Flame front tracking in turbulent lean premixed flames using stereo PIV and time-sequenced planar LIF of OH

This paper describes the simultaneous application of time-sequenced laser-induced fluorescence imaging of OH radicals and stereoscopic particle image velocimetry for measurements of the flame front dynamics in lean and premixed LP turbulent flames. The studied flames could be acoustically driven, to simulate phenomena important in LP combustion technologies. In combination with novel image post processing techniques we show how the data obtained can be used to track the flame front contour in a plane defined by the illuminating laser sheets. We consider effects of chemistry and convective fluid motion on the dynamics of the observed displacements and analyse the influence of turbulence and acoustic forcing on the observed contour velocity, a quantity we term as s2D d . We show that this quantity is a valuable and sensitive indicator of flame turbulence interactions, as (a) it is measurable with existing experimental methodologies, and (b) because computational data, e.g. from large eddy simulations, can be post processed in an identical fashion. s2D d is related (to a twodimensional projection) of the three-dimensional flame displacement speed sd , but artifacts due to out of plane conG. Hartung · J. Hult · M.R. Mackley · C.F. Kaminski ( ) University of Cambridge, Department of Chemical Engineering, Pembroke Street, Cambridge, CB2 3RA, UK e-mail: [email protected] R. Balachandran University College London, Department of Mechanical Engineering, Torrington Place, London, WC1E 7JE, UK C.F. Kaminski SAOT School of Advanced Optical Technologies, Max Planck Institute for the Science of Light, Division III, University of Erlangen-Nuremberg, Günther-Scharowsky-Str. 1, 91058 Erlangen, Germany vective motion of the flame surface and the uncertainty in the angle of the flame surface normal have to be carefully considered. Monte Carlo simulations were performed to estimate such effects for several distributions of flame front angle distributions, and it is shown conclusively that s2D d is a sensitive indicator of a quantity related to sd in the flames we study. s2D d was shown to increase linearly both with turbulent intensity and with the amplitude of acousting forcing for the range of conditions studied.