Experimental Technology and Management

[Objective] The morphology of large-scale wildfire fronts is a crucial factor in assessing wildfire spread and determining safe distances for transmission corridors. Understanding the dynamic evolution of these fronts is essential for effective real-time wildfire monitoring and prevention. Most existing research focuses on small-scale experimental scenarios that struggle to replicate the complex interactions among multiple factors, such as fuel types and meteorological parameters, during actual wildfires. Few studies have examined fire front morphology in large-scale scenarios that incorporate meteorological conditions, and current research often falls short of the accuracy needed for effective wildfire prevention and control. This study aims to investigate the effects of different fuel types and meteorological conditions on wildfire front morphology through large-scale experiments, providing experimental data and theoretical support for the development of fire front spread models applicable to actual wildfire situations. [Methods] A 50 m×40 m full-scale wildfire combustion experimental platform was constructed for this study, integrating UAV thermal infrared imaging, tower-based visual monitoring, and multi-source meteorological sensing systems. We conducted large-scale, systematic experiments on wildfire spread using two common surface fuels(wheat straw and pine needle litter) under varying meteorological conditions. The analysis focused on the effects of fuel type, wind direction, and wind speed on key parameters, including fire front morphology, temporal variation in stable fire front length, and fire front propagation angle. We systematically compared surface fire-front spread under various working conditions. [Results] The results revealed the following: 1) Fire front morphology is significantly affected by fuel type, where wheat straw produces a smooth arc-shaped front, and pine needles result in a sharp, multi-branched, and irregular morphology. The fire front angle increases continuously during combustion, with the temperature decay rate in the burned area of pine needles being significantly faster than that of wheat straw. Wind direction dictates the overall spread direction of the front, whereas wind speed primarily affects the size of the front angle. 2) The variation trend and fluctuation amplitude of stable fire front length are jointly influenced by fuel and meteorological conditions. The fire front length of wheat straw decreases steadily over time, whereas that of pine needles exhibits significant short-term oscillations. Greater differences in maximum and minimum wind directions lead to more intense fluctuations in fire front length. Under identical wind directions, higher average wind speeds correspond to greater extreme values of fire front length. 3) The fire front propagation angle gradually decreases during the spread process. The wheat straw fire front is generally smooth with minor fluctuations, whereas the pine needle fire front displays significant local curvature and irregular trajectories. Greater stability in wind direction and higher average wind speeds result in a smaller average fire front propagation angle, causing the front to approach a straighter line. [Conclusions] Through large-scale surface fire spread experiments, this study elucidates the influence of fuel type and meteorological conditions on key parameters such as fire front morphology, temporal variation of stable fire front length, and fire front propagation angle. It reveals the comprehensive influence mechanism between meteorological conditions and fuel properties regarding fire front morphology, offering a large-scale experimental basis and critical parameter support for developing wildfire spread prediction models and improving wildfire prevention and control strategies in transmission corridors. Future research will expand these large-scale wildfire experiments to include more complex scenarios, thereby enhancing our understanding of real wildfire behavior.