Title: Fuel molecular structure effect on autoignition of highly branched iso-alkanes at low-to-intermediate temperatures: Iso-octane versus iso-dodecane

Abstract

Highly branched iso-alkanes are an important class of hydrocarbons found in conventional petroleum-derived and alternative renewable fuels used for combustion applications. Recognizing that chemical kinetics for most of these iso-alkanes, especially at low-to-intermediate temperatures, has not been well studied, an experimental and modeling investigation of two selected iso-alkanes, iso-octane (2,2,4-trimethylpentane, iC8) and iso-dodecane (2,2,4,6,6-pentamethylheptane, iC12), is conducted to understand the fuel molecular structure effect on their autoignition characteristics. Using a rapid compression machine (RCM), the ignition responses of iC8 and iC12 at varying pressures, temperatures, and equivalence ratios are characterized and compared. The newly-acquired experimental ignition delay times have been compared with the literature RCM and shock tube data, demonstrating the complementary nature of the current dataset. Further comparison of the experimental pressure traces and ignition delay times illustrates the reactivity crossover between iC8 and iC12. Namely, there exists a temperature window in the negative temperature coefficient regime within which iC12 is less reactive than iC8, but iC12 becomes more reactive outside this temperature window. Furthermore, a chemical kinetic model of iso-alkanes including both iC8 and iC12 is developed. Simulated results using this model are then compared to the experimental data obtained in this study and available in the literature,more » showing its ability to predict the experimental trends. Chemical kinetic analyses have also been conducted to identify the important reaction pathways controlling autoignition at varying conditions, and to elucidate the underlying mechanism leading to different reactivity trends between iC8 and iC12.« less

Authors:

Fang, R  ^[1];

• Search DOE PAGES for author "Fang, R"
• Search DOE PAGES for ORCID "0000-0003-4831-5100"

Kukkadapu, G ^[2]; Wang, M  ^[1];

• Search DOE PAGES for author "Wang, M"
• Search DOE PAGES for ORCID "0000-0002-8958-5943"

Wagnon, S W ^[2]; Zhang, K ^[2]; Mehl, M ^[2]; Westbrook, C K ^[2]; Pitz, W J ^[2]; Sung, C J ^[1]

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+ Show Author Affiliations

1. Univ. of Connecticut, Storrs, CT (United States)
2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Wed Apr 01 00:00:00 EDT 2020

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1605059

Alternate Identifier(s):

OSTI ID: 1603693

Report Number(s):

LLNL-JRNL-789972
Journal ID: ISSN 0010-2180; 988029

Grant/Contract Number:  

AC52-07NA27344; B630575

Resource Type:

Accepted Manuscript

Journal Name:

Combustion and Flame

Additional Journal Information:

Journal Volume: 214; Journal Issue: C; Journal ID: ISSN 0010-2180

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Iiso-octaneIiso-dodecane; Autoignition; Rapid compression machine; Low temperature chemistry