Time Resolved Thermometry by Simultaneous Thermocouple and Rayleigh Scattering Measurements in a Turbulent Flame

Abstract

This paper investigates the utility and accuracy of the use of fine-wire thermocouples for time resolved thermometry in turbulent flames. The problem, if course, is that there is no unique time constant in a turbulent flame with widely fluctuating temperature. An analytical formulation is presented which shows that while little error may be expected in determination of r.m.s. values of temperature, there may be a substantial error made in deduction of the mean temperature, under certain circumstances. Experimentally, in a premixed methane-air flame, a comparison is made of a time resolved compensated thermocouple measurement with a simultaneous measurement by molecular Rayleigh scattering, and the results compared with the theoretical predictions. The thermocouple, compensated through a single time constant, behaved admirably, under these conditions.