乙醇对柴油燃烧碳烟前驱体的影响分析

Study on the Effect of Ethanol on Soot Precursor During Diesel Combustion

采用CHEMKIN柴油机燃烧模型,选取正庚烷作为柴油的模拟燃料,研究了乙醇对柴油燃烧碳烟前驱体PAH(苯、萘、菲、芘)的影响规律。构建了乙醇/柴油PAH形成机理,探讨了乙醇掺混比、过量空气系数及燃烧温度等因素对PAH形成的影响。结果表明,乙醇燃烧生成的HCCO、HCO、OH自由基消耗了C_2H_2、C3H3和CH_3等小分子中间燃烧产物,减小了通过甲基加成环化和脱氢加乙炔形成PAH的几率,降低了PAH的生成量。随着乙醇掺混比的增加,最高燃烧温度降低;与正庚烷燃烧相比,掺混30%乙醇后,苯、萘、芘循环生成量的降幅分别为8.7%、16.8%、94.9%;随着过量空气系数的增加,苯和芘的循环生成量呈先降低后升高的趋势,萘的循环生成量有所增加,菲的循环生成量减少了46.6%。

The polycyclic aromatic hydrocarbons （PAH） formation mechanism of ethanol/n-heptane was built using the CHEMKIN software. The role of ethanol in PAH （benzene, naphthalene, phenanthrene, pyrene） formation during n-heptane combustion was studied. The effect of ethanol blending ratio, air-fuel ratio, and combustion temperature on PAH formation were analyzed. Study results showed that the formation of HCCO, HCO, and OH radicals during ethanol combustion can consume C2H2, C3H3, and CHa. The decrease of C2H2, C3H3, and CH3 concentration reduced the possibility of PAH formed through the chemical reactions of methyl addition and cyclization, and hydrogen abstraction and acetylene addition. The maximum combustion temperature was reduced with the increase of ethanol blend ratios. Compared with n-heptane, the amount of benzene, naphthalene, and pyrene during one cycle after blending with 30% ethanol were reduced by 8.7%, 16.8%, and 94.9% respectively. With the increase of air-fuel ratio, the amount of benzene and pyrene during one cycle first decreased and then increased, the amount of naphthalene during one cycle increased slightly, and the amount of pyrene during one cycle was reduced by 46.6%.