Nascent soot particle size distributions down to 1 nm from a laminar premixed burner-stabilized stagnation ethylene flame

In this study, spatially resolved measurement of soot particle size distribution functions (PSDFs) down to ∼1 nm from a laminar premixed burner-stabilized stagnation ethylene flame was made by paralleling a commercial 3936 Scanning Mobility Particle Spectrometer (3936 SMPS) and a Diethylene Glycol (DEG) SMPS. While the 3936 SMPS may detect particles with a mobility diameter of 3-150 nm, DEG SMPS can be used to measure incipient soot particles of 1-10 nm. We found that the minimum diameter of the incipient soot particles appeared at ∼1.5 nm (though with some uncertainty caused by the classification device). A complete bimodality of the PSDFs was observed quantitatively when the burner-to-stagnation surface separation distance (Hp) was greater than 0.6 cm. Characterized by a lognormal distribution, the first peak appears to be relatively stable at different Hp, with the geometric standard deviation varying from 1.1 to 1.3 and the peak diameter ranging from 1.9 to 2.9 nm. The absolute number density of particles no bigger than the first peak diameter was found to be positively related to the first peak diameter and the geometric mean diameter of these particles.