Coupling Laser Sheet Tomography and P.L.I.F. for the Study of Atmospheric Stratified Charge Combustion

An experimental study is conducted to investigate the flame kernel characteristics for mixtures with several heterogeneous fuel distributions, in order to provide fundamental knowledges of the effect of small scale heterogeneities on global and local flame structure. One of the interests of this study is to characterize the flame propagation in a medium not so far from engine conditions, in terms of propagation time and turbulent length scales. In a vertical wind tunnel, a propane/air flame is spark-ignited in a given grid-generated turbulence at atmospheric pressure. For different initial fuel distributions and various flame propagation times, Laser Sheet Tomography and Planar Laser Induced Fluorescence (P.L.I.F.) measurements on acetone are performed simultaneously in order to characterize the flame front propagation as well as the local equivalence ratio in front of the flame. The equivalence ratio distribution is characterized in terms of heterogeneity scales and compared with the turbulence scales. Geometrical flame parameters such as flame radii, wrinkling ratio and absolute flame displacement speeds are also presented and compared with homogenous conditions. The temporal evolution of flame radius analysis indicates that lean heterogeneous conditions can lead to flame sizes close to stoichiometric homogeneous conditions. Simultaneously, it is worth nothing that heterogeneities reduce the large-scale wrinkles of the flame, adding small wrinkles and smoothing the flame front.