Effect of exhaust gas recirculation (EGR) and multiple injections on diesel soot nano-structure and reactivity
Effect of exhaust gas recirculation (EGR) and multiple injections on diesel soot nano-structure and reactivity
复制标题
DOI：
10.1016/j.applthermaleng.2016.11.116
复制
发表时间：
2017-04
影响因子：
6.4
通讯作者：
B. Rohani;C. Bae
中科院分区：
文献类型：
--
作者：
B. Rohani;C. Bae
碳烟颗粒的物理化学特性对柴油机后处理系统的性能有重要影响。采用热重分析（TGA）、X射线衍射（XRD）、拉曼显微光谱和高分辨透射电子显微镜（HRTEM）对单缸重型柴油机碳烟颗粒的纳米结构、氧化反应性和挥发性有机物（VOF）进行了研究。五种不同的喷射策略，包括单次喷射和多次喷射与各种先导喷射量和停留时间进行了测试，有和没有废气再循环（EGR），而燃烧相位，发动机转速，和燃料喷射量匹配的所有情况下。结果表明，对于EGR条件下生成的碳烟，纳米结构有序性（由XRD和拉曼分析得到的AD 1/AG表征）可以解释碳烟的反应性。然而，在没有EGR的情况下，反应性趋势不能用结构顺序来解释。据讨论，一个可能的原因可以是在非EGR的情况下（由较高水平的表面官能团表示），其粗糙化的碳烟表面的缸内氧化的较高水平，并通过增加比碳烟表面积增强氧化。研究还发现，在无EGR的情况下，不同的喷射策略对碳烟反应性和VOF含量的影响主要通过进气预混程度和缸内碳烟氧化程度以及碳烟表面粗糙度的影响来解释。随着EGR的增加，喷油策略对碳烟反应性和VOF含量的影响趋于消失。
The physio-chemical characteristics of soot particles are of importance with regard to performance of diesel after-treatment systems. In this study, the soot particles generated in a single-cylinder heavy-duty diesel engine are examined in terms of nanostructure, oxidative reactivity and volatile organic fraction (VOF), using thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman micro-spectroscopy, and high resolution transmission electron microscopy (HRTEM). Five different injection strategies including single injection and multiple injections with various pilot injection amounts and dwell times were tested with and without exhaust gas recirculation (EGR), while combustion phasing, engine speed, and fuel injection quantity was matched for all cases. Results indicate that for the soot produced under EGR condition, nano-structural order (indicated by crystallite size obtained from XRD and AD1/AG resulted from the Raman Analysis) can explain the soot reactivity. However, in the absence of EGR, the reactivity trend cannot be explained by the structural order. It is discussed that a possible reason can be a higher level of in-cylinder oxidation in non-EGR cases (indicated by higher level of surface functional groups) which roughens the soot surface, and enhances the oxidation by increasing the specific soot surface area. It is also found that in the absence of EGR, different injection strategies impact the soot reactivity and VOF content, which can be explained mainly through the level of charge premixed-ness and the in-cylinder soot oxidation, and the consequent effect on the soot surface roughness. Results also show that the influence of injection strategy on the soot reactivity and VOF content tends to vanish as EGR is added.