Experimental study of flame stabilization in low Reynolds and Dean number flows in curved mesoscale ducts Franck Richecoeur 1 , Dimitrios C. Kyritsis * Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Abstract Flame stabilization during non-premixed combustion in curved ducts with a diameter of the order of magnitude of the premixed flame thickness of the reactants was investigated experimentally, since it has been established that this is a configuration with potential advantages in the context of ‘‘micro’’-combus- tion. It was shown that, in such ‘‘mesoscale’’ tubes, a stable flame oscillation including extinction/re-igni- tion phenomena can be established for steady boundary conditions. These oscillations lead, under appropriate conditions, to sound emission in the 50–350 Hz range. This was a mode of stabilization in addition to the ‘‘classical’’ steady flamelet, stabilized through thermal losses to the duct walls at higher val- ues of the Reynolds number. Curvature of the duct was shown to have minimal effect on reactant mixing, which was diffusion-controlled, but significantly affected flame thickness and stabilization. To probe the fuel-oxidizer mixing in the U-shaped, optically accessible tubes, laser induced fluorescence of acetone fuel dopant was used, and the flame structure was studied using OH PLIF. The various stabilization regimes are discussed in terms of the Reynolds and Dean numbers of the tube flow. Ó 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Micro-combustors; Flame propagation; Acoustics; Laser induced fluorescence 1. Introduction The potential of curved-duct combustor de- signs for combustion-based, efficient power gener- ation was realized in the early work of Lloyd and Weinberg [1,2] who demonstrated a decrease in the flammability limit of a methane/air mixture in a ‘‘Swiss-roll’’ burner due to extensive heat recirculation. Ronney and co-workers [3–5] exten- sively examined such burners in the context of ‘‘micro-combustion’’ for autonomous, portable power generation, pursued miniaturization of the design, and discussed in detail thermal manage- ment of these systems as well as possible coupling with thermoelectric devices. The dynamics of the excess enthalpy flames involved was recently ana- lyzed theoretically by Ju and Choi [6] who studied the problem of two flat flames propagating in opposite directions in two parallel ducts. The computational studies of Cadou and Leach [7] addressed thermal management issues with a particular emphasis on fluid-hardware coupling. 1540-7489/$ - see front matter Ó 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2004.08.015 * Corresponding author. Fax: +1 217 244 6534. E-mail address: kyritsis@uiuc.edu (D.C. Kyritsis). 1 Present address: EM2C-CNRS Ecole Centrale Paris, Cha ˆtenay-Malabry, France. Proceedings of the Combustion Institute 30 (2005) 2419–2427 www.elsevier.com/locate/proci Proceedings of the Combustion Institute