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Branched-chain fatty acid methyl esters (FAME), known for cold flow improvers for biodiesel, have received less attention to their chemical kinetics in flames. This study proposes a detailed mechanism reduced to be a compact form to predict the formation of non-fuel small hydrocarbons and light-weight polycyclic aromatic hydrocarbons (PAH) from the oxidation of methyl isobutanoate [MIB, (CH 3) 2 CHC(=O)OCH 3 ], a C5-branched methyl ester. Using the path flux analysis, the newly constructed MIB oxidation mechanism with 344 species and 2147 reactions is shrunk and refined to 63 species and 288 reactions, a minimum size for its application to computational fluid dynamics. The minimized MIB mechanism incorporated into a 2D axisymmetric coflow model is used to validate mass-spectrometric data obtained from a laminar coflow diffusion flame of methane doped with MIB. For the first time, ten experimentally measured centerline profiles in the flame are computationally interpreted by nine C3–C6 unsaturated hydrocarbons, three carbonyls and four aromatics. Furthermore, we analyze the spatial distribution of the investigated intermediates and reveal their corresponding reaction pathways linked to the MIB decomposition. • Compact kinetic mechanism for methyl isobutanote oxidation is proposed. • CFD coupled with the kinetic mechanism describes chemistry in a nonpremixed flame. • Non-fuel hydrocarbons measured by mass-spectrometry are modeled for the first time. • Reaction pathway analyses elucidate abundant formation of aromatics correlated with the fuel. [ABSTRACT FROM AUTHOR]

Abstract: Growth of the biodiesel industry has motivated increased study of the combustion characteristics of its constituent molecules and building combustion modeling capability. Understanding how these characteristics differ between bio-derived and conventional diesel fuels can help in evaluating biodiesel performance. A kinetic modeling comparison of methyl butanoate and n-butane, its corresponding alkane, contrasted the combustion of methyl esters and normal alkanes, towards understanding the effect of the methyl ester moiety. Utilizing a combined n-heptane and methyl butanoate kinetic mechanism in shock tube simulations, the results predicted no region of negative temperature coefficient (NTC) behavior for methyl butanoate, compared to a well defined NTC region for n-butane. We observed that oxidation pathways associated with the methyl ester moiety inhibited NTC behavior, through increased production of hydroperoxy radicals (HO2) instead of hydroxyl radicals (OH). In addition, we compared the evolution of carbon monoxide, carbon dioxide, ethylene and acetylene. The early formation of CO and CO2, directly from methyl butanoate, revealed unique reaction pathways that also influenced a reduction in soot precursor formation. Overall, these results will help to understand how combustion processes change with the inclusion of oxygenated fuels, which will inform the study and design of combustion technologies. [Copyright &y& Elsevier]

Abstract: Burgeoning global demand for energy has increased concerns about the fuel security issues and deleterious environmental impacts that result from the ubiquitous use of fossil fuels to meet these needs. This article is a review of completed work towards the goal of creating chemical kinetic mechanisms for biodiesel, which will aid in the development of clean and efficient combustors that utilize alternative fuels. As the composition of biodiesel is too complex to directly model, efforts have instead focused on the development of mechanisms for surrogates, simpler molecules that can produce the primary characteristics of biodiesel combustion. Research initially targeted smaller molecules like methyl butanoate to investigate the role of the characteristic ester group that is present in the fatty acid alkyl esters that comprise biodiesel. The study of isomers and similar unsaturated compounds elucidated the effects of molecular structure on combustion. Subsequent efforts involved the study of larger molecules that are close in scale to biodiesel molecules, such as methyl decanoate, as well as molecules that are present in biodiesel, such as methyl stearate. Applications of kinetic modeling demonstrate its utility in the study of combustion through, for example, revealing the chemistry in the early formation of CO2 in biodiesel and its soot reduction tendencies. The results of this review illustrate key limitations in kinetic modeling, namely a need for high-pressure kinetic methodology and a need for continuous improvement of kinetic mechanisms through theory and experiment. These limitations suggest direction for future research; further experimental and theoretical work will produce accurate mechanisms for appropriate biodiesel surrogates. All of these efforts represent significant advances in kinetic modeling that are important towards the goal of building a predictive capability for biodiesel combustion. Such predictive capability will aid the development of combustion technologies that will help society meet its energy needs in an environmentally conscious manner. [Copyright &y& Elsevier]