DIESEL FUEL FOR LOW-EMISSION BUS ENGINES. PILOT STUDY

The possibilities of reducing emissions from city buses are discussed. Using a model of the combustion process, in the diesel engine, factors are described which influence the emissions of soot, particulates, unburned fuel, nitrogen oxides, and polyaromatics. The hydrocarbon types of the diesel oil have different properties for the diesel process. The occurrence of polyaromatics in the fuel is mentioned. The possibilities of influencing the properties of the diesel oil by known refining processes are discussed with special reference to reduced content of sulphur and aromatics and increased stability. Such possibilities exist but lead to at least 10-30% higher fuel cost. The developments of engines and fuel injection systems will lead to considerable reductions of unwanted emissions. It is, however, important that the optimization of engines and fuels are performed together because of the interrelations. Swedish investigations with light diesel oils have yielded improvements only of emitted particulates and their mutagenicity compared with standard diesel oil. The conclusion is that an environmentally more benign diesel oil will require more extensive hydrogenation at the refineries, which will occur only if a sufficiently high demand is created. Changes/additions to the fuel specification is discussed. More tests with tailor-made fuels are proposed. (Author/TRRL)