A Study of Ion Concentration Fluctuations in Turbulent Diffusion Flames using Correlation Techniques

Abstract

An investigation of the interaction between chemistry and turbulence has been made by studying the effects of non equilibrium ion chemical kinetics in a turbulent diffusion flame. In such a system the charged species undergo a chemical reaction concurrently with turbulent mixing. Where the chemical reaction rate is greater than the appropriate mixing rate it has been theoretically predicted that a measurable difference should exist between the statistical functions used to describe the fluctuating species concentration field and that of a chemically inert constituent. Experimental evidence for this phenomenon has been established by sampling the local ion concentration fluctuations in a turbulent diffusion flame, of nozzle Reynolds number 1.0 x 10 *4 using a stationary electrostatic probe. The random positive ion saturation current collected by the probe was analysed to determine its auto correlation function. The ionisation field was generated by seeding the flame with acetylene and other metal salt solutions preselected on the basis of their Damkohler number values in the flame. Studies have also been conducted to map the flame determining both autocorrelation and cross correlation functions to obtain further information for the interaction phenomenon and of the structure of the ion concentration field throughout the flame.