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Title: A comprehensive iso-octane combustion model with improved thermochemistry and chemical kinetics

Abstract

Iso-Octane (2,2,4-trimethylpentane) is a primary reference fuel and an important component of gasoline fuels. Furthermore, it is a key component used in surrogates to study the ignition and burning characteristics of gasoline fuels. This paper presents an updated chemical kinetic model for iso-octane combustion. Specifically, the thermodynamic data and reaction kinetics of iso-octane have been re-assessed based on new thermodynamic group values and recently evaluated rate coefficients from the literature. The adopted rate coefficients were either experimentally measured or determined by analogy to theoretically calculated values. New alternative isomerization pathways for peroxy-alkyl hydroperoxide ($$\dot{O}$$OQOOH) radicals were added to the reaction mechanism. The updated kinetic model was compared against new ignition delay data measured in rapid compression machines (RCM) and a high-pressure shock tube. Our experiments were conducted at pressures of 20 and 40 atm, at equivalence ratios of 0.4 and 1.0, and at temperatures in the range of 632–1060 K. The updated model was further compared against shock tube ignition delay times, jet-stirred reactor oxidation speciation data, premixed laminar flame speeds, counterflow diffusion flame ignition, and shock tube pyrolysis speciation data available in the literature. Finally, the updated model was used to investigate the importance of alternative isomerization pathways in the low temperature oxidation of highly branched alkanes. When compared to available models in the literature, the present model represents the current state-of-the-art in fundamental thermochemistry and reaction kinetics of iso-octane; and thus provides the best prediction of wide ranging experimental data and fundamental insights into iso-octane combustion chemistry.

Authors:
ORCiD logo [1];  [2];  [1];  [1];  [3];  [4];  [3];  [1];  [1];  [2];  [4];  [4];  [2];  [1];  [2];  [3];  [1]
  1. King Abdullah Univ. of Science and Technology (KAUST), Thuwal (Saudi Arabia). Clean Combustion Research Center (CCRC)
  2. Univ. of Connecticut, Storrs, CT (United States). Dept. of Mechanical Engineering
  3. National Univ. of Ireland, Galway (Ireland). Combustion Chemistry Centre
  4. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
National Science Foundation (NSF); USDOE Office of Energy Efficiency and Renewable Energy (EERE), Vehicle Technologies Office (EE-3V)
OSTI Identifier:
1361588
Alternate Identifier(s):
OSTI ID: 1415304
Report Number(s):
LLNL-JRNL-711699
Journal ID: ISSN 0010-2180
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Combustion and Flame
Additional Journal Information:
Journal Volume: 178; 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; iso-octane; combustion kinetics; thermodynamics; gauche; alternative isomerisation

