Experimental-Numerical Study of CO2/H2O Effects on Soot Formation in High-Pressure Ethylene Laminar Diffusion Flames

Abstract

Abstract

Abstract This study investigates the effects of H2O and CO2 on soot formation in high-pressure ethylene flames under oxygen-rich atmospheres. The soot yield increases with rising pressure, whereas both the flame temperature and its associated peak values exhibit a gradual decline across all oxygen-rich conditions. Under high-pressure oxygen-rich environments, the HACA mechanism plays a dominant role in soot formation, followed by PAH condensation. As the pressure increases, the peak rates of soot generation and oxidation are enhanced, and the nucleation rate transitions from a single-peak to a double-peak profile within the same oxygen-rich atmosphere. At elevated pressures, the O2/H2O atmosphere exerts the strongest inhibitory effect on soot formation, followed by O2/CO2, while O2/N2 displays the weakest suppression. Quantitatively, the O2/N2 atmosphere yields the highest peak rates for both soot formation and oxidation: the formation rate reaches 1.25 × 10−3 g/cm3/s, and the O2 oxidation rate attains a maximum of 0.35 × 10−3 g/cm3/s. Conversely, the O2/CO2 atmosphere results in the lowest soot generation rates, . Under the O2/H2O atmosphere, soot generation is slightly higher than that under O2/CO2; however, oxidation is predominantly governed by OH radicals, with a peak value of 0.25 × 10−3 g/cm3/s, rather than by O2. Furthermore, the mole fractions of A1, A4, and C2H2 are found to decrease monotonically with increasing pressure.