Exploring low temperature oxidation of iso-octane under atmospheric pressure

Iso-octane is the dominant component of primary reference fuel (PRF), with high knock resistance during the combustion process. Understanding the low temperature oxidation chemistry of iso-octane aids in clarifying the auto-ignition properties of gasoline surrogates and developing their kinetic models. How-ever, its low temperature oxidation performance has only been observed under high pressure conditions; no report in the literature includes detailed speciation, hindering a comprehensive examination of the iso-octane low temperature oxidation mechanism. In this work, low temperature oxidation behavior of iso-octane was clearly observed in jet-stirred reactors (JSRs) under an initial fuel mole fraction of 0.01, resi-dence time of 2 s, equivalence ratio of 0.25, and pressure of 1 bar. The low temperature oxidation reaction networks of iso-octane were explored by measuring low temperature oxidation intermediates in three ex-perimental approaches: synchrotron vacuum-ultraviolet photoionization mass spectrometry (SVUV-PIMS), gas chromatography (GC), and cw-cavity ring-down spectroscopy (cw-CRDS). More than 80 intermediates were qualitatively analyzed in combination with the photoionization efficiency (PIE) spectrum, quantum chemistry calculation of the ionization energies, and GC analysis. Hydroperoxides derived from iso-octane low temperature oxidation were reported experimentally for the first time, including keto-hydroperoxides (KHP) and/or hydroperoxyl cyclic ethers (HPCE). Approximately 40 products were quantified, including aldehydes, ketones, olefins, and carboxylic acids, etc. Kinetic models in the literature have been exam-ined using the datasets obtained from this work and reaction pathways for the important intermediates discussed. Comparison indicated that the iso-octane models in the literature must be improved to accu-rately capture the performance of iso-octane low temperature oxidation.(c) 2022 Published by Elsevier Inc. on behalf of The Combustion Institute.

Automated summary

This study investigates the low temperature oxidation behavior of iso-octane using experimental methods. More than 80 intermediates and approximately 40 products were analyzed. The results provide insights for improving the kinetic models of iso-octane.