Search

Cyclohexadienes (CHDs) are important intermediates in the pyrolysis and oxidation of many C 6 cyclic hydrocarbons. Under combustion relevant conditions, these dienes may either eliminate H 2 directly or lose H atoms sequentially to produce the first aromatic ring, i.e., benzene. This is one of the major reaction pathways for the formation of benzene from C 6 cyclic hydrocarbons. Despite its importance in PAH and soot formation process, the chemistry of CHD has attracted less attention from the scientific community. In this work, we have investigated hydrogen abstraction reactions of 1,3- and 1,4-CHD by OH radicals using a shock tube and UV laser absorption over the temperature range of 900 – 1100 K and pressures of ∼ 1 – 3 atm. Reaction kinetics was followed by monitoring OH radicals near 307 nm. At high temperatures, both isomers of CHDs are found to exhibit comparable reactivity with OH radicals. These reactions show a weak positive temperature dependence. Measured rate coefficients can be represented by the following Arrhenius expressions in units of cm3 molecule−1 s −1: k 1 (1 , 3 − CHD + OH) = 1.76 × 10 − 10 exp ( − 1761 K T) k 2 (1 , 4 − CHD + OH) = 2.23 × 10 − 10 exp ( − 1813 K T) To gain further insights into these reactions, various ab initio methods were employed to compute relevant thermochemical data. This study reports the first high-temperature kinetic data for cyclohexadienes which will be beneficial to improve the performance of the oxidation kinetic models of C6 cyclic hydrocarbons. [ABSTRACT FROM AUTHOR]

Abstract: Flame-sampling molecular-beam mass spectrometry of premixed, laminar, low-pressure flat flames has been demonstrated to be an efficient tool to study combustion chemistry. In this technique, flame gases are sampled through a small opening in a quartz probe, and after formation of a molecular beam, all flame species are separated using mass spectrometry. The present review focuses on critical aspects of the experimental approach including probe sampling effects, different ionization processes, and mass separation procedures. The capability for isomer-resolved flame species measurements, achievable by employing tunable vacuum-ultraviolet radiation for single-photon ionization, has greatly benefited flame-sampling molecular-beam mass spectrometry. This review also offers an overview of recent combustion chemistry studies of flames fueled by hydrocarbons and oxygenates. The identity of a variety of intermediates in hydrocarbon flames, including resonantly stabilized radicals and closed-shell intermediates, is described, thus establishing a more detailed understanding of the fundamentals of molecular-weight growth processes. Finally, molecular-beam mass-spectrometric studies of reaction paths in flames of alcohols, ethers, and esters, which have been performed to support the development and validation of kinetic models for bio-derived alternative fuels, are reviewed. [Copyright &y& Elsevier]