Thesis of Quan Do

Amphithéâtre Pierre Glorieux (CERLA) Thesis defense of Quan Do - laboratory PC2A Impact of hydrogen on formation of soot particles and their gaseous precursors in flames Abstract : Our energy needs, which increase by more than 2 % each year worldwide, are provided for nearly 80 % by the combustion of fossil fuels, which potentially generate pollutants harmful to our health and environment, such as soot particles, and gaseous compounds contributing to global warming, such as carbon dioxide (CO₂). Therefore, in order to meet this growing energy demand while trying to limit its negative effects, different alternative energy sources are now being studied. Among these new energies, the combination of dihydrogen (H₂) and natural gas (Hydrogen-enriched natural gas-HENG) appears to be a credible alternative solution both in terms of energy efficiency and compatible with environmental constraints. The work carried out during this thesis is part of the specific framework of studies aimed at characterizing this type of fuel, i.e. its combustion efficiency but also and more particularly here the impact of H₂ as an additive, on the methane combustion process and the formation of associated pollutant emissions. During this work, we have thus characterized the influence of H₂ both on the formation of gaseous species (aliphatics and aromatics), some of which being potentially majors pollutants and, the formation of particulate species (soot) in rich premix flames stabilized at atmospheric pressure for different conditions of equivalence ratios and mixtures with H₂. To do this, a large arsenal of experimental techniques was implemented to allow the measurement of mole fraction profiles of gaseous species (C1-C16) and those of volume fraction profiles of soot particles, as well as the size distributions of the particles formed. These measurements were carried out under carefully chosen flame conditions (nucleation flames in particular) in order to provide relevant and innovative information on the role of H₂ in the soot formation process, more particularly on the nucleation process characterizing the transformation of gaseous precursor species, potentially polycyclic aromatic hydrocarbons (PAHs), into solid soot particles. On the basis of the large panel of measured experimental data, we thus propose a discussion on the impact of equivalence ratio on the formation of soot particles in methane flames and more specifically on the nucleation process of soot particles. This work appears all the more crucial as the mechanisms related to the nucleation process in flames are still very poorly known. In addition, an important part of this thesis is devoted to the analysis of the impact of the addition of H₂ on the process of soot formation in methane flames. The work carried out in this thesis demonstrates very clearly the decisive influence of H₂ on the formation of PAHs and soot particles, an influence that proves to be intimately dependent on the process of introducing hydrogen (addition or substitution) to the mixture of the initial CH₄/O₂/N₂ reagents. Key Words : Hydrogen, Methane, Premix Flames, PAHs, Soot Nucleation, Soot