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chapter 5 turbulent diffusion flames - FedOA

chapter 5 turbulent diffusion flames - FedOA

LIF, cm -1 sr -1 LII, cm

LIF, cm -1 sr -1 LII, cm -1 sr -1 1.2E-07 1.0E-07 8.0E-08 6.0E-08 4.0E-08 2.0E-08 0.0E+00 8.0E-08 7.0E-08 6.0E-08 5.0E-08 4.0E-08 3.0E-08 2.0E-08 1.0E-08 0.0E+00 0 2 4 6 8 10 12 14 16 18 20 22 HAB, mm 62 LIF C/O=0,92 P=1,3 LIF C/O=0,92 P=1,7 LIF C/O=0,92 P=2,1 Fig. 3.4 LIF signals as function of HAB for a ethylene/air flame with C/O=0,92 and velocity of cold gas 10cm/s. The different symbol are relative to different laser power. LII C/O=0,77 P=1,3 LII C/O=0,77 P=1,7 LII C/O=0,77 P=2,1 0 2 4 6 8 10 12 14 16 18 20 22 HAB, mm Fig. 3.5 LII signals as function of HAB for a ethylene/air flame with C/O=0,77 and velocity of cold gas 10cm/s. The different symbol are relative to different laser power.

LII, cm -1 sr -1 1.2E-07 1.0E-07 8.0E-08 6.0E-08 4.0E-08 2.0E-08 0.0E+00 LII C/O=0,92 P=1,3 LII C/O=0,92 P=1,7 LII C/O=0,92 P=2,1 0 2 4 6 8 10 12 14 16 18 20 22 HAB, mm Fig. 3.6 LII signals as function of HAB for a ethylene/air flame with C/O=0,92 and velocity of cold gas 10cm/s. The different symbol are relative to different laser power. Figures from 3.1 up to 3.6 shown several LIF and LII data collected in premixed ethylene/air flames as function of HAB changing the C/O ratio and the incident laser power. For all conditions both LIF and LII intensity do not change in the investigated power range being within the typical plateau region. Moreover considering the particle temperature, subsequent the laser heating, reported in Fig. 3.7, which was obtained by fitting the experimental laser induced emission spectra with the Planck’s Law equation, can be observed that above 1.5 mJ the particles vaporization temperature of about 4000K is reached and incandescence, as well as the C2 signal due to vaporization, remains constant. This observation justify the choice to operate at of laser power of 1.5 mJ for a correct use of the technique, as previously reported in literature [50, 51]. The influence of the delay acquisition times is reported in Figure 3.8. Signals are collected fixing the duration of the acquisition at 20 nm and changing the delay time every 2 ns. Figure 3.8 (a) shows a LIF signal (at 300 nm) faster than typical C2 63

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