Probing the antiknock effect of anisole through an ignition, speciation and modeling study of its blends with isooctane
Carolina S. Mergulhão, Hans-Heinrich Carstensen, Hwasup Song, Scott W. Wagnon, William J. Pitz, Guillaume Vanhove
"Probing the antiknock effect of anisole through an ignition, speciation and modeling study of its blends with isooctane"
PROCEEDINGS OF THE COMBUSTION INSTITUTE. p.p. [10] 2021.
In order to unravel the reaction pathways relevant to anisole co-oxidation within a fuel blend, a detailed
study of isooctane/anisole blends was performed with the ULille RCM. Ignition delays as well as mole frac-
tion profiles were measured during a two-stage ignition delay using sampling and GC techniques. These re-
sults are used to validate a kinetic model developed from ab initio calculations for the most relevant rate
constants which included H-atom abstraction reactions from anisole, and reactions on the potential energy
surfaces of methoxyphenyl + O 2 and anisyl + O 2 . Pressure dependent rate constants were computed
for the methoxyphenyl + O 2 and anisyl + O 2 reactive systems using master equation code analysis. The new
kinetic model shows good agreement with the experimental data. Dual brute-force sensitivity analysis was
performed, on both first- and second-stages of ignition, allowing the identification of the most important re-
actions in the prediction of both ignition delays. It was observed that while pure anisole does not show NTC
behavior, a 60/40 isooctane/anisole blend displays such behavior, as well as two-stage ignition. This suggests
anisole addition may not be as beneficial to knock resistance as expected from its high octane number. The kinetic
modeling results demonstrate the importance of H-abstraction reactions both from the methoxy group and from the aryl ring in ortho-position and the addition of the resultant radicals to O 2 , mostly leading to
the formation of polar or non-aromatic products.
In order to unravel the reaction pathways relevant to anisole co-oxidation within a fuel blend, a detailed
study of isooctane/anisole blends was performed with the ULille RCM. Ignition delays as well as mole frac-
tion profiles were measured during a two-stage ignition delay using sampling and GC techniques. These re-
sults are used to validate a kinetic model developed from ab initio calculations for the most relevant rate
constants which included H-atom abstraction reactions from anisole, and reactions on the potential energy
surfaces of methoxyphenyl + O 2 and anisyl + O 2 . Pressure dependent rate constants were computed
for the methoxyphenyl + O 2 and anisyl + O 2 reactive systems using master equation code analysis. The new
kinetic model shows good agreement with the experimental data. Dual brute-force sensitivity analysis was
performed, on both first- and second-stages of ignition, allowing the identification of the most important re-
actions in the prediction of both ignition delays. It was observed that while pure anisole does not show NTC
behavior, a 60/40 isooctane/anisole blend displays such behavior, as well as two-stage ignition. This suggests
anisole addition may not be as beneficial to knock resistance as expected from its high octane number. The kinetic
modeling results demonstrate the importance of H-abstraction reactions both from the methoxy group and from the aryl ring in ortho-position and the addition of the resultant radicals to O 2 , mostly leading to
the formation of polar or non-aromatic products.