Volatility Characteristics of Gasoline-Alcohol and Gasoline-Ether Fuel Blends

During several test programs involving evaporative emissions and driveability, the vapor pressures and distillation characteristics of a large number of gasoline-alcohol and gasoline-ether fuel blends were measured. The maximum increases in Reid vapor pressure (RVP) above that of the gasoline alone ranged from 1.0 kPa (0.2 psi) for tertiary-butyl alcohol to 23.4 kPa (3.1 psi) for methanol. As little as 0.25 percent methanol, ethanol, or Oxinol ™ 50 (a 1:1 mixture of methanol and gasoline-grade tertiary-butyl alcohol) produced measurable increases in RVP.

Because of the nonlinear response of RVP to alcohol concentration, mixing a gasoline and a gasoline-alcohol blend of the same RVP can produce a fuel with a higher RVP.

The vapor pressures of fifteen gasolines and gasoline-alcohol blends were measured at several vapor-to-liquid ratios (V/L), With an increase in V/L, the vapor pressures of the gasolines were reduced more than the vapor pressures of the blends. Thus, the blends behaved as more volatile fuels than gasolines of equal RVP.