Assessment of the use of ethanol instead of MTBE as an oxygenated compound in Mexican regular gasoline: combustion behavior and emissions.

The energy reforms implemented in Mexico promote the use of ethanol in gasoline but exclude the country's ozone nonattainment areas oxygenated with methyl-tert-butyl ether (MTBE) in view that further scientific studies are required. To address a potential implementation scenario in areas of ozone high VOC-sensitive regimes, the impact on performance and emissions characteristics between the regular MTBE fuel available and a formulated gasoline containing 10% v/v ethanol having similar Reid vapor pressure (RVP) were compared in a single cylinder spark-ignited engine and a set of tier I vehicles. Included in the assessment were the "criteria" pollutants (THC, CO, and NOx), toxic compounds, and speciated hydrocarbons in order to calculate the ozone-forming potential (OFP). The change in combustion speed of ethanol fuel vs. regular gasoline seems to be small and depends mainly on base gasoline formulation. Vehicle dynamometer testing showed no statistically significant differences in the average THC, CO, and NOx results when comparing both fuels. Statistically significant differences were seen in total speciated hydrocarbons, total carbonyls emitted, the increases in acetaldehyde emissions, and the decreases in OFP with E10. The results show roughly 20% increase in evaporative emissions when E10 is used, but the OFP of the emissions is lower than that of the Metropolitan Area of Mexico City fuel (MAMC). The increase in the oxygen content using ethanol fuel seems to have no deleterious effect on the vintage of vehicles tested. Taking into consideration that the evaporative emissions standard in Mexico is less stringent than that in other countries, the substitution of the actual regular gasoline for ethanol fuels should uphold the least volatile AA class in areas with ozone problems.