Numerical Study of the Formation of Soot Precursors during Low-Temperature Combustion of a n-Butanol-Diesel Blend

摘要

To study the soot precursor emission characteristics of a n-butanol-diesel blend during low-temperature combustion (LTC), a model of n-heptane, n-butanol, polycyclic aromatic hydrocarbons (PAHs), and toluene was chosen. Computational fluid dynamics (CFD) software was used to establish a three-dimenisonal (3D) numerical model and to couple it with the chemical kinetics mechanism. The factors studied on soot precursor production were n-butanol blending ratio, exhaust gas recirculation (EGR) rate, injection tuning, and intake pressure. The results showed that the formation of four types of soot precursors benzene (A_1), naphthalene (A_2), phenanthrene (A_3), and pyrene (A_4) was delayed and the final amount of precursor produced decreased with increasing the n-butanol blending ratio. The delay in formation of these precursors and the reactions mostly occurred during the premixed combustion stage and with increasing the EGR rate. The final amount of A_1 produced increased with the EGR rate; however, those of A_2, A_3, and A_4 showed a decreasing trend after an initial increase, and the EGR rate corresponding to the peak decreased with increasing the n-butanol blend ratio. The final amounts of A_2, A_3, and A_4 produced increased with increasing the intake pressure. Soot precursors A_1 A_2 A_3 and A_4 formed in advance during the injection timing advancing with the final amounts of A_1 and A_3 produced were less. The final amounts of A_2, and A_4 produced showed a decreasing trend after an initial increase.