Fine Wire Thermocouple Measurements of Fluctuating Temperature

Abstract

A technique for the measurement of the statistics of the temperature fluctuation, notably probability density function and power spectrum, in turbulent diffusion flames which employs fine wire thermocouples, compensated for the effects of thermal inertia, is assessed. Measurements made in an open turbulent methane diffusion flame are reported and compared, from the standpoint of identifying the interaction between measurement technique and turbulent flame structure, with simple model predictions. The flame-intermittent zone is seen to be characterised by large fluctuations in temperature and velocity which lead to significant local variations in heat transfer to the thermocouple and hence in its time constant. Attention is therefore focussed on an assessment of the impact on measured temperature statistics of both the level of compensation and the manner it is effected. Techniques involving electrical networks and computational procedures are discussed.