Student researcher

Sergio Zarate Research Leader

Experimental inconsistencies have been found in the mechanisms of heat transfer in fuel particle heating and ignition. Radiation has been often assumed as the dominant heat transfer model for rate of fire spread (RoS). Nevertheless, some experimental results have suggested that for fine-sized particles, the radiative heating can be insufficient to offset the convective cooling during the preheating stage. As a result, flame impingement and convection from hot gases could be the principal mechanism of fire spread and responsible for ignition in small fuel particles.

This research aims to provide insight into the fundamental process of fire growth of bushland fine-sized fuels, focusing on how the ignition and subsequent fire spread of fuel particles are affected when different convective and radiative conditions are applied. The study focuses on the effect of aforementioned heat transfer modes on the RoS of particles with different surface area to volume ratio (SA/V). In order to achieve this aim, an experimental apparatus that can recreate similar conditions to those of a real surface fire needed to be designed and commissioned. This is because there was not any commercial option that allows testing the horizontal fire spread in a fuel bed exposed to convective heating and radiative heat flux at the same time. Surface fires were considered for the experimental conditions because these fires generally have a place on small-size bushland fuels, such as grasslands, shrubland and forest litter. The design conditions of the piece of equipment were defined by the heat fluxes, air temperature and velocities, and fuel bed properties measured by other researchers in field experiments of surface fires.

The experimental results obtained to date have shown that the RoS over fuel beds with fine-sized particles can be considerably affected by changes in the convective conditions. Analytical and empirical models validated by the experimental results are being developed. This analytical and empirical approach based on the fuel characteristics and the convective and radiative conditions aims to predict the RoS of fine-sized fuel beds. The models' outcomes and experimental results will be compared with results obtained from existing surface fire models. The results of this research will show how significant the convective heat exchange is for fine-sized particles, and if the effect of convection needs to be included in both empirical and physical models intended for predicting RoS in vegetation with similar size characteristics.