Effect of Ozone on Polycyclic Aromatic Hydrocarbon Formation in Combustion of Biodiesel Surrogate

Studying the effect of Ozone (O₃) on polycyclic aromatic hydrocarbon (PAH) during the combustion process of biodiesel can provide new insights for reducing soot emissions. A skeletal reaction mechanism of biodiesel surrogates coupled with an O₃ reaction mechanism and a PAH reaction mechanism was constructed for modeling the effect and mechanism of O₃ on PAH formation in a counterflow flame of biodiesel surrogates. The final mechanism consists of 138 species and 608 reactions. Analysis show that the addition of O₃ creates a localized rapid temperature rise zone on the fuel side. As the initial O₃ mole fraction increases, the temperature rise rate in this zone intensifies and its position shifts closer to the fuel outlet, resulting from the preliminary oxidation of the fuel releasing heat. Furthermore, the maximum mole fraction of PAH initially increases and subsequently decreases with increasing initial O₃ mole fraction. When initial O₃ mole fraction increases to 0.04, the maximum mole fraction of major PAH such as benzene (A₁), naphthalene (A₂), anthracene (A₃), and pyrene (A₄) are 4.57, 6.76, 16.16, 12.38 times that at initial O₃ mole fraction of 0.00, respectively. The addition of O₃ has a significant impact on the concentration of PAH, and has the greatest impact on A₃. At the same time, the pathway of benzene (A₁) generation shifts from C₂H₂-dominated to C₂H₃-dominated mechanisms. And when initial O₃ mole fraction increases to 0.12, the maximum mole fractions of A₁, A₂, A₃, and A₄ are 0.880, 0.357, 0.375, and 0.143 times that at initial O₃ mole fraction of 0.00. It is because that the C₂H₃ radicals are oxidized, thereby inhibiting the production of A₁.