One of the major technological challenges for the transport sector is to cut emissions of particulate matter (PM) and nitrogen oxides (NOx) simultaneously from diesel vehicles to meet future emission standards and to reduce their contribution to the pollution of ambient air. Installation of particle filters in all existing diesel vehicles (for new vehicles, the feasibility is proven) is an efficient but expensive and complicated solution; thus other short-term alternatives have been proposed. It is well known that water/diesel (W/ D) emulsions with up to 20% water can reduce PM and NOx emissions in heavy-duty (HD) engines. The amount of water that can be used in emulsions for the technically more susceptible light-duty (LD) vehicles is much lower, due to risks of impairing engine performance and durability. The present study investigates the potential emission reductions of an experimental 6% W/D emulsion with EURO-3 LD diesel vehicles in comparison to a commercial 12% W/D emulsion with a EURO-3 HD engine and to a Cerium-based combustion improver additive. For PM, the emulsions reduced the emissions with -32% for LD vehicles (mass/km) and -59% for the HD engine (mass/ kWh). However, NOx emissions remained unchanged, and emissions of other pollutants were actually increased forthe LD vehicles with +26% for hydrocarbons (HC), +18% for CO, and +25% for PM-associated benzo[a]pyrene toxicity equivalents (TEQ). In contrast, CO (-32%), TEQ (-14%), and NOx (-6%) were reduced by the emulsion for the HD engine, and only hydrocarbons were slightly increased (+16%). Whereas the Cerium-based additive was inefficient in the HD engine for all emissions except for TEQ (-39%), it markedly reduced all emissions for the LD vehicles (PM -13%, CO -18%, HC -26%, TEQ -25%) except for NOx, which remained unchanged. The presented data indicate a strong potential for reductions in PM emissions from current diesel engines by optimizing the fuel composition.

In view of a new amendment to the European legislative regulation on emissions from two-stroke mopeds a study was carried out to comprehensively characterize exhaust gases of mopeds complying current EURO-2 emission standards. Three mopeds with different engine types (carburetor, direct injection, and electronic carburetion system ECS) where investigated by applying two different driving cycles, the legislative cycle ECE47 and the worldwide motorcycle test cycle WMTC. Thereby, particulate matter (PM), regulated compounds, carbonyls, volatile hydrocarbons (VOC), and particle-associated polyaromatic hydrocarbons (PAH) were analyzed and ozone formation potentials (OFP) as well as toxicity equivalents (TEQ) determined. The ECE47 emission factors for almost all species and moped types were much higher in the nonregulated, prior cold phase than in the hot phase, which is considered for legislation. Great differences for the mopeds could be observed for NO(x), VOC, and PM, whereas discrepancies between the driving cycles ECE47 and WMTC were smaller. In addition, a positive influence on exhaust composition caused by technical modifications of the ECS engine was determined. Results indicate that regulation of total hydrocarbons (THC) alone might not be sufficient to regulate PM, especially for direct injection engines. Moreover, recommendations for a revised future test protocol are demonstrated and discussed, whereby the cold phase and the hot phase are taken into account.