Laser-Induced Ionization and Mobility Measurements of Very Small Particles in Premixed Flames at the Sooting Limit

Abstract

Laser-induced ionization signals are observed in a premixed C2H2/air flame at the sooting limit and are attributed to thermal ionization of very small particles. The mobilities of these species are derived from io n velocity measurements and compared with the mobility of Na! for identical flame conditions. From a series of measured mobil ities, estimates are made for the particle mass (2300-6100 amu) and diameter (1.6-2.2 nm) . This experimental method is thus a new optical means for probing the early stages of soot formation.

Simultaneous detection of two types of soot precursor particles using photoionization mass spectrometry

“…Low particle sizes down to less than 2 nm are characteristic of these particles. Such particles have also been found in other studies 10, 11. The transition of small incipient particles to mature soot was measured recently by small angle X‐ray scattering (SAXS) 12…”

On Combustion Generated Nanoparticles and their Biological Effects. Part I:Measurement of Nanoparticles and their Detection in and Behind Flames

“…Both types of nanoparticles seem to have in common that their H fractions are above 0.3 [15,20,21], which is high when compared to soot for which H fractions around 0.1 are normally found. Low particle sizes down to less than 2 nm that are characteristic for both types of particles have been found by other workes, too [22,23].…”

Use of laser-induced ionization to detect soot inception in premixed flames

“…Laser-induced ionization is an attractive diagnostic for soot-inception studies because it is a technique that has been used to detect small soot particles ͑Ϸ2 nm͒ and atomic ions in premixed flames. 5,6 The advantage of the laser-inducedionization technique is that a sampling line is not required for detecting soot inception in premixed flames. Recent work 7,8 has employed a dilution probe coupled with a nanodifferential mobility analyzer to measure incipient soot-particle size distributions in premixed flames.…”

“…Thus the ionization signals reported were thought to arise from laser-induced heating of 2 nm particles followed by thermal ionization. 5 In previously published studies a single biased electrode was used to generate the electric field, with the burner head serving as the path to ground. 5 In the WSR, as well as in many other practical combustion systems, a path to ground is not readily available.…”

“…5 In previously published studies a single biased electrode was used to generate the electric field, with the burner head serving as the path to ground. 5 In the WSR, as well as in many other practical combustion systems, a path to ground is not readily available. Accordingly, to apply the laser-induced-ionization diagnostic to these geometries, a dual-electrode geometry must be employed.…”