The introduction of sulphur-free fuels will enable advanced engine and exhaust after-treatment technologies to meet increasingly stringent exhaust emissions regulations. As these cleaner fuels and vehicles are introduced, the potential for further improvements in air quality through changes to fuel properties can be expected to diminish. Nevertheless, CONCAWE has continued to update knowledge by evaluating fuel effects on emissions from new engine/vehicle technologies as they approach the market.
In this work, carried out as part of CONCAWE's contribution to the EU “PARTICULATES” consortium [1], two advanced light-duty diesel vehicles and three heavy-duty diesel engines covering Euro-3 to Euro-5 technologies, were tested. The fuels tested covered a range of sulphur content and compared conventional fuels with extreme fuel compositions such as Swedish Class 1 and Fischer Tropsch diesel fuels.
The emissions benefits from the advanced engine/vehicle technologies operating on sulphur-free fuels are impressive and likely to bring substantial improvements in European air quality as the vehicle fleet is replaced. Particulate filters have the potential to reduce diesel particulate mass (PM) emissions by more than an order of magnitude. Capability for substantial improvements in control of NOx emissions is also evident.
Fuel effects on PM and NOx emissions were also observed. In Euro-3 engines, the effects from extreme fuel changes were in the range of 10-20%. When advanced emission control technologies such as diesel particulate filters (DPFs) were used, PM emissions were so low that the impact of changing fuel properties became negligible. Extreme fuel changes continued to affect NOx emissions even with the advanced engine technologies, although these fuels also reduced maximum power. Optimisation of the exhaust after-treatment was also important, with increasing urea rate reducing NOx emissions. Further progress on NOx emissions can be expected as control of engine-out emissions improves and NOx after-treatment technology matures, with the availability of sulphur-free fuels.