柴油高压喷雾燃烧火焰碳烟颗粒形貌及其纳观结构分析

Morphology and nano-structure analysis of soot particles sampled within high-pressure diesel reacting jet flames under diesel-like conditions

柴油机是热效率最高、单位体积和比功率密度最大、应用最广泛的动力装置之一.但柴油机喷雾混合扩散燃烧的本质会导致颗粒物的大量产生.为了深入了解柴油机缸内温度和压力条件下喷雾火焰中碳烟颗粒的生成及其演化的详细机制,本研究利用热泳探针采样及高分辨透射电子显微镜成像(HRTEM)的方法对定容燃烧弹(CVCC)中柴油喷雾火焰中生成的颗粒进行了采集并结合成像分析研究了其表观形貌、纳观结构的特性,并进一步提取了其形貌结构的参数.本文还详细考察了不同负荷(喷油量)对基元颗粒和团聚体的形态特征及分形几何参数的影响.结果表明,随着喷油量的升高,团聚体分形维数增加,团聚体颗粒结构越来越紧凑.不同喷油量下的基元粒径呈正态分布,粒径随喷油量的增加而增加.颗粒的微晶长度随喷油量增加而增加,但微晶曲率和微晶碳层间距随喷油量增加而减少,由此表明随着喷油量的增加,颗粒样品的石墨化程度提高,氧化活性下降.我们在此基础之上还进一步分析了回转半径、颗粒投影面积、圆度和球度、基元粒子数等相关参数的结果.

A diesel engine is one of the most widely used power devices with the highest thermal efficiency, largest unit volume, and specific power density. However, the essence of diesel spray diffusion combustion will lead to mass production of particulate matter. In order to understand further the mechanisms of formation and evolution of soot particles in the spray flame of a diesel engine under cylinder temperature and pressure, the thermally swimming probe sampling and high-resolution transmission electron microscopy imaging are used to capture and analyze the spray particles generated by diesel spray in a constant volume combustion bomb(CVCC). Along with imaging analysis, the apparent morphology, characteristics of nano-structure, and parameters of its morphology and structure are further studied. The effects of different loads(fuel injection) on the morphology and fractal geometry parameters of the primary particles and aggregates are investigated in detail. The results show that the fractal dimension of aggregates increases with the increase of load, while the structure of aggregates becomes more and more compact. The primary particle size obeys normal distribution under different loads, and the particle size also increases with the increase of load. The length of microcrystalline in particles increases with an increase in load, but the curvature of microcrystalline and spacing of the microcrystalline carbon layer decreases as the load increases, indicating an increase in the graphitization degree of granular samples and a decrease in the oxidation activity with the load. The parameters such as radius of rotation, projection area of particles, circularity, and sphericity, and the number of primary particles are further analyzed.