Detailed chemical kinetic reaction mechanisms for soy and rapeseed biodiesel fuels

Abstract

A detailed chemical kinetic reaction mechanism is developed for the five major components of soy biodiesel and rapeseed biodiesel fuels. These components, methyl stearate, methyl oleate, methyl linoleate, methyl linolenate, and methyl palmitate, are large methyl ester molecules, some with carbon-carbon double bonds, and kinetic mechanisms for them as a family of fuels have not previously been available. Of particular importance in these mechanisms are models for alkylperoxy radical isomerization reactions in which a C=C double bond is embedded in the transition state ring. The resulting kinetic model is validated through comparisons between predicted results and a relatively small experimental literature. The model is also used in simulations of biodiesel oxidation in jet-stirred reactor and intermediate shock tube ignition and oxidation conditions to demonstrate the capabilities and limitations of these mechanisms.Differences in combustion properties between the two biodiesel fuels, derived from soy and rapeseed oils, are traced to the differences in the relative amounts of the same five methyl ester components. † Lawrence

Experimental and Kinetic Modeling Study of 2-Methyl-2-Butene: Allylic Hydrocarbon Kinetics

“…This sequence especially characterized development of models for combustion of small molecule fuels such as hydrogen, methane, methanol, propane, and others, where often the experimental studies had preceded kinetic models by as much as 20 or 30 years 1 . More recently, improvements in kinetic modeling techniques, along with dramatic advances in computer capacities and speed have somewhat reversed this process, and kinetic reaction mechanisms for much larger and more complex fuels such as large n-alkanes 2 , lightly branched alkanes 3 , other large alkane fuels such as 2,2,4,4,6,8,8-heptamethyl nonane 4 , and even biodiesel fuels 5 have appeared in advance of experimental kinetic and other studies that confirm and correct assumptions made during the kinetic model development. Kinetic models and associated sensitivity analyses can identify specific chemical reactions, reaction rates, reaction pathways, bond energies and other thermochemical parameters that are particularly important and can accelerate development of models and general understanding of many practical combustion processes.…”

“…New experimental results of shock-tube ignition and jet-stirred reactor (JSR) oxidation of 2M2B are presented below, and a detailed chemical kinetic reaction mechanism is developed to describe the reactions involved in both sets of experiments. Overall, there are few experimental sources of data to assist in developing and testing kinetic mechanisms for C 5 and larger olefin fuels. It is also perhaps surprising that none of the past experimental or kinetic modeling papers provided intermediate species measurements for any branched unsaturated hydrocarbon fuels larger than iso-butene.…”

Theoretical and Kinetic Study of the Hydrogen Atom Abstraction Reactions of Esters with HȮ2 Radicals

“…However, biofuels contain oxygen atoms which change the rates and mechanism of the reactions, leading to different products. 3 Some biofuels, like ethanol or butanol, can be incorporated into conventional gasoline and used in spark-ignition engines, while others can be used as supplements or replacements in diesel engines. 3 In the combustion temperature range of 500-2000 K, the oxidation reactions of radicals likė H,Ȯ,ȮH, HȮ 2 andĊH 3 are always important when abstracting a hydrogen atom from the fuel molecules.…”

“…3 Some biofuels, like ethanol or butanol, can be incorporated into conventional gasoline and used in spark-ignition engines, while others can be used as supplements or replacements in diesel engines. 3 In the combustion temperature range of 500-2000 K, the oxidation reactions of radicals likė H,Ȯ,ȮH, HȮ 2 andĊH 3 are always important when abstracting a hydrogen atom from the fuel molecules. 4 When HȮ 2 radicals abstract a hydrogen atom from an ester, hydrogen peroxide (H 2 O 2 ) and an ester radical are formed.…”

“…2 Bio-derived fuels, however, present several challenges such as the difficulty and cost of production in large quantities and their impact on the animal and human food chains. 3 Theoretical investigations such as chemical kinetic studies can be used, together with experimental studies, in order to predict the reactivity of these fuels. Oxygen atoms are not present within the primary fuel molecule of conventional fuels.…”