EXPLANATION
Diethylene Glycol Monomethyl Ether (DiEGME) is miscible with water and can be readily extracted from the fuel by contact with water during shipping and in storage. Methods are therefore needed to check the additive content in the fuel to ensure proper additive concentration in the aircraft. This test method is applicable to analyses performed in the field or a laboratory.
This test method covers a technique for measuring the DiEGME concentration in aviation fuels using HB and Brix scale refractometers. The extraction ratios are high enough that portable hand-held refractometers can be used, but not so high as to sacrifice accuracy or linearity, or both, in the 0.01 - 0.25 vol % range of interest.
TEST SUMMARY
A measured volume of fuel is extracted with a fixed ratio of water. The extraction procedure includes sufficient agitation and contacting time to ensure that equilibrium distributions are attained. With the HB refractometer, several drops of the water extract are placed on the prism face and the volume % DiEGME is read directly from a custom graduated scale printed on the reticule. When using the Brix refractometer, a temperature correction factor is first applied to the reading, multiplied by 2 and divided by 100 to calculate volume % DiEGME.
TEST PRECISION
Accuracy and precision in the field can be lower than a similar test done under controlled laboratory conditions using a temperature controlled precision refractometer.