Experimental and modeling studies of exo-tetrahydrobicyclopentadiene and tetrahydrotricyclopentadiene pyrolysis at 1 and 30 atm

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To better understand the decomposition behaviors of exo-tetrahydrobicyclopentadiene (exo-TCD, a main component of JP-10) and tetrahydrotricyclopentadiene (THTCPD), the experiments were performed in a flow tube reactor at 1.0-30.0 atm over a temperature range of 773–1148 K with high helium dilution. The mole fraction profiles of pyrolysis products, involving C1-C5 small hydrocarbons, monocyclic and polycyclic aromatic hydrocarbons (MAHs and PAHs), were obtained using online GC–MS/FID. A universal kinetic model of exo-TCD and THTCPD pyrolysis was developed by coupling a common base mechanism and their respective sub-mechanisms. It was validated against a wide range of pyrolysis experimental data, newly measured in this work as well as taken from the literature covering the intermediate-to-high temperature range in different reactors. The rate of production analysis shows that for the decomposition of two fuels, the unimolecular C-C dissociations and H-abstractions by H and aC3H5 attacking play a dominant role at both 1.0 and 30.0 atm. Due to the lower C-C bond dissociation energy and more H-abstraction sites, THTCDP exhibits a faster pyrolysis curve and covers a lower temperature range than exo-TCD. The simultaneously formed fuel radicals in exo-TCD and THTCPD pyrolysis impact the formation pathways of C1–C5 small products and MAHs. Notably, an extra five-membered ring in THTCPD results in slightly high production of C5 cycloalkenes, involving 1,3-cyclopentadiene and cyclopentene. The formation of MAHs, such as benzene, toluene and ethylbenzene, is also affected by fuel-specific reaction channels, yielding different peak concentrations. Concerning the two- and four-ring PAHs, the speciation profiles show a large extent of similarity in the decomposition of two fuels, which is mainly attributed to the similar formation pathways, especially at high temperature. Their formation is dominated by the bi-molecular addition reactions of c-C5H5 with c-C5H5, c-C5H6, as well as a series of resonantly stabilized radicals, which are barely influenced by the specific fuel chemistry.