An experimental and kinetic modelling study of the oxidation of the four isomers of butanol

TL;DR

This study experimentally measured ignition delay times and developed a detailed kinetic model for the high-temperature oxidation of four butanol isomers, providing new insights into their reactivity relevant for biofuel applications.

Contribution

It presents the first ignition delay measurements and oxidation mechanism for 2-butanol, iso-butanol, and tert-butanol, enhancing understanding of their combustion behavior.

Findings

1-butanol and iso-butanol are more reactive, mainly undergoing H-atom abstraction.

Tert-butanol and 2-butanol are less reactive, primarily oxidized via dehydration to alkenes.

Reaction flux analysis highlights different dominant pathways for reactive and less reactive isomers.

Abstract

Butanol, an alcohol which can be produced from biomass sources, has received recent interest as an alternative to gasoline for use in spark ignition engines and as a possible blending compound with fossil diesel or biodiesel. Therefore, the autoignition of the four isomers of butanol (1-butanol, 2-butanol, iso-butanol, and tert-butanol) has been experimentally studied at high temperatures in a shock tube and a kinetic mechanism for description of their high-temperature oxidation has been developed. Ignition delay times for butanol/oxygen/argon mixtures have been measured behind reflected shock waves at temperatures and pressures ranging from approximately 1200 to 1800 K and 1 to 4 bar. Electronically excited OH emission and pressure measurements were used to determine ignition delay times. A detailed kinetic mechanism has been developed to describe the oxidation of the butanol isomers and validated by comparison to the shock tube measurements. Reaction flux and sensitivity analysis indicate that the consumption of 1 butanol and iso-butanol, the most reactive isomers, takes place primarily by H-atom abstraction resulting in the formation of radicals, the decomposition of which yields highly reactive branching agents, H-atoms and OH radicals. Conversely, the consumption of tert butanol and 2-butanol, the least reactive isomers, takes place primarily via dehydration, resulting in the formation of alkenes, which lead to resonance stabilized radicals with very low reactivity. To our knowledge, the ignition delay measurements and oxidation mechanism presented here for 2-butanol, iso-butanol, and tert butanol are the first of their kind..