Soot sheet dimensions in turbulent nonpremixed flames

摘要

A method is presented to automate the generation of the statistics of the characteristic length (L) and width (W) of the 2-D slices through 3-D soot sheets in turbulent nonpremixed flames. The method employs the simplified approximation of fitting an equivalent ellipse. The effectiveness of the method is first evaluated by comparison with two types of manual assessment. It is then applied to assess the evolution of the soot sheet dimensions in two turbulent nonpremixed propane flames. These two flames, had the same fuel flow rates but different global mixing rates, were produced by a precessing jet (PJ) and a simple jet (SJ) burner. The global mixing rate of the flames was observed to affect the shape of probability density functions (PDFs) of soot sheets L and W. The shapes of the PDFs of the flames reveal that burnout of the soot sheets in the PJ and SJ flame proceeded predominantly through the reduction of the soot sheet dimensions, and the number of soot sheets, respectively. Finally, a convenient way to estimate the actual maximum width of the single-branched soot sheets is proposed, and this value is estimated to be ～20 mm for both flames.