Diagnostics of Reactive Zone in Premixed Flames via Acetone-OH Simultaneous PLIF

Imaging scheme based on Acetone-OH simultaneous PLIF (Planer Laser-Induced Fluorescence) is applied for diagnostics of reactive zone over the premixed flames and the reactive zone imaging are demonstrated for turbulent premixed flame conditions. In the present study, visualization of reactive zone is brought by simultaneous measurement of unburned zone through acetone (seeded into the fuel flow) and burned zone through OH (naturally generated by combustion), instead of looking for minor species formed only at thin reaction zone (like CH, CHO, C2). One huge advantage of the present scheme is to use only one laser and one detector combination to access multiple flame quantities (e.g. shape of flame surface, flame thickness, relative flame intensity) in wide range of equivalence ratio of the mixture, mostly in lean conditions. Applied excitation line is 283.22nm, which corresponds to OH Q1(7) (1,0) band absorption line and is within the acetone absorption band to excite acetone and OH simultaneously. Instantaneous 2-D reactive zone is imaged by single ICCD camera with band-pass filter which transmits both acetone and OH fluorescence spectra. Demonstrations of reactive zone imaging show a distinct dark zone (non-signal zone) sandwiched by acetone (unburned zone) and OH (burned zone) fluorescence regimes in all images beyond the extinction conditions. In the previous study, we have found that the two boundaries of the observed dark zone correspond to the fuel decomposition edge (unburned side) and ignition point (burned side), respectively, and the dark zone is equal to the important radical pool (e.g. H2O2, HO2) to initiate the subsequent chain branching reactions. Pocket structures (unburned pocket in hot region and burned pocket in cold region) are properly captured in turbulent flame conditions. Local extinction phenomena are also captured as “distorted” dark zone (no obvious sandwiched structure is found, but clear acetone front are there). Capabilities on the present scheme for further flame study are addressed.