Ignition of Wildland Fuels Exposed to a Time-Decreasing Incident Heat Flux

F. Valenzuela, J. I. Rivera, F. Ebensperger, C. Alvarez, P. Reszka, F. Auat Cheein, A. Fuentes*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


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 (Formula presented.) is observed. For slopes steeper than this critical value, ignition is not attained.

Original languageEnglish
Pages (from-to)3596-3611
Number of pages16
JournalCombustion Science and Technology
Issue number14
Early online date8 Aug 2023
Publication statusPublished - 26 Oct 2023


  • Firebrand
  • Spotting fires
  • Thermal model
  • Wildfires

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering
  • Fuel Technology
  • Energy Engineering and Power Technology
  • General Physics and Astronomy


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