Effects of New Ab Initio Rate Coefficients on Predictions of Species Formed during <i>n</i>‑Butanol Ignition and Pyrolysis

Experimental, time-resolved species profiles provide critical tests in developing accurate combustion models for biofuels such as n-butanol. A number of such species profiles measured by Karwat et al. [Karwat, D. M. A.; et al. J. Phys. Chem. A 2011, 115, 4909] were discordant with predictions from a well-tested chemical kinetic mechanism developed by Black et al. [Black, G.; et al. Combust. Flame 2010, 157, 363]. Since then, significant theoretical and experimental efforts have focused on determining the rate coefficients of primary n-butanol consumption pathways in combustion environments, including H atom abstraction reactions from n-butanol by key radicals such as HO2 and OH, as well as the decomposition of the radicals formed by these H atom abstractions. These reactions not only determine the overall reactivity of n-butanol, but also significantly affect the concentrations of intermediate species formed during n-butanol ignition. In this paper we explore the effect of incorporating new ab initio predictions into the Black et al. mechanism on predictions of ignition delay time and species time histories for the experimental conditions studied by Karwat et al. The revised predictions for the intermediate species time histories are in much improved agreement with the measurements, but some discrepancies persist. A rate of production analysis comparing the effects of various modifications to the Black et al. mechanism shows significant changes in the predicted consumption pathways of n-butanol, and of the hydroxybutyl and butoxy radicals formed by H atom abstraction from n-butanol. The predictions from the newly revised mechanism are in very good agreement with the low-pressure n-butanol pyrolysis product species measurements of Stranic et al. [Stranic, I.; et al. Combust. Flame 2012, 159, 3242] for all but one species. Importantly, the changes to the Black et al. mechanism show that concentrations of small products from n-butanol pyrolysis are sensitive to different reactions than those presented by Stranic et al.时间分辨物种剖面（time-resolved species profiles）可为正丁醇（n-butanol）等生物燃料的高精度燃烧模型开发提供关键验证依据。Karwat等人[Karwat, D. M. A. 等. 《物理化学学报A辑》, 2011, 115, 4909]测得的多组此类物种剖面，与Black等人[Black, G. 等. 《燃烧与火焰》, 2010, 157, 363]开发的经过充分验证的化学动力学机理的预测结果存在显著偏差。自此之后，学界开展了大量理论与实验研究，旨在确定燃烧环境中正丁醇主要消耗路径的速率系数，包括HO₂、OH等关键自由基对正丁醇的氢原子抽提反应，以及上述抽氢反应生成的自由基的分解过程。此类反应不仅决定了正丁醇的整体反应活性，还显著影响正丁醇点火过程中生成的中间物种浓度。本文针对Karwat等人的实验工况，探究将新的从头算（ab initio）预测结果整合至Black等人的机理中，对点火延迟时间及物种时间演化历程预测的影响。修正后的中间物种时间演化历程预测结果与实测值的吻合度大幅提升，但仍存在部分偏差。通过产率速率分析对比Black等人机理的各项修改带来的影响，结果显示正丁醇、以及由正丁醇氢抽提生成的羟丁基（hydroxybutyl）与丁氧基（butoxy）自由基的预测消耗路径发生了显著变化。新修正机理的预测结果，与Stranic等人[Stranic, I. 等. 《燃烧与火焰》, 2012, 159, 3242]测得的低压正丁醇热解产物物种数据（仅一种物种除外）吻合度极佳。值得注意的是，对Black等人机理的修改表明，正丁醇热解的小分子产物浓度，其敏感反应与Stranic等人提出的敏感反应并不相同。