Pyrolysis front tracking using the spectral fluorescence signature of PMMA

The ability to track the progression of a pyrolysis front on a solid fuel is essential in many applications such as the study of flame spread. Tracking the pyrolysis front in cases such as upwards flame spread becomes increasingly difficult due to the obstruction of the luminous flame. This work identifies the occurrence of light-induced fluorescence in the pyrolysis region of polymethyl methacrylate (PMMA) during flame spread and demonstrates its use in explicitly identifying the pyrolysis front. PMMA fluorescence is achieved through excitation using 266 nm, 395 nm, and 450 nm light (both coherent laser and LED sources). The fluorescence response was characterized through UV–VIS spectroscopy. Pyrolyzed PMMA excited with 266 or 395 nm light provided a fluorescence signature with a strong peak at ∼532 nm and a half width of ∼160 nm. The ability to visualize and track the pyrolysis region is demonstrated for both downwards and upwards flame spread. For downward spread, the onset of fluorescence was found to occur within 1 mm of the leading edge of the flame. Upward flame spread experiments demonstrated that pyrolysis fluorescence can be detected through the obscuration of the luminous flame, allowing for pyrolysis front tracking while simultaneously tracking the flame front through chemiluminescence imaging.