Imaging of local flame extinction due to the interaction of scalar dissipation layers and the stoichiometric contour in turbulent non-premixed flames

Abstract

This paper presents images of local flame extinction that occurs when strong scalar dissipation layers overlap with the stoichiometric contour in a turbulent non-premixed flame. Previous experimental techniques to image mixture fraction ( ξ) and scalar dissipation rate ( χ) fields are not suitable for flames experiencing a high degree of local flame extinction. To measure ξ and χ near regions of flame extinction, a new combined laser-induced fluorescence (LIF) and Rayleigh scattering technique is used that allows mixture fraction, scalar dissipation rate, temperature, and fuel consumption rate to be measured simultaneously. Local extinction events were identified and analyzed with this new technique. Local extinction was defined to occur where both the fuel consumption rate and temperature were sufficiently lowered. It was found that local flame extinction was associated with an overlap of a strong dissipation layer and the stoichiometric contour. A strong correlation was found between an increase in the scalar dissipation rate at the stoichiometric contour and a decrease in the fuel consumption rate. This implies that the interaction of a strong dissipation layer and the stoichiometric contour is an important cause of local extinction.