Propagation of Darrieus-Landau unstable laminar and turbulent expanding flames

The propagation of laminar and turbulent expanding flames subjected to Darrieus-Landau (DL), hydro-dynamic instability was experimentally studied by employing stoichiometric H-2/O-2/N-2 flames under quiescent and turbulent conditions performed in a newly developed medium-scale, fan-stirred combustion chamber. In quiescent environment, DL unstable laminar flame exhibits three-stage propagation, i.e. smooth expansion, transition acceleration, and self-similar acceleration. The self-similar acceleration is characterized by a power-law growth of acceleration exponent, alpha, with normalized Peclet number, which is different from the usually suggested self-similar propagation with a constant alpha. The imposed turbulence advances the onset of both transition acceleration and self-similar acceleration stages and promotes the strength of flame acceleration as additional wrinkles are invoked by turbulence eddies. A DL-turbulent interaction regime is confirmed to be the classical corrugated flamelets regime. Furthermore, the DL instability significantly facilitates the propagation of expanding flames in medium and even intense turbulence. The development of DL cells is not suppressed by turbulence eddies, and it needs to be considered in turbulent combustion. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The experimental study investigates the propagation of laminar and turbulent expanding flames under Darrieus-Landau instability using stoichiometric H-2/O-2/N-2 flames in a medium-scale, fan-stirred combustion chamber. It was found that turbulence accelerates the flame propagation and induces additional wrinkles, advancing the onset of acceleration stages. The interaction between DL instability and turbulence is identified as the corrugated flamelets regime, facilitating flame propagation even in intense turbulence.