进气压力对柴油机缸内碳烟颗粒微观形貌的影响

采用全气缸取样系统获取不同进气条件下柴油机燃烧过程中的缸内碳烟颗粒,运用透射电子显微镜(TEM)测量碳烟样品在微观尺度下的二维形貌,并计算碳烟颗粒的分形维数和碳烟基本粒子直径,进而研究不同进气压力对柴油机缸内碳烟颗粒物微观形貌的影响.结果表明:在碳烟生成主导阶段,进气压力的升高会增大生成的碳烟基本粒子的平均直径;而在碳烟氧化主导阶段,进气压力的升高会导致碳烟氧化过程加快,从而使碳烟基本粒子的平均直径快速减小.另外,进气压力的增加对尾气碳烟中基本粒子的平均直径影响不显著.在碳烟氧化主导阶段,碳烟破碎现象会导致碳烟分形维数下降,增加进气压力会使下降起始点提前.

Effects of Intake Pressure on the Morphology of In-Cylinder Diesel Soot Particles

The soot particles during the diesel combustion process were collected using a full in-cylinder sampling system.A transmission electron microscope(TEM)was used to obtain the 2-D images of the soot samples,which were digitized to acquire the fractal dimension of soot particles and the diameter of primary soot particles.Based on the information obtained,the effect of intake pressure on the morphology of in-cylinder soot particles was investigated.Results show that the increase of intake pressure results in larger average diameter of the primary soot particles during soot formation-dominated period.However,the primary particle diameter rapidly decreases during the soot oxidation-dominated period due to the enhanced soot oxidation reactions by the increase of intake pressure.The increase of intake pressure exerts no significant influence on the average diameter of primary soot particles in the exhaust.During soot oxidation-dominated period,the fragmentation of soot particles results in a decrease in fractal dimensions,while such a decrease is advanced when increasing the intake pressure.