Effect of methyl tertiary butyl ether concentrations on exhaust emissions from gasoline used in the Metropolitan Area of Mexico City

In this work, the primary objective was to assess the impact of oxygenated fuel on the exhaust emissions from an important fraction of vehicles in the Metropolitan Area of Mexico City (MAMC). The results aim to provide inform ation on the actual effect of MTBE on a fleet that represents more than 60% of the in-use vehicles in the MAMC. Ten vehicles were tested with a low-oc tane base gasoline, and 10 more with a regular-grade unleaded base gasoline . Three MTBE concentrations, 5, 10, and 15 vol %, were tested following the U.S. Federal Test Procedure (FTP). CO, total HC, and NOx from the exhaust gases were quantitatively evaluated and also characterized for FTP speciate d organic emissions. From this data, the O-3(-) forming potential of the fu els was calculated. Results show that for the fleet using low-octane gasoli ne, the addition of 10% MTBE substantially reduced CO emissions, but total HC concentration in the exhaust showed a modest decrease. For the regular g asoline, the 10%, MTBE blend seemed to be the best choice, but there was no t a significant decrease in emissions. The specific reactivity of each fuel , expressed in grams of O-3 per gram of nonmethane organic gases, increased with MTBE concentration in both cases. This result is important to conside r, especially for a region like Mexico City, which has high atmospheric O-3 concentrations.