Measurement of Flame Temperature by Optical Fiber Thermometer with a Blackbody Cavity Sensor

Abstract

The characteristics of an optical fiber thermometer (OFT) having a blackbody cavity sensor, constructed with a thin sputtered platinum film on a sapphire rod tip, have been discussed and compared with those of bare or sheathed thermocouples. For time averaged temperature measurements by the OFT, the amount of correction for radiative heat losses is significant for the temperature range of flames. For fluctuating temperatures, on the other hand, the OFT output shows a considerably slow response due to its thermal inertia, which depends on the diameter of the sensor and flow conditions. The waveform of response predicted by a numerical simulation agrees satisfactorily with the measured one, which proves that the major factor affecting the thermal inertia of an OFT sensor is the heat capacity of sapphire. A special compensation technique is needed to improve the response of OFT.