Small direct injection diesel engine sensitivity to the diesel fuel characteristics

Among the technical solutions that can lead to energy converters with low pollutant emissions and low fuel consumption, diesel engines rank, by nature, in a good position. On this base, direct injection diesel engine has been developed and are now spreading in private passanger cars because of their performances, especially in terms of fuel consumption. However, this equipment requires an efficient injection system, electronically driven, needs EGR and an oxidation catalyst to improve the pollutant emissions and the noise level. Thus, it is a major concern to be able to assess precisely the sensitivity to fuel characteristics of direct injection engines as to take the best advantage of this technology. With a set of fuels formulated to cover a large range of chemical nature, viscosity, cetane number and density, an Audi direct injection engine (1Z model) was run at the test bench. The impact of the fuel characteristics on pollutant emissions, regulated or unregulated (PAH, aldehydes), and on noise levels was assessed either under standard tuning conditions, either by changing the EGR rate and the injection timing. The results obtained at the end of this program point out the main criteria that have an influence on emissions. They also allow a comparison between direct injection engines and their homologues with prechambers. The works this communication is dealing with have been conducted as part of the program of the ''Groupement Moteur Carburant Lubrifiant' (GMCL), in collaboration with ELF, Octel, PSA, Renault and Total.