Simultaneous multi-species and temperature visualization of premixed flames in the distributed reaction zone regime Bo Zhou a , Christian Brackmann a , Zhongshan Li a,⇑ , Marcus Alde ´n a , Xue-Song Bai b a Division of Combustion Physics, Lund University, P.O. Box 118, S-221 00 Lund, Sweden b Division of Fluid Mechanics, Lund University, P.O. Box 118, S-221 00 Lund, Sweden Abstract Structures of turbulent premixed flames, operating in the thin and distributed reaction zone regimes, were investigated for stoichiometric premixed methane/air jet flames with jet Reynolds number up to 40,000 and corresponding Karlovitz number up to 286. Multi-species planar laser-induced fluorescence with high spatial resolution was applied to simultaneously image combinations of CH/OH/CH 2 O and HCO/OH/CH 2 O. In addition, OH/CH 2 O imaging was performed in combination with simultaneous Ray- leigh scattering thermometry. The CH and HCO layers showed progressive broadening along the axial dis- tance for flames with Reynolds number above 21,000 and the corresponding Karlovitz number above 126. At Reynolds number 40,000 and the corresponding Karlovitz number of 286, a mean CH layer thickness more than 10 times larger than that under laminar condition was observed, providing a clear experimental evidence of distributed reaction zone owing to turbulence/flame interaction. Additionally, spatial correla- tions between species show that OH and CH 2 O locate at mutually exclusive regions. In contrast, both CH and HCO can overlap substantially with CH 2 O. The regions of strong CH/HCO signals correspond to regions with weak CH 2 O signals. Moreover, CH and HCO are shown to be able to penetrate deeper into the OH layer than CH 2 O. Regions where CH and HCO appear distributed show a rather homogeneous temperature distribution with reduced maximum temperature compared with non-distributed conditions. Ó 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Planar laser-induced fluorescence; Distributed reaction zone; CH and HCO radicals; Turbulent combustion; Premixed methane/air flame 1. Introduction Modeling and understanding of high-intensity and small-scale turbulent premixed combustion remain a scientific challenge. Turbulent premixed combustion has been theoretically categorized into regimes depending on the interactions between turbulence and chemistry. For low-inten- sity and large-scale turbulent flames, the laminar flamelet concept [1] is widely adopted in numerical simulations based on the assumption that the http://dx.doi.org/10.1016/j.proci.2014.06.107 1540-7489/Ó 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved. ⇑ Corresponding author. Fax: +46 46 222 4542. E-mail address: Zhongshan.li@forbrf.lth.se (Z. Li). Available online at www.sciencedirect.com ScienceDirect Proceedings of the Combustion Institute xxx (2014) xxx–xxx www.elsevier.com/locate/proci Proceedings of the Combustion Institute Please cite this article in press as: B. Zhou et al., Proc. Combust. Inst. (2014), http://dx.doi.org/10.1016/ j.proci.2014.06.107