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Title: A comprehensive detailed kinetic mechanism for the simulation of transportation fuels

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Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
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Conference: Presented at: 10th US National Combustion Meeting, College Park, MD, United States, Apr 23 - Apr 26, 2017
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United States

Citation Formats

Mehl, M, Wagnon, S, Tsang, K, Kukkadapu, G, Pitz, W J, Westbrook, C K, Tsang, Y, Curran, H J, Atef, N, Rachidi, M A, Sarathy, M S, and Ahmed, A. A comprehensive detailed kinetic mechanism for the simulation of transportation fuels. United States: N. p., 2017. Web.
Mehl, M, Wagnon, S, Tsang, K, Kukkadapu, G, Pitz, W J, Westbrook, C K, Tsang, Y, Curran, H J, Atef, N, Rachidi, M A, Sarathy, M S, & Ahmed, A. A comprehensive detailed kinetic mechanism for the simulation of transportation fuels. United States.
Mehl, M, Wagnon, S, Tsang, K, Kukkadapu, G, Pitz, W J, Westbrook, C K, Tsang, Y, Curran, H J, Atef, N, Rachidi, M A, Sarathy, M S, and Ahmed, A. Mon . "A comprehensive detailed kinetic mechanism for the simulation of transportation fuels". United States. doi:.
title = {A comprehensive detailed kinetic mechanism for the simulation of transportation fuels},
author = {Mehl, M and Wagnon, S and Tsang, K and Kukkadapu, G and Pitz, W J and Westbrook, C K and Tsang, Y and Curran, H J and Atef, N and Rachidi, M A and Sarathy, M S and Ahmed, A},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Feb 27 00:00:00 EST 2017},
month = {Mon Feb 27 00:00:00 EST 2017}

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  • n-Hexadecane and 2,2,4,4,6,8,8-heptamethylnonane represent the primary reference fuels for diesel that are used to determine cetane number, a measure of the ignition property of diesel fuel. With the development of chemical kinetics models for these two primary reference fuels for diesel, a new capability is now available to model diesel fuel ignition. Also, we have developed chemical kinetic models for a whole series of large n-alkanes and a large iso-alkane to represent these chemical classes in fuel surrogates for conventional and future fuels. Methyl decanoate and methyl stearate are large methyl esters that are closely related to biodiesel fuels, andmore » kinetic models for these molecules have also been developed. These chemical kinetic models are used to predict the effect of the fuel molecule size and structure on ignition characteristics under conditions found in internal combustion engines.« 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
  • The influence of oxygenated hydrocarbons as additives to diesel fuels on ignition, NOx emissions and soot production has been examined using a detailed chemical kinetic reaction mechanism. N-heptane was used as a representative diesel fuel, and methanol, ethanol, dimethyl ether and dimethoxymethane were used as oxygenated fuel additives. It was found that addition of oxygenated hydrocarbons reduced NOx levels and reduced the production of soot precursors. When the overall oxygen content in the fuel reached approximately 25% by mass, production of soot precursors fell effectively to zero, in agreement with experimental studies. The kinetic factors responsible for these observations aremore » discussed.« less
  • Thermodynamic properties and detailed chemical kinetic models have been developed for the combustion of two oxygenates: methyl butanoate, a model compound for biodiesel fuels, and methyl formate, a related simpler molecule. Bond additivity methods and rules for estimating kinetic parameters were adopted from hydrocarbon combustion and extended. The resulting mechanisms have been tested against the limited combustion data available in the literature, which was obtained at low temperature, subatmospheric conditions in closed vessels, using pressure measurements as the main diagnostic. Some qualitative agreement was obtained, but the experimental data consistently indicated lower overall reactivities than the model, differing by factorsmore » of 10 to 50. This discrepancy, which occurs for species with well-established kinetic mechanisms as well as for methyl esters, is tentatively ascribed to the presence of wall reactions in the experiments. The model predicts a region of weak or negative dependence of overall reaction rate on temperature for each methyl ester. Examination of the reaction fluxes provides an explanation of this behavior, involving a temperature-dependent competition between chain-propagating unimolecular decomposition processes and chain-branching processes, similar to that accepted for hydrocarbons. There is an urgent need to obtain more complete experimental data under well-characterized conditions for thorough testing of the model.« less
  • Fischer-Tropsch (FT) fuels can be synthesized from a syngas stream generated by the gasification of biomass. As such they have the potential to be a renewable hydrocarbon fuel with many desirable properties. However, both the chemical and physical properties are somewhat different from the petroleum-based hydrocarbons that they might replace, and it is important to account for such differences when considering using them as replacements for conventional fuels in devices such as diesel engines and gas turbines. FT fuels generally contain iso-alkanes with one or two substituted methyl groups to meet the pour-point specifications. Although models have been developed formore » smaller branched alkanes such as isooctane, additional efforts are required to properly capture the kinetics of the larger branched alkanes. Recently, Westbrook et al. developed a chemical kinetic model that can be used to represent the entire series of n-alkanes from C{sub 1} to C{sub 16} (Figure 1). In the current work, the model is extended to treat 2,2,4,4,6,8,8-heptamethylnonane (HMN), a large iso-alkane. The same reaction rate rules used in the iso-octane mechanism were incorporated in the HMN mechanism. Both high and low temperature chemistry was included so that the chemical kinetic model would be applicable to advanced internal combustion engines using low temperature combustion strategies. The chemical kinetic model consists of 1114 species and 4468 reactions. Concurrently with this effort, work is underway to improve the details of specific reaction classes in the mechanism, guided by high-level electronic structure calculations. Attention is focused upon development of accurate rate rules for abstraction of the tertiary hydrogens present in branched alkanes and properly accounting for the pressure dependence of the ?-scission, isomerization, and R + O{sub 2} reactions.« less