基于碳烟粒径分布预测的柴油燃烧机理构建与氧含量影响研究

Study on Construction of Diesel Combustion Mechanism Based on Soot Particle Size Distribution Prediction and the Impact of Oxygen Concentration

为预测柴油机碳烟排放的粒径分布,选用90%摩尔分数的正庚烷和10%摩尔分数的甲苯作为柴油替代物,分别构建气相动力学机理和表面动力学机理,并将二者耦合,构建成柴油替代物机理(简称HTS机理),将HTS机理结合矩量法数值模型进行了机理验证,并通过改变进气发动机进气氧的体积分数,进一步研究了氧浓度对碳烟粒径分布的影响。研究结果表明,在滞燃期、层流火焰速度、预混火焰关键组分、预混火焰碳烟粒径分布、柴油机缸压与放热率以及柴油机排放物生成等方面,应用HTS机理计算的模拟值与试验值基本一致。使用HTS机理研究氧浓度对碳烟粒径分布的影响表明:随着氧浓度的增加,碳烟颗粒平均数密度降低、数密度峰值减小、数密度峰值对应的颗粒物直径增大;且小粒径(直径0~50 nm)碳烟的数密度随之降低。

In order to predict the particle size distribution of the diesel engine soot emission, 90% mole fraction n-heptane and 10% mole fraction toluene are chosen as diesel substitutes to construct gas phase dynamics mechanism and surface dynamics mechanism respectively, which are coupled to form the diesel substitute mechanism(HTS mechanism). Combined with the method of moments numeical model, validation of the HTS mechanism is conducted. Then the effect of oxygen concentration on soot particle size distribution is studied by changing the volume fraction of intake oxygen. The results show that the simulation values calculated by the HTS mechanism are basically consistent with the experimental data in terms of ignition delay period, laminar flame speeds, key species and soot particle size distribution in laminar premixed flames, in-cylinder pressure, heat release rate and emissions of the diesel engine. According to the study on the impact of the oxygen concentration on soot particle size distribution by the HTS mechanism, with the increase of oxygen concentration, the average and peak values of soot particle number density decrease, while particle diameters corresponding to the peak particle number density increase.Moreover, the number density of small soot particles(0~50 nm) decreases as oxygen concentration increases.