STRUCTURE AND DISPOSITION OF PARTICLES FROM A SPARK-IGNITION ENGINE

Particles generated in the exhaust of a spark-ignition engine operated with leaded and unleaded fuel exhibit significant changes of size, structure and surface chemical composition on changing the temperature T of the carrier gas. Total mass, mass of black carbon (BC), diameter and the photoelectric yield of the particles have been measured in situ as a function of temperature. Concomitantly the particles have also been deposited on a substrate and imaged by transmission electron microscopy. Diameter and total mass of the particles decrease significantly with increasing T, whereas the BC mass remains nearly unaffected. From diameter and photoyield vs T curve a shell structure of the particles emerges, where the outermost shell is made up of volatile organic components followed by a layer of polycyclic aromatic hydrocarbons (PAHs) with less volatility on a core of BC and, depending on the type of fuel, also lead. Transmission electron micrographs indicate that lead and carbonaceous fractions segregate at T = 275-degrees-C. For T > 275-degrees-C an almost perfect crystalline order of lead appears.