The benefits of diesel fuel additives have been demonstrated in a broad range of performance and operational areas, from the refinery, through storage and distribution, to fuel dispensing and vehicle operation. The customer is certainly aware of their effects on fuel performance in many of these respects, such as cold-weather operation, ease of starting, foaming, odour, etc. An area of particular interest in customer perception, however, is fuel economy. Excluding the use of after-market fuel-treatment devices, it is claimed that additives of different types can improve fuel economy, for example by improving combustion, by maintaining injection equipment in optimum condition, or by reducing engine frictional losses. Although the effects of fuel type and additives on vehicle emissions have been studied, the effects on fuel economy are notoriously difficult to measure with precision, with the statistically most reliable data coming from extended fleet trials under closely controlled conditions. It was therefore the object of this study to devise a method to measure the effects of individual additives on fuel economy, at conditions representative of urban driving conditions, and to make preliminary measurements of the effects of a detergent and ignition improver.
In this study, a vehicle was prepared and run on a chassis dynamometer under steady-state urban cruise conditions according to a specially designed procedure. A range of standard nozzle fouling values was established by using selected fuel/detergent additive combinations. At each nozzle fouling level, repeated gravimetric measurements were taken of fuel consumption and emissions levels of CO, NOx and particulates. At a selected nozzle fouling level, fuel dosed with ignition improver was also used to give a direct comparison between the two additive functions.
The results show that benefits in fuel economy can be gained both by using detergents - in avoiding the build-up of excessive nozzle fouling and maintaining fuel injection equipment close to its design conditions - and also by using ignition improver. Changes in emissions consistent with previous studies were noted in both cases.