Chemical kinetics of hydroxyl reactions with cyclopentadiene and indene

Oxidation reactions of highly unsaturated cyclic hydrocarbons are very important in combustion, competing with their participation in PAH and soot growth. One of the key oxidation pathways at combustion conditions is the reaction with hydroxyl radicals. Cyclopentadiene (C5H6) and indene (C9H8) are typical PAH precursors, which have highly unsaturated penta-ring structure. In this study, rate coefficients of the reactions of hydroxyl radical with cyclopentadiene and indene were measured behind reflected shock waves over the temperature range of 828–1390 K and pressure near 1 atm. Hydroxyl radicals were monitored by a narrow line-width laser absorption near 306.7 nm. The measured rate coefficients may be expressed as kC5H6+OH=3.68−0.23+0.27×1013e−(1742.5−77+75)/T and kC9H8+OH=1.44−0.14+0.10×1013e−(1497.8−72+130)/T cm3 mol−1 s−1. Our experimental results showed that the reaction of hydroxyl radicals with cyclopentadiene is about two times faster than that of indene, and the indene + OH reaction exhibited a relatively weaker temperature dependence. Chemical kinetic simulations, carried out with a detailed model, showed the sensitivity of model performance to these reactions and the potential of model improvement with our measured rate coefficients.