Temperature dependence of ethanol and dimethyl ether chemical mixing effects on soot and gas products in ethylene pyrolysis

The present work aims to understand the temperature dependence of the fuel chemical mixing effects on soot and gas product formation in ethylene pyrolysis in a laminar flow reactor. The chemical and dilution effects of ethanol and dimethyl ether addition were studied experimentally by gas chromatography measurements and computationally using a detailed soot model coupled with PAHs chemistry. The chemical effects of ethanol and dimethyl ether mixing increased the production of CO, H-2, and CH4, but the dilution effects decreased the production of H-2, CH4, and C2H2. The chemical mixing effects inhibited the formation of C2H2 except for the case in which 50% ethanol was mixed with 50% ethylene at 1273 K. Ethanol and dimethyl ether mixing inhibited soot production, but the fuel mixing effects on soot reduction decreased with increasing temperature. The temperature dependence of the fuel mixing effects on soot production was dominated by the chemical effects rather than the dilution effects. Kinetic analysis of the soot formation process indicated that the methyl radical (CH3) from ethanol and dimethyl ether decomposition combined with C2 species (C2H2, C2H4) from ethylene pyrolysis to generate plenty of C3 species (C3H4-P, C3H6, C3H5-A, C3H4-A, C3H3), which further converted into benzene (C6H6) and polycyclic aromatic hydrocarbons (C10H8, C14H10, and C16H10). The reaction rate of the above C1+C2 -> C3 -> C6 -> PAHs pathway increased noticeably with increasing pyrolysis temperature, which strengthened the chemical effects of ethanol and dimethyl ether mixing on soot surface growth rate contributed by PAHs and therefore soot yield under high-temperature conditions.