DOC与POC耦合柴油机燃用调合生物柴油颗粒物的排放特性

在一台高压共轨柴油机上进行燃用调合生物柴油(B0、B10和B20)台架试验,利用MOUDI颗粒分级采样系统和气相色谱-质谱联用仪(GC-MS)分别研究氧化催化器(diesel oxidation catalyst,DOC)结合颗粒氧化催化器(particle oxidation catalyst,POC)对颗粒物的粒径质量浓度分布和可溶性有机组分(SOF)的影响。结果表明:随着生物柴油的掺混比增加,各粒径范围的排气颗粒物质量浓度均下降,质量浓度峰值均在0.18~0.32μm;颗粒物SOF中脂类、酸类质量分数增加,烷烃类、芳香烃、酚类物质质量分数减少;B0和B20的碳原子数质量分数均呈现近似以C16为峰值的正态分布。加装DOC+POC后,3种燃料颗粒物的质量浓度均降低,聚集态颗粒的质量浓度转化率高于粗颗粒态,其中B20聚集态转化率最高,为58.36%;随着生物柴油的掺混比增加,DOC+POC对SOF的转化率增大,其中B20颗粒中SOF转化率达65.15%;DOC+POC对脂类和酸类物质净化作用明显,加装DOC+POC后,B20脂类和酸类物质的质量分数降幅分别为55.45%和43.27%;DOC+POC对B20颗粒物中SOF的C12~C18氧化作用明显。

Effects of DOC+POC on characteristics of particulate matter from diesel engine fueled with biodiesel blends

Particulate matter (PM) emissions from diesel engines are being recognized as the pollutants having adverse effects on the environment as well as on human health. Therefore, the combination of using clean alternative fuels and particulate matter after-treatment devices is one of the effective ways to reduce particulate emissions. Biodiesel as an alternative fuel can significantly reduce particulate emissions. The diesel oxidation catalysts (DOC) are commonly used to oxidize carbon monoxide (CO) and hydrocarbon (HC) emissions as well as partial particles. The particulate oxidation catalyst (POC) is considered as an alternative PM reduction aftertreatment technology to the wall-flow diesel particulate filter (DPF). The combination of DOC and POC is a commonly and widely used to reduce PM. In order to analyze the influence of biodiesel blending ratio, DOC+POC on PM emissions and components of soluble organic fractions (SOF), bench test was carried out on a high pressure common rail diesel engine fueled with diesel-biodiesel dual fuels (B0, B10 and B20). Particles were collected at rated condition. Particle samples with different size grades were achieved from micro-orifice uniform deposition impactor (MOUDI) and mass concentration was obtained by weighting the particle samples. Using the Soxhlet extraction method to extract SOF component from particulates. The effects of biodiesel blending ratio and DOC+POC on SOF content were studied by gas chromatography-mass spectrometer (GC-MS) analysis. The distribution of carbon atoms of B0 and B20 were obtained by analyzing the GC-MS data. The results showed that when the content of biodiesel percentage was increased, DOC + POC conversion rate of particulate matter was increased, the conversion of total mass concentration of B0, B10 and B20 were 42.57%, 48.91% and 52.25% respectively. The mass concentration within each size grade was decreased. The mass concentration peak value of particulate matter emitted from three fuels all ranged from 0.18 to 0.32μm. The mass fraction of lipids and acids components in SOF were increased and alkanes, aromatic hydrocarbons and phenols compounds were decreased. Moreover, the increase of biodiesel percentage promotes the oxidation of high-carbon atoms into low-carbon atoms. the mass fraction of carbon atoms in SOF of B0 and B20 showed a normal distribution with a peak at C16. After the installation of DOC+POC, the mass concentration of particulate matter was decreased and the convert efficiency of accumulation state particles was higher than that of coarse particles. Meanwhile, the convert efficiency of accumulation state particles with B20 reached 58.36%. With the increase of biodiesel percentage, the convert efficiency of SOF was increased, and the convert efficiency of SOF reached 65.15% when B20 fuel was used. DOC+POC had a significant effect on the conversion of lipid and acid substances. The mass fraction of lipid and acid substances changed from 15.4% to 6.86% and 9.43% to 5.35% respectively. Moreover, DOC+POC had obvious effect on the oxidation of C12-C18 in SOF of B20.These results could provide a theoretical basis for the aftertreatment of biodiesel combustion particulates, and it is helpful to improve and optimize of diesel oxidation catalysts and particulate oxidation catalyst,according to the biodiesel emission characteristics.