Vaporization of JP-8 Jet Fuel in a Simulated Aircraft Fuel Tank ...

5.1.2 Isooctane Fuel Vaporization Test
Figure 5.5 shows results from single component fuel vaporization at atmospheric pressure
and reduced ambient temperature. Isooctane being quite volatile, it was necessary to
allow the fuel to cool for several hours to near 3°F in order to obtain fuel vapor
concentrations within the FID calibration range of 0-4% propane equivalent. Figure 5.5
shows that at the start of the test, after cooling, there was very good agreement between
the measured and calculated vapor concentration. As the fuel temperature increased, the
ullage vapor concentration also increased due to increasing vaporization. The fuel vapor
measurement was carried out intermittently at some times during the test to preserve the
purity of the sample, as the test time was almost 2 hours. During the latter part of the test
the FID vapor concentration measurements fluctuated at high vapor concentrations above
30,000 ppm. This was later seen in other experiments at high vapor concentrations as
well, and was most likely due to some condensation occurring in the sample lines at cold
spots and subsequent vaporization at warmer locations. Considering the difficulties
involved in using isooctane as the test fuel, the agreement between the measured and
calculated fuel vapor concentrations was considered satisfactory.
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