A comprehensive kinetic study on the speciation from propylene and propyne pyrolysis in a single-pulse shock tube

摘要

This work is centered on the speciation from propylene and propyne pyrolysis by means of shock tube experimentsand detailed kinetic modeling. A wealth of intermediates and products, covering small acyclichydrocarbons up to four-ring aromatics, are probed from the C_3 fuels pyrolysis at a nominal pressureof 20 bar over 1050–1650 K. With updates in reactions involving C_3 species, our on-going polycyclicaromatic hydrocarbon (PAH) formation kinetic model can well predict the measurements obtained inthe current work as well as relevant literature data. Propyne exhibits a unique two-stage decompositionprofile, as the characteristic isomerization to allene dominates in its consumption at moderate temperaturesbelow 1300 K. Overall, propylene pyrolysis results in more diverse small hydrocarbons, butmuch lower contents of aromatics, in comparison to propyne pyrolysis. In both studied cases, the formationof benzene is dependent upon the propargyl recombination, and since propyne decompositioninduces a more rapid and more plentiful propargyl production, benzene mole fractions are much higherin propyne pyrolysis. In both cases, naphthalene is observed as the most abundant PAH species, followedby acenaphthalene. Modeling analyses indicate that similar reaction pathways are responsible for thePAH formation in propylene and propyne pyrolysis. Indene is formed from the interactions between benzene/phenyl and C_3 species, through its non-PAH isomers as intermediates. The subsequent reactions ofindenyl radical with methyl and propargyl are essential pathways leading to naphthalene and acenaphthalene,respectively. Naphthyl radical further participates in the formation of different larger PAHs. Themethylene-substituted cyclopenta-ring species are deemed as important precursors of their aromatic isomers,as is noted from the fulvene-to-benzene, benzofulvene-to-naphthalene and 9-methylene-fluoreneto-phenanthrene conversions.