Investigation of the effect of dilution air on soot production and oxidation in a lab scale rich-quench-lean (RQL) burner

Abstract

This paper examines soot fields in turbulent, swirl-stabilized, non-premixed, ethylene/air flames in a Rich-Quench-Lean (RQL) model burner. The focus is on investigating the effect of dilution air on soot production and oxidation by varying the ratio of primary to dilution air while keeping the total amount of air and overall equivalence ratio constant. Planar Laser-Induced Fluorescence (PLIF) imaging was used to qualitatively reveal the spatial distributions and relative amounts of PAH. Additionally, Laser-Induced Incandescence (LII) imaging was employed to visualize soot distributions and qualitatively compare the effects of air dilution on overall soot production. Results reveal that dilution air plays a major role in mitigating soot. The penetration length of the fuel jet and the PAH were decreased as the dilution air increased. Moreover, the LII signal was decreased by orders of magnitude with the addition of dilution air. The drastic reduction in soot is attributed to the quicker mixing between the fuel jet and the upstream-flowing air from the dilution jets after they impinge upon each other at the centerline. These results can also be used in the validation of models that investigate soot formation in turbulent swirling flames.