optical fibers made of sapphire were used to transmit the radiative signal from the postcombustion zone to a Fourier transform infrared (FTIR) spectrometer. The ratio of spectral bands of H₂O, nominally 100 cm⁻¹ wide between 4600 and 6200 cm⁻¹, was used to infer temperature. ISBR and thermocouple measurements were obtained during two temperature sweeps: one at high load and one at low load (pressures of 1.2 and 0.7 MPa, respectively). The average of three thermocouples 76 mm downstream of the ISBR measurements was on the order of 200 K lower than the ISBR temperatures, consistent with a radiative correction and the heat loss between the two measurements. The change in ISBR temperature (95 K) during the sweep was similar to the change in average thermocouple temperature (89 K). Repeatability of the optical measurement at a given operating condition was on the order of ±15 K and the absolute uncertainty of a single ISBR temperature measurement was estimated to be ±61 K. A linear correlation with an R² value of 0.97 was also found between raw optical signal and thermocouple measurements, suggesting that once a calibrated measurement is obtained.