Thermal decomposition of propene: A shock-tube/H-ARAS and modeling study

Abstract

The thermal decomposition of propene (C3H6) was studied in a shock tube behind reflected shock waves in the temperature range 1340–1910K at pressures around 4.6, 2.1, and 0.4bar with argon as bath gas. The initial concentrations of C3H6 were in the range 3.5×10−11–1.8×10−10mol/cm3. Hydrogen atoms were detected time-resolved with atom resonance absorption spectroscopy (ARAS), and rate coefficients, k1a, of the decomposition reaction C3H6+M→C3H5+H+M (1a) were determined. A medium-sized reaction mechanism (29 reactions, 15 species) with kinetic data from the literature was set up, and the [H](t) profiles were simulated and fitted to the experimental profiles with k1a being the only adjustable parameter. The simulations have shown that despite the low initial concentrations of C3H6, a direct determination of k1a from the initial slopes of the [H](t) profiles would result in an overestimation of about 30% mainly because of H-atom production in the fast consecutive decomposition reaction C3H5+M→aC3H4+H+M (aC3H4: allene). The observed temperature and pressure dependence of k1a was modeled with a master equation. At the conditions of our experiments, the rate coefficient of reaction (1a) was found to be close to its low-pressure limit, and the observed temperature and pressure dependence could be characterized by the following bimolecular rate coefficient: k1abim(T)=(8.8±3.8)×1018 exp[–(39970±680) K T–1] cm3/mol s. We recommend the use of this expression for the calculation of k1a in the temperature range 1300–2000K for pressures between 0.3bar and 5bar with Ar or similar colliders as bath gas.