Abstract:

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 poly-aromatic hydrocarbon (PAH) formation in a counterflow flame of biodiesel surrogates. The final mechanism consists of 138 species and 608 reactions. The results indicate that the maximum concentration of PAH initially increasing and subsequently decreasing with the increase of initial O₃ volume fraction. When initial O₃ volume fraction increases to 4%, the maximum concentrations of major PAH such as benzene (A₁), naphthalene (A₂), anthracene (A₃), and phenanthrene (A₄) are 4.57, 6.76, 16.16, 12.38 times that at O₃ volume fraction of 0%, 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 changes, the main reaction for generation of A₁ changes from C₂H₂ ＋ C₄H₅ ＝ A₁ ＋ H to C₂H₃ ＋ C₄H₄ ＝ A₁ ＋ H. And When initial O₃ volume fraction increases to 12%, they respectively 0.88, 0.357, 0.375, 0.143 times that at O₃ volume fraction of 0%. It is because that the C₂H₃ radicals are oxidized, thereby inhibiting the production of A₁.

Key words: biodiesel, poly-aromatic hydrocarbon, ozone, nitrogen oxides, reaction mechanism, reaction kinetics