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chapter 5 turbulent diffusion flames - FedOA

chapter 5 turbulent diffusion flames - FedOA

CHAPTER 4 LAMINAR

CHAPTER 4 LAMINAR DIFFUSION FLAMES 4.1 LAMINAR DIFFUSION ETHYLENE FLAMES After preliminary investigation of laminar premixed flames, that allowed us to validate the use of the diagnostic based on the fifth harmonic as laser source for laser induced emission spectroscopy in order to simultaneously characterize soot and NOC in combustion systems. The second step has been focused on the study of laminar diffusion flame, firstly burning ethylene and subsequently burning methane. The importance of diffusion flames is due to the fact that they are more representative of real combustion environments. Moreover the potential of LIF and LII, high spatial resolution, respect to extinction measurements, that need a “light of sight”, are much more evident in diffusion flames as previously reported in the paragraph 2.3.3. 4.1.1 LASER INDUCED EMISSION AND EXINCTION DATA Based on the experience relative to the study of laminar premixed flames, temporally and spatially resolved LIF and LII measurements have been performed in a ethylene laminar diffusion flame previously investigated by Rolando et al. [42] using UV and visible extinction measurements to obtain information on nanoparticles and soot particles concentration. Typical LIF and LII was identical to those collected in premixed conditions and therefore very similar to those reported in Fig. 3.1. 4.1.2 SOOT AND NOC VOLUME FRACTIONS AND MEAN DIAMETERS LIF and LII data measured at several heights within the flame have been then compared respectively with the NOC and the soot volume fraction estimated by extinction measurements [42]. (Fig. 3.21 – 3.27) 80

fluorescence signal, cm -1 sr -1 fluorescence signal, cm -1 sr -1 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 0.0E+00 0 1 2 3 4 5 6 r, mm 81 LIF z10 fv NOC z10 3.5E-06 3.0E-06 2.5E-06 2.0E-06 1.5E-06 1.0E-06 5.0E-07 0.0E+00 Fig. 3.21 LIF signals and NOC volume fraction at 10 mm as function of the radial position. 4.5E-08 4.0E-08 3.5E-08 3.0E-08 2.5E-08 2.0E-08 1.5E-08 1.0E-08 5.0E-09 LIF z20 fv nano z20 0 1 2 3 4 5 6 r, mm 3.5E-06 3.0E-06 2.5E-06 2.0E-06 1.5E-06 1.0E-06 5.0E-07 0.0E+00 Fig. 3.22 LIF signals and NOC volume fraction at 20 mm as function of the radial position. NOC volume fraction, cm 3 /cm 3 NOC volume fraction, cm 3 /cm 3

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