Butyl acetate (BA) is identified as a potential biomass-derived blendstock for advanced spark-ignition engines and a potential bio-based diesel additive for reducing soot and greenhouse gas emissions. Understanding its combustion chemistry is crucial for fuel screening and formulating. However, unlike long-chain fatty acid esters and small esters, there is a gap of knowledge in combustion chemistry for esters with a relatively long and complicated alkoxy group as shown in BA isomers. In this work, detailed kinetic mechanisms for oxidation of four BA isomers (namely normal-, sec-, tert-, and iso-butyl acetate) were developed using the Reaction Mechanism Generator (RMG) package. Quantum chemistry calculations were performed to obtained thermodynamic properties for the fuels, combustion products, and critical intermediates and rates for retro-ene and H abstraction reactions that are the primary reactions involved in the BA oxidation. Besides in-house calculation, well-validated butene and acetic acid sub-mechanisms and other accurate rates for oxygenated-species-involved reactions were included as building blocks for model generation. Although there is no experimental result available for BA oxidation, the obtained models exhibit a reasonable agreement with experimental data collected in this work under pyrolysis conditions. More specifically, carbon monoxide time-histories were measured behind the reflected shockwave at 1296 – 1533 K, 1.2 – 1.5 atm, and 0.5% initial concentration. The branching ratio between the primary retro-ene and H abstraction reactions is determined by the alkoxyl group structure over the temperature range of 700 – 1400 K, with further impact on the dominant pathways and combustion properties (e.g., ignition delay time). The insights from this work broaden the knowledge of ester combustion chemistry and provide a building block for studies on BA blending effect.

Differences among quadruplets: A study on combustion chemistry for butyl acetate biofuel isomers

ACS Spring Meeting 2021

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