柴油喷雾燃烧火焰内部碳烟采集与分析

为研究碳烟颗粒在柴油喷雾火焰内部的演变规律,在可视化定容弹喷雾燃烧系统中增加一种基于热泳原理的碳烟颗粒采集装置,获得了喷雾燃烧火焰内部的碳烟颗粒样本,并在高倍透射电镜下获得样本中不同尺度的碳烟形态图像。根据图像中碳烟宏观和微观形态结构特征分析了碳烟生成、聚合等演变历程。通过自行开发的图像处理程序,分析得到碳烟颗粒尺寸参数随喷射距离的变化特征。研究表明,该方法实现柴油机缸内高温高压特征环境下碳烟颗粒的采集与高倍电镜分析技术的有机结合,有效获取柴油喷雾火焰内部碳烟颗粒微观信息,为减少柴油机碳烟排放提供了重要研究手段和基础研究信息。

Capture and Analysis of Soot Formed inside Combustion Diesel Spray Flame

In order to investigate the evolution principle of soot formed inside the diesel spray flame, a soot trapping device was developed based on the thermophoretic phenomenon. The device was applied to a constant-volume combustion chamber to capture the soot formed during the combustion process of diesel spray. The soot captured was then observed and imaged by the high-resolution transmission electron microscopy. Soot images were taken at 200 nm and 10 nm scales to investigate their overall and local detailed features. The evolution of soot was analyzed according to its macro and micro structure characters. Furthermore, the soot particle size along the spray flame axial was investigated by image processing program based on Matlab. The result showed that the production of primary particles formed inside the flame promoted the aggregation of soot, the number of primary particles was increased at 60 mm and 80 mm downstream of the spray, and then it was decreased at 80 mm and 100 mm downstream of the spray. Meanwhile, the number of aggregated soot particles was increased along the spray axis. The diameter of the primary particles was about 30 nm, and the diameter of soot aggregation particles was no larger than 100 nm. In addition, the internal arrangement of the primary particles trended to be less chaos. The carbon coated copper gird survived the extreme environments inside the chamber without being burnt, warped, melted or oxidized. The device works well and it provides a new experimental method for the soot formation mechanism research at typical high pressure and high temperature environment inside the modern diesel engine.