Study of flame spread over JP8 using 2-D holographic interferometry

Despite the widespread use of JP8 as a transportation fuel, and hence its i mportance to fire safety in the event of an accident, the characteristics o f flame spread over JP8 are not well known. In order to better estimate fir e growth rates, flame spread rates over JP8 and n-butanol were measured in this study as functions of initial liquid temperature. A Holographic Interf erometry (HI) technique was employed in conjunction with a photographic rec ording system to rapidly detect small temperature changes over an area incl uding the liquid and gas phases. The laboratory-scale experiments were perf ormed using the same apparatus employed in previous studies of flame spread over alcohol to allow comparison of the two sets of results. Flame spread data were obtained for JP8 fuel as a function of initial fuel temperatures between 15 degrees C: and 40 degrees C. The four common spread patterns (ps eudo-uniform, pulsating, uniform, and superflash) observed for alcohol by A kita [1] were also observed for flame spread over JP8. In order to estimate the heat flux carried by the subsurface convective flow, an energy balance in the liquid phase was performed by considering a control volume of the l iquid ahead of the flame. From this analysis, the liquid-phase convection ( Q(cv)) was found to be larger than both the gas-phase convection (Q(g)) and the heat loss (Q(L)). This trend indicates that (Q(cv)) is the main mode o f heat transfer for flame spread over liquid in the uniform regime of these experiments. It was also observed that JP8 requires a much higher ignition energy, in comparison with butanol, to initiate the flame spread, although both JP8 and butanol have approximately equal closed-cup flash point (T-f approximate to 37 degrees C). The difference is partly due to the low visco sity and relatively large surface-tension force of JP8 which generate a liq uid convection flow more effectively than butanol.