An experimental apparatus to measure soot morphology at high pressures using multi-angle light scattering

Abstract

In this work, a novel experimental setup is described which is designed and built specifically to study soot morphology using light scattering and extinction techniques at elevated pressures. The experimental setup consists of a counterflow burner housed inside a pressure vessel. A unique feature of this pressure vessel is the four curved optical windows which can provide the required optical access for light scattering measurements in order to infer the morphological parameters of soot. Using this setup, N 2-diluted ethylene and air counterflow flames are stabilized from 3 to 5 atm. Global strain rate (a) of 30 s−1 is maintained at all conditions and all the flames studied are soot formation (SF) flames. Light scattering by soot is measured between 15° to 165° at different locations along the axis of the burner. Ratio of total scattering to absorption (ρ sa), path averaged soot volume fraction (f v), mean primary particle size (d p), mean radius of gyration of aggregates (R gm) and fractal dimension (D f) are calculated from multi-angle light scattering and extinction data using Rayleigh–Debye–Gans theory for fractal aggregates (RDG-FA). ρ sa, f v, d p, and R gm increase as the pressure is raised. The scattering contribution in these measurements vary from 1.3% to 16% of absorption which suggests that wide angle optical access is essential for accurate measurements of f v. D f equal to 1.27 is measured near the flame at 3 atm which increases as the particles are convected away from the flame and D f increases to 1.98 at 5 atm.

Effects of Ambient Oxygen and Density on Primary Soot Size under Diesel-Like Conditions Using a Lagrangian Soot Tracking Model

“…However, experimental studies on SVF have shown that decreasing ambient oxygen [58] and increasing ambient density [62] can increase SVF in diesel spray flame. In addition, measurement of primary soot size in canonical flame setups also showed similar findings regarding the effect of oxygen [63] and ambient density [64][65][66] on primary soot sizes.…”

Flame Synthesis of Carbon and Metal-Oxide Nanoparticles: Flame Types, Effects of Combustion Parameters on Properties and Measurement Methods

“…The application of light-induced scattering techniques proved the existence of nascent soot, particle size, mass fractal dimension, aggregate size, and number of primary particles per aggregate [ 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 ]. Generally, the laser beam is focused first on a point in the probe volume with a diameter near 1 mm; the scattered light is detected by a photomultiplier tube.…”

A layer-peeling method for signal trapping correction in planar LII measurements of statistically steady flames

“…Understanding soot formation during the burning of hydrocarbon fuels is challenging because flames represent an extreme environment where complex physical and chemical processes take place simultaneously and there are very large gradients of temperature, species concentrations, and properties of flamegenerated soot particles. Non-intrusive and quasi non-intrusive laser-based techniques have been developed over the years for measurements of detailed soot properties, such as morphology and maturity, and global properties such as total mass and volume fraction (f s ) [1][2][3][4][5][6][7][8]. f s is an important flame property because it controls the radiative intensity emitted by the reactive system.…”

“…However, the soot particles present along the path between the probe volume (source of emission) and the detector can attenuate a portion of S LII through absorption and scattering, causing the detected LII signal (S c ) after attenuation to be lower than the actual one, leading to an underestimation of f s if the trapping effect is not corrected. The signal trapping effect represents a source of uncertainty in the determination of f s and primary particle size using LII, which can become important in large pool-fires [7], high-pressure flames [4,8] or in general, flames presenting a combination of large optical path and soot loading (large optical thickness) [15,17], especially for short-wavelength detection [18]. Some methods have been proposed to correct the signal trapping in 2D [18][19][20][21][22] axisymmetric flames by conducting additional light extinction (LE) measurements.…”