COMBUSTION BEHAVIOR OF THERMOPLASTIC POLYMER SPHERES BURNING IN QUIESCENT ATMOSPHERES OF AIR.
PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF FUEL SCIENCE
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Thermoplastic polymer spheres of 1 or 2 m.m. initial diameter, burning in air while attached to silica fibres, have been found to burn like oil drops with a surrounding diffusion flame. Eleven different materials of CH ratios from 0.5 to 1.2 were studied photographically to determine the variation of diameter with time. In general the materials followed the classic Nusselt square-law relation thus generating a burning constant, K. Experimental values of K for the eleven materials ranged from 10 to 80 c.g.s. units. Being half to one quarter of the oil drop values this showed that their burning rates were 2 to 4 times faster because of the much closer approach of the surrounding flame to the drop surface. The overall oil-drop-equivalent behavior, however, is misleading as an explanation of mechanism since the material has to pyrolyze before vaporizing so the rate limiting process is not heat supply for evaporation, but heat supply for surface pyrolysis since volumetric pyrolysis does not lead to a square law. To account for this, a sequence of pyrolysis steps of increasing activation energy is therefore postulated with only the last one, occurring at the slightly higher surface temperature, leading to vaporization effectively at the surface. Author
- Combustion and Ignition
- Solid Rocket Propellants