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chapter 5 turbulent diffusion flames - FedOA

chapter 5 turbulent diffusion flames - FedOA

Size, nm 45 40 35 30 25

Size, nm 45 40 35 30 25 20 15 10 5 0 0 1 2 3 4 5 6 r, mm Fig. 3.29 Mean particle diameters by scattering measurements vs. radial position. 4.2 LAMINAR DIFFUSION METHANE FLAMES A realistic comparison between ethylene and methane combustion, in terms of particulate formation, can not be attempted basing only on premixed combustion results. Therefore, in order to improve the actual knowledge on the effective particulate emissions by methane combustion, and to better understand the relative impact on NOC and soot of the two fuels, several measures of LIF and LII have been also performed in a methane laminar diffusion flame. The flame was the same previously investigated by Smooke et a. [79] by TPD measurements. By previously calibrated LIF and LII measurements, NOC and soot concentrations have been evaluated in the methane flame, Fig. 3.30 – 3.31. As in the case of the ethylene flame, in methane flame soot formation is located in a narrow annular region closer to the maximum temperature zone, and its maximum volume fraction is measured just after the decrease of organic carbon particle volume fraction. The radial position of the maximum soot volume fraction shifts, at increasing heights, towards the centreline NOC are preferentially formed in the lower part of the flame and closer to the flame axis. The maximum volume fraction of organic 86 z10 z20 z30 z70

carbon particles decreases at increasing heights in the flame shifting toward the centreline. It becomes negligible at the flame tip. NOC volume fraction, cm 3 /cm 3 Soot volume fraction, cm 3 /cm 3 1.0E-06 8.0E-07 6.0E-07 4.0E-07 2.0E-07 0.0E+00 1.8E-07 1.6E-07 1.4E-07 1.2E-07 1.0E-07 8.0E-08 6.0E-08 4.0E-08 2.0E-08 0.0E+00 0 1 2 3 4 5 6 r, mm 87 z20 z25 z30 Fig. 3.30 NOC volume fraction in the methane laminar diffusion flame by calibrated LIF signals. z20 z25 z30 z35 0 1 2 3 4 5 6 r, mm Fig. 3.31 Soot volume fraction in the methane laminar diffusion flame by calibrated LIF signals.

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