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Vehicle tests showed that evaporative emissions were increased significantly by adding 10 percent ethanol to gasoline, but were increased less with 15 percent MTBE in gasoline. The quantity of ethanol or MTBE in evaporative emissions was investigated in laboratory tests. Exhaust HC, CO, and NOx emissions from a car without closed-loop fuel control were significantly lower with the ethanol and MTBE fuel blends than with gasoline. For cars equipped with closed-loop carburetors, the absolute differences in exhaust emissions among the fuels were small. Fuel economy and drive-ability were worse with ethanol and MTBE fuel blends than with gasoline.

An experimental test program was conducted to determine the detailed hydrocarbon composition of the vapor emitted from a vehicle fuel tank during refueling with gasoline. The composition of the equilibrium vapor in the tank was strongly dependent on the composition of the liquid gasoline, but, as expected, the vapor was composed primarily of the more volatile components of the gasoline. The composition of the vapor could be calculated satisfactorily from the liquid composition, using ideal solution theory. In the refueling tests in which the tank fuel and dispensed fuel were the same, there was little difference in the composition of the equilibrium vapor in the tank before refueling and the vapor expelled during refueling. When the tank fuel and dispensed fuel had different compositions, the vapor expelled during refueling was composed of about two-thirds dispensed fuel vapor and about one-third tank fuel vapor.

An investigation was conducted to determine the change in Reid vapor pressure (RVP) which results when gasoline and various gasoline-alcohol blends are mixed. Such mixing occurs in vehicle fuel tanks when a motorist buys gasolines and blends alternately. When mixing a gasoline with a gasoline-alcohol blend of the same RVP, the resulting mixture always had a higher RVP, due to the non-linear effect of alcohol concentration in gasoline on RVP. Even when a blend had a much lower RVP than gasoline, some mixtures of the two still had higher RVP's than the gasoline. When two common commercial blends, 10 percent ethanol and 10 percent Oxinol™ 50, both having the same RVP, were mixed in various proportions there was essentially no change in RVP. The results of this study suggest that the presence of both gasolines and blends in the marketplace can lead to higher in-use evaporative emissions from vehicles, even if the blends meet the same volatility standards as gasoline.