掺混含氧燃料的柴油替代物部分预混火焰中多环芳香烃的荧光光谱和碳烟浓度

Fluorescence Spectra of Polycyclic Aromatic Hydrocarbons and Soot Concentration in Partially Premixed Flames of Diesel Surrogate Containing Oxygenated Additives

为研究不同含氧燃料与柴油掺混后碳烟降低机理,本文在自行设计的燃烧器上构建部分预混层流火焰,采用甲苯和正庚烷混合物(T20,20%(体积分数)甲苯、80%正庚烷)作为柴油替代物,并分别添加甲醇、乙醇、正丁醇、丁酸甲酯和2,5-二甲基呋喃(DMF),且保证混合燃料的含氧量均为4%.进而应用激光诱导荧光法和激光诱导炽光法分别测量不同混合燃料的火焰中多环芳香烃(PAHs)的荧光光谱和碳烟浓度.结果表明:通过PAHs的荧光光谱可测量不同燃料火焰中PAHs的生成和增长历程.四环芳香烃(A4)的生成氧化规律和碳烟基本一致,说明通过分析A4变化可以预测碳烟变化.添加含氧燃料后,T20燃料中甲苯含量降低是导致PAHs的荧光光谱强度降低和碳烟生成量减少的主要原因;同时不同含氧燃料本身对多环芳香烃的生成贡献能力也是影响PAHs的荧光强度和碳烟生成的重要原因.含氧量相当时,掺混正丁醇后PAHs的荧光光谱强度和碳烟浓度比添加甲醇、乙醇、丁酸甲酯和DMF这四种含氧燃料的更低.因此从含氧燃料结构来讲,正丁醇掺混入T20燃料中降低PAHs和碳烟作用最显著.

Partially premixed laminar flames were formed using our purpose-built burner. The soot reduction mechanism of blends of diesel and oxygenated fuel was explored. The mixture of toluene and n-heptane （volume ratio, 20：80） （T20） was used as a diesel surrogate. Methanol, ethanol, n-butanol, methyl butyrate, and 2,5-dimethylfuran （DMF） were blended with T20, whilst retaining a 4% oxygen content. Laser-induced fluorescence （LIF） was used to obtain spatial fluorescence spectra of polycyclic aromatic hydrocarbons （PAHs） in partially premixed co-flow flames. Laser-induced incandescence （LII） was used to measure soot concentration （volume fraction）. The formation and growth of PAHs in flames varied with the fuel blend. Four-ring aromatics （A4） exhibited similar formation and oxidation to soot, so A4 was suitable for estimating soot formation and oxidation. With oxygenated additives, the content of toluene is reduced in T20 fuel, which is the major reason for the reduction of PAH fluorescence spectral intensity and soot concentration. The contribution of different oxygenated additives to PAH formation also affected soot reduction. The PAH-LIF spectral intensity and soot concentration of n-butanol/T20 blends were lower than those of fuels containing methanol, ethanol, methyl butyrate, and DMF. Therefore, n-butanol more effectively reduced PAHs and soot emission during the combustion of the diesel surrogate （T20）.