VAPOR PRESSURE OF PETROLEUM PRODUCTS: D5191
(Equivalent Test Methods: IP 394 and AFNOR M07-079)
EXPLANATION
Vapor pressure is an important physical property of liquid spark-ignition engine fuels. It provides an indication of how a fuel will perform under different operating conditions, such as whether it will cause vapor lock at high ambient temperature or at high altitude, or will provide easy starting at low ambient temperature. Petroleum product specifications generally include vapor pressure limits to ensure products of suitable volatility performance. Vapor pressure of fuels is regulated by various government agencies. This test method is, however, more precise, uses a small sample size (1 to 10 mL), and requires about 7 min to complete the test.
TEST SUMMARY
The chilled sample cup of the automatic vapor pressure instrument is filled with chilled sample and is coupled to the instrument inlet fitting. The sample is then automatically forced from the sample chamber to the expansion chamber where it is held until thermal equilibrium at 100° F is reached. In this process the sample is expanded to five times its volume (4:1 vapor-to-liquid ratio). The vapor pressure is measured by a pressure transducer. The measured vapor pressure is automatically converted to a dry vapor pressure equivalent value by the instrument.
TEST PRECISION
Repeatability: 0.00807(DVPE+124)
Reproducibility: 0.0161(DVPE+124)
Bias has not been determined.
