Shock-tube study on the influence of oxygenated co-reactants on ethylene decomposition under pyrolytic conditions

The influence of various oxygenated co-reactants on soot formation was addressed by studying the pyrolysis of gas mixtures using ethylene as a base fuel in the absence of molecular oxygen. Alcohols (methanol, ethanol, and n-butanol) and ethers (diethyl ether, dimethoxymethane, furan, and tetrahydrofuran) were selected as oxygenated co-reactants. The pyrolysis process was studied behind reflected shock waves at around 3 bar. Laser extinction at 633 nm was used to determine soot-inception times and the related optical densities as a function of reaction time. The temporal variation in temperature was measured via time-resolved two-color CO absorption using two quantum-cascade lasers at 4.73 and 4.56 & mu;m. Soot particle sizes were determined by time-resolved laser-induced incandescence using a Nd:YAG laser at a wavelength of 1064 nm. The major finding is that based on C 2 H 4 as soot precursor, only CH 3 OH does not have a soot-promoting effect, whereas the addition of all other oxygenated hydrocarbons results in increased soot yields. The measured temperatures were compared with simulations based on a detailed chemical kinetics mechanism from ing of hydrocarbon pyrolysis, PAH formation and soot growth was performed in OpenSMOKE ++ software to give qualitative insight in the experimental results using the CRECK mechanism and an assembled mechanism composed of the CRECK and the recent PAH sub-mechanism (Sun et al. Proc. Combust. Inst. (2021)). The simulation reveals that the observed promotion of soot formation in presence of oxygenated co-reactants is associated with the release of CH 3 and C 3 H 3 during the thermal decomposition resulting in acceleration of C 6 H 6 ring formation.& COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The effects of various oxygenated co-reactants on the formation of soot during the pyrolysis of gas mixtures containing ethylene as a base fuel were studied. Alcohols (methanol, ethanol, and n-butanol) and ethers (diethyl ether, dimethoxymethane, furan, and tetrahydrofuran) were used as the oxygenated co-reactants. The pyrolysis process was investigated using laser extinction and time-resolved spectroscopy techniques. The results showed that only methanol did not promote soot formation, while the addition of other oxygenated hydrocarbons increased soot yields. Simulations based on a detailed chemical kinetics mechanism provided qualitative insights into the experimental results, revealing that the promotion of soot formation by oxygenated co-reactants was related to the release of CH3 and C3H3 during thermal decomposition, leading to accelerated formation of C6H6 rings.