Citation Formats

Atef, Nour, Kukkadapu, Goutham, Mohamed, Samah Y., Rashidi, Mariam Al, Banyon, Colin, Mehl, Marco, Heufer, Karl Alexander, Nasir, Ehson F., Alfazazi, A., Das, Apurba K., Westbrook, Charles K., Pitz, William J., Lu, Tianfeng, Farooq, Aamir, Sung, Chih-Jen, Curran, Henry J., and Sarathy, S. Mani. A comprehensive iso-octane combustion model with improved thermochemistry and chemical kinetics. United States: N. p., 2017. Web. doi:10.1016/j.combustflame.2016.12.029.
Atef, Nour, Kukkadapu, Goutham, Mohamed, Samah Y., Rashidi, Mariam Al, Banyon, Colin, Mehl, Marco, Heufer, Karl Alexander, Nasir, Ehson F., Alfazazi, A., Das, Apurba K., Westbrook, Charles K., Pitz, William J., Lu, Tianfeng, Farooq, Aamir, Sung, Chih-Jen, Curran, Henry J., & Sarathy, S. Mani. A comprehensive iso-octane combustion model with improved thermochemistry and chemical kinetics. United States. doi:10.1016/j.combustflame.2016.12.029.
Atef, Nour, Kukkadapu, Goutham, Mohamed, Samah Y., Rashidi, Mariam Al, Banyon, Colin, Mehl, Marco, Heufer, Karl Alexander, Nasir, Ehson F., Alfazazi, A., Das, Apurba K., Westbrook, Charles K., Pitz, William J., Lu, Tianfeng, Farooq, Aamir, Sung, Chih-Jen, Curran, Henry J., and Sarathy, S. Mani. Sun . "A comprehensive iso-octane combustion model with improved thermochemistry and chemical kinetics". United States. doi:10.1016/j.combustflame.2016.12.029. https://www.osti.gov/servlets/purl/1361588.
@article{osti_1361588,
title = {A comprehensive iso-octane combustion model with improved thermochemistry and chemical kinetics},
author = {Atef, Nour and Kukkadapu, Goutham and Mohamed, Samah Y. and Rashidi, Mariam Al and Banyon, Colin and Mehl, Marco and Heufer, Karl Alexander and Nasir, Ehson F. and Alfazazi, A. and Das, Apurba K. and Westbrook, Charles K. and Pitz, William J. and Lu, Tianfeng and Farooq, Aamir and Sung, Chih-Jen and Curran, Henry J. and Sarathy, S. Mani},
abstractNote = {Iso-Octane (2,2,4-trimethylpentane) is a primary reference fuel and an important component of gasoline fuels. Furthermore, it is a key component used in surrogates to study the ignition and burning characteristics of gasoline fuels. This paper presents an updated chemical kinetic model for iso-octane combustion. Specifically, the thermodynamic data and reaction kinetics of iso-octane have been re-assessed based on new thermodynamic group values and recently evaluated rate coefficients from the literature. The adopted rate coefficients were either experimentally measured or determined by analogy to theoretically calculated values. New alternative isomerization pathways for peroxy-alkyl hydroperoxide ($\dot{O}$OQOOH) radicals were added to the reaction mechanism. The updated kinetic model was compared against new ignition delay data measured in rapid compression machines (RCM) and a high-pressure shock tube. Our experiments were conducted at pressures of 20 and 40 atm, at equivalence ratios of 0.4 and 1.0, and at temperatures in the range of 632–1060 K. The updated model was further compared against shock tube ignition delay times, jet-stirred reactor oxidation speciation data, premixed laminar flame speeds, counterflow diffusion flame ignition, and shock tube pyrolysis speciation data available in the literature. Finally, the updated model was used to investigate the importance of alternative isomerization pathways in the low temperature oxidation of highly branched alkanes. When compared to available models in the literature, the present model represents the current state-of-the-art in fundamental thermochemistry and reaction kinetics of iso-octane; and thus provides the best prediction of wide ranging experimental data and fundamental insights into iso-octane combustion chemistry.},
doi = {10.1016/j.combustflame.2016.12.029},
journal = {Combustion and Flame},
number = C,
volume = 178,
place = {United States},
year = {Sun Feb 05 00:00:00 EST 2017},
month = {Sun Feb 05 00:00:00 EST 2017}
}

