Recently, environmental problems (that are related to global warming and reduced visibility etc.) and side effects on the human body such as heart and respiratory diseases due to an increase in particulate matters (PMs) have become social issues. For an accurate measurement and reduction of PMs released to an atmosphere, the optical, physical and chemical properties of PMs must be known. Since such properties of the PMs depending on the types of fuel, combustion conditions, and flame configurations can greatly influence the measurements of dimensionless light extinction coefficient which are required to accurately determine the PM concentration using an optical method. There have been a number of previous investigations of the measurement of the dimensionless light extinction coefficient of PMs released from premixed flame configurations while those measured from diffusion flame configurations are limited. Considering the optical characteristics of PMs that vary along with the height of diffusion flames, the present study aims to investigate the optical, physical and chemical properties of PM produced from burning Ultra Low Sulfur Diesel (ULSD) in a co-axial diffusion flame burner.
To this end, the dimensionless light extinction coefficient of PMs and flame temperature and length were measured for USLD-air co-axial diffusion flames burning in different the ratio of air to fuel. In addition, Transmission Electron Microscope (TEM) and Raman spectroscopy analysis were performed to understand physical and chemical properties of PMs. As the flame length is adjusted with feeding more fuel, the size and structure of PMs and flame temperature are changed, affecting measured dimensionless light extinction coefficient. The flame length and residence time is found to increase with more fuel added and thus the particle size of PM. The TEM analysis clearly shows that increased graphitized structure of PM enhances the influence of light scattering and light absorption, resulting in an increase in the dimensionless light extinction coefficient.