Droplet Statistics and Flame Stabilization Behavior of Jet Fuels and Their Surrogates

Jet fuel surrogates are used to simplify the physics and chemistry of distillate jet fuels for computational tractability, but previous investigations have come to various conclusions on how near-limit combustion behaviors are affected by liquid fuel properties such as volatility and droplet size. This study investigates the flame stabilization behavior and droplet statistics of three reference jet fuels and four surrogate jet fuels in a piloted spray burner. The experiments show that the surrogate fuels have substantially higher average flame liftoff heights than the reference fuels; however, the droplet statistics of the two groups of fuels are fairly similar. Because the differences in flame stabilization behavior for airblast atomizers under the conditions of this study cannot be explained by differences in droplet statistics, a detailed comparison of the distillation curves and derived cetane numbers is conducted. It is shown that the derived cetane numbers at 20% liquid volume distilled correlate remarkably well with the liftoff heights. The differences in derived cetane number between the surrogate fuels and the reference fuels at 20% volume distilled are caused by the preferential vaporization of low-reactivity species in the surrogates. The results of this study have important implications for surrogate fuel formulation methodologies.