Butyl Acetate Pyrolysis and Combustion Chemistry: Mechanism Generation and Shock Tube Experiments

The combustion and pyrolysis behaviors of light esters
and fatty
acid methyl esters have been widely studied due to their relevance
as biofuel and fuel additives. However, a knowledge gap exists for
midsize alkyl acetates, especially ones with long alkoxyl groups.
Butyl acetate, in particular, is a promising biofuel with its economic
and robust production possibilities and ability to enhance blendstock
performance and reduce soot formation. However, it is little studied
from both experimental and modeling aspects. This work created detailed
oxidation mechanisms for the four butyl acetate isomers (normal-,
sec-, tert-, and iso-butyl acetate) at temperatures varying from 650
to 2000 K and pressures up to 100 atm using the Reaction Mechanism
Generator. About 60% of species in each model have thermochemical
parameters from published data or in-house quantum calculations, including
fuel molecules and intermediate combustion products. Kinetics of essential
primary reactions, retro-ene and hydrogen atom abstraction by OH or
HO2, governing the fuel oxidation pathways, were also calculated
quantum-mechanically. Simulation of the developed mechanisms indicates
that the majority of the fuel will decompose into acetic acid and
relevant butenes at elevated temperatures, making their ignition behaviors
similar to butenes. The adaptability of the developed models to high-temperature
pyrolysis systems was tested against newly collected high-pressure
shock experiments; the simulated CO mole fraction time histories have
a reasonable agreement with the laser measurement in the shock tube.
This work reveals the high-temperature oxidation chemistry of butyl
acetates and demonstrates the validity of predictive models for biofuel
chemistry established on accurate thermochemical and kinetic parameters.

轻质酯类与脂肪酸甲酯的燃烧及热解特性已被广泛研究，因其可作为生物燃料与燃料添加剂，具备重要应用价值。然而，中等链长乙酸烷基酯，尤其是带有长烷氧基的品类，相关研究仍存在空白。其中，乙酸丁酯作为极具潜力的生物燃料，其生产经济性优异、产能潜力充足，且可提升调合组分性能并减少炭黑生成。然而，目前针对其实验与建模两方面的研究均较为匮乏。本研究借助反应机理生成器（Reaction Mechanism Generator），构建了四种乙酸丁酯异构体（乙酸正丁酯、乙酸仲丁酯、乙酸叔丁酯与乙酸异丁酯）在650~2000 K温度区间、最高100 atm压力下的详细氧化机理。各机理模型中约60%的物种（包括燃料分子与燃烧中间产物）的热化学参数均来自已发表数据或本团队自主开展的量子化学计算。主导燃料氧化路径的关键基元反应（如逆烯反应、羟基自由基（OH）或过氧羟基自由基（HO₂）抽氢反应）的动力学参数也通过量子力学方法完成了计算。对所构建机理的模拟结果表明，在高温环境下，大部分乙酸丁酯燃料会分解为乙酸与相应的丁烯类物质，因此其点火特性与丁烯类燃料相近。针对全新获取的高压激波实验数据，我们验证了所建模型在高温热解体系中的适配性；模拟得到的CO摩尔分数时间历程与激波管激光测量结果吻合良好。本研究阐明了乙酸丁酯类物质的高温氧化化学机制，并验证了基于精确热化学与动力学参数构建的生物燃料化学预测模型的有效性。