Production of Aliphatic-Linked Polycyclic Hydrocarbons during Radical-Driven Particle Formation from Propyne and Propene Pyrolysis

The Identity and Chemistry of C7H7 Radicals Observed during Soot Formation

“…Previous results have demonstrated the production of key RSRs associated with particle formation during the combustion and pyrolysis of hydrocarbon fuels. − ,,− ,, Figure shows examples of some of these RSRs recorded using VUV-AMS on samples extracted from flames (left panels) and a high-temperature flow reactor (right panels). More detailed information regarding the flame and pyrolysis conditions is given in Table and Section .…”

“…This mechanism, known as the Clustering of Hydrocarbons by Radical Chain Reactions (CHRCR), requires the formation of RSRs, a selected sequence of which has been observed under a range of combustion conditions during soot formation. − ,,− Generation of these RSRs has been proposed to involve the sequential addition of acetylene or vinyl radical to RSRs in the series, starting with propargyl, the smallest of these RSRs. ,− These key RSRs then initiate chain reactions that cluster hydrocarbons on reactive growth centers, a process that is distinct from distributed molecular-weight growth. Experiments performed in flames and high-temperature flow reactors have provided strong experimental support for the CHRCR mechanism through observations of key RSRs during soot inception and growth. − ,,− ,, Experiments on vaporized incipient particles or particle coatings have also yielded the identification of species containing odd numbers of carbon atoms and 5-membered rings associated with these RSRs. ,,,− Measurements on samples extracted from an inverse diffusion flame have yielded evidence of covalently clustered PAHs with these persistent radicals …”

“…Radical species with the chemical formula C 7 H 7 are part of the sequence of RSRs observed during soot formation and are proposed to be important to soot inception . Aerosol mass spectra of particles produced in sooting flames and pyrolysis systems have demonstrated the production of species with a mass of 91 u, corresponding to one or more isomers of C 7 H 7 . ,, C 7 H 7 species have also been investigated as intermediates in the formation of larger PAHs in interstellar environments. , Martí et al recently performed an extensive theoretical study of the isomers of C 7 H 7 and calculated rate coefficients for C 7 H 7 production, loss, and isomerization reactions. Figure provides a summary of what appear to be the most important reactions, as suggested by the large breadth of experimental and theoretical work published previously.…”

Comprehensive Kinetics on the C7H7 Potential Energy Surface under Combustion Conditions

“…The two processes are synergistic and can occur simultaneously. Experimental studies performed in flames and high-temperature flow reactors have provided strong evidence to support this clustering mechanism. ,− …”

“…A radical species with a mass of 91 u and chemical formula C 7 H 7 has been observed during soot formation in both flames and pyrolysis systems. ,, This species has been proposed to be produced via the reaction of propargyl with two acetylene molecules, ,,, two vinyl radicals, or vinylacetylene, but there is currently considerable debate about the isomeric identities of the C 7 H 7 product and the C 5 H 5 intermediate formed during the sequential addition of acetylene or vinyl. Given that C 7 H 7 is one of the smallest and first-formed RSRs in the sequence hypothesized to initiate particle inception during CHRCR, its identity and kinetic and thermodynamic characteristics are critical to predicting soot inception if CHRCR is indeed an important mechanism for inception.…”