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

The thermal decomposition of propene (C3H6) was studied in a shock tube behind reflected shock waves in the temperature range 1340-1910 K at pressures around 4.6, 2.1, and 0.4 bar with argon as bath gas. The initial concentrations of C3H6 were in the range 3.5 × 10−11-1.8 × 10−10 mol/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 1300-2000 K for pressures between 0.3 bar and 5 bar with Ar or similar colliders as bath gas.