Solid elements with high volumetric and/or gravimetric heating values, so-called the high-energy-density fuels, have attracted special interests as fuels that can contribute much for enhancing performance of propellants. In the present study, endeavor has been made, not only numerically but also analytically, to elucidate the critical condition that the high-energy-density fuels can move to the combustion after the initial heating. Material chosen for this aim, as a representative fuel, is the solid carbon whose combustion characteristics have well been understood, by virtue of basic researches for the coal combustion, compared to the others. It is found from numerical calculations that there appear abrupt increases in the particle burn-out time when the dominant parameters, such as the initial particle size, oxygen concentration, ambient temperature, and pressure, are below the critical values， respectively. In addition, by conducting asymptotics for the particle in the quasi-steady state established after the initial heating, in the same manner as that for the spontaneous ignition of gaseous combustibles, conducted in the 1930s, it has succeeded in analytically deriving the lower bound of particle size to be burned completely, as well as the critical condition for the surface reaction to be activated. A comprehensive parameter, consisting of the initial particle size, oxygen concentration, and ambient pressure, has also been obtained, which only depends on the ambient temperature. A fair degree of agreement has further been demonstrated between the present analytical results and experimental data in the literature, as far as the trend and the approximate magnitude are concerned, suggesting that the present analysis has captured the essential feature of the phenomena considered. As for the combustion of boron particles, after removal of oxide films on the particle surfaces at high temperatures, by conducting the same analysis as that for the carbon particle, not only the lower bound of the particle size, but also the comprehensive parameter can be derived, with presenting fair agreement between the analytical and experimental results.
炭素やホウ素といった高エネルギ密度燃料粒子の燃焼完結に不可欠な条件に関して
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