Study On The Fractal Dimension And Carbon Fraction Of Diesel Particulates

Most of the countries have been facing the serious problem of ambient air quality. PM2.5 has become a main factor that deteriorates the air quality in recent years. Particulate emitted by vehicles is one of the most important resources for urban PM2.5. Especially, the diesel particulates with extremely complex morphology and tiny diameter may put a range of adverse effects upon human health and atmospheric visibility. Therefore, this study on physical and chemical properties of diesel particulates would further reveal the particle characteristics. It will also provide a scientific basis of the source appointment of particulates in the atmosphere.This study is financially supported by National Nature Science Foundation of China(51376095). Particulates from diesel engines were collected on bench. A detailed research on physical and chemical properties of diesel particulates was carried out. The main researches are as follows:The diesel engine was tested on a bench. Diesel particulates were collected at high and low loads respectively with a Micro-Orifice Uniform Deposition Impactors(MOUDI). Then the feature of particle size distribution was analyzed. It is clearly revealed that the mass concentration of particulates approximately presents a lognormal distribution with the particle size at both high and low loads. The maximum mass concentration of particulates locates in 0.18~1μm.The organic groups, elements and volatile characteristic of diesel particulates were investigated with Fourier transform infrared spectra(FT-IR), energy dispersive X-ray spectroscopy(EDS) and thermo-gravimetric analyzer(TGA). The results from FT-IR showed that there are various kinds of aliphatic groups in diesel particulates. The EDS tests revealed that particulates are not only abundant in C, O but also containing a few metal elements. The volatile characteristic of diesel particulates with various sizes was tested by TGA, and the mass fraction of soluble organics is revealed increasing with the decrease in particulate size.The surface morphology of diesel particulates with various sizes was investigated with field emission scanning microscope(FESEM) at both high and low loads. And their fractal features were analyzed based on the fractal theory. The results show that the morphology of diesel particulates is extremely complex. However the morphology is much more obscure, the particle size become smaller and the particulates closely get together at low load. The box dimensions calculated by MATLAB at low load are slightly greater than that at high load for the particulates of same size. The box dimensions show an increasing tendency with decrease in particle size at the same load.Finally, the carbonaceous components tests of diesel particulates were systematically conducted in an organic carbon/elemental carbon analyzer. It was shown that the value of OC/EC which can be used in source appointment arranges from 0.54 to 0.70 at high load, 10.77 to 11.36 at low load. All of the values reduce with the increase in particle size.