On the interaction of the Darrieus-Landau instability with weak initial turbulence

In this work, the development of the Darrieus-Landau instability is examined at large scale using atmospheric-pressure methane-air flames in the presence of weak initial turbulence, as well as in quiescent conditions. In the absence of initial turbulence, the critical flame radius for the onset of instability is found to be on the order of 20-35 cm, increasing with methane concentration. In addition, an oscillatory flame acceleration is observed that is directly analogous to the behavior of propane-air mixtures seen in a previous study. Weakly-turbulent initial conditions lead to an earlier onset of flame instability that eliminates the rapid acceleration that occurs during global cell formation along with the oscillatory flame acceleration. It is also shown that weak initial turbulence does not significantly affect the burning velocity during the initial, laminar, flame propagation. Instead, initial turbulence triggers both an earlier onset of instability as well as an increase in the rate of flame acceleration. As a result, significant increases in overall flame velocity is observed in the presence of weak initial turbulence, and this difference increases with flame radius. (C) 2016 by The Combustion Institute. Published by Elsevier Inc.