Soot particle size measurements in ethylene diffusion flames at elevated pressures

Abstract

Soot particle size is investigated in laminar nitrogen-diluted ethylene coflow diffusion flames at 4, 8, 12 and 16 atm. Line of sight attenuation and scattering are used to measure two-dimensional soot volume fraction and particle size fields for the first time at elevated pressures. Soot volume fraction dependence on pressure is consistent with the observations of similar studies, scaling approximately with the square of pressure. Scattering intensity is analyzed through Rayleigh and Rayleigh-Debye-Gans polydisperse fractal aggregate theories to provide two estimates of particle size. An increase in overall particle sizes with pressure is found, consistent with similar one-dimensional studies. Particle diameters in the annulus of the flame increase faster with pressure than those on centerline. Contrary to previous studies, the dependence of particle size on pressure was found to taper off between 8 and 12 atm, with little observed growth beyond 12 atm. The measurements provide additional data for one of the International Sooting Flame (ISF) workshop's target pressurized flames.

Soot measurements by two angle scattering and extinction in an N2-diluted ethylene/air counterflow diffusion flame from 2 to 5 atm

“…Little is known about the effects of pressure on soot morphology. Most of the flames studied at high pressure are coflow flames in which the valuable conclusion obtained is the relation between the soot volume fraction and the pressure [8][9][10][11] . For example, McCrain and Roberts [8] studied methane-air and ethylene-air coflow flames at pressures up to 25 atm and 16 atm, respectively, and found that the local peak soot volume fraction scales with pressure as P 1.2 for methane and P 1.7 for ethylene flames.…”

Measurements of Pressure Effects on PAH Distribution and 2D Soot Volume Fraction Diagnostics in a Laminar Non-premixed Coflow Flame

“…Previous non-premixed coflow experiments with an ethylene/nitrogen mixture running at similar dilutions reported that particle growth with pressure is highest between 4 and 8 bar and mostly ceases between 8 and 12 bar 11 . PLIF measurements show that this is likely due to limited PAHs at higher flame locations.…”

“…PAH location shifting towards the burner was expected, as the rate of pyrolysis increases with increasing pressure 11,37 . Previous non-premixed coflow experiments with an ethylene/nitrogen mixture running at similar dilutions reported that particle growth with pressure is highest between 4 and 8 bar and mostly ceases between 8 and 12 bar 11 .…”

“…Measurements done in 11 and in this work show significant variation in primary particle size between the centerline and wings of the flame. In this work, a comparison between measurements obtained using LOSA as compared to LII show that as pressure increases, assuming ߩ ௦ changes only in the axial direction is no longer a valid assumption.…”

“…Several techniques have been used to limit or eliminate effects from beam steering in an effort to effectively use non-intrusive diagnostics at high pressure [10][11][12] . One technique that has become increasingly utilized in high pressure diagnostic is 2D diffuse line of sight attenuation (2D LOSA).…”