Combustion of Polymer Fuel-Spheres at Elevated Pressures
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概要
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Two kinds of polymer spheres polyurethane (PU) and carboxyl-terminated poly butadiene (CTPB), <I>ca.</I> 3 and 5 mm, respectively, in diameter and used currently as fuel and/or binder constituents in solid and hybrid rocket propellants, were ignited electrically with a nichrome fiber in several oxidizing gases over the range 5–30 kg/cm<SUP>2</SUP>. Their combustion phenomena were studied photographically with a 16 mm movie camera. The combustion flame was observed by means of direct photographs, both the variation of diameter with time and the location of contact surface being measured with shadow photographs. It was shown that PU spheres are entirely liquefied, involving slight swelling just after ignition, and then burn in a similar manner to that of distilled hydrocarbon droplets. CTPB spheres were found to expand remarkably after ignition. At the first stage the surrounding product gases formed a diffusion flame, their apparent diameters remaining nearly constant for a short time. At the second stage the remainder of the carbonaceous substance continued to burn, turning to surface combustion. It can be predicted that in an actual rocket combustion chamber the surface of the fuel-binder for PU propellants is wet and that of GTPB propellants is covered with carbonaceous layer during the course of steady state burning. The overall mass burning rate is proportional to a half and 0.3 power of total pressure for PU and CTPB, respectively, depending slightly on the kind of inert gas for dilution of the oxidizing atmosphere in both cases. A combustion model for CTPB is presented and Compared with experimental results.
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