Combustion characteristics of magnesium borides and their agglomerated particles

Abstract

Boron is an attractive fuel for propellants because of its high energy density. However, its combustion is inhibited by the oxide layer that covers the particles. The use of magnesium borides instead of boron was shown to promote the combustion of boron-based propellant. The combustion behavior of magnesium borides and their agglomerated particles in CH4/O2/N2 premixed flames were studied using flat-flame burner, high-speed camera and spectrometer. The experimental results showed that the combustion of magnesium dominated the early stage of magnesium borides combustion process. As the combustion reaction proceeding, the combustion of boron gradually replaced magnesium to dominate the combustion of magnesium borides. When oxygen mole fraction was 0.13, MgB2 and MgB4 agglomerated particles would extinguish after ignition within the temperature range explored (1364K–1541 K). When oxygen mole fraction increased to 0.22 and 0.31, the burning time of MgB2 and MgB4 agglomerated particles were much shorter than that of amorphous boron agglomerated particles between 1400 K and 1600 K, which could improve the combustion performance of boron-based propellant. When temperature increased to 1600 K, the burning time of MgB4 agglomerated particles was close to that of amorphous boron agglomerated particles, while the burning time of MgB2 agglomerated particles was still shorter than amorphous boron agglomerated particles.