n-Heptane cool flame chemistry: Unraveling intermediate species measured in a stirred reactor and motored engine

Zhandong Wang, Bingjie Chen, Kai Moshammer, Denisia M. Popolan-Vaida, Salim Sioud, Vijai Shankar, David Vuilleumier, Tao Tao, Lena Ruwe, Eike Bräuer, Nils Hansen, Philippe Dagaut, Katharina Kohse-Höinghaus, Misjudeen Raji, Mani Sarathy

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Abstract

This work identifies classes of cool flame intermediates from n-heptane low-temperature oxidation in a jet-stirred reactor (JSR) and a motored cooperative fuel research (CFR) engine. The sampled species from the JSR oxidation of a mixture of n-heptane/O2/Ar (0.01/0.11/0.88) were analyzed using a synchrotron vacuum ultraviolet radiation photoionization (SVUV-PI) time-of-flight molecular-beam mass spectrometer (MBMS) and an atmospheric pressure chemical ionization (APCI) Orbitrap mass spectrometer (OTMS). The OTMS was also used to analyze the sampled species from a CFR engine exhaust. Approximately 70 intermediates were detected by the SVUV-PI-MBMS, and their assigned molecular formulae are in good agreement with those detected by the APCI-OTMS, which has ultra-high mass resolving power and provides an accurate elemental C/H/O composition of the intermediate species. Furthermore, the results show that the species formed during the partial oxidation of n-heptane in the CFR engine are very similar to those produced in an ideal reactor, i.e., a JSR.The products can be classified by species with molecular formulae of C7H14Ox (x = 0–5), C7H12Ox (x = 0–4), C7H10Ox (x = 0–4), CnH2n (n = 2–6), CnH2n−2 (n = 4–6), CnH2n+2O (n = 1–4), CnH2nO (n = 1–6), CnH2n−2O (n = 2–6), CnH2n−4O (n = 4–6), CnH2n+2O2 (n = 0–4, 7), CnH2nO2 (n = 1–6), CnH2n−2O2 (n = 2–6), CnH2n−4O2 (n = 4–6), and CnH2nO3 (n = 3–6). The identified intermediate species include alkenes, dienes, aldehyde/keto compounds, olefinic aldehyde/keto compounds, diones, cyclic ethers, peroxides, acids, and alcohols/ethers. Reaction pathways forming these intermediates are proposed and discussed herein. These experimental results are important in the development of more accurate kinetic models for n-heptane and longer-chain alkanes.
Original languageEnglish (US)
Pages (from-to)199-216
Number of pages18
JournalCombustion and Flame
Volume187
DOIs
StatePublished - Oct 3 2017

Bibliographical note

KAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was initiated by the Clean Combustion Research Center with funding from King Abdullah University of Science and Technology (KAUST), Office of Sponsored Research (OSR) under Award No. 767 OSR-2016-CRG5-3022, and Saudi Aramco under the FUELCOM program. The work of N.H. and K.M. was supported by Division of Chemical Sciences, Geosciences and Biosciences, BES/USDOE. D.M.P.V. was supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-05CH11231, the gas phase chemical physics program through the Chemical Sciences Division of Lawrence Berkeley National Laboratory (LBNL). L.R., E.B., and K.K.H. are grateful for German DFG project under contract KO1363/31-1. P.D. has received funding from European Research Council under FP7/2007-2013/ERC grant 291049-2G-CSafe. Tao Tao is supported by China Scholarship Council (Grant No. 201506210349). Z. Wang wishes to thank Dr. Jean-Baptiste Masurier for his help in the CFR engine experiment and discussion. Sandia is a multi-mission laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under contract DE-AC04-94-AL85000. The Advanced Light Source is supported by the Director, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

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