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chapter 5 turbulent diffusion flames - FedOA

chapter 5 turbulent diffusion flames - FedOA

The first measurable LII

The first measurable LII signal is detected at about X/D=46 showing a peak value at r/R=6 (Fig.3.34 b). Increasing the flame height up to X/D=81, LII the signal increases and moves towards the outer flame region where the LIF signal decreases sharply to negligible values. The maximum LII signal in the radial direction shifts, with increasing height, towards the flame centerline and merges with the central region at X/D=115. At higher axial locations, the LII signal is observed to decrease. The radial and axial distributions of the LII signals are in excellent agreement with the soot volume fractions reported by Kent and Honnery [80]. Fig. 3.34 Fluorescence (a) and incandescence (b) signals in Flame A. �X/D=17; ○ X/D =23; ▲ X/D =46; ● X/D =81; ◊ X/D =115; ♦ X/D =161. 92

Quite the same behavior is shown by Flame B (Fig.3.35). Fluorescence emission is the dominant signal at the beginning of the flame and it is located essentially in a narrow region close to the flame axis. Incandescence appears at greater heights and it extends to the outer flame region. The intensity of the LIF signal is higher in Flame B than Flame A and it is detected in a narrower region close to the centerline. Fig.3.35 Fluorescence (top) and incandescence (bottom) signals in Flame B. �X/D=10;● X/D =25; ◊ X/D =40; ○ X/D =70; ♦ X/D =100. Scattering measurements at 213 nm are made at selected flame heights. Figure 3.36 reports the scattering cross section (QVV) measured at X/D=23 (Fig.3.36a) and X/D=115 (Fig.3.36b) in Flame A. In the same figure, the estimated scattering values due to gas-phase products (line in the figures) are also reported. The gas species scattering is evaluated from the scattering cross 93

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