Interaction of acoustic waves with flame front propagation

International audienceThe mechanisms of laminar premixed flame propagation have been intensively studied over the last century. Numerous authors have highlighted intrinsic phenomena in flame propagation such as Darrieus-Landau instability and Rayleigh-Taylor instability. Rayleigh-Taylor instability is often linked to the interaction between the flame front and an acoustic wave. To better characterize the interaction between a flame and aerodynamic conditions, we designed a special vertical closed tube apparatus. Our analysis focused on the behavior of a flame that propagates in a uniform stoichiometric mixture of H2 and O2 diluted with nitrogen. The experimental investigation revealed that acoustic waves emitted as the flame formed near the ignition point could increase the flame front surface by a factor of 10. An acoustic node with an amplitude of 1.3 m was identified and seemed to be responsible for the disappearance of one of the acoustic modes and for a reduction in the average flame surface. This could explain why the flame trajectory had two distinct parts: one corresponding to propagation at a high speed in the lower part of the tube, and the other with a slower speed in the upper part of the tube. The flame surface seemed to depend primarily on the frequencies of vibration and marginally on the nature of the reactive components. Propagation velocities, obtained by multiplying these flame surfaces by the fundamental burning velocity, strongly depended on the mixture reactivity