Dynamic ignition and combustion characteristics of agglomerated boron-magnesium particles in hot gas flow

Boron-based fuel is the most attractive energy source for ramjets and scramjets because of its high calorific value. Due to magnesium's excellent combustion performance, adding magnesium as a promoter for boron ignition and combustion was proposed. The combustion mechanisms of boron-based fuel become more complicated after adding magnesium. At the same time, because of the high viscosity B₂O₃ on boron's surface, fuels always come into combustion in agglomerated state. Therefore, the dynamic ignition and combustion characteristics of agglomerated boron-magnesium particles were investigated experimentally in this paper, which could provide the basic and key parameters for combustor design. The particles investigated here were prepared by drying a mixture of micron sized boron and magnesium slurry. The experiment results indicated that the combustion process of agglomerated boron-magnesium particles can be divided into agglomerated combustion and micro-explosion combustion. The micro-explosion phenomenon is related to the core-shell structure formed during the particle's heating process. With magnesium content being increased, the combustion type will transit from agglomerated combustion to micro-explosion combustion. The transition region of combustion type is the condition that when magnesium content reaches 10-20%. When magnesium content reaches 30%, it has no obvious effect on the combustion of agglomerated boron-magnesium particles. The critical ignition temperature for magnesium containing samples is ranging from 1279 K to 1346 K, and for magnesium free sample is 1670 K. The ignition delay time for samples with magnesium is shortened from 132-164 ms at 1279 K to 26-38 ms at 1673 K, with a reduction of 80%.