Search Results

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.

The effects of aromatics and mid-range volatility (E100) were investigated in a fleet of sixteen prototype European gasoline vehicles calibrated to meet the 1996 European emissions limits. A 3x3 fuel matrix was blended with independently varying aromatics and E100, other fuel properties being held constant. The test fleet was chosen with a wide variation in emissions, and vehicles fitted with close-coupled catalysts gave lowest emissions. There was also a wide variation in vehicle response to fuel properties. High HC emissions on some vehicles for fuels with low E100 (35% v/v) were attributed to driveability problems caused by these fuels. Reducing aromatics reduced composite cycle fleet average emissions of Carbon Monoxide (CO), Total Hydrocarbons (THC) and Carbon Dioxide (CO2) but increased Oxides of Nitrogen (NOx). Increasing volatility reduced HC emissions, increased NOx, had no effect on Carbon Dioxide and showed minimum CO at 50% v/v aromatics.