Thesis of Jessy Elias

Defense of thesis of Jessy Elias - laboratory PC2A

Identification and characterization of the chemical species at the origin of the nucleation of soot particles in flames

Abstract :

The formation of soot particles in combustion is a major research issue due to their negative impact on our health and our environment. The link between the inhalation of these particles and certain pathologies affecting mainly the respiratory tract is indeed well established and it is also proven that these particles have an impact on climate change. For these reasons, their emission rate from devices involving combustion processes (aircraft engines, thermal or hybrid engines of land or sea vehicles, wood boilers...) is increasingly regulated. However, the state of the art concerning the formation mechanisms of soot particles reveals many deficiencies, notably regarding the nature of the chemical species and reaction pathways involved. The nucleation step, which is the crucial step of these mechanisms since it corresponds to the transformation of gaseous precursors into soot particles, raises many questions and interrogations. Currently, several hypotheses are considered in the literature involving in particular the formation of polycyclic aromatic hydrocarbons (PAHs) and potentially that of intermediate species (PAH dimers, resonantly stabilized radicals of PAHs) between PAHs and soot particles. However, there is very little direct experimental evidence in the literature on the formation of these compounds in flames.
The work carried out in this thesis focused on the characterization of the key species involved in the soot nucleation process in a methane diffusion flame. In that context, we have implemented a set of in situ and ex situ experimental methodologies (ToF-SIMS, Raman, LII, LIF and EPR) which have allowed us to obtain a large panel of experimental data able to provide relevant and innovative information on the main molecular species and reaction pathways involved in the nucleation process. The coupling of these different methods and the analysis of the obtained data, in particular by means of multivariate data analysis, reveals important correlations between the nucleation process and the successive formation of different species (PAHs, resonance stabilized radical of PAHs, incipient soot particles, mature particles). This work brings crucial information on the size, mass, structure and nature of the species involved and their evolution in the nucleation process, which will allow the development of kinetic models and significantly improve our knowledge of this complex physicochemical process.

Keyworks : Soot,PAHs,Nucleation,Combustion,Physicochemical characterization