Gasification of Boron Oxide Drops in Combustion Gases

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Abstract
The behavior of boron oxide drops was studied in the post flame region of a flat-flame burner. Individual particles were supported on a probe and rapidly could be placed in the gas environment. Measurements were made of the variation of particle size and temperature with time. Burner operating conditions were varied to give fuel equivalence ratios in the range 0.3–0.7 and gas temperatures in the range 1500–1975 K at atmospheric pressure. Flame environments both with and without water vapor present were con sidered. Results show that boron oxide gasification is a relatively slow process with 1000 μm initial diameter drop lifetimes ranging from two minutes to two hours. The presence of water vapor speeds gasification, as suggested by King, and probably accounts for the shorter ignition delay s observed for the oxidation of bo ron particles in wet en vironments. Application of a diffusion-limited equilibrium model provided excellent agreement with oxide drop-life histories at all conditions except for the low-temperature (Tp < 1300 K) wet environment. In th is case, results of a partial-equilibrium analysis suggest chemical kinetics limit gasification rates.