Experimental investigation of vertical flame spread over non-planar PMMA surfaces

Burning of PMMA slabs with non-planar surfaces is presented in this paper. Non-planar surfaces have been produced using steps fabricated in transparent thermally thick PMMA slabs. The step size is kept constant and three step locations have been used in this study. Either the plate portion or the step portion of the slab is ignited, but keeping the ignition location at the bottom. Concurrent, vertically upward flame spread over stepped slabs is analyzed in detail. The results indicate that the main influence of the step at any location has been to increase the mass loss rate and therefore, the burning rate. The flow fields are quite different between the step ignition and the plate ignition cases. As a result, secondary flame zones are observed in the wake zone downstream of the step for step ignition cases and the flames influenced by stagnation point flow field are observed for plate ignition cases. The influences of step size for step ignition and location of step for plate ignition cases are also studied. Further, the effect of the presence of step on the pyrolysis zone is also analyzed by quenching the flame after 1800 s and measuring the depth of the pyrolysis zone as a function of slab height for all the cases.