INVESTIGATION OF FUNDAMENTAL ASPECTS OF FUEL TANK FILLING

摘要

This paper will present the findings of small-scale electrostatic measurement tests carried out in order to improve the understanding of fundamental aspects of electrostatic charge in fuel tanks during filling. In particular, the effects of different distributions of charge within the fuel on the electric fields within the tank were assessed. The trials involved running a number of different fuel tank filling scenarios with electric field meters positioned at different locations within the tank. A purpose-built test rig was designed and built which although was not representative of aircraft structure or systems, enabled the fundamental processes to be observed. Measurements were made for several fuel conductivities and fill rates, with and without fuel agitation (stirring), with and without the presence of metal cladding on the tank walls and for a variety of meter positions within the tank. Several flow visualisation tests were conducted. It was found that the relative timescales of the tank filling, the intrinsic relaxation time of the fuel and the rate of charge relaxation through the walls are crucial in determining the electrostatic environment of the fuel tank. Flow visualisation videos showed complex fuel motion during tank fill, particularly during the earlier stages of the fill. We observed that the electric fields in the tank ullage varied when the fuel was agitated with a stirrer and were dependent on the fill rate and fuel charging mechanism. The presence of the metal cladding strongly affected the tank's electrostatic environment and the E-field measurements also showed that the electrostatic environment can linger in a tank after filling ceases The paper will present measurement data arising from these tests and explain how our key conclusions have been drawn. Implications of these conclusions on future modelling strategies will also be discussed.