Biomass fuels represent a promising renewable alternative energy source, and so the mechanismsthat produce toxic byproducts and soot precursors from oxygenated hydrocarbons are of interest. Estershave the form R-(C=O)-O-R, and are components of biodiesel fuels. The five specific esters studiedhere are isomers of C5H10O2. The experiments were performed in atmospheric pressure coflowingmethane/air nonpremixed flames. A series of flames were generated by separately doping the fuelmixture with 5,000 ppm of each ester. This concentration is sufficiently large to produce measurablechanges in intermediate hydrocarbon concentrations, yet small enough to not disturb the overall flamestructure. Since the overall structure is not perturbed, the measured changes in the intermediatehydrocarbons can be directly attributed to the reactions of the esters. Analysis of these changes revealsthat the primary reaction pathway is a unimolecular six-center reaction for the three esters withmolecular arrangements able to undergo that mechanism. The remaining two esters exhibiteddecomposition rates and products that are consistent with a simple fission primary mechanism, thoughwe do not exclude other pathways from playing a significant role in their decomposition. All of theesters produce aromatic soot precursors at higher rates than the undoped fuel, and the moleculararrangement of the ester isomers plays a role in the degree of aromatic formation. Isomer variations alsoinfluence the type and quantity of toxic oxygenates that are produced in the flames.
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