Charging and ignition of sprayed fuel

There have been many recorded incidents of aircraft fuel tank ignition. While electrostatic discharges have undoubtedly started fires during fuelling on the ground, the cause of in-flight fuel tank explosions is difficult to establish and attributing these events to static electricity is very controversial. This paper describes an experimental investigation into the charging of isolated objects in a fuel spray. The results presented here show that while charging readily occurs, insufficient charge is retained by the target objects under the present conditions even to cause sparking. The influence of fuel conductivity on the balance between the rates of charging and charge leakage from the target is examined. The data shows that while fluids with considerable conductivity may wet the insulating material supporting the target object, the leakage resistance can be high. It is concluded that under certain circumstances, increasing fuel conductivity may, therefore, exacerbate the electrostatic problem.