Impact of Gasohol on Automobile Evaporative and Tailpipe Emissions 810438

National interest is growing in the use of gasohol, a blend of ethanol and unleaded gasoline, as an alternate fuel to gasoline. In order to assess its viability as a transportation fuel, gasohol's impact on vehicle emissions, fuel economy, and driveability must be considered, along with the cost of production and the physical compatibility of ethanol with gasoline.

Both tailpipe and evaporative emissions were examined on two passenger cars, a 1977 Ford Mustang II and a 1979 Ford LTD II. In addition to determining total hydrocarbon, ethanol, carbon monoxide and nitrogen oxides content, fuel economy and driveability were also examined. The procedures used for emissions measurement are described in the Federal Register for LDV Certification.

Five fuels were used in the program, including two base fuels and three gasohol blends, each car tested with the fuels in sequential order. Generally, the addition of ethanol to gasoline reduced tailpipe emissions of hydrocarbons and carbon monoxide, but increased emissions of nitrogen oxides. Since the stoichiometric air/fuel (A/F) ratio for ethanol is lower than that for gasoline, adding ethanol to gasoline results in a lean shift in combustion stoichiometry, which generally results in a decrease of hydrocarbons and carbon monoxide emissions and an increase in oxides of nitrogen emissions. Coldstart driveability problems were experienced with the LTD II. Little change in fuel economy was observed with either vehicle. The use of gasohol substantially increased the evaporative emissions of both vehicles.

Two final areas examined during this program were the adequacy of a one hour test period for determination of hot soak evaporative emissions and the sensitivity of the emissions to vehicle preconditioning. Hot soak evaporative emissions increased during the second hour of examination and both tailpipe and evaporative emissions were sensitive to vehicle preconditioning.