Pyrolysis of phenylacetylene with and without the presence of C-2 hydrocarbons (acetylene or ethylene) was studied in a single-pulse shock tube coupled to gas chromatography/gas chromatography-mass spectrometry equipment for speciation diagnostics. Quantitative speciation profiles were probed from each reaction system over the temperature range of 1100-1700 K at a nominal pressure of 20 bar. A kinetic model was proposed to interpret how phenylacetylene is consumed under high-pressure pyrolytic conditions and how the resulting intermediates react to form polycyclic aromatic hydrocarbons (PAHs), and furthermore, how the extra acetylene or ethylene alter the reaction schemes. It was found that the bimolecular reaction between phenylacetylene and hydrogen atom leading to phenyl and acetylene dominates phenylacetylene decomposition throughout the temperature window. The addition/elimination reactions between phenylacetylene and phenyl not only produce hydrogen atoms to maintain the reactivity of the fuel decay, but also directly lead to the formation of several C14H10 PAH isomers including diphenylacetylene, 9-methylene-fluorene and phenanthrene. Intermediates pools, regarding both species categories and abundance, are changed by the two C-2 fuels introduced into the reaction system. The added acetylene enables the Hydrogen-Abstraction-Acetylene-Addition (HACA) mechanism starting from the phenylacetylene radical to occur at relatively low temperatures. But the yielded naphthyl core does not stabilize in naphthalene due to the lack of hydrogen atoms in the reaction system, and instead, it carries on the HACA route by further combining with another acetylene molecule, ending up in acenaphthylene. Differently, the added ethylene intensifies the HACA routes by contributing to the acetylene formation, and more importantly, provides hydrogen atoms participating in the naphthalene formation from naphthyl radical. (C) 2020 The Authors. Published by Elsevier Inc. on behalf of The Combustion Institute.