Optical detection of large soot precursors

Abstract

We have recently proposed a model of the soot particle inception process that involves the conversion, largely by coagulation and coalescence, of high-molecular-weight hydrocarbon molecules into incipient soot particles. In this work we make absorption measurements at a series of wavelengths between 488 and 1100 nm that show that in the immediate postinception zone the surface growth kinetics follows the profile of the very-high-molecular weight hydrocarbons (we estimate >500 amu) which then disappear. This result confirms an important prediction of our model. The rate at which these species disappear is consistent with the observed rate of mass increase of very young particles. Surface growth is dominated by acetylene only after the disappearance of these species.