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Alvarez, C.; Moreno, G.; Valenzuela, F.; Rivera, J.I.; Ebensperger, F.; Reszka, P.; Fuentes, A. |
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Title |
Use of an electric heater as an idealized firebrand to determine ignition delay time of Eucalyptus globulus leaves |
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2023 |
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Fire Safety Journal |
Abbreviated Journal |
Fire Saf. J. |
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141 |
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103923 |
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Keywords |
Wildfires; Spotting fires; Thermal model |
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The Idealized-Firebrand Ignition Test (I-FIT) protocol was used to evaluate the piloted ignition delay times of fuel beds composed of leaves of Eucalyptus globulus (Labill.). The amount of fuel layer used for evaluation ranged between the fraction volume (������) of 0.03 to 0.07 which are values expected to be found in forest bed fuels. A theoretical model was developed to describe the heating and ignition of the fuel beds, based on the thermal ignition theory. The model, which was originally developed for pine needle beds, considers the penetration of radiation to the porous matrix. The model is able to accurately predict the ignition delay time for different values of ������, but shows a poorer accuracy for the temperature evolution. This is explained by the large variability observed for the Eucalyptus leaves. |
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0379-7112 |
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WOS:001072435400001 |
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UAI @ alexi.delcanto @ |
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1889 |
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Parot, R.; Rivera, J.I.; Reszka, P.; Torero, J.L.; Fuentes, A. |
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Title |
A simplified analytical model for radiation dominated ignition of solid fuels exposed to multiple non-steady heat fluxes |
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2022 |
Publication |
Combustion and Flame |
Abbreviated Journal |
Combust. Flame |
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237 |
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111866 |
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Ignition delay time; Fire safety; Integral heat equation; Solid ignition; Translucent solids; In-depth absorption of radiation |
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Heat fluxes from fires are strongly time-dependent. Historically, the thermal ignition theory in its classical form has neglected this time dependency until recent years, where theories have been developed to include time-varying incident heat fluxes. This article proposes a simplified general model formulation for the heating of solid fuels exposed to four different heat flux behaviors, considering the penetration of radiation into the medium. The incident heat flux cases developed where: Constant, Linear, Exponential and Polynomial, which represent different situations related to structural and wildland fires. The analytical models consider a spatially averaged medium temperature and exact and approximate solutions are presented, based on the critical ignition temperature criterion, which are valid for solids of any optical thickness. The results were validated by comparison with various models presented in the literature, where the model granted in this work was capable to adjust to all of them, especially when high heat fluxes are involved. Therefore, the proposed model acquires a significant engineering utility since it provides a single model to be used as a general and versatile tool to predict the ignition delay time in a manageable way for solid fuels exposed to different fire conditions. |
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0010-2180 |
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WOS:000735880500007 |
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UAI @ alexi.delcanto @ |
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1521 |
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Rivera, J.I.; Ebensperger, F.; Valenzuela, F.; Escandar, L.; Reszka, P.; Fuentes, A. |
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Title |
Understanding the role of fire retardants on the discontinuous ignition of wildland fuels |
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2023 |
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Proceedings Of The Combustion Institute |
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Proc. Combust. Inst. |
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39 |
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3 |
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3775-3783 |
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Ignition delay time; Critical heat flux; Thermal model; Effective properties; Pine needles |
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This work reports on a theoretical and experimental study on the role of fire retardant treatments on the discontinuous ignition of wildland fuels. The effect of the concentration of fire retardant in the solution applied to the vegetation is as expected to increase the ignition delay time. We found that the fire retardant modifies the fuel bed effective thermophysical properties, delaying the thermal response of the specimen when subjected to an incident heat flux. Nevertheless, the critical heat flux remains unaltered within the experimental error. We followed a proven approach based on the thermal ignition theory and testing which however has not been previously employed to study fire retardants on wildland fuels. To carry this out, we performed experiments on the I-FIT apparatus, which yields repeatable results and controlled boundary conditions. The theoretical model shows a good agreement with the experimental results, delivering simple expressions for pencil-and-paper calculations of the ignition delay time and analytical tools to evaluate effective fuel properties. These results will help CONAF and other forest services around the world to gain insight on the optimal concentrations and delivery methods for these types of products during wildfire response. & COPY; 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved. |
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1540-7489 |
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WOS:001019726900001 |
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UAI @ alexi.delcanto @ |
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1842 |
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Valenzuela, F.; Rivera, J.I.; Ebensperger, F.; Alvarez, C.; Reszka, P.; Auat Cheein, F.; Fuentes, A. |
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Title |
Ignition of Wildland Fuels Exposed to a Time-Decreasing Incident Heat Flux |
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2023 |
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Combustion Science and Technology |
Abbreviated Journal |
Combust. Sci. Technol. |
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195 |
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14 |
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3596-3611 |
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Wildfires; Spotting fires; Thermal model; Firebrand |
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The effect of decreasing incident heat fluxes on the ignition delay time of dry pine needles is addressed in the present study. A customized modular instrument (I-FIT) that uses radiant heaters to simulate idealized firebrands ensures experimental repeatability for combustion experiments. Linear incident heat flux ramps are obtained by controlling the power of the heating element, thus simulating idealized firebrands. An analytical model based on the thermal ignition theory was developed and solved analytically using an integral approach. This model includes convective losses and in-depth penetration of radiation. Radiation was modeled using the P1 approximation. The theoretical model is complemented and validated by experimental data, showing increments of the ignition delay times when the negative slope steepness over time increases for the same heat flux. For given values of the initial incident heat flux on the sample, a critical slope beta(cri) is observed. For slopes steeper than this critical value, ignition is not attained. |
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0010-2202 |
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WOS:001044563300001 |
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UAI @ alexi.delcanto @ |
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1865 |
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