Scope
This standard specifies an ambient temperature procedure for the rapid
determination of the presence of compounds in middle distillate fuels which
affect the potential instability in storage. The fuel types include automotive
and marine diesel fuels, heating fuels and gas turbine fuels, in which products
of fuel degradation lead to performance problems. The test method uses a
portable spectrophotometer to measure the absorbance of light caused by the
presence of phenalene and/or phenalenones, and can thus be carried out on site
or in the laboratory. It is applicable to distillate fuels from both petroleum
and non-petroleum origin, and at all points in the distribution chain from
refinery to end use. It is also applicable to fuels containing dyes and/or
markers, but not those containing residues from petroleum processing. It may not
give the same predictive power on potentially unstable fuels containing other
degradation precursors.
NOTE 1 - Def Stan 91-4 , allows the requirement for test by Def Stan 05-50 Part 40 to be waived, if the result by this standard is less than 0,20 absorbance units (AU). This level of absorbance has been shown to be equivalent to 10 mg/l total sediment.
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