Shock-tube study of the influence of oxygenated additives on benzene pyrolysis: Measurement of optical densities, soot inception times and comparison with simulations

The influence of the addition of oxygenated hydrocarbons (methanol, ethanol, and n-butanol) and ethers (diethyl ether, dimethoxymethane, furan, and tetrahydrofuran) on soot formation from benzene pyrolysis was studied. The pyrolysis process was investigated behind reflected shock waves at pressures around 1.4 bar and in the temperature range of 1670–2680 K. Extinction was measured at 633 nm to determine soot optical densities and soot-inception times. For extinction measurements, the studied gas mixtures contain 2.00 mol% C6H6 and 0.75 mol% additives diluted in argon. Since particle-inception times strongly depend on temperature and the reactive system cannot be considered isothermal because of the high reactant concentration in the shock tube, the temperature was measured as a function of time by two-color infrared absorption based on CO using two quantum-cascade lasers. For this purpose, 0.80 mol% CO and 5.00 mol% He were added to the studied gas mixtures as thermometry target species and enhancing species for vibrational relaxation, respectively. Both, temperature and measured optical densities were compared to simulations based on a detailed chemical kinetics mechanism from the CRECK Modeling Group. Additionally, simulations with a new mechanism composed of the CRECK mechanism (Pejpichestakul et al. 2009) and the recent PAH sub-mechanism of Sun et al. (2021) were performed. The agreement of experiments and simulations of the optical density were considerably improved using the aforementioned merged mechanism.