Emissions from Light Duty Vehicles Operating on Oxygenated Fuels at Low Ambient Temperatures: A Review of Published Studies

Abstract

This paper reviews several published studies which examine the effects of oxygenated fuels on exhaust and evaporative emissions, fuel economy, and vehicle driveability at low ambient temperatures. These studies represent a wide range of vehicle technologies, oxygenated fuels, and testing facilities. The primary objective of the review is to survey the results of these studies and contrast the magnitude of the oxygenate effects with those obtained at the nominal Federal Test Procedure (FTP) temperature of 75 F. Hydrocarbon (HC) and carbon monoxide (CO) exhaust emissions were found to increase at low ambient temperature. Addition of 2--3 wt% oxygen to gasoline generally decreases fleet emissions of CO and HC at low ambient temperatures. Oxygenate effects on exhaust emissions at low ambient temperatures show the same dependency on vehicle technology as has been previously observed at 75 F. Vehicles with carbureted fuel systems and open loop emissions control responded most favorably to the oxygenates in reducing CO and HC emissions. In contrast, more recent models with fuel injection systems, closed loop emissions control, and three-way catalysts showed smaller improvements when oxygenates were used. The effect of oxygenates on nitrogen oxides (NO{sub x}) at low ambient temperature tended to be highly variable, similarmore » to the findings at 75 F. The effects of oxygenate blending on exhaust toxics also appear to be unchanged at low ambient temperature; splash blending oxygenates decreases benzene and butadiene emissions but increases aldehyde emissions. Evaporative emissions and vehicle driveability were generally insensitive to oxygenate addition at low ambient temperature within the range of fuels studied. Vehicles operating on oxygenates showed a decrease of 2--4% in fuel economy, independent of vehicle technology.« less