Comprehensive Characterization of Pyrolysis and Combustion of Genista Salzmannii Needles (GSN) for Fire Hazard Analysis

Abstract

This article presents a first attempt of implementation of a lab scale methodology proposed to describe the thermal decomposition behavior of vegetative fuels, by using thermogravimetric (TG) methods, with respect to forest fire. Experiments within this method include testing the usual grinded form of samples compared to a continues fuel layer (intact form), which can render reliable and useful information to improve the understanding of the ignitability and combustibility of forest fuels along with predicting fire propagation. Moreover, slow (20 and 40 °C/min) and fast (60, 80 and 100 °C/min) heating rate were chosen to get close from the actual conditions of wildland fires (preheating/smoldering and flame region, respectively). In this work, we report the thermal decomposition behavior under inert (N2) and oxidative (air) atmospheres of Genista Salzmannii Needles (GSN) involved in fires of Mediterranean forests. TG analyses were performed to assess thermal reactivity and combustion indices (ignition, devolatilization, combustion and burnout indices) of grinded and cut GSN samples at fives heating rates of 20, 40, 60, 80 and 100 °C/min. The use of the set of thermal indices practical investigation, ignitability, combustibility and sustainability of forest fuels are important properties to be determined when talking to efficient wildland fire management. Moreover, Activation energy was calculated by means of two iso-conversional methods. The results showed that the cut GSN was characterized by a higher mass loss rate compared to grinded samples. As the heating rate increases, reactivity and combustion indices increase linearly. At low heating rates (20 and 40 °C/min), these parameters are quite similar for both samples, while the gap becomes more and more significant at elevated heating rates (60, 80 and 100 °C/min). High correlation coefficients (R2 > 0.96) were obtained, which indicate a good degree of fitting reliability between combustion characteristics and the tested heating rates. Furthermore, the variation of activation energy (Ea) with the conversion rate has exhibited a quite similar behavior during the whole pyrolysis and combustion process. Char formation, at the end of an intense devolatilization, was the most complex process. The oxidation of the remaining char was characterized by a significant decrease of Ea, which is not considered as a major event in the combustion process. Finally, the obtained data provide systematic knowledge for understanding the thermal decomposition of forest fuels (considered as the first stage in fire process), while the developed methodology can be used for comparison and classification of vegetative fuels related to fire risk potential.