AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Size, Mass-Mobility, Effective Density, and Volatility of Soot Particles Generated from Large-Scale Turbulent Diffusion Flames
MOHSEN KAZEMIMANESH, Melina Jefferson, Alireza Moallemi, Kevin Thomson, Matthew Johnson, Jason S. Olfert, University of Alberta
Abstract Number: 742 Working Group: Combustion
Abstract Size distribution, mass-mobility, effective density, and volatility of soot particles generated from a large-scale turbulent diffusion flame was characterized under various fuel composition and exit velocity conditions. The turbulent diffusion flame was set up at Carleton University Lab-scale Flare (CULF) facility which allowed controlled experiments on turbulent flames up to approximately three meters tall at fuel gas flow rates up to ~250 SLPM (standard litres per minute at 0°C and 101.325 kPa). Three different burner sizes with a diameter of 38.1, 50.8, and 76.2 mm were used in this study. The fuel exit velocities at the burner tip were 0.5, 0.9, and 1.5 m/s and the fuel flow rates were adjusted accordingly for each burner size, which resulted in a range of flow rates from 60.5 to 246.2 SLPM. Three different fuel mixture compositions (light, medium, heavy) were tested which resembled Alberta flare gas composition. The fuel gas mixture had 6 components (i.e., C1 to C4 alkanes, carbon dioxide, and nitrogen) and the mole fraction of methane in the light, medium, and heavy composition was 0.925, 0.866, and 0.769, respectively.
Combustion products were diluted by the ambient air on the order of ~20:1 to ~120:1 as they were drawn in the collecting fume hood and insulated duct using a variable speed fan. Size distribution of soot particles was measured using a scanning mobility particle sizer (SMPS), sampling from the downstream of the duct and after the sample was further diluted by a factor of ~8:1 using an ejector diluter. Mass-mobility relation of soot particles were studied by a tandem arrangement of a differential mobility analyzer (DMA), a centrifugal particle mass analyzer (CPMA), and a condensation particle counter (CPC). Such arrangement was also used to determine the effective density of soot particles. The volatility of particles was studied by adding a catalytic stripper denuder between the DMA and the CPMA. Results showed that the total particle concentration ranged from 9.13×106 cm-3 to 4.85×107 cm-3 corresponding to light fuel mixture burned in the 76.2 mm burner at 232.5 SLPM and heavy fuel mixture burned in the 50.8 mm burner at 60.7 SLPM, respectively. The particle median diameter did not change significantly for medium and heavy fuel mixtures with various burner sizes and fuel flow rates and was approximately 100 nm; however, it was consistently smaller at ~55 nm for light fuel mixture and different burner sizes and fuel flow rates. Mass-mobility and effective density results showed that the average mass-mobility exponent, Dm, was approximately 2.55 for all combustion conditions, which is in good agreement with the reported values for the mass-mobility exponent of particles from different combustion sources in the literature (i.e., 2.49). Finally, the results showed that the mass fraction of volatile coating on the soot particles was negligible for all studied combustion conditions.