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

Abstract

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, and2,5-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