Formation\nof Polycyclic Aromatic Hydrocarbons in Fuel-Rich\nOxidation of Toluene, Toluene/Dimethyl Ether Blend, and Toluene/Oxymethylene\nEther‑3 Blend

Ethers are considered as a potential alternative or fuel\nadditive\nto existing fuels due to their various advantages in reducing the\nlevel of CO<sub>2</sub> and pollutant emissions. Although the blending\neffects of ethers with the existing hydrocarbons on the formation\nof polycyclic aromatic hydrocarbons (PAHs) are crucial for their use\nas drop-in fuels, they have not been well understood. In this study,\nwe employed two ethers, dimethyl ether (DME) and oxymethylene ether-3\n(OME<sub>3</sub>). The fuel-rich oxidation of neat toluene, toluene/DME,\nand toluene/OME<sub>3</sub> was investigated using an atmospheric\nflow reactor at temperatures of 1050–1350 K, an equivalence\nratio of 9.0, and a residence time of 1.2 s. The identified and quantified\nPAHs with one to five aromatic rings were analyzed using gas chromatography\nmass spectrometry. PAH production was reduced by blending ethers at\na temperature above 1250 K, while greater production of PAHs was observed\nin toluene/DME and toluene/OME<sub>3</sub> blends compared to neat\ntoluene at a temperature below 1150 K. A chemical kinetic model that\ncontains not only the PAH formation mechanism but also the oxidation\nreactions of DME, OME<sub>3</sub>, and toluene was developed based\non a combination of the existing models. The developed model could\nreasonably reproduce the experimental results of the PAHs obtained\nhere. To investigate the temperature dependence of PAH formation,\nkinetic analyses using the proposed model were conducted to examine\nthe formation pathways of PAHs in the three fuels, as well as the\nconsumption pathways of DME and OME<sub>3</sub>. The blending effects\nof DME and OME<sub>3</sub> to enhance PAH production were pronounced\nat a low temperature such as 1050 K, while they inhibited PAH formation\nwith increasing temperature. At 1050 K, DME and OME<sub>3</sub> exhibited\nreactivity higher than that of toluene, resulting in the abundant\nproduction of reactive radicals and promoting toluene consumption.\nThis led to larger PAH production in the blends at a low temperature.\nWhen comparing the mixing effects of DME and OEM<sub>3</sub>, the\nreactivity of OME<sub>3</sub> was higher than that of DME, leading\nto a greater production of PAHs in the toluene/OME<sub>3</sub> blend\ncompared to the toluene/DME blend at a low temperature.