<p>As critical compounds of kerosene, aromatic hydrocarbons contain one or more planar six-carbon rings, which can significantly contribute to soot emissions. Previous studies have mainly investigated the effects of either monoaromatic or diaromatic hydrocarbons on soot formation, whereas the both coexist in comparable concentrations in kerosene fuels. In this work, the effects of n-propylbenzene (n-C₉H₁₂) and/or 1-methylnaphthalene (C₁₁H₁₀) addition on different soot formation and oxidation processes in n-dodecane coflow diffusion flames are numerically investigated using a detailed sectional soot model. The results show that 30% C₁₁H₁₀ addition exhibits the strongest promotion effect on the soot formation, followed by the co-addition of 15% n-C₉H₁₂ and 15% C₁₁H₁₀, while 30% n-C₉H₁₂ addition shows the weakest effect. The increase in soot volume fraction (SVF) under co-addition condition exceeds half of the combined increments from the individual additions, revealing a clear synergistic effect on the soot formation. This synergy is primarily attributed to the enhanced soot nucleation rate, arising from a significant increase in the mole fractions of naphthyl radical (A2-) and ethynylphenyl radical (AlC₂H), and the emergence of a new Benzo(ghi)-fluoranthene (BGHIF) formation pathway (A2-+AlC₂H→BGHIF). The promoting effects of n-C₉H₁₂ and/or C₁₁H₁₀ on soot condensation are similar to those on the soot inception, but stronger than those on the hydrogen-abstraction-acetylene-addition (HACA) surface growth due to a higher C₂H₂ consumption rate. In contrast, their influence on OH oxidation is minor, as the decrease in the mole fraction of OH radical offsets the growth in soot surface area available for oxidation.</p>