Study on Diagnostics of Nano Boron-Based Composite Metal Particles in Dispersion Combustion

Adding metal fuel can improve the energy density of the propellant and alleviate the instability phenomenon of high frequency combustion of the ramjet. Boron has been of considerable interest as fuel for propellants and explosives due to its high gravimetric and volumetric calorific values. However, its combustion is inhibited by the high melting point, the high boiling point and the oxide layer that covers the particles. Aluminum and iron have high combustion heat, fast energy release rate and high theoretical combustion heat utilization. Aluminum and iron are introduced to improve boron's combustion efficiency and actual combustion heat value. Aluminum and iron increases the exothermic heat of surface reaction and promotes the ignition and combustion of boron. Boron is mixed with aluminum and iron to make composite metal fuel to solve the problems of difficult ignition and poor combustion performance. Solid fuel with great ignition performance and high energy density can be obtained. The effects of ignition and combustion characteristics of boron-based composite fuel were explored using a dispersion combustion system. The ignition phenomenon of boron-based composite metal fuel was recorded by the high-speed camera, and the temperature distribution was calculated by using the two-color pyrometry method. The combustion mechanism of boron-based composite metal fuel was analyzed using characterization methods. The results showed that adding aluminum and iron reduced the ignition delay time and combustion time. The number of boron particles ignited increased at the same time. The combustion process of boron was intense. The addition of nano-aluminum increased the combustion temperature, while the addition of nano iron decreased the combustion temperature. The obvious green light was observed during the temperature measurement of boron-based composite metal particles in dispersion combustion. The emission spectrum showed that the green light come from the intermediate product BO2 generated by boron combustion. After dispersion combustion, the agglomerates of boron-based composite metal particles were mainly oxidation products, which also contained a small amount of nitrogen. The product agglomeration phenomenon of the boron-based composite metal particles after dispersion combustion was obvious, and the fracture of the irregular block boron was aggravated. After the boron-based composite metal particles entered the drop tube furnace, the temperature of the additive nanoparticles rose rapidly in a short time by thermal radiation. The aluminum and iron particles started to burn and release heat energy. The heat released by combustion accumulates inside the particles. Then the heat was absorbed by the boron particles, which broke the oxide layer on the boron surface. The internal boron contacted the air. The temperature continued to the ignition point of boron. The mixed metal started to burn and release heat energy. The heat was absorbed by the boron particles, which promoted the combustion of boron.