Experimental Investigation on the Symmetry and Stabilization of Ethanol Spray Swirling Flames Utilizing Simultaneous PIV/OH-PLIF Measurements

A detailed experimental study of ethanol spray swirling flames was performed in an axial bluff body stabilized burner. The characteristics of the non-reacting and reacting sprays were recorded by particle imaging velocimetry (PIV) and planar laser-induced fluorescence (PLIF) of the OH radical. A few typical flames with different structures (outer-side-flame-lifting, stable, and near-blow-off) were compared and analyzed. The parameters of the spray, including the spray half-angle (alpha) and droplet number density (nd), are quantified, and it has been found the flame structure and stability were strongly correlated with the droplet distribution. Several parameters of the flow field, such as velocity magnitude (|U| vorticity (omega z), and turbulent kinetic energy (TKE), are quantitively analyzed, and it is observed that the local strain rate rose as the air flow rate increased, which is not conducive to local flame stability. Regarding the flame, quantities such as progress variable (<c>), flame height (Lf), lift-off height (hlf), and symmetry factor (Snd and S<c>) are calculated, and it can be observed that the flame symmetry keeps worsening when approaching blow-off, and the inner flame branch exhibits a worse stabilization than the outer one. Our comprehensive investigations offer a deeper understanding of stable combustion in such two-phase flames.