A Comparative Study of the Kinetics of Ethyl and Methyl Esters in Diffusion Flame Extinction

Abstract

The rapid growth of eco-friendly biomass derived fuels in transportation requires a fundamental understanding of the uniqueness of their oxidation and combustion characteristics. This paper focuses on one specific class of biofuels, namely Fatty Acids Ethyl Esters (FAEE). A counterflow configuration was employed to measure the extinction limits of the diffusion flames of four ethyl esters (ethyl-butanoate, pentanoate, heptanoate, and nonanoate). The results were compared to that of methyl esters (Diévart et al., 2012, Proceedings of the Combustion Institute, 34). It was observed that both methyl esters and ethyl esters exhibit similar high temperature reactivity against extinction. The use of the transport-weighted enthalpy metric has revealed that all esters share similar chemical kinetics in the near extinction conditions of the present study. A previous detailed kinetic model has been extended to include the oxidation chemistry of ethyl esters, and used to interpret the experimental observations. Good agreement between the computed and experimental extinction limits was observed. The rates of consumption pathway analysis have shown that ethyl esters exclusively decomposed into ethylene and a carboxylic acid through an endothermic six-centered unimolecular decomposition reaction, while methyl esters oxidation preferentially progresses through H abstraction reactions. However, the growth of the radical pool was observed to be driven indifferently between ethyl and methyl esters, therefore resulting in similar global flame reactivity.