Shock-tube spectroscopic water measurements and detailed kinetics modeling of 1-pentene and 3-methyl-1-butene

To understand the effects of the chemical structure of two C₅ alkene isomers on their combustion properties, and to highlight the major chemical reactions occurring during their high-temperature oxidation, water time histories were measured behind reflected shock waves for the oxidation of 1-pentene (C₅H₁₀-1) and 3-methyl-1-butene (3M1B) in 99.5% Ar. The experiments were carried out at three different equivalence ratios (φ = 0.5, 1.0, and 2.0) at pressures and temperatures ranging from 1.29 to 1.47 atm and 1 331 to 1 877 K, respectively. The H₂O quantification extends the database for 1-pentene and provides new insights for 3M1B. These unique results were used to validate and to develop a new detailed kinetics model. Numerical predictions are presented, and the new model was able to capture the results with suitable accuracy, with 3M1B being notably more reactive than C₅H₁₀-1. Sensitivity and rate-of-production analyses were performed to help explain the results. Under the present conditions, the reactivity is rapidly initiated by molecular dissociation of a fraction of the pentene isomers. The initiation phase then induces H-atom abstraction by active radicals (H, OH, O, HO₂, and CH₃) to first produce alkenyl C₅H₉ radicals (or an alkyl radical and an alkenyl radical by breaking a C─C bond) and subsequent, smaller fragments. The difference in terms of reactivity between the isomers is essentially due to the fact that 3M1B has one particularly weak tertiary allylic C─H bond, which allows for fast H-atom abstraction compared with 1-pentene.