An ab Initio/Transition State Theory Study of the Reactions of Ċ₅H₉ Species of Relevance to 1,3-Pentadiene, Part II: Pressure Dependent Rate Constants and Implications for Combustion Modeling

Abstract

The temperature-and pressure-dependence of rate constants for several radical and unsaturated hydrocarbon reactions (1,3-C5H8/1,4-C5H8/cyC5H8 + Ḣ, C2H4 + Ċ3H5-a, C3H6 + Ċ2H3) are analysed in this paper. The abstraction reactions of these systems are also calculated and compared with available literature data. Ċ5H9 radicals can be produced via Ḣ atom addition reactions to the pentadiene isomers and cyclopentene, and also by H-atom abstraction reactions from 1-and 2-pentene and cyclopentane. Comprehensive Ċ5H9 potential energy surface (PES) analyses and high-pressure limiting rate constants for related reactions have been explored in Part I of this work (J. Phys. Chem. A 2019, 123(22), 9019-9052). In this work, a chemical kinetic model is constructed based on the computed thermochemistry and high-pressure limiting rate constants from Part I, to further understand the chemistry of different C5H8 molecules. The most important channels for these addition reactions are discussed in the present work based on reaction pathway analyses. The dominant reaction pathways for these five systems are combined together to generate a simplified Ċ5H9 PES including nine reactants, 25 transition states (TSs) and nine products. Spin-restricted single point energies are calculated for radicals and TSs on the simplified PES at the ROCCSD(T)/aug-cc-pVTZ level of theory with basis set corrections from MP2/aug-cc-pVXZ (where X = T and Q). Temperature-and pressure-dependent rate constants are calculated using RRKM theory with a Master Equation analysis, with restricted energies used for minima on the simplified Ċ5H9 PES and unrestricted energies for other species, over a temperature range of 300-2000 K and in the pressure range 0.01-100 atm. The rate constants calculated are in good agreement with the ones in the literature. The chemical kinetic model is updated with pressure-dependent rate constants and is used to simulate the species concentration profiles for Ḣ atom addition to cyclopentane and cyclopentene. Through detailed analyses and comparison, this model can reproduce the experimental measurements of species qualitatively and quantitatively with reasonably good agreement.

Experimental and kinetic modeling study of the oxidation of cyclopentane and methylcyclopentane at atmospheric pressure

“…Figure 3 illustrates a comparison of the different branching ratios; in this figure, R2 and R3, calculated at 1 atm, were gathered in order to compare with the C H and the C C β-scission routes. As can be seen from this figure, for Tsang 34 and Sirjean et al 11 the C H βscission pathway involving the formation of cyclopentene dominates over the temperature range of interest while for Manion and Awan 35 and for Sun et al 36 the C C β-scission channel (R2+R3) dominates. Intermediately, Al-Rashidi et al 5 calculated a crossover temperature (ca.…”

“…For most of these authors, two pathways are considered: (i) the CH β‐scission yielding cyclopentene from cyclopentyl (reaction R1) and (ii) the ring opening (CC β‐scission) of cyclopentyl yielding pent‐1‐en‐5‐yl (reaction R2). Sun et al 36 . proposed a third pathway, accounting for the prompt dissociation of pent‐1‐en‐5‐yl yielding ethylene and allyl radicals (R3).…”

“…As can be seen from this figure, for Tsang 34 and Sirjean et al 11 . the CH β‐scission pathway involving the formation of cyclopentene dominates over the temperature range of interest while for Manion and Awan 35 and for Sun et al 36 . the CC β‐scission channel (R2+R3) dominates.…”

“…The global reactivity of cyclopentane under fuel‐rich conditions and high pressure was found to be highly sensitive to this competition between the ring opening and the CH β‐scission. The pressure‐dependent rate constants calculated by Sun et al 36 allow to capture this behavior remarkably well (see Figure S2 in the Supporting Information) and were thus preferred in this study.…”

“…For most of these authors, two pathways are considered: (i) the C H β-scission yielding cyclopentene from cyclopentyl (reaction R1) and (ii) the ring opening (C C β-scission) of cyclopentyl yielding pent-1-en-5-yl (reaction R2). Sun et al 36 proposed a third pathway, accounting for the prompt dissociation of pent-1-en-5-yl yielding ethylene and allyl radicals (R3). Figure 3 illustrates a comparison of the different branching ratios; in this figure, R2 and R3, calculated at 1 atm, were gathered in order to compare with the C H and the C C β-scission routes.…”