A comparative analysis of flame surface density metrics inpremixed and stratified flames

Abstract

Flame surface density (FSD) is an important quantity in premixed turbulent combustion models, many of which use it in order to predict flame behaviour and characteristics. This quantity may be determined using a statistical method based on measurements of temperature and its gradient, or a geometric method based on 2D temperature or LIF imaging. Measurements of FSD obtained using both methods have been reported in the literature, but no direct comparisons have been made between these methods in premixed or stratified flames. This paper compares these methods in both premixed and stratified datasets (up to a stratification ratio of 3) from a slot burner and a swirl burner. Temperature, local equivalence ratio and three dimensional flame normal orientations were obtained from simultaneous cross plane OH-LIF and Rayleigh–Raman line measurements. Three dimensional progress variable gradients, which are used in the statistical FSD calculations, are derived by angle-correcting gradients along the measurement line. Differences between the statistical and geometrical methods of evaluating FSD are shown to be negligible for values of progress variable between 0.2 and 0.9, and differences at extreme values are detailed and explained. This good agreement between methods is demonstrated to hold over a broad range of flame operating condition.