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In a cooperative programme between BMW and Shell, the effects of gasoline properties and composition on regulated emissions (HC, CO, NOx), CO2, fuel consumption and catalyst performance have been studied. The objective of the test programme was to investigate the effect of different hydrocarbon groups from typical refinery streams on exhaust emissions with a detailed analysis not only of the tailpipe emissions but also engine out emissions and catalyst performance. In total thirteen fuels with widely varying physical properties and chemical composition were evaluated in a 1991 series production BMW 525i, and a subset of three of these fuels in two other BMW models to verify their sensitivity to fuel quality. The results for the BMW 525i showed that significant reductions in HC, CO and NOx emissions were seen for fuels containing splashblended oxygenates and with aromatics replaced by isoparaffins.

An acknowledged consequence of utilising oxygenates such as MTBE as a gasoline component is known to be a lowering of CO exhaust emissions from mature technology vehicles due to the “natural” leaning effect that the inclusion of MTBE can provide. A small decrease in THC is also commonly seen in these circumstances, while the effect of MTBE on NOx emissions is more variable and not usually beneficial. The present paper describes the results of recent studies in the European arena, covering the effects of fuel oxygenates (notably MTBE) on regulated emissions for non-catalyst and catalyst car fleets examined in in-house programmes. It looks at emissions effects according to the broad classification of the onboard vehicle technology employed. It further cites experimental work that has featured MTBE replacement in gasolines by a single saturated hydrocarbon (2,3-dimethyl butane) that is isoelectronic with MTBE. Some related work conducted concurrently on splashblending is also described.

Evaporative emission levels have been determined in a CONCAWE* programme for a range of ten uncontrolled European vehicles using a modified SHED test procedure as developed by the CEC*. Three extra vehicles were tested which were equipped with evaporative and exhaust emission control systems, but of the same make and model as three of the uncontrolled test cars. The vehicles were tested using several warm-up cycles and on a range of fuels whose volatility parameters were independently varied, including oxygenate blends. Exhaust emissions were determined and a few measurements of true diurnal emissions carried out. Vehicle fuel system design had the greatest effect on evaporative emissions which varied between 4 to 16 g/test on a typical European summer fuel. Gasoline volatility had a significant but smaller effect and RVP was shown to be the dominant fuel parameter. At the same volatility, oxygenate blends gave similar or lower emissions than hydrocarbon fuels.

Europe is currently on the threshold of introduction of unleaded gasoline. However, this will not proceed uniformly, as some countries such as Germany. Austria. Switzerland and now Scandinavia are moving much more quickly than others. In those countries where unleaded fuel is available, registrations of catalyst cars and the build-up of the gasoline retail network and sales volumes are described. Possible future developments in these areas are discussed. The potentials and limitations on the manufacture of unleaded gasoline are discussed together with the role of oxygenates. The development of specifications in various countries is described and on the basis of market surveys actual quality is compared with the minimum requirements of these specifications. Results of road tests are presented showing the effects of both gasoline with maximum lead content and engine oil with a relatively high phosphorous content on deterioration of catalyst efficiency.