WATER SEPARATION CHARACTERISTICS OF DIESEL FUELS BY PORTABLE SEPARATOMETER: ASTM D7261
EXPLANATION
This test method provides a measure of the presence of surfactants in diesel fuels, and can be performed in the field or in a laboratory. It is a rapid portable means to rate the diesel fuels to release entrained or emulsified water when passed through fiberglass coalescing material. Similar to Test Method ASTM D3948 used for jet fuels, this test method can detect traces of some refinery treating chemicals left in the fuel. It can also detect surface active substances added to or picked up by the fuel during handling from point of production to point of use.
Certain additives, which can act as weak surfactants, give a slightly reduced DSEP rating. Other substances which are strong surfactants give much lower DSEP ratings. Results from this test method do not have a known relationship to the rate of water settling in the tanks. The Micro-Separator has a measurement range from 50 to 100. Values obtained outside these limits are undefined and invalid. This test method is applicable to diesel fuels such as ASTM D975 Grade No. 1 and Grade No. 2 of all sulfur levels, and MIL-F-16884, naval distillate fuel (NATO F-76).
TEST SUMMARY
A 50 mL water/fuel sample emulsion is created in a syringe using a high-speed mixer. The emulsion is then expelled from the syringe at a programmed rate through a standard fiberglass coalescer and the effluent is analyzed for uncoalesced water by a light transmission measurement. The results are reported on a 0 to 100 scale to the nearest whole number; however, the effective range of the test equipment is from 50 to 100. Higher ratings indicate that water is easily coalesced, implying that the fuel is relatively free of surfactants.
Interferences - Any suspended particles, whether solids or water droplets or haze, in a sample will interfere with this test method. Non-hydrocarbon components such as oxygenates, especially alcohols, or emulsified water have not been verified for this test method and will likely interfere.
TEST PRECISION
The repeatability and reproducibility of this test method has not been obtained at this time. The procedure in this test method has no bias because the value of DSEP is defined only in terms of this test method.
