Study of Flame Spread Over JP8 Using 2-D Holographic Interferometry

Abstract

Despite the widespread use of JP8 as a transportation fuel, and hence its importance to fire safety in the event of an accident, the characteristics of flame spread over JP8 are not well known. In order to better estimate fire growth rates, flame spread rates over JP8 and n-butanol were measured in this study as functions of initial liquid temperature. A Holographic Interferometry (HI) technique was employed in conjunction with a photographic recording sys tem to rapidly detect small temperature changes over an area including the liquid and gas phases. The laboratory-scale experiments were performed using the same apparatus employed in previous studies of flame spread over alcohol to al low comparison of the two sets of results. Flame spread data were obtained for JP8 fuel as a function of initial fuel temperatures between 15°C and 40°C. The four common spread patterns (pseudo-uniform, pulsating, uniform, and superflash) observed for alcohol by Akita [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 con trol volume of the liquid ahead of the flame. From this analysis, the liquid-phase convection (Qcv) was found to be larger than both the gas-phase convection ( Qg) and the heat loss (QL). This trend indicates that (Qcv) is the main mode of 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 compari son with butanol, to initiate the flame spread, although both JP8 and butanol have approximately equal closed-cup flash point ( Tf ~37°C). The difference is partly due to the low viscosity and relatively large surface-tension force of JP8 which generate a liquid convection flow more effectively than butanol.