A comparative study of the chemical kinetic characteristics of small methyl esters in diffusion flame extinction

The diffusive extinction limits of a series of methyl ester flames, from methyl formate to methyl decanoate, have been measured in the counterflow configuration. Kinetic and transport effects are decoupled by use of the transport-weighted enthalpy term and reveal that the smaller methyl esters (C2 to C4) exhibit unique behavior while methyl esters inclusive and larger than methyl butanoate exhibit similar global reactivity to that of the n-alkanes. In order to interpret the experimental observations, a previous kinetic model for methyl butanoate and methyl decanoate has been extended to encompass the oxidation of the smaller methyl esters. Model rate of production analyses highlight the chemical kinetic specificities of methyl formate, methyl ethanoate, and methyl propanoate, through distinctive fuel reaction channels in methanol elimination, methyl radical production, and H atom production respectively. The similarity of global reactivity among the larger methyl esters and n-alkanes is elucidated based on the formation of formaldehyde and ethylene, which drive indifferently the growth of the radical pool at high temperature, thus the flame oxidation rate is similar at the global level.