The influence of iso-butene kinetics on the reactivity of di-isobutylene and iso-octane

The continuous development of a core C0 – C4 kinetic mechanism generally involves updating it using reliable kinetics and thermodynamics and may also involve the inclusion of missing reaction pathways to improve the integrity, prediction accuracy and applicability of the mechanism over a wider range of combustion relevant conditions. Accurate kinetic descriptions of the core mechanism can have a substantial influence on accurate predictions of higher hydrocarbon combustion models as the consumption of these larger species rely heavily on the core mechanism. This study is motivated by a severe under prediction in the reactivity of the high temperature experimental targets of di-isobutylene (DIB), an important component used in surrogate fuel formulations. It is worth noting that isobutene (iC4H8) laminar burning velocities are also severely under-predicted in the recent publication of Zhou et al. [1], which is regarded as a critical fragment formed in the decomposition of DIB, that dictates its fate. We discuss the latest developments to the isobutene kinetics and illustrate the influence that these updates have on the oxidation of higher order hydrocarbons, such as DIB and iso-octane (iC8H18). Improving the kinetic accuracy of the C0 – C4 core mechanism improved not only the iC4H8 predictions but also the predictions of higher hydrocarbons which hierarchically rely on it, for instance, the peak flame speeds for specific cases of iso-octane, iso-butene and di-isobutylene have improved by 3, 6, 12 cm s–1, respectively. In addition, the new iC4H8 model is in excellent agreement with the new laminar burning velocity measurements taken in this study at 1 atm and 428 K. The contribution of the new iC4H8 kinetics alone for the improvement in the LBV predictions is significant, in particular the Ċ3H5-t + ĊH3 = iĊ4H7 + Ḣ and iC4H8 = iĊ4H7 + Ḣ reactions are very sensitive at high temperatures. In addition, the new isobutene model is in very good agreement with experimental ignition delay times and species profiles measured during pyrolysis and oxidation conditions.