丙醇/正庚烷混合燃料的着火特性

Autoignition of Propanol Isomers/n-Heptane Blend Fuels

在一台快速压缩机上研究了不同比例的丙醇/正庚烷二元混合燃料在当量比为1.0、压缩上止点压力2,MPa、压缩温度为650~850,K时的着火延迟.利用混合燃料的详细动力学机理开展了丙醇/正庚烷着火特性的化学反应动力学分析.研究结果表明,在本文实验条件下和温度范围内,丙醇/正庚烷的着火延迟在不同的温度范围呈现不同的变化规律.在丙醇比例较低时,正丙醇/正庚烷混合燃料的着火延迟高于异丙醇/正庚烷混合燃料;丙醇比例较高时,二者的着火延迟非常接近.化学动力学分析表明,由于正庚烷低温反应根池的建立,丙醇在着火过程中也呈现出两阶段燃烧现象.路径分析表明,上止点温度的提高可使部分羟丙烷基发生裂解并增强系统活性.进一步的敏感性分析表明,对正丙醇/正庚烷混合燃料,正庚烷的脱氢反应和链分支反应对促进着火始终有重要影响,随着正丙醇比例的增加,正丙醇对混合燃料着火的抑制与促进都有较大的影响.异丙醇/正庚烷混合燃料的着火在异丙醇比例较大或上止点温度较高时对异丙醇的氧化更加敏感,抑制着火的反应始终为小分子基团的反应.

Ignition delay time of propanol isomers/n-heptane mixtures was measured using a rapid compression machine at compressed pressure of 2,MPa,within the compressed temperature range of 650—850,K and with equivalence ratio of 1.0. Reaction kinetics analysis was performed using a detailed mechanism of blend fuels. Under the experimental conditions in this study,the ignition delay of the blend fuels displays different varying patterns in different temperature ranges. The ignition delay time of i-propanol/n-heptane is shorter than that of n-propanol/n-heptane when the propanol fraction is low. When the propanol fraction is high,their ignition delay times become very close to each other. The chemical kinetics analysis indicates that propanol isomers also exhibit two-stage oxidation behavior because of the low temperature reactivity radical pool produced by n-heptane. The higher compressed temperature can make a small part of the hydroxypropyl radicals undergo scission reaction and improve system activity. Sensitivity analysis shows that for the n-propanol/n-heptane blends,H-abstraction and chain-branching reaction from the n-heptane always play a dominant role in the reaction with a promoting effect,while the H-abstraction from the n-propanol becomes important when the n-propanol fraction is high. For i-propanol/n-heptane mixtures,the ignition of the blend fuels is more sensitive to the oxidation of the i-propanol at high compressed temperature or propanol fractions,while the major inhibiting reactions are always some elementary reactions of small radicals.