Turbulent Premixed Flame Acceleration in Duct Flows

Unlike traditional flame acceleration studies in closed or half-open pipes, a flowing system can provide new insights into the mechanisms responsible for rapid flame acceleration in early stages of burning. The current flowing facility has advantages over the classical static facility: turbulence generation without the need for blockages in front of the flame, large number flame of ensembles, and a modular test section for studying specific stages of flame acceleration. A blow-down facility is used to study flame acceleration in a 50 x 50 mm² subsonic tunnel in which methane-air kernels are ignited with a 532 nm Nd:YAG laser. As the kernel convects downstream, it becomes confined and accelerates, with the leading flame tip propagating downstream and reaching peak velocities of ~100 m/s and accelerations of ~5000 m/s² before exiting the test section. The background turbulence intensity is controlled by changing upstream turbulence-enhancing grids, with higher turbulence intensities causing greater acceleration. High-speed simultaneous Schlieren and PIV are used to evaluate flame evolution at multiple downstream locations. The results are compared to classical static system experiments, showing similar qualitative trends and enhanced flame tip acceleration.