Unveiling trends in soot nucleation and growth: When secondary ion mass spectrometry meets statistical analysis

At the present day, ultrafine soot particles have become the object of increasing attention due to their well-documented adverse effects on human health and climate. In particular, understanding soot nucleation is one of the most challenging problems toward a more controlled and cleaner combustion. Detailed information on the chemistry of nascent soot particles (NSPs) is expected to provide clues on the soot formation and growth reaction pathways. Herein, the early steps of soot formation in flames are addressed by investigating the chemical composition of NSPs and their molecular precursors by secondary ion mass spectrometry. The originality of this work lies on the combination of several factors that include: two different approaches to gain access to soot nucleation in premixed flames (analysis of a nucleation flame in which NSPs nucleate all along the reaction coordinate without growing in size) and in diffusion flames (separation of the precursors and soot regions); a sampling procedure that allows a rough separation of the condensable gas phase from soot particles; a large database of collected samples and high mass resolution that enable the use of an improved data reduction protocol based on hierarchical cluster analysis and principal component analysis for the data mining and interpretation. (C) 2018 Elsevier Ltd. All rights reserved.