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

Abstract: 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.