Rivera, J., Hernandez, N., Consalvi, J. L., Reszka, P., Contreras, J., & Fuentes, A. (2021). Ignition of wildland fuels by idealized firebrands. Fire Saf. J., 120, 103036.
Abstract: Experiments were carried out in the Idealized-Firebrand Ignition Test (I-FIT), a bench scale apparatus specifically designed to test the ignition of forest fuel layers from a representative firebrand. A cylindrical heater was used to model the firebrand, which allowed to control the incident radiative heat flux on the specimen, from the critical heat flux up to 25 kW/m2, for five different porosities of the fuel layer. Experimental ignition delay times were interpreted based on a theoretical model of the radiative heating of the fuel layer. Radiative heat transfer within the fuel layer was modeled by using the P1 approximation. In the limit of small ignition delay times an analytical expression was derived to correlate the inverse of the ignition time to the incident heat flux. This analytical expression is used to obtain the ignition temperature and effective properties for the forest fuel layers, namely the product of the fuel volume fraction by solid fuel density and solid heat capacity. Analytical solutions were found to be consistent with experimental data and a correlation relating the inverse of the non-dimensional time-toignition to the non-dimensional heat flux is provided.
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Rivera, J. I., Ebensperger, F., Valenzuela, F., Escandar, L., Reszka, P., & Fuentes, A. (2023). Understanding the role of fire retardants on the discontinuous ignition of wildland fuels. Proc. Combust. Inst., 39(3), 3775–3783.
Abstract: 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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