fv, ppm 0.25 0.2 0.15 0.1 0.05 0 PAH 0 5 10 15 20 25 HAB, mm 70 Soot NOC Fig. 3.14 Soot and NOC volume fraction at Ф = 2.00 (C/O=0.50) vs. the HAB. 3.2.2 SOOT AND NOC MEAN DIAMETERS In order to estimate the mean size of the particles, scattering measurements were performed in the same flame conditions. Figure 3.15 shows, the scattering profile measured by using the fifth harmonic (213 nm), for the flame with Ф=2, at different HAB. On the same figure the estimated gas contribution is reported too. It is possible observe that the Qvv signal measured is larger than the gas one, also in flame zones where soot is absent and only NOC particles are present. From the scattering coefficients, after subtraction of the gas contribution, and from the particles volume fraction, previously determined, the mean particles diameter, D63, was estimated using the Rayleigh theory. Figure 3.16, shows, the mean particles size which is about 3 nm in a region of the flame where only NOC particles are present, and increases at higher HAB where soot begins to appear.
Scattering coefficient, cm -1 sr -1 D 63, nm 1.0E-05 1.0E-06 1.0E-07 12 10 8 6 4 2 0 0 5 10 15 20 HAB, mm Fig. 3.15 Scattering coefficient measured in the laminar premixed flame with equivalent ratio 2 at different HAB. 0 5 10 15 20 HAB, mm Fig. 3.16 Mean particles diameter estimated by using the Rayleigh theory in the laminar premixed flame with equivalent ratio 2 at different HAB. 71