Experimental and modeling study of C5H10O2 ethyl and methyl esters

Due to the world's over-reliance on fossil fuels there has been a developing interest in the production of renewable biofuels such as methyl and ethyl esters derived from vegetable oils and animal fats. To increase our understanding of the combustion chemistry of esters, the oxidation of methyl butanoate and ethyl propanoate, both with a molecular formula of C5H10O2, have been studied in a series of high-temperature shock tube experiments. Ignition delay times for a series of mixtures, of varying fuel/oxygen equivalence ratios (phi = 0.25-1.5), were measured behind reflected shock waves over the temperature range 1100-1670 K, and at pressures of 1.0, and 4.0 atm. It was found that ethyl propanoate was consistently faster to ignite than methyl butanoate, particularly at lower temperatures. Detailed chemical kinetic mechanisms have been assembled and used to simulate these experiments with good agreement observed. Rate of production analyses using the detailed mechanisms shows that the faster reactivity of ethyl propanoate can be explained by a six-centered unimolecular decomposition reaction with a relatively low activation energy barrier producing propanoic acid and ethylene. The elimination reaction itself is not responsible for the increased reactivity; it is the faster reactivity of the two products, propanoic acid and ethylene that leads to this behavior.