Flame Diagnostics with Acetone-OH Simultaneous PLIF

Abstract

Instantaneous, 2-D-sliced flame visualization scheme based on acetone-OH simultaneous PLIF (Planar Laser-Induced Fluorescence) concept is proposed and its applicability to flame diagnostics on premixed combustion is addressed. Acetone seeded in the fuel flow and flame-generated OH are visualized simultaneously via PLIF with one line (which corresponds to OH Q₁(7) (1,0) band absorption line: 283.2 nm) and fluorescence signals from acetone/OH are corrected by one detector; thus only conventional PLIF set (one laser and one detector combination) is required. In the present system, acetone and OH act as marker of unburned and burned zone, respectively. Qualitative behaviors of "no-signal zone (dark zone)" formed between these fluorescence signals are examined in methane-air flames (both laminar and turbulent conditions). Results show that the thickness of the dark zone varies depending on the equivalence ratio and the flame thickness experimentally defined as fuel 50 % -OH 50 % distance is well correlated to corresponding theoretical results (distance from starting point of preheated zone to heat release zone) in wide range of mixture conditions, indicating the validity of the present-proposed visualization scheme. Distinct dark zone can be clearly observed even in turbulentcases and some images show unburned 'island' flame structures, suggesting the applicability of this scheme to the complex turbulent combustion diagnostics. Under the condition of unity Le (Lewis number), this scheme may show thethree-dimensional flame configuration through the difference of the dark zone thickness. Advantage and disadvantage of the present-proposed scheme are addressed and milestones for further study are pointed.