Flaming Ignition of PMMA, Pine Wood and Pine Needle by External Radiation: Autoignition and Radiant Distance Effect

Flame radiation is one of the important causes of wildland–urban interface (WUI) fires. PMMA, pine needle and pine wood are the most common fuels in WUI fires, but the radiant distance effect on the flaming ignitions as well as the subsequent burning behavior is still poorly understood. This work represents an experiment to investigate the flaming autoignition of PMMA, pine-needle and pine-wood fuel beds with different radiant distances (25 mm–100 mm) under a uniform incident radiant heat flux, 25 kW/m² The experiment results show that for PMMA and pine wood, they all transition from gas-phase ignition near the cone heater to solid-phase ignition. For pine needle, it has smoldering ignition and smoldering-to-flaming ignition. The relationship between radiant distance and ignition delay time is an approximately inverted u-shape curve, and there exists a critical radiant distance (D = 60 mm) for the minimum ignition delay time. For pine wood and PMMA, when D < 60 mm, there exists a linear relationship between radiant distance, D, and $t_{ig}^{-1/2}$.