柴油机颗粒在氧化过程中拉曼光谱参数的变化

Changes in Raman Spectra of Particulates Emitted from Diesel Engine During Oxidation

为研究柴油机排放颗粒在氧化过程中化学结构的变化规律,通过一台燃用国Ⅴ标准柴油的电控高压共轨增压中冷柴油机CY4102-CE4B上进行颗粒取样,对所得颗粒进行了热重处理,分别得到不同氧化程度的颗粒,采用拉曼光谱仪测取样品的拉曼光谱,比较了在氧化过程中颗粒随失重量变化的拉曼光谱特征.结果表明:颗粒的石墨化程度随着柴油机负荷的增大而增加;氧化催化剂(DOC)作用后,颗粒的结构有序性增强;随着氧化的进行,颗粒的石墨化程度整体呈现上升趋势.颗粒的氧化活性与其结构有一定的关系;小负荷时,颗粒表现出较高的氧化活性,其中颗粒所具有的无序结构具有较大影响.DOC作用后,颗粒的内部结构发生了变化,颗粒的氧化模式发生了改变,石墨化程度不再是影响氧化活性的主要因素.

Particulate samples under engine different operating conditions with electronic control high pressure com- mon rail, turbocharged and inter-cooler engine were collected. Particulate samples of different oxidation degree were obtained through thermo-gravimetric process. Raman spectra of particulates before and during oxidation process were recorded and spectral parameters were determined by curve fitting with five bands （G, D1--D4）. Results indicated that the degree of graphitization of the particulates increase with the increase of engine load. The structural order of particulates was collected after DOC. During oxidation process, the graphitization degree of particulates is increased. Oxidation reactivity of particulates is related to their chemical structure. At light loads, the particulates exhibit higher oxidation reactivity than that at heavy loads. However, after DOC, the change of interior structure of particulates leads to the change of oxidation mode. Graphitization degree is not the main factor that influences the oxidation reac- tivity of particulates.