Probing the low-temperature chemistry of di-n-butyl ether: Detection of previously unobserved intermediates

Di-n-butyl ether (DBE, C8H18O) has been proposed as a promising biofuel for diesel engines, but details of its low-temperature (LT) oxidation chemistry are not well understood. This paper reports new speciation data obtained in the temperature range of 400-1100 K at phi=1 and nearly-atmospheric pressure, using a plug flow reactor combined with electron ionization molecular-beam mass spectrometry (MBMS) and two different jet-stirred reactors coupled with either online gas chromatography or tunable synchrotron vacuum ultraviolet photoionization-MBMS. The experimental results confirm that DBE is very reactive and exhibits two negative-temperature coefficient (NTC) zones around 500-550K and 650-750K. Speciation data with about 40 C-0-C-8 species are presented, including about 20 LT species not reported previously. Among those, fuel-specific C8H16O2 cyclic ethers were quantified. Also, butanoic acid, which is present in highest amounts among the detected LT intermediates, and C8H14O3 diones, were found to peak already near 500K, suggesting their importance in the LT chemistry of DBE. Signals of several highly oxygenated peroxides (e.g., C8H14O5 and C8H O-16(6)) were detected, indicating third O-2 addition steps. Respective reaction pathways are suggested and discussed based on these experimental results. To better understand the LT chemistry of DBE, the present data were compared to two recent DBE models (Cai et al., 2014; Thion et al., 2017). Significant discrepancies between the experimental data and both models were found for important LT intermediates, of which many were not included in the respective mechanisms. The results reported in the present study thus provide new opportunities for refining DBE kinetic models. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.