The role of radical-radical chain-propagating pathways in the phenyl plus propargyl reaction

Well-skipping radical-radical reactions can provide a chain-propagating pathway for formation of polycyclic radicals implicated in soot inception. Here we use controlled pyrolysis in a microreactor to isolate and examine the role of well-skipping channels in the phenyl (C 6 H 5 ) + propargyl (C 3 H 3 ) radical-radical reaction at temperatures of 800-1600 K and pressures near 25 Torr. The temperature and concentration dependence of the closed-shell (C 9 H 8 ) and radical (C 9 H 7 ) products are observed using electron-ionization mass spectrometry. The flow in the reactor is simulated using a boundary layer model employing a chemical mechanism based on recent rate coefficient calculations. Comparison between simulation and experiment shows reasonable agreement, within a factor of 3, while suggesting possible improvements to the model. In contrast, eliminating the well-skipping reactions from the chemistry mechanism causes a much larger discrepancy between simulation and experiment in the temperature dependence of the radical concentration, revealing that the well-skipping pathways, especially to form indenyl radical, are significant at temperatures of 1200 K and higher. While most C 9 H 7 forms by well-skipping at 25 Torr, an additional simulation indicates that the wellskipping channels only contribute around 3% of the C 9 H x yield at atmospheric pressure, thus indicating a negligible role of the well-skipping pathways at atmospheric and higher pressures. & COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

This study investigates the radical-radical reaction of phenyl (C6H5) and propargyl (C3H3) and finds that the propargyl radical reaction can contribute to the formation of polycyclic radicals related to soot inception. By conducting experiments and simulations, it is observed that the radical concentration is positively correlated with temperature under the conditions of 800-1600 K and 25 Torr pressure, and eliminating the radical reactions leads to a discrepancy between simulation and experiment.