Experimental study of the emissivity of flames resulting from the combustion of forest fuels

• Published in: International journal of thermal sciences Vol. 49; no. 3; pp. 543 - 554
• Main Authors: Àgueda, A., Pastor, E., Pérez, Y., Planas, E.
• Format: Journal Article Publication
• Language: English
• Published: Kidlington Elsevier Masson SAS 01.03.2010; Elsevier
• Subjects: Analytical and numerical techniques; Applied sciences; Biological and medical sciences; Calor; Combustibles vegetals; Combustion. Flame; Ecologia dels focs; Energy; Energy. Thermal use of fuels; Enginyeria química; Exact sciences and technology; Extinction coefficient; Flame transmissivity; Forest fires; Forestry; Fundamental and applied biological sciences. Psychology; Fundamental areas of phenomenology (including applications); General forest ecology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Heat flux transducer; Heat transfer; Impacte ambiental; Infrared thermography; Long-term retardants; Miscellaneous; Physics; Radiació; Radiation; Theoretical studies. Data and constants. Metering; Transmissió; Àrees temàtiques de la UPC; Extinction coefficient; Infrared thermography; Heat flux transducer; Long-term retardants; Radiation; Flame transmissivity; Forest fires; Blackbody; Extinction; Infrared detection; Flame retardant; Heat flow; Combustion; Fuels; Experimental study; Stationary condition; Flames; Thermal radiation; Fire development; Correlations; Modelling; Forest fire; Heat transfer
• ISSN: 1290-0729; 1778-4166
• DOI: 10.1016/j.ijthermalsci.2009.09.006

Heat transfer by radiation is taken into account in most models that predict the propagation of forest fires. This heat transfer mechanism is normally formulated according to the Stefan–Boltzmann law in terms of flame temperature and flame emissivity. This study focused on flame emissivity. Experimental studies carried out to compute the emissivity of the flames generated during the combustion of forest fuels were reviewed, thereby highlighting differences in methodologies and results. Since the results of these studies with regard to the exponential relationship between flame emissivity and flame thickness were not in agreement, two methods based on IR imagery were used in the present study to calculate flame emissivity values. Nine circular fuel beds with a diameter of 0.3–2.5 m were prepared with common Mediterranean species and burned as stationary fires. An exponential correlation between flame emissivity and flame thickness was observed for both methods. According to the results of this study, only flames thicker than 3.2 m would exhibit an emissivity close to that of a blackbody (0.9), and the associated extinction coefficient would be 0.72. A long-term retardant product was used to treat the fuel of two of the nine tests that were carried out and no effect on flame emissivity was observed.