CeO2纳米颗粒催化柴油燃烧氧化特性分析

为了深入了解柴油中添加Ce O2纳米催化剂后生成颗粒的氧化特性,该文配制了Ce O2质量分数分别为0、50、100 mg/kg的纳米催化燃油,利用微粒分级采样装置采集柴油机燃用3种燃料生成的颗粒样品,采用扫描电镜研究了Ce O2质量分数对颗粒形貌特征的影响,通过热重分析方法研究了升温速率、Ce O2质量分数对颗粒氧化特性的影响并采用Coast-Redfern方法计算了颗粒的活化能。结果表明:颗粒群为团簇状结构,粒径范围在20~70 nm之间;随着Ce O2质量分数增加,颗粒平均粒径减小,粒径向小粒径方向移动,计盒维数增大。随着升温速率的增加,颗粒氧化过程出现滞后现象,氧化反应区域变宽,初始氧化温度、峰值失重温度和氧化终止温度增高,失重率峰值变小。升温速率对颗粒反应活化能影响较小。升温速率相同时,随着Ce O2质量分数的增加,颗粒的反应活化能、初始氧化温度、峰值失重温度和氧化终止温度均降低,Ce O2质量分数越高,降幅越大。Ce O2纳米催化剂添加到柴油后,使颗粒粒径变小,并能促进颗粒的氧化,降低颗粒起燃温度,可有效降低柴油机微粒捕集器(diesel particulate filter,DPF)再生温度和延长再生周期,对柴油机排气净化具有重要的意义。

Analysis of oxidation characteristics on combustion of diesel fuels with CeO2 nano-catalyst particulates

Diesel particle emission is a major resource of particulate matter 2.5 (PM2.5) and is harmful to human health. Diesel particulate filter (DPF) is a principal method to reduce diesel PM emission. The DPF requires periodical regeneration by oxidizing the particulates deposited in filters to prevent plugging. The exhaust gas temperature of the diesel engine is considerably lower than the ignition temperature of diesel particulates. Adding a nano-catalyst directly to the fuel to lower the ignition temperature of the diesel particulates is a good method. CeO2 nano-catalyst is proved to oxide the soot with high catalytic activity and stability, and is considered as a promising catalyst for application in DPF. The influence of CeO2 nano-catalyst added in diesel oil on the oxidation and structure characteristics of diesel particulates was studied using thermogravimetric analysis (TGA) and scanning electron microscope (SEM) in this article. Three kinds of CeO2 nano-catalyst fuels were confected, in which CeO2mass fractions were 0, 50 and 100 mg/kg (F0, F50 and F100), respectively. The micro-orifice uniform deposition impactor (MOUDI) was used to collect the particulates generated by burning P0, P50 and P100. The SEM was used to study the influence of CeO2 mass fraction on the particle morphology characteristics. The effects of heating rates and CeO2 mass fraction on particle thermal oxidation characteristics were studied by thermogravimetric analysis method. The activation energy of particulates was calculated with Coast-Redfern integrate method. The results show that there were obvious clusters morphology of particulates from diesel engine fueled with the three CeO2 nano-catalyst fuels, and the particle distribution sizes were mainly concentrated between 20 nm and 70 nm, which were single peak curves. With the increase of CeO2 mass fraction, the particle sizes of P0, P50 and P100, the mean diameter of particulates decreased and the box dimension increased, accordingly. The mean particle size of P50 and P100 decreased by 13% and 20% compared with P0, respectively. For the three particulates, the thermogravimetric (TG) curves and differential thermogravimetric (DTG) curves moved to high temperature region, the temperatures of initial oxidation, peak weight-loss rate and termination reaction increased, and the oxidation reaction areas widened, the thermal weight-loss rate peaks decreased as the heating rate increased. The heating rate scarcely influenced the activation energy for the same particulates. With the same heating rate, the activation energy,the initial oxidation temperature, the peak weight-loss rate temperature and the termination reaction temperature of particulates decreased with the increase of CeO2 mass fraction. Compared with P0, the initial oxidation temperature decreased by 4.2%, 8.5%, peak weight-loss rate temperature decreased by 5%, 6.3%, and the termination reaction temperatures decreased by 4.9%, 6.1% for P50 and P100, respectively. It is found that CeO2 nano-catalysts could reduce the activation energy of particulates oxidation, lower the initial oxidation temperature, decrease the particulates diameter, and promote the oxidation of particulates. This article can provide a theoretical reference for the CeO2 nano-catalyst added to diesel oil to reduce the ignition temperature of diesel particulates in DPF.