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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.

Hot-weather driveability performance is influenced by vehicle design, ambient temperature and fuel volatility. For individual markets, the gasoline producer can control this aspect of performance by adjusting the fuel volatility level to meet the requirements of the car population under the seasonal ambient temperature conditions. The volatility expression that has been successfully used for several years to control hot-weather iriveability is (RVP + 0.7E70). A standard CBC test procedure is used by a volatility data-sharing group of European oil companies to characterise the performance of modern car models available in European markets. The data thus produced are used to determine the hot-weather driveability performance of European car populations. The data reveal that the performance of these car populations has improved significantly over recent years, although some modern car models with high under-bonnet temperatures show some deterioration.

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.