Theoretical analysis and kinetic modeling of hydrogen abstraction and addition of 1,3-cyclopentadiene and associated reactions on the C5H7 potential energy surface

Abstract

1,3-Cyclopentadiene (c-C5H6) is one of the important intermediate species in the combustion of cyclic hydrocarbon fuels and the formation of aromatics. In this study, the thermodynamic properties and the chemical kinetics for the hydrogen abstraction and addition of c-C5H6 and the associated reactions on the C5H7 potential energy surface (PES) are investigated by high-level quantum chemistry calculations. The high-pressure limit rate constants for the hydrogen abstraction reactions are computed using conventional transition state theory. It is found that under typical combustion conditions, the hydrogen abstraction reaction prefers to take place at the methylene group of c-C5H6. The temperature- and pressure-dependent rate constants for reactions on the C5H7 PES are calculated by the RRKM/master equation. The results indicate that the H addition reactions of c-C5H6, forming allylic and alkylic cyclopentenyl, are important at low temperatures and high pressures. On the contrary, the chemically activated reactions forming bimolecular products prevail at high temperatures and low pressures. Compared to the chemically activated reaction of c-C5H6 + H = C2H2 + A-C3H5 (allyl), the rate constant for the reaction of c-C5H6 + H = C2H4 + C3H3 (propargyl) is much lower. The calculated thermodynamic properties and rate constants are updated and incorporated into a chemical kinetic model. Significant changes are observed for the c-C5H6 consumption flux and the mole fractions of important intermediate species in both the c-C5H6 oxidation and pyrolysis in plug flow reactors. Modifications in the chemical kinetic model also improve the prediction of the laminar flame speeds under fuel-rich conditions.