Following a small scouting programme to examine the scale of emissions benefits achievable by different degrees of gasoline base fuel redesign (SAE
930372), a larger programme has been initiated to investigate more systematically the influence of individual fuel parameters on tailpipe emissions. This coordinated study has been spread across five participating Shell Group laboratories, using a set of common fuels specifically designed and centrally blended for this purpose. Additionally, subsets of these fuels have been used for detailed systematic examination of selected topics within the overall programme scope.
This paper summarises the plan for the integrated study. It describes the composition and properties of the fuels and their blending. The results covered here are those of chassis dynamometer-based regulated emissions studies conducted on a composite fleet designed to represent a range of vehicle technologies, using a variety of regulatory driving cycles.
While there is some car-to-car variation evident, the results indicate that fuel effects on CO and HC emissions are similar for both catalyst and non-catalyst cars. The beneficial effect of MTBE on these emissions (particularly CO) was confirmed. Fuel effects on NOx were seen to depend on driving cycle, to be different for non-catalyst and catalyst cars, and furthermore to be car-dependent. For some catalyst cars, lowering the aromatics content appeared to increase emitted NOx. Otherwise, reduction of aromatics content appeared to reduce regulated emissions somewhat, but there was some evidence that these effects might also correlate with distillation properties and further work will be needed to clarify this point. Lower fuel olefin content tended to increase HC emissions but decrease NOx. Within the range 11-116ppm, allowing for the car- and cycle-dependence observed, sulphur variation appeared to have little influence on the regulated emissions obtained from catalyst cars.
Hydrocarbon speciation results and other selected topics within the overall scope of this integrated study (e.g. the effects of various oxygenates, of aromatics distribution, and fuel effects at lower temperatures) will be reported in detail separately.