Large eddy simulation of soot formation and oxidation for different ambient temperatures and oxygen levels

This paper presents the numerical study of soot formation and oxidation processes across different ambient temperatures (900K, 1000K, and 1100K) and oxygen levels (15% and 21% O₂) using large eddy simulation coupled with a two-equation soot model. The predicted ignition delay time, lift-off length and soot distribution show good agreements with the corresponding experimental data. A stronger oxidation of the precursor (C₂H₂) in the 21% O₂ cases results in a lower C₂H₂ formed, as compared to the 15% O₂ cases. The increasing ambient temperature leads to the fuel-richer region (roughly equivalence ratio > 1.6) becoming more favorable for C₂H₂ formation and, consequently, soot formation. This is more apparent in the 15% O₂ cases due to a weaker oxidation of C₂H₂ via O and OH radicals. As a result, the difference in the soot mass between the 15% and 21% O₂ cases becomes larger as the ambient temperature increases. The effects of ambient temperature and O₂ level on soot sub-processes are investigated. In addition to the flame temperature, OH mass and soot surface area are the dominant parameters in the oxidation processes via OH and O₂ at varying O₂ levels, respectively.