ASTM D5188-10a

The tendency of a fuel to vaporize in automotive engine fuel systems is indicated by the vapor-liquid ratio of the fuel.

Automotive fuel specifications generally include T _{(V/L = 20)} limits to ensure products of suitable volatility performance. For high ambient temperatures, a fuel with a high value of T _{(V/L = 20)}, indicating a fuel with a low tendency to vaporize, is generally specified; conversely for low ambient temperatures, a fuel with a low value of T _{(V/L = 20)} is specified.

1.1 This test method covers the determination of the temperature at which the vapor formed from a selected volume of volatile petroleum product saturated with air at 0 to 1°C (32 to 34°F) produces a pressure of one atmosphere in an evacuated chamber of fixed volume. This test method is applicable to samples for which the determined temperature is between 36 and 80°C (97 and 176°F) and the vapor-liquid ratio is between 8 to 1 and 75 to 1.

Note 1—When the vapor-liquid ratio is 20:1, the result is intended to be comparable to the results determined by Test Method D2533.

Note 2—This test method may also be applicable at pressures other than one atmosphere, but the stated precision may not apply.

1.2 This test method is applicable to both gasoline and gasoline-oxygenate blends.

1.2.1 Some gasoline-oxygenate blends may show a haze when cooled to 0 to 1°C. If a haze is observed in 12.5, it shall be indicated in the reporting of results. The precision and bias statements for hazy samples have not been determined (see Note 10).

1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are provided for information only.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. For specific warnings, see 7.2 and 8.1.1.