Toward carbon-neutral combustion: Synergistic CO2/H2O dilution for soot mitigation in oxy-fuel systems

Soot emissions pose significant environmental and health challenges, necessitating innovative strategies to advance cleaner combustion technologies for sustainable energy generation. This study explores the thermochemical interactions of CO₂ and H₂O as effective diluents in oxygen-enriched ethylene diffusion flames, focusing on their impact on soot suppression and flame dynamics. Combined CO₂/H₂O dilution achieves intermediate suppression, redistributing soot closer to the burner outlet, thereby enhancing oxidation efficiency. Elevated oxygen concentrations increase flame temperature and soot nucleation but are counterbalanced by intensified OH and O₂ oxidation rates, highlighting the dual role of oxygen in promoting combustion efficiency while mitigating soot accumulation. Mechanistic insights into soot nucleation, surface growth via hydrogen-abstraction–C₂H₂–addition (HACA)/polycyclic aromatic hydrocarbons (PAHs) pathways, and oxidation dynamics underscore the dominance of radical chemistry (OH/O₂) and thermal-dilution effects in soot suppression. The findings demonstrate that optimizing CO₂/H₂O ratios in oxy-fuel systems significantly reduces soot emissions, offering a viable pathway for low-carbon combustion technologies.