MAN and Shell have jointly investigated the effect of fuel properties on exhaust emissions from advanced engine technologies. MAN Nutzfahrzeuge AG, the Austrian subsidiary Steyr Nutzfahrzeuge AG and Deutsche Shell AG started this bilateral cooperation in 1990 with the objective of identifying key fuel properties that influence emissions from a MAN heavy-duty engine meeting the EURO-I legislation. The intention of that investigation was to determine the effect of cetane number, total and poly-aromatics content and backend distillation [T90] on particulates and gaseous emissions. In parallel both companies participated in the EPEFE (European Program on Emissions, Fuels and Engine Technologies) program which provided a broader understanding of fuel effects on emissions with different engine technologies under European test conditions.Because of the importance of cetane quality MAN and Shell have initiated a specific investigation to determine the effect of increasing cetane number on combustion, emissions and fuel consumption from an advanced MAN EURO-II engine. The results of this joint reserach project are presented in this SAE paper.In total 6 fuels with a cetane number range of about 51 to 61 were tested over both the currently legislated test cycle ECE R49 (13-mode cycle) and the proposed new European cycle for heavy-duty engines. The test fuels included cetane increases achieved by an ignition improver additive and by hydrocarbon composition. Great care was applied during blending to keep other fuel properties as constant as possible.The results showed a very similar behaviour of both natural and ignition improved cetane number for particulates, gaseous emissions and combustion noise. Increasing cetane number decreased fuel consumption with natural cetane number showing the greater effect, particularly over the proposed new European test cycle. It thus may be possible to further improve the fuel consumption-NOx performance compromise by optimizing injection timing to fuel cetane number.