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 1279K to 1346K, and for magnesium free sample is 1670K. The ignition delay time for samples with magnesium is shortened from 132-164ms at 1279K to 26-38ms at 1673K, with a reduction of 80%. (C) 2020 Elsevier Masson SAS. All rights reserved.