Modeling wing tank flammability.

摘要

An investigation into the fire safety of a wing fuel tank has been performed to aid in the effort to eliminate or reduce the possibility of a wing fuel tank explosion in a commercial aircraft. A computational model is built to predict the generation of flammable mixtures in the ullage of wing fuel tanks. The model predicts the flammability evolution within the tank based on in-flight conditions of a wing fuel tank. The model is validated through supporting experiments performed in an altitude chamber, the wind tunnel facility as well as data obtained from flight tests. The results from the experiments are compared to the computational results. Computational results from the altitude chamber follow the general trend of the experimental results, but produce them at a different flash point. This is due to the replenishment of species with lower flash point at the surface of the fuel which emulates the flash point of the entire fuel to be lower. Experimental results for the aluminum wing tests from the wind tunnel experiments are in good agreement with the computational results as well.;A simpler model is developed from a program that calculates fuel air ratio within the ullage of fuel tanks in order to reduce the required number of inputs to the model. This model is applied to the data sets for the experiments performed in the altitude chamber and wind tunnel. For the tests conducted in the altitude chamber, the correlation estimates the hydrocarbon concentrations extremely well during ascent and descent. During the on-ground condition the estimation is good, but not as accurate as the ascent or descent conditions. For the tests conducted in the wind tunnel, the computational values follow the general trend of the experimental values, but the computational values estimates the total hydrocarbon concentration approximately 10% lower than the experimental value consistently.;Flammability studies are also performed in order to track the effects of temperature, pressure, and oxygen concentration on the upper and lower flammability limits. For the temperature and pressure profiles considered in this work, it is found that the temperature and pressure effects on the flammability limits are minimal. In contrast, the oxygen concentration has a significant effect on the flammability limits of the vapor; the flammable region narrows with a decrease in oxygen concentration.