Two-dimensional temperature measurement of burning flammable solid along the limiting oxygen index test using fluorescent two-color method

To reveal the heat transfer process inside a combustible solid, we investigated temperature distribution during flame spread along plate-formed specimens (PMMA, PS and PC) in the limiting oxygen index (LOI) test (ISO4589-2) for several oxygen concentration levels. Temperature was measured by phosphor thermometry based on the two-color intensity ratio obtained from up-conversion phosphor, Y2O3:Yb, Er, which can be used at wavelengths of 527 and 548 nm. Specimen dimensions were 100-mm long, 10-mm wide, and 2-, 4- or 10-mm thick, and phosphor was inserted at cross-sections in the width and diagonal directions of specimens. Results showed that temperature was higher near the surface than at the center of test specimens under high oxygen concentration, so that heat transfer progressed radially from the leading edge of the flame spread in all materials. Meanwhile, temperature distribution was uniform in the width direction under low oxygen concentration, especially near the extinction limit; therefore, heat transfer progressed uniformly only in the flame-spread direction in all materials. Flame-spread rate, V, increased with increasing heat flux value inside the specimen in the flame-propagation direction qz, but the tendency varied depending on the type of material. These findings provide valuable insight into the characteristics of flame spread and flammability in the LOI test.