Hierarchical Auto-Ignition and Structure-Reactivity Trends of C 2 –C 4 1-Alkenes

Wuchuan Sun, Yingjia Zhang, Yang Li and Zuohua Huang
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Wuchuan Sun: State Key Laboratory of Multiphase Flows in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Yingjia Zhang: State Key Laboratory of Multiphase Flows in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China
Yang Li: Science and Technology on Combustion, Internal Flow and Thermostructure Laboratory, School of Astronauties, Northwestern Polytechnical University, Xi’an 710072, China
Zuohua Huang: State Key Laboratory of Multiphase Flows in Power Engineering, Xi’an Jiaotong University, Xi’an 710049, China

Energies, 2021, vol. 14, issue 18, 1-31

Abstract: Ignition delay times of small alkenes are a valuable constraint for the refinement of the core kinetic mechanism of hydrocarbons used in representing combustion properties of real fuels. Moreover, the chemical reactivity comparison of those small alkenes provides a reference in object-oriented fuel design and logical combustion utilization. In this study, the ignition delay times of C 2 –C 4 alkenes (ethylene, propene and 1-butene) were measured behind reflected shock waves first, with a fixed oxygen concentration ( X O2 = 6%) and equivalence ratio ( φ = 1.0) at various pressures of 1.2, 4.0 and 16.0 atm, in order to facilitate the comparison. Three chemical-based-Arrhenius-type correlations covering a wide range of temperature, pressure, equivalence ratio, and dilution were proposed. The simplified reaction network for pyrolysis and oxidation of 1-alkenes was depicted relying on the reaction classes of alkenes. Nine generally accepted mechanisms were used to simulate the ignition delay times measured by this study as well as literature. All the kinetic models show reasonable structure-reactivity trends for all of the three alkenes, but only NUIGMech 1.1 is capable of representing quantificationally the chemical reactivity at all tested conditions. Generally, ethylene exhibits the highest reactivity while propene presents the lowest at high temperatures. Analyses of sensitivity and flux indicate that the main oxidation pathway of ethylene is chain-branching, which accelerates the accumulation of free radical pools, especially for the Ḣ atom, Ȯ atom and ȮH radical, which results in the highest reactivity of ethylene. For propene and 1-butene, due to the presence of the allylic site, consumption of allylic radicals becomes the decisive step of oxidation and allylic radicals are mostly consumed by the HȮ 2 radical. However, there are no such efficient reaction pathways for the formation of HȮ 2 radicals during the propene oxidation process, while reaction pathways for HȮ 2 formation in 1-butene are efficient. Thus, 1-butene presents higher reactivity compared to propene.

Keywords: 1-alkenes; Arrhenius correlation; reactivity comparison; chemical kinetics (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2021
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