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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%。
Using CHEMKIN diesel combustion model, n-heptane was selected as a simulated fuel for diesel to study the effect of ethanol on the combustion of diesel-burned soot precursor PAH (benzene, naphthalene, phenanthrene and pyrene). The formation mechanism of ethanol / diesel PAH was established, and the effects of ethanol blending ratio, excess air ratio and combustion temperature on the formation of PAH were discussed. The results showed that the HCCO, HCO and OH radicals produced by the combustion of ethanol consumed small intermediate combustion products such as C_2H_2, C3H_3 and CH_3, reduced the probability of PAH formation by methyl addition cyclization and dehydrogenation plus acetylene, PAH generation. With the increase of ethanol blending ratio, the maximum combustion temperature decreased. Compared with the n-heptane combustion, the decline of the circulating production of benzene, naphthalene and pyrene was respectively 8.7%, 16.8% and 94.9% after 30% ethanol was blended. With the increase of excess air coefficient, the production of benzene and pyrene decreased first and then increased, the naphthalene cycle generation increased, and the generation of phenanthrene decreased by 46.6%.