Method for analyzing the effect of projectile impact on aircraft fuel tank inerting for survivability design

Inerting is an important measure to prevent fire and explosion, and enhance the survivability of an aircraft. In the battle environment, the hits from the projectiles or fragments on the fuel tank may affect the inerting effectiveness. By modifying the traditional scrubbing inerting model, this paper proposes a new inerting analysis method considering the impact of the projectiles. A series of events are introduced including the changes in either of the velocity and temperature of the projectiles, the air increase in the ullage brought by the projectiles, and the heat transfer between the projectiles and the surroundings. Examples show that the fuel load has significant effect on the oxygen concentration and the vapor/air ratio, while the velocity, the mass and the temperature of the projectile have less effect on the two parameters. In addition, the changes in the flight altitude have almost no effect on the vapor/air ratio, while having little effect on the oxygen concentration. Moreover, when the fuel tank suffers multiple hits by the projectiles, the ignition possibility or vulnerability in the ullage will increase significantly.