Topology and Brush Thickness of Turbulent Premixed V-shaped Flames

Abstract

Topology and brush thickness of turbulent premixed V-shaped flames were investigated using Mie scattering and Particle Image Velocimetry techniques. Mean bulk flow velocities of 4.0, 6.2, and 8.3 m/s along with two fuel-air equivalence ratios of 0.6 and 0.7 were tested in the experiments. Using a novel experimental turbulence generating apparatus, three turbulence intensities of approximately 2 %, 6 %, and 17 % were tested in the experiments. The results show that topology of the flame front is significantly altered by changing the turbulence intensity. Specifically, at relatively small turbulence intensities, the flame fronts feature wrinkles which are symmetric with respect to the vertical axis. At moderate values of turbulence intensities, the flame fronts form cusps. The formation of cusps is more pronounced at large mean bulk flow velocities. The results associated with relatively large turbulence intensity show that flame surfaces feature: mushroom-shaped structures, freely propagating sub-flames, pocket formation, localized extinction, and horn-shaped structures. Analysis of the results show that the flame brush thickness follows a linear correlation with the root-mean-square of the flame front position. The correlation is in agreement with the results of past experimental investigations associated with moderately turbulent premixed V-shaped flames, and holds for the range of turbulence conditions tested. This suggests that the underlying mechanism associated with the dynamics of moderately turbulent premixed V-shaped flames proposed in past studies can potentially be valid for the the wide range of turbulence conditions examined in the present investigation.