Investigations on the flamelet inner structure of turbulent premixed flames F. Halter*, C. Chauveau, I. Gökalp Laboratoire de Combustion et Systèmes Réactifs Centre National de la Recherche Scientifique 1 C avenue de la Recherche scientifique 45071 Orléans cedex 2, France Corresponding author: F. Halter : halter@cnrs-orleans.fr Introduction: Interactions between flame and turbulence are of primary importance to understand the combustion mechanisms in all practical combustion systems. Numerous studies have been performed to classify premixed turbulent flames and investigate their regimes [1-9]. Numerical simulations [4, 3] have shown that the flamelet regime, which corresponds to the regime where the flame front behave like a quasi-laminar flame, can be extended away from the Klimov- Williams criterion, where small turbulent eddies enter the preheat zone but are not energetic enough nor small to disturb the reaction zone. Bray [1] and Peters [2] have presented combustion diagrams taking in account these extensions. In the present study, we investigate the flamelet inner structure of Bunsen type turbulent premixed flames by using planar Rayleigh measurements. We mainly focus on curvature/flame front thickness interactions. Experimental setup A stainless steel cylindrical combustion chamber shown in Figure 1-a has been developed enabling to work under pressure up to 1 MPa. The burner, shown in Figure 1-b, is a classical axisymmetric Bunsen burner, fed by premixed methane-air. The internal burner diameter is 25 mm. A perforated plate is located 50 mm upstream the burner exit and generates the flow turbulence. An annular laminar methane-air pilot flame stabilizes the turbulent main flame. Optical access PF MF PP Figure 1 : a) Combustion chamber. b) Schematic view of the burner (PF = pilot flame; PP = perforated plate; MF = main flow). A 15 Hz pulsed Nd-Yag laser at 532.5 nm is used for Rayleigh scattering. The pulse energy is 180 mJ. The laser beam passing through a 500 mm focal length spherical lens and a -50 mm focal length cylindrical lens produces a light sheet 50 µm thick and approximately 50 mm high.