The combustion kinetics of the lignocellulosic biofuel, ethyl levulinate

Abstract
Ethyl levulinate (Ethyl 4-oxopentanoate) is a liquid molecule at ambient temperature, comprising of ketone and ethyl ester functionalities and is one of the prominent liquid fuel candidates that may be easily obtained from lignocellulosic biomass. The combustion kinetics of ethyl levulinate have been investigated. Shock tube and rapid compression machine apparatuses are utilised to acquire gas phase ignition delay measurements of 0.5% ethyl levulinate/O2 mixtures at ϕ = 1.0 and ϕ = 0.5 at ∼ 10 atm over the temperature range 1000–1400 K. Ethyl levulinate is observed not to ignite at temperatures lower than ∼1040 K in the rapid compression machine. The shock tube and rapid compression machine data are closely consistent and show ethyl levulinate ignition delay to exhibit an Arrhenius dependence to temperature. These measurements are explained by the construction and analysis of a detailed chemical kinetic model. The kinetic model is completed by establishing thermochemical-kinetic analogies to 2-butanone, for the ethyl levulinate ketone functionality, and to ethyl propanoate for the ethyl ester functionality. The so constructed model is observed to describe the shock tube data very accurately, but computes the rapid compression machine data set to a lesser but still applicable fidelity. Analysis of the model suggests the autooxidation mechanism of ethyl levulinate to be entirely dominated by the propensity for the ethyl ester functionality to unimolecularly decompose to form levulinic acid and ethylene. The subsequent reaction kinetics of these species is shown to dictate the overall rate of the global combustion reaction. This model is then use to estimate the Research and Motored Octane Numbers of ethyl levulinate to be ≥97.7 and ≥ 93, respectively. With this analysis ethyl levulinate would be best suited as a gasoline fuel component, rather than as a diesel fuel as suggested in the literature. Indeed it may be considered to be useful as an octane booster. The ethyl levulinate kinetic model is constructed within a state-of-the-art gasoline surrogate combustion kinetic model and is thus available as a tool with which to investigate the use of ethyl levulinate as a gasoline additive.

Citation
Ghosh MK, Howard MS, Zhang Y, Djebbi K, Capriolo G, et al. (2018) The combustion kinetics of the lignocellulosic biofuel, ethyl levulinate. Combustion and Flame 193: 157–169. Available: http://dx.doi.org/10.1016/j.combustflame.2018.02.028.

Acknowledgements
Research (University of Limerick, Trinity College Dublin & KAUST) reported in this publication was carried out under the Future Fuels project supported by the Competitive Center Funding (CCF) program at King Abdullah University of Science and Technology (KAUST). Research conducted at National University of Ireland, Galway and Trinity College Dublin was supported by Science Foundation Ireland. Computational resources were provided by the Irish Centre for High-End Computing, ICHEC.

Publisher
Elsevier BV

Journal
Combustion and Flame

DOI
10.1016/j.combustflame.2018.02.028

Additional Links
http://www.sciencedirect.com/science/article/pii/S0010218018301007

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