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Abstract  

The processes involved in flame spreading over liquid fuels are subject of this work. A heat and momentum transfer analysis has been undertaken for fuel temperatures below the flash-point that confirms (within this range of temperatures studied in this work) that flame spreading is assisted by a convection pattern ahead of the flame. This assistance mechanism, which is not observed for solid fuels, is the origin (for lower temperatures) of a pulsating behaviour of the flame. A first experimental determination of the characteristic horizontal length of this assistance zone will be given. The analysis of our data lead us to conclude that flame spreading can be reduced by simultaneously preventing the formation of the convection zone and reducing the fuel surface temperature.

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Abstract  

Fire safety on fuel containers can be improved at its initial stage if flame spreading can be controlled. Therefore, the understanding of the fundamental processes that control flame spreading will help us to determine a few control parameters that could be useful to improve security in fuel deposits. A series of experiments have been conducted in different fuel containers that helped to understand the basic mechanisms involved. A new phenomenon of convection ahead of the flame is observed in liquid fuels that do not appear in solid fuels. Finally, two control factors have been found useful to control fire spread: the initial fuel surface temperature and the convection zone observed in front of the flame. The first experimental results observed controlling these two factors led flame to spreading velocities of order 1 cm s–1 and, in some cases, flame extinguishes.

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Flame propagation over liquid alcohols

Part I. Experimental results

Journal of Thermal Analysis and Calorimetry
Authors:
E. Degroote
and
P. L. García Ybarra

Summary The different spreading regimes above liquid fuels have been experimentally described for a wide range of initial surface temperatures. Five different spreading regimes are observed. The flame spreading driving parameter has been found. The critical transition temperatures between these regimes have been characterized; they present common characteristics for the four alcohols (methanol, ethanol, propanol and butanol) used in the experiments. A preheating zone ahead of the flame (produced by thermocapillarity) has been observed. The initial surface temperature of the liquid fuel results to be a control parameter of flame spreading; therefore, it can be applied to improve fire safety conditions in fuel containers.

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Flame propagation over liquid alcohols

Part II. Steady propagation regimes

Journal of Thermal Analysis and Calorimetry
Authors:
E. Degroote
and
P. L. García Ybarra

Summary The different spreading regimes above liquid fuels have been experimentally characterized for surface temperatures close to the flash-point temperature. Two different spreading regimes are observed: for temperatures larger than some critical value, flame spreading velocity is well described by the De Ris solid fuel-like model. For temperature values lower than the critical one, a preheating thermocapillary region has been observed in the fuel, which can be described by a purely thermodynamic non-reactive model. The critical transition temperature has shown to present common characteristics for the four alcohols used in the experiments.

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Flame propagation over liquid alcohols

Part III. Pulsating regime

Journal of Thermal Analysis and Calorimetry
Authors:
E. Degroote
and
P. L. García Ybarra

Summary The pulsating regime of flame spreading liquid fuels has been experimentally characterized. The mechanism that produces this oscillating behavior has been proposed, that correlates very well with our experimental data. The existence of a preheated region preceding the flame has been found; the characteristic horizontal length has also been experimentally measured. The transition temperatures have been found to possess common features for all fuels and geometrical configurations used in our experiments that can be used to improve fire safety in fuel containers.

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