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Cited by: 13works
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  • A previously described methodology for deriving a reduced kinetic mechanism for alkane oxidation and tested for n-heptane is here shown to be valid, in a slightly modified version, for iso-octane and its mixtures with n-pentane, iso-hexane and n-heptane. The model is still based on partitioning the species into lights, defined as those having a carbon number smaller than 3, and heavies, which are the complement in the species ensemble, and mathematically decomposing the heavy species into constituents which are radicals. For the same similarity variable found from examining the n-heptane LLNL mechanism in conjunction with CHEMKIN II, the appropriately scaledmore » total constituent molar density still exhibits a self-similar behavior over a very wide range of equivalence ratios, initial pressures and initial temperatures in the cold ignition regime. When extended to larger initial temperatures than for cold ignition, the self-similar behavior becomes initial temperature dependent, which indicates that rather than using functional fits for the enthalpy generation due to the heavy species' oxidation, an ideal model based on tabular information extracted from the complete LLNL kinetics should be used instead. Similarly to n-heptane, the oxygen and water molar densities are shown to display a quasi-linear behavior with respect to the similarity variable, but here their slope variation is no longer fitted and instead, their rate equations are used with the ideal model to calculate them. As in the original model, the light species ensemble is partitioned into quasi-steady and unsteady species; the quasi-steady light species mole fractions are computed using the ideal model and the unsteady species are calculated as progress variables using rates extracted from the ideal model. Results are presented comparing the performance of the model with that of the LLNL mechanism using CHEMKIN II. The model reproduces excellently the temperature and species evolution versus time or versus the similarity variable, with the exception of very rich mixtures, where the predictions are still very good but the multivalued aspect of these functions at the end of oxidation is not captured in the reduction. The ignition time is predicted within percentages of the LLNL values over a wide range of equivalence ratios, initial pressures and initial temperatures. (author)« less
  • Detailed chemical kinetic reaction mechanisms have been developed to describe the pyrolysis and oxidation of nine n-alkanes larger than n-heptane, including n-octane (n-C{sub 8}H{sub 18}), n-nonane (n-C{sub 9}H{sub 20}), n-decane (n-C{sub 10}H{sub 22}), n-undecane (n-C{sub 11}H{sub 24}), n-dodecane (n-C{sub 12}H{sub 26}), n-tridecane (n-C{sub 13}H{sub 28}), n-tetradecane (n-C{sub 14}H{sub 30}), n-pentadecane (n-C{sub 15}H{sub 32}), and n-hexadecane (n-C{sub 16}H{sub 34}). These mechanisms include both high temperature and low temperature reaction pathways. The mechanisms are based on previous mechanisms for the primary reference fuels n-heptane and iso-octane, using the reaction classes first developed for n-heptane. Individual reaction class rules are as simple asmore » possible in order to focus on the parallelism between all of the n-alkane fuels included in the mechanisms. These mechanisms are validated through extensive comparisons between computed and experimental data from a wide variety of different sources. In addition, numerical experiments are carried out to examine features of n-alkane combustion in which the detailed mechanisms can be used to compare reactivities of different n-alkane fuels. The mechanisms for these n-alkanes are presented as a single detailed mechanism, which can be edited to produce efficient mechanisms for any of the n-alkanes included, and the entire mechanism, with supporting thermochemical and transport data, together with an explanatory glossary explaining notations and structural details, is available for download from our web page. (author)« less
  • This article uses a chemical kinetic modeling approach to study the influences of fuel molecular structure on Octane Sensitivity (OS) in Spark Ignition (SI) engines. Octane Sensitivity has the potential to identify fuels that can be used in next-generation high compression, turbocharged SI engines to avoid unwanted knocking conditions and extend the range of operating conditions that can be used in such engines. While the concept of octane numbers of different fuels has been familiar for many years, the variations of their values and their role in determining Octane Sensitivity have not been addressed previously in terms of the basicmore » structures of the fuel molecules. In particular, the importance of electron delocalization on low temperature hydrocarbon reactivity and its role in determining OS in engine fuel is described here for the first time. Finally, the role of electron delocalization on fuel reactivity and Octane Sensitivity is illustrated for a very wide range of engine fuel types, including n-alkane, 1-olefin, n-alcohol, and n-alkyl benzenes, and the unifying features of these fuels and their common trends, using existing detailed chemical kinetic reaction mechanisms that have been collected and unified to produce an overall model with unprecedented capabilities.« less
  • Toluene is often used as a fluorescent tracer for fuel concentration measurements, but without considering whether it affects the auto-ignition properties of the base fuel. We investigate the auto-ignition of pure toluene and its influence on the auto-ignition of n-heptane and iso-octane/air mixtures under engine-relevant conditions at typical tracer concentrations. Ignition delay times {tau}{sub ign} were measured behind reflected shock waves in mixtures with air at {phi}=1.0 and 0.5 at p=40 bar, over a temperature range of T=700-1200 K and compared to numerical results using two different mechanisms. Based on the models, information is derived about the relative influence ofmore » toluene on {tau}{sub ign} on the base fuels as function of temperature. For typical toluene tracer concentrations {<=}10%, the ignition delay time {tau}{sub ign} changes by less than 10% in the relevant pressure and temperature range. (author)« less