Experiments and simulations of the freezing of jet fuel in forced flow

Under low-temperature environmental conditions, the cooling of aircraft fuel results in reduced fluidity with the potential for freezing. To study the freezing behavior of jet fuel under forced flow conditions, a quartz duct was fabricated. The duct walls were cooled below the solidification temperatures of JP-8 and JPTS fuel samples by means of an environmental chamber. Freezing was also simulated using computational fluid dynamics, and the validity of the calculations was established by comparing them with experimental measurements. As they were unavailable, the low-temperature properties of a sample of JPTS were measured experimentally and were used in the simulations. The calculated temperature and solidified area of the fuel inside the duct agree well with those values measured in the experiments. This work demonstrates that computational fluid dynamics techniques can potentially be used to predict the fuel holdup in aircraft fuel tanks. The effect of flow rate on solidification was also simulated, and it was found that lower flow rates result in relatively more solidification of the fuel than do higher flow rates. The simulations of the freezing behaviors of JP-8 and JPTS samples were found to have essentially the same value of morphology constant. However, the crystal structures of these two fuels were studied in experiments and were found to be very different. This shows the inability of the model to capture small-scale details like the crystal microstructure. However, this limitation is not fatal because the focus here is on the overall flow and freezing behavior of jet fuels.