Flame Surface Properties of Premixed Flames in Isotropic Turbulence: Measurements and Numerical Simulations

An experimental and theoretical investigation of free turbulent premixed flames propagating in isotropic turbulence at neutrally stable preferential diffusion conditions is described. Experiments were limited to the wrinkled thin laminar ftamelet regime and involved mixtures of hydrogen, air, and nitrogen ignited within a fan-stirred combustion chamber. Measurements included flame tomography for flame surface statistics and two-point laser velocimetry for unburned gas turbulence properties. Flame surface properties were numerically simulated using a two-dimensional flame propagation algorithm combined with statistical time series simulation of unburned gas velocities along the flame surface. Measurements showed progressively increasing flame radius fluctuations, flame surface fractal dimensions, and turbulent/laminar flame perimeters with increasing mean frame radius. The rate of increase of these properties all increased with increasing turbulence intensities relative to the laminar flame speed. Simulated flame properties duplicated these trends but underestimated the effects of turbulence--a deficiency mainly attributed to the limitations of a two-dimensional simulation. Extension of the method to a three-dimensional simulation, to obtain a more definitive evaluation of the simulation, appears to be computationally feasible.