Combustion characteristics of boron nanoparticles

An experimental investigation of the combustion characteristics of boron nanoparticles in the post flame region of a flat flame burner has been conducted. Boron is attractive as a fuel or a fuel supplement in propellants and explosives due to its high heats of combustion on both a gravimetric and volumetric basis. A relatively large database exists for combustion characteristics of large (greater than 1 μm) boron particles, but very little exists for nano-sized boron. Ignition and combustion characteristics have been studied in the post flame region of a fuel lean CH₄/Air/O₂ flame, with burner temperatures ranging from about 1600 K to 1900 K, and oxygen mole fractions ranging between 0.1 and 0.3. As in earlier investigations on boron combustion, a two-stage combustion phenomenon was observed. Ensemble-averaged burning times of boron nanoparticles were obtained, while the ignition time measurements for boron nanoparticles were extended into a lower temperature range previously unavailable in the literature. The measured burning times were between 1.5 ms and 3.0 ms depending on both the temperature and oxygen mole fraction. The ignition times were relatively insensitive to oxygen concentration in the range studied, and were affected only by temperature. The measured ignition times were inversely related to the temperature, ranging from 1.5 ms at 1810 K to 6.0 ms at 1580 K. The burning time results were compared to both diffusion and kinetic limited theories of particle combustion. It was found that the size dependence on particle burning times did not follow either theory.