A chemical kinetic analysis of knock propensity of methanol-to-gasoline fuel

IF 6.7 1区 工程技术 Q2 ENERGY & FUELS
Fuel Pub Date : 2024-11-23 DOI:10.1016/j.fuel.2024.133787
James MacDonald , Dario Lopez-Pintor , Naoyoshi Matsubara , Koji Kitano , Ryota Yamada
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引用次数: 0

Abstract

Production of low carbon gasoline-like fuels such as methanol-to-gasoline (MTG) is a promising approach to achieve rapid greenhouse gas emission reduction of the transportation sector. Despite the fact that gasoline that meets the ASTM D4814 standard for automotive spark-ignition engine fuel can be readily produced from these processes, it is unclear how the composition of MTG may affect engine performance and emissions. In this paper, a surrogate for an MTG is used to numerically study the effects of gasoline composition on knock propensity and on the sensitivity of knock to thermal and fuel stratification, to oxygen dilution and to nitric oxide from exhaust gas recirculation of residual gases.
Simulations were performed in ANSYS CHEMKIN-PRO using a comprehensive chemical kinetic mechanism for gasoline surrogates, and results of the MTG surrogate were compared against those of a petroleum-based regular E10 gasoline, termed PACE-20. A premium-grade MTG fuel was also formulated by adding ethanol to the MTG surrogate, and results were compared against those of four premium-grade, gasoline-like fuels representative of future alternative gasoline formulations. Surrogates and mechanism were evaluated by comparison against experimental engine data, and the model showed high accuracy at stoichiometric conditions (mean absolute error of ignition timing equal to 1.46 crank angle degrees) but larger deviations at lean conditions (mean absolute error of ignition timing equal to 5.52 crank angle degrees). Despite the fact that the MTG surrogate has a RON 1.1 units higher than that of PACE-20, it may show higher knock propensity at medium temperature conditions due to a less intense NTC behavior. MTG autoignition was more temperature- and equivalence ratio-sensitive than that of PACE20, suggesting that MTG can benefit more from naturally-occurring thermal stratification or from induced fuel stratification of the end gas to mitigate knock intensity. The sensitivity of autoignition reactivity to oxygen dilution and to NO concentration was higher for MTG than for regular gasoline at medium loads, but the opposite trend was observed at high loads due to the effect of pressure on the low-temperature chemistry of regular gasoline. Approximately 14 %vol ethanol content was required to upgrade the octane rating of MTG from regular grade to premium grade. Adding 13.6 %vol ethanol made the fuel autoignition less sensitive to both oxygen dilution and NO content (ignition time varies approx. 17 % and 50 % less with oxygen dilution and NO addition, respectively, when adding ethanol at high engine loads).
甲醇汽油燃料爆震倾向的化学动力学分析
甲醇制汽油(MTG)等低碳汽油类燃料的生产是实现交通领域温室气体快速减排的一种可行方法。尽管符合 ASTM D4814 汽车火花点火发动机燃料标准的汽油很容易从这些工艺中生产出来,但 MTG 的成分会如何影响发动机性能和排放还不清楚。本文使用 MTG 的替代品,以数值方法研究汽油成分对爆震倾向的影响,以及爆震对热分层和燃料分层、氧气稀释和残余气体废气再循环产生的一氧化氮的敏感性。模拟在 ANSYS CHEMKIN-PRO 中进行,使用了汽油替代品的综合化学动力学机制,并将 MTG 替代品的结果与石油基普通 E10 汽油(称为 PACE-20)的结果进行了比较。通过在 MTG 代用品中添加乙醇,还配制出了高级 MTG 燃料,并将结果与代表未来替代汽油配方的四种高级汽油燃料进行了比较。通过与发动机实验数据进行对比,对代用燃料和机理进行了评估,结果表明该模型在化学计量条件下具有较高的准确性(点火正时的平均绝对误差等于 1.46 曲柄角度),但在贫油条件下偏差较大(点火正时的平均绝对误差等于 5.52 曲柄角度)。尽管 MTG 代用品的 RON 值比 PACE-20 高 1.1 个单位,但由于其 NTC 行为强度较低,在中温条件下可能会表现出更高的爆震倾向。与 PACE20 相比,MTG 的自燃对温度和当量比更为敏感,这表明 MTG 更能受益于自然产生的热分层或终端气体的诱导燃料分层,从而减轻爆震强度。在中等负荷下,MTG 的自燃反应性对氧气稀释和氮氧化物浓度的敏感性高于普通汽油,但在高负荷下,由于压力对普通汽油低温化学性质的影响,观察到了相反的趋势。要将 MTG 的辛烷值从普通汽油提升到高级汽油,大约需要 14%vol 的乙醇含量。添加 13.6%vol 乙醇可降低燃料自燃对氧气稀释和氮氧化物含量的敏感性(在发动机高负荷下添加乙醇时,点火时间随氧气稀释和氮氧化物添加量的变化分别降低约 17% 和 50%)。
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来源期刊
Fuel
Fuel 工程技术-工程:化工
CiteScore
12.80
自引率
20.30%
发文量
3506
审稿时长
64 days
期刊介绍: The exploration of energy sources remains a critical matter of study. For the past nine decades, fuel has consistently held the forefront in primary research efforts within the field of energy science. This area of investigation encompasses a wide range of subjects, with a particular emphasis on emerging concerns like environmental factors and pollution.
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