Non-unity Lewis Number Effects on Curvature Statistics in Prevaporized, Turbulent Liquid Fuel Jet Flames: Curvature Calculation Methodology

A new image processing technique with topology tracking is introduced to calculate curvature statistics as extracted by CH radical planar laser-induced fluorescence (PLIF) measurements. The aim is to develop a capability to investigate non-unity Lewis number (Le ≠ 1) effects on curvature statistics and distributions in prevaporized, turbulent liquid fuel jet flames. Such flames typically exhibit significant levels of local extinction, so that the ability to determine the curvature sign from CH layer information is non-trivial if based only on the orientation of the CH layer relative to the reactant stream. This study proposes a simple topology tracking technique that allows for the calculation of curvature statistics on isolated reaction zones, classified based on pre-determined topology arguments. Binarized CH PLIF images are first utilized to distinguish between reaction zones and holes, pockets, or small isolated patches, which are generally not expected to alter curvature statistics. Consequently, a skeletonized model of the remaining reaction zones is employed and combined with the zone boundaries to assign each point of the reaction zone edge to the reactants or products stream. The latter allows for the correct sign and probability density functions of curvature to be evaluated. In this direction, curvature statistics are calculated here for a representative dataset of three prevaporized liquid fuel jet flames with Re = 10,000, equivalence ratio of 1.2, and a preheat temperature of 470 K. This work presents the first statistical curvature study using CH PLIF exclusively for liquid fuels