Emission of highly activated soot particulate--the other side of the coin with modern diesel engines.

increase in the proportion of new cars with diesel engines in the past 20 years in Western Europe is illustrated in Figure 1. [2] This trend is expected to further increase over the next few years [3] until the development of cheap and competitive hybrid technology brings the share of diesel and gasoline motors down to an expected 15–35 % in 2030. [4] The major disadvantage of diesel engines with regard to environmental and health protection is the typically enhanced production of black soot (more specifically: diesel particulate matter), which consists of unburned carbonaceous compounds. This is mainly caused by local cold spots, where the fuel is not fully oxidized. Relatively low temperatures appear at the walls of the combustion chamber and at the outside of poorly vaporized large fuel droplets. The surface of condensed fuel has less air to burn and partly pyrolizes to finally turn into a carbon deposit, which leads to the formation of soot. The presence of aromatic compounds in the diesel fuel typically enhances the soot emission through the facile condensation of aromatic units to form larger polyaromatic