添加正丁醇对柴油机燃烧路径影响的模拟研究

摘要

为了研究含氧燃料正丁醇对正庚烷和甲苯燃烧的化学反应过程以及对碳烟生成过程和排放的影响,使用正丁醇-正庚烷-甲苯简化机理耦合多步碳烟生成模型作为柴油-正丁醇混合燃烧的化学反应动力学机理,在计算流体动力学(CFD)软件上建立三维数值模型来模拟柴油机的燃烧和排放过程.通过对比分析纯柴油(B0)和纯柴油中掺入15%正丁醇(B15)两种燃料燃烧过程表明,正丁醇能使低温反应阶段的HO2的浓度升高,B15相对B0增加了约11%;由于正丁醇脱氢反应与正庚烷对OH的争夺,使正庚烷的消耗变慢;正庚烷含量与为反应提供大量OH的H2O2有着直接关系;正丁醇为反应提供了大量的OH,H2O2的浓度B15相对B0降低了约27%,OH的浓度却略有上升.正丁醇能降低生成碳烟前驱物的重要物质乙炔的浓度,而且影响甲苯向苯环的形成过程,能减少苯(A1)的生成量,B15相对B0降低约15%,从而减少了碳烟前驱物的生成,碳烟排放降低,为含氧燃料正丁醇在柴油机上的应用提供参考.%To explore the influence of n-butanol to the chemical reaction process of n-heptane with toluene, and the smoke generation process and emission, the n-heptane-n-butanol-toluene reduced mechanism is used as the chemical reaction kinetics of n-butanol-diesel blend, and the soot emissions are predicted by a multi-step phenomenological soot model.Engine combustion model is built by using the computational fluid dynamics(CFD) software to explore the effects of n-butanol on the combustion process and soot emissions of diesel engine.Through the comparative analysis of diesel (B0) and diesel blended with 15% n-butanol(B15) of two kinds of fuel combustion process, the results show that the addition of n-butanol leads to the increase of HO2 concentration in the low temperature reaction stage, B15 than B0 increased by about 11%;The n-butanol dehydrogenation reaction with n-heptane struggle for OH, resulting in slower n-heptane consuming;The content of n-heptane expresses a direct relevancy to H2O2 which provides a lot of OH for the reaction.The addition of n-butanol also provides part of the OH which is very important for reaction, B15 than B0 reduced about 27% which is the concentration of H2O2, but the concentration of OH rise slightly.The addition of n-butanol leads to the decrease of concentration of acetylene which is the important material to generate carbon smoke precursors and has an influence on the formation process from toluene to benzene, B15 than B0 reduced about 15% which is the concentration of benzene (A1).The reduction of A1 production results in the decrease of production of carbon smoke precursorsand the emission of carbon smoke.This study would provide the reference for the application of n-butanol on diesel engine.