Introducing a Back Filter: The Impact of Metal Type on Reducing Particulate Matter and Sulfide Emissions from Diesel Engine Exhaust

This study introduces a back filter installed at the end of the exhaust pipes of city buses, examining how the type of metal used in its construction affects the absorption of suspended particles and the reduction of sulfides in diesel engine exhaust gases. The back filter is constructed from three metals: copper, zinc, and nickel. The nickel sample was prepared by electroplated of nickel on the 316 steel surfaces (316SNi), while hot-dip galvanized steel was used as a substitute for zinc (SZinc). Poly tetrafluoroethylene (PTFE) powder was utilized to enhance soot adsorption, sandwiched between two metal plates in each back filter. The results indicated that the amount of soot deposited on the 316SNi filter was approximately five and three times greater than that on the filters made of copper and SZinc in the absence and presence of PTFE powder. Additionally, the sulfide absorption on the 316SNi filter was ten times higher than on the other two types. To interpret these results, impedance spectroscopy was employed to assess the electrical resistance of the absorbed soot, and X-ray diffraction was utilized to identify the mineral compounds formed on the filter's surface. The significant differences observed can be attributed to the lower thermal conductivity of 316SNi compared to the other metals, the reduced electrical resistance of soot adsorbed on 316SNi, and the formation of nickel sulfide as a kinetic product on its surface.