Abstract
This work quantifies water contamination in jet fuel (Jet A-1), using silica-based Bragg gratings. The optical sensor geometry exposes the evanescent optical field of a guided mode to enable refractometery. Quantitative analysis is made in addition to the observation of spectral features consistent with the emulsification of water droplets and Stokes’ settling. The measurements are observed for cooling and heating cycles between ranges of 22 °C and −60 °C. The maximum spectral sensitivity for water contamination was 2.4 pm/ppm-v, with a resolution of <5 ppm-v.
Highlights
THE hygroscopic nature of jet fuel means that over time water accumulates in the tank
Gratings 1 and 2 only have a transverse magnetic (TM) peak in the presence of fuel as the orthogonal polarization (TE mode) is in a cut-off region. This has occurred as the commercial probe is designed to operate at a refractive index of 1.33, not that of jet fuel which is of the order 1.45
It should be noted that the specific commercial sensor used is designed for operation at refractive indices about 1.33 not that of jet fuel which is of the order 1.45
Summary
THE hygroscopic nature of jet fuel means that over time water accumulates in the tank. If unmanaged this can form large quantities of hazardous ice due the large temperature decreases associated with high altitude flying, which can immobilize an aircraft’s engine. Whilst it is generally accepted by the industry that water accumulation in any form is undesirable, tolerable levels are considered to be no more than 90 parts per million by volume (ppm-v) for normal operation and 260 ppm-v for emergency operation [1,2]. The test is subjective rather than quantitative, sampling points are extremely limited, and monitoring is not continuous or conducted during flight